Predicting rates of in vivo degradation of recombinant spider silk proteins

Abstract

Developing fundamental tools and insight into biomaterial designs for predictive functional outcomes remains critical for the field. Silk is a promising candidate as a biomaterial for tissue engineering scaffolds, particularly where high mechanical loads or slow rates of degradation are desirable. Although bioinspired synthetic spider silks are feasible biomaterials for this purpose, insight into how well the degradation rate can be programmed by fine tuning the sequence remains to be determined. Here we integrated experimental approaches and computational modelling to investigate the degradation of two bioengineered spider silk block copolymers, H(AB) 2 and H(AB) 12 , which were designed based on the consensus domains of Nephila clavipes dragline silk. The effect of protein chain length and secondary structure on degradation was analysed in vivo. The degradation rate of H(AB) 12 , the silk with longer chain length/higher molecular weight, and higher crystallinity, was slower when compared to H(AB) 2 . Using full atomistic modelling, it was determined that the faster degradation of H(AB) 2 was due to the lower folded molecular structure of the silk and the greater accessibility to solvent. Comparison of the specific surface areas of proteins via modelling showed that higher exposure of random coil and lower exposure of ordered domains in H(AB) 2 led to the more reactive silk with a higher degradation rate when compared with H(AB) 12 , as validated by the experimental results. The study, based on two simple silk designs demonstrated that the control of sequence can lead to programmable degradation rates for these biomaterials, providing a suitable model system with which to study variables in protein polymer design to predict degradation rates in vivo. This approach should reduce the use of animal screening, while also accelerating translation of such biomaterials for repair and regenerative systems.

Multiscale Modeling of Silk and Silk‐Based Biomaterials—A Review

“…Longer chains had more ordered domains with a lower solvent accessible area. These results were validated experimentally in in vivo assays …”

“…Longer chains assembled into larger micelles of a diameter of 32 ± 5 nm, whereas small chains led to small micelles of 2 ± 0.5 nm. Furthermore, not only the mechanical properties of silk‐based materials, but also its biodegradability, were studied through MD: shorter lengths resulted in less ordered molecular structures in the silk, facilitating the access of solvents, which facilitates its degradation. Longer chains had more ordered domains with a lower solvent accessible area.…”

Recombinant Spider Silk Forms Tough and Elastic Nanomembranes that are Protein‐Permeable and Support Cell Attachment and Growth

“…[39] Membranes with nanoscale thickness could be used in tissue engineering, serving as in vitro interfacial barriers that mimic the physiological microenvironment conditions of, e.g., the basal lamina in vivo. [1,4] Previous work shows that recombinant spider silk triggers only a limited immune response [18,21] and is degraded in vivo within 2-4 weeks. [7,21] This biocompatibility and biodegradability, combined with the herein demonstrated nanothickness, elasticity, toughness, protein permeability and cell adherence, make our silk nanomembranes uniquely suited for novel or improved tissue engineering applications.…”

“…[1] Membranes with a sub-µm thickness (from here on "nanomembranes") of fibrous material have an especially great appeal thanks to their high porosity, large surface area, high flexibility, [2] nanomembranes formed from silk have therefore required reinforcement with inorganic fillers [6] or film compression, [2] which has resulted in protein impermeability. With respect to biocompatibility and biodegradability, recombinant spider silk proteins are of specific interest, as materials made thereof trigger only a limited immune response [18,21] and are degraded within 2-4 weeks. [7,21] Recombinant spider silk proteins can also be functionalized with cell adhesion motifs from, e.g., fibronectin to promote cell attachment and proliferation, e.g., FN-4RepCT.…”

“…With respect to biocompatibility and biodegradability, recombinant spider silk proteins are of specific interest, as materials made thereof trigger only a limited immune response [18,21] and are degraded within 2-4 weeks. [7,21] Recombinant spider silk proteins can also be functionalized with cell adhesion motifs from, e.g., fibronectin to promote cell attachment and proliferation, e.g., FN-4RepCT. [22] Interestingly, FN-4RepCT spider silk proteins with the introduced FN-motif can form silk structures with increased stability and bioactivity.…”