Laser-Assisted Micromachining of Hydrogel Films for Biomedical Applications
thesisposted on 03.01.2019 by Hongjie Jiang
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Hydrogels are soft polymers comprising of a three-dimensional network capable of absorbing significant amount of water or other aqueous bio-fluids. A group of hydrogels, commonly referred to as “environmentally-sensitive hydrogels” are designed such that they can undergo reversible volume change in response to a variety of physical and chemical stimuli. Although mechanically soft, embedding organic and inorganic micro and nanoparticles into the hydrogel network increases their mechanical strength. Hydrogels have been extensively explored as scaffolding for tissue engineering or smart materials for biomedical transducers. Hydrogels in the mm-scale are typically associated with a slow response time. At micro-scale, however, they can be fast and useful as smart sensors and actuators. Several micromachining techniques have been employed to pattern thin films of hydrogel. Micro-patterning methods are based on traditional fabrication techniques such as lithography, etching, and micro-molding. These methods are time consuming, expensive, and do not scale well to large production. In addition, they have limitations as related to processing composite gels (e.g., UV light cannot penetrate through the gel and particles can mask dry etch). In this work, we outline a doctoral research aimed at alternative solution based on direct laser patterning, allowing low cost, fast, and scalable fabrication for mass production.
We characterized and analyzed a series of transient features of the laser-engineered patterns, including the ablated width, sidewall quality and resolution, as a function of laser beam parameters and hydrogel thermal & optical properties by laser-machining the hydrogels at different moisture level of hydrogels till fully dry at an interval of one hour. All the optimal patterns appear at 1-2 hours of drying (hydrogel losing 35%-65% weight), thus identifying an optimal window for a rapid end-to-end fabrication. Then, two types of composite gels were created and laser engineered, consisting of nano-iron particles embedded hydrogel (“ferrogel”) and micro-silica beads loaded hydrogel (“silicagel”); the results show comparable features similar to the bare hydrogel, confirming the processability of laser micro-machining on the composite gels. Next, we studiedthe swelling kinetics of the laser-machined hydrogels and identified tradeoffs between swelling speed and mechanical force. At the final, we used the laser patterning method to design and fabricate two pH-regulated autonomous drug delivery devices, a 3D printed smart capsule for targeted drug delivery in small intestine and a flexible patch for delivering antibiotics to infected chronic wounds. In both cases, their delivery capabilities can be tuned by either controlling the spatial resolution of the hydrogel actuator (the former) or using an n × n array (the latter).