Comparative effects of scaffold pore size, pore volume, and total void volume on cranial bone healing patterns using microsphere-based scaffolds

An overview of stem cells and cell products involved in trauma injury

Trauma injuries represent a significant public health burden worldwide, often leading to long-term disability and reduced quality of life. This review provides a comprehensive overview of the therapeutic potential of stem cells and cell products for traumatic injuries. The extraordinary characteristics of stem cells, such as self-renewal and transdifferentiation, make them definitive candidates for tissue regeneration. Mesenchymal stem cells (MSCs), neural stem cells (NSCs), and hematopoietic stem cells (HSCs) have been tested in preclinical studies for treating distinct traumatic injuries. Stem cell mechanisms of action are addressed through paracrine signaling, immunomodulation, differentiation, and neuroprotection. Cell products such as conditioned media, exosomes, and secretomes offer cell-free resources, thereby avoiding the risks of live cell transplantation. Clinical trials have reported many effective outcomes; however, variability exists across trauma types. Some challenges include tumorigenicity, standardized protocols, and regulatory issues. Collaboration and interdisciplinary research are being conducted to harness stem cells and products for trauma treatment. This emerging field is promising for improving patient recovery and quality of life after traumatic injuries.

A 3D-printed microdevice encapsulates vascularized islets composed of iPSC-derived β-like cells and microvascular fragments for type 1 diabetes treatment

Transplantation of insulin-secreting cells provides a promising method for re-establishing the autonomous blood glucose control ability of type 1 diabetes (T1D) patients, but the low survival of the transplanted cells hinder the therapeutic efficacy. In this study, we 3D-printed an encapsulation system containing β-like cells and microvascular fragments (MVF), to create a retrivable microdevice with vascularized islets in vivo for T1D therapy. The functional β-like cells were differentiated from the urine epithelial cell-derived induced pluripotent stem cells (UiPSCs). Single-cell RNA sequencing provided an integrative study and macroscopic developmental analyses of the entire process of differentiation, which revealed the developmental trajectory of differentiation in vitro follows the developmental pattern of embryonic pancreas in vivo. The MVF were isolated from the epididymal fat pad. The microdevice with a groove structure were rapidly fabricated by the digital light processing (DLP)-3D printing technology. The β-like cells and MVF were uniformly distributed in the device. After subcutaneous transplantation into C57BL/6 mice, the microdevice have less collagen accumulation and low immune cell infiltration. Moreover, the microdevice encapsulated vascularized islets reduced hyperglycemia in 33 % of the treated mice for up to 100 days without immunosuppressants, and the humanized C-peptide was also detected in the serum of the mice. In summary, we described the microdevice-protected vascularized islets for long-term treatment of T1D, with high safety and potential clinical transformative value, and may therefore provide a translatable solution to advance the research progress of β cell replacement therapy for T1D.

Poly(HEMA-co-MMA) Hydrogel Scaffold for Tissue Engineering with Controllable Morphology and Mechanical Properties Through Self-Assembly

Poly(2-hydroxyethyl methacrylate) (PHEMA) has been widely used in medical materials for several decades. However, the poor mechanical properties of this material have limited its application in the field of tissue engineering. The purpose of this study was to fabricate a scaffold with suitable mechanical properties and in vitro cell responses for soft tissue by using poly(HEMA-co-MMA) with various concentration ratios of hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA). To customize the concentration ratio of HEMA and MMA, the characteristics of the fabricated scaffold with various concentration ratios were investigated through structural morphology, FT-IR, mechanical property, and contact angle analyses. Moreover, in vitro cell responses were observed according to the various concentration ratios of HEMA and MMA. Consequently, various morphologies and pore sizes were observed by changing the HEMA and MMA ratio. The mechanical properties and contact angle of the fabricated scaffolds were measured according to the HEMA and MMA concentration ratio. The results were as follows: compressive maximum stress: 254.24-932.42 KPa; tensile maximum stress: 4.37-30.64 KPa; compressive modulus: 16.14-38.80 KPa; tensile modulus: 0.5-2 KPa; and contact angle: 36.89-74.74°. In terms of the in vitro cell response, the suitable cell adhesion and proliferation of human dermal fibroblast (HDF) cells were observed in the whole scaffold. Therefore, a synthetic hydrogel scaffold with enhanced mechanical properties and suitable fibroblast cell responses could be easily fabricated for use with soft tissue using a specific HEMA and MMA concentration ratio.

The potent osteo-inductive capacity of bioinspired brown seaweed-derived carbohydrate nanofibrous three-dimensional scaffolds

This study aimed to investigate the osteo-inductive capacity of a fucoidan polysaccharide network derived from brown algae on human adipose-derived stem cells (HA-MSCs) for bone regeneration. The physiochemical properties of the scaffold including surface morphology, surface chemistry, hydrophilicity, mechanical stiffness, and porosity were thoroughly characterized. Both in vitro and in vivo measurements implied a superior cell viability, proliferation, adhesion, and osteo-inductive performance of obtained scaffolds compared to using specific osteogenic induction medium with increased irregular growth of calcium crystallites, which mimic the structure of natural bones. That scaffold was highly biocompatible and suitable for cell cultures. Various examinations, such as quantification of mineralization, alkaline phosphatase, gene expression, and immunocytochemical staining of pre-osteocyte and bone markers confirmed that HAD-MSCs differentiate into osteoblasts, even without an osteogenic induction medium. This study provides evidence for the positive relationship and synergistic effects between the physical properties of the decellularized seaweed scaffold and the chemical composition of fucoidan in promoting the osteogenic differentiation of HA-MSCs. Altogether, the natural matrices derived from brown seaweed offers a sustainable, cost-effective, non-toxic bioinspired scaffold and holds promise for future clinical applications in orthopedics.

Scaffold-based spheroid models of glioblastoma multiforme and its use in drug screening

Among several types of brain cancers, glioblastoma multiforme (GBM) is a terminal and aggressive disease with a median survival of 15 months despite the most intensive surgery and chemotherapy. Preclinical models that accurately reproduce the tumor microenvironment are vital for developing new therapeutic alternatives. Understanding the complicated interactions between cells and their surroundings is essential to comprehend the tumor's microenvironment, however the monolayer cell culture approach falls short. Numerous approaches are used to develop GBM cells into tumor spheroids, while scaffold-based spheroids provides the opportunity to investigate the synergies between cells as well as cells and the matrix. This review summarizes the development of various scaffold-based GBM spheroid models and the prospective for their use as drug testing systems.

