Zein-induced immune response and modulation by size, pore structure and drug-loading: application for sciatic nerve regeneration.

Abstract Zein is a biodegradable material with great potential in biomedical applications. However, as a plant-derived protein material, the body's immune response is the key factor to determine the clinical performance. Herein, for the first time, the zein-induced immune responses are evaluated systemically and locally, comparing with typical materials including alginate (ALG), poly(lactic-co-glycolic) acid (PLGA) and polystyrene (PS). Zein triggers an early inflammatory response consistent with the non-degradable PS, but this response decreases to the same level of the biosafety ALG and PLGA with zein degradation. Changing sphere sizes, pore structure and encapsulating dexamethasone can effectively modulate the zein-induced immune responses, especially the pore structure which also inhibits neutrophil recruitment and promotes macrophages polarizing towards M2 phenotype. Thus, porous zein conduits with high and low porosity are further fabricated for the 15-mm sciatic nerve defect repair in rats. The conduits with high porosity induce more M2 macrophages to accelerate nerve regeneration with shorter degradation period and better nerve repair efficacy. These findings suggest that the pore structure in zein materials can alleviate the zein-induced early inflammation and promote M2 macrophages polarization to accelerate nerve regeneration. Statement of Significance Zein is a biodegradable material with great potential in biomedical applications. However, as a plant protein, its possible immune response in vivo is always the key issue. Until now, the systemic study on the immune responses of zein in vivo is still very limited, especially as an implant. Herein, for the first time, the zein-induced immune responses were evaluated systemically and locally, comparing with typical materials including alginate, poly(lactic-co-glycolic) acid and polystyrene. Changing sphere sizes, pore structure and encapsulating dexamethasone could effectively modulate the zein-induced immune responses, especially the pore structure which also inhibited neutrophil recruitment and promoted macrophages polarizing towards M2 phenotype. Furthermore, the pore structures in zein nerve conduits was proved to alleviate the early inflammation and promote M2 macrophages polarization to accelerate nerve regeneration.