Redox-Responsive "Catch and Release" Cryogels: A Versatile Platform for Capture and Release of Proteins and Cells

Macroporous cryogels are attractive scaffolds for biomedical applications, such as biomolecular immobilization, diagnostic sensing, and tissue engineering. In this study, thiol-reactive redox-responsive cryogels with a porous structure are prepared using photopolymerization of a pyridyl disulfide poly(ethylene glycol) methacrylate (PDS-PEG-MA) monomer. Reactive cryogels are produced using PDS-PEG-MA and hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) monomers, along with a PEG-based cross-linker and photoinitiator. Functionalization of cryogels using a fluorescent dye via the disulfide-thiol exchange reactions is demonstrated, followed by release under reducing conditions. For ligand-mediated protein immobilization, first, thiol-containing biotin or mannose is conjugated onto the cryogels. Subsequently, fluorescent dye-labeled proteins streptavidin and concanavalin A (ConA) are immobilized via ligand-mediated conjugation. Furthermore, we demonstrate that the mannose-decorated cryogel could capture ConA selectively from a mixture of lectins. The efficiency of protein immobilization could be easily tuned by changing the ratio of the thiol-sensitive moiety in the scaffold. Finally, an integrin-binding cell adhesive peptide is attached to cryogels to achieve successful attachment, and the on-demand detachment of integrin-receptor-rich fibroblast cells is demonstrated. Redox-responsive cryogels can serve as potential scaffolds for a variety of biomedical applications because of their facile synthesis and modification.

Enhancement of Bone Tissue Regeneration with Multi-Functional Nanoparticles by Coordination of Immune, Osteogenic, and Angiogenic Responses

Inorganic nanoparticles are promising materials for bone tissue engineering due to their chemical resemblance to the native bone structure. However, most studies are unable to capture the entirety of the defective environment, providing limited bone regenerative abilities. Hence, this study aims to develop a multifunctional nanoparticle to collectively control the defective bone niche, including immune, angiogenic, and osteogenic systems. The nanoparticles, self-assembled by biomimetic mineralization and tannic acid (TA)-mediated metal-polyphenol network (MPN), are released sustainably after the incorporation within a gelatin cryogel. The released nanoparticles display a reduction in M1 macrophages by means of reactive oxygen species (ROS) elimination. Consequently, osteoclast maturation is also reduced, which is observed by the minimal formation of multinucleated cells (0.4%). Furthermore, the proportion of M2 macrophages, osteogenic differentiation, and angiogenic potential are consistently increased by the effects of magnesium from the nanoparticles. This orchestrated control of multiple systems influences the in vivo vascularized bone regeneration in which 80% of the critical-sized bone defect is regenerated with new bones with mature lamellar structure and arteriole-scale micro-vessels. Altogether, this study emphasizes the importance of the coordinated modulation of immune, osteogenic, and angiogenic systems at the bone defect site for robust bone regeneration.

In-Bath 3D Printing of Anisotropic Shape-Memory Cryogels Functionalized with Bone-Bioactive Nanoparticles

Cryogels exhibit unique shape memory with full recovery and structural stability features after multiple injections. These constructs also possess enhanced cell permeability and nutrient diffusion when compared to typical bulk hydrogels. Volumetric processing of cryogels functionalized with nanosized units has potential to widen their biomedical applications, however this has remained challenging and relatively underexplored. In this study, we report a novel methodology that combines suspension 3D printing with directional freezing for the fabrication of nanocomposite cryogels with configurable anisotropy. When compared to conventional bulk or freeze-dried hydrogels, nanocomposite cryogel formulations exhibit excellent shape recovery (>95%) and higher pore connectivity. Suspension printing, assisted with a prechilled metal grid, was optimized to induce anisotropy. The addition of calcium- and phosphate-doped mesoporous silica nanoparticles into the cryogel matrix enhanced bioactivity toward orthopedic applications without hindering the printing process. Notably, the nanocomposite 3D printed cryogels exhibit injectable shape memory while also featuring a lamellar topography. The fabrication of these constructs was highly reproducible and exhibited potential for a cell-delivery injectable cryogel with no cytotoxicity to human-derived adipose stem cells. Hence, in this work, it was possible to combine a gravity defying 3D printed methodology with injectable and controlled anisotropic macroporous structures containing bioactive nanoparticles. This methodology ameliorates highly tunable injectable 3D printed anisotropic nanocomposite cryogels with a user-programmable degree of structural complexity.

