In situ visualization of lamellar crystal growth in poly[(S)-lactide] thin film by temperature-controlled atomic force microscopy

Yoshihiro Kikkawa^{1, 2}, Hideki Abe¹, Tadahisa Iwata¹, Yoshio Inoue², and Yoshiharu Doi¹

1) Polymer Chemistry Laboratory, RIKEN Institute, Hirosawa, Wako-shi, Saitama 351-0198, Japan
2) Department of Biomolecular Engineering, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8501, Japan

Poly[(S)-lactide] (P[(S)-LA]) is known as a biodegradable and biocompatible thermoplastic. To elucidate the crystal growth and biodegradation mechanisms, in situ visualization was first performed for growing crystals in P[(S)-LA] thin film (thickness: 30-200 nm) by temperature-controlled atomic force microscopy. An initial stage of crystallization and following development of lamellar crystals were successfully observed during isothermal crystallization at 165C. First, an edge-on crystal was formed, and then, dendritic or hexagonal flat-on crystals were developed from the edge-on crystal depending on the film thickness. Enzymatic degradation of P[(S)-LA] thin film crystallized at 160C was performed with Proteinase K at 37C. Even a few hours of degradation period, an amorphous region of the thin film was completely removed by hydrolysis. After enzymatic degradation for 12 h, the hexagonal crystal was degraded into small pieces of lamellae. A correlation between crystal growth and enzymatic degradation processes will be discussed.