Composite microgranular scaffolds with surface modifications for improved initial osteoblastic cell proliferation

Polyester-based granular scaffolds are a potent material for tissue engineering due to their porosity, controllable pore size, and potential to be molded into various shapes. Additionally, they can be produced as composite materials, e.g., mixed with osteoconductive β-tricalcium phosphate or hydroxyapatite. Such polymer-based composite materials often happen to be hydrophobic, which disrupts cell attachment and decreases cell growth on the scaffold, undermining its primary function. In this work, we propose the experimental comparison of three modification techniques for granular scaffolds to increase their hydrophilicity and cell attachment. Those techniques include atmospheric plasma treatment, polydopamine coating, and polynorepinephrine coating. Composite polymer/β-tricalcium phosphate granules have been produced in a solution-induced phase separation (SIPS) process using commercially available biomedical polymers: poly(lactic acid), poly(lactic-co-glycolic acid), and polycaprolactone. We used thermal assembly to prepare cylindrical scaffolds from composite microgranules. Atmospheric plasma treatment, polydopamine coating, and polynorepinephrine coating showed similar effects on polymer composites' hydrophilic and bioactive properties. All modifications significantly increased human osteosarcoma MG-63 cell adhesion and proliferation in vitro compared to cells cultured on unmodified materials. In the case of polycaprolactone/β-tricalcium phosphate scaffolds, modifications were the most necessary, as unmodified polycaprolactone-based material disrupted the cell attachment. Modified polylactide/β-tricalcium phosphate scaffold supported excellent cell growth and showed ultimate compressive strength exceeding this of human trabecular bone. This suggests that all investigated modification techniques can be used interchangeably for increasing wettability and cell attachment properties of various scaffolds for medical applications, especially those with high surface and volumetric porosity, like granular scaffolds.

Controlled formation of highly porous polylactic acid‑calcium phosphate granules with defined structure

Synthetic bone repair materials are becoming increasingly popular in tissue engineering as a replacement for autografts and human/animal-based bone grafts. The biomedical application requires precise control over the material composition and structure, as well as over the size of granulate used for filling the bone defects, as the pore size and interconnectivity affect the regeneration process. This paper proposes a process of alloplastic and biodegradable polylactic acid/β-tricalcium phosphate granulates preparation and its parameters described. Using solvent-induced phase separation technique, porous spheres have been obtained in various sizes and morphologies. The design of the experiment's approach generated an experimental plan for further statistical modeling using the resulting data. The statistical modeling approach to the data from conducting a designed set of experiments allowed analysis of the influence of process parameters on the properties of the resulting granules. We confirmed that the content of β-tricalcium phosphate plays the most significant role in the size distribution of prepared granulate. The shape of the particles becomes less spherical with higher phosphate concentration in the emulsion. The proposed technique allows preparing porous granulates in the 0.2-1.8 mm diameter range, where granules' mean diameter and sphericity are tunable with polymer and phosphate concentrations. The granulate created a potentially implantable scaffold for resected bone regeneration, as cytotoxicity tests assured the material is non-cytotoxic in vitro, and human mesenchymal stem cells have been cultured on the surface of granulates. Results from cell cultures seeded on the Resomer LR 706S granulates were the most promising.

Computer-aided patterning of PCL microspheres to build modular scaffolds featuring improved strength and neovascularized tissue integration

In the past decade, modular scaffolds prepared by assembling biocompatible and biodegradable building blocks (e.g. microspheres) have found promising applications in tissue engineering (TE) towards the repair/regeneration of damaged and impaired tissues. Nevertheless, to date this approach has failed to be transferred to the clinic due to technological limitations regarding microspheres patterning, a crucial issue for the control of scaffold strength, vascularization and integration in vivo. In this work, we propose a robust and reliable approach to address this issue through the fabrication of polycaprolactone (PCL) microsphere-based scaffolds with in-silico designed microarchitectures and high compression moduli. The scaffold fabrication technique consists of four main steps, starting with the manufacture of uniform PCL microspheres by fluidic emulsion technique. In the second step, patterned polydimethylsiloxane (PDMS) moulds were prepared by soft lithography. Then, layers of 500 µm PCL microspheres with geometrically inspired patterns were obtained by casting the microspheres onto PDMS moulds followed by their thermal sintering. Finally, three-dimensional porous scaffolds were built by the alignment, stacking and sintering of multiple (up to six) layers. The so prepared scaffolds showed excellent morphological and microstructural fidelity with respect to the in-silico models, and mechanical compression properties suitable for load bearing TE applications. Designed porosity and pore size features enabled in vitro human endothelial cells adhesion and growth as well as tissue integration and blood vessels invasion in vivo. Our results highlighted the strong impact of spatial patterning of microspheres on modular scaffolds response, and pay the way about the possibility to fabricate in silico-designed structures featuring biomimetic composition and architectures for specific TE purposes.

Treatment options for critical size defects - Comparison of different materials in a calvaria split model in sheep

Bone defects of the craniofacial skeleton are often associated with aesthetic and functional impairment as well as loss of protection to intra- and extracranial structures. Solid titanium plates and individually adapted bone cements have been the materials of choice, but may lead to foreign-body reactions and insufficient osseointegration. In contrast, porous scaffolds are thought to exhibit osteoconductive properties to support bone ingrowth. Here, we analyse in critical size defects of the calvaria in sheep whether different bone replacement materials may overcome those remaining challenges. In a critical size defect model, bilateral 20 × 20 × 5-mm craniectomies were performed on either side of the sagittal sinus in 24 adult female blackheaded sheep. Bony defects were randomised to one of five different bone replacement materials (BRMs): titanium scaffold, biodegradable poly(d,l-lactic acid) calcium carbonate scaffold (PDLLA/CC), polyethylene 1 (0.71 mm mean pore size) or 2 (0.515 mm mean pore size) scaffolds and polymethyl methacrylate (PMMA)-based bone cement block. Empty controls (n = 3) served as references. To evaluate bone growth over time, three different fluorochromes were administered at different time points. At 3, 6 and 12 months after surgery, animals were sacrificed and the BRMs and surrounding bone analysed by micro-CT and histomorphometry. The empty control group verified that the calvaria defect in this study was a reliable critical size defect model. Bone formation in vivo was detectable in all BRMs after 12 months by micro-CT and histomorphometric analysis, except for the non-porous PMMA group. A maximum of bone formation was detected in the 12-months group for titanium and PDLLA/CC. Bone formation in PDLLA/CC starts to increase rapidly between 6 and 12 months, as the BRM resorbs over time. Contact between bone and BRM influenced bone formation inside the BRM. Empty controls exhibited bone formation solely at the periphery. Overall, porous BRMs offered bone integration to different extent over 12 months in the tested calvaria defect model. Titanium and PDLLA/CC scaffolds showed remarkable osseointegration properties by micro-CT and histomorphometric analysis. PDLLA/CC scaffolds degraded over time without major residues. Pore size influenced bone ingrowth in polyethylene, emphasising the importance of porous scaffold structure.

