Thermoresponsive Hydrogels in Catalysis

Review: 54 refs.

Multifunctional and thermoresponsive methylcellulose composite hydrogels with photothermal effect

Thermo-responsive hydrogels from hyaluronic acid functionalized with poly(2-alkyl-2-oxazoline) copolymers with tuneable transition temperature

Thermo-responsive hydrogels containing poly(N-isopropylacrylamide) (PNIPAAm), reinforced both with covalent and non-covalent interactions with cellulose nanocrystals (CNC), were synthesized via free-radical polymerization in the absence of any additional cross-linkers. The properties of PNIPAAm-CNC hybrid hydrogels were dependent on the amounts of incorporated CNC. The thermal stability of the hydrogels decreased with increasing CNC content. The rheological measurement indicated that the elastic and viscous moduli of hydrogels increased with the higher amounts of CNC addition, representing stronger mechanical properties of the hydrogels. Moreover, the hydrogel injection also supported the hypothesis that CNC reinforced the hydrogels; the increased CNC content exhibited higher structural integrity upon injection. The PNIPAAm-CNC hybrid hydrogels exhibited clear thermo-responsive behavior; the volume phase transition temperature (VPTT) was in the range of 36 to 39 °C, which is close to normal human body temperature. For wound dressing purposes, metronidazole, an antibiotic and antiprotozoal often used for skin infections, was used as a target drug to study drug-loading and the release properties of the hydrogels. The hydrogels showed a good drug-loading capacity at room temperature and a burst drug release, which was followed by slow and sustained release at 37 °C. These results suggested that newly developed drugs containing injectable hydrogels are promising materials for wound dressing.

Thermoresponsive hydrogels with high elasticity and rapid response synthesized by RAFT polymerization via special crosslinking

Chapter 11 - Thermoresponsive hydrogel: a carrier for tissue engineering and regenerative medicine

Dual-crosslinked, self-healing and thermo-responsive methylcellulose/chitosan oligomer copolymer hydrogels

ObjectivesPrevious studies have exhibited the protective effects of synthesised polymers alone oras scaffold for myocardial infractions (MI) treatment. However, the exact roll of synthesised polymers when used for MI treatment...

Thermo-responsive polymer hydrogels with superior strength and toughness are potential candidate materials in biomedical field, such as drug delivery system and tissue engineering. By introducing maleylgelatin (MAGEL) into the conventional PNIPAAm hydrogel, a series of composite P(NIPAAm-co-MAGEL) hydrogels with combined features were fabricated. Thermo-responsive behaviors, equilibrium swelling ratio (ESR), compression strength, tensile strength (TS) and elongation at-break (E), cyclic compression tests, and thermal stability properties of hydrogels with different amount of MAGEL were investigated. Experimental data indicated that the amount of MAGEL could modulate the mechanical property of the composite hydrogel. With the increase of the MAGEL contents from 0 to 50%, the composite hydrogel with relatively high water content possessed good compressive strength, tensile strength and stretrability. Only when the weight ratio of MAGEL/NIPAAm was 30:70, did the P(NIPAAm-co-MAGEL) have a homogeneous distribution and stable 3D networks which played a significant role in the properties of the hydrogels. Cyclic compression tests results indicated that P(NIPAAm-co-MAGEL) hydrogel had an excellent thermo-reversible ability. This research would expand the scope of the PNIPAAm hydrogel applications.

Poloxamer hydrogels are thermoresponsive hydrogels that become fluid when cooled and gel-like when heated. Adding poloxamer 188 to a poloxamer 407 solution increases the overall gelation temperature, thereby allowing adjustments to the window of operating temperatures. The rheological properties of the poloxamer hydrogel, including gelation temperature and gelation time, were investigated, and the biocompatibility, drug release, and antibacterial properties of a gentamicin-loaded hydrogel were determined. An injectable hydrogel was successfully formulated using 20 wt% of poloxamer 407 and 3 wt% of poloxamer 188. This system became fluid at room temperature (25 °C) in the presence of deionized water; at human body temperature (37 °C), it changed to a gel-like state. The gelation time was approximately 95 seconds. The poloxamer hydrogels showed no cytotoxicity to L929 cells after seven days of culturing. A poloxamer hydrogel loaded with gentamicin sulfate, an antibiotic, was studied for its antibacterial properties against E. coli, B. cereus, S. aureus, and MRSA using gentamicin solution as the control. The results showed that the gentamicin-loaded poloxamer hydrogel inhibited bacteria from the first hour of testing. Moreover, the zone of inhibition of the gentamicin-loaded poloxamer hydrogel was larger than that of the gentamicin solution for a similar concentration of gentamicin sulfate. It can be a potent drug carrier for infected cavity wounds.

