Agarose hydrogels embedded with pH-responsive diblock copolymer micelles for triggered release of substances

Emerging horizons and prospects of polysaccharide-constructed gels in the realm of wound healing

Polysaccharides, with the abundant availability, biodegradability, and inherent safety, offer a vast array of promising applications. Leveraging the remarkable attributes of polysaccharides, biomimetic and multifunctional hydrogels have emerged as a compelling avenue for efficacious wound dressing. The gels emulate the innate extracellular biomatrix as well as foster cellular proliferation. The distinctive structural compositions and profusion of functional groups within polysaccharides confer excellent physical/chemical traits as well as distinct restorative involvements. Gels crafted from polysaccharide matrixes serve as a robust defense against bacterial threats, effectively shielding wounds from harm. This comprehensive review delves into wound physiology, accentuating the significance of numerous polysaccharide-based gels in the wound healing context. The discourse encompasses an exploration of polysaccharide hydrogels tailored for diverse wound types, along with an examination of various therapeutic agents encapsulated within hydrogels to facilitate wound repair, incorporating recent patent developments. Within the scope of this manuscript, the perspective of these captivating gels for promoting optimal healing of wounds is vividly depicted. Nevertheless, the pursuit of knowledge remains ongoing, as further research is warranted to bioengineer progressive polysaccharide gels imbued with adaptable features. Such endeavors hold the promise of unlocking substantial potential within the realm of wound healing, propelling us toward multifaceted and sophisticated solutions.

Ionic Strength Impacts the Physical Properties of Agarose Hydrogels

Agarose is a natural polysaccharide known for its ability to form thermoreversible hydrogels. While the effects of curing temperature and polysaccharide concentration on mechanical properties have been discussed in the literature, the role of ionic strength has been less studied. In the present manuscript, we investigate the effects of supporting salt concentration and the role of cation (i.e. Na+ or Li+, neighbors in the Hofmeister series), on the setting and performance of agarose hydrogels. Compressive and rheological measurements show that the supporting salts reduce the immediate elastic response of agarose hydrogels, with Li+ showing a stronger effect than Na+ at high ionic strength, while they significantly increase the extent of linear stress-strain response (i.e., linear elasticity). The presence of increasing amounts of added supporting salt also leads to a reduction in hysteresis during mechanical deformation due to loading and unloading cycles, which is more pronounced with Li+ than with Na+. The combination of rheological measurements and NMR relaxometry shows a mesh size in agarose hydrogels in the order of 6-17 nm, with a thickness of the water layer bound to the biopolymer of about 3 nm. Of note, the different structuring of the water within the hydrogel network due to the different alkali seems to play a role for the final performance of the hydrogels.

Controlled Quenching of Agarose Defines Hydrogels with Tunable Structural, Bulk Mechanical, Surface Nanomechanical, and Cell Response in 2D Cultures

The scaffolding of agarose hydrogel networks depends critically on the rate of cooling (quenching) after heating. Efforts are made to understand the kinetics and evolution of biopolymer self-assembly upon cooling, but information is lacking on whether quenching might affect the final hydrogel structure and performance. Here, a material strategy for the fine modulation of quenching that involves temperature-curing steps of agarose is reported. Combining microscopy techniques, standard and advanced macro/nanomechanical tools, it is revealed that agarose accumulates on the surface when the curing temperature is set at 121 °C. The inhomogeneity can be mostly recovered when it is reduced to 42 °C. This has a drastic effect on the stiffness of the surface, but not on the viscoelasticity, roughness, and wettability. When hydrogels are strained at small/large deformations, the curing temperature has no effect on the viscoelastic response of the hydrogel bulk but does play a role in the onset of the non-linear region. Cells cultured on these hydrogels exhibit surface stiffness-sensing that affects cell adhesion, spreading, F-actin fiber tension, and assembly of vinculin-rich focal adhesions. Collectively, the results indicate that the temperature curing of agarose is an efficient strategy to produce networks with tunable mechanics and is suitable for mechanobiology studies.