3D printed biocompatible graphene oxide, attapulgite, and collagen composite scaffolds for bone regeneration

Tissue-engineered bone material is one of the effective methods to repair bone defects, but the application is restricted in clinical because of the lack of excellent scaffolds that can induce bone regeneration as well as the difficulty in making scaffolds with personalized structures. 3D printing is an emerging technology that can fabricate bespoke 3D scaffolds with precise structure. However, it is challenging to develop the scaffold materials with excellent printability, osteogenesis ability, and mechanical strength. In this study, graphene oxide (GO), attapulgite (ATP), type I collagen (Col I) and polyvinyl alcohol were used as raw materials to prepare composite scaffolds via 3D bioprinting. The composite materials showed excellent printability. The microcosmic architecture and properties was characterized by scanning electron microscopy, Fourier transform infrared and thermal gravimetric analyzer, respectively. To verify the biocompatibility of the scaffolds, the viability, proliferation and osteogenic differentiation of Bone Marrow Stromal Cells (BMSCs) on the scaffolds were assessed by CCK-8, Live/Dead staining and Real-time PCR in vitro. The composited scaffolds were then implanted into the skull defects on rat for bone regeneration. Hematoxylin-eosin staining, Masson staining and immunohistochemistry staining were carried out in vivo to evaluate the regeneration of bone tissue.The results showed that GO/ATP/COL scaffolds have been demonstrated to possess controlled porosity, water absorption, biodegradability and good apatite-mineralization ability. The scaffold consisting of 0.5% GO/ATP/COL have excellent biocompatibility and was able to promote the growth, proliferation and osteogenic differentiation of mouse BMSCs in vitro. Furthermore, the 0.5% GO/ATP/COL scaffolds were also able to promote bone regeneration of in rat skull defects. Our results illustrated that the 3D printed GO/ATP/COL composite scaffolds have good mechanical properties, excellent cytocompatibility for enhanced mouse BMSCs adhesion, proliferation, and osteogenic differentiation. All these advantages made it potential as a promising biomaterial for osteogenic reconstruction.

Solvent-Free Approaches for the Processing of Scaffolds in Regenerative Medicine

The regenerative medicine field is seeking novel strategies for the production of synthetic scaffolds that are able to promote the in vivo regeneration of a fully functional tissue. The choices of the scaffold formulation and the manufacturing method are crucial to determine the rate of success of the graft for the intended tissue regeneration process. On one hand, the incorporation of bioactive compounds such as growth factors and drugs in the scaffolds can efficiently guide and promote the spreading, differentiation, growth, and proliferation of cells as well as alleviate post-surgical complications such as foreign body responses and infections. On the other hand, the manufacturing method will determine the feasible morphological properties of the scaffolds and, in certain cases, it can compromise their biocompatibility. In the case of medicated scaffolds, the manufacturing method has also a key effect in the incorporation yield and retained activity of the loaded bioactive agents. In this work, solvent-free methods for scaffolds production, i.e., technological approaches leading to the processing of the porous material with no use of solvents, are presented as advantageous solutions for the processing of medicated scaffolds in terms of efficiency and versatility. The principles of these solvent-free technologies (melt molding, 3D printing by fused deposition modeling, sintering of solid microspheres, gas foaming, and compressed CO2 and supercritical CO2-assisted foaming), a critical discussion of advantages and limitations, as well as selected examples for regenerative medicine purposes are herein presented.

Engineering the vasculature for islet transplantation

The microvasculature in the pancreatic islet is highly specialized for glucose sensing and insulin secretion. Although pancreatic islet transplantation is a potentially life-changing treatment for patients with insulin-dependent diabetes, a lack of blood perfusion reduces viability and function of newly transplanted tissues. Functional vasculature around an implant is not only necessary for the supply of oxygen and nutrients but also required for rapid insulin release kinetics and removal of metabolic waste. Inadequate vascularization is particularly a challenge in islet encapsulation. Selectively permeable membranes increase the barrier to diffusion and often elicit a foreign body reaction including a fibrotic capsule that is not well vascularized. Therefore, approaches that aid in the rapid formation of a mature and robust vasculature in close proximity to the transplanted cells are crucial for successful islet transplantation or other cellular therapies. In this paper, we review various strategies to engineer vasculature for islet transplantation. We consider properties of materials (both synthetic and naturally derived), prevascularization, local release of proangiogenic factors, and co-transplantation of vascular cells that have all been harnessed to increase vasculature. We then discuss the various other challenges in engineering mature, long-term functional and clinically viable vasculature as well as some emerging technologies developed to address them. The benefits of physiological glucose control for patients and the healthcare system demand vigorous pursuit of solutions to cell transplant challenges. STATEMENT OF SIGNIFICANCE: Insulin-dependent diabetes affects more than 1.25 million people in the United States alone. Pancreatic islets secrete insulin and other endocrine hormones that control glucose to normal levels. During preparation for transplantation, the specialized islet blood vessel supply is lost. Furthermore, in the case of cell encapsulation, cells are protected within a device, further limiting delivery of nutrients and absorption of hormones. To overcome these issues, this review considers methods to rapidly vascularize sites and implants through material properties, pre-vascularization, delivery of growth factors, or co-transplantation of vessel supporting cells. Other challenges and emerging technologies are also discussed. Proper vascular growth is a significant component of successful islet transplantation, a treatment that can provide life-changing benefits to patients.

3D gelatin-chitosan hybrid hydrogels combined with human platelet lysate highly support human mesenchymal stem cell proliferation and osteogenic differentiation

Bone marrow and adipose tissue human mesenchymal stem cells were seeded in highly performing 3D gelatin–chitosan hybrid hydrogels of varying chitosan content in the presence of human platelet lysate and evaluated for their proliferation and osteogenic differentiation. Both bone marrow and adipose tissue human mesenchymal stem cells in gelatin–chitosan hybrid hydrogel 1 (chitosan content 8.1%) or gelatin–chitosan hybrid hydrogel 2 (chitosan 14.9%) showed high levels of viability (80%–90%), and their proliferation and osteogenic differentiation was significantly higher with human platelet lysate compared to fetal bovine serum, particularly in gelatin–chitosan hybrid hydrogel 1. Mineralization was detected early, after 21 days of culture, when human platelet lysate was used in the presence of osteogenic stimuli. Proteomic characterization of human platelet lysate highlighted 59 proteins mainly involved in functions related to cell adhesion, cellular repairing mechanisms, and regulation of cell differentiation. In conclusion, the combination of our gelatin–chitosan hybrid hydrogels with hPL represents a promising strategy for bone regenerative medicine using human mesenchymal stem cells.

