Biotechnical Properties of Poly(HEMA-co-HPMA) Hydrogels Are Governed by Distribution among Water States

Abstract

Controlling the biotechnical properties of synthetic hydrogels allows their application in a wide range of biomedical fields. Cross-linker concentration and monomer mole ratio of poly­(2-hydroxyethylmethacrylate-co-N-(2-hydroxypropyl) methacrylamide) [poly­(HEMA-co-HPMA)]-based hydrogels were used to control the degree of hydration and water distribution within constructs. Cross-linker concentrations corresponding to 0.1, 0.5, 1.0, and 3.0 mol % tetraethylene glycol (TEGDA) with HEMA/HPMA mole ratios of 1:0 and 4:1, and poly­(HEMA-co-HPMA) of cross-linker concentration corresponding to 1.0 mol % TEGDA with a HEMA/HPMA ratio of 1:1 were investigated for their degree of hydration, water distribution, and corresponding physiochemical and mechanical properties. Copolymerization of HEMA and HPMA was confirmed by Fourier-transform infrared spectroscopy. Both cross-linker concentration and chemical composition (HEMA/HPMA) systematically changed the water content and free/bound water distribution in the polymer, which resulted in different biochemical and transport properties. The addition of 20% HPMA (poly­(HEMA-co-HPMA) (4:1)) increased total hydration (25%) and glass-transition temperature (9%) and decreased elastic modulus (31%) and nonfreezable bound water (33%) of the hydrogel. Increasing cross-linker concentration resulted in a stiffer hydrogel with less total water but larger nonfreezable water content. Evaluation of poly­(HEMA-co-HPMA) (1:1) revealed that further increase of HPMA content increased the degree of hydration by 25% and decreased nonfreezable water content and elastic modulus by 33 and 16%, respectively, compared to that of poly­(HEMA-co-HPMA) (4:1). The hydrogel correspondingly had a higher void fraction and rougher freeze-fractured surface. The diffusion-related processes depended more on water distribution within the hydrogel. The poly­(HEMA) showed the fastest swelling kinetics with a concomitant burst release profile of fluorescein isothiocyanate–dextran (a drug surrogate), while the compositions containing HPMA showed a sustained release pattern. The biotechnical properties are illustrative examples of key properties that are influenced by the water distribution rather than the absolute water content of hydrogels.

Development of Thermoinks for 4D Direct Printing of Temperature‐Induced Self‐Rolling Hydrogel Actuators

“…A decrease in crosslinker concentration enables higher hydrogel expansion and water absorption. [ 47 ] Although the addition of the hydrophilic crosslinker did not affect the microporosity of the hydrogels, it insignificantly increased the swelling degree of the hydrogels because of the enhanced overall hydrophilicity of the polymeric backbone (Figure S2b, Supporting Information). Similarly to samples S1–S4, increasing nanoclay concentrations significantly reduced the swelling ratio of the hydrogels from 5.0 ± 0.1 (S5) to 4.6 ± 0.0 (S7) at 12 °C but seemed not to affect the water content at 42 °C.…”

“…It had also one of the highest Young's moduli, which suggests that the water content of the hydrogels controlled their mechanical properties. [ 47 ] The swelling ratio decreases with the increase in the concentration of polymer in hydrogel composition. The interpenetrating network of alginate and PNIPAAm has a denser structure than its alginate‐less equivalent.…”

The Role of Thermal Accumulation on the Fabrication of Diffraction Gratings in Ophthalmic PHEMA by Ultrashort Laser Direct Writing

“…The repetition rate at which the cross over from non-thermal to the thermal regime is produced is called the critical frequency and can be estimated as [ 20 ]: where D th is the thermal diffusivity and d laser is the laser beam diameter at the focal plane. The thermal diffusivity of PHEMA polymers ranges 10 −7 m 2 /s [ 41 ]. In the case of a diffraction-limited focusing by a numerical aperture lens, the minimum waist diameter is given by d 0 = 2⸱1.22⸱ λ / NA [ 11 ] giving rise to beam diameters of 4.6, 4.3, and 2.3 µm for 796, 750, and 400 nm, respectively.…”

Carbon coated Nickel Nanoparticles in Polyacrylamide Ferrogels: Interaction with Polymeric Network and Impact on Swelling

“…If applied to the specific surface area of the MNPs in air-dry powder equation (1) gives the average value of the diameter for the ensemble of MNPs. If S is in m 2 /g and r is in g/cm 3 equation (1) yields the average diameter in micron.…”

“…Despite the fact that it contains large amount of water, hydrogel is not a fluid but an elastic material maintaining its shape. Due to their unique properties such as mechanical elasticity, softness, and biocompatibility, hydrogels have been applied in a variety of fields, including smart devices that respond to stimuli and soft actuators in biomedicine and agriculture [1,2].…”