Cryogels of cellulose derivatives prepared via UV irradiation of moderately frozen systems

Crosslinking strategies in modulating methylcellulose hydrogel properties

Methylcellulose (MC) hydrogels are ideal materials for the design of thermo-responsive platforms capable of exploiting the environment temperature as a driving force to activate their smart transition. However, MC hydrogels usually show reduced stability in an aqueous environment and low mechanical properties, limiting their applications' breadth. A possible approach intended to overcome these limitations is chemical crosslinking, which represents a simple yet effective strategy to modify the MC hydrogels' properties (e.g., physicochemical, mechanical, and biological). In this regard, understanding the selected crosslinking method's role in modulating the MC hydrogels' properties is a key factor in their design. This review offers a perspective on the main MC chemical crosslinking approaches reported in the literature. Three main categories can be distinguished: (i) small molecule crosslinkers, (ii) crosslinking by high-energy radiation, and (iii) crosslinking via MC chemical modification. The advantages and limitations of each approach are elucidated, and special consideration is paid to the thermo-responsive properties after crosslinking towards the development of MC hydrogels with enhanced physical stability and mechanical performance, preserving the thermo-responsive behavior.

Highly Elastic Super-Macroporous Cryogels Fabricated by Thermally Induced Crosslinking of 2-Hydroxyethylcellulose with Citric Acid in Solid State

Biopolymer materials have been considered a “green” alternative to petroleum-based polymeric materials. Biopolymers cannot completely replace synthetic polymers, but their application should be extended as much as possible, exploiting the benefits of their low toxicity and biodegradability. This contribution describes a novel strategy for the synthesis of super-macroporous 2-hydroxyethylcellulose (HEC) cryogels. The method involves cryogenic treatment of an aqueous solution of HEC and citric acid (CA), freeze drying, and thermally induced crosslinking of HEC macrochains by CA in a solid state. The effect of reaction temperature (70–180 °C) and CA concentration (5–20 mass % to HEC) on the reaction efficacy and physico-mechanical properties of materials was investigated. Highly elastic cryogels were fabricated, with crosslinking carried out at ≥100 °C. The storage modulus of the newly obtained HEC cryogels was ca. 20 times higher than the modulus of pure HEC cryogels prepared by photochemical crosslinking. HEC cryogels possess an open porous structure, as confirmed by scanning electron microscopy (SEM), and uptake a relatively large amount of water. The swelling degree varied between 17 and 40, depending on the experimental conditions. The degradability of HEC cryogels was demonstrated by acid hydrolysis experiments.

Tuning the Mechanical and Thermal Properties of Hydroxypropyl Methylcellulose Cryogels with the Aid of Surfactants

The mechanical and thermal properties of cryogels depend on their microstructure. In this study, the microstructure of hydroxypropyl methylcellulose (HPMC) cryogels was modified by the addition of ionic (bis (2-ethylhexyl) sodium sulfosuccinate, AOT) and non-ionic (Kolliphor^® EL) surfactants to the precursor hydrogels (30 g/L). The surfactant concentrations varied from 0.2 mmol/L to 3.0 mmol/L. All of the hydrogels presented viscous behavior (G″ > G′). Hydrogels containing AOT (c > 2.0 mmol/L) led to cryogels with the lowest compressive modulus (13 ± 1 kPa), the highest specific surface area (2.31 m²/g), the lowest thermal conductivity (0.030 W/(m·°C)), and less hygroscopic walls. The addition of Kolliphor^® EL to the hydrogels yielded the stiffest cryogels (320 ± 32 kPa) with the lowest specific surface area (1.11 m²/g) and the highest thermal conductivity (0.055 W/(m·°C)). Density functional theory (DFT) calculations indicated an interaction energy of −31.8 kcal/mol due to the interaction between the AOT sulfonate group and the HPMC hydroxyl group and the hydrogen bond between the AOT carbonyl group and the HPMC hydroxyl group. The interaction energy between the HPMC hydroxyl group and the Kolliphor^® EL hydroxyl group was calculated as −7.91 kcal/mol. A model was proposed to describe the effects of AOT or Kolliphor^® EL on the microstructures and the mechanical/thermal properties of HPMC cryogels.

Nanocomposite Cryogel Carriers from 2-Hydroxyethyl Cellulose Network and Cannabidiol-Loaded Polymeric Micelles for Sustained Topical Delivery

In this contribution, we report the development of original nanocomposite cryogels for sustained topical delivery of hydrophobic natural active substances such as cannabidiol (CBD). The cryogels were fabricated by a method involving cryogenic treatment and photo-crosslinking of aqueous systems containing biodegradable 2-hydroxyethyl cellulose (HEC) and CBD-loaded polymeric micelles. The preparation of the water-soluble form of CBD was a key element for the successful drug loading in the one-pot reaction. The main physical, mechanical and biological characteristics of CBD-loaded and blank cryogels such as gel fraction yield, swelling degree, morphology, storage and loss moduli, and cytotoxicity were studied in detail. The advantage of nanocomposite over pure HEC cryogel carriers in terms of achieving a sustained release profile was also demonstrated.