BM-MSC-Loaded Graphene-Collagen Cryogels Ameliorate Neuroinflammation in a Rat Spinal Cord Injury Model

A major obstacle to axonal regeneration following spinal cord injury (SCI) is neuroinflammation mediated by astrocytes and microglial cells. We previously demonstrated that graphene-based collagen hydrogels alone can decrease neuroinflammation in SCI. Their regenerative potential, however, is poorly understood and incomplete. Furthermore, stem cells have demonstrated both neuroprotective and regenerative properties in spinal cord regeneration, although there are constraints connected with the application of stem cell-based therapy. In this study, we have analyzed the regeneration capability of human bone marrow mesenchymal stem cell (BM-MSC)-loaded graphene-cross-linked collagen cryogels (Gr-Col) in a thoracic (T10-T11) hemisection model of SCI. Our study found that BM-MSC-loaded Gr-Col improves axonal regeneration, reduces neuroinflammation by decreasing astrocyte reactivity, and promotes M2 macrophage polarization. BM-MSC-loaded-Gr-Col demonstrated enhanced regenerative potential compared to Gr-Col and the injury group control. Next-generation sequencing (NGS) analysis revealed that BM-MSC-loaded-Gr-Col modulates the JAK2-STAT3 pathway, thus decreasing the reactive and scar-forming astrocyte phenotype. The decrease in neuroinflammation in the BM-MSC-loaded-Gr-Col group is attributed to the modulation of Notch/Rock and STAT5a/b and STAT6 signaling. Overall, Gene Set Enrichment Analysis suggests the promising role of BM-MSC-loaded-Gr-Col in promoting axonal regeneration after SCI by modulating molecular pathways such as the PI3/Akt pathway, focal adhesion kinase, and various inflammatory pathways.

Cryogel wound dressings based on natural polysaccharides perfectly adhere to irregular wounds for rapid haemostasis and easy disassembly

Skin injuries can have unexpected surfaces, leading to uneven wound surfaces and inadequate dressing contact with these irregular surfaces. This can decrease the dressing's haemostatic action and increase the healing period. This study recommends the use of sticky and flexible cryogel coverings to promote faster haemostasis and efficiently handle uneven skin wounds. Alginate cryogels have a fast haemostatic effect and shape flexibility due to their macroporous structure. The material demonstrates potent antibacterial characteristics and enhances skin adherence by adding grafted chitosan with gallic acid. In irregular defect wound models, cryogels can cling closely to uneven damage surfaces due to their amorphous nature. Furthermore, their macroporous structure allows for quick haemostasis by quickly absorbing blood and wound exudate. After giving the dressing a thorough rinse, its adhesive strength reduces and it is simple to remove without causing any damage to the wound. Cryogel demonstrated faster haemostasis than gauze in a wound model on a rat tail, indicating that it has considerable potential for use as a wound dressing in the biomedical area.

Cryogels and Monoliths: Promising Tools for Chromatographic Purification of Nucleic Acids

The increasing demand for highly pure biopharmaceuticals has put significant pressure on the biotechnological industry to innovate in production and purification processes. Nucleic acid purification, crucial for gene therapy and vaccine production, presents challenges due to the unique physical and chemical properties of these molecules. Meeting regulatory standards necessitates large quantities of biotherapeutic agents of high purity. While conventional chromatography offers versatility and efficiency, it suffers from drawbacks like low flow rates and binding capacity, as well as high mass transfer resistance. Recent advancements in continuous beds, including monoliths and cryogel-based systems, have emerged as promising solutions to overcome these limitations. This review explores and evaluates the latest progress in chromatography utilizing monolithic and cryogenic supports for nucleic acid purification.