Polysaccharide based transdermal patches for chronic wound healing: Recent advances and clinical perspective

Polysaccharides form a major class of natural polymers with diverse applications in biomedical science and tissue engineering. One of the key thrust areas for polysaccharide materials is skin tissue engineering and regeneration, whose market is estimated to reach around 31 billion USD globally by 2030, with a compounded annual growth rate of 10.46 %. Out of this, chronic wound healing and management is a major concern, especially for underdeveloped and developing nations, mainly due to poor access to medical interventions for such societies. Polysaccharide materials have shown promising results and clinical potential in recent decades with regard to chronic wound healing. Their low cost, ease of fabrication, biodegradability, and ability to form hydrogels make them ideal candidates for managing and healing such difficult-to-heal wounds. The present review presents a summary of the recently explored polysaccharide-based transdermal patches for managing and healing chronic wounds. Their efficacy and potency of healing both as active and passive wound dressings are evaluated in several in-vitro and in-vivo models. Finally, their clinical performances and future challenges are summarized to draw a road map towards their role in advanced wound care.

A novel pH-responsive nanoniosomal emulsion for sustained release of curcumin from a chitosan-based nanocarrier: emphasis on the concurrent improvement of loading, sustained release, and apoptosis induction

Curcumin application as an anti-cancer drug is faced with several impediments. This study has developed a platform that facilitates the sustained release of curcumin, improves loading efficiency, and anti-cancer activity. Montmorillonite (MMT) nanoparticles were added to chitosan (CS)-agarose (Aga) hydrogel and then loaded with curcumin (Cur) to prepare a curcumin-loaded nanocomposite hydrogel. The loading capacity increased from 63% to 76% by adding MMT nanoparticles to a chitosan-agarose hydrogel. Loading the fabricated nanocomposite in the nanoniosomal emulsion resulted in sustained release of curcumin under acidic conditions. Release kinetics analysis showed diffusion and erosion are the dominant release mechanisms, indicating non-fickian (or anomalous) transport based on the Korsmeyer-Peppas model. FTIR spectra confirmed that all nanocomposite components were present in the fabricated nanocomposite. Besides, XRD results corroborated the amorphous structure of the prepared nanocomposite. Zeta potential results corroborated the stability of the fabricated nanocarrier. Cytotoxicity of the prepared CS-Aga-MMT-Cur on MCF-7 cells was comparable to that of curcumin-treated cells (p <0.001). Moreover, the percentage of apoptotic cells increased due to the enhanced release profile resulting from the addition of MMT to the hydrogel and the incorporation of the fabricated nanocomposite into the nanoniosomal emulsion. To recapitulate, the current delivery platform improved loading, sustained release, and curcumin anti-cancer effect. Hence, this platform could be a potential candidate to mitigate cancer therapy restrictions with curcumin. This article is protected by copyright. All rights reserved.

Diffusion of dyes in polyelectrolyte-surfactant hydrogels

In this work, hydrogels formed by interaction of biopolymeric electrolytes and oppositely charged surfactants are studied from the point of view of their ability to incorporate model hydrophobic dyes in their micelle-like structure. Two types of hydrogels were investigated. The first type was based on cationized dextran cross-linked by sodium dodecylsulphate. The second type was prepared by interactions of hyaluronan with carbethoxypendecinium bromide (septonex). Nile red and Atto488 were used as model dyes for the diffusion experiments. The dyes were dissolved in two different media: surfactant and physiological saline. The diffusion of dyes into hydrogel was monitored over time. Effective diffusion coefficients were determined. It was found that their values are strongly influenced by the hydrogel character, the types of dye used and the solvent. The obtained effective coefficients were higher in comparison with the values determined for the diffusion in the opposite direction (release from the hydrogel). The dyes are presented as free in physiological saline and in the form of micelles or micelle aggregates in surfactants. During diffusion into the hydrogel, they can be gradually incorporated in a "pearl necklace structure" which suppresses their mobility. In contrast, this partial immobilization of dyes can increase the concentration gradient which is a driving force of diffusion. Also, the gradual incorporation of dyes into hydrogel structures influences the values of the effective diffusion coefficients.

Multicompartment Hydrogels

Hydrogels belong to the most promising materials in polymer and materials science at the moment. As they feature soft and tissue-like character as well as high water-content, a broad range of applications are addressed with hydrogels, e.g. tissue engineering and wound dressings but also soft robotics, drug delivery, actuators and catalysis. Ways to tailor hydrogel properties are crosslinking mechanism, hydrogel shape and reinforcement, but new features can be introduced by variation of hydrogel composition as well, e.g. via monomer choice, functionalization or compartmentalization. Especially, multicompartment hydrogels drive progress towards complex and highly functional soft materials. In the present review the latest developments in multicompartment hydrogels are highlighted with a focus on three types of compartments, i.e. micellar/vesicular, droplets or multi-layers including various sub-categories. Furthermore, several morphologies of compartmentalized hydrogels and applications of multicompartment hydrogels will be discussed as well. Finally, an outlook towards future developments of the field will be given. The further development of multicompartment hydrogels is highly relevant for a broad range of applications and will have a significant impact on biomedicine and organic devices. This article is protected by copyright. All rights reserved.

