Melt electrowriting scaffolds with fibre-guiding features for periodontal attachment

Periodontal regeneration requires the re-attachment of oblique and perpendicular periodontal ligament (PDL) fibres to newly formed cementum and alveolar bone, which has proven elusive with existing approaches. In this study, multiple fibre-guiding biphasic tissue engineered constructs were fabricated by melt electrowriting. The biphasic scaffolds were 95 % porous and consisted of a pore size gradient bone compartment and periodontal compartment made of fibre-guiding channels with micro-architectural features ranging from 100 to 60 µm aimed to direct PDL fibre alignment and attachment. In vitro evaluations over 3 and 7 days demonstrated a marked improvement in collagen fibre orientation (over 60 % fully aligned) for scaffolds with micro-architecture ≤100 µm. The biphasic scaffolds were placed on a dentine slice and implanted ectopically, and this demonstrated that all micro-channels groups facilitated oblique and perpendicular alignment and attachment on the dentine with a mean nuclei angle and mean collagen fibre angle of approximately 60° resembling the native periodontal ligament attachment. A further in vivo testing using a surgically created rodent periodontal model highlighted the 80 µm micro-channel group's effectiveness, showing a significant increase in oblique PDL fibre attachment (72 %) and periodontal regeneration (56 %) when compared to all other groups onto the tooth root compared to control groups. Further to this, immunohistochemistry demonstrated the presence of periostin in the newly formed ligament indicating that functional regeneration occurred These findings suggest that scaffold micro-architectures of 100 µm or below can play a crucial role in directing periodontal tissue regeneration, potentially addressing a critical gap in periodontal therapy. STATEMENT OF SIGNIFICANCE: Periodontal regeneration remains a significant clinical challenge. Essential to restoring dental health and function is the proper attachment of the periodontal ligament, which is functionally oriented, to regenerated bone and cementum. Our research presents an innovative biphasic scaffold, utilizing Melt Electrowriting to systematically guide tissue growth. Distinct from existing methods, our scaffold is highly porous, adaptable, and precisely guides periodontal ligament fibre attachment to the opposing tooth root and alveolar bone interfaces, a critical step for achieving periodontal functional regeneration. Our findings not only bridge a significant gap in biomaterial driven tissue guidance but also promise more predictable outcomes for patients, marking a transformative advancement in the field.

Hydrogel based soft tissue expanders for orodental reconstruction

Tension-free flap closure to prevent soft tissue dehiscence is a prerequisite for successful bone augmentation in orodental reconstructive surgery. Since soft tissue contour follows the underlying jaw bony architecture, resorption of alveolar (jaw) bone limits the availability of soft tissue for wound closure following major bone reconstruction, required to facilitate oral rehabilitation with endosseous dental implants following tooth loss. Although there are several clinical procedures to increase soft tissue volume, these techniques are complicated and technically demanding. Soft tissue expansion, an established technique in reconstructive surgery, is an ideal alternative to generate surplus soft tissue prior to bone augmentation and dental implant placement. Increase in tissue volume can be achieved by using soft tissue expanders (STEs). Contemporary STEs have evolved from silicone balloons to osmotically inflating hydrogel-based systems. Here, we provide an overview of STEs in clinical oral surgery, outline the current research in STEs, and an update on recent clinical trials as well as the associated complications. Also, the mechanism governing soft tissue expansion and the critical factors that control the expansion process are covered. Design considerations for STEs for intraoral applications are given particular attention. Finally, we present our perspectives on utilization of minimally invasive methods to administer STEs for orodental applications. STATEMENT OF SIGNIFICANCE: Soft tissue expansion is required for a range of reconstructive applications and more notably in regenerative dentistry for vertical bone augmentation. This review describes the commercially available soft tissue expanders along with the latest systems being currently developed. This review insightfully discusses the biological and physical mechanisms leading to soft tissue expansion and critically assesses the design criteria of soft tissue expanders. A particular focus is given on the development of a new generation of hydrogel-based soft tissue expanders; their chemistry and required physical properties for tissue expansion is described and the obstacles towards clinical translations are identified. Finally, the review elaborates on promising minimally invasive injectable hydrogel-based tissue expanders and highlights the beneficial features of these systems.

BMP2 and GDF5 for Compartmentalized Regeneration of the Scapholunate Ligament

Background  Chronic injuries to the scapholunate ligament (SLIL) alter carpal kinematics and may progress to early degenerative osteoarthritis. To date, there is no consensus for the best method for SLIL reconstruction. This study aims to assess the use of growth factors (bone morphogenetic protein [BMP]2 and growth and differentiation factor 5 [GDF5]) for compartmentalized regeneration of bone and ligament in this multiphasic scaffold in a rabbit knee model. Case Description  A total of 100 µg of BMP2 and 30 µg of GDF5 were encapsulated into a heparinized gelatin-hyaluronic acid hydrogel and loaded into the appropriate compartment of the multiphasic scaffold. The multiphasic scaffold was implanted to replace the native rabbit medial collateral ligament ( n  = 16). The rabbits were randomly assigned to two different treatment groups. The first group was immobilized postoperatively with the knee pinned in flexion with K-wires for 4 weeks ( n  = 8) prior to sacrifice. The second group was immobilized for 4 weeks, had the K-wires removed followed by a further 4 weeks of mobilization prior to sample harvesting. Literature Review  Heterotopic ossification as early as 4 weeks was noted on gross dissection and confirmed by microcomputed tomography and histological staining. This analysis revealed formation of a bony bridge located within and over the ligament compartment in the intra-articular region. Biomechanical testing showed increased ultimate force of the ligament compartment at 4 weeks postimplantation consistent with the presence of bone formation and higher numbers of scaffold failures at the bone-tendon junction. This study has demonstrated that the addition of BMP2 and GDF5 in the bone-ligament-bone (BLB) scaffold resulted in heterotopic bone formation and failure of the ligament compartment. Clinical Relevance  The implantation of a three-dimensional-printed BLB scaffold alone demonstrated superior biomechanical and histological results, and further investigation is needed as a possible clinical reconstruction for the SLIL.

3D printing for bone regeneration: challenges and opportunities for achieving predictability

3D printing offers attractive opportunities for large-volume bone regeneration in the oro-dental and craniofacial regions. This is enabled by the development of CAD-CAM technologies that support the design and manufacturing of anatomically accurate meshes and scaffolds. This review describes the main 3D-printing technologies utilized for the fabrication of these patient-matched devices, and reports on their pre-clinical and clinical performance including the occurrence of complications for vertical bone augmentation and craniofacial applications. Furthermore, the regulatory pathway for approval of these devices is discussed, highlighting the main hurdles and obstacles. Finally, the review elaborates on a variety of strategies for increasing bone regeneration capacity and explores the future of 4D bioprinting and biodegradable metal 3D printing.

Harnessing the Native Extracellular Matrix for Periodontal Regeneration Using a Melt Electrowritten Biphasic Scaffold

Scaffolds have been used to promote periodontal regeneration by providing control over the spacio-temporal healing of the periodontium (cementum, periodontal ligament (PDL) and alveolar bone). This study proposes to enhance the biofunctionality of a biphasic scaffold for periodontal regeneration by means of cell-laid extracellular matrix (ECM) decoration. To this end, a melt electrowritten scaffold was cultured with human osteoblasts for the deposition of bone-specific ECM. In parallel, periodontal ligament cells were used to form a cell sheet, which was later combined with the bone ECM scaffold to form a biphasic PDL-bone construct. The resulting biphasic construct was decellularised to remove all cellular components while preserving the deposited matrix. Decellularisation efficacy was confirmed in vitro, before the regenerative performance of freshly decellularised constructs was compared to that of 3-months stored freeze-dried scaffolds in a rodent periodontal defect model. Four weeks post-surgery, microCT revealed similar bone formation in all groups. Histology showed higher amounts of newly formed cementum and periodontal attachment in the fresh and freeze-dried ECM functionalised scaffolds, although it did not reach statistical significance. This study demonstrated that the positive effect of ECM decoration was preserved after freeze-drying and storing the construct for 3 months, which has important implications for clinical translation.

Effect of In Vitro Culture Length on the Bone-Forming Capacity of Osteoblast-Derived Decellularized Extracellular Matrix Melt Electrowritten Scaffolds

Recent advancements in decellularization have seen the development of extracellular matrix (ECM)-decorated scaffolds for bone regeneration; however, little is understood of the impact of in vitro culture prior to decellularization on the performances of these constructs. Therefore, this study investigated the effect of in vitro culture on ECM-decorated melt electrowritten polycaprolactone scaffold bioactivity. The scaffolds were seeded with osteoblasts and cultured for 1, 2, or 4 weeks to facilitate bone-specific ECM deposition and subsequently decellularized to form an acellular ECM-decorated scaffold. The utilization of mild chemicals and DNase was highly efficient in removing DNA while preserving ECM structure and composition. ECM decoration of the melt electrowritten fibers was observed within the first week of culture, with increased ECM at 2 and 4 week culture periods. Infiltration of re-seeded cells as well as overall bone regeneration in a rodent calvarial model was impeded by a longer culture period. Thus, it was demonstrated that the length of culture has a key influence on the osteogenic properties of decellularized ECM-decorated scaffolds, with long-term culture (2+ weeks) causing pore obstruction and creating a physical barrier which interfered with bone formation. These findings have important implications for the development of effective ECM-decorated scaffolds for bone regeneration.

