(G-250) CONTROLLING SWELLING/SHRINKING OF HYDROGEL USING POLY(DIMETHYLSILOXANE) NANOFIBER ENCAPSULATION FOR WOUND HEALING APPLICATIONS

Introduction:: The human body has a delicate self-defense mechanism against wounds via hemostasis, inflammation, proliferation, and remodeling [1]. Interruptions (e.g., neuropathy, poor circulation, difficulty moving, and repeated mechanical stress/strain) to such process may cause a time-consuming and expensive problem in the form of chronic wounds [2]. Current treatment plans follow a process of inflammation reduction, debridement, biological manipulations such as collagen injections, and finally amputation if all other methods fail [3]. However, regulating the natural wound-healing process in the early phase is more important before amputations to increase the quality of life. In this abstract, we report a hydrogel-based wound healing strategy. The hydrogel responds to the wound state, i.e., pH, in real-time and swells or shrinks to, for example, deliver localized treatment via microneedle (Fig. 1 (a)). Furthermore, the hydrogel is encapsulated in electrospun poly(dimethylsiloxane) (PDMS) nanofibrous membrane to provide high precision in swelling and shrinking behavior, reducing the variance by 3-fold (Fig. 1 (b)).


Materials and Methods:: Hydrogel swelling and shrinking are often irregular and hard to control. To increase precision in hydrogel actuation, we encapsulate it in a nanofiber membrane. To achieve this, a thin square mold (12 ´ 12 ´ 0.6 mm³) was coated with electrospun PDMS nanofibers and treated with gamma-methacryloxyproplytrimethoxysilane (MPS, Sigma) to promote hydrogel adhesion. For PDMS nanofibers, we utilized a coaxial electrospinning technique involving core and sheath fibers (Fig. 2) [4]. Specifically, we used polyvinylpyrrolidone (PVP) in N,N-Dimethylmethanamide (DMF, Sigma) at 40% weight creating our sheath. PVP was selected due to its ease of electrospinning and dissolvability in water [4]. For the core, pre-gel PDMS (Sylgard 184) was mixed in a 95% weight solution in Tetrahydrofuran (THF, Sigma). Core and sheath pre-gel solutions were fed into a coaxial stainless-steel spinneret (Ramé Hart, 100-10-COAXIAL-2217) at a ratio of 1.25: 0.5 ml/hr (PVP: PDMS); allowing the PVP solution to coat the PDMS solution as it exited the spinneret. At a potential of 15kV between the spinneret and collector, the fibers stretched and deposited onto a heated mold forming a nanofiber mat. Lastly, the hydrogel was cast on the PDMS nanofiber-coated mold to complete the encapsulation (Fig 2).



The hydrogel is prepared by pre-gel solutions consisting of acrylamide (AAm, Sigma), methacrylic acid (mAA, Sigma), tetramethylethylenediamine (accelerator, Sigma) and N,N’-methylenebisacrylamide (crosslinker, Sigma). The internal acidic ionic chains build up charge when external conditions contain a higher ionization. Lower pH values increase charge and push the acidic chains away, resulting in swelling [5].


Results, Conclusions, and Discussions:: Applying a nanofiber membrane on a hydrogel actuator base was anticipated to increase precision in swelling and shrinking behavior despite restricting the overall actuation. After pre-swelling in deionized water (pH 7), both control (bare hydrogel) and the PDMS nanofiber-coated hydrogels were introduced to a pH 10 solution, which mimics chronic wounds (swelling) [6]. The changes in height were monitored via photographing every 2 minutes for 4 hours. While both control (bare hydrogel) and PDMS nanofiber-encapsulated hydrogel exhibited swelling (Fig. 3 (a)), the control showed a net displacement of 461 µm, and PDMS nanofiber-coated hydrogel exhibited 122 µm. Such a decrease in displacement can be attributed to the constriction caused by nanofiber and its additional weight. It is noted that, however, the encapsulated hydrogel did eventually reach 415 µm after 14 hours. Despite sacrificing the total displacement, the PDMS nanofiber improved swelling variation across the entire hydrogel film (Fig. 3 (b)). The PDMS nanofiber-coated hydrogel produced a variation in displacements of 36.94 µm, which is a three times improvement compared to the control (113.45 µm). Our future work includes increasing this displacement and integrating microneedles into each cell.


Acknowledgements (Optional): : The project was supported by the National Science Foundation (ECCS- 2245092)


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