Pan, Yusong, Chuyang Xu, and Guoxin Ding. 2012. “Stress Relaxation Behaviour and Model of Multi-Layered Nano-Hydroxyapatite Reinforced PVA Gel Biocomposites”. Asian Journal of Chemistry 24 (9):4106-8. https://asianpubs.org/index.php/ajchem/article/view/9560.