Supramolecular Polymer Nanocomposites for Biomedical Applications

Polymer nanocomposites, a class of innovative materials formed by polymer matrixes and nanoscaled fillers (e.g., carbon-based nanomaterials, inorganic/semiconductor nanoparticles, metal/metal-oxide nanoparticles, polymeric nanostructures, etc.), display enhanced mechanical, optoelectrical, magnetic, catalytic, and bio-related characteristics, thereby finding a wide range of applications in the biomedical field. In particular, the concept of supramolecular chemistry has been introduced into polymer nanocomposites, which creates myriad “smart” biomedical materials with unique physicochemical properties and dynamic tunable structures in response to diverse external stimuli. This review aims to provide an overview of the chemical composition, morphological structures, biological functionalities, and reinforced performances of supramolecular polymer nanocomposites. Additionally, recent advances in biomedical applications such as therapeutic delivery, bioimaging, and tissue engineering are also discussed, especially their excellent properties leveraged in the development of multifunctional intelligent biomedical materials.

Photo-Responsive Polymersomes as Drug Delivery System for Potential Medical Applications

Due to a strong retardation effect of o-nitrobenzyl ester on polymerization, it is still a great challenge to prepare amphiphilic block copolymers for polymersomes with a o-nitrobenzyl ester-based hydrophobic block. Herein, we present one such solution to prepare amphiphilic block copolymers with pure poly (o-nitrobenzyl acrylate) (PNBA) as the hydrophobic block and poly (N,N'-dimethylacrylamide) (PDMA) as the hydrophilic block using bulk reversible addition-fragmentation chain transfer (RAFT) polymerization of o-nitrobenzyl acrylate using a PDMA macro-RAFT agent. The developed amphiphilic block copolymers have a suitable hydrophobic/hydrophilic ratio and can self-assemble into photoresponsive polymersomes for co-loading hydrophobic and hydrophilic cargos into hydrophobic membranes and aqueous compartments of the polymersomes. The polymersomes demonstrate a clear photo-responsive characteristic. Exposure to light irradiation at 365 nm can trigger a photocleavage reaction of o-nitrobenzyl groups, which results in dissociation of the polymersomes with simultaneous co-release of hydrophilic and hydrophobic cargoes on demand. Therefore, these polymersomes have great potential as a smart drug delivery nanocarrier for controllable loading and releasing of hydrophilic and hydrophobic drug molecules. Moreover, taking advantage of the conditional releasing of hydrophilic and hydrophobic drugs, the drug delivery system has potential use in medical applications such as cancer therapy.

Nanocomposite hydrogel with NIR/magnet/enzyme multiple responsiveness to accurately manipulate local drugs for on-demand tumor therapy

Chemotherapy is one of the most commonly utilized approaches to treat malignant tumor. However, the well-controlled chemotherapy able to accurately manipulate local drugs for on-demand tumor treatment is still a challenge. Herein, a magnet and light dual-responsive hydrogel combining thermosensitive poly(N-acryloyl glycinamide) (PNAGA), doxorubicin (DOX) loaded and polyester (PE) capped mesoporous silica nanocarriers (MSNs) as well as Fe₃O₄ nanoparticles (Fe₃O₄ NPs) grafted graphene oxide (GO) was fabricated to address above issue. The Fe₃O₄ NPs and GO respectively serve as magnetothermal agent and photothermal agent to perform hyperthermia, meanwhile to generate chain motion of PNAGA with varying degrees under different conditions of magnetic field and/or NIR irradiation. This strategy not only allowed the gel-sol transition of the hydrogel by prior heating for tumor injection, but performed controllable release routes of DOX-MSNs-PE (DMP for short) nanocarriers to meet various requirements from different patients and the changing states of tumor. Furthermore, these escaped DMP nanocarriers could be taken by surrounding tumor cells, and then deliver their drug to these cells after rapid hydrolysis of the PE cap triggered by esterase, resulting in accurate chemotherapy. Both in vitro and in vivo results indicated that the PNAGA-DMP-Fe₃O₄@GO hydrogel combining well-controllable chemotherapy and hyperthermia can eliminate more than 90% tumor cells and effectively inhibit the tumor growth in mice model, demonstrating the great candidate of our hydrogel for accurate tumor therapy.