Characterization of the Protein Corona of Three Chairside Hemoderivatives on Melt Electrowritten Polycaprolactone Scaffolds

In tissue engineering, the relationship between a biomaterial surface and the host's immune response during wound healing is crucial for tissue regeneration. Despite hemoderivative functionalization of biomaterials becoming a common tissue-engineering strategy for enhanced regeneration, the characteristics of the protein-biomaterial interface have not been fully elucidated. This study characterized the interface formed by the adsorbed proteins from various hemoderivatives with pristine and calcium phosphate (CaP)-coated polycaprolactone (PCL) melt electrowritten scaffolds. PCL scaffolds were fabricated by using melt electrospinning writing (MEW). Three hemoderivatives (pure platelet-rich plasma (P-PRP), leucocyte platelet-rich plasma (L-PRP) and injectable platelet-rich fibrin (i-PRF)) and total blood PLASMA (control) were prepared from ovine blood. Hemoderivatives were characterized via SEM/EDX, cross-linking assay, weight loss, pH and protein quantification. The interface between PCL/CaP and hemoderivative was examined via FTIR, XPS and electrophoresis. i-PRF/PCL-CaP (1653 cm^-1), PLASMA/PCL-CaP (1652 cm^-1) and i-PRF/PCL (1651 cm^-1) demonstrated a strong signal at the Amide I region. PLASMA and i-PRF presented similar N1s spectra, with most of the nitrogen involved in N-C=O bonds (≈400 eV). i-PRF resulted in higher adsorption of low molecular weight (LMW) proteins at 60 min, while PLASMA exhibited the lowest adsorption. L-PRP and P-PRP had a similar pattern of protein adsorption. The characteristics of biomaterial interfaces can be customized, thus creating a specific hemoderivative-defined layer on the PCL surface. i-PRF demonstrated a predominant adsorption of LMW proteins. Further investigation of hemoderivative functionalized biomaterials is required to identify the differential protein corona composition, and the resultant immune response and regenerative capacity.

Additively manufactured polyethylene terephthalate scaffolds for scapholunate interosseous ligament reconstruction

The regeneration of the ruptured scapholunate interosseous ligament (SLIL) represents a clinical challenge. Here, we propose the use of a Bone-Ligament-Bone (BLB) 3D-printed polyethylene terephthalate (PET) scaffold for achieving mechanical stabilisation of the scaphoid and lunate following SLIL rupture. The BLB scaffold featured two bone compartments bridged by aligned fibres (ligament compartment) mimicking the architecture of the native tissue. The scaffold presented tensile stiffness in the range of 260 ± 38 N/mm and ultimate load of 113 ± 13 N, which would support physiological loading. A finite element analysis (FEA), using inverse finite element analysis (iFEA) for material property identification, showed an adequate fit between simulation and experimental data. The scaffold was then biofunctionalized using two different methods: injected with a Gelatin Methacryloyl solution containing human mesenchymal stem cell spheroids (hMSC) or seeded with tendon-derived stem cells (TDSC) and placed in a bioreactor to undergo cyclic deformation. The first approach demonstrated high cell viability, as cells migrated out of the spheroid and colonised the interstitial space of the scaffold. These cells adopted an elongated morphology suggesting the internal architecture of the scaffold exerted topographical guidance. The second method demonstrated the high resilience of the scaffold to cyclic deformation and the secretion of a fibroblastic related protein was enhanced by the mechanical stimulation. This process promoted the expression of relevant proteins, such as Tenomodulin (TNMD), indicating mechanical stimulation may enhance cell differentiation and be useful prior to surgical implantation. In conclusion, the PET scaffold presented several promising characteristics for the immediate mechanical stabilisation of disassociated scaphoid and lunate and, in the longer-term, the regeneration of the ruptured SLIL.

Cell Seeding on 3D Scaffolds for Tissue Engineering and Disease Modeling Applications

Scaffold cell seeding is a crucial step for the standardization and homogeneous maturation of tissue engineered constructs. This is particularly critical in the context of additively manufactured scaffolds whereby large pore size and high porosity usually impedes the retention of the seeding solution resulting in poor seeding efficacy and heterogeneous cell distribution. To circumvent this limitation, a simple yet efficient cell seeding technique is described in this chapter consisting of preincubating the scaffold in 100% serum for 1 h leading to reproducible seeding. A proof of concept is demonstrated using highly porous melt electrowritten polycaprolactone scaffolds as the cell carrier. As cell density, cell distribution, and differentiation within the scaffold are important parameters, various assays are proposed to validate the seeding and perform quality control of the cellularized construct using techniques such as alizarin red, Sirius red, and immunostaining.

Workflow for Fabricating 3D-Printed Resorbable Personalized Porous Scaffolds for Orofacial Bone Regeneration

Resorption of alveolar bone following tooth extraction is a physiological process that can often prevent the placement of dental implants due to the limited bone remaining. In severe cases, vertical bone augmentation, which aims to restore bone in an extraskeletal dimension (outside of the skeletal envelope), is required prior to implant placement. While current treatment strategies rely on autologous grafts, or "Guided Bone Regeneration" involving the placement of particulate bone grafting biomaterials under a protective membrane, the field is shifting to patient-matched solutions. Herein, we describe the various steps required for modeling the patient data, creating the patient-matched scaffold geometry and 3D-printing using the biodegradable polymer polycaprolactone for application in the oro-dental and craniofacial areas.

Tissue integration and biodegradation of soft tissue substitutes with and without compression: an experimental study in the rat

OBJECTIVES

To analyze the influence of compression on tissue integration and degradation of soft tissue substitutes.

MATERIAL AND METHODS

Six subcutaneous pouches in twenty-eight rats were prepared and boxes made of Al₂O₃ were implanted and used as carriers for soft tissue substitutes: a collagen matrix (MG), two volume-stable collagen matrices (FG/MGA), and a polycaprolactone scaffold(E). The volume-stable materials (FG/MGA/E) were further implanted with a twofold (2) and a fourfold (4) compression, created by the stacking of additional layers of the substitute materials. The samples were retrieved at 1, 2, and 12 weeks (10 groups, 3 time points, n = 5 per time point and group, overall, 150 samples). The area fraction of infiltrated fibroblasts and inflammatory cells was evaluated histologically. Due to within-subject comparisons, mixed models were conducted for the primary outcome. The level of significance was set at 5%.

RESULTS

The area fraction of fibroblasts increased in all groups over time. At 12 weeks, the densely compressed materials FG4 (1.1%), MGA4 (1.7%), and MGA2 (2.5%) obtained lower values as compared to the other groups, ranging between 4.7 (E2) and 6.5% (MG). Statistically significant differences (p ≤ 0.05) were observed between groups FG4 vs MG/FG2/E/E4 as well as between MGA4 vs MG/FG2/E/E4 and E vs MGA2.

CONCLUSIONS

Higher levels of compression led to delayed tissue integration. The effect of different compression levels was more distinct when compared to the differences between the materials.

CLINICAL RELEVANCE

All biomaterials demonstrated tissue integration and a minimal concomitant inflammatory reaction. Clinically, it might be more favorable to obtain a sufficient flap release or to reduce the material size to improve the tissue integration processes.

Fibre-guiding biphasic scaffold for perpendicular periodontal ligament attachment

Periodontal regeneration is characterized by the attachment of oblique periodontal ligament fibres on the tooth root surface. To facilitate periodontal ligament attachment, a fibre-guiding tissue engineered biphasic construct was manufactured by melt electrowriting (MEW) for influencing reproducible cell guidance and tissue orientation. The biphasic scaffold contained fibre-guiding features in the periodontal ligament component comprising of 100 µm spaced channels (100CH), a pore size gradient in the bone component and maintained a highly porous and fully interconnected interface between the compartments. The efficacy of the fibre-guiding channels was assessed in an ectopic periodontal attachment model in immunocompromised rats. This demonstrated an unprecedented and systematic tissue alignment perpendicular to the dentin in the 100CH group, resulting in the close mimicry of native periodontal ligament architecture. In addition, the histology revealed high levels of tissue integration between the two compartments as observed by the perpendicular collagen attachment on the dentin surface, which also extended and infiltrated the scaffold's bone compartment. In conclusion, the 100 µm fibre-guiding scaffold induced a systematic tissue orientation at the dentin-ligament interface, resembling the native periodontium and thus resulting in enhanced alignment mimicking periodontal ligament regeneration. STATEMENT OF SIGNIFICANCE: Periodontitis is a prevalent inflammatory disease affecting a large portion of the adult population and leading to the destruction of the tooth-supporting structures (alveolar bone, periodontal ligament, and cementum). Current surgical treatments are unpredictable and generally result in repair rather than functional regeneration. A key feature of functional regeneration is the re-insertion of the oblique or perpendicularly orientated periodontal ligament fibre in both the alveolar bone and root surface. This study demonstrates that a highly porous scaffold featuring 100 µm width channels manufactured by the stacking of melt electrospun fibres, induced perpendicular alignment and attachment of the neo-ligament onto a dentine surface. The fibre guiding micro-architecture may pave the way for enhanced and more functional regeneration of the periodontium.

