Supplementary information files for Stability and mechanical performance of collagen films under different environmental conditions

Supplementary files for article Stability and mechanical performance of collagen films under different environmental conditions Protein-based biomaterials are becoming increasingly popular for biomedical applications as they can replicate both chemical and mechanical properties of native tissues. Type I collagen is widely available and used for such applications, particularly as 2D structures (films and membranes). The degradation mechanism and mechanical performance of collagen films are investigated in this study for long-term exposure to three different environments – ambient laboratory conditions (Type A), water immersion (<em>in-aqua</em>) (Type B) and rehydration (replenishment of water lost in dehydration) (Type C) conditions. Specimens exposed to Type A conditions showed an increased stiffness with reduction in the ductility over the exposure period (1 year) due to the loss of physically bonded water without any change of chemical and structural properties. Another group of specimens were exposed to Type B conditions for a period of only 14 days due to quick deterioration in both the global (tensile) and local (nanoindentation) modulus. The decrease in the dimensions of the exposed specimens, their weight loss over time and changes in surface morphology through erosion and formation of micro-pores indicate that degradation might have occurred via surface erosion mechanisms. Interestingly, the chemical functional groups and triple-helix conformation of the exposed specimens remained intact over the exposure time. An increase of about 53% in the global modulus occurred on day 3 of <em>in-aqua</em> exposure (compared to day 1) due to rearrangement of the collagen nano-fibrils. Type C conditions were implemented by exposing the specimens <em>in-aqua</em> for a specific time and then dehydrating them. Such specimens exhibited poorer mechanical properties compared to the freshly manufactured ones.

本文补充文件：不同环境条件下胶原膜（collagen films）的稳定性与力学性能研究 基于蛋白质的生物材料（protein-based biomaterials）在生物医学应用（biomedical applications）中日益受到青睐，因其可复制天然组织（native tissues）的化学与力学特性。I型胶原（Type I collagen）来源广泛，常用于此类应用，尤其作为二维结构（2D structures，如膜与薄膜）。本研究探讨了胶原膜在三种不同环境长期暴露下的降解机制（degradation mechanism）与力学性能（mechanical performance）——实验室环境条件（A型）、水浸泡（<em>in-aqua</em>，B型）及再水化（补充脱水过程中流失的水分，C型）条件。暴露于A型条件的样品刚度增加，延展性降低，原因是物理结合水（physically bonded water）流失，而化学与结构特性未变。暴露于B型条件的样品仅持续14天，因其整体（拉伸）模量（global (tensile) modulus）与局部（纳米压痕）模量（local (nanoindentation) modulus）快速下降。样品尺寸减小、随时间的重量损失及表面侵蚀与微孔形成导致的形态变化表明，降解可能通过表面侵蚀机制（surface erosion mechanisms）发生。值得注意的是，暴露样品的化学官能团（chemical functional groups）与三螺旋构象（triple-helix conformation）在暴露期间保持完整。水浸泡第3天，整体模量较第1天提升约53%，这归因于胶原纳米纤维（collagen nano-fibrils）的重排。C型条件通过将样品在水中暴露特定时间后脱水实现，此类样品的力学性能劣于新鲜制备的样品。