Agarose-based biomaterials for advanced drug delivery

Agarose is a prominent marine polysaccharide representing reversible thermogelling behavior, outstanding mechanical properties, high bioactivity, and switchable chemical reactivity for functionalization. As a result, agarose has received particular attention in the fabrication of advanced delivery systems as sophisticated carriers for therapeutic agents. The ever-growing use of agarose-based biomaterials for drug delivery systems resulted in rapid growth in the number of related publications, however still, a long way should be paved to achieve FDA approval for most of the proposed products. This review aims at a classification of agarose-based biomaterials and their derivatives applicable for controlled/targeted drug delivery purposes. Moreover, it attempts to deal with opportunities and challenges associated with the future developments ahead of agarose-based biomaterials in the realm of advanced drug delivery. Undoubtedly, this class of biomaterials needs further advancement, and a lot of critical questions have yet to be answered.

Dynamic-Covalent Hydrogel with NIR-Triggered Drug Delivery for Localized Chemo-Photothermal Combination Therapy

Near-infrared (NIR) light-responsive, injectable hydrogels are among the most promising drug delivery systems for localized anticancer therapy owing to its minimally invasive administration and remote-controlled manner. However, most currently reported NIR-responsive hydrogels were usually generated through physical mixing of thermosensitive polymers and photothermal conversion agents. In this study, a novel type of dynamic-covalent hydrogel (GelPV-DOX-DBNP) with NIR light-triggered drug release behavior was rationally designed for chemo-photothermal combination treatment of tumors. Concretely, this NIR-responsive hydrogel was formed by specific benzoxaborole-carbohydrate interactions between benzoxaborole (BOB)-modified hyaluronic acid (BOB-HA) and fructose-based glycopolymer (PolyFru), where photosensitizer perylene diimide zwitterionic polymer (PDS), reductant ascorbic acid (Vc), anticancer drug doxorubicin (DOX) as well as photothermal nanoparticles (DB-NPs) were encapsulated, simultaneously. Upon 660 nm light irradiation, both PDS and Vc within the designed hydrogel can convert oxygen into hydrogen peroxide, which could make hydrogel be degraded through the breakage of dynamic covalent bonds based on benzoxaborole-carbohydrate interactions, leading to NIR light-activatable release of DOX and DB-NPs from GelPV-DOX-DBNP. Furthermore, the released DB-NPs can convert 915 nm light irradiation into heat, enabling the application of GelPV-DOX-DBNP as a NIR-responsive drug delivery platform for both chemotherapy and photothermal therapy (PTT). In vivo results prove that GelPV-DOX-DBNP exhibited a markedly enhanced chemo-photothermal synergistic therapy for 4T1 tumor model mice, compared to chemotherapy alone or PTT. This work presents a new strategy to construct NIR light-responsive hydrogel as one alternative drug delivery system for anticancer applications.

Bidirectional transfer of particles across liquid-liquid interface under electric pulse

HYPOTHESIS

The controllable transfer of colloidal particles across liquid-liquid interfaces has attracted great interests in synthesis of new materials and stabilization of emulsions. Can we find new ways of controlled transferring particles across liquid-liquid interface with reversible transfer directions and size manipulation?

EXPERIMENTS

A technique of bidirectional transfer of colloidal particles in an aqueous two-phase system (ATPS) under electric pulse was developed. The influences of electric pulse, ATPS composition, surfactant concentration, ionic strength and particle size on the particle transfer were investigated systematically.

FINDINGS

Under electric pulses, particles overcome the energy barrier at the liquid-liquid interface and transfer into the other phase. The action of particle transfer is determined by the voltage of electric pulse, and the transfer direction is reversible by exchanging the direction of electric pulse. The ATPS composition, surfactant concentration, ionic strength and particle size affect the particle transfer by changing the free energy of particle detachment. With this method, the targeted transfer of particles by size can be realized by controlling the strength of electric pulse. The proposed method provides a promising technique for transfer of particles across liquid-liquid interface with advantages of fast response and precise control.