3D-printed poly(lactic acid) scaffolds for trabecular bone repair and regeneration: scaffold and native bone characterization

PURPOSE

Study objectives were set to (i) fabricate 3D-printed scaffolds/grafts with varying pore sizes, (ii) characterize surface and mechanical properties of scaffolds, (iii) characterize biomechanical properties of bovine trabecular bone, and (iv) evaluate attachment and proliferation of human bone marrow mesenchymal stem cells on 3D-printed scaffolds.

MATERIALS AND METHODS

Poly(lactic acid) scaffolds were fabricated using 3D-printing technology, and characterized in terms of their surface as well as compressive mechanical properties. Trabecular bone specimens were obtained from bovine and characterized biomechanically under compression. Human bone marrow mesenchymal stem cells were seeded on the scaffolds, and their attachment capacity and proliferation were evaluated.

RESULTS

Contact angles and compressive moduli of scaffolds decreased with increasing pore dimensions of 0.5 mm, 1.0 mm, and 1.25 mm. Biomechanical characterization of trabecular bone yielded higher modulus values as compared to scaffolds with all pore sizes studied. Human bone marrow mesenchymal stem cells attached to the surfaces of all scaffolds yet proliferated more on scaffolds with 1.25 mm pore size.

CONCLUSIONS

Collectively, given the similarity between 3D-printed scaffolds and native bone in terms of pore size, porosity, and appropriate mechanical properties of scaffolds, the 3D-printed poly(lactic acid) (PLA) scaffolds of this study appear as candidate substitutes for bone repair and regeneration.

Antibacterial 3D bone scaffolds for tissue engineering application

Open bone fractures are not only difficult to heal but also are at a high risk of infections. Annual cases of fractures which result from osteoporosis amount to approximately 9 million. Endogenously released nitric oxide (NO) has been shown to play a role in osteogenic differentiation in addition to eradicating infection against a wide variety of pathogens. In the current work, antimicrobial NO releasing 3D bone scaffolds were fabricated using S-nitroso-N-acetyl-penicillamine (SNAP) as the NO donor. During fabrication, nano-hydroxyapatite (nHA) was added to each of the scaffolds in the concentration range of 10-50 wt % in nHA-starch-alginate and nHA-starch-chitosan scaffolds. The mechanical strength of the scaffolds increased proportionally to the concentration of nHA and 50 wt % nHA-starch-alginate possessed the highest load bearing capacity of 203.95 ± 0.3 N. The NO flux of the 50 wt % nHA-starch-alginate scaffolds was found to be 0.50 ± 0.06 × 10-10 mol/min/mg initially which reduced to 0.23 ± 0.02 × 10-10 over a 24 h period under physiological conditions. As a result, a 99.76% ± 0.33% reduction in a gram-positive bacterium, Staphylococcus aureus and a 99.80% ± 0.62% reduction in the adhered viable colonies of gram-negative bacterium, Pseudomonas aeruginosa were observed, which is a significant stride in the field of antibacterial natural polymers. The surface morphology and pore size were observed to be appropriate for the potential bone cell growth. The material showed no toxic response toward mouse fibroblast cells. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1068-1078, 2019.

Stem cells combined 3D electrospun nanofibrous and macrochannelled matrices: a preliminary approach in repair of rat cranial bones

Repair of cranial bone defects is an important problem in the clinical area. The use of scaffolds combined with stem cells has become a focus in the reconstruction of critical-sized bone defects. Electrospinning became a very attracting method in the preparation of tissue engineering scaffolds in the last decade, due to the unique nanofibrous structure of the electrospun matrices. However, they have a limitation for three dimensional (3D) applications, due to their two-dimensional structure and pore size which is smaller than a cellular diameter which cannot allow cell migration within the structure. In this study, electrospun poly(ε-caprolactone) (PCL) membranes were spirally wounded to prepare 3D matrices composed of nanofibers and macrochannels. Mesenchymal stromal/stem cells were injected inside the scaffolds after the constructs were implanted in the cranial bone defects in rats. New bone formation, vascularisation and intramembranous ossification of the critical size calvarial defect were accelerated by using mesenchymal stem cells combined 3D spiral-wounded electrospun matrices.

An injectable and thermosensitive hydrogel: Promoting periodontal regeneration by controlled-release of aspirin and erythropoietin

Periodontitis is an inflammatory disease induced by complex interactions between host immune system and plaque microorganism. Alveolar bone resorption caused by periodontitis is considered to be one of the main reasons for tooth loss in adults. To terminate the alveolar bone resorption, simultaneous anti-inflammation and periodontium regeneration is required, which has not appeared in the existing methods. In this study, chitosan (CS), β-sodium glycerophosphate (β-GP), and gelatin were used to prepare an injectable and thermosensitive hydrogel, which could continuously release aspirin and erythropoietin (EPO) to exert pharmacological effects of anti-inflammation and tissue regeneration, respectively. The releasing profile showed that aspirin and EPO could be continuously released from the hydrogels, which exhibited no toxicity both in vitro and in vivo, for at least 21 days. Immunohistochemistry staining and micro-CT analyses indicated that administration of CS/β-GP/gelatin hydrogels loaded with aspirin/EPO could terminate the inflammation and recover the height of the alveolar bone, which is further confirmed by histological observations. Our results suggested that CS/β-GP/gelatin hydrogels are easily prepared as drug-loading vectors with excellent biocompatibility, and the CS/β-GP/gelatin hydrogels loaded with aspirin/EPO are quite effective in anti-inflammation and periodontium regeneration, which provides a great potential candidate for periodontitis treatment in the dental clinic. Statement of Significance To terminate the alveolar bone resorption caused by periodontitis, simultaneous anti-inflammation and periodontium regeneration is required, which has not appeared in the existing methods. Here, (1) the chitosan (CS)/β-sodium glycerophosphate/gelatin hydrogels loaded with aspirin/erythropoietin (EPO) can form at body temperature in 5 min with excellent biocompatibility in vitro and in vivo; (2) The faster release of aspirin than EPO in the early stage is beneficial for anti-inflammation and provides a microenvironment for ensuring the regeneration function of EPO in the following step. In vivo experiments revealed that the hydrogels are effective in the control of inflammation and regeneration of the periodontium. These results indicate that our synthesized hydrogels have a great potential in the future clinical application.

Wicking Property of Graft Material Enhanced Bone Regeneration in the Ovariectomized Rat Model

Background

Recruitment and homing cells into graft materials from host tissue is crucial for bone regeneration.

Methods

Highly porous, multi-level structural, hydroxyapatite bone void filler (HA-BVF) have been investigated to restore critical size bone defects. The aim was to investigate a feasibility of bone regeneration of synthetic HA-BVF compared to commercial xenograft (Bio-Oss). HA-BVF of 0.7 mm in average diameter was prepared via template coating method. Groups of animals (n = 6) were divided into two with normal (Sham) or induced osteoporotic conditions (Ovx). Subsequently, subdivided into three treated with HA-BVF as an experiment or Bio-Oss as a positive control or no treatment as a negative control (defect). The new bone formation was analyzed by micro-CT and histology.

