To advance biomaterial engineering: a novel pH-responsive MOF for eco-friendly modification of collagen fibers with applications in recyclable, alkali-free Knoevenagel catalysis

Zirconium based MOFs demonstrate potential for ecofriendly modification of collagen fibers. However, achieving high utilization efficiency of zirconium ions remains challenging. Herein, a novel boronate ester functionalized MOF (Zr-TB) with pH-dependent structural stability is disclosed. It maintains structural integrity under neutral conditions but decomposes under acidic conditions below pH 4.0. Based on this, a novel modifier for collagen fibers is developed by loading zirconium complex (ZTA) into Zr-TB. This system enables controlled release of ZTA, thereby preventing excessive binding between zirconium ions and collagen fibers. EDS analysis confirms the uniform distribution of zirconium ions in the modified collagen fibers, resulting in excellent hydrothermal stability characterized by a shrinkage temperature of over 80 °C. DFT calculations reveal that the zirconium cluster complex generated from the decomposition of Zr-TB can also effectively bind to the -COOH of collagen fibers, thereby significantly improving the utilization efficiency of zirconium ions. Notably, after ball milling, the modified collagen fibers serve as an efficient catalyst for the Knoevenagel reaction and exhibit excellent cycling stability, maintaining a yield above 87% over five consecutive cycles, attributable to the uniform distribution of zirconium ions on the collagen support. Furthermore, the presence of -NH 2 on the collagen fibers effectively eliminates the need for additional alkaline catalysts. This work presents a highly efficient strategy for modification of collagen fibers and highlights the promising potential of collagen fibers as carriers for organic synthesis catalysts.