Dr ZHAO Xin, Member of the Research Institute for Intelligent Wearable Systems (RI-IWEAR), and her team developed artificial cilia that help to preserve the sensitivity and bioactivity of a growth factor protein, bone morphogenetic protein-2 (BMP-2), for tissue engineering.
In the field of biomedical engineering, the restoration of damaged tissues requires the immobilisation of proteins onto tissue surfaces. However, scaffolding remains a great challenge in tissue engineering. To address this issue, the team developed a stable and soft surface modification strategy. BMP-2 (a growth factor) was covalently immobilised onto poly glycidyl methacrylate (PGMA) polymer brushes which were grafted onto substrate surfaces (of gold, quartz glass, silica wafer, or common biomaterials).
This surface modification method is simple, fast, gentle, and provides stability to the loaded protein due to cilia motility (i.e., the ability of cilia to beat in a coordinated manner to generate a directional fluid flow along cell surfaces). The study yielded three important observations. First, the immobilised BMP-2 (i-BMP-2) on the surface of the PGMA polymer brushes exhibited excellent bioactivity (⁓87% of the bioactivity of free BMP-2 in vitro, and 20–50% higher than scaffolds with free BMP-2 in vivo). Second, the conformation and secondary structure of i-BMP-2 were well-preserved after covalent immobilisation and ethanol sterilisation. Third, i-BMP-2 arranged in a pattern of nanolines (PGMA-poly (N-isopropylacrylamide)) exhibited approximately 110% of the bioactivity of free BMP-2.
In sum, the strategy is a superior alternative to conventional protein covalent immobilisation strategies in terms of both bioactivity preservation and therapeutic efficacy. In the long run, PGMA polymer brushes can be used to modify the surfaces of different tissue-engineered scaffolds, thus facilitating the in-situ immobilisation of growth factors and, hence, tissue repair.
