Early osteogenic signal expression of rat bone marrow stromal cells is influenced by both hydroxyapatite nanoparticle content and initial cell seeding density in biodegradable nanocomposite scaffolds

Three-Dimensional Printing of Drug-Eluting Implantable PLGA Scaffolds for Bone Regeneration

Despite rapid progress in tissue engineering, the repair and regeneration of bone defects remains challenging, especially for non-homogenous and complicated defects. We have developed and characterized biodegradable drug-eluting scaffolds for bone regeneration utilizing direct powder extrusion-based three-dimensional (3D) printing techniques. The PLGA scaffolds were fabricated using poly (lactic-co-glycolic acid) (PLGA) with inherent viscosities of 0.2 dl/g and 0.4 dl/g and ketoprofen. The effect of parameters such as the infill, geometry, and wall thickness of the drug carrier on the release kinetics of ketoprofen was studied. The release studies revealed that infill density significantly impacts the release performance, where 10% infill showed faster and almost complete release of the drug, whereas 50% infill demonstrated a sustained release. The Korsmeyer-Peppas model showed the best fit for release data irrespective of the PLGA molecular weight and infill density. It was demonstrated that printing parameters such as infill density, scaffold wall thickness, and geometry played an important role in controlling the release and, therefore, in designing customized drug-eluting scaffolds for bone regeneration.

A Bioinspired Gelatin-Amorphous Calcium Phosphate Coating on Titanium Implant for Bone Regeneration

Biocompatible and bio-active coatings can enhance and accelerate osseointegration via chemical binding onto substrates. Amorphous calcium phosphate (ACP) has been shown as a precursor to achieve mineralization in vertebrates and invertebrates under the control of biological macromolecules. This work presents a simple bioinspired Gelatin-CaPO4 (Gel-CaP) composite coating on titanium surfaces to improve osseointegration. The covalently bound Gel-CaP composite is characterized as an ACP-Gel compound via SEM, FT-IR, XRD, and HR-TEM. The amorphous compound coating exhibits a nanometer range thickness and improved elastic modulus, good wettability, and nanometric roughness. The amount of grafted carboxyl groups and theoretical thickness of the coatings are also investigated. More importantly, MC3T3 cells, an osteoblast cell line, show excellent cell proliferation and adhesion on the Gel-CaP coating. The level of osteogenic genes is considerably upregulated on Ti with Gel-CaP coatings compared to uncoated Ti, demonstrating that Gel-CaP coatings possess a unique osteogenic ability. To conclude, this work offers a new perspective on functional, bioactive titanium coatings, and Gel-CaP composites can be a low-cost and promising candidate in bone regeneration.

Human gelatin-based composite hydrogels for osteochondral tissue engineering and their adaptation into bioinks for extrusion, inkjet, and digital light processing bioprinting

The investigation of novel hydrogel systems allows for the study of relationships between biomaterials, cells, and other factors within osteochondral tissue engineering. Three-dimensional (3D) printing is a popular research method that can allow for further interrogation of these questions via the fabrication of 3D hydrogel environments that mimic tissue-specific, complex architectures. However, the adaptation of promising hydrogel biomaterial systems into 3D-printable bioinks remains a challenge. Here, we delineated an approach to that process. First, we characterized a novel methacryloylated gelatin composite hydrogel system and assessed how calcium phosphate and glycosaminoglycan additives upregulated bone- and cartilage-like matrix deposition and certain genetic markers of differentiation within human mesenchymal stem cells (hMSCs), such as RUNX2 and SOX9. Then, new assays were developed and utilized to study the effects of xanthan gum and nanofibrillated cellulose, which allowed for cohesive fiber deposition, reliable droplet formation, and non-fracturing digital light processing (DLP)-printed constructs within extrusion, inkjet, and DLP techniques, respectively. Finally, these bioinks were used to 3D print constructs containing viable encapsulated hMSCs over a 7 d period, where DLP printed constructs facilitated the highest observed increase in cell number over 7 d (∼2.4×). The results presented here describe the promotion of osteochondral phenotypes via these novel composite hydrogel formulations, establish their ability to bioprint viable, cell-encapsulating constructs using three different 3D printing methods on multiple bioprinters, and document how a library of modular bioink additives affected those physicochemical properties important to printability.

Icariin regulates miR-23a-3p-mediated osteogenic differentiation of BMSCs via BMP-2/Smad5/Runx2 and WNT/β-catenin pathways in osteonecrosis of the femoral head

Icariin is commonly used for the clinical treatment of osteonecrosis of the femoral head (ONFH). miR-23a-3p plays a vital role in regulating the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). The present study aimed to investigate the roles of icariin and miR-23a-3p in the osteogenic differentiation of BMSCs and an ONFH model. BMSCs were isolated and cultured in vitro using icariin-containing serum at various concentrations, and BMSCs were also transfected with a miR-23a inhibitor. The alkaline phosphatase (ALP) activity and cell viability as well as BMP-2/Smad5/Runx2 and WNT/β-catenin pathway-related mRNA and protein expression were measured in BMSCs. Additionally, a dual-luciferase reporter assay and pathway inhibitors were used to verify the relationship of icariin treatment/miR-23a and the above pathways. An ONFH rat model was established in vivo, and a 28-day gavage treatment and lentivirus transfection of miR-23a-3p inhibitor were performed. Then, bone biochemical markers (ELISA kits) in serum, femoral head (HE staining and Digital Radiography, DR) and the above pathway-related proteins were detected. Our results revealed that icariin treatment/miR-23a knockdown promoted BMSC viability and osteogenic differentiation as well as increased the mRNA and protein expression of BMP-2, BMP-4, Runx2, p-Smad5, Wnt1 and β-catenin in BMSCs and ONFH model rats. In addition, icariin treatment/miR-23a knockdown increased bone biochemical markers (ACP-5, BAP, NTXI, CTXI and OC) and improved ONFH in ONFH model rats. In addition, a dual-luciferase reporter assay verified that Runx2 was a direct target of miR-23a-3p. These data indicated that icariin promotes BMSC viability and osteogenic differentiation as well as improves ONFH by decreasing miR-23a-3p levels and regulating the BMP-2/Smad5/Runx2 and WNT/β-catenin pathways.

Multiple Ion Scaffold-Based Delivery Platform for Potential Application in Early Stages of Bone Regeneration

Bone has the intrinsic capacity to regenerate itself, as long as the damage is small, through the sequential stimulation of specific phases, such as angiogenesis followed by osteogenesis. However, when the damage is extensive it is unable to regenerate and bone tissue engineering is used as an alternative. In this study, we developed a platform to allow the triple ion delivery with sequential delivery capacity to potentially stimulate antibacterial, angiogenic and osteogenic processes. The scaffold-based platform consisted of alginate/hydroxyapatite (HA) microparticles embedded in alginate fibers. Firstly, microparticles were developed using different ratios of alginate:HA using the spraying method, resulting in a high reproducibility of the technique. Microparticle size between 100–300 µm and ratio 1:40 resulted in a more spherical morphology and were selected for their incorporation into alginate fiber. Different amounts of copper and cobalt were added with the microparticles and alginate fiber, respectively, were used as model ions which could eventually modulate and mimic antimicrobial and angiogenic processes. Moreover, calcium ion was also incorporated in both, in order to provide the system with potential osteogenic properties together with HA. The multiple delivery of copper, cobalt and calcium released were in the therapeutic range as measured by induced coupled plasma (ICP), providing a promising delivery strategy for tissue engineering.

