Research
Overview
We are exploring both applied and fundamental research in the areas of surface modification, interfacial phenomena, and polymer thin films. Currently, two research areas are being emphasized: area 1 – simple and cost-effective approaches for surface patterning and biomaterial fabrications; area 2 – anti-adhesions, antifouling, biofilm and biocorrosion. The following are some current research projects.
(1) Mechanically strong hydrogels based on squid ring teeth proteins: Mechanically strong hydrogels are desirable for tissue engineering applications, especially for cartilage and bone repairs. Protein-based hydrogels have their added advantages due to the ability of proteins to retain their functionality both in vivo and ex vivo, excellent biocompatibility and biodegradability. However, in general, protein-based hydrogels are mechanically weak, tear easily, and have a low sol-to-gel transition temperature, rendering them little use in regenerative medicine. One way to improve their mechanical strength is to incorporate a mechanically tough protein. One of the attractive candidate is recently discovered suckerins or the proteins from squid ring teeth (SRT) that have a compatible modulus (4 - 12 GPa) to that of Plexiglas. We are currently carrying our some preliminary studies on generating mechanically strong suckerin based hydrogels. Some tasks include the optimization of the processing conditions, fabrication of suckerin-collagen composites, and evaluations of physical and mechanical properties, and biocompatibility of the resulting gels.
(2) Generating thermo-responsive cell culture supports using siloxane networks: Silane coupling agents have mainly been utilized to enhance the adhesion between polymers and metals. Some organosilanes not only can be easily grafted to a glass/silicon substrate, but also can form tight cross-linked siloxane networks upon thermal annealing. Such networks can be utilized to entrap polymer chains and create a polymer layer that otherwise cannot be easily retained on a surface. As an example, poly(N-isopropylacrylamide) (pNIPAAm), a thermal-responsive polymer that exhibits a phase change behavior in a physiologically relevant temperature range and has attracted special interests in recent years in cell sheet engineering can be immobilized using these cross-linked siloxane networks. Generally, in order to immobilize pNIPAAm on a surface, the polymer chains are grafted by either electron beam irradiation or plasma polymerization. Accessing an e-beam facility might not be feasible for many researchers and the plasma based polymerization could be laborious. So far, we have demonstrated the feasibility of immobilizing pNIPAAm on the substrates by entrapping pNIPAAm using several siloxane network forming organosilanes, including 3-aminopropyltriethoxysilane (APTES), via a simple two-step approach: spin-coating of a blended solution of pNIPAAm and APTES followed by thermal annealing. The resulting siloxane network entrapped pNIPAAm supports cell attachment and proliferation and is capable of detaching the formed cell sheet or attached individual cells within minutes.
In addition to entrapping and immobilizing pNIPAAm chains on the surface, the organosilanes containing different functional groups would allow the desired surface properties to be designed. The simplicity and versatility of the approach could broaden its application by entrapping other polymers (e.g., conducting polymers for energy harvesting and electronic applications) that need to be retained on hydroxylated surfaces.
(3) Creating gradient surfaces via contact printing based approach: The contact printing based approach allows generation of step-wise and continuous gradients from micrometer scale to centimeter scale. As a result, from screening material behaviors to creating platforms for molecular architectures, gradient surfaces created by contact printing based approach could be more attractive than gradients generated via the traditional approaches. However, in order to realize such applications, the surface properties of the underlying gradient surfaces should be well-defined. In this project, the experimental parameters and transport processes of “ink” molecules from the stamp to the substrate will be evaluated, and the overall goal is to optimum the experimental conditions to generate well-defined gradient surfaces, based on contact printing, for their designated applications.
(4) Alternative, non-lithography based pattern fabrications: Simpler and cost-effective non-lithography based techniques are attractive alternatives to the photolithography based approach for creating patterns. Such techniques provide an easy access for researchers to create desired featured templates or patterns. We are utilizing spontaneous naturally occurring phenomena, such as decaying of liquid films (i.e. dewetting) on a solid support, “tears of wine” (i.e. Marangoni flow), and patterns generated by peeling (i.e. fracture-induced structuring) to develop some fast, simple and in-expensive alternatives. The followings are some movie clips showing the real-time processes on generating.
(a) Creating water droplet arrays via Marangoni-flow: hexagonal arrays, square arrays, receding velocity dependent
(b) Fracture-induced patterns via simple peeling: from edge, high magnification, slightly tilted
(5) Preventing formation of surgical adhesions: Surgical adhesions, especially pelvic adhesions, represents a significant, costly morbidity typically expressed as pain and infertility in the patient. Availability of a reliable method to decrease occurrence of adhesions would constitute a beneficial advance in current surgical practice. However, the efficacy and utility in both open and laparoscopic surgery of currently approved standard adhesion barriers is limited. We propose to design a delivery system that allows an initial burst of the anti-adhesion agent, zosteric acid (ZA), followed by a sustained release of the agent. Zosteric acid, a natural product extracted from eelgrass Zostera Marina, shows an extremely low toxicity but effectiveness in preventing adhesion formation of various organisms. It will be directly integrated, along with its nanoparticle-encapsulated form, into a thermo-reversible gel made of Pluronic® F-127 and Hydroxyl propyl methyl cellulose, which can then be easily applied in both open and laparoscopic surgeries to prevent adhesion development.
(6) Bacterial attachment and biofilm formation and Microbiologically influenced corrosion (MIC): Biofouling has significant impacts on surface corrosion and structural damage of aquatic infrastructures and, consequently, causes greater safety concerns and higher maintenance and replacement costs. Biofouling has other negative economic and ecological effects. Clearly, gaining a better understanding of biofouling and MIC is essential to developing effective management/control strategies against biofouling and its associated corrosion. We have designed and constructed flow chamber systems with slow shear at the wall of the chamber to allow accurate and reproducible investigation of bacterial cell attachment to surface and biofilm development under various conditions simulating relevant aquatic environments. These flow systems are utilized to in-situ monitor examine how various bacteria strains, including the dominant MIC bacteria strains, attach to model metal and organic coating surfaces and how the attached cells retain on the surface under shear and how they develop into biofilm to induce corrosion to the coupons.
We also design and evaluate materials/surfaces to combat biofouling. A negatively charged and hydrophilic surface could be low fouling due to its enhanced electrostatic repulsions and reduced hydrophobic interactions. We investigate the potential of thermal cross-linking, by a simple thermal curing process, a blend consisting of polystyrene sulfonic acid (PSS) and polyethylene glycol (PEG) to generate such negatively charged and highly hydrophilic films. The fouling resistance of these PSS-PEG films towards various foulants: bacteria, colloids, protein and mammalian cells was found to be better than those of sulfonic acid (SA) and PEG modified surfaces. The low-fouling performance of PSS-PEG, a cross-linked film by a simple thermal curing process, could allow this material to be used for applications in aqueous environments, where most low fouling hydrophilic polymers, such as PSS or PEG, could not be easily retained.
(7) Wettability of powders and porous media: Due to the wide utilization of powders and porous materials in various technological fields, reliable methods for determining wettability of powders and porous media should be re-visited. We focus on applying the liquid penetration into a packed column (i.e., the Washburn capillary rise (WCR) method) for determining the wettability of powders and porous media. The details on the selection of capillary tube for packing, bottom support, powder properties, reference wetting liquid, packing method as well as the suitability of the WCR method are being re-examined.
