Cross-linking of a biopolymer-peptide co-assembling system

The ability to guide molecular self-assembly at the nanoscale into complex macroscopic structures could enable the development of functional synthetic materials that exhibit properties of natural tissues such as hierarchy, adaptability, and self-healing. However, the stability and structural integrity of these kinds of materials remains a challenge for many practical applications. We have recently developed a dynamic biopolymer-peptide co-assembly system with the capacity to grow and undergo morphogenesis into complex shapes. Here we explored the potential of different synthetic (succinimidyl carboxymethyl ester, poly (ethylene glycol) ether tetrasuccinimidyl glutarate and glutaraldehyde) and natural (genipin) cross-linking agents to stabilize membranes made from these biopolymer-peptide co-assemblies. We investigated the cross-linking efficiency, resistance to enzymatic degradation, and mechanical properties of the different cross-linked membranes. We also compared their biocompatibility by assessing the metabolic activity and morphology of adipose-derived stem cells (ADSC) cultured on the different membranes. While all cross-linkers successfully stabilized the system under physiological conditions, membranes cross-linked with genipin exhibited better resistance in physiological environments, improved stability under enzymatic degradation, and a higher degree of in vitro cytocompatibility compared to the other cross-linking agents. The results demonstrated that genipin is an attractive candidate to provide functional structural stability to complex self-assembling structures for potential tissue engineering or in vitro model applications.

Statement of significance: Molecular self-assembly is widely used for the fabrication of complex functional biomaterials to replace and/or repair any tissue or organ in the body. However, maintaining the stability and corresponding functionality of these kinds of materials in physiological conditions remains a challenge. Chemical cross-linking strategies (natural or synthetic) have been used in an effort to improve their structural integrity. Here we investigate key performance parameters of different cross-linking strategies for stabilising self-assembled materials with potential biomedical applications using a novel protein-peptide co-assembling membrane as proof-of-concept. From the different cross-linkers tested, the natural cross-linker genipin exhibited the best performance. This cross-linker successfully enhanced the mechanical properties of the system enabling the maintenance of the structure in physiological conditions without compromising its bioactivity and biocompatibility. Altogether, we provide a systematic characterization of cross-linking alternatives for self-assembling materials focused on biocompatibility and stability and demonstrate that genipin is a promising alternative for the cross-linking of such materials with a wide variety of potential applications such as in tissue engineering and drug delivery.