Biomedical applications pertaining to stents, vascular grafts, etc., require an external material implanted inside the body. Ideally, the materials used for these applications should have properties such as In-vivo trigger, biocompatible, biodegradable, design mechanical strength and functionality in controlled drug release and controlling cell behaviour. Existing materials used for these applications are metal alloys with polymer coating. Various other materials like shape memory alloys (SMAs), shape memory polymers (SMPs), and hydrogel-based systems are also being tested to find suitable replacements with desired properties. However, SMAs and SMPs also lacks properties such as biodegradability, and since most of the SMPs are thermo-responsive, designing these types of material with suitable in-vivo trigger is challenging.
We work on a chitosan smart polymer, which responds to solvent. Chitosan polymer has distinctive properties such as biodegradability, biocompatibility required for biomedical applications and is inexpensive. When kept on a solvent surface, the chitosan thin film actuates due to the concentration gradient developed across the thickness but remains flat when dipped inside the solvent. The actuation characteristics of the film can be controlled by varying matrix properties and by changing solvent characteristics. Most applications for drug delivery and soft robotics require under-solvent actuation control. Our primary objective is to design a material system that can actuate inside solvent and provide better direction control. These can be achieved by a) developing a bilayer with both active or one active and one passive layer, b) making an asymmetric porous structure that can form the concentration gradient required for actuation. The actuation of developed bilayer films has been shown to have control over biofilm removal, bidirectionality, and drug delivery. With the help of layer-by-layer assembled bilayer and tunable solvent characteristics, we could understand the mechanism and mimic the actual scroll of descemet membrane endothelial keratoplasty (DMEK) grafts. We illustrated through experiments that the medium can be engineered to reduce the scroll tightness and thus reduce the surgical inconveniences and improve post-transplant recovery. The designed solvent-responsive bilayer actuators have shown an enormous potential required for various biomedical applications.