Swelling equilibria and volume phase transition of polyelectrolyte gel with strongly dissociated groups

Advances in cellulose-based hydrogels: tunable swelling dynamics and their versatile real-time applications

Cellulose-derived hydrogels have emerged as game-changing materials in biomedical research, offering an exceptional combination of water absorption capacity, mechanical resilience, and innate biocompatibility. This review explores the intricate mechanisms that drive their swelling behaviour, unravelling how molecular interactions and network architectures work synergistically to enable efficient water retention and adaptability. Their mechanical properties are explored in depth, with a focus on innovative chemical modifications and cross-linking techniques that enhance strength, elasticity, and functional versatility. The versatility of cellulose-based hydrogels shines in applications such as wound healing, precision drug delivery, and tissue engineering, where their biodegradability, biocompatibility, and adaptability meet the demands of cutting-edge healthcare solutions. By weaving together recent breakthroughs in their development and application, this review highlights their transformative potential to redefine regenerative medicine and other biomedical fields. Ultimately, it emphasizes the urgent need for continued research to unlock the untapped capabilities of these extraordinary biomaterials, paving the way for new frontiers in healthcare innovation.

Dual-network hydrogel capsules for controlled molecular transport via pH and temperature responsiveness

We have developed innovative core-shell hydrogel capsules with a dual-network shell structure designed for precise control of molecular transport in response to external stimuli such as pH and temperature. The capsules were fabricated using a combination of microfluidic electrospray techniques and water-in-water (w/w) core-shell droplets templating. The primary network of the shell, calcium alginate (Ca-Alg), with a pKa around 3.4, exhibits sensitivity to pH. The secondary network of the shell, poly(ethylene glycol) methyl ether methacrylate (PEGMA), undergoes a volume phase transition near 60 °C. These properties enable precise molecular transport control in/out of the capsules by modulating the surface charges through varying pH and modifying pore size through temperature changes. Moreover, the dual-network shell structure not only significantly enhances the mechanical strength of the capsules but also improves their stability under external stimulus, ensuring structural integrity during the transport of molecules. This research lays the groundwork for further investigations into the multimodal stimuli-responsive hydrogel systems to control molecular transport, important in applications such as sensors and reactors for chemical cascade reactions.

A Layer-by-Layer Approach To Retain a Fluorescent Glucose Sensing Assay within the Cavity of a Hydrogel Membrane

A continuous glucose monitoring device that resides fully in the subcutaneous tissue has the potential to greatly improve the management of diabetes. Toward this goal, we have developed a competitive binding glucose sensing assay based on fluorescently labeled PEGylated concanavalin-A (PEGylated-TRITC-ConA) and mannotetraose (APTS-MT). In the present work, we sought to contain this assay within the hollow central cavity of a cylindrical hydrogel membrane, permitting eventual subcutaneous implantation and optical probing through the skin. A "self-cleaning" hydrogel was utilized because of its ability to cyclically deswell/reswell in vivo, which is expected to reduce biofouling and therefore extend the sensor lifetime. Thus, we prepared a hollow, cylindrical hydrogel based on a thermoresponsive electrostatic double network design composed of N-isopropylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid. Next, a layer-by-layer (LbL) coating was applied to the inner wall of the central cavity of the cylindrical membrane. It consisted of 5, 10, 15, 30, or 40 alternating bilayers of positively charged poly(diallyldimethylammonium chloride) and negatively charged poly(sodium 4-styrenesulfonate). With 30 bilayers, the leaching of the smaller-sized component of the assay (APTS-MT) from the membrane cavity was substantially reduced. Moreover, this LbL coating maintained glucose diffusion across the hydrogel membrane. In terms of sensor functionality, the assay housed in the hydrogel membrane cavity tracked changes in glucose concentration (0 to 600 mg/dL) with a mean absolute relative difference of ∼11%.

Self-Cleaning, Thermoresponsive P (NIPAAm-co-AMPS) Double Network Membranes for Implanted Glucose Biosensors

A self-cleaning membrane that periodically rids itself of attached cells to maintain glucose diffusion could extend the lifetime of implanted glucose biosensors. Herein, we evaluate the functionality of thermoresponsive double network (DN) hydrogel membranes based on poly(N-isopropylacrylamide) (PNIPAAm) and an electrostatic co-monomer, 2-acrylamido-2-methylpropane sulfonic acid (AMPS). DN hydrogels are comprised of a tightly crosslinked, ionized first network [P(NIPAAm-co-AMPS)] containing variable levels of AMPS (100:0-25:75 wt% ratio of NIPAAm:AMPS) and a loosely crosslinked, interpenetrating second network [PNIPAAm]. To meet the specific requirements of a subcutaneously implanted glucose biosensor, the volume phase transition temperature is tuned and essential properties, such as glucose diffusion kinetics, thermosensitivity, and cytocompatibility are evaluated. In addition, the self-cleaning functionality is demonstrated through thermally driven cell detachment from the membranes in vitro.

Magnetic thermoresponsive ionic nanogels as novel draw agents in forward osmosis

Magnetic thermosensitive ionic nanogels were prepared based on strong ionic monomer AMPS and thermosensitive monomer NIPAM via precipitation polymerization in the presence of Fe₃O₄ nanoparticles and investigated as draw solutes in FO.

Ultra-strong thermoresponsive double network hydrogels

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels are widely studied smart materials, particularly for biomedical applications, but are limited by their mechanical strength. In this study, double network (DN) hydrogels were prepared with an asymmetric crosslink design and inclusion of an electrostatic co-monomer, 2-acrylamido-2-methylpropane sulfonic acid (AMPS). These P(NIPAAm-co-AMPS)/PNIPAAm DN hydrogels were sequentially formed with a tightly crosslinked 1^st network comprised of variable levels of AMPS (100 : 0 to 25 : 75 wt% ratio of NIPAAm:AMPS) and a loosely crosslinked 2^nd network comprised of PNIPAAm. The impact of AMPS content in the 1^st network on the volume phase transition temperature (VPTT), morphology, deswelling-reswelling kinetics and mechanical properties was evaluated. Without substantially altering the VPTT of conventional PNIPAAm hydrogels but with improving thermosensitivity, the DN hydrogel formed with 25 : 75 wt% of NIPAAm:AMPS achieved exceptional strength, high modulus and high %strain at break.

Ion-permeable membrane for on-chip preconcentration and separation of cancer marker proteins

Cancer marker proteins have been electrophoretically concentrated and then separated in a microfluidic device. On-chip preconcentration was achieved using an ion-permeable membrane, consisting of acrylamide, N,N'-methylene-bisacrylamide and 2-(acrylamido)-2-methylpropanesulfonate. This negatively charged membrane was photopolymerized in the microdevice near the injection intersection. Anionic proteins were excluded from the porous membrane based on both size and charge, which concentrated target components in the injection intersection prior to separation by microchip capillary electrophoresis (μ-CE). Bovine serum albumin was used in the initial characterization of the system and showed a 40-fold enrichment in the μ-CE peak with 4 min of preconcentration. Adjustment of buffer pH enabled baseline resolution of two cancer biomarkers, α-fetoprotein (AFP) and heat shock protein 90 (HSP90), while fine control over preconcentration time limited peak broadening. Our optimized preconcentration and μ-CE approach was applied to AFP and HSP90, where enrichment factors of >10-fold were achieved with just 1 min of preconcentration. Overall, the process was simple and rapid, providing a useful tool for improving detection in microscale systems.

Hydrophobic-electrostatic balance driving the LCST offset aggregation-redissolution behavior of N-alkylacrylamide-based ionic terpolymers

A series of random terpolymers composed of N-isopropylacrylamide (NIPAAm), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and N-tert-butylacrylamide (NTBAAm) monomers were synthesized by free radical polymerization. The molar fraction of the negatively charged monomer (AMPS) was maintained constant (0.05) for all studied terpolymer compositions. Turbidity measurements were used to evaluate the influence of the relative amount of NIPAAm and NTBAAm, polymer concentration, and solution ionic strength on the cloud point and redissolution temperatures (macroscopic phase separation). Dynamic light scattering (DLS) was employed to elucidate some aspects regarding the molecular scale mechanism of the temperature-induced phase separation and to determine the low critical solution temperature (LCST). The aqueous solutions of terpolymers remained clear at all studied temperatures; turbidity was only observed in the presence of NaCl. The cloud point temperature (CPT) determined by turbidimetry was found to be systematically much higher than the LCST determined by DLS; nanosized aggregates were observed at temperatures between the LCST and the CPT. Both CPT and LCST decreased when increasing the molar ratio of NTBAAm (increased hydrophobicity). It was found that above a critical molar fraction of NTBAAm (0.25-0.30) the aggregation rate suddenly decreased. Polymers with NTBAAm content lower than 0.25 showed a fast macroscopic phase separation, but the formed large aggregates are disaggregating during the cooling ramp at temperatures still higher than the LCST. On the contrary, polymers with NTBAAm contents above 0.30 showed a slow macroscopic phase separation, and the formed large aggregates only redissolved when LCST was reached. These differences were explained on the basis of a delicate balance between the electrostatic repulsion and the hydrophobic attractive forces, which contribute cooperatively to the formation of metastable nanosized aggregates.