Co-Axial Gyro-Spinning of PCL/PVA/HA Core-Sheath Fibrous Scaffolds for Bone Tissue Engineering

The present study aspires towards fabricating core-sheath fibrous scaffolds by state-of-the-art pressurized gyration for bone tissue engineering applications. The core-sheath fibers comprising dual-phase poly-ε-caprolactone (PCL) core and polyvinyl alcohol (PVA) sheath are fabricated using a novel "co-axial" pressurized gyration method. Hydroxyapatite (HA) nanocrystals are embedded in the sheath of the fabricated scaffolds to improve the performance for application as a bone tissue regeneration material. The diameter of the fabricated fiber is 3.97 ± 1.31 µm for PCL-PVA/3%HA while pure PCL-PVA with no HA loading gives 3.03 ± 0.45 µm. Bead-free fiber morphology is ascertained for all sample groups. The chemistry, water contact angle and swelling behavior measurements of the fabricated core-sheath fibrous scaffolds indicate the suitability of the structures in cellular activities. Saos-2 bone osteosarcoma cells are employed to determine the biocompatibility of the scaffolds, wherein none of the scaffolds possess any cytotoxicity effect, while cell proliferation of 94% is obtained for PCL-PVA/5%HA fibers. The alkaline phosphatase activity results suggest the osteogenic activities on the scaffolds begin earlier than day 7. Overall, adaptations of co-axial pressurized gyration provides the flexibility to embed or encapsulate bioactive substances in core-sheath fiber assemblies and is a promising strategy for bone healing.

3D Printing and Bioprinting to Model Bone Cancer: The Role of Materials and Nanoscale Cues in Directing Cell Behavior

Bone cancer, both primary and metastatic, is characterized by a low survival rate. Currently, available models lack in mimicking the complexity of bone, of cancer, and of their microenvironment, leading to poor predictivity. Three-dimensional technologies can help address this need, by developing predictive models that can recapitulate the conditions for cancer development and progression. Among the existing tools to obtain suitable 3D models of bone cancer, 3D printing and bioprinting appear very promising, as they enable combining cells, biomolecules, and biomaterials into organized and complex structures that can reproduce the main characteristic of bone. The challenge is to recapitulate a bone-like microenvironment for analysis of stromal-cancer cell interactions and biological mechanics leading to tumor progression. In this review, existing approaches to obtain in vitro 3D-printed and -bioprinted bone models are discussed, with a focus on the role of biomaterials selection in determining the behavior of the models and its degree of customization. To obtain a reliable 3D bone model, the evaluation of different polymeric matrices and the inclusion of ceramic fillers is of paramount importance, as they help reproduce the behavior of both normal and cancer cells in the bone microenvironment. Open challenges and future perspectives are discussed to solve existing shortcomings and to pave the way for potential development strategies.

Assessment of decellularized pericardial extracellular matrix and poly(propylene fumarate) biohybrid for small-diameter vascular graft applications

Autologous grafts are the current gold standard of care for coronary artery bypass graft surgeries, but are limited by availability and plagued by high failure rates. Similarly, tissue engineering approaches to small diameter vascular grafts using naturally derived and synthetic materials fall short, largely due to inappropriate mechanical properties. Alternatively, decellularized extracellular matrix from tissue is biocompatible and has comparable strength to vessels, while poly(propylene fumarate) (PPF) has shown promising results for vascular grafts. This study investigates the integration of decellularized pericardial extracellular matrix (dECM) and PPF to create a biohybrid scaffold (dECM+PPF) suitable for use as a small diameter vascular graft. Our method to decellularize the ECM was efficient at removing DNA content and donor variability, while preserving protein composition. PPF was characterized and added to dECM, where it acted to preserve dECM against degradative effects of collagenase without disturbing the material's overall mechanics. A transport study showed that diffusion occurs across dECM+PPF without any effect from collagenase. The modulus of dECM+PPF matched that of human coronary arteries and saphenous veins. dECM+PPF demonstrated ample circumferential stress, burst pressure, and suture retention strength to survive in vivo. An in vivo study showed re-endothelialization and tissue growth. Overall, the dECM+PPF biohybrid presents a robust solution to overcome the limitations of the current methods of treatment for small diameter vascular grafts. STATEMENT OF SIGNIFICANCE: In creating a dECM+PPF biohybrid graft, we have observed phenomena that will have a lasting impact within the scientific community. First, we found that we can reduce donor variability through decellularization, a unique use of the decellularization process. Additionally, we coupled a natural material with a synthetic polymer to capitalize on the benefits of each: the cues provided to cells and the ability to easily tune material properties, respectively. This principle can be applied to other materials in a variety of applications. Finally, we created an off-the-shelf alternative to autologous grafts with a newly developed material that has yet to be utilized in any scaffolds. Furthermore, bovine pericardium has not been investigated as a small diameter vascular graft.

Icariin Accelerates Fracture Healing via Activation of the WNT1/β-catenin Osteogenic Signaling Pathway

BACKGROUND

Icariin has been shown to enhance bone formation.

OBJECTIVE

The present study aimed to investigate whether icariin also promotes bone fracture healing and its mechanisms.

METHODS

First, we isolated and cultured rat bone marrow stromal cells (rBMSCs) with icariincontaining serum at various concentrations (0%, 2.5%, 5% and 10%) and then measured alkaline phosphatase (ALP) activity and the expression of Core-binding factor, alpha 1 (Cbfα1), bone morphogenetic protein-2 (BMP-2) and bone morphogenetic protein-4 (BMP-4) in the rBMSCs. Second, we established a model of fracture healing in rats and performed gavage treatment for 20 days. Then, we detected bone biochemical markers (ELISA kits) in the serum, fracture healing (digital radiography, DR), and osteocalcin expression (immunohistochemistry).

RESULTS

Icariin treatment increased ALP activity and induced the expression of Cbfα1, BMP-2 and BMP-4 in rBMSCs in a dose-dependent manner. In addition, Icariin increased the serum levels of osteocalcin (OC), bone-specific alkaline phosphatase (BAP), N-terminal telopeptides of type I collagen (NTX-1), C-terminal telopeptide of type I collagen (CTX-1) and tartrate-resistant acid phosphatase 5b (TRACP-5b); promoted osteocalcin secretion at the fracture site; and accelerated fracture healing.