A Macroscopic Diffusion-Based Gradient Generator to Establish Concentration Gradients of Soluble Molecules Within Hydrogel Scaffolds for Cell Culture

Concentration gradients of soluble molecules are ubiquitous within the living body and known to govern a number of key biological processes. This has motivated the development of numerous in vitro gradient-generators allowing researchers to study cellular response in a precise, controlled environment. Despite this, there remains a current paucity of simplistic, convenient devices capable of generating biologically relevant concentration gradients for cell culture assays. Here, we present the design and fabrication of a compartmentalized polydimethylsiloxane diffusion-based gradient generator capable of sustaining concentration gradients of soluble molecules within thick (5 mm) and thin (2 mm) agarose and agarose-collagen co-gel matrices. The presence of collagen within the agarose-collagen co-gel increased the mechanical properties of the gel. Our model molecules sodium fluorescein (376 Da) and FITC-Dextran (10 kDa) quickly established a concentration gradient that was maintained out to 96 h, with 24 hourly replenishment of the source and sink reservoirs. FITC-Dextran (40 kDa) took longer to establish in all hydrogel setups. The steepness of gradients generated are within appropriate range to elicit response in certain cell types. The compatibility of our platform with cell culture was demonstrated using a LIVE/DEAD® assay on terminally differentiated SH-SY5Y neurons. We believe this device presents as a convenient and useful tool that can be easily adopted for study of cellular response in gradient-based assays.

Agarose-based biomaterials for tissue engineering

Agarose is a natural polysaccharide polymer having unique characteristics that give reason to consider it for tissue engineering applications. Special characteristics of agarose such as its excellent biocompatibility, thermo-reversible gelation behavior and physiochemical features support its use as a biomaterial for cell growth and/or controlled/localized drug delivery. The resemblance of this natural carbohydrate polymer to the extracellular matrix results in attractive features that bring about a strong interest in its usage in the field. The scope of this review is to summarize the extensive researches addressing agarose-based biomaterials in order to provide an in-depth understanding of its tissue engineering-related applications.

Light-Induced Hydrogel Based on Tumor-Targeting Mesoporous Silica Nanoparticles as a Theranostic Platform for Sustained Cancer Treatment

Herein, we report a facile fabrication of a polymer (azobenzene and α-cyclodextrin-functionalized hyaluronic acid) and gold nanobipyramids (AuNBs) conjugated mesoporous silica nanoparticles (MSNs) to be used as an injectable drug delivery system for sustained cancer treatment. Because of the specific affinity between the hyaluronic acid (HA) on MSNs and the CD44 antigen overexpressed on tumor cells, the MSNs can selectively attach to tumor cells. The nanocomposite material then exploits thermoresponsive interactions between α-cyclodextrin and azobenzene, and the photothermal properties of gold nanobipyramids, to in situ self-assemble into a hydrogel under near-infrared (NIR) radiation. Upon gelation, the drug (doxorubicin)-loaded MSNs carriers were enclosed in the HA network of the hydrogel, whereas further degradation of the HA in the hydrogel due to the upregulation of hyaluronidase (HAase) around the tumor tissue will result in the release of MSNs from the hydrogel, which can then be taken by tumor cells and deliver their drug to the cell nuclei. This design is able to provide a microenvironment with rich anticancer drugs in, and around, the tumor tissue for time periods long enough to prevent the recrudescence of the disease. The extra efficacy that this strategy affords builds upon the capabilities of conventional therapies.

Composites of Polymer Hydrogels and Nanoparticulate Systems for Biomedical and Pharmaceutical Applications

Due to their unique structures and properties, three-dimensional hydrogels and nanostructured particles have been widely studied and shown a very high potential for medical, therapeutic and diagnostic applications. However, hydrogels and nanoparticulate systems have respective disadvantages that limit their widespread applications. Recently, the incorporation of nanostructured fillers into hydrogels has been developed as an innovative means for the creation of novel materials with diverse functionality in order to meet new challenges. In this review, the fundamentals of hydrogels and nanoparticles (NPs) were briefly discussed, and then we comprehensively summarized recent advances in the design, synthesis, functionalization and application of nanocomposite hydrogels with enhanced mechanical, biological and physicochemical properties. Moreover, the current challenges and future opportunities for the use of these promising materials in the biomedical sector, especially the nanocomposite hydrogels produced from hydrogels and polymeric NPs, are discussed.

