Investigation into the use of a chitosan scaffold for tarsal plate substitution in eyelid reconstruction.

We previously described the production of hydrophilic hydrogel scaffolds of cross-linked chitosan that closely matched the biomechanical properties of native human tarsus. In the present preclinical study we appraised the spatio-temporal tissue response to the implantation of these chitosan scaffolds into rat eyelids. Acellular hydrogel scaffolds were produced from Good Manufacturing Practice (GMP)-compliant chitosan and implanted into rat eyelids. Tissue was harvested and fixed up to 24 weeks post-surgery for histological examination of the tissue response to both the surgical procedure itself and to the chitosan implantation. Assessment encompassed inflammation, the foreign body reaction (FBR) and infiltration of native cells into the implant region, along with scaffold degradation. Three days after implantation of the chitosan into rat eyelids, neutrophils were observed in the vicinity of the chitosan but their prevalence declined rapidly thereafter. Both pro-inflammatory M1-macrophages and anti-inflammatory M2-macrophages were also observed post-implantation at the scaffold-tissue interface but the former cells declined after 4 weeks. Unlike the M1-macrophages, the M2-macrophages rarely infiltrated the scaffold at any time point. T cells and MHC class II antigen-presenting cells were predominantly increased at the tissue-scaffold interface and, to a minor degree, within the scaffold, in the weeks following surgery. In the weeks following implantation, a fibro-collagenous capsule gradually formed at the margins of the scaffolds, denoting the classic FBR. This was accompanied by the appearance of foreign body giant cells, moderate to substantial degradation and engulfment of chitosan by infiltrating cells, and localized tissue remodelling characterized by proliferation of fibroblasts, deposition of collagenous extracellular matrix (ECM) material and rudimentary formation of vascular elements within the scaffold. Although the chitosan scaffolds initially elicited widespread inflammation and an FBR, longer-term tissue remodelling and scaffold degradation suggested their biocompatibility. These data support that chitosan hydrogel scaffolds could, therefore, serve as suitable tarsal substitute material in situ.