Design of an apoptotic cell-mimetic wound dressing using phosphoserine-chitosan hydrogels

Inflammatory M1 macrophages create a hostile environment that impedes wound healing. Phosphoserine (PS) is a naturally occurring immunosuppressive molecule capable of polarizing macrophages from an inflammatory phenotype (M1) to an anti-inflammatory phenotype (M2). In this study, we designed, fabricated, and characterized PS-immobilized chitosan hydrogels as potential wound dressing materials. A PS group precursor was synthesized via a phosphoramidite reaction and subsequently immobilized onto the chitosan chain through an EDC/N-hydroxysuccinimide reaction using a crosslink moiety HPA. The PS/HPA-conjugated chitosan (CS-PS) was successfully synthesized by deprotecting the PS group in HCl. In addition, the hydrogels were prepared by the HRP/H2O2 enzyme-catalyzed reaction with different PS group contents (0, 7.27, 44.28 and 56.88 mu mol g-1). The immobilization of the PS group improved the hydrophilicity of the hydrogels. Interestingly, CS-PS hydrogel treatment upregulated both pro-inflammatory and anti-inflammatory cytokines. This treatment also resulted in alterations in the macrophage cell morphology from the M1 to M2 phenotype. The CS-PS hydrogel significantly accelerated diabetic wound healing. Overall, this study provides insights into the potential of PS-immobilized hydrogel materials for improved inflammatory disease therapy. Phosphoserine-immobilized chitosan hydrogels stimulate macrophages to secrete TGF-beta 1 and improve diabetic wound healing equivalent to non-diabetic wound healing.