In vitro evaluation of porous poly(hydroxybutyrate-co-hydroxyvalerate)/akermanite composite scaffolds manufactured using selective laser sintering

Incorporation of a bioactive mineral filler in a biodegradable polyester scaffold is a promising strategy for scaffold assisted bone tissue engineering (TE). The current study evaluates the in vitro behavior of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)/Akermanite (AKM) composite scaffolds manufactured using selective laser sintering (SLS). Exposure of the mineral filler on the surface of the scaffold skeleton was evident from in vitro mineralization in PBS. PHBV scaffolds and solvent cast films served as control samples and all materials showed preferential adsorption of fibronectin compared to serum albumin as well as non-cytotoxic response in human osteoblasts (hOB) at 24 h. hOB culture for up to 21 days revealed that the metabolic activity in PHBV films and scaffolds was significantly higher than that of PHBV/AKM scaffolds within the first two weeks of incubation. Afterwards, the metabolic activity in PHBV/AKM scaffolds exceeded that of the control samples. Confocal imaging showed cell penetration into the porous scaffolds. Significantly higher ALP activity was observed in PHBV/AKM scaffolds at all time points in both basal and osteogenic media. Mineralization during cell culture was observed on all samples with PHBV/AKM scaffolds exhibiting distinctly different mineral morphology. This study has demonstrated that the bioactivity of PHBV SLS scaffolds can be enhanced by incorporating AKM, making this an attractive candidate for bone TE application.

The utilisation of resolvins in medicine and tissue engineering

Recent advances in the field of regenerative medicine and biomaterial science have highlighted the importance of controlling immune cell phenotypes at the biomaterial interface. These studies have clearly indicated that a rapid resolution of the inflammatory process, mediated by a switch in the macrophage population towards a reparative phenotype, is essential for tissue regeneration to occur. While various biomaterial surfaces have been developed in order to impart immunomodulatory properties to the resulting constructs, an alternative strategy involving the use of reparative biological cues, known as resolvins, is emerging in regenerative medicine. This review reports on the mechanisms via which resolvins participate in the resolution of inflammation and describes their current utilisation in pre-clinical and clinical settings, along with their effectiveness when combined with biomaterial constructs in tissue engineering applications. STATEMENT OF SIGNIFICANCE: The resolution of the inflammatory process is necessary for achieving tissue healing and regeneration. Resolvins are lipid mediators and play a key role in the resolution of the inflammatory response and can be used in as biological cues to promote tissue regeneration. This review describes the various biological inflammatory mechanisms and pathways involving resolvins and how their action results in a pro-healing response. The use of these molecules in the clinical setting is then summarised for various applications along with their limitations. Lastly, the review focuses on the emergence resolvins in tissue engineering products including the use of a more stable form which holds greater prospect for regenerative purposes.

Interleukin-1 Is Overexpressed in Injured Muscles Following Spinal Cord Injury and Promotes Neurogenic Heterotopic Ossification

Neurogenic heterotopic ossifications (NHOs) form in periarticular muscles after severe spinal cord (SCI) and traumatic brain injuries. The pathogenesis of NHO is poorly understood with no effective preventive treatment. The only curative treatment remains surgical resection of pathological NHOs. In a mouse model of SCI-induced NHO that involves a transection of the spinal cord combined with a muscle injury, a differential gene expression analysis revealed that genes involved in inflammation such as interleukin-1β (IL-1β) were overexpressed in muscles developing NHO. Using mice knocked-out for the gene encoding IL-1 receptor (IL1R1) and neutralizing antibodies for IL-1α and IL-1β, we show that IL-1 signaling contributes to NHO development after SCI in mice. Interestingly, other proteins involved in inflammation that were also overexpressed in muscles developing NHO, such as colony-stimulating factor-1, tumor necrosis factor, or C-C chemokine ligand-2, did not promote NHO development. Finally, using NHO biopsies from SCI and TBI patients, we show that IL-1β is expressed by CD68⁺ macrophages. IL-1α and IL-1β produced by activated human monocytes promote calcium mineralization and RUNX2 expression in fibro-adipogenic progenitors isolated from muscles surrounding NHOs. Altogether, these data suggest that interleukin-1 promotes NHO development in both humans and mice. © 2021 American Society for Bone and Mineral Research (ASBMR).

Recent Advances in Vertical Alveolar Bone Augmentation Using Additive Manufacturing Technologies

Vertical bone augmentation is aimed at regenerating bone extraskeletally (outside the skeletal envelope) in order to increase bone height. It is generally required in the case of moderate to severe atrophy of bone in the oral cavity due to tooth loss, trauma, or surgical resection. Currently utilized surgical techniques, such as autologous bone blocks, distraction osteogenesis, and Guided Bone Regeneration (GBR), have various limitations, including morbidity, compromised dimensional stability due to suboptimal resorption rates, poor structural integrity, challenging handling properties, and/or high failure rates. Additive manufacturing (3D printing) facilitates the creation of highly porous, interconnected 3-dimensional scaffolds that promote vascularization and subsequent osteogenesis, while providing excellent handling and space maintaining properties. This review describes and critically assesses the recent progress in additive manufacturing technologies for scaffold, membrane or mesh fabrication directed at vertical bone augmentation and Guided Bone Regeneration and their in vivo application.

Lymphocytes Are Not Required for Neurogenic Heterotopic Ossification Development after Spinal Cord Injury

Neurogenic heterotopic ossifications (NHOs) are incapacitating complications of traumatic brain and spinal cord injuries (SCI) that manifest as abnormal bone formation in periarticular muscles. Using a unique model of NHO after SCI in genetically unmodified mice, we have previously established that the innate immune system plays a key driving role in NHO pathogenesis. The role of adaptive immune cells in NHO pathogenesis, however, remains unexplored in this model. Here we established that B lymphocytes were reduced in the spleen and blood after SCI and increased in muscles of mice in which NHO develops, whereas minimal changes in T cell frequencies were noted. Interestingly, Rag1^-/- mice lacking mature T and B lymphocytes, developed NHO, similar to wild-type mice. Finally, mice that underwent splenectomy before SCI and muscle damage also developed NHO to the same extent as non-splenectomized SCI controls. Overall, our findings show that functional T and B lymphocytes have minimal influence or dispensable contributions to NHO development after experimental SCI in mice.

Local delivery of hydrogel encapsulated vascular endothelial growth factor for the prevention of medication-related osteonecrosis of the jaw

The anti-angiogenic effects of bisphosphonates have been hypothesized as one of the major etiologic factors in the development of medication-related osteonecrosis of the jaw (MRONJ), a severe debilitating condition with limited treatment options. This study evaluated the potential of a gelatine-hyaluronic acid hydrogel loaded with the angiogenic growth factor, vascular endothelial growth factor (VEGF), as a local delivery system to aid in maintaining vascularization in a bisphosphonate-treated (Zoledronic Acid) rodent maxillary extraction defect. Healing was assessed four weeks after implantation of the VEGF-hydrogel into extraction sockets. Gross examination and histological assessment showed that total osteonecrosis and inflammatory infiltrate was significantly reduced in the presence of VEGF. Also, total vascularity and specifically neovascularization, was significantly improved in animals that received VEGF hydrogel. Gene expression of vascular, inflammatory and bone specific markers within the defect area were also significantly altered in the presence of VEGF. Furthermore, plasma cytokine levels were assessed to determine the systemic effect of locally delivered VEGF and showed similar outcomes. In conclusion, the use of locally delivered VEGF within healing extraction sockets assists bone healing and prevents MRONJ via a pro-angiogenic and immunomodulatory mechanism.

Iron accumulation is associated with periodontal destruction in a mouse model of HFE-related haemochromatosis

OBJECTIVE

To investigate the effect of Hfe gene mutation on the distribution of iron and periodontal bone loss in periodontal tissues.

