A comparative study of bone bioactivity and osteogenic potential of different bioceramics in methacrylated collagen hydrogels

Decoupling the Effects of Collagen Alignment and Bioceramic Incorporation on Osteoblast Proliferation, Differentiation, and Mineralization

Biomimetic scaffolds provide the essential biophysical (e.g., surface topography, stiffness) and biochemical cues (e.g., composition) to guide cell morphology, proliferation, and differentiation. Although the effects of biomaterial-directed cues on cell response have been widely reported, few studies have sought to decouple these effects to better understand the interplay between the different physicochemical factors on tissue-specific cell function. Herein, beta-tricalcium phosphate (β-TCP) was incorporated into electrochemically aligned collagen (ELAC) and random collagen threads, and the individual and interactive effects of collagen alignment (i.e., biophysical) and bioceramic incorporation (i.e., biochemical) on osteoblast cell morphology, proliferation, differentiation, and mineralization were investigated. Results showed that collagen alignment in ELAC threads was retained upon β-TCP incorporation. Collagen alignment significantly improved (p < 0.05) the swelling capacity and stability of collagen threads, while β-TCP incorporation showed no such effects. Tensile tests revealed that β-TCP incorporation significantly decreased (p < 0.05) the strength and stiffness of ELAC threads. Significant increase (p < 0.05) in Saos-2 cell orientation and alkaline phosphatase (ALP) activity was observed on ELAC compared to random collagen threads indicating that aligned collagen serves as a key driving factor for osteogenesis. β-TCP incorporation into random collagen threads had no effect on Saos-2 cell function. On the other hand, presence of β-TCP significantly augmented (p < 0.05) Saos-2 cell metabolic activity, differentiation, and mineralization on ELAC threads. Together, these findings suggest that combining collagen alignment and β-TCP incorporation can create robust tissue-mimicking scaffolds for bone regeneration applications.

Structure, rheological properties, and biocompatibility of Laponite® cross-linked starch/polyvinyl alcohol hydrogels

Hydrogels, owing to their unique porous structures, hydrophilic properties, and biocompatibility, are being developed as scaffolds for bone grafts. However, the use of toxic initiators or cross-linking agents is a drawback. To overcome this, we developed Laponite®/cross-linked starch/polyvinyl alcohol (PVA) hydrogels prepared by one-step solution mixing. The structure, rheological properties, and biocompatibility of the hydrogels were investigated. Zeta potential, Fourier transform infrared, and X-ray diffraction analyses showed that hydrogen bonding and electrostatic interactions jointly maintained the structure of the cross-linked hydrogel systems. At a Laponite® concentration of 10 %, the hydrogel with a starch/PVA ratio of 2:2 exhibited a uniform porous structure, the highest storage modulus (G'), and the lowest degradation rate. At a starch/PVA ratio of 2:2, the G' increased; however, the degradation rate decreased with the increase in Laponite® content from 5 % to 20 %. These results indicate that the mechanical strength and degradation rate of the hydrogels could be adjusted by altering the starch/PVA ratio and the amount of Laponite®. In vitro cytotoxicity experiments showed that the Laponite®/starch/PVA (LSP) hydrogels were non-toxic to MC3T3-E1 cells. The starch/PVA ratio had no obvious effect on the proliferation of MC3T3-E1 cells, but an increase in Laponite® content significantly promoted cell proliferation. In summary, the results suggest that these LSP hydrogels have great potential for applications in bone tissue engineering.

Photobiomodulation effects of blue light on osteogenesis are induced by reactive oxygen species

Blue light-mediated photobiomodulation (PBM) is a promising approach to promote osteogenesis. However, the underlying mechanisms of PBM in osteogenesis are poorly understood. In this study, a human osteosarcoma cell line (i.e., Saos-2 cells) was subjected to intermittent blue light exposure (2500 µM/m2/s, 70 mW/cm2, 4.2 J/cm2, once every 48 h) and the effects on Saos-2 cell viability, metabolic activity, differentiation, and mineralization were investigated. In addition, this study addressed a possible role of blue light induced cellular oxidative stress as a mechanism for enhanced osteoblast differentiation and mineralization. Results showed that Saos-2 cell viability and metabolic activity were maintained upon blue light exposure compared to unilluminated controls, indicating no negative effects. To the contrary, blue light exposure significantly increased (p < 0.05) alkaline phosphatase activity and Saos-2 cell mediated mineralization. High-performance liquid chromatography (HPLC) assay was used for measurement of reactive oxygen species (ROS) activity and showed a significant increase (p < 0.05) in superoxide (O2•-) and hydrogen peroxide (H2O2) formed after blue light exposure. Together, these results suggest that the beneficial effects of blue light-mediated PBM on osteogenesis may be induced by controlled release of ROS.

Collagen and Beyond: A Comprehensive Comparison of Human ECM Properties Derived from Various Tissue Sources for Regenerative Medicine Applications

Collagen, along with proteoglycans, glycosaminoglycans, glycoproteins, and various growth factors, forms the extracellular matrix (ECM) and contributes to the complexity and diversity of different tissues. Herein, we compared the physicochemical and biological properties of ECM hydrogels derived from four different human tissues: skin, bone, fat, and birth. Pure human collagen type I hydrogels were used as control. Physical characterization of ECM hydrogels and assessment of cell response of cord-tissue mesenchymal stem cells (CMSCs) were performed. Decellularization efficiency was found to be >90% for all ECM. Hydroxyproline quantification assay showed that collagen content in birth ECM was comparable to collagen control and significantly greater than other sources of ECM. Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed the presence of γ, β, α₁ and α₂ collagen chains in all ECMs. Gelation kinetics of ECM hydrogels was significantly slower than collagen control. Compressive modulus of skin ECM was the highest and birth ECM was the lowest. Skin and birth ECM hydrogels were more stable than bone and fat ECM hydrogels. CMSCs encapsulated in birth ECM hydrogels exhibited the highest metabolic activity. Rheological characterization revealed that all ECM-derived inks exhibited shear thinning properties, and skin-derived ECM inks were most suitable for extrusion-based bioprinting for the concentration and printing conditions used in this study. Overall, results demonstrate that the physicochemical and biological properties of ECM hydrogels vary significantly depending on the tissue source. Therefore, careful selection of tissue source is important for development of ECM-based biomimetic tissue constructs for regenerative medicine applications.

Effectiveness of biomechanically stable pergola-like additively manufactured scaffold for extraskeletal vertical bone augmentation

Objective: Extraskeletal vertical bone augmentation in oral implant surgery requires extraosseous regeneration beyond the anatomical contour of the alveolar bone. It is necessary to find a better technical/clinical solution to solve the dilemma of vertical bone augmentation. 3D-printed scaffolds are all oriented to general bone defect repair, but special bone augmentation design still needs improvement.

Methods: This study aimed to develop a structural pergola-like scaffold to be loaded with stem cells from the apical papilla (SCAPs), bone morphogenetic protein 9 (BMP9) and vascular endothelial growth factor (VEGF) to verify its bone augmentation ability even under insufficient blood flow supply. Scaffold biomechanical and fluid flow optimization design by finite element analysis (FEA) and computational fluid dynamics (CFD) was performed on pergola-like additive-manufactured scaffolds with various porosity and pore size distributions. The scaffold geometrical configuration showing better biomechanical and fluid dynamics properties was chosen to co-culture for 2 months in subcutaneously into nude mice, with different SCAPs, BMP9, and (or) VEGF combinations. Finally, the samples were removed for Micro-CT and histological analysis.

Results: Micro-CT and histological analysis of the explanted scaffolds showed new bone formation in the “Scaffold + SCAPs + BMP9” and the “Scaffold + SCAPs + BMP9 + VEGF” groups where the VEGF addition did not significantly improve osteogenesis. No new bone formation was observed either for the “Blank Scaffold” and the “Scaffold + SCAPs + GFP” group. The results of this study indicate that BMP9 can effectively promote the osteogenic differentiation of SCAPs.

Conclusion: The pergola-like scaffold can be used as an effective carrier and support device for new bone regeneration and mineralization in bone tissue engineering, and can play a crucial role in obtaining considerable vertical bone augmentation even under poor blood supply.