Collagen types I and III are primary structural proteins that maintain human skin integrity, and their ratio is disrupted during aging. In this study, we developed a biomimetic 3D skin model with vascularization potential to evaluate the effects of nano-zinc oxide (nano-ZnO) in a physiologically relevant context. The model used methacrylated recombinant human collagen (RHC-MA) bioinks with tunable collagen I/III ratios that mimic the skin of children and adults. The bioinks exhibited excellent printability and mechanical properties that enabled the 3D bioprinting of full-thickness skin products, including dermal layers with human skin fibroblasts (HSFs) and human umbilical vein endothelial cells (HUVECs), as well as epidermal layers with keratinocytes (KCs). The model recapitulated native skin architecture, and key markers such as keratin 10 (K10), keratin 14 (K14), and cluster of differentiation 31 (CD31) were determined. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that nano-ZnO significantly modulated genes associated with apoptosis, inflammation, and oxidative stress in skin cells.

Corneal disease is a cause of vision loss worldwide, while conventional keratoplasty is constrained by limited donor tissue and immune rejection. This indication-guided review examines functional polymer platforms for corneal tissue engineering, including natural polymers, synthetic polymer networks and scaffolds, and hybrid polymer composites. It examines how molecular composition, crosslinking, architecture, surface functionalization, and fabrication influence hydrogels, films, fibrous scaffolds, injectable matrices, delivery systems, and polymeric keratoprosthetic components for epithelial, stromal, and endothelial contexts. Using an indication-guided design trade-off framework, the review compares these systems across optical performance, mechanical performance and surgical handling, mass transport and degradation behavior, biological function and tissue integration, host response, and manufacturability. Natural polymers can provide biological cues that support cell interactions, with limitations in mechanical robustness and compositional consistency. Synthetic polymers offer greater control of network properties and processing but often require biofunctionalization to support tissue integration. Hybrid constructs can distribute optical, structural, and therapeutic functions across components or regions, with added fabrication complexity. No material class is universally optimal, and polymer selection should be guided by the target corneal layer and clinical indication. Standardized evaluation, reproducible reporting of polymer composition and fabrication conditions, scalable manufacturing, and transparent reporting of evidence maturity are priorities for clinical translation.