BACKGROUND DATA

It remains unclear how tissue iron loading affects the periodontium architectures in a genetic animal model of hereditary haemochromatosis (HH).

METHODS

Male C57BL/6 Hfe^-/- (8 weeks old) and wild-type (WT) mice were utilized to examine the iron distribution in periodontal tissues, as well as periodontal tissues changes using micro-computed tomography and histomorphometric analysis. Furthermore, tissue inflammatory mediators, bone markers and periodontal pathogens were carried out in PFA-fixed paraffin-embedded tissues using ELISA, RT-qPCR and genomic DNA qPCR, respectively.

RESULTS

Excessive iron deposition was found in the periodontal ligament, gingiva and alveolar bone in Hfe^-/- mice relative to their WT counterparts. This, in turn, was associated with significant periodontal bone loss, increased cemento-enamel junction-alveolar bone crest distance and decreased expression of molecules involved in bone development and turnover. Furthermore, the pro-inflammatory cytokine - interleukin 6 and periodontal bacteria - Campylobacter rectus were significantly increased in Hfe^-/- mice compared with WT controls.

CONCLUSION

Our results suggest that the iron loading in a mouse model of HH decreases alveolar bone formation and leads to alterations in the inflammatory state in the periodontium. Periodontal health should be assessed during the clinical assessment of HFE-HH patients.

Finite element analysis of the performance of additively manufactured scaffolds for scapholunate ligament reconstruction

Rupture of the scapholunate interosseous ligament can cause the dissociation of scaphoid and lunate bones, resulting in impaired wrist function. Current treatments (e.g., tendon-based surgical reconstruction, screw-based fixation, fusion, or carpectomy) may restore wrist stability, but do not address regeneration of the ruptured ligament, and may result in wrist functional limitations and osteoarthritis. Recently a novel multiphasic bone-ligament-bone scaffold was proposed, which aims to reconstruct the ruptured ligament, and which can be 3D-printed using medical-grade polycaprolactone. This scaffold is composed of a central ligament-scaffold section and features a bone attachment terminal at either end. Since the ligament-scaffold is the primary load bearing structure during physiological wrist motion, its geometry, mechanical properties, and the surgical placement of the scaffold are critical for performance optimisation. This study presents a patient-specific computational biomechanical evaluation of the effect of scaffold length, and positioning of the bone attachment sites. Through segmentation and image processing of medical image data for natural wrist motion, detailed 3D geometries as well as patient-specific physiological wrist motion could be derived. This data formed the input for detailed finite element analysis, enabling computational of scaffold stress and strain distributions, which are key predictors of scaffold structural integrity. The computational analysis demonstrated that longer scaffolds present reduced peak scaffold stresses and a more homogeneous stress state compared to shorter scaffolds. Furthermore, it was found that scaffolds attached at proximal sites experience lower stresses than those attached at distal sites. However, scaffold length, rather than bone terminal location, most strongly influences peak stress. For each scaffold terminal placement configuration, a basic metric was computed indicative of bone fracture risk. This metric was the minimum distance from the bone surface to the internal scaffold bone terminal. Analysis of this minimum bone thickness data confirmed further optimisation of terminal locations is warranted.

The Mechanosensing and Global DNA Methylation of Human Osteoblasts on MEW Fibers

Cells interact with 3D fibrous platform topography via a nano-scaled focal adhesion complex, and more research is required on how osteoblasts sense and respond to random and aligned fibers through nano-sized focal adhesions and their downstream events. The present study assessed human primary osteoblast cells’ sensing and response to random and aligned medical-grade polycaprolactone (PCL) fibrous 3D scaffolds fabricated via the melt electrowriting (MEW) technique. Cells cultured on a tissue culture plate (TCP) were used as 2D controls. Compared to 2D TCP, 3D MEW fibrous substrates led to immature vinculin focal adhesion formation and significantly reduced nuclear localization of the mechanosensor-yes-associated protein (YAP). Notably, aligned MEW fibers induced elongated cell and nucleus shape and highly activated global DNA methylation of 5-methylcytosine, 5-hydroxymethylcytosine, and N-6 methylated deoxyadenosine compared to the random fibers. Furthermore, although osteogenic markers (osterix-OSX and bone sialoprotein-BSP) were significantly enhanced in PCL-R and PCL-A groups at seven days post-osteogenic differentiation, calcium deposits on all seeded samples did not show a difference after normalizing for DNA content after three weeks of osteogenic induction. Overall, our study linked 3D extracellular fiber alignment to nano-focal adhesion complex, nuclear mechanosensing, DNA epigenetics at an early point (24 h), and longer-term changes in osteoblast osteogenic differentiation.

Multiphasic scaffold for scapholunate interosseous ligament reconstruction: A study in the rabbit knee

Scapholunate interosseous ligament tears are a common wrist injury in young and active patients that can lead to suboptimal outcomes after repair. This research aims to assess a multiphasic scaffold using 3D-printing for reconstruction of the dorsal scapholunate interosseous ligament. The scaffold was surgically implanted in vivo in the position of the native rabbit medial collateral ligament. Two branches of treatment were implemented in the study. In the first group, the rabbits (n = 8) had the knee joint fixed in flexion for 4 weeks using 1.4 mm K-wires prior to sample harvesting. The second group (n = 8) had the rabbit knee joint immobilized for 4 weeks prior to K-wire removal and mobilization for an additional 4 weeks prior to sample harvesting. Overall, samples were harvested at 4 weeks post-surgery (immobilized group) and eight weeks post-surgery (mobilized group). Mechanical tensile testing (n = 5/group) and histology (n = 3/group) of the constructs were conducted. Tissue integration and maturation were observed resulting in increased mechanical strength of the operated joint at 8 weeks (P < .05). Bone and ligament tissues were regenerated in their respective compartments with structural and mechanical properties approaching those reported for the human dorsal SLIL ligament. Clinical Significance: This proof of concept study has demonstrated that the synthetic multiphasic scaffold was capable of regenerating both bone and ligament while also withstanding the physiological load once implanted in the rabbit knee. The artificial scaffold may provide an alternative to current techniques for reconstruction of scapholunate instability or other ligament injuries in the hand and wrist.

Effect of Dual Pore Size Architecture on In Vitro Osteogenic Differentiation in Additively Manufactured Hierarchical Scaffolds

The combination of macro- and microporosity is a potent manner of enhancing osteogenic potential, but the biological events leading to this increase in osteogenesis are not well understood. In this study, we investigated the effect of a dual pore size scaffold on the physical and biological properties, with the hypothesis that cell condensation is the determining factor for enhanced osteogenic differentiation. To this end, a hierarchical scaffold possessing a dual (large and small) pore size was fabricated by combining two additive manufacturing techniques: melt electrospinning writing (MEW) and fused deposition modeling (FDM). The scaffolds showed a mechanical stiffness of 23.2 ± 1.5 MPa similar to the FDM control scaffold, while the hybrid revealed an increased specific surface area of 1.4 ± 0.1 m²/g. The scaffold was cultured with primary human osteoblasts for 28 days, which showed enhanced cell adhesion and proliferation. The hierarchical structure was also beneficial for in vitro alkaline phosphate activity and mineralization and showed an increased expression of osteogenic protein and genes. Mesenchymal condensation markers related to osteoblastic differentiation (CDH2, RhoA, Rac1, and Cdc42) were upregulated in the hybrid construct, demonstrating that the MEW membrane provided an environment more suitable for the recapitulation of cell condensation, which in turn leads to higher osteogenic differentiation. In summary, this study demonstrated that the hierarchical scaffold developed in this paper leads to a significant improvement in the scaffold properties such as increased specific surface area, initial cell adhesion, cell proliferation, and in vitro osteogenesis.

Fibroblastic differentiation of mesenchymal stem/stromal cells (MSCs) is enhanced by hypoxia in 3D cultures treated with bone morphogenetic protein 6 (BMP6) and growth and differentiation factor 5 (GDF5)

INTRODUCTION

Culture conditions and differentiation cocktails may facilitate cell maturation and extracellular matrix (ECM) secretion and support the production of engineered fibroblastic tissues with applications in ligament regeneration. The objective of this study is to investigate the potential of two connective tissue-related ligands (i.e., BMP6 and GDF5) to mediate collagenous ECM synthesis and tissue maturation in vitro under normoxic and hypoxic conditions based on the hypothesis that BMP6 and GDF5 are components of normal paracrine signalling events that support connective tissue homeostasis.

METHODS

Human adipose-derived MSCs were seeded on 3D-printed medical-grade polycaprolactone (PCL) scaffolds using a bioreactor and incubated in media containing GDF5 and/or BMP6 for 21 days in either normoxic (5% oxygen) or hypoxic (2% oxygen) conditions. Constructs were harvested on Day 3 and 21 for cell viability analysis by live/dead staining, structural analysis by scanning electron microscopy, mRNA levels by RTqPCR analysis, and in situ deposition of proteins by immunofluorescence microscopy.

