Title : Using excimer laser to manufacture stimulative and stimuli responsive membranes
Abstract:
248 nm KrF excimer laser can be used to manufacture temperature and pH (stimuli) responsive polymer-based membranes for controlled transport applications. This is done by a two-step approach: In the first step, well-defined/(shaped) and orderly pores are created on commercially available polymer films by ablation using excimer laser. The same laser is used subsequently for energetic grafting and polymerization of a responsive hydrogel polymer using pulsed laser polymerization (PLP) inside the pores fabricated during the first step. This is a fast process which offers flexible tuning of flux using laser operation parameters. Thus, these ‘smart’ membranes allow controllable solute transport. In this presentation, determination of appropriate laser parameters and grafting solution characteristics are illustrated to obtain the desired membrane performance. We first discuss fabrication of membranes with 600 nm to 25 μm pore sizes using the laser through different metal mesh templates. The size of the pores generated by excimer laser ablation for flux in the direction perpendicular to the planar surface of the polymer film, can be reduced down to the nano scale (< 100 nm) for flux in directions transverse to the film (i.e., in the film plane) by using the excimer laser in conjunction with an innovative self-assembly technique. Polymer films processed in this manner can be stacked on top of each other and can even be incorporated with responsive hydrogels by PLP within the channels created on their surfaces (preferably prior to stacking) to be used as membranes with flux in their planar direction. The films to be irradiated are manufactured using polystyrene (PS) / polyisoprene copolymers to produce densely packed PS and silicon (carrier plate) nano-dots using a top-down/bottom-up hybrid method by employing excimer laser irradiation on perpendicular (PS) cylinder-containing block copolymer films. The ablative procedures can be used to modify surfaces of poly(ethylene terephthalate) (PET), polyimide (PI), poly(3-hydroxybutyrate) (PHB), poly(lactic acid) (PLA), poly(methyl methacrylate) (PMMA), and polyurethane (PU)/poly(dimethylsiloxane) (PDMS) films using 248 nm KrF excimer laser. Some of these membranes were used for tissue engineering based on cell–polymer film interfacial interactions of human fibroblast cells cultured on laser-modified (stimulative) membrane films revealing that laser-induced perforation of biodegradable PLA and non-biodegradable PMMA polymer films with perforation sizes of up to 43 μm can render them effective scaffold materials for tissue engineering. Experimental results show that membranes manufactured by excimer laser are excellent choices for applications where transport/transition uniformity are the prime requirements as they possess uniform pore sizes and distribution.