Thermoresponsive hydrogels with covalently incorporated trehalose as protein carriers

Two series of nanoclay reinforced, thermoresponsive hydrogels were prepared, one based on poly(N‐isopropylacrylamide) (PNIPA) and the other on semi‐interpenetrating networks containing PNIPA and poly(N‐vinyl pyrrolidone) (PVP), designated as SIPNs. The gels were crosslinked with 1, 3, and 5 wt % inorganic clay (hectorite) and SIPN gels additionally contained 1 wt % of PVP. The hydrogels were tested in the “as‐prepared state,” i.e., at 10 wt % PNIPA concentration in water and at equilibrium (maximum) swelling. Increasing the concentration of nanoclays increases crosslink density, modulus, tensile strength, elongation (except in equilibrium swollen gels), hysteresis and with decreases in the degree of swelling, broadening of the phase transition region, and a decrease in elastic recovery at high deformations. The presence of linear PVP in the networks increases porosity and the pore size, increases swelling, deswelling rates, and hysteresis, but decreases slightly lower critical solution temperature (LCST), tensile strength, elongation, and elastic recovery. The strongest hydrogels were ones with 10 wt % PNIPA and 5 wt % of nanoclays, displaying tensile strengths of 85 kPa and elongation of 955%. All properties of hydrogels at the equilibrium swollen state are lower than in the as‐prepared state, due to the lower concentration of chains per unit volume, but the trends are preserved. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thermoresponsive hydrogels based on ionic cellulose/chitosan are widely used various fields, such as smart windows and tissue engineering, while the effect of carbohydrate backbones of cellulose/chitosan on the thermal response and mechanical properties of hydrogels has received less attention so far. Herein, poly(2(dimethylamino)ethyl methacrylate) (PDMAEMA)-grafted cellulose sulfate (P-CS) and PDMAEMA-grafted chitosan sulfate (P-CHS) as research models are successfully synthesized through multi-step reactions. The P-CS and P-CHS polymers are further applied in crosslinked polyacrylamide networks, resulting in the P-CS and P-CHS hydrogels. Compared to P-CS hydrogels, P-CHS hydrogels could obviously block the transmission of visible light when the temperature is changed from 25 to 42 °C. In contrast to P-CHS hydrogels, the P-CS hydrogels change easily from soft and weak state to stiff and strong state according to their mechanical behaviors. These results indicate that different carbohydrate backbones of cellulose and chitosan should have caused distinct aggregation behaviors of corresponding P-CS and P-CHS hydrogels, which are accompanied by different light transmittance and mechanical properties.Graphical abstract Thermoresponsive hydrogels using PDMAEMA-grafted ionic cellulose sulfate (P-CS) and chitosan sulfate (P-CHS) are successfully prepared. Distinct carbohydrate backbone displayed different effects on the thermoresponsive and mechanical properties of hydrogels.

Loss of skeletal muscle tissue caused by traumatic injury or damage due to myopathies produces a deficit of muscle function for which there is still no clinical treatment. Transplantation of myogenic cells, themselves or combined with materials, has been proposed to increase the regenerative capacity of skeletal muscle but it is hampered by many limitations, such as low cell survival and engraftment or immunological reaction and low biocompatibility of the exogenous materials. Recently, myoblast sheet engineering, obtained with thermoresponsive culture dishes, has attracted attention as a new technique for muscle damage treatment. For this purpose, a series of thermoresponsive hydrogels, constituted by poly(N-isopropylacrylamide-co-2-hydroxyethylmethacrylate) [p(NIPAAM-co-HEMA)] were synthesized by a simple and inexpensive free-radical polymerization of the two co-monomers with a redox initiator. Different ratios of N-isopropylacrylamide (NIPAAm) and 2-hydroxyethylmethacrylate (HEMA) have been examined to evaluate the effects on physicochemical, mechanical and optical hydrogel properties. The murine muscle cell line C2 C12 has been exploited to test the cytotoxicity of the thermoresponsive hydrogels, depending on different synthesis conditions. In this study, we have identified a thermoresponsive hydrogel that allows cell adhesion and viability, together with the detachment of viable sheet of muscle cells, giving the chance to develop further applications for muscle damage and disease. Copyright © 2014 John Wiley & Sons, Ltd.

Controlling the properties of radiation-synthesized thermoresponsive oligoether methacrylate hydrogels by varying the monomer side-chain length; self-composite network containing crystalline phase