RESULTS

Pro-fibroblastic gene expression is enhanced by hypoxic culture conditions compared to normoxic conditions. Hypoxia renders cells more responsive to treatment with BMP6 as reflected by increased expression of ECM mRNA levels on Day 3 with sustained expression until Day 21. GDF5 was not particularly effective either in the absence or presence of BMP6.

CONCLUSIONS

Fibroblastic differentiation of MSCs is selectively enhanced by BMP6 and not GDF5. Environmental factors (i.e., hypoxia) also influenced the responsiveness of cells to this morphogen.

Enamel matrix derivative promotes new bone formation in xenograft assisted maxillary anterior ridge preservation-A randomized controlled clinical trial

OBJECTIVES

To compare the effectiveness of deproteinized bovine bone mineral with 10% collagen alone (DBBMC) or with enamel matrix derivative (DBBMC-EMD) in ridge preservation.

METHODS

42 maxillary anterior teeth were extracted and received either a DBBMC (control) or DBBMC-EMD (test) treatment protocol. CBCT taken before and 4 months after the extraction procedure was used to measure changes in alveolar ridge width (RW), buccal bone height (BH) and palatal bone height (PH). Bone cores were harvested during implant osteotomy preparation, and the samples processed histomorphometrically to assess the fraction of new bone (%NB), residual graft (%RG) and soft tissue matrix (%STM).

RESULTS

Overall, both treatment groups showed significant reductions in mean RW from baseline to 4 months after extraction, but no significant change in either mean BH or PH over this time. When CBCT measurements were analysed according to the initial thickness of the buccal wall (BT < 1 mm vs. BT ≥ 1 mm), significant reductions in all ridge dimensions (RW, BH and PH) were noted in the <1 mm BT group. Histomorphometrically, the DBBMC-EMD test group showed significantly increased new bone formation (%NB): (control = 16.5 ± 6.9% cf.; test = 45.1 ± 8.8%) with less residual graft (%RG): (control = 36.8 ± 8.8% cf.; test = 20.3 ± 7.2%) compared to the DBBMC control group.

CONCLUSIONS

Both DBBMC alone and DBBMC-EMD treated sites 4 months after extraction lost RW but showed no significant change in BH or PH. Irrespective of treatment, maxillary anterior teeth with thick initial buccal walls (≥1 mm) exhibited less alveolar ridge reduction 4 months after treatment. The addition of EMD to DBBMC resulted in more new bone formation in the test group.

Combination of BMP2 and EZH2 Inhibition to Stimulate Osteogenesis in a 3D Bone Reconstruction Model

High concentrations of bone morphogenetic protein 2 (BMP2) in bone regeneration cause adverse events (e.g, heterotopic bone formation and acute inflammation). This study examines novel epigenetic strategies (i.e., EZH2 inhibition) for augmenting osteogenesis, thereby aiming to reduce the required BMP2 dose in vivo for bone regeneration and minimize these adverse effects. Human bone marrow-derived mesenchymal stem cells (BMSCs) were grown on three-dimensional (3D)-printed medical-grade polycaprolactone scaffolds and incubated in osteogenic media containing 50 ng/mL BMP2 and/or 5 μM GSK126 (EZH2 inhibitor) for 6 days (n = 3 per group and timepoint). Constructs were harvested for realtime quantitative polymerase chain reaction analysis at Day 10 and immunofluorescence (IF) microscopy at Day 21. After pretreating for 6 days and maintaining in osteogenic media for 4 days, BMSC-seeded scaffolds were also implanted in an immunocompromised subcutaneous murine model (n = 39; 3/group/donor and 3 control scaffolds) for histological analysis at 8 weeks. Pretreatment of BMSCs with BMP2 and BMP2/GSK126 costimulated expression of osteoblast-related genes (e.g., IBSP, SP7, RUNX2, and DLX5), as well as protein accumulation (e.g., collagen type 1/COL1A1 and osteocalcin/BGLAP) based on IF staining. While in vivo implantation for 8 weeks did not result in bone formation, increased angiogenesis was observed in BMP2 and BMP2/GSK126 groups. This study finds that BMP2 and GSK126 costimulate osteogenic differentiation of MSCs on 3D scaffolds in vitro and may contribute to enhanced vascularization when implanted in vivo to support bone formation. Thus, epigenetic priming with EZH2 inhibitors may have translational potential in bone healing by permitting a reduction of BMP2 dosing in vivo to mitigate its side effects. Impact statement While autografts are still the gold standard for bone reconstruction, tissue availability and donor morbidity are significant limitations. Previous attempts to use high concentrations of bone morphogenetic protein 2 (BMP2) have been shown to cause adverse events such as excessive bone formation and acute inflammation. Overall, the utilization of EZH2 inhibitors to modulate gene expression in favor of bone healing has been demonstrated in vitro in a tissue engineering strategy. Our study will pave the way to developing tissue engineering strategies involving GSK126 as an adjuvant to increase the effects of BMP2 for stimulating cells of interest on a three-dimensional scaffold for bone regeneration.

Resorbable additively manufactured scaffold imparts dimensional stability to extraskeletally regenerated bone

Dimensionally stable vertical bone regeneration outside of the existing bony envelope is a major challenge in the field of orofacial surgery. In this study, we demonstrate that a highly porous, resorbable scaffold fabricated using additive manufacturing techniques enables reproducible extra-skeletal bone formation and prevents bone resorption. An additively manufactured medical grade polycaprolactone (mPCL) biphasic scaffold mimicking the architecture of the jaw bone, consisting of a 3D-printed outer shell overlying an inner highly porous melt electrowritten scaffold, was assessed for its ability to support dimensionally stable bone regeneration in an extraskeletal ovine calvarial model. To investigate bone formation capacity (stage 1), 7 different constructs placed under a protective dome were assessed 8 weeks post-implantation: Empty control, Biphasic scaffold with hydrogel (PCL-Gel), PCL-Gel with 75 or 150 μg of BMP-2 (PCL-BMP-75 and PCL-BMP-150), hydrogel only (Gel), Gel containing 75 or 150 μg of BMP-2 (Gel-BMP-75 and Gel-BMP-150). To assess dimensional stability (stage 2), in a separate cohort, 5 animals were similarly implanted with 2 samples of each of the Gel-BMP-150 and PCL-BMP-150 groups, and after 8 weeks of healing, the protective domes were removed and titanium implants were placed in the regenerated bone and allowed to heal for a further 8 weeks. Bone formation and osseointegration were assessed using micro-computed tomography, histology and histomorphometry. In stage 1, enhanced bone formation was found in the BMP-2 containing groups, especially the PCL-BMP constructs whereby regeneration of full bone height was achieved in a reproducible manner. There was no significant bone volume increase with the higher dose of BMP-2. In the dimensional stability assessment (stage 2), after the rtemoval of the protective dome, the biphasic scaffold prevented bone resorption whereas in the absence of the scaffold, the bone previously formed in the hydrogel underwent extensive resorption. This was attributed to the space maintenance properties and dimensional stability of the biphasic scaffold. Titanium implants osseointegrated into the newly formed bone within the biphasic scaffolds. In conclusion, additively manufactured biphasic scaffolds functionalized with BMP-2 facilitated dimensionally stable bone regeneration that supported dental implant osseointegration.

Layered Antimicrobial Selenium Nanoparticle-Calcium Phosphate Coating on 3D Printed Scaffolds Enhanced Bone Formation in Critical Size Defects

Preventing bacterial colonization on scaffolds while supporting tissue formation is highly desirable in tissue engineering as bacterial infection remains a clinically significant risk to any implanted biomaterials. Elemental selenium (Se⁰) nanoparticles have emerged as a promising antimicrobial biomaterial without tissue cell toxicity, yet it remains unknown if their biological properties are from soluble Se ions or from direct cell-nanoparticle interactions. To answer this question, in this study, we developed a layered coating consisting of a Se nanoparticle layer underneath a micrometer-thick, biomimetic calcium phosphate (CaP) layer. We showed, for the first time, that the release of soluble HSe^- ions from the Se nanoparticles strongly inhibited planktonic growth and biofilm formation of key bacteria, Staphylococcus aureus. The Se-CaP coating was found to support higher bone formation than the CaP-only coating in critical-size calvarial defects in rats; this finding could be directly attributed to the released soluble Se ions as the CaP layers in both groups had no detectable differences in the porous morphology, chemistry, and release of Ca or P. The Se-CaP coating was highly versatile and applicable to various surface chemistries as it formed through simple precipitation from aqueous solutions at room temperature and therefore could be promising in bone regeneration scaffolds or orthopedic implant applications.