A facile method to fabricate versatile keratin cryogels for tissue engineering applications

Human hair keratin (HHK) has been extensively explored as a biomaterial for soft tissue regeneration due to their excellent bioactivity and biocompatibility. The possibility to fabricate HHK into three-dimensional (3D) hydrogels with physical properties resembling soft tissues has been well demonstrated. However, conventional keratin hydrogels often exhibit a dense architecture that could hinder cell filtration. In the present study, HHK-based cryogels were fabricated using a freeze-thaw (FT) method, where oxidized dopamine (ODA) was employed to covalently crosslink thiol/amine rich-keratin molecules at sub-zero temperatures. The obtained HHK-ODA cryogels have micron-sized pores ranging between 100 and 200 μm and mechanical properties that can be tuned by varying the crosslinking density between ODA and HHK. Through optimization of the weight content of ODA and the number of FT cycles, the compressive strengths and stiffnesses of these cryogels achieved 15-fold increments from ∼1.5 kPa to ∼22 kPa and ∼300 Pa to ∼5000 Pa, respectively. The HHK-ODA cryogels competently supported human dermal fibroblast spreading and proliferation. Overall, this study exhibited a facile method to fabricate mechanically superior keratin-based cryogels with cell compatible microarchitecture, circumventing the need for complicated chemical modifications and the use of cytotoxic crosslinkers.

How the Crosslinker Amount Influences the Final Properties of Hydroxyethyl Methacrylate Cryogels

The investigation of the mechanical, thermal, and adsorption properties of hydroxyethyl methacrylate (HEMA) cryogels as a function of a reactant ratio is herein reported to better address materials for specific applications. To this aim, cryogels have been synthesized using different monomer/crosslinker (N,N'-methylene-bisacrylamide-MBAA) ratios. The study of SEM images made it possible to identify the trend in the material's macroporosity. As would be expected, the average measured pore width decreased as the amount of MBAA increased while the number of pores grew. Swelling capacity ranges from 8.7 gW/ggel (grams of water per gram of gel) to 9.3 gW/ggel. These values are strictly connected with the pore's size and distribution, revealing that the water uptake for the most crosslinked sample is inferior to other samples. The equilibrium-adsorption capacity (Qe) towards the methylene violet (MV) was also assessed, revealing no remarkable differences after 24 h of a batch test. As expected, thermogravimetric analysis (TGA) also showed no significant changes in stability that ranged from a maximum weight loss temperature (T Max) of 420 °C to 425 °C, which increased as a function of crosslinker content. Conversely, compression strength measurements showed a notable difference of about 50% in modulus (Ec), moving from the higher to the lower HEMA/MBAA ratio. These new comparative results indicate how slight variations in the reactant's ratio can steadily improve the mechanical properties of the HEMA cryogel without affecting its adsorption efficiency. This can be helpful in the design of materials for water and energy purposes. Since swelling properties are needed in the case of biomedical applications, the HEMA/MBAA ratio should be tuned versus high values.

Gelatin Methacryloyl Based Injectable Cryogels with Tunable Degradability for Cell Delivery

Scaffold-based cell delivery can improve therapeutic effects of transplanted cells in cell therapy. Biomaterial scaffolds serveas niche for cell growth and proliferation which improves cell survival and overall function post cell delivery. In this study, gelatin methacryloyl based injectable scaffolds made using poly(ethylene)glycol as a sacrificial polymer and cryogelation as a technique, are demonstrated to have tunable degradability and porosity that is required for cell and drug delivery applications. The pore size (10-142 µm) of these gels makes them suitable for loading different cell types as per the application. In vitro studies using mammalian cells confirm that these cryogels are cytocompatible. These cell-laden scaffolds are injectable and have a cell retention ability of up to 90% after injection. Rheology is done to evaluate stiffness and shape recovery property, and it is found that these gels can maintain their original shape even after applying 7 cycles of strain from 0.1% to 20%. Furthermore, their degradability can be modulated between 6 and 10 days by changing the overall polymer composition. Thus, injectability and degradability of these cryogels can circumvent invasive surgical procedures, thereby making them useful for a variety of applications including delivery of cells and bioactive factors.

