Responsive Biomaterial Surfaces

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Title: Responsive Biomaterial Surfaces
Author: Wang, Xiaoling
Advisors: Sam Hudson, Committee Co-Chair
Lola Reid, Committee Member
Marian McCord, Committee Co-Chair
Abstract: Responsive biomaterial surfaces were fabricated by grafting stimuli-responsive polymers onto polymer material surfaces via a novel Atmospheric Plasma Treatment (APT). They have potential uses in cell adhesion/detachment control, tissue engineering, medical device, drug delivery, bioreactor, bioseparation, and responsive clothing. Temperature sensitive poly(N-isopropylacrylamide) (PNIPAM) was grafted onto various substrates via two novel methods using APT, i.e., atmospheric plasma treatment followed by free radical graft copolymerization (two- step method), and atmospheric plasma treatment of a NIPAM monomer coated surface (coating method). The substrates included nylon film, non-tissue culture treated polystyrene (PS) plates, and cotton fabrics. FTIR confirms the grafting of PNIPAM. The addition of Mohr's salt in the two-step method suppresses homopolymerizaiton and enhances graft yields. The contact angle of PNIPAM-grafted polymer surfaces increases dramatically at ca. 32oC, indicating the temperature sensitivity of the grafted surface, i.e., the change of surfaces from hydrophilic to hydrophobic as temperature increases. Atomic Force Microscope (AFM) shows different topography of original, plasma treated, and PNIPAM grafted surfaces. For the first time, AFM was employed to characterize the grafted surface topography upon changes from dry to wet conditions and from below to above the LCST of PNIPAM. The grafted surface is rough when dry at 22oC, and smooth when wet at 22oC. However, the surface becomes rough again in water at 40oC in response to conformation changes in the PNIPAM hydrogel. Human epithelial cell line HEPG2 cells adhere and proliferate on PNIPAM grafted PS plates at 37oC as on tissue culture plates. However, they detach from the surface automatically at 0oC because of the phase change of PNIPAM. The detachment of HEPG2 cells upon cooling down can be used to recover continuous sheets of tissues from a bioreactor. The tensile property of PNIPAM grafted cotton fabrics was studied. The grafting of PNIPAM still have good tensile property. Comfort test shows thermal sensitivity of the PNIPAM grafted cotton. At 10oC in wet conditions (sweating), less heat transfers from the skin model through the grafted cotton than through the original cotton (control); however at 35oC, more heat transfers from the skin model through the fabric than control. pH responsive Poly(acrylic acid) (PAA) was also grafted on the nylon surface via atmospheric plasma treatment two- step method. The FTIR and water contact angle confirmed the grafting. Compared with conventional vacuum grafting methods, the APT method has several advantages, including no vacuum requirement, low cost, availability to be integrated into a continuous process, and no effect no bulk properties. The APT coating method is especially suitable for industry continuous process.
Date: 2006-07-26
Degree: MS
Discipline: Biomedical Engineering
Textile Engineering

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