3D-printed cryomilled poly(ε-caprolactone)/graphene composite scaffolds for bone tissue regeneration

In this study, composite scaffolds based on poly(caprolactone) (PCL) and non-covalently functionalized few-layer graphene (FLG) were manufactured by an extrusion-based system for the first time. For that, functionalized FLG powder was obtained through the evaporation of a functionalized FLG aqueous suspension prepared from a graphite precursor. Cryomilling was shown to be an efficient mixing method, producing a homogeneous dispersion of FLG particles onto the PCL polymeric matrix. Thereafter, fused deposition modeling (FDM) was used to print 3D scaffolds and their morphology, thermal, biodegradability, mechanical, and cytotoxicity properties were analysed. The presence of functionalized FLG demonstrated to induce slight changes in the microstructure of the scaffold, did not affect the thermal stability and enhanced significantly the compressive modulus. The composite scaffolds presented a porosity of around 40% and a mean pore size in the range of 300 μm. The cell viability and proliferation of SaOs-2 cells were assessed and the results showed good cell viability and long-term proliferation onto produced composite scaffolds. Therefore, these new FLG/PCL scaffolds comprised adequate morphological, thermal, mechanical, and biological properties to be used in bone tissue regeneration.

Patient-Specific Bone Particles Bioprinting for Bone Tissue Engineering

Although bioinks with both high printability and shape fidelity while maintaining high cell viability are developed, the biofunctionality of the resulting bioprinted construct is often overlooked. To address this, a methacrylated gelatin (GelMA)-based bioink biofunctionalized with bone particles (BPs) is developed as a personalized treatment strategy for bone regeneration. The bioink consists of incorporating BPs of various sizes (0-500 µm) in GelMA at various concentrations (ranging from 5 to 15% w/v). The printability of the bioink is systematically investigated and it is demonstrated that a 15% w/v BP-loading results in high print quality for 10% and 12.5% GelMA concentrations. Rheological evaluation reveals a strong shear thinning behavior essential for printing and a high gel strength in bioink with 15% w/v 0-500 µm BPs for both GelMA concentrations. In addition, the printability of the bioink and the metabolic activity of the resulting scaffolds are dependent on both the concentration of hydrogel and size of the BPs. Importantly, the cells initially contained in the BPs are able to migrate and colonize the bioprinted scaffold while maintaining their capacity to express early osteogenic markers. This study demonstrates the feasibility of bioprinted viable BPs and may have some potential for chairside clinical translation.

Multiscale porosity in mesoporous bioglass 3D-printed scaffolds for bone regeneration

In order to increase the bone forming ability of MBG-PCL composite scaffold, microporosity was created in the struts of 3D-printed MBG-PCL scaffolds for the manufacturing of a construct with a multiscale porosity consisting of meso- micro- and macropores. 3D-printing imparted macroporosity while the microporosity was created by porogen removal from the struts, and the MBG particles were responsible for the mesoporosity. The scaffolds were 3D-printed using a mixture of PCL, MBG and phosphate buffered saline (PBS) particles, subsequently leached out. Microporous-PCL (pPCL) as a negative control, microporous MBG-PCL (pMBG-PCL) and non-microporous-MBG-PCL (MBG-PCL) were investigated. Scanning electron microscopy, mercury intrusion porosimetry and micro-computed tomography demonstrated that the PBS removal resulted in the formation of micropores inside the struts with porosity of around 30% for both pPCL and pMBG-PCL, with both constructs displaying an overall porosity of 8090%. In contrast, the MBG-PCL group had a microporosity of 6% and an overall porosity of 70%. Early mineralisation was found in the pMBG-PCL post-leaching out and this resulted in the formation a more homogeneous calcium phosphate layer when using a biomimetic mineralisation assay. Mechanical properties ranged from 5 to 25 MPa for microporous and non-microporous specimens, hence microporosity was the determining factor affecting compressive properties. MC3T3-E1 metabolic activity was increased in the pMBG-PCL along with an increased production of RUNX2. Therefore, the microporosity within a 3D-printed bioceramic composite construct may result in additional physical and biological benefits.

Neurogenic Heterotopic Ossifications Develop Independently of Granulocyte Colony-Stimulating Factor and Neutrophils

Neurogenic heterotopic ossifications (NHOs) are incapacitating heterotopic bones in periarticular muscles that frequently develop following traumatic brain or spinal cord injuries (SCI). Using our unique model of SCI-induced NHO, we have previously established that mononucleated phagocytes infiltrating injured muscles are required to trigger NHO via the persistent release of the pro-inflammatory cytokine oncostatin M (OSM). Because neutrophils are also a major source of OSM, we investigated whether neutrophils also play a role in NHO development after SCI. We now show that surgery transiently increased granulocyte colony-stimulating factor (G-CSF) levels in blood of operated mice, and that G-CSF receptor mRNA is expressed in the hamstrings of mice developing NHO. However, mice defective for the G-CSF receptor gene Csf3r, which are neutropenic, have unaltered NHO development after SCI compared to C57BL/6 control mice. Because the administration of recombinant human G-CSF (rhG-CSF) has been trialed after SCI to increase neuroprotection and neuronal regeneration and has been shown to suppress osteoblast function at the endosteum of skeletal bones in human and mice, we investigated the impact of a 7-day rhG-CSF treatment on NHO development. rhG-CSF treatment significantly increased neutrophils in the blood, bone marrow, and injured muscles. However, there was no change in NHO development compared to saline-treated controls. Overall, our results establish that unlike monocytes/macrophages, neutrophils are dispensable for NHO development following SCI, and rhG-CSF treatment post-SCI does not impact NHO development. Therefore, G-CSF treatment to promote neuroregeneration is unlikely to adversely promote or affect NHO development in SCI patients. © 2020 American Society for Bone and Mineral Research.

A comprehensive comparison of cell seeding methods using highly porous melt electrowriting scaffolds

Cell seeding is challenging in the case of additively manufactured 3-dimensional scaffolds, as the open macroscopic pore network impedes the retention of the seeding solution. The present study aimed at comparing several seeding conditions (no fetal bovine serum, 10% or 100% serum) and methods (Static seeding in Tissue Culture Treated plate (CT), Static seeding of the MES in non-Culture Treated plate (nCT), Seeding in nCT plate placed on an orbital shaker at 20 rpm (nCTR), Static seeding of the MES previously incubated with 100% FBS for 1 h to allow for protein adsorption (FBS)) commonly utilised in tissue engineering using highly porous melt electrowritten scaffolds, assessing their seeding efficacy, cell distribution homogeneity and reproducibility. Firstly, we demonstrated that the incubation in 100% serum was superior to the 10% serum pre-incubation and that 1 h only was sufficient to obtain enhanced cell attachment. We further compared this technique to the other methods and demonstrated significant and beneficial impact of the 100% serum pre-incubation, which resulted in enhanced efficacy, homogeneous cell distribution and high reproducibility, leading to accelerated colonisation/maturation of the tissue engineered constructs. We further showed the superior performance of this method using 3D-printed scaffolds also made of different polymers, demonstrating its capacity for up-scaling. Therefore, the pre-incubation of the scaffold in 100% serum is a simple yet highly effective method for enhancing cell adhesion and ensuring seeding reproducibility. This is crucial for tissue engineering applications, especially when cell availability is scarce, and for product standardisation from a translational perspective.

Fibre guiding scaffolds for periodontal tissue engineering

The periodontium is a highly hierarchically organized organ composed of gingiva, alveolar bone, periodontal ligament and cementum. Periodontitis leads to the destruction of hard and soft tissues ultimately leading to a loss of the teeth supporting apparatus. Current treatments are capable of limiting the disease progression; however, true regeneration, characterized by perpendicularly oriented periodontal ligament fibre attachment to cementum on the root surface remains challenging. Tissue engineering approaches have been developed to enhance regeneration via micro-engineered topographical features, purposely designed to guide the insertion of the regenerated ligament to the root surface. This review reports on the recent advancements in scaffold manufacturing methodologies for generating fibre guiding properties and provides a critical insight in the current limitations of these techniques for the formation of functional periodontal attachment.