Cryogel Scaffolds for Tissue-Engineering: Advances and Challenges for Effective Bone and Cartilage Regeneration

Critical-sized bone defects and articular cartilage injuries resulting from trauma, osteonecrosis, or age-related degeneration can be often non-healed by physiological repairing mechanisms, thus representing a relevant clinical issue due to a high epidemiological incidence rate. Novel tissue-engineering approaches have been proposed as an alternative to common clinical practices. This cutting-edge technology is based on the combination of three fundamental components, generally referred to as the tissue-engineering triad: autologous or allogenic cells, growth-stimulating factors, and a scaffold. Three-dimensional polymer networks are frequently used as scaffolds to allow cell proliferation and tissue regeneration. In particular, cryogels give promising results for this purpose, thanks to their peculiar properties. Cryogels are indeed characterized by an interconnected porous structure and a typical sponge-like behavior, which facilitate cellular infiltration and ingrowth. Their composition and the fabrication procedure can be appropriately tuned to obtain scaffolds that match the requirements of a specific tissue or organ to be regenerated. These features make cryogels interesting and promising scaffolds for the regeneration of different tissues, including those characterized by very complex mechanical and physical properties, such as bones and joints. In this review, state-of-the-art fabrication and employment of cryogels for supporting effective osteogenic or chondrogenic differentiation to allow for the regeneration of functional tissues is reported. Current progress and challenges for the implementation of this technology in clinical practice are also highlighted.

Effect of caseinate salt addition on the structural characteristics of kefiran systems

Sodium caseinates-kefiran systems were studied to explore whether any potential interactions between them might exist. The study was performed using low-deformation rheological techniques, which were dynamic and creep tests. The systems were prepared under various experimental conditions such as heating and acidification. Besides, the structure development of the systems in relation to time was also monitored using oscillatory shear rheometry. The results indicated that the structural characteristics of the systems were mainly affected by the state of the caseinates such as the formation of aggregates and to a lesser degree by the interactions of kefiran molecules with the caseinates. Freeze-thaw treatment produced cryogels with good thermal stability and fairly satisfactory mechanical properties. The morphology of the caseinate-kefiran systems was also investigated by means of confocal laser scanning microscopy.

Development of a novel cryostructured composite coating of xanthan-bovine collagen-oregano essential oil spraying applied for the preservation of commercial biscuits marketed in Mexico

Cryostructured gels, better known as cryogels, are a very important emerging class of biomaterials that have diverse applications in food preservation. This work shows a novel alternative to prepare a cryostructured composite coating made from a blend of xanthan, bovine collagen, and oregano essential oil. The composite coating was suitably applied onto the surface of preservative-free biscuits which were stored for 15 days at 25 ± 2°C and 52% ± 1% relative humidity. The evaluation focused mainly on the changes in the physicochemical, textural, and microbiological characteristics of the biscuits. It was found that the coated samples significantly (p < 0.05) decreased moisture absorption, water activity, and fungal growth. However, the composite coating minimally impacted the quality of biscuits in terms of color, texture profile, and surface microstructure. Overall, the cryostructured composite coating constitutes an advance in technological strategies aimed at the preservation of baked products. This will allow, in the future, the development of novel coatings on bakery products to generate new trends in the conservation of their properties and extension of shelf life. This could be achieved through the implementation of new technologies in the food industry, with the aim of making them more environmentally friendly and contributing to the generation of less plastic waste. PRACTICAL APPLICATION: The study and application of cryogels, as innovative systems in the food industry, allow to expand and diversify the materials that can function as coatings to maintain some quality characteristics, in this case in bakery products, so it is important to analyze their effects and consider them to improve conservation processes.

