No abstract

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

No abstract

In this work, a new family of multiphasic materials composed of the same amount of silica gel and variable amount of three calcium phosphates with very different solubilities, monetite > amorphous calcium phosphate > hydroxyapatite (HAp), was studied. Silicon was added to calcium phosphate to increase bioactivity and osteinductivity. The influence of the HAp/monetite ratio on the material resorption and bone regeneration was investigated in critical bone defects in sheep and was related to their chemical and physical properties. It was concluded that a minimum rate of HAp/monetite is necessary to achieve an appropriate compromise between material resorption and bone regeneration. Above this minimum rate, bone regeneration and material resorbtion did not change significantly. Physical properties such as particle size, specific surface area, porosity, and granulate cohesion played a more critical role on material resorption than the solubility of their components. A huge difference between in vitro solubility and in vivo resorption was observed. It was related to the fastest cellular-mediated resorption of monetite compared to the other components. Computerized axial tomography, histology, histomorphometric, and multiple fluorochrome labeling studies showed a very advanced bone regeneration of the defects when materials with the highest HAp/monetite rate were implanted. It was also demonstrated that all materials induce bone formation and vascularization.

In craniofacial tissue regeneration, the current gold standard treatment is autologous bone grafting, however, it presents some disadvantages. Although new alternatives have emerged there is still an urgent demand of biodegradable scaffolds to act as extracellular matrix in the regeneration process. A potentially useful element in bone regeneration is strontium. It is known to promote stimulation of osteoblasts while inhibiting osteoclasts resorption, leading to neoformed bone. The present paper reports the preparation and characterization of strontium (Sr) containing hybrid scaffolds formed by a matrix of ionically cross-linked chitosan and microparticles of poly(ε-caprolactone) (PCL). These scaffolds of relatively facile fabrication were seeded with osteoblast-like cells (MG-63) and human bone marrow mesenchymal stem cells (hBMSCs) for application in craniofacial tissue regeneration. Membrane scaffolds were prepared using chitosan:PCL ratios of 1:2 and 1:1 and 5 wt % Sr salts. Characterization was performed addressing physico-chemical properties, swelling behavior, in vitro biological performance and in vivo biocompatibility. Overall, the composition, microstructure and swelling degree (≈245%) of scaffolds combine with the adequate dimensional stability, lack of toxicity, osteogenic activity in MG-63 cells and hBMSCs, along with the in vivo biocompatibility in rats allow considering this system as a promising biomaterial for the treatment of craniofacial tissue regeneration.

Regenerative therapies based on tissue engineering are becoming the most promising alternative for the treatment of osteoarthritis and rheumatoid arthritis. However, regeneration of full-thickness articular osteochondral defects that reproduces the complexity of native cartilage and osteochondral interface still remains challenging. Hence, in this work, we present the fabrication, physic-chemical characterization, and in vitro and in vivo evaluation of biomimetic hierarchical scaffolds that mimic both the spatial organization and composition of cartilage and the osteochondral interface. The scaffold is composed of a composite porous support obtained by cryopolymerization of poly(ethylene glycol) dimethacrylate (PEGDMA) in the presence of biodegradable poly(D,L-lactide-co-glycolide) (PLGA), bioactive tricalcium phosphate β-TCP and the bone promoting strontium folate (SrFO), with a gradient biomimetic photo-polymerized methacrylated hyaluronic acid (HAMA) based hydrogel containing the bioactive zinc folic acid derivative (ZnFO). Microscopical analysis of hierarchical scaffolds showed an open interconnected porous open microstructure and the in vitro behaviour results indicated high swelling capacity with a sustained degradation rate. In vitro release studies during 3 weeks indicated the sustained leaching of bioactive compounds, i.e., Sr2+, Zn2+ and folic acid, within a biologically active range without negative effects on human osteoblast cells (hOBs) and human articular cartilage cells (hACs) cultures. In vitro co-cultures of hOBs and hACs revealed guided cell colonization and proliferation according to the matrix microstructure and composition. In vivo rabbit-condyle experiments in a critical-sized defect model showed the ability of the biomimetic scaffold to promote the regeneration of cartilage-like tissue over the scaffold and neoformation of osteochondral tissue.

The purpose of the current study was to investigate whether the cryopolymerization technique is capable of producing suitable scaffolds for bone tissue engineering. Cryopolymers made of 2-hydroxyethyl methacrylate and acrylic acid with (W1 and W20) and without (W0) wollastonite particles were prepared. The elastic modulus of the specimens rose one order of magnitude from W1 to W20. Total porosity reached 56% for W0, 72% for W1 and 36% for W20, with pore sizes of up to 2 mm, large interconnection sizes of up to 1 mm and small interconnection sizes of 50-80 µm on dry specimens. Cryogels swell up to 224 ± 17% for W0, 315 ± 18% for W1 and 231 ± 27% for W20 specimens, while maintaining the integrity of the bodies. Pore sizes > 5 mm can be observed for swollen specimens. The biocompatibility of the samples was tested using human mesenchymal stem cells isolated from bone marrow and adipose tissues. Both types of cells attached and grew on the three tested substrates, colonized their inner regions and organized an extracellular cell matrix. Fibronectin and osteopontin levels decreased in the media from cells cultured on W20 samples, likely due to increased binding on the ECM deposited by cells. The osteoprotegerin-to-receptor activator of nuclear factor-κB ligand secretion ratios increased with increasing wollastonite content. Altogether, these results indicate that an appropriate balance of surface properties and structure that favours stromal cell colonization in the porous cryogels can be achieved by modulating the amount of wollastonite.

Significant research efforts have been undertaken during the last decades to treat musculoskeletal disorders and improve patient's mobility and quality of life. The goal is the return of function as quickly and completely as possible. Cellular therapy has been increasingly employed in this setting. The design of this study was focused on cell-based alternatives. The present study aimed at investigating the bone regeneration capacity of xenogeneic human bone marrow-derived mesenchymal stromal cell (hMSC) implantation with tricalcium phosphate (TCP) granules in an immunocompetent rabbit model of critical-size bone defects at the femoral condyles. Two experimental groups, TCP and hMSC + TCP, were compared. Combination of TCP and hMSC did not affect cell viability or osteogenic differentiation. We also observed significantly higher bone regeneration in vivo in the hMSC + TCP group, which also displayed better TCP osteointegration. Also, evidence of hMSC contribution to a better TCP osteointegration was noticed. Finally, no inflammatory reaction was detected, besides the xenotransplantation of human cells into an immunocompetent recipient. In summary, hMSC combined with TCP granules is a potential combination for bone regeneration purposes that provides better preclinical results compared to TCP alone.