The effect of melt electrospun writing fiber orientation onto cellular organization and mechanical properties for application in Anterior Cruciate Ligament tissue engineering

The effect of melt electrospun writing fiber arrangement on cellular behavior has not yet been thoroughly investigated. Cellular orientation is particularly important in the context of ligament tissue engineering for orthopedic applications whereby a high degree of cell alignment is present in the native tissue. The aim of this study was to investigate the response of human mesenchymal stem cells (hMSC) to three different patterned porous polycaprolactone scaffolds (aligned, crimped and random) fabricated by melt electrospinning writing, resulting in 20 μm diameter electrospun fibers. Cell orientation was investigated over 4 weeks in vitro and it was demonstrated that the aligned pattern was capable of orientating the hMSCs towards the main direction of the fibers and this feature was maintained over the entire culture period whereas the orientation was rapidly lost in the crimped pattern. In order to fabricate a functional scaffold for ligament tissue engineering, the scaffolds were rolled in three bundles, subsequently braided and combined with a bone compartment (consisting of a melt electrospun scaffold seeded with osteogenically induced hMSCs) for the development of a Bone-Ligament-Bone (BLB) construct. The mechanical properties of non-cellularized and cellularized BLB constructs were assessed under both quasi-static and cyclic conditions. This revealed that the in vitro maturation significantly softened the BLB constructs and that the mechanical properties were several fold lower than those of native tissue. The cyclic testing demonstrated that the presence of cell sheets resulted in increased resilience and elasticity, even though the global mechanical properties were decreased for the in vitro matured constructs (regardless of the pattern). In conclusion, we demonstrated that melt electrospinning writing fiber organization can induce spontaneous cell alignment and that large cellularized BLB constructs with complex geometry can achieve mechanical resilience under cyclic stretching.

The effect of biomimetic mineralization of 3D-printed mesoporous bioglass scaffolds on physical properties and in vitro osteogenicity

Three-dimensional Mesoporous bioactive glasses (MBGs) scaffolds has been widely considered for bone regeneration purposes and additive manufacturing enables the fabrication of highly bioactive patient-specific constructs for bone defects. Commonly, this process is performed with the addition of polymeric binders that facilitate the printability of scaffolds. However, these additives cover the MBG particles resulting in the reduction of their osteogenic potential. The present work investigates a simple yet effective phosphate-buffered saline immersion method for achieving polyvinyl alcohol binder removal while enables the maintenance of the mesoporous structure of MBG 3D-printed scaffolds. This resulted in significantly modifying the surface of the scaffold via the spontaneous formation of a biomimetic mineralized layer which positively affected the physical and biological properties of the scaffold. The extensive surface remodeling induced by the deposition of the apatite-like layer lead to a 3-fold increase in surface area, a 5-fold increase in the roughness, and 4-fold increase in the hardness of the PBS-immersed scaffolds when compared to the as-printed counterpart. The biomimetic mineralization also occurred throughout the bulk of the scaffold connecting the MBGs particles and was responsible for the maintenance of structural integrity. In vitro assays using MC3T3-E1 pre-osteoblast like cells demonstrated a significant upregulation of osteogenic-related genes for the scaffolds previously immersed in PBS when compared to the as-printed PVA-containing scaffolds. Although the pre-immersion scaffolds performed equally towards osteogenic cell differentiation, our data suggest that a short immersion in PBS of MBG scaffolds is beneficial for the osteogenic properties and might accelerate bone formation after implantation.

An overview of decellularisation techniques of native tissues and tissue engineered products for bone, ligament and tendon regeneration

Decellularised tissues and organs have been successfully used in a variety of tissue engineering/regenerative medicine applications. Because of the complexity of each tissue (size, porosity, extracellular matrix (ECM) composition etc.), there is no standardised protocol and the decellularisation methods vary widely, thus leading to heterogeneous outcomes. Physical, chemical, and enzymatic methods have been developed and optimised for each specific application and this review describes the most common strategies utilised to achieve decellularisation of soft and hard tissues. While removal of the DNA is the primary goal of decellularisation, it is generally achieved at the expense of ECM preservation due to the harsh chemical or enzymatic processing conditions. As denaturation of the native ECM has been associated with undesired host responses, decellularisation conditions aimed at effectively achieving simultaneous DNA removal and minimal ECM damage will be highlighted. Additionally, the utilisation of decellularised matrices in regenerative medicine is explored, as are the most recent strategies implemented to circumvent challenges in this field. In summary, this review focusses on the latest advancements and future perspectives in the utilisation of natural ECM for the decoration of synthetic porous scaffolds.

Additively Manufactured Multiphasic Bone-Ligament-Bone Scaffold for Scapholunate Interosseous Ligament Reconstruction

The scapholunate interosseous ligament (SLIL) is a frequently torn wrist ligament, and current surgical options for SLIL tears are suboptimal. This research aims to develop a novel multiphasic bone-ligament-bone scaffold (BLB) with a porous interface using 3D-printing and cell sheet technology for the reconstruction of the dorsal scapholunate interosseous ligament. The BLB comprises two bone compartments bridged by aligned polycaprolactone fibers mimicking the architecture of the native tissue. Mechanical testing of the BLBs shows their ability to withstand physiological forces. Combination of the BLB with human bone marrow mesenchymal stem cell sheet demonstrates that the harvesting did not compromise cell viability, while allowing homogeneous distribution in the ligament compartment. The BLBs are loaded with cell sheets and bone morphogenetic protein-2 in the ligament and bone compartment respectively prior to ectopic implantation into athymic rats. The histology demonstrates rapid tissue infiltration, high vascularization, and more importantly the maintenance of the compartmentalization as bone formation remains localized to the bone compartment despite the porous interface. The cells in the ligament compartment become preferentially aligned, and this proof-of-concept study demonstrates that the BLB can provide sufficient compartmentalization and fiber guiding properties necessary for the regeneration of the dorsal SLIL.

Periodontal Tissue Engineering with a Multiphasic Construct and Cell Sheets

This study reports on scaffold-based periodontal tissue engineering in a large preclinical animal model. A biphasic scaffold consisting of bone and periodontal ligament compartments manufactured by melt and solution electrospinning, respectively, was used for the delivery of in vitro matured cell sheets from 3 sources: gingival cells (GCs), bone marrow-derived mesenchymal stromal cells (Bm-MSCs), and periodontal ligament cells (PDLCs). The construct featured a 3-dimensional fibrous bone compartment with macroscopic pore size, while the periodontal compartment consisted of a flexible porous membrane for cell sheet delivery. The regenerative performance of the constructs was radiographically and histologically assessed in surgically created periodontal defects in sheep following 5 and 10 wk of healing. Histologic observation demonstrated that the constructs maintained their shape and volume throughout the entirety of the in vivo study and were well integrated with the surrounding tissue. There was also excellent tissue integration between the bone and periodontal ligament compartments as well as the tooth root interface, enabling the attachment of periodontal ligament fibers into newly formed cementum and bone. Bone coverage along the root surface increased between weeks 5 and 10 in the Bm-MSC and PDLC groups. At week 10, the micro-computed tomography results showed that the PDLC group had greater bone fill as compared with the empty scaffold, while the GC group had less bone than the 3 other groups (control, Bm-MSC, and PDLC). Periodontal regeneration, as measured by histologically verified new bone and cementum formation with obliquely inserted periodontal ligament fibers, increased between 5 and 10 wk for the empty, Bm-MSC, and PDLC groups, while the GC group was inferior to the Bm-MSC and PDLC groups at 10 wk. This study demonstrates that periodontal regeneration can be achieved via the utilization of a multiphasic construct, with Bm-MSCs and PDLCs obtaining superior results as compared with GC-derived cell sheets.

Tissue Engineered Constructs for Periodontal Regeneration: Current Status and Future Perspectives

The periodontium, consisting of gingiva, periodontal ligament, cementum, and alveolar bone, is a hierarchically organized tissue whose primary role is to provide physical and mechanical support to the teeth. Severe cases of periodontitis, an inflammatory condition initiated by an oral bacterial biofilm, can lead to significant destruction of soft and hard tissues of the periodontium and result in compromised dental function and aesthetics. Although current treatment approaches can limit the progression of the disease by controlling the inflammatory aspect, complete periodontal regeneration cannot be predictably achieved. Various tissue engineering approaches are investigated for their ability to control the critical temporo-spatial wound healing events that are essential for achieving periodontal regeneration. This paper reviews recent progress in the field of periodontal tissue engineering with an emphasis on advanced 3D multiphasic tissue engineering constructs (TECs) and provides a critical analysis of their regenerative potential and limitations. The review also elaborates on the future of periodontal tissue engineering, including scaffold customization for individual periodontal defects, TEC's functionalization strategies for imparting enhanced bioactivity, periodontal ligament fiber guidance, and the utilization of chair-side regenerative solutions that can facilitate clinical translation.

The effect of decellularized tissue engineered constructs on periodontal regeneration

AIM

To evaluate the effect of decellularized tissue engineered constructs on cell differentiation in vitro and periodontal regeneration in vivo.

MATERIALS AND METHODS

Periodontal ligament cell (PDLC) sheets were loaded on polycaprolactone (PCL) scaffolds and then decellularized. Constructs were assessed for their effect on allogenic PDLC and mesenchymal stem cell (MSC) differentiation in vitro, as evaluated by gene expression of bone and periodontal ligament tissue markers post-seeding. Expression of MSC marker STRO-1 was assessed by immunostaining. Decellularized constructs were evaluated in a rat periodontal defect model to assess their biocompatibility and tissue integration. Microcomputed topography (μCT) and histological assessment were performed to assess the regenerative potential of the constructs at 2 and 4 weeks postoperatively.