Results

At 4 weeks post-surgery, new bone formation was initiated from all groups. At 8 weeks post-surgery, new bone formation in the HA-BVF groups was greater than Bio-Oss groups. Extraordinarily greater bone regeneration within the Ovx-HA group than Sham-Bio-Oss or Ovx-Bio-Oss group (p < 0.05).

Conclusion

This study suggests that the immediate wicking property of HA-BVF from host tissue activates a natural healing cascade without the addition of exogeneous factors or progenitor cells. HA-BVF may be an effective alternative for repairing bone defects under both normal and osteoporotic bone conditions.

Highly porous scaffolds of PEDOT:PSS for bone tissue engineering

Conjugated polymers have been increasingly considered for the design of conductive materials in the field of regenerative medicine. However, optimal scaffold properties addressing the complexity of the desired tissue still need to be developed. The focus of this study lies in the development and evaluation of a conductive scaffold for bone tissue engineering. In this study PEDOT:PSS scaffolds were designed and evaluated in vitro using MC3T3-E1 osteogenic precursor cells, and the cells were assessed for distinct differentiation stages and the expression of an osteogenic phenotype.

Ice-templated PEDOT:PSS scaffolds presented high pore interconnectivity with a median pore diameter of 53.6 ± 5.9 µm and a total pore surface area of 7.72 ± 1.7 m²·g⁻¹. The electrical conductivity, based on I-V curves, was measured to be 140 µS·cm⁻¹ with a reduced, but stable conductivity of 6.1 µS·cm⁻¹ after 28 days in cell culture media. MC3T3-E1 gene expression levels of ALPL, COL1A1 and RUNX2 were significantly enhanced after 4 weeks, in line with increased extracellular matrix mineralisation, and osteocalcin deposition. These results demonstrate that a porous material, based purely on PEDOT:PSS, is suitable as a scaffold for bone tissue engineering and thus represents a promising candidate for regenerative medicine.

Statement of Significance

Tissue engineering approaches have been increasingly considered for the repair of non-union fractions, craniofacial reconstruction or large bone defect replacements. The design of complex biomaterials and successful engineering of 3-dimensional tissue constructs is of paramount importance to meet this clinical need. Conductive scaffolds, based on conjugated polymers, present interesting candidates to address the piezoelectric properties of bone tissue and to induce enhanced osteogenesis upon implantation. However, conductive scaffolds have not been investigated in vitro in great measure. To this end, we have developed a highly porous, electrically conductive scaffold based on PEDOT:PSS, and provide evidence that this purely synthetic material is a promising candidate for bone tissue engineering.

Design and evaluation of antibiotic releasing self- assembled scaffolds at room temperature using biodegradable polymer particles

Biodegradable polymer-based drug-eluting implants offer many advantages such as predictable drug release kinetics, safety, and acceptable drug loading under ambient conditions. Herein, we describe fabrication and evaluation of antibiotic loaded scaffolds for localized delivery and tissue engineering applications. PDLLA particles entrapping gentamycin were formulated using solvent evaporation method and used for scaffold fabrication. Optimization of formulation parameters such as pH of the internal aqueous phase and combination of excipients like glycerol, polyvinyl alcohol (PVA) resulted in high entrapment efficiencies up to 96% of gentamicin in particles with drug load of 16-18μg/mg of polymer particles. These microparticles were fused in presence of methanol at ambient temperatures to form scaffolds of different geometry having reasonable mechanical strength. Porosity of these scaffolds was found to be more than 80%. Antibiotic released from the scaffolds was found to be bioactive as tested against Staphylococcus aureus and the release pattern was biphasic over a period of one week. The scaffolds were found to be non-toxic to murine fibroblasts cultures in vitro as well as to mice upon subcutaneous implantation. This method provides a novel and easy way of fabricating antibiotic loaded polymer scaffolds for varieties of applications.

Collagen-grafted porous HDPE/PEAA scaffolds for bone reconstruction

After tumor resection, bone reconstruction such as skull base reconstruction using interconnected porous structure is absolutely necessary. In this study, porous scaffolds for bone reconstruction were prepared using heat-pressing and salt-leaching methods. High-density polyethylene (HDPE) and poly(ethylene-co-acrylic acid) (PEAA) were chosen as the polymer composites for producing a porous scaffold of high mechanical strength and having high reactivity with biomaterials such as collagen, respectively. The porous structure was observed through surface images, and its intrusion volume and porosity were measured. Owing to the carboxylic acids on PEAA, collagen was successfully grafted onto the porous HDPE/PEAA scaffold, which was confirmed by FT-IR spectroscopy and electron spectroscopy for chemical analysis. Osteoblasts were cultured on the collagen-grafted porous scaffold, and their adhesion, proliferation, and differentiation were investigated. The high viability and growth of the osteoblasts suggest that the collagen-grafted porous HDPE/PEAA is a promising scaffold material for bone generation.

Multilayered Graphene Hydrogel Membranes for Guided Bone Regeneration

A multilayered graphene hydrogel (MGH) membrane is used as an excellent barrier membrane for guided bone regeneration. The unique multilayered nanostructure of the MGH membrane results in improved material properties, which benefits protein adsorption, cell adhesion, and apatite deposition, and allows higher quality and fast bone regeneration.

Functional biomedical hydrogels for in vivo imaging

In vivo imaging of biomedical hydrogels enables real-time and non-invasive visualization of the status of structure and function of hydrogels.

Influence of hydroxyapatite granule size, porosity, and crystallinity on tissue reaction in vivo. Part A: synthesis, characterization of the materials, and SEM analysis

OBJECTIVE

The aim of this study was the synthesis and analysis of the tissue reaction to three different Hydroxyapatite (HA)-based bone substitute materials differing only in granule size, porosity, and crystallinity through an animal experimental model at 60 days.

MATERIALS AND METHODS

Three different HA-based biomaterials were synthesized and characterized by X-ray diffraction, SEM, and EDS analysis, the resultant product was ground in three particle sizes: Group I (2000-4000 μm), Group II (1000-2000 μm), and Group III (600-1000 μm). Critical size defects were created in both tibias of 15 rabbits. Four defects per rabbit for a total of 60 defects were grafted with the synthesized materials as follows: Group I (15 defects), Group II (15 defects), Group III (15 defects), and empty (15 defects control). After animals sacrifice at 60 days samples were obtained and processed for SEM and EDS evaluation of Ca/P ratios, elemental mapping was performed to determine the chemical degradation process and changes to medullary composition in all the four study groups.