SDF-1 Bound Heparin Nanoparticles Recruit Progenitor Cells for Their Differentiation and Promotion of Angiogenesis after Stroke

Angiogenesis after stroke is correlated with enhanced tissue repair and functional outcomes. The existing body of research in biomaterials for stroke focuses on hydrogels for the delivery of stem cells, growth factors, or small molecules or drugs. Despite the ability of hydrogels to enhance all these delivery methods, no material has significantly regrown vasculature within the translatable timeline of days to weeks after stroke. Here, two novel biomaterial formulations of granular hydrogels are developed for tissue regeneration after stroke: highly porous microgels (i.e., Cryo microgels) and microgels bound with heparin-norbornene nanoparticles with covalently bound SDF-1α. The combination of these materials results in perfused vessels throughout the stroke core in only 10 days, in addition to increased neural progenitor cell recruitment, maintenance, and increased neuronal differentiation.

Natural Polysaccharide Delivery Platforms with Multiscale Structure Used for Cancer Chemoimmunotherapy

Chemoimmunotherapy is an effective cancer treatment method. Drugs are always combined and used in treating cancer. However, the characteristic of drugs varies, making it challenging to control their release kinetics utilizing delivery devices with a single microstructure. In this study, we attempted to uniformly size drugs of varying molecular weights and confine them in a compartment where immune cells may be recruited and moved freely. Dextran microgels were created as modular drug libraries to address the cryogel burst release of small molecule drugs. Then, modular drug libraries and granulocyte-macrophage colony-stimulating factor (GM-CSF) were integrated into cryogels for a combined treatment. Herein, alginate was zwitterion modified to avoid the immune reaction generated by the material. Because of its macroporous structure, the cryogel could be injected into the body, eliminating invasive surgical procedures. Results demonstrated that multiscale delivery platforms could improve the synergistic effect of various medications on tumor treatment.

Bioactive Glasses-Based Nanozymes Composite Macroporous Cryogel with Antioxidative, Antibacterial, and Pro-Healing Properties for Diabetic Infected Wound Repair

The treatment for diabetic ulcers still remains a big clinic challenge owing to the adverse repair microenvironment. Bioactive glasses (BGs) play an important role in the late stages of healing due to their ability to promote vascularization and collagen fiber deposition, but fail to improve infection and oxidative stress in the early stage.Therefore, it is critical to develop a material involved in regulating the whole healing phases. In this work, BGs-based nanozymes (MnO2 @PDA-BGs) with antioxidation, antibacterial and pro-healing abilities are synthesized by the redox deposition of MnO2 on mesoporous BGs. Afterward, cryogel with the interconnected macropore structure is fabricated by the polymerization of methacrylate anhydride gelatin (GelMA) at -20 °C. MnO2 @PDA-BGs are loaded into the cryogel to obtain nanocomposite cryogel (MnO2 @PDA-BGs/Gel) with multiple enzymes-like- activities to eliminate reactive oxygen species (ROS). Besides, MnO2 @PDA-BGs/Gel has intensive peroxidase-like activity under acidic condition and near infrared photothermal responsiveness to achieve excellent antibacterial performance. Cells experiments demonstrate that MnO2 @PDA-BGs/Gel recruits L929s and promotes their proliferation. Furthermore, MnO2 @PDA-BGs/Gel eliminates intracellular overexpressed ROS and maintains the viability of L929s. Animal experiments confirm that MnO2 @PDA-BGs/Gel promotes wound healing and avoided scarring by killing bacteria, reversing inflammation, promoting vascularization, and improving the deposition of collagen III.