RESULTS

There was upregulation of bone marker gene expression by PDLCs especially on the 14th day. MSCs lacked bone markers expression, but showed increased collagen I marker expression on day 14. STRO-1 expression by the MSCs decreased over the three timepoints when seeded on decellularized sheets. Histological assessment demonstrated the biocompatibility of the decellularized constructs in vivo. More new attachment formation was observed on the decellularized constructs compared to scaffold only controls.

CONCLUSION

Decellularized tissue engineered constructs are capable of inducing cell differentiation in vitro and have the potential to facilitate periodontal regeneration in vivo.

Using democracy to award research funding: an observational study

BACKGROUND

Winning funding for health and medical research usually involves a lengthy application process. With success rates under 20%, much of the time spent by 80% of applicants could have been better used on actual research. An alternative funding system that could save time is using democracy to award the most deserving researchers based on votes from the research community. We aimed to pilot how such a system could work and examine some potential biases.

METHODS

We used an online survey with a convenience sample of Australian researchers. Researchers were asked to name the 10 scientists currently working in Australia that they thought most deserved funding for future research. For comparison, we used recent winners from large national fellowship schemes that used traditional peer review.

RESULTS

Voting took a median of 5 min (inter-quartile range 3 to 10 min). Extrapolating to a national voting scheme, we estimate 599 working days of voting time (95% CI 490 to 728), compared with 827 working days for the current peer review system for fellowships. The gender ratio in the votes was a more equal 45:55 (female to male) compared with 34:66 in recent fellowship winners, although this could be explained by Simpson's paradox. Voters were biased towards their own institution, with an additional 1.6 votes per ballot (inter-quartile range 0.8 to 2.2) above the expected number. Respondents raised many concerns about the idea of using democracy to fund research, including vote rigging, lobbying and it becoming a popularity contest.

CONCLUSIONS

This is a preliminary study of using voting that does not investigate many of the concerns about how a voting system would work. We were able to show that voting would take less time than traditional peer review and would spread the workload over many more reviewers. Further studies of alternative funding systems are needed as well as a wide discussion with the research community about potential changes.

Tissue Engineering in Hand Surgery: A Technology Update

The field of hand surgery is constantly evolving to meet the challenges of repairing intricate anatomical structures with limited availability of donor tissue. The past 10 years have seen an exponential growth in tissue engineering, which has broadened the perspectives of tackling these age-old problems. Various fabrication techniques such as melt electrospinning and fused deposition modelling have been employed to synthesize 3-dimensional bioscaffolds that can be used to replace lost tissue. These bioscaffolds with strategic biomimicry have been shown to allow for integrative and functional repair of tissue injuries. This review article summarizes the most current advances in tissue engineering and its applications in the field of hand surgery. It outlines the current tissue engineering techniques commonly used for tackling musculoskeletal problems and highlights the most promising approaches according to clinical evidence. In particular, the paper explores regenerative medicine concepts applied to specific tissues including nerve, bone, cartilage, tendon, ligament, and vessels. In the face of innovative and pioneering research, tissue engineering will undoubtedly play a key role in reconstructive hand surgery in the not too distant future.

Antimicrobial and Immunomodulatory Surface-Functionalized Electrospun Membranes for Bone Regeneration

Guided bone regeneration (GBR) is a surgical procedure utilizing occlusive membranes for providing space maintenance and enabling selective repopulation of the damaged area. While this technique is effective in regenerating bone, bacterial infiltration occurs frequently and can compromise the regenerative outcome. In this study, the authors describe the development and characterization of a GBR membrane made of medical grade polycaprolactone (mPCL) electrospun fibers with antibacterial and immunomodulatory properties. This is achieved by the immobilization of the antibiotic azithromycin into the membrane via a solvent evaporation technique leading to a sustained release of the drug over 14 d. In vitro testing shows that this controlled release of azithromycin is proficient at inhibiting the growth of Staphylococcus aureus for 14 d. Implantation of azithromycin loaded mPCL membrane in a rodent calvarial defect induces macrophage polarization toward the M2 phenotype after one week and results in significantly more bone regeneration eight weeks post-surgery. The results suggest that this antibacterial membrane should be effective at preventing infection and also impacts on the macrophage polarization enhancing bone regeneration. The drug loading technique developed in this study is simple, effective with a strong potential for clinical translation and can be applied to different types of scaffolds and implants for applications in craniofacial and orthopedics applications.

Engineering a humanized bone organ model in mice to study bone metastases

Current in vivo models for investigating human primary bone tumors and cancer metastasis to the bone rely on the injection of human cancer cells into the mouse skeleton. This approach does not mimic species-specific mechanisms occurring in human diseases and may preclude successful clinical translation. We have developed a protocol to engineer humanized bone within immunodeficient hosts, which can be adapted to study the interactions between human cancer cells and a humanized bone microenvironment in vivo. A researcher trained in the principles of tissue engineering will be able to execute the protocol and yield study results within 4-6 months. Additive biomanufactured scaffolds seeded and cultured with human bone-forming cells are implanted ectopically in combination with osteogenic factors into mice to generate a physiological bone 'organ', which is partially humanized. The model comprises human bone cells and secreted extracellular matrix (ECM); however, other components of the engineered tissue, such as the vasculature, are of murine origin. The model can be further humanized through the engraftment of human hematopoietic stem cells (HSCs) that can lead to human hematopoiesis within the murine host. The humanized organ bone model has been well characterized and validated and allows dissection of some of the mechanisms of the bone metastatic processes in prostate and breast cancer.

3-Dimensional functionalized polycaprolactone-hyaluronic acid hydrogel constructs for bone tissue engineering

AIM

Alveolar bone regeneration remains a significant clinical challenge in periodontology and dental implantology. This study assessed the mineralized tissue forming potential of 3-D printed medical grade polycaprolactone (mPCL) constructs containing osteoblasts (OB) encapsulated in a hyaluronic acid (HA)-hydrogel incorporating bone morphogenetic protein-7 (BMP-7).

MATERIALS AND METHODS

HA-hydrogels containing human OB ± BMP-7 were prepared. Cell viability, osteogenic gene expression, mineralized tissue formation and BMP-7 release in vitro, were assessed by fluorescence staining, RT-PCR, histological/μ-CT examination and ELISA respectively. In an athymic rat model, subcutaneous ectopic mineralized tissue formation in mPCL-hydrogel constructs was assessed by μ-CT and histology.

RESULTS

Osteoblast encapsulation in HA-hydrogels did not detrimentally effect cell viability, and 3-D culture in osteogenic media showed mineralized collagenous matrix formation after 6 weeks. BMP-7 release from the hydrogel was biphasic, sustained and increased osteogenic gene expression in vitro. After 4 weeks in vivo, mPCL-hydrogel constructs containing BMP-7 formed significantly more volume (mm³ ) of vascularized bone-like tissue.

CONCLUSIONS

Functionalized mPCL-HA hydrogel constructs provide a favourable environment for bone tissue engineering. Although encapsulated cells contributed to mineralized tissue formation within the hydrogel in vitro and in vivo, their addition did not result in an improved outcome compared to BMP-7 alone.

Combining electrospinning and cell sheet technology for the development of a multiscale tissue engineered ligament construct (TELC)

Ligament tissue rupture is a common sport injury. Although current treatment modalities can achieve appropriate reconstruction of the damaged ligament, they present significant drawbacks, mostly related to reduced tissue availability and pain associated with tissue harvesting. Stem cell based tissue regeneration combined with electrospun scaffolds represents a novel treatment method for torn ligaments. In this study, a low fiber density polycaprolactone (PCL) electrospun mesh and sheep mesenchymal stem cells (sMSCs) were used to develop tissue engineered ligament construct (TELC) in vitro. The assembly of the TELC was based on the spontaneous capacity of the cells to organize themselves into a cell sheet once seeded onto the electrospun mesh. The cell sheet matured over 4 weeks and strongly integrated with the low fiber density electrospun mesh which was subsequently processed into a ligament-like bundle and braided with two other bundles to develop the final construct. Live/dead assay revealed that the handling of the construct through the various phases of assembly did not cause significant difference in viability compared to the control. Mechanical evaluation demonstrated that the incorporation of the cell sheet into the braided construct resulted in significantly modifying the mechanical behavior. A stress/displacement J-curve was observed for the TELC that was similar to native ligament, whereas this particular feature was not observed in the non-cellularized specimens. The regenerative potential of the TELC was evaluated ectopically in immunocompromized rats, compared to non cellularized electrospun fiber mesh and this demonstrated that the TELC was well colonized by host cells and that a significant remodelling of the implanted construct was observed. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 399-409, 2018.