Thermoresponsive Semi-IPN Hydrogel Microfibers from Continuous Fluidic Processing with High Elasticity and Fast Actuation

Abstract

Hydrogels with rapid and strong response to external stimuli and possessing high elasticity and strength have been considered as platform materials for numerous applications, e.g., in biomaterials engineering. Thermoresponsive hydrogels based on semi-interpenetrating polymer networks (semi-IPN) featuring N-isopropylacrylamide with copolymers of poly(N-isopropylacrylamide-co-hydroxyethyl methacrylate) p(NIPAM-HEMA) chains are prepared and described. The copolymer was characterized by FTIR, NMR, and GPC. The semi-IPN structured hydrogel and its responsive properties were evaluated by dynamic mechanical measurements, SEM, DSC, equilibrium swelling ratio, and dynamic deswelling tests. The results illustrate that the semi-IPN structured hydrogels possess rapid response and high elasticity compared to conventional pNIPAM hydrogels. By using a microfluidic device with double coaxial laminar flow, we succeeded in fabricating temperature responsive ("smart") hydrogel microfibers with core-shell structures that exhibit typical diameters on the order of 100 μm. The diameter of the fibers can be tuned by changing the flow conditions. Such hydrogel fibers can be used to fabricate "smart" devices, and the core layer can be potentially loaded with cargos to incorporate biological function in the constructs. The platforms obtained by this approach hold promise as artificial "muscles", and also "smart" hydrogel carriers providing a unique biophysical and bioactive environment for regenerative medicine and tissue engineering.

Dynamic Mechanics‐Modulated Hydrogels to Regulate the Differentiation of Stem‐Cell Spheroids in Soft Microniches and Modeling of the Nonlinear Behavior

“…The spectrum of the nanogels exhibited main peaks at 1645 and 1540 cm −1 , which represented the chemical bond for amide I and amide II of NIPAM, respectively . The band around 1713 cm −1 was assigned to the carbonyl group of HEMA, which indicated that the poly(NIPAM‐HEMA) nanogels successfully formed (Figure S1, Supporting Information). The modulus‐cyclable hydrogel was fabricated by introducing the thermoreversible nanogel into the GelMA to form interpenetrating networks throughout UV irradiation (10 mW cm −2 , 365 nm, 80 s) in the presence of lithium acylphosphinate (LAP) as a photoinitiator, as shown in Table 1 .…”

Fast swelling behaviors of thermosensitive poly(N‐isopropylacrylamide‐co‐methacryloxyethyltrimethyl ammonium chloride)/Na2WO4 cationic composite hydrogels

“…The preparation scheme of the P(NIPAM‐ co ‐DMC)/Na 2 WO 4 hydrogel was depicted in Scheme . During the copolymerization of NIPAM and DMC in the presence of Na 2 WO 4 , WO 4 – is more inclined to interact with ammonium groups of DMC by salt bonding according to HSAB principle. As a result, the resultant NaCl was washed out to leave the hydrogel with porous structure after the washing.…”

Multifunctional temperature‐responsive polymers as advanced biomaterials and beyond

“…Liu et al . synthesized a core–shell microfiber system with a sodium alginate core and semi interpenetrating polymer network shell consisting of PNIPAAm copolymerized with poly( n ‐isopropylacrylamide‐ co ‐hydroxyethylmethacrylate), as shown in Figure . The elasticity of these microfibers was examined by attaching a load of 3.6 g at one end and raising the environmental temperature to above LCST, where the microfiber collapsed in length, and subsequently lowering the temperature, finding the microfiber returning to its original length.…”