RESULTS

The tendency for the density was to increase with the increasing annealing temperature; in this way it was possible to observe that the sample that shows highest crystallinity and crystal size corresponding to that of group I. The SEM morphological examination showed that group III implant showed numerous resorption regions, group II implant presented an average resorption rate of all the implants. The group I displayed smoother surface features, in comparison with the other two implants.

CONCLUSION

The data from this study show that changing the size, porosity, and crystallinity of one HA-based bone substitute material can influence the integration of the biomaterials within the implantation site and the new bone formation.

Poly(L-Lactide)/Poly(ε-Caprolactone) and Collagen/β-Tricalcium Phosphate Scaffolds for the Treatment of Critical-Sized Rat Alveolar Defects: A Microtomographic, Molecular-Biological, and Histological Study

OBJECTIVE

To determine the efficacy of a newly developed scaffold (col/β-TCP) in a preclinical rat model as compared with the gold standard treatment (autograft) and control scaffolds (PLLA/PCL).

DESIGN

Fifty-six Sprague-Dawley rats were randomized into four experimental groups, and critical-sized alveolar defects (7 × 4 × 3 mm) were created in each animal. Group A was the blank defect group, group B received autograft, group C received col/β-TCP scaffolds, and group D received PLLA/PCL blend scaffolds to fill the bone defects. New bone formation was assessed radiomorphometrically, histomorphometrically, and molecular-biologically at 1 and 4 months following surgery.

RESULTS

Radiomorphometrically, the best new bone volume rate at 1 month (43.7%) and 4 months (45.4%) was observed in the autograft group, and the difference was significantly higher than in the other three groups (P < .005, P < .001, P < .001 for 1 month and P = .004, P < .001, P < .001 for 4 months). Even though the new bone volume rate in the col/β-TCP group (21.5%) was higher than that of the PLLA/PCL group (18.2%), the difference was not significant (P = .08). Molecular-genetic analysis revealed significantly higher BSP and ALP gene expression levels in the autograft and col/β-TCP groups than in the blank defect group (P = .002 and P = .004).

CONCLUSION

The engineered tissue scaffolds described herein have great potential as an alternative treatment option when cost, donor region morbidity, and duration of hospitalization are considered.

Distinctive Capillary Action by Micro-channels in Bone-like Templates can Enhance Recruitment of Cells for Restoration of Large Bony Defect

Without an active, thriving cell population that is well-distributed and stably anchored to the inserted template, exceptional bone regeneration does not occur. With conventional templates, the absence of internal micro-channels results in the lack of cell infiltration, distribution, and inhabitance deep inside the templates. Hence, a highly porous and uniformly interconnected trabecular-bone-like template with micro-channels (biogenic microenvironment template; BMT) has been developed to address these obstacles. The novel BMT was created by innovative concepts (capillary action) and fabricated with a sponge-template coating technique. The BMT consists of several structural components: inter-connected primary-pores (300-400 µm) that mimic pores in trabecular bone, micro-channels (25-70 µm) within each trabecula, and nanopores (100-400 nm) on the surface to allow cells to anchor. Moreover, the BMT has been documented by mechanical test study to have similar mechanical strength properties to those of human trabecular bone (~3.8 MPa)¹².

The BMT exhibited high absorption, retention, and habitation of cells throughout the bridge-shaped (Π) templates (3 cm height and 4 cm length). The cells that were initially seeded into one end of the templates immediately mobilized to the other end (10 cm distance) by capillary action of the BMT on the cell media. After 4 hr, the cells homogenously occupied the entire BMT and exhibited normal cellular behavior. The capillary action accounted for the infiltration of the cells suspended in the media and the distribution (active migration) throughout the BMT. Having observed these capabilities of the BMT, we project that BMTs will absorb bone marrow cells, growth factors, and nutrients from the periphery under physiological conditions.

The BMT may resolve current limitations via rapid infiltration, homogenous distribution and inhabitance of cells in large, volumetric templates to repair massive skeletal defects.

Biomimetic approaches in bone tissue engineering: Integrating biological and physicomechanical strategies

The development of responsive biomaterials capable of demonstrating modulated function in response to dynamic physiological and mechanical changes in vivo remains an important challenge in bone tissue engineering. To achieve long-term repair and good clinical outcomes, biologically responsive approaches that focus on repair and reconstitution of tissue structure and function through drug release, receptor recognition, environmental responsiveness and tuned biodegradability are required. Traditional orthopedic materials lack biomimicry, and mismatches in tissue morphology, or chemical and mechanical properties ultimately accelerate device failure. Multiple stimuli have been proposed as principal contributors or mediators of cell activity and bone tissue formation, including physical (substrate topography, stiffness, shear stress and electrical forces) and biochemical factors (growth factors, genes or proteins). However, optimal solutions to bone regeneration remain elusive. This review will focus on biological and physicomechanical considerations currently being explored in bone tissue engineering.

Influence of hydroxyapatite on thermoplastic foaming performance of water-plasticized poly(vinyl alcohol)

Water states in the system are adjusted by changing HA content to obtain proper PVA/HA composite foams through thermoplastic processing.

Viscoelasticity of repaired sciatic nerve by poly(lactic-co-glycolic acid) tubes

Medical-grade synthetic poly(lactic-co-glycolic acid) polymer can be used as a biomaterial for nerve repair because of its good biocompatibility, biodegradability and adjustable degradation rate. The stress relaxation and creep properties of peripheral nerve can be greatly improved by repair with poly(lactic-co-glycolic acid) tubes. Ten sciatic nerve specimens were harvested from fresh corpses within 24 hours of death, and were prepared into sciatic nerve injury models by creating a 10 mm defect in each specimen. Defects were repaired by anastomosis with nerve autografts and poly(lactic-co-glycolic acid) tubes. Stress relaxation and creep testing showed that at 7 200 seconds, the sciatic nerve anastomosed by poly(lactic-co-glycolic acid) tubes exhibited a greater decrease in stress and increase in strain than those anastomosed by nerve autografts. These findings suggest that poly(lactic-co-glycolic acid) exhibits good viscoelasticity to meet the biomechanical require-ments for a biomaterial used to repair sciatic nerve injury.