CONCLUSION

Icariin can promote the levels of bone-formation markers, accelerate fracture healing, and activate the WNT1/β-catenin osteogenic signaling pathway.

A review of calcium phosphate cements and acrylic bone cements as injectable materials for bone repair and implant fixation

Treatment of bone defects caused by trauma or disease is a major burden on human healthcare systems. Although autologous bone grafts are considered as the gold standard, they are limited in availability and are associated with post-operative complications. Minimally invasive alternatives using injectable bone cements are currently used in certain clinical procedures, such as vertebroplasty and balloon kyphoplasty. Nevertheless, given the high incidence of fractures and pathologies that result in bone voids, there is an unmet need for injectable materials with desired properties for minimally invasive procedures. This paper provides an overview of the most common injectable bone cement materials for clinical use. The emphasis has been placed on calcium phosphate cements and acrylic bone cements, while enabling the readers to compare the opportunities and challenges for these two classes of bone cements. This paper also briefly reviews antibiotic-loaded bone cements used in bone repair and implant fixation, including their efficacy and cost for healthcare systems. A summary of the current challenges and recommendations for future directions has been brought in the concluding section of this paper.

Nanotechnological Applications Hold a Pivotal Position in Boosting Stem Cells Osteogenic Activity: In Vitro and In Vivo Studies

This approach was constructed to appraise the therapeutic effectiveness of a single i.v. dose of osteoblasts generated from co-culturing BM-MSCs with nano-HA, Pt-NPs, or Pt-HA-nanocomposite in osteoporotic rats. MSCs were grown, propagated in culture, and characterized. The effect of the suggested nanoplatforms on the survival, osteogenic differentiation, and mineralization of BM-MSCs was assessed by MTT assay, real-time PCR analysis, and Alizarin red S staining, respectively. Thereafter, the generated osteoblasts were employed for the treatment of ovariectomized rats. Our results revealed that the selected nanoplatforms upregulate the expression of osteogenic differentiation related genes (Runx-2 and BMP-2) significantly and enhance calcium deposition in BM-MSCs after 7 and 21 days, respectively, whereas the in vivo study validated that the infusion of the generated osteoblasts considerably downturn serum BALP, BSP, and SOST levels; upswing OSX level; and regain femur bone mineralization and histoarchitecture. Conclusively, the outcomes of this work provide scientific evidence that transplanting osteoblasts derived from differentiation of BM-MSCs in the presence of nanoplatforms in ovariectomized rats restores bone remodeling balance which constitutes a new hope for the treatment of osteoporosis.

Key components of engineering vascularized 3-dimensional bioprinted bone constructs

Vascularization has a pivotal role in engineering successful tissue constructs. However, it remains a major hurdle of bone tissue engineering, especially in clinical applications for the treatment of large bone defects. Development of vascularized and clinically-relevant engineered bone substitutes with sufficient blood supply capable of maintaining implant viability and supporting subsequent host tissue integration remains a major challenge. Since only cells that are 100-200 µm from blood vessels can receive oxygen through diffusion, engineered constructs that are thicker than 400 µm face a challenging oxygenation problem. Following implantation in vivo, spontaneous ingrowth of capillaries in thick engineered constructs is too slow. Thus, it is critical to provide optimal conditions to support vascularization in engineered bone constructs. To achieve this, an in-depth understanding of the mechanisms of angiogenesis and bone development is required. In addition, it is also important to mimic the physiological milieu of native bone to fabricate more successful vascularized bone constructs. Numerous applications of engineered vascularization with cell-and/or microfabrication-based approaches seek to meet these aims. Three-dimensional (3D) printing promises to create patient-specific bone constructs in the future. In this review, we discuss the major components of fabricating vascularized 3D bioprinted bone constructs, analyze their related challenges, and highlight promising future trends.

Role of nanoparticles in osteogenic differentiation of bone marrow mesenchymal stem cells

The present study aimed to investigate the osteoinductive potentiality of some selected nanostructures; Hydroxyapatite (HA-NPs), Gold (Au-NPs), Chitosan (C-NPs), Gold/hydroxyapatite (Au/HA-NPs) and Chitosan/hydroxyapatite (CH-NPs) on bone marrow- derived mesenchymal stem cells (BM-MSCs). These nanostructures were characterized using transmission electron microscope and Zetasizer. MSCs were isolated from bone marrow of rat femur bones and their identity was documented by morphology, flow cytometry and multi-potency capacity. The influence of the selected nanostructures on the viability, osteogenic differentiation and subsequent matrix mineralization of BM-MSCs was determined by MTT assay, molecular genetic analysis and alizarin red S staining, respectively. MTT analysis revealed insignificant toxicity of the tested nanostructures on BM-MSCs at concentrations ranged from 2 to 25 µg/ml over 48 h and 72 h incubation period. Notably, the tested nanostructures potentiate the osteogenic differentiation of BM-MSCs as evidenced by a prominent over-expression of runt-related transcription factor 2 (Runx-2) and bone morphogenetic protein 2 (BMP-2) genes after 7 days incubation. Moreover, the tested nanostructures induced matrix mineralization of BM-MSCs after 21 days as manifested by the formation of calcium nodules stained with alizarin red S. Conclusively, these data provide a compelling evidence for the functionality of the studied nanostructures as osteoinductive materials motivating the differentiation of BM-MSCs into osteoblasts with the most prominent effect observed with Au-NPs and Au/HA-NPs, followed by CH-NPs.

Identification of a prolonged action molecular GLP-1R agonist for the treatment of femoral defects

Poly-GLP-1 promotes angiogenesis to accelerate bone formationviaBMSC differentiation and M2 polarization.

Stem cells in the periodontal ligament differentiated into osteogenic, fibrogenic and cementogenic lineages for the regeneration of the periodontal complex

OBJECTIVE

Human periodontal ligament stem cells (hPDLSCs) are promising for periodontal regeneration. However, to date, there has been no report of hPDLSC differentiation into the fibrogenic lineage. There has been no report demonstrating hPDLSC differentiation into all three (osteogenic, fibrogenic and cementogenic fibrogenic) lineages in the same report. The objectives of this study were to harvest hPDLSCs from the periodontal ligaments (PDL) of the extracted human teeth, and use the same vial of hPDLSCs to differentiate into all three (osteogenic, fibrogenic and cementogenic) lineages for the first time.

METHODS

hPDLSCs were harvested from PDL tissues of the extracted premolars. The ability of hPDLSCs to form bone, cementum and collagen fibers was tested in culture mediums. Gene expressions were analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). Immunofluorescence, alizarin red (ARS), Xylenol orange, picro sirius red staining (PSRS), alcian blue staining (ABS) and alkaline phosphatase (ALP) staining were evaluated.

RESULTS

In osteogenic medium, hPDLSCs had high expressions of osteogenic genes (RUNX2, ALP, OPN and COL1) at 14 and 21 days (15-20 folds of that of control), and produced mineral nodules and ALP activity (5 and 10 folds those of the control). hPDLSCs in fibrogenic medium expressed high levels of PDL fibrogenic genes (COL1, COL3, FSP-1, PLAP-1 and Elastin) at 28 days (20-70 folds of control). They were stained strongly with F-actin and fibronection, and secreted PDL collagen fibers (5 folds of control). hPDLSCs in cementogenic medium showed high expressions of cementum genes (CAP, CEMP1 and BSP) at 21 days (10-15 folds of control) and synthesized mineralized cementum (50 folds via ABS, and 40 folds via ALP staining, compared to those of control).

CONCLUSIONS

hPDLSCs differentiated into bone-, fiber- and cementum-forming cells, with potential for regeneration of periodontium to form the bone-PDL-cementum complex.

Human periodontal ligament stem cell seeding on calcium phosphate cement scaffold delivering metformin for bone tissue engineering

OBJECTIVES

(1) develop a CPC-metformin scaffold with hPDLSC seeding for bone tissue engineering; and (2) investigate the effects of CPC-metformin scaffold on hPDLSC proliferation, osteogenic differentiation and bone matrix mineralization for the first time.

METHODS

hPDLSCs were harvested from extracted teeth. CPC scaffolds (with or without metformin) were prepared. Three groups were tested: (1) control group (growth medium); (2) osteogenic group (osteogenic medium); (3) metformin + osteogenic group (CPC-metformin scaffold, cultured in osteogenic medium). hPDLSC viability, osteogenic differentiation and mineralization were measured. SEM was used to examine cell morphology.

RESULTS

After culturing for 14 days, all three groups demonstrated excellent hPDLSC attachment and viability, as shown in live-dead staining, CCK-8 assay, and SEM examinations. The osteogenic group had 3-8 folds, 5 folds and 6 folds of increases in osteogenic gene expressions, ALP activity and mineral synthesis, compared to control group. Furthermore, the metformin + osteogenic group had 3-fold to 4-fold increases over those of the osteogenic group in osteogenic gene expressions, ALP activity and mineral synthesis.

CONCLUSIONS

hPDLSCs were demonstrated to be a potent cell source for bone engineering. The novel CPC-metformin-hPDLSC construct is highly promising to enhance bone repair and regeneration efficacy in dental, craniofacial and orthopedic applications.

GNAS knockdown suppresses osteogenic differentiation of mesenchymal stem cells via activation of Hippo signaling pathway

Bone marrow-derived mesenchymal stem cells (BMSCs) are a suitable option for cell-based tissue engineering therapies due to their ability to renew and differentiate into multiple different tissue types, such as bone. Over the last decade, the effect of GNAS on the regulation of osteoblast differentiation has attracted great attention. Herein, this study aimed to explore the role of GNAS in osteogenic differentiation of MSCs. A total of 85 GNAS^f/f male mice were selected for animal experiments and 10 GNAS^f/f male mice for BMSC isolation to conduct cell experiments. The mice and BMSCs were treated with Verteporfin (a Hippo signaling pathway inhibitor) to inhibit the Hippo signaling pathway or recombinant adenovirus-expressing Cre to knockout the GNAS expression. Next, computed tomography scan, Von Kossa staining, and alizarin red staining were performed to detect osteogenic differentiation ability. Moreover, immunohistochemistry and alkaline phosphatase (ALP) staining were used to assess the expression of Oc and Osx in femur tissues and ALP activity. At last, the expression of GNAS, osteogenic markers, and factors related to the Hippo signaling pathway was evaluated. Initially, the results displayed successful knockout of the GNAS gene from mice and BMSCs. Moreover, the data indicated that GNAS knockout inhibits expression of Oc, Osx, ALP, BMP-2, and Runx2, and ALP activity. Additionally, GNAS knockout promotes activation of the Hippo signaling pathway, so as to repress osteogenic differentiation. Collectively, depleted GNAS exerts an inhibitory role in osteogenic differentiation of MSCs by activating Hippo signaling pathway, providing a candidate mediator for osteoporosis.

Fabrication and Evaluation of 3D Printed Poly(l-lactide) Scaffold Functionalized with Quercetin-Polydopamine for Bone Tissue Engineering

Quercetin (Qu), a bioflavonoid, has been reported to positively affect bone metabolism. For the first time, Qu with different concentrations was utilized to functionalize 3D-printed poly(l-lactide) (PLLA) scaffold with the aid of a polydopamine (PDA) layer through a convenient and effective way in this study. Results revealed that the coexistence of PDA and Qu can capacitate the 3D-printed PLLA scaffold to possess rougher surface, as well as better hydrophilicity and compressive properties. The resulting PDA- and Qu-modified PLLA scaffolds (Qu/PD-PLLA) can sustainably release Qu to some extent, which is more beneficial to the proliferation and attachment of MC3T3-E1 cells, upregulating ALP activity and calcium nodules as well as promoting the expression of related osteogenic genes and proteins. More significantly, such a positive impact of the Qu on the cell affinity and osteogenic activity played in a dose-dependent manner. This study revealed the potential of the 3D-printed Qu/PD-PLLA scaffolds with a certain amount of Qu as bone-repair materials.

Poly(propylene fumarate)-based materials: Synthesis, functionalization, properties, device fabrication and biomedical applications

Poly(propylene fumarate) (PPF) is a biodegradable polymer that has been investigated extensively over the last three decades. It has led many scientists to synthesize and fabricate a variety of PPF-based materials for biomedical applications due to its controllable mechanical properties, tunable degradation and biocompatibility. This review provides a comprehensive overview of the progress made in improving PPF synthesis, resin formulation, crosslinking, device fabrication and post polymerization modification. Further, we highlight the influence of these parameters on biodegradation, biocompatibility, and their use in a number of regenerative medicine applications, especially bone tissue engineering. In particular, the use of 3D printing techniques for the fabrication of PPF-based scaffolds is extensively reviewed. The recent invention of a ring-opening polymerization method affords precise control of PPF molecular mass, molecular mass distribution (Ɖ_M) and viscosity. Low Ɖ_M facilitates time-certain resorption of 3D printed structures. Novel post-polymerization and post-printing functionalization methods have accelerated the expansion of biomedical applications that utilize PPF-based materials. Finally, we shed light on evolving uses of PPF-based materials for orthopedics/bone tissue engineering and other biomedical applications, including its use as a hydrogel for bioprinting.

Effects of Silicon Compounds on Biomineralization, Osteogenesis, and Hard Tissue Formation

Bioinspired stem cell-based hard tissue engineering includes numerous aspects: The synthesis and fabrication of appropriate scaffold materials, their analytical characterization, and guided osteogenesis using the sustained release of osteoinducing and/or osteoconducting drugs for mesenchymal stem cell differentiation, growth, and proliferation. Here, the effect of silicon- and silicate-containing materials on osteogenesis at the molecular level has been a particular focus within the last decade. This review summarizes recently published scientific results, including material developments and analysis, with a special focus on silicon hybrid bone composites. First, the sources, bioavailability, and functions of silicon on various tissues are discussed. The second focus is on the effects of calcium-silicate biomineralization and corresponding analytical methods in investigating osteogenesis and bone formation. Finally, recent developments in the manufacturing of Si-containing scaffolds are discussed, including in vitro and in vivo studies, as well as recently filed patents that focus on the influence of silicon on hard tissue formation.

Polydopamine-modified poly(l-lactic acid) nanofiber scaffolds immobilized with an osteogenic growth peptide for bone tissue regeneration

It is highly desirable for bone tissue engineering scaffolds to have significant osteogenic properties and capability to improve cell growth and thus enhance bone regeneration. In this study, a poly(l-lactic acid) (PLLA) nanofiber scaffold-immobilized osteogenic growth peptide (OGP) was prepared via polydopamine (PDA) coating. X-ray photoelectron spectroscopy (XPS), contact angle measurement, and scanning electron microscopy (SEM) were used to determine the OGP immobilization, hydrophilicity and surface roughness of the samples. The SEM and fluorescence images demonstrate that the PLLA nanofiber scaffolds immobilized with the OGP have excellent cytocompatibility in terms of cell adhesion and proliferation. The ALP activity and the Runx2 and OPN expression results indicated that the PLLA nanofiber scaffolds immobilized with OGP significantly enhanced the osteogenic differentiation and calcium mineralization of hMSCs in vitro. A rat model of critical skull bone defect was selected to evaluate the bone formation capacity of the scaffolds. Micro CT analysis and histological results demonstrated that the PLLA scaffolds immobilized with OGP significantly promoted bone regeneration in critical-sized bone defects. This study verifies that the PLLA scaffold-immobilized OGP has significant potential in bone tissue engineering.

Polydopamine-modified PLLA nanofiber scaffolds immobilized with osteogenic growth peptide were designed and prepared for promoting bone formation.

Functionalized graphene oxide coating on Ti6Al4V alloy for improved biocompatibility and corrosion resistance

The present study focused on the development of magnesium-functionalized graphene oxide (FGO) coating on titanium alloy (Ti6Al4V) by electrophoretic deposition. Graphene oxide (GO) was synthesized by modified Hummers' method and functionalized with magnesium ions. X-ray diffraction, infrared spectroscopy (IR) and Raman spectroscopy were employed to confirm the synthesis of GO and GO-coatings on Ti6Al4V. Functionalization of GO with Mg ions was confirmed by energy dispersive X-ray spectroscopy. The surface morphology of coated samples was examined through scanning electron microscopy. Reduction of FGO coating (labelled as rFGO) by heating at 200 °C was confirmed by IR. The rFGO coated Ti6Al4V was found to be hydrophilic in nature as determined by contact angle measurement which showed reduction in the contact angle of Ti6Al4V from 95.4° to 42.1°. The percent cell viability over the coated sample was appreciably improved compared to as-received Ti6Al4V sample owing to hydrophilicity of the former. The positive shift in open circuit potential and increase in polarization resistance was observed after coating Ti6Al4V samples with FGO. The significant decrease in the corrosion current density and negative polarization loop in the reverse scan of samples also confirmed the improved corrosion resistance of rFGO-coated Ti6Al4V over uncoated Ti6Al4V in the PBS solution. Furthermore, the impedance spectroscopy revealed that the preferential adsorption of ionic species (indicated by large R_ads) at the surface improved the barrier characteristics of rFGO coated samples and exhibited an order of magnitude higher R_ct compared to as-received samples.

Osteogenic differentiation of encapsulated rat mesenchymal stem cells inside a rotating microgravity bioreactor: in vitro and in vivo evaluation

The objective of this study is to evaluate the in vitro and in vivo osteogenic potential of rat bone marrow mesenchymal stem cells (BM-MSCs) using chitosan/hydroxyapatite (C/HAp) microbeads as encapsulation matrix under osteoinductive medium and dynamic culture conditions. The degradation characteristics of C/HAp microbeads were evaluated under in vitro and in vivo conditions for 180 days. BM-MSCs were encapsulated in C/HAp microbeads with > 85% viability, and were cultured in a slow turning lateral vessel-type rotating bioreactor simulating microgravity conditions for 28 days, under the effect of osteogenic inducers. MTT assay showed that the metabolic activity of encapsulated cells was preserved > 80% after a week. In vitro experiments confirmed that the encapsulated BM-MSCs differentiated into osteoblastic cells, formed bone-like tissue under osteogenic microgravity bioreactor conditions. Preliminary in vivo study indicated C/HAp microbeads containing BM-MSCs were able to repair the surgically-created small bone defects in the rat femur. BM-MSCs-C/HAp composite microbeads may have potential for modular bone regeneration.

Improved in situ seeding of 3D printed scaffolds using cell-releasing hydrogels

The design of tissue engineered scaffolds based on polymerized high internal phase emulsions (polyHIPEs) has emerged as a promising bone grafting strategy. We previously reported the ability to 3D print emulsion inks to better mimic the structure and mechanical properties of native bone while precisely matching defect geometry. In the current study, redox-initiated hydrogel carriers were investigated for in situ delivery of human mesenchymal stem cells (hMSCs) utilizing the biodegradable macromer, poly(ethylene glycol)-dithiothreitol. Hydrogel carrier properties including network formation time, sol-gel fraction, and swelling ratio were modulated to achieve rapid cure without external stimuli and a target cell-release period of 5-7 days. These in situ carriers enabled improved distribution of hMSCs in 3D printed polyHIPE grafts over standard suspension seeding. Additionally, carrier-loaded polyHIPEs supported sustained cell viability and osteogenic differentiation of hMSCs post-release. In summary, these findings demonstrate the potential of this in situ curing hydrogel carrier to enhance the cell distribution and retention of hMSCs in bone grafts. Although initially focused on improving bone regeneration, the ability to encapsulate cells in a hydrogel carrier without relying on external stimuli that can be attenuated in large grafts or tissues is expected to have a wide range of applications in tissue engineering.

Role of TGF‑β1 expressed in bone marrow‑derived mesenchymal stem cells in promoting bone formation in a rabbit femoral defect model

Bone defects represent a major clinical and socioeconomic problem without suitable treatment options. Previous studies have shown that transforming growth factor β1 (TGF‑β1) is important in the development of various diseases. The present study aimed to investigate the therapeutic potential of rabbit bone marrow‑derived mesenchymal stem cells (BMSCs) expressing TGF‑β1 in the treatment of rabbit femoral defects. First, rabbit BMSCs were identified and cultured. TGF‑β1 was then stably overexpressed in the rabbit BMSCs by lentivirus transfection, which was expressed at a high level in the femoral defects treated with TGF‑β1‑overexpressing BMSCs, compared with PBS‑treated controls. In addition, the TGF‑β1‑overexpressing BMSCs promoted new bone formation in the rabbit femoral defect model, and increased the expression of bone‑related markers at week 2 and week 6. Therefore, the study demonstrated that BMSCs overexpressing TGF‑β1 may provide a novel therapeutic option for femoral defects.

Crystallinity of hydroxyapatite drives myofibroblastic activation and calcification in aortic valves

Calcific aortic valve disease (CAVD) is an inexorably degenerative pathology characterized by progressive calcific lesion formation on the valve leaflets. The interaction of valvular cells in advanced lesion environments is not well understood yet highly relevant as clinically detectable CAVD exhibits calcifications composed of non-stoichiometric hydroxyapatite (HA). In this study, Fourier transform infrared spectroscopic imaging was used to spatially analyze mineral properties as a function of disease progression. Crystallinity (size and perfection) increased with increased valve calcification. To study the relationship between crystallinity and cellular behavior in CAVD, valve cells were seeded into 3D mineral-rich collagen gels containing synthetic HA particles, which had varying crystallinities. Lower crystallinity HA drove myofibroblastic activation in both valve interstitial and endothelial cells, as well as osteoblastic differentiation in interstitial cells. Additionally, calcium accumulation within gels depended on crystallinity, and apoptosis was insufficient to explain differences in HA-driven cellular activity. The protective nature of endothelial cells against interstitial cell activation and calcium accumulation was completely inhibited in the presence of less crystalline HA particles. Elucidating valve cellular behavior post-calcification is of vital importance to better predict and treat clinical pathogenesis, and mineral-containing hydrogel models provide a unique 3D platform to evaluate valve cell responses to a later stage of valve disease.

STATEMENT OF SIGNIFICANCE

We implement a 3D in vitro platform with embedded hydroxyapatite (HA) nanoparticles to investigate the interaction between valve interstitial cells, valve endothelial cells, and a mineral-rich extracellular environment. HA nanoparticles were synthesized based on analysis of the mineral properties of calcific regions of diseased human aortic valves. Our findings indicate that crystallinity of HA drives activation and differentiation in interstitial and endothelial cells. We also show that a mineralized environment blocks endothelial protection against interstitial cell calcification. Our HA-containing hydrogel model provides a unique 3D platform to evaluate valve cell responses to a mineralized ECM. This study additionally lays the groundwork to capture the diversity of mineral properties in calcified valves, and link these properties to progression of the disease.

Evaluation of Poly(Lactic-co-glycolic) Acid Alone or in Combination with Hydroxyapatite on Human-Periosteal Cells Bone Differentiation and in Sinus Lift Treatment

Most recent advances in tissue engineering in the fields of oral surgery and dentistry have aimed to restore hard and soft tissues. Further improvement of these therapies may involve more biological approaches and the use of dental tissue stem cells in combination with inorganic/organic scaffolds. In this study, we analyzed the osteoconductivity of two different inorganic scaffolds based on poly (lactic-co-glycolic) acid alone (PLGA-Fisiograft) or in combination with hydroxyapatite (PLGA/HA-Alos) in comparison with an organic material based on equine collagen (PARASORB Sombrero) both in vitro and in vivo. We developed a simple in vitro model in which periosteum-derived stem cells were grown in contact with chips of these scaffolds to mimic bone mineralization. The viability of cells and material osteoconductivity were evaluated by osteogenic gene expression and histological analyses at different time points. In addition, the capacity of scaffolds to improve bone healing in sinus lift was examined. Our results demonstrated that the osteoconductivity of PLGA/HA-Alos and the efficacy of scaffolds in promoting bone healing in the sinus lift were increased. Thus, new clinical approaches in sinus lift follow-up should be considered to elucidate the clinical potential of these two PLGA-based materials in dentistry.

Effects of cellular parameters on the in vitro osteogenic potential of dual-gelling mesenchymal stem cell-laden hydrogels

This work investigated the effects of cellular encapsulation density and differentiation stage on the osteogenic capacity of injectable, dual physically and chemically gelling hydrogels comprised of thermogelling macromers and polyamidoamine crosslinkers. Undifferentiated and osteogenically predifferentiated mesenchymal stem cells (MSCs) were encapsulated within 20 wt% composite hydrogels with gelatin microparticles at densities of six or 15 million cells/mL. We hypothesized that a high encapsulation density and predifferentiation would promote increased cellular interaction and accelerate osteogenesis, leading to enhanced osteogenic potential in vitro. Hydrogels were able to maintain the viability of the encapsulated cells over a period of 28 days, with the high encapsulation density and predifferentiation group possessing the highest DNA content at all time points. Early alkaline phosphatase activity and mineralization were promoted by encapsulation density, whereas this effect by predifferentiation was only observed in the low seeding density groups. Both parameters only demonstrated short-lived effects when examined independently, but jointly led to greater levels of alkaline phosphatase activity and mineralization. The combined effects suggest that there may be optimal encapsulation densities and differentiation periods that need to be investigated to improve MSCs for biomaterial-based therapeutics in bone tissue engineering.

Effect of Nano-HA/Collagen Composite Hydrogels on Osteogenic Behavior of Mesenchymal Stromal Cells

This study aimed to comparatively evaluate the in vitro effect of nanosized hydroxyapatite and collagen (nHA/COL) based composite hydrogels (with different ratios of nHA and COL) on the behavior of human mesenchymal stromal cells (MSCs), isolated from either adipose tissue (AT-MSCs) or bone marrow (BM-MSCs). We hypothesized that (i) nHA/COL composite hydrogels would promote the osteogenic differentiation of MSCs in an nHA concentration dependent manner, and that (ii) AT-MSCs would show higher osteogenic potential compared to BM-MSCs, due to their earlier observed higher proliferation and osteogenic differentiation potential in 2D in vitro cultures [1]. The obtained results indicated that AT-MSCs show indeed high proliferation, differentiation and mineralization capacities in nHA/COL constructs compared to BM-MSCs, but this effect was irrespective of nHA concentration. Based on the results of alkaline phosphatase (ALP) activity and osteocalcin (OCN) protein level, the osteogenic differentiation of BM-MSCs started in the beginning of the culture period and for AT-MSCs at the end of the culture period. At a molecular level, both cell types showed high expression of osteogenic markers (bone morphogenic protein 2 [BMP2], runt-related transcription factor 2 [RUNX2], OCN or COL1) in both an nHA concentration and time dependent manner. In conclusion, AT-MSCs demonstrated higher osteogenic potential in nHA/COL based 3D micro-environments compared to BM-MSCs, in which proliferation and osteogenic differentiation were highly promoted in a time dependent manner, irrespective of nHA amount in the constructs. The fact that AT-MSCs showed high proliferation and mineralization potential is appealing for their application in future pre-clinical research as an alternative cell source for BM-MSCs.