Integrated Piezoelectric/Conductive Composite Cryogel Creates Electroactive Microenvironment for Enhanced Bone Regeneration

Natural bone tissue possesses inherent electrophysiological characteristics, displaying conductivity and piezoelectricity simultaneously; hence, the reconstruction of local electrical microenvironment at defect site provides an effective strategy to enhance osteogenesis. Herein, a composite cryogel-type scaffold (referred to as Gel-PD-CMBT) is developed for bone regeneration, utilizing gelatin (Gel) in combination with a conductive poly(ethylene dioxythiophene)/polystyrene sulfonate matrix and Ca/Mn co-doped barium titanate (CMBT) nanofibers as the piezoelectric filler. The incorporation of these components results in the formation of an integrated piezoelectric/conductive network within the scaffold, facilitating charge migration and yielding a conductivity of 0.59 S cm-1 . This conductive scaffold creates a promising electroactive microenvironment, which is capable of up-regulating biological responses. Furthermore, the interconnected porous structure of the Gel-PD-CMBT scaffold not only provides mechanical stability but also offered ample space for cellular and tissue ingrowth. This Gel-PD-CMBT scaffold demonstrates a greater capacity to promote cellular osteogenic differentiation in vitro and neo-bone formation in vivo. In summary, the Gel-PD-CMBT scaffold, with its integrated piezoelectricity and conductivity, effectively restores the local electroactive microenvironment, offering an ideal platform for the regeneration of electrophysiological bone tissue.

Agarose Cryogels: Production Process Modeling and Structural Characterization

A cryogel is a cross-linked polymer network with different properties that are determined by its manufacturing technique. The formation of a cryogel occurs at low temperatures and results in a porous structure whose pore size is affected by thermal conditions. The adjustable pore sizes of cryogels make them attractive for diverse applications. In this study, the influence of the external operational temperature, which affects the cooling and freezing rates, on the production of cryogels with 2% w/w agarose is investigated. Moreover, a mathematical model is developed to simulate the cryogel production process and provide an initial estimate of the pore size within the structure. The predictions of the model, supported by qualitative light microscopy images, demonstrate that cryogels produced at higher process temperatures exhibit larger pore sizes. Moreover, the existence of pore size distribution within the gel structure is confirmed. Finally, stress relaxation tests, coupled with an image analysis, validates that cryogels produced at lower temperatures possess a higher stiffness and slower water release rates.

Cryogels: Advancing Biomaterials for Transformative Biomedical Applications

Cryogels, composed of synthetic and natural materials, have emerged as versatile biomaterials with applications in tissue engineering, controlled drug delivery, regenerative medicine, and therapeutics. However, optimizing cryogel properties, such as mechanical strength and release profiles, remains challenging. To advance the field, researchers are exploring advanced manufacturing techniques, biomimetic design, and addressing long-term stability. Combination therapies and drug delivery systems using cryogels show promise. In vivo evaluation and clinical trials are crucial for safety and efficacy. Overcoming practical challenges, including scalability, structural integrity, mass transfer constraints, biocompatibility, seamless integration, and cost-effectiveness, is essential. By addressing these challenges, cryogels can transform biomedical applications with innovative biomaterials.

Carrageenan/Chitin Nanowhiskers Cryogels for Vaginal Delivery of Metronidazole

The development of polymeric carriers based on partially deacetylated chitin nanowhiskers (CNWs) and anionic sulfated polysaccharides is an attractive strategy for improved vaginal delivery with modified drug release profiles. This study focuses on the development of metronidazole (MET)-containing cryogels based on carrageenan (CRG) and CNWs. The desired cryogels were obtained by electrostatic interactions between the amino groups of CNWs and the sulfate groups of CRG and by the formation of additional hydrogen bonds, as well as by entanglement of carrageenan macrochains. It was shown that the introduction of 5% CNWs significantly increased the strength of the initial hydrogel and ensured the formation of a homogeneous cryogel structure, resulting in sustained MET release within 24 h. At the same time, when the CNW content was increased to 10%, the system collapsed with the formation of discrete cryogels, demonstrating MET release within 12 h. The mechanism of prolonged drug release was mediated by polymer swelling and chain relaxation in the polymer matrix and correlated well with the Korsmeyer-Peppas and Peppas-Sahlin models. In vitro tests showed that the developed cryogels had a prolonged (24 h) antiprotozoal effect against Trichomonas, including MET-resistant strains. Thus, the new cryogels with MET may be promising dosage forms for the treatment of vaginal infections.