Oxygen-tension controlled matrices for enhanced osteogenic cell survival and performance

The success of a clinically-applicable bone tissue engineering construct for large area bone defects depends on its ability to allow for homogeneous bone regeneration throughout the construct. Insufficient vascularization, and consequently inadequate oxygen tension, throughout constructs has been largely cited as the most significant obstacle facing successful bone regeneration in large area defects. The development of constructs that support bone and vessel-forming cell growth and function throughout the scaffold structure are desired for large-area bone defect repair. Here, we developed oxygen tension-controlled matrices that support more homogenous oxygen levels throughout the constructs. Specifically, we examined polylactic co-glycolic acid (PLGA) scaffolds with optimized pore distribution and the percent pore volumes, and demonstrated significantly decreased oxygen and pH gradient from the exterior of the construct to the interior after long-term cell culture in vitro. We confirmed the ability of these optimized constructs to support the cellular survival via live/dead assay. In addition, we examined their ability to support the maintenance of two clinically relevant progenitor cell populations for bone tissue engineering and vascularization, namely mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs), and confirmed the expression of key bone and vascular markers via immunofluorescence.

Subcritical CO2 sintering of microspheres of different polymeric materials to fabricate scaffolds for tissue engineering

The aim of this study was to use CO2 at sub-critical pressures as a tool to sinter 3D, macroporous, microsphere-based scaffolds for bone and cartilage tissue engineering. Porous scaffolds composed of ~200 μm microspheres of either poly(lactic-co-glycolic acid) (PLGA) or polycaprolactone (PCL) were prepared using dense phase CO2 sintering, which were seeded with rat bone marrow mesenchymal stromal cells (rBMSCs), and exposed to either osteogenic (PLGA, PCL) or chondrogenic (PLGA) conditions for 6 weeks. Under osteogenic conditions, the PLGA constructs produced over an order of magnitude more calcium than the PCL constructs, whereas the PCL constructs had far superior mechanical and structural integrity (125 times stiffer than PLGA constructs) at week 6, along with twice the cell content of the PLGA constructs. Chondrogenic cell performance was limited in PLGA constructs, perhaps as a result of the polymer degradation rate being too high. The current study represents the first long-term culture of CO2-sintered microsphere-based scaffolds, and has established important thermodynamic differences in sintering between the selected formulations of PLGA and PCL, with the former requiring adjustment of pressure only, and the latter requiring the adjustment of both pressure and temperature. Based on more straightforward sintering conditions and more favorable cell performance, PLGA may be the material of choice for microspheres in a CO2 sintering application, although a different PLGA formulation with the encapsulation of growth factors, extracellular matrix-derived nanoparticles, and/or buffers in the microspheres may be advantageous for achieving a more superior cell performance than observed here.

Hydroxyapatite scaffold pore architecture effects in large bone defects in vivo

To examine the effect of scaffold pore size on bone regeneration within hydroxyapatite scaffolds in large segmental defects, this study evaluated two porous interconnected architectures having similar porosity and strut thickness but different pore sizes. Using a 10 mm segmental rabbit radius defect model, a bilayer scaffold architecture mimicking the cortical-cancellous organization of bone (pore size 200 µm outer layer, 450 µm inner layer) was compared to a purely trabecular-like architecture (pore size 340 µm) and an untreated defect. Bone regeneration was measured using micro-computed tomography and histology after four and eight weeks of in vivo implantation, and the mechanical strength of the defect site after eight weeks' implantation was assessed using flexural testing. Although both bilayer and trabecular architectures promoted bone growth, the trabecular scaffolds were observed to have more uniform new bone distribution within the scaffold interior at four weeks and greater bone regeneration overall after eight weeks' implantation (149 ± 9 mm³ compared to 121 ± 8 mm³ in the bilayer and 66 ± 14 mm³ in the defect). Additionally, the trabecular scaffolds were observed to exhibit significantly greater flexural strength (124% increase) and toughness (388% increase) when compared to the empty defects after eight weeks' implantation. It was concluded from this study that a larger uniform pore size led to greater functional bone regeneration over a longer implantation period for large segmental defects.

Percutaneous gene therapy heals cranial defects

Nonhealing bone defects are difficult to treat. As the bone morphogenic protein and transforming growth factor beta pathways have been implicated in bone healing, we hypothesized that percutaneous Smad7 silencing would enhance signaling through both pathways and improve bone formation. Critical sized parietal trephine defects were created and animals received percutaneous injection of: agarose alone or agarose containing nonsense or Smad7 small interfering RNA (siRNA). At 12 weeks, SMADs1, 2, 3, 5, 7 and 8 levels were assessed. Smad1/5/8 osteogenic target, Dlx5, and SMAD2/3 angiogenic target, plasminogen activator inhibitor-1 (Pai1), transcription levels were measured. Noncanonical signaling through TGFβ activated kinase-1 (Tak1) and target, runt-related transcription factor 2 (Runx2) and collagen1α1 (Col1α1), transcription were also measured. Micro-computed tomography and Gomori trichome staining were used to assess healing. Percutaneous injection of Smad7 siRNA significantly knocked down Smad7 mRNA (86.3 ± 2.5%) and protein levels (46.3 ± 3.1%). The SMAD7 knockdown resulted in a significant increase in receptor-regulated SMADs (R-SMAD) (Smad 1/5/8 and Smad2/3) nuclear translocation. R-SMAD nuclear translocation increased Dlx5 and Pai1 transcription. Additionally, noncanonical signaling through Tak1 increased Runx2 and Col1α1 target transcription. Compared with animals treated with agarose alone (33.9 ± 2.8% healing) and nonsense siRNA (31.5 ± 11.8% healing), animals treated Smad7 siRNA had significantly great (91.2 ± 3.8%) healing. Percutaneous Smad7 silencing increases signal transduction through canonical and noncanonical pathways resulting in significant bone formation. Minimally invasive gene therapies may prove effective in the treatment of nonhealing bone defects.

Tailoring of processing parameters for sintering microsphere-based scaffolds with dense-phase carbon dioxide

Microsphere-based polymeric tissue-engineered scaffolds offer the advantage of shape-specific constructs with excellent spatiotemporal control and interconnected porous structures. The use of these highly versatile scaffolds requires a method to sinter the discrete microspheres together into a cohesive network, typically with the use of heat or organic solvents. We previously introduced subcritical CO(2) as a sintering method for microsphere-based scaffolds; here we further explored the effect of processing parameters. Gaseous or subcritical CO(2) was used for making the scaffolds, and various pressures, ratios of lactic acid to glycolic acid in poly(lactic acid-co-glycolic acid), and amounts of NaCl particles were explored. By changing these parameters, scaffolds with different mechanical properties and morphologies were prepared. The preferred range of applied subcritical CO(2) was 15-25 bar. Scaffolds prepared at 25 bar with lower lactic acid ratios and without NaCl particles had a higher stiffness, while the constructs made at 15 bar, lower glycolic acid content, and with salt granules had lower elastic moduli. Human umbilical cord mesenchymal stromal cells (hUCMSCs) seeded on the scaffolds demonstrated that cells penetrate the scaffolds and remain viable. Overall, the study demonstrated the dependence of the optimal CO(2) sintering parameters on the polymer and conditions, and identified desirable CO(2) processing parameters to employ in the sintering of microsphere-based scaffolds as a more benign alternative to heat-sintering or solvent-based sintering methods.

Fabrication of poly-DL-lactide/polyethylene glycol scaffolds using the gas foaming technique

The aim of this study was to prepare poly-DL-lactide/polyethylene glycol (PDLLA/PEG) blends to improve medium absorption and cell proliferation in the three-dimensional (3-D) structure of their scaffolds. Carbon dioxide (CO2) was used as a foaming agent to create porosity in these blends. The results of Fourier transform infrared (FTIR) spectroscopy demonstrated that the blends were homogeneous mixtures of PDLLA and PEG. The peak shifts at 1092 and 1744 cm(-1) confirmed the presence of molecular interactions between these two compounds. Increasing the PEG weight ratio enhanced the relative crystallinity and hydrophilicity. The PDLLA/PEG blends (especially 80/20 and 70/30 weight ratios) exhibited linear degradation profiles over an incubation time of 8 weeks. The mechanical properties of PDLLA/PEG blends having less than 30 wt.% PEG were suitable for the fabrication of porous scaffolds. Increasing the concentration of PEG to above 50% resulted in blends that were brittle and had low mechanical integrity. Highly porous scaffolds with controllable pore size were produced for 30 wt.% PEG samples using the gas foaming technique at temperatures between 25 and 55 °C and pressures between 60 and 160 bar. The average pore diameters achieved by gas foaming process were between 15 and 150 μm, and had an average porosity of 84%. The medium uptake and degradation rate of fabricated PDLLA/PEG scaffolds were increased compared with neat PDLLA film due to the presence of PEG and porosity. The porous scaffolds also demonstrated a lower modulus of elasticity and a higher elongation at break compared to the non-porous film. The fabricated PDLLA/PEG scaffolds have high potential for various tissue-engineering applications.

Dura mater stimulates human adipose-derived stromal cells to undergo bone formation in mouse calvarial defects

Human adipose-derived stromal cells (hASCs) have a proven capacity to aid in osseous repair of calvarial defects. However, the bone defect microenvironment necessary for osseous healing is not fully understood. In this study, we postulated that the cell-cell interaction between engrafted ASCs and host dura mater (DM) cells is critical for the healing of calvarial defects. hASCs were engrafted into critical sized calvarial mouse defects. The DM-hASC interaction was manipulated surgically by DM removal or by insertion of a semipermeable or nonpermeable membrane between DM and hASCs. Radiographic, histologic, and gene expression analyses were performed. Next, the hASC-DM interaction is assessed by conditioned media (CM) and coculture assays. Finally, bone morphogenetic protein (BMP) signaling from DM was investigated in vivo using novel BMP-2 and anti-BMP-2/4 slow releasing scaffolds. With intact DM, osseous healing occurs both from host DM and engrafted hASCs. Interference with the DM-hASC interaction dramatically reduced calvarial healing with abrogated BMP-2-Smad-1/5 signaling. Using CM and coculture assays, mouse DM cells stimulated hASC osteogenesis via BMP signaling. Through in vivo manipulation of the BMP-2 pathway, we found that BMP-2 plays an important role in DM stimulation of hASC osteogenesis in the context of calvarial bone healing. BMP-2 supplementation to a defect with disrupted DM allowed for bone formation in a nonhealing defect. DM is an osteogenic cell type that both participates in and stimulates osseous healing in a hASC-engrafted calvarial defect. Furthermore, DM-derived BMP-2 paracrine stimulation appears to play a key role for hASC mediated repair.

Biodegradable composite scaffolds incorporating an intramedullary rod and delivering bone morphogenetic protein-2 for stabilization and bone regeneration in segmental long bone defects

In this study, a two-part bone tissue engineering scaffold was investigated. The scaffold consists of a solid poly(propylene fumarate) (PPF) intramedullary rod for mechanical support surrounded by a porous PPF sleeve for osseointegration and delivery of poly(dl-lactic-co-glycolic acid) (PLGA) microspheres with adsorbed recombinant human bone morphogenetic protein-2 (rhBMP-2). Scaffolds were implanted into critical size rat segmental femoral defects with internal fixation for 12 weeks. Bone formation was assessed throughout the study via radiography, and following euthanasia, via microcomputed tomography and histology. Mechanical stabilization was evaluated further via torsional testing. Experimental implant groups included the PPF rod alone and the rod with a porous PPF sleeve containing PLGA microspheres with 0, 2 or 8 μg of rhBMP-2 adsorbed onto their surface. Results showed that presence of the scaffold increased mechanical stabilization of the defect, as evidenced by the increased torsional stiffness of the femurs by the presence of a rod compared to the empty defect. Although the presence of a rod decreased bone formation, the presence of a sleeve combined with a low or high dose of rhBMP-2 increased the torsional stiffness to 2.06 ± 0.63 and 1.68 ± 0.56 N·mm, respectively, from 0.56 ± 0.24 N·mm for the rod alone. The results indicate that, while scaffolds may provide structural support to regenerating tissues and increase their mechanical properties, the presence of scaffolds within defects may hinder overall bone formation if they interfere with cellular processes.

BMP-2 gene-fibronectin-apatite composite layer enhances bone formation

Background

Safe and efficient gene transfer systems are needed for tissue engineering. We have developed an apatite composite layer including the bone morphogenetic protein-2 (BMP-2) gene and fibronectin (FB), and we evaluated its ability to induce bone formation.

Methods

An apatite composite layer was evaluated to determine the efficiency of gene transfer to cells cultured on it. Cells were cultured on a composite layer including the BMP-2 gene and FB, and BMP-2 gene expression, BMP-2 protein concentrations, alkaline phosphatase (ALP) activity, and osteocalcin (OC) concentrations were measured. A bone defect on the cranium of rats was treated with hydroxyapatite (HAP)-coated ceramic buttons with the apatite composite layer including the BMP-2 gene and FB (HAP-BMP-FB). The tissue concentration of BMP-2, bone formation, and the expression levels of the BMP-2, ALP, and OC genes were all quantified.

Results

The apatite composite layer provided more efficient gene transfer for the cultured cells than an apatite composite layer without FB. The BMP-2 concentration was approximately 100~600 pg/mL in the cell-culture medium. Culturing the cells on the apatite composite layer for 27 days increased ALP activity and OC concentrations. In animal experiments, the tissue concentrations of BMP-2 were over 100 pg/mg in the HAP-BMP-FB group and approximately 50 pg/mg in the control groups. Eight weeks later, bone formation was more enhanced in the HAP-BMP-FB group than in the control groups. In the tissues surrounding the HAP button, the gene expression levels of ALP and OC increased.

Conclusion

The BMP-2 gene-FB-apatite composite layer might be useful for bone engineering.