Collagen and Hydroxyapatite Scaffolds Activate Distinct Osteogenesis Signaling Pathways in Adult Adipose-Derived Multipotent Stromal Cells

Osteogenic cell signaling pathway disruption varies among bone diseases. This investigation was designed to identify adipose-derived multipotent stromal cell (ASC) and bone graft scaffold combinations for local, targeted restoration of gene expression and extracellular matrix (ECM) deposition. Human ASC osteogenesis on bone graft materials was quantified following culture in stromal (S), osteogenic (O), or osteogenic for 48 h followed by stromal medium (OS) to test the two-part hypothesis: (1) identical ASC isolates on distinct bone graft scaffolds demonstrate unique viability, differentiation, ECM production, and gene expression in the same culture conditions; (2) identical ASC-bone graft scaffold combinations have different cell viability, differentiation, ECM production, and gene expression when cultured in S, O, or OS medium. Three commercially available bone graft scaffold materials, type I bovine collagen (C), hydroxyapatite + β-tricalcium phosphate + type I bovine collagen (HT), and β-tricalcium phosphate + type I bovine collagen (CT) were evaluated. Passage 3 ASCs were loaded onto scaffold blocks with a spinner flask bioreactor, and constructs were cultured up to 28 days. Cell viability, gene expression (alkaline phosphatase [ALPL], osteoprotegerin [TNFRSF11B], osteocalcin [BGLAP], cannabinoid receptors type I [CNR1] and II [CNR2], receptor activator of nuclear factor kappa β ligand [TNFSF11]), as well as ECM DNA, collagen, sulfated glycosaminoglycan, and protein content were quantified. Matrix organization was evaluated with scanning electron microscopy. Effects of scaffold, medium, or culture duration on cell viability were minimal. Significantly higher initial ALPL expression decreased with time, while BGLAP expression increased in HT constructs in O medium, and the constructs had the most abundant ECM components and ultrastructural organization. There was a similar, although delayed, pattern of gene expression and greater ECM collagen with less organization in C constructs in O medium. Higher CNR1 expression in C versus higher TNFRSF11B/TNFSF11 expression in HT constructs throughout the study support stimulation of unique osteogenic signaling pathways by identical cell isolates. These results suggest that bone scaffold composition may be used to selectively target specific osteogenic cell signaling pathways in ASC constructs to stimulate ECM deposition based on therapeutic needs.

Engineering human bone grafts with new macroporous calcium phosphate cement scaffolds

Bone engineering opens the possibility to grow large amounts of tissue products by combining patient-specific cells with compliant biomaterials. Decellularized tissue matrices represent suitable biomaterials, but availability, long processing time, excessive cost, and concerns on pathogen transmission have led to the development of biomimetic synthetic alternatives. We recently fabricated calcium phosphate cement (CPC) scaffolds with variable macroporosity using a facile synthesis method with minimal manufacturing steps and demonstrated long-term biocompatibility in vitro. However, there is no knowledge on the potential use of these scaffolds for bone engineering and whether the porosity of the scaffolds affects osteogenic differentiation and tissue formation in vitro. In this study, we explored the bone engineering potential of CPC scaffolds with two different macroporosities using human mesenchymal progenitors derived from induced pluripotent stem cells (iPSC-MP) or isolated from bone marrow (BMSC). Biomimetic decellularized bone scaffolds were used as reference material in all experiments. The results demonstrate that, irrespective of their macroporosity, the CPC scaffolds tested in this study support attachment, viability, and growth of iPSC-MP and BMSC cells similarly to decellularized bone. Importantly, the tested materials sustained differentiation of the cells as evidenced by increased expression of osteogenic markers and formation of a mineralized tissue. In conclusion, the results of this study suggest that the CPC scaffolds fabricated using our method are suitable to engineer bone grafts from different cell sources and could lead to the development of safe and more affordable tissue grafts for reconstructive dentistry and orthopaedics and in vitro models for basic and applied research.

Loading of BMP-2-related peptide onto three-dimensional nano-hydroxyapatite scaffolds accelerates mineralization in critical-sized cranial bone defects

Extrusion free-forming, as a rapid prototyping technique, is extensively applied in fabricating ceramic material in bone tissue engineering. To improve the osteoinductivity of nano-hydroxyapatite (nHA) scaffold fabricated by extrusion free-forming, in this study, we incorporated a new peptide (P28) and optimized the superficial microstructure after shaping by controlling the sintering temperature. P28, a novel bone morphogenic protein 2 (BMP-2)-related peptide, was designed in this study. Analysis of the structure, physicochemical properties and release kinetics of P28 from nHA sintered at temperatures ranging from 1000 °C to 1400 °C revealed that nHA sintered at 1000 °C had higher porosity, preferable pore size and better capacity to control P28 release than that sintered at other temperatures. Moreover, the nHA scaffold sintered at 1000 °C with P28 showed improved adhesion, proliferation and osteogenic differentiation of MC3T3-E1 cells compared with scaffolds lacking P28 or BMP-2. In vivo, nHA scaffolds sintered at 1000 °C with P28 or BMP-2 induced greater bone regeneration in critical-sized rat cranial defects at 6 and 12 weeks post-implantation compared with scaffolds lacking P28 or BMP-2. Thus, nHA scaffolds sintered at 1000 °C and loaded with P28 may be excellent biomaterials for bone tissue engineering. Copyright © 2016 John Wiley & Sons, Ltd.

Extrusion-based 3D printing of poly(propylene fumarate) scaffolds with hydroxyapatite gradients

The primary focus of this work is to present the current challenges of printing scaffolds with concentration gradients of nanoparticles with an aim to improve the processing of these scaffolds. Furthermore, we address how print fidelity is related to material composition and emphasize the importance of considering this relationship when developing complex scaffolds for bone implants. The ability to create complex tissues is becoming increasingly relevant in the tissue engineering community. For bone tissue engineering applications, this work demonstrates the ability to use extrusion-based printing techniques to control the spatial deposition of hydroxyapatite (HA) nanoparticles in a 3D composite scaffold. In doing so, we combined the benefits of synthetic, degradable polymers, such as poly(propylene fumarate) (PPF), with osteoconductive HA nanoparticles that provide robust compressive mechanical properties. Furthermore, the final 3D printed scaffolds consisted of well-defined layers with interconnected pores, two critical features for a successful bone implant. To demonstrate a controlled gradient of HA, thermogravimetric analysis was carried out to quantify HA on a per-layer basis. Moreover, we non-destructively evaluated the tendency of HA particles to aggregate within PPF using micro-computed tomography (μCT). This work provides insight for proper fabrication and characterization of composite scaffolds containing particle gradients and has broad applicability for future efforts in fabricating complex scaffolds for tissue engineering applications.

Hydroxyapatite-doped alginate beads as scaffolds for the osteoblastic differentiation of mesenchymal stem cells

This work investigates the role of an osteoblastic matrix component, hydroxyapatite (HA), in modular alginate scaffolds to support osteoblastic differentiation of human mesenchymal stem cells for the purpose of tissue engineered bone constructs. This system is first evaluated in a tubular perfusion bioreactor, which has been shown to improve osteoblastic differentiation over static culture conditions. HMSCs in alginate scaffolds that contain HA show increased osteoblastic gene expression compared to cells in pure alginate scaffolds, as well as significantly more matrix production and mineralization. The differentiated hMSCs and cell-laid matrix are ultimately evaluated in an in vivo site specific model. Implantation of these scaffolds with preformed matrix into the rat femoral condyle defects results in abundant bone growth and significant incorporation of the scaffold into the surrounding tissue. The developed mineralized matrix, induced in part by the HA component in the scaffold, could lead to increased tissue development in critically sized defects, and should be included in future implant strategies. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2325-2333, 2016.

Physically entrapped gelatin in polyethylene glycol scaffolds for three-dimensional chondrocyte culture

Developing tissue-engineered constructs for clinical use must satisfy the fundamental biologic parameters of biocompatibility, cell adhesiveness, and biodegradability. Physical entrapment of bioactive agents into synthetic polymers, as three-dimensional scaffolds, holds great promise for cell culture applications. Here, in an attempt to elucidate the effects of physical interlocking of natural and synthetic gel networks on cell responses within three-dimensional microenvironments, gelatin (of different concentrations) was physically incorporated into macroporous polyethylene glycol (PEG) hydrogels to fabricate PEG-GEL1 (10:1, PEG:gelatin) and PEG-GEL5 (10:5, PEG:gelatin). The effect of the physically entrapped gelatin on primary chondrocytes was investigated in relation to cell distribution, morphology and viability, proliferation, gene expression, and extracellular matrix accumulation in vitro. Our findings have shown successful incorporation of two different concentrations of gelatin into polyethylene glycol macroporous hydrogels through physical mixing. These physical blends not only enhanced chondrocyte adhesion and proliferation but also boosted gene expression of collagen II and aggrecan after 14 days in culture. Although results demonstrated that gelatin levels dropped sharply in PEG-GEL1 and PEG-GEL5 in the first 7 days, however evidently, after days 14 and 21 gelatin levels in both groups remained substantially unchanged and in turn enhanced glycosaminoglycan formation in vitro. Thus, the modification of polyethylene-glycol-based scaffolds with physically entrapped gelatin may be sufficient for dictating three-dimensional microenvironments for chondrocyte cultures.

Prospect of Stem Cells in Bone Tissue Engineering: A Review

Mesenchymal stem cells (MSCs) have been the subject of many studies in recent years, ranging from basic science that looks into MSCs properties to studies that aim for developing bioengineered tissues and organs. Adult bone marrow-derived mesenchymal stem cells (BM-MSCs) have been the focus of most studies due to the inherent potential of these cells to differentiate into various cell types. Although, the discovery of induced pluripotent stem cells (iPSCs) represents a paradigm shift in our understanding of cellular differentiation. These cells are another attractive stem cell source because of their ability to be reprogramed, allowing the generation of multiple cell types from a single cell. This paper briefly covers various types of stem cell sources that have been used for tissue engineering applications, with a focus on bone regeneration. Then, an overview of some recent studies making use of MSC-seeded 3D scaffold systems for bone tissue engineering has been presented. The emphasis has been placed on the reported scaffold properties that tend to improve MSCs adhesion, proliferation, and osteogenic differentiation outcomes.

Bone marrow-derived mesenchymal stem cells assembled with low-dose BMP-2 in a three-dimensional hybrid construct enhances posterolateral spinal fusion in syngeneic rats

BACKGROUND CONTEXT

The combination of potent osteoinductive growth factor, functional osteoblastic cells, and osteoconductive materials to induce bone formation is a well-established concept in bone tissue engineering. However, supraphysiological dose of growth factor, such as recombinant human bone morphogenetic protein 2 (rhBMP-2), which is necessary in contemporary clinical application, have been reported to result in severe side effects.

PURPOSE

We hypothesize that the synergistic osteoinductive capacity of low-dose bone morphogenetic protein 2 (BMP-2) combined with undifferentiated bone marrow-derived stromal cells (BMSCs) is comparable to that of osteogenically differentiated BMSCs when used in a rodent model of posterolateral spinal fusion.

STUDY DESIGN/SETTING

A prospective study using a rodent model of posterolateral spinal fusion was carried out.

PATIENT SAMPLE

Thirty-six syngeneic Fischer rats comprised the patient sample.

METHODS

Six groups of implants were evaluated as follows (n=6): (1) 10 µg BMP-2 with undifferentiated BMSCs; (2) 10 µg BMP-2 with osteogenic-differentiated BMSCs; (3) 2.5 µg BMP-2 with undifferentiated BMSCs; (4) 2.5 µg BMP-2 with osteogenic-differentiated BMSCs; (5) 0.5 µg BMP-2 with undifferentiated BMSCs; and (6) 0.5 µg BMP-2 with osteogenic-differentiated BMSCs. Optimal in vitro osteogenic differentiation of BMSCs was determined by quantitative real-time polymerase chain reaction (qRT-PCR) gene analysis whereas in vivo bone formation capacity was evaluated by manual palpation, micro-computed tomography, and histology.

RESULTS

Rat BMSCs cultured in fibrin matrix that was loaded into the pores of medical-grade poly epsilon caprolactone tricalcium phosphate scaffolds differentiated toward osteogenic lineage by expressing osterix, runt-related transcription factor 2, and osteocalcium mRNA when supplemented with dexamethasone, ascorbic acid, and β-glycerophosphate. Whereas qRT-PCR revealed optimal increase in osteogenic genes expression after 7 days of in vitro culture, in vivo transplantation study showed that pre-differentiation of BMSCs before transplantation failed to promote posterolateral spinal fusion when co-delivered with low-dose BMP-2 (1/6 or 17% fusion rate). In contrast, combined delivery of undifferentiated BMSCs with low-dose BMP-2 (2.5 µg) demonstrated significantly higher fusion rate (4/6 or 67%) as well as significantly increased volume of new bone formation (p<.05).

CONCLUSION

In summary, this study supports the combination of undifferentiated BMSCs and low-dose rhBMP-2 for bone tissue engineering construct.

Polymeric scaffolds in tissue engineering: a literature review

The tissue engineering scaffold acts as an extracellular matrix that interacts to the cells prior to forming new tissues. The chemical and structural characteristics of scaffolds are major concerns in fabricating of ideal three-dimensional structure for tissue engineering applications. The polymer scaffolds used for tissue engineering should possess proper architecture and mechanical properties in addition to supporting cell adhesion, proliferation, and differentiation. Much research has been done on the topic of polymeric scaffold properties such as surface topographic features (roughness and hydrophilicity) and scaffold microstructures (pore size, porosity, pore interconnectivity, and pore and fiber architectures) that influence the cell-scaffold interactions. In this review, efforts were given to evaluate the effect of both chemical and structural characteristics of scaffolds on cell behaviors such as adhesion, proliferation, migration, and differentiation. This review would provide the fundamental information which would be beneficial for scaffold design in future. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 431-459, 2017.