Pterostilbene loaded poly(vinyl alcohol)-gelatin cryogels as potential bioactive wound dressing material

Cryogels are support materials which are good at mimicking extracellular matrix due to their excellent hydrophilicity, biocompatibility, and macroporous structure, thus they are useful in facilitating cell activities during healing process. In this study, polyvinyl alcohol-gelatin (PVA-Gel) based cryogel membranes loaded with pterostilbene (trans-3,5-dimethoxy-4-hydroxystilbene; PTS) (PVA-Gel/PTS) was synthesized as wound dressing materials. PVA-Gel and PVA-Gel/PTS were synthesized with the polymerization yields of 96% ± 0.23% and 98% ± 0.18%, respectively, and characterized by swelling tests, Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) analysis. The swelling ratios were calculated as 98.6% ± 4.93% and 102% ± 5.1%, macroporosities were determined as 85% ± 2.13% and 88% ± 2.2%, for PVA-Gel and PVA-Gel/PTS, respectively. It was determined that PVA-Gel and PVA-Gel/PTS have 17 m² /g ± 0.76 m² /g and 20 m² /g ± 0.92 m² /g surface areas, respectively. SEM studies were demonstrated that they have ~100 μm pore sizes. According to 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), trypan blue exclusion and live-dead assay results, it was observed that cell proliferation, cell number and cell viability were higher in PVA-Gel/PTS cryogel at 24, 48, and 72 h compared to PVA-Gel. A strong and transparent fluorescent light intensity was observed indicating higher cell population in PVA-Gel/PTS in comparison with PVA-Gel, according to 4',6-diamidino-2-phenylindole (DAPI) staining. SEM, F-Actin, Giemsa staining and inverted-phase microscope image of fibroblasts in PVA-Gel/PTS cryogels revealed that dense fibroblast proliferation and spindle-shaped morphology of cells were preserved. Moreover, DNA agarose gel data demonstrated that PVA-Gel/PTS cryogels had no effect on DNA integrity. Consequently, produced PVA-Gel/PTS cryogel can be used as wound dressing material to promote wound therapies, inducing cell viability and proliferation.

Tough Porous Silk Nanofiber-Derived Cryogels with Osteogenic and Angiogenic Capacity for Bone Repair

Tough porous cryogels with angiogenesis and osteogenesis features remain a design challenge for utility in bone regeneration. Here, building off of the recent efforts to generate tough silk nanofiber-derived cryogels with osteogenic activity, deferoxamine (DFO) is loaded in silk nanofiber-derived cryogels to introduce angiogenic capacity. Both the mechanical cues (stiffness) and the sustained release of DFO from the gels are controlled by tuning the concentration of silk nanofibers in the system, achieving a modulus above 400 kPa and slow release of the DFO over 60 days. The modulus of the cryogels and the released DFO induce osteogenic and angiogenic activity, which facilitates bone regeneration in vivo in femur defects in rat, resulting in faster regeneration of vascularized bone tissue. The tunable physical and chemical cues derived from these nanofibrous-microporous structures support the potential for silk cryogels in bone tissue regeneration.

