Irgacure 2959 (I2959) is widely used as a photoinitiator for photochemical crosslinking of hydrogels. However, the free radicals generated from I2959 have been reported to be highly cytotoxic. In this study, methacrylated collagen (CMA) hydrogels were photochemically crosslinked using two different photoinitiators (i.e., I2959 and VA086) and the effect of photoinitiator type, photoinitiator concentration (i.e., 0.02 and 0.1%) and crosslinking time (1 and 10 min) on gel morphology, compressive modulus, and stability were investigated. In addition, Saos‐2 cells were encapsulated within the hydrogels and the effect of photochemical crosslinking conditions on cell viability, metabolic activity, and osteoblast functionality was assessed. Scanning electron microscopy imaging showed that photochemical crosslinking decreased the porosity of the hydrogels resulting in decrease in water retention ability compared to uncrosslinked hydrogels. On the other hand, photochemical crosslinking improved the stability of CMA hydrogels (p < 0.05). Uniaxial compression tests showed that increasing the photoinitiator concentration significantly improved the compressive modulus of CMA hydrogels (p < 0.05). Results from the live–dead assay showed that VA086 crosslinked hydrogels exhibited higher cell viability compared to I2959 (p < 0.05) crosslinked hydrogels indicating that VA086 is more cytocompatible compared to I2959. Furthermore, Alizarin Red S staining revealed a significantly more pronounced cell‐mediated mineralization on VA086 crosslinked hydrogels (p < 0.05) indicating that Saos‐2 cells retain their normal functionality in the presence of VA086. In summary, these results indicate that VA086 is a more biocompatible photoinitiator compared to I2959 for the generation of photochemically crosslinked CMA hydrogels for tissue engineering applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

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Application of tissue-engineered vascular grafts (TEVGs) for the replacement of small-diameter arteries is limited due to thrombosis and intimal hyperplasia. Previous studies have attempted to address the limitations of TEVGs by developing scaffolds that mimic the composition (collagen and elastin) of native arteries to better match the mechanical properties of the graft with the native tissue. However, most existing scaffolds do not recapitulate the aligned topography of the collagen fibers found in native vessels. In the current study, based on the principles of isoelectric focusing, two different types of elastin (soluble and insoluble) were incorporated into highly oriented electrochemically aligned collagen (ELAC) fibers and the effect of elastin incorporation on the mechanical properties of the ELAC fibers and smooth muscle cell (SMC) phenotype was investigated. The results indicate that elastin incorporation significantly decreased the modulus of ELAC fibers to converge upon that of native vessels. Further, a significant increase in yield strain and decrease in Young's modulus was observed on all fibers post SMC culture compared with before the culture. Real-time polymerase chain reaction results showed a significant increase in the expression of α-smooth muscle actin and calponin on ELAC fibers with insoluble elastin, suggesting that incorporation of insoluble elastin induces a contractile phenotype in SMCs after two weeks of culture on ELAC fibers. Immunofluorescence results showed that calponin expression increased with time on all fibers. In conclusion, insoluble elastin incorporated ELAC fibers have the potential to be used for the development of functional TEVGs for the repair and replacement of small-diameter arteries.

Loss of vision due to corneal disease is a significant problem worldwide. Transplantation of donor corneas is a viable treatment option but limitations such as short supply and immune-related complications call for alternative options for the treatment of corneal disease. A tissue engineering-based approach using a collagen scaffold is a promising alternative to develop a bioengineered cornea that mimics the functionality of native cornea. In this study, an electrochemical compaction method was employed to synthesize highly dense and transparent collagen matrices. We hypothesized that chemical crosslinking of electrochemically compacted collagen (ECC) matrices will maintain transparency, improve stability, and enhance the mechanical properties of the matrices to the level of native cornea. Further, we hypothesized that keratocyte cell viability and proliferation will be maintained on crosslinked ECC matrices. The results indicated that uncrosslinked and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-N-hydroxysuccinimide (EDC-NHS) crosslinked ECC matrices were highly transparent with light transmission measurements comparable to native cornea. Stability tests showed that while the uncrosslinked ECC matrices degraded within 6 h when treated with collagenase, EDC-NHS or genipin crosslinking significantly improved the stability of ECC matrices (192 h for EDC-NHS and 256 h for genipin). Results from the mechanical tests showed that both EDC-NHS and genipin crosslinking significantly improved the strength and modulus of ECC matrices. Cell culture studies showed that keratocyte cell viability and proliferation are maintained on EDC-NHS crosslinked ECC matrices. Overall, results from this study suggest that ECC matrices have the potential to be developed as a functional biomaterial for corneal repair and regeneration.

Biomimetic tissue-engineered vascular grafts (TEVGs) have immense potential to replace diseased small-diameter arteries (<4 mm) for the treatment of cardiovascular diseases. However, biomimetic approaches developed thus far only partially recapitulate the physicochemical properties of the native vessel. While it is feasible to fabricate scaffolds that are compositionally similar to native vessels (collagen and insoluble elastic matrix) using freeze-drying, these scaffolds do not mimic the aligned topography of collagen and elastic fibers found in native vessels. Extrusion-based scaffolds exhibit anisotropic collagen orientation but these scaffolds are compositionally dissimilar (cannot incorporate insoluble elastic matrix). In this study, an electrochemical fabrication technique was employed to develop a biomimetic elastin-containing bi-layered collagen scaffold which is compositionally and structurally similar to native vessels and the effect of insoluble elastin incorporation on scaffold mechanics and smooth muscle cell (SMC) response was investigated. Further, the functionality of human umbilical vein endothelial cells (HUVECs) on the scaffold lumen surface was assessed via immunofluorescence. Results showed that incorporation of insoluble elastin maintained the overall collagen alignment within electrochemically aligned collagen (ELAC) fibers and this underlying aligned topography can direct cellular orientation. Ring test results showed that circumferential orientation of ELAC fibers significantly improved scaffold mechanics. Real-time PCR revealed that the expression of α-smooth muscle actin (Acta2) and myosin heavy chain (MyhII) was significantly higher on elastin containing scaffolds suggesting that the presence of insoluble elastin can promote contractility in SMCs. Further, mechanical properties of the scaffolds significantly improved post-culture indicating the presence of a mature cell-synthesized and remodeled matrix. Finally, HUVECs expressed functional markers on collagen lumen scaffolds. In conclusion, electrochemical fabrication is a viable method for the generation of a functional biomimetic TEVG with the potential to be used in bypass surgery.