Acetylsalicylic Acid (ASA) on Hydroxyethylcellulose/Polyacrylamide Gel (HEC/PAAm) as a Proposal for a Dermatological Compress: Mathematical Modeling of ASA Release Kinetics

Currently, acne in adolescents and adults is caused by an infection in follicles caused by hormonal changes, stress, water pollution, air, and earth; the last one comes into contact with the skin through the hands of patients. This project presents the incorporation of acetylsalicylic acid (ASA) to the hydroxyethylcellulose/polyacrylamide gel (HEC/PAAm) in the synthesis of gel or by its swelling. The results show us that the incorporation of ASA is possible by both methods; first, the incorporation by synthesis of degradation of the gel is more visible. The infrared spectroscopic analysis shows the functional groups of gel and ASA, 2921 and 2863 cm−1, whose assignments correspond to CH3 and CH2 groups, which are part of both the polymer and the ASA molecule, which confirms the interaction between the two groups. The microscopy photographs (SEM) show on the surface the drug in irregular whitish orthorhombic forms due to swelling; arborescent structures are observed in the case of the incorporation of the ASA drug by synthesis. Swelling kinetics has a Fickian form. The Higuchi model conforms to the release of ASA because the level of confidence is 90%. This gel was allowed to release 0.35 mg/hour, thus allowing the patient to have a continuous form of the release, in the affected area in a short period of time.

Novel electrically conducting 2-hydroxyethylcellulose/polyaniline nanocomposite cryogels: Synthesis and application in tissue engineering

Novel electrically conducting 2-hydroxyethylcellulose/polyaniline (HEC/PANI) nanocomposite cryogels were fabricated via the combination of cryogenic treatment and photochemical crosslinking. PANI nanofillers (one-dimentional tubes and three-dimentional particles) were synthesized via oxidative polymerization of aniline in aqueous media and, then, embedded in the HEC matrix. The effect of PANI content and morphology on the gel fraction yield and electrical conductivity of material was studied. Nanocomposite cryogels of high gel fraction yield (65-95%) and rather high electrical conductivity (0.02-0.1S/m) were obtained by using a relatively small amount (0.5-3wt.% to HEC) of pre-formed PANI nanofillers. The behavior of L929 cells adhered on HEC/PANI cryogels in the presence of electric field were also investigated. Cytotoxicity test showed very good survival and proliferation of cells on cryogels, while the electrical stimulation triggered changes in cell morphology as well as a specific alignment of cells in parallel to the electrical field.

Stimuli sensitive super-macroporous cryogels based on photo-crosslinked 2-hydroxyethylcellulose and chitosan

Original pH sensitive cryogels, based on two biodegradable natural polymers chitosan (CS) and 2-hydroxyethylcellulose (HEC), were obtained via cryogenic treatment of semi-dilute aqueous solutions and UV induced crosslinking in frozen state. H₂O₂ and N,N'-methylenebisacrylamide (BisAAm) were used as photoinitiator and crosslinking agent, respectively. BisAAm facilitated the formation of polymer co-network and increased both the gel fraction yield and mechanical strength of cryogels. The influence of chitosan content on the physico-mechanical properties of HEC-CS cryogels was investigated. In general, the increase of CS fraction in the polymer co-network increased the degree of swelling and enhanced significantly the storage modulus of materials. All HEC-CS cryogels obtained were opalescent sponge-like materials, which quickly release/uptake water due to their open porous structure. The incorporation of CS provided pH dependent swelling and good bioadhesive properties of cryogels. HEC-CS cryogels were further exploited as drug delivery systems of the highly water soluble drug metronidazole belonging to BCS Class l.

Mechanical, thermal and surface properties of polyacrylamide/dextran semi-interpenetrating network hydrogels tuned by the synthesis temperature

The mechanical, rheological, thermal, and surface behaviors of three polyacrylamide/dextran (PAAm/Dx) semi-interpenetrating polymer network (semi-IPN) hydrogels, prepared at 22°C, 5°C and −18°C, were investigated. The results were compared with those obtained on cross-linked PAAm without Dx synthesized under the same conditions. Hydrogels prepared at the lowest temperature were the most mechanically stable. The thermal stability of the semi-IPN hydrogels is slightly lower than the corresponding PAAm gels, irrespective of preparation temperature. The water vapor sorption capacity depended on the presence of Dx as well as preparation temperature, which determines the network morphology.

Variations in rigidity and ligand density influence neuronal response in methylcellulose-laminin hydrogels

Cells are continuously sensing their physical and chemical environment, generating dynamic interactions with the surrounding microenvironment and neighboring cells. Specific to neurons, neurite outgrowth is influenced by many factors, including the mechanical properties and adhesive signals of the growth substrata. In designing biomaterials for neural regeneration, it is important to understand the influence of substrate material, rigidity and bioadhesion on neurite outgrowth. To this end, we developed and characterized a tunable 3-D methylcellulose (MC) hydrogel polymeric system tethered to laminin-1 (MC-x-LN) across a range of substrate rigidities (G* range = 50-565 Pa) and laminin densities. Viability and neurite outgrowth of primary cortical neurons plated within 3-D MC hydrogels were used as cell outcome measures. After 4 days in culture, neuronal viability was significantly augmented with increasing rigidity for MC-x-LN as compared to control non-bioactive MC; however, neurite outgrowth was only observed in MC hydrogels with complex moduli of 565 Pa. Varying LN while maintaining a constant MC formulation (G* = 565 Pa) revealed a threshold response for neuronal viability, whereas a direct dose-dependent response to LN density was observed for neurite outgrowth. Collectively, these data demonstrate the synergistic play between material compliance and bioactive ligand concentrations within MC hydrogels. Such results can be used to better understand the adhesive and mechanical factors that mediate neuronal response to MC-based, tissue-engineered materials.