Browsing by Subject "Elastomers"

Biofouling, the accumulation of biomolecules, cells, organisms and their deposits on submerged and implanted surfaces, is a ubiquitous problem across various human endeavors including maritime operations, medicine, food industries and biotechnology. Since several decades, there have been substantial research efforts towards developing various types of antifouling and fouling release approaches to control bioaccumulation on man-made surfaces. In this work we hypothesized, investigated and developed dynamic change of the surface area and topology of elastomers as a general approach for biofouling management. Further, we combined dynamic surface deformation of elastomers with other existing antifouling and fouling-release approaches to develop multifunctional, pro-active biofouling control strategies.

This research work was focused on developing fundamental, new and environment-friendly approaches for biofouling management with emphasis on marine model systems and applications, but which also provided fundamental insights into the control of infectious biofilms on biomedical devices. We used different methods (mechanical stretching, electrical-actuation and pneumatic-actuation) to generate dynamic deformation of elastomer surfaces. Our initial studies showed that dynamic surface deformation methods are effective in detaching laboratory grown bacterial biofilms and barnacles. Further systematic studies revealed that a threshold critical surface strain is required to debond a biofilm from the surface, and this critical strain is dependent on the biofilm mechanical properties including adhesion energy, thickness and modulus. To test the dynamic surface deformation approach in natural environment, we conducted field studies (at Beaufort, NC) in natural seawater using pneumatic-actuation of silicone elastomer. The field studies also confirmed that a critical substrate strain is needed to detach natural biofilm accumulated in seawater. Additionally, the results from the field studies suggested that substrate modulus also affect the critical strain needed to debond biofilms. To sum up, both the laboratory and the field studies proved that dynamic surface deformation approach can effectively detach various biofilms and barnacles, and therefore offers a non-toxic and environmental friendly approach for biofouling management.

Deformable elastomer systems used in our studies are easy to fabricate and can be used as complementary approach for existing commercial strategies for biofouling control. To this end, we aimed towards developed proactive multifunctional surfaces and proposed two different approaches: (i) modification of elastomers with antifouling polymers to produce multifunctional, and (ii) incorporation of silicone-oil additives into the elastomer to enhance fouling-release performance.

In approach (i), we modified poly(vinylmethylsiloxane) elastomer surfaces with zwitterionic polymers using thiol-ene click chemistry and controlled free radical polymerization. These surfaces exhibited both fouling resistance and triggered fouling-release functionalities. The zwitterionic polymers exhibited fouling resistance over short-term (∼hours) exposure to bacteria and barnacle cyprids. The biofilms that eventually accumulated over prolonged-exposure (∼days) were easily detached by applying mechanical strain to the elastomer substrate. In approach (ii), we incorporated silicone-oil additives in deformable elastomer and studied synergistic effect of silicone-oils and surface strain on barnacle detachment. We hypothesized that incorporation of silicone-oil additive reduces the amount of surface strain needed to detach barnacles. Our experimental results supported the above hypothesis and suggested that surface-action of silicone-oils plays a major role in decreasing the strain needed to detach barnacles. Further, we also examined the effect of change in substrate modulus and showed that stiffer substrates require lower amount of strain to detach barnacles.

In summary, this study shows that (1) dynamic surface deformation can be used as an effective, environmental friendly approach for biofouling control (2) stretchable elastomer surfaces modified with anti-fouling polymers provides a pro-active, dual-mode approach for biofouling control, and (3) incorporation of silicone-oils additives into stretchable elastomers improves the fouling-release performance of dynamic surface deformation technology. Dynamic surface deformation by itself and as a supplementary approach can be utilized biofouling management in biomedical, industrial and marine applications.

In many instances of soft tissue applications, implants based on compliant polymers have proven to exhibit superior performance over those based on stiffer polymers. Combined with the capability of 3D-printing to create complex structures, many innovative implants based on compliant polymers can be envisioned. However, current literature on 3D-printed compliant polymers is limited. The motivation behind this work is to contribute to the development of 3D-printed biomedical implants that are based on compliant, elastomeric polymer for soft tissue applications. The two aims that comprise this work look to shed light on two particularly sparse areas of study, the fatigue of elastomeric 3D-printed architected structures and the structure-property relationship of 3D-printed bioresorbable elastomeric polymer. The two aims are: 1) to investigate the behavior and durability of 3D-printed polycarbonate urethane (PCU) porous membrane under cyclic loading, and 2) to study the structure-property relationships of 3D-printed poly(L-lactide-co-ε-caprolactone).

In the first aim, the mechanical properties of bulk PCU of various grades were first characterized, followed by a comprehensive dimensional and mechanical characterization of 3D-printed PCU membranes of two different pore shapes, square and bowtie. In addition to the PCU membranes, a PCU-PETG laminate membrane were also studied. The strong dependence of bulk 3D-printed PCU’s mechanical properties on its testing environment were first shown via monotonic tensile testing. Tests of samples printed with various raster angles showed differences in the defect tolerance of each PCU grade. Cyclic loading of printed PCU membrane shows a strong dependence of fatigue performance on membrane shape and loading orientation. In certain configurations, PCU membrane exhibited comparable performance to commercial polypropylene mesh. However, the PCU membranes also showed an undesirable ratcheting under cyclic loading. A PCU-PETG laminate membrane was then shown as one approach to minimize ratcheting. In the second aim, the impact of 3D-printing and annealing processes toward PLCL morphology is first evaluated. Then, the hydrolytic degradation profile of both annealed and unannealed 3D-printed PLCL scaffolds is studied. The results show that printed samples were initially fully amorphous. Subsequent aging and annealing process induced significant change in morphology via crystallization and in turn affected its physical properties. However, degradation behavior was largely unaffected by the annealing induced crystallization.

In summary, we first demonstrated the potential of PCU membranes for use in prolapse mesh application by evaluating their mechanical properties, particularly their fatigue behavior. Then, we demonstrated the structure-property relationship of 3D-printed PLCL scaffolds, with a focus on the impact of the fabrication process on degradation behavior. The results shown here should contribute well to further development of elastomeric 3D-printed implant devices.