Tunable degradation of low-fouling carboxybetaine-hyaluronic acid hydrogels for applications in cell encapsulation

Modulating pentenoate-functionalized hyaluronic acid hydrogel network properties for meniscal fibrochondrocyte mechanotransduction

Knee meniscus tears are one of the most common musculoskeletal injuries. While meniscus replacements using allografts or biomaterial-based scaffolds are available, these treatments rarely result in integrated, functional tissue. Understanding mechanotransducive signaling cues that promote a meniscal cell regenerative phenotype is critical to developing therapies that promote tissue regeneration rather than fibrosis after injury. The purpose of this study was to develop a hyaluronic acid (HA) hydrogel system with tunable crosslinked network properties by modulating the degree of substitution (DoS) of reactive-ene groups to investigate mechanotransducive cues received by meniscal fibrochondrocytes (MFCs) from their microenvironment. A thiol-ene step-growth polymerization crosslinking mechanism was employed using pentenoate-functionalized hyaluronic acid (PHA) and dithiothreitol to achieve tunability of the chemical crosslinks and resulting network properties. Increased crosslink density, reduced swelling, and increased compressive modulus (60-1020 kPa) were observed with increasing DoS. Osmotic deswelling effects were apparent in PBS and DMEM+ compared to water; swelling ratios and compressive moduli were decreased in the ionic buffers. Frequency sweep studies showed storage and loss moduli of hydrogels at 1 Hz approach reported meniscus values and showed increasing viscous response with increasing DoS. The degradation rate increased with decreasing DoS. Lastly, modulating PHA hydrogel surface modulus resulted in control of MFC morphology, suggesting relatively soft hydrogels (E = 60 ± 35 kPa) promote more inner meniscus phenotype compared to rigid hydrogels (E = 610 ± 66 kPa). Overall, these results highlight the use of -ene DoS modulation in PHA hydrogels to tune crosslink density and physical properties to understand mechanotransduction mechanisms required to promote meniscus regeneration.

New injectable self-assembled hydrogels that promote angiogenesis through a bioactive degradation product

Hydrogels used in regenerative medicine are often designed to allow cellular infiltration, degradation, and neovascularization. Low molecular weight hydrogels (LMWHs), formed by self-assembly via non-covalent interactions, are gaining significant interest because they are soft, easy to use and injectable. We propose LMWHs as suitable body implant materials that can stimulate tissue regeneration. We produced four new LMWHs with molecular entities containing nucleic acid and lipid building blocks and analyzed the foreign body response upon subcutaneous implantation into mice. Despite being infiltrated with macrophages, none of the hydrogels triggered detrimental inflammatory responses. Most macrophages present in the hydrogel-surrounding tissue acquired an immuno-modulatory rather than inflammatory phenotype. Concomitantly, no fibrotic capsule was formed after three weeks. Our glyconucleolipid LMWHs exhibited different degradation kinetics in vivo and in vitro. LMWHs with high angiogenic properties in vivo, were found to release glyconucleoside (glucose covalently linked to thymidine via a triazole moiety) as a common by-product of in vitro LMWH degradation. Chemically synthesized glyconucleoside exhibited angiogenic properties in vitro in scratch assays with monolayers of human endothelial cells and in vivo using the chick chorioallantoic membrane assay. Collectively, LMWHs hold promise as efficient scaffolds for various regenerative applications by displaying good biointegration without causing fibrosis, and by promoting angiogenesis through the release of a pro-angiogenic degradation product. STATEMENT OF SIGNIFICANCE: The main limitations of biomaterials developed in the field of tissue engineering remains their biocompatibility and vascularisation properties. In this context, we developed injectable Low Molecular Weight Hydrogels (LMWH) exhibiting thixotropic (reversible gelation) and thermal reversible properties. LMWH having injectability is of great advantage since it allows for their delivery without wounding the surrounding tissues. The resulting gels aim at forming scaffolds that the host cells colonize without major inflammation, and that won't be insulated by a strong fibrosis reaction. Importantly, their molecular degradation releases a product (a glycosyl-nucleoside conjugate) promoting angiogenesis. In this sense, these LMWH represent an important advance in the development of biomaterials promoting tissue regeneration.