Bio-interface properties of guanidinylated chitosans: Effects of degree of acetylation, degree of guanidinylation, and molecular weight.

We previously reported a low molecular weight water-soluble guanidinylated chitosan (GCS) with a controlled degree of acetylation (DA). However, the effects of DA, degree of guanidinylation (DG), and molecular weight on the solubility, functions, and biocompatibility of GCS remain unclear, even though water-soluble GCSs with varying parameters would contribute to the development of novel biomaterials. Here we show the bio-interface properties of acetylated chitosans (CSs) and GCSs with systematically varied DA, DG, and molecular weight, including their solubility, antibacterial activity, and cytotoxic effects. Solubility tests revealed that guanidinylation generally reduced solubility, particularly in DA-uncontrolled samples and at higher molecular weights, whereas GCSs with DA values of 32-37% specifically exhibited improved solubility. In other words, we revealed that the control of DA represents the critical factor for enhancing the solubility of GCS. The minimum inhibitory concentration assays of representative acetylated CSs and GCSs against Escherichia coli and Staphylococcus epidermidis revealed that reduced acetyl content is more critical for antibacterial activity than positive charge, and that guanidinylation induces antibacterial activity under neutral conditions. The cytotoxicity and cell proliferation results suggest that water-soluble GCSs show low cytotoxicity, comparable to acetylated CSs, while strongly inhibiting cell proliferation, supporting their potential as anticancer agents.