Functional modification mediated value addition of seaweed polysaccharides – a perspective

Value addition of seaweed polysaccharides by their functional modification with various substrates leading to new effects.

Insight in the phase separation peculiarities of poly(dialkylaminoethyl methacrylate)s

The thermoresponsive and pH-sensitive behavior of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA), and poly(N,N-diisopropylaminoethyl methacrylate) (PDiPAEMA) is compared by use of different techniques. We employed temperature- and pH-dependent turbidimetry, fluorescence spectroscopy (of the polarity indicator 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran, 4HP, which is sometimes also abbreviated as DCM), and IR spectroscopy (of the carbonyl band). Within specific pH windows, all polymers showed phase separation at elevated temperatures (showing a lower critical solution temperature behavior, an LCST behavior). By increasing the hydrophobicity of the dialkylaminoethyl substituent, the phase separation is shifted to lower pH (at constant temperatures; pH(PDMAEMA) > pH(PDEAEMA) > pH(PDiPAEMA)) or to lower temperatures (at constant pH; T(PDMAEMA) > T(PDEAEMA) > T(PDiPAEMA)). While PDMAEMA does not exhibit pronounced changes in polarity upon phase separation (as seen by fluorescence spectroscopy), PDEAEMA and PDiPAEMA provide a nonpolar surrounding for the 4HP uptake above their collapse. In addition, PDiPAEMA causes the sharpest transition (as seen by the 4HP probe), although the carbonyl hydration experiences a more gradual (sigmoidal) transition for all polymers (as seen by IR). These observations allow a distinction of the phase separation mechanisms. While the LCST properties of PDMAEMA are mainly caused by backbone/carbonyl interactions, its rather polar dimethylaminoethyl group does not inflict pronounced hydrophobicity, but promotes a higher water content within the phase-separated polymer. In contrast, the phase separation of PDEAEMA and PDiPAEMA is mainly influenced by the less polar dialkylaminoethyl groups, leading to drastic changes in the hydrophobicity around the cloud points. Further, the IR data suggest that the diisopropylaminoethyl groups of PDiPAEMA tend to backfold to the carbonyl groups/backbone to minimize water-polymer contact already in its soluble state. Finally, this study might lead to advanced lasing applications of the laser dye 4HP.

Tertiary-amine-containing thermo- and pH-sensitive hydrophilic ABA triblock copolymers: effect of different tertiary amines on thermally induced sol-gel transitions

This Article reports on the synthesis of a series of well-defined, tertiary-amine-containing ABA triblock copolymers, composed of a poly(ethylene oxide) (PEO) central block and thermo- and pH-sensitive outer blocks, and the study of the effect of different tertiary amines on thermally induced sol-gel transition temperatures (T(sol-gel)) of their 10 wt % aqueous solutions. The doubly responsive ABA triblock copolymers were prepared from a difunctional PEO macroinitiator by atom transfer radical polymerization of methoxydi(ethylene glycol) methacrylate and ethoxydi(ethylene glycol) methacrylate at a feed molar ratio of 30:70 with ∼5 mol % of either N,N-diethylaminoethyl methacrylate (DEAEMA), N,N-diisopropylaminoethyl methacrylate, or N,N-di(n-butyl)aminoethyl methacrylate. The chain lengths of thermosensitive outer blocks and the molar contents of tertiary amines were very similar for all copolymers. Using rheological measurements, we determined the pH dependences of T(sol-gel) of 10 wt % aqueous solutions of these copolymers in a phosphate buffer. The T(sol-gel) versus pH curves of all polymers exhibited a sigmoidal shape. The T(sol-gel) increased with decreasing pH; the changes were small on both high and low pH sides. At a specific pH, the T(sol-gel) decreased with increasing the hydrophobicity of the tertiary amine, and upon decreasing pH the onset pH value for the T(sol-gel) to begin to increase noticeably was lower for the more hydrophobic tertiary amine-containing copolymer. In addition, we studied the effect of different tertiary amines on the release behavior of FITC-dextran from 10 wt % micellar gels in an acidic medium at 37 and 27 °C. The release profiles for three studied hydrogels at 37 °C were essentially the same, suggesting that the release was dominated by the diffusion of FITC-dextran. At 27 °C, the release was significantly faster for the DEAEMA-containing copolymer, indicating that both diffusion and gel dissolution contributed to the release at this temperature.