Hypoxia-inducing cryogels uncover key cancer-immune cell interactions in an oxygen-deficient tumor microenvironment

Hypoxia, an important feature of solid tumors, is a major factor shaping the immune landscape, and several cancer models have been developed to emulate hypoxic tumors. However, to date, they still have several limitations, such as the lack of reproducibility, inadequate biophysical cues, limited immune cell infiltration, and poor oxygen (O 2 ) control, leading to non-pathophysiological tumor responses. As a result, it is essential to develop new and improved cancer models that mimic key features of the tumor extracellular matrix and recreate tumor-associated hypoxia while allowing cell infiltration and cancer-immune cell interactions. Herein, hypoxia-inducing cryogels (HICs) have been engineered using hyaluronic acid (HA) as macroporous scaffolds to fabricate three-dimensional microtissues and model a hypoxic tumor microenvironment. Specifically, tumor cell-laden HICs have been designed to deplete O 2 locally and induce long-standing hypoxia. This state of low oxygen tension, leading to HIF-1α stabilization in tumor cells, resulted in changes in hypoxia-responsive gene expression and phenotype, a metabolic adaptation to anaerobic glycolysis, and chemotherapy resistance. Additionally, HIC-supported tumor models induced dendritic cell (DC) inhibition, revealing a phenotypic change in plasmacytoid B220 + DC (pDC) subset and an impaired conventional B220 - DC (cDC) response in hypoxia. Lastly, our HIC-based melanoma model induced CD8+ T cell inhibition, a condition associated with the downregulation of pro-inflammatory cytokine secretion, increased expression of immunomodulatory factors, and decreased degranulation and cytotoxic capacity of T cells. Overall, these data suggest that HICs can be used as a tool to model solid-like tumor microenvironments and identify a phenotypic transition from cDC to pDC in hypoxia and the key contribution of HA in retaining cDC phenotype and inducing their hypoxia-mediated immunosuppression. This technology has great potential to deepen our understanding of the complex relationships between cancer and immune cells in low O 2 conditions and may pave the way for developing more effective therapies.

Fast Transport and Transformation of Biomacromolecular Substances via Thermo-Stimulated Active "Inhalation-Exhalation" Cycles of Hierarchically Structured Smart pNIPAM-DNA Hydrogels

Although smart hydrogels hold great promise in biosensing and biomedical applications, their response to external stimuli is governed by the passive diffusion-dependent substance transport between hydrogels and environments and within the 3D hydrogel matrices, resulting in slow response to biomacromolecules and limiting their extensive applications. Herein, inspired by the respiration systems of organisms, an active strategy to achieve highly efficient biomolecular substance transport through the thermo-stimulated "inhalation-exhalation" cycles of hydrogel matrices is demonstrated. The cryo-structured poly(N-isopropylacrylamide) (pNIPAM)-DNA hydrogels, composed of functional DNA-tethered pNIPAM networks and free-water-containing macroporous channels, exhibit thermally triggered fast and reversible shrinking/swelling cycles with high-volume changes, which drive the formation of dynamic water stream to accelerate the intake of external substances and expelling of endogenous substances, thus promoting the functional properties of hydrogel systems. Demonstrated by catalytic DNAzyme and CRISPR-Cas12a-incorporating hydrogels, significantly enhanced catalytic efficiency with up to 280% and 390% is achieved, upon the introduction of active "inhalation-exhalation" cycles, respectively. Moreover, remotely near-infrared (NIR)-triggering of "inhalation-exhalation" cycles is achieved after the introduction of NIR-responsive MXene nanosheets into the hydrogel matrix. These hydrogel systems with enhanced substance transport and transformation properties hold promise in the development of more effective biosensing and therapeutic systems.

Designing Silk-Based Cryogels for Biomedical Applications

There is a need to develop the next generation of medical products that require biomaterials with improved properties. The versatility of various gels has pushed them to the forefront of biomaterials research. Cryogels, a type of gel scaffold made by controlled crosslinking under subzero or freezing temperatures, have great potential to address many current challenges. Unlike their hydrogel counterparts, which are also able to hold large amounts of biologically relevant fluids such as water, cryogels are often characterized by highly dense and crosