Improved alginate bio-ink by recombinant self-assembled cell-sized spider-silk inspired-biopolymer

Alginate is a natural linear polysaccharide polymer that is extracted from brown seaweed. It is extensively used due to its biocompatibility, ease of handling in aqueous environments, and relatively low cost. Alginate easily forms a hydrogel when crosslinked with a bivalent ion such as calcium. However, alginate hydrogel exhibits low mechanical strength and is cell-inert, having no cell-matrix interactions. To address these limitations and enhance alginate's utility as a bioink for bioprinting, we developed a novel alginate matrix combined with spider- silk, known for its exceptional resilience, elasticity, and strength, as well as its capacity to facilitate cell attachment. The unique recombinant spider-silk biopolymer used in our study (SVX), is synthetically produced, and self-assembles into water-insoluble cell-sized particles that are limited by the cell size in the expression system. These are characterized by a sponge-like structure, and are both biocompatible and non-immunogenic. Incorporating synthetic spider-silk into alginate significantly increased the hydrogel's viscosity and compression resilience compared to alginate alone. SVX-enriched alginate exhibited superior printability, characterized by a lower spreading ratio at reduced pressures that is favorable for cell printing. The SVX-enriched alginate also demonstrated higher consistency in spreading ratios across a range of setup conditions. Bioprinting of cells within the SVX-enriched alginate bioink resulted in more homogenous cultures with prolonged and higher cell viability, compared to the larger, more condensed spheroids with lower cell viability observed in alginate bioprinted constructs. These enhanced cell cultures in the SVX-enriched constructs can be attributed to the improved stability of the constructs as well as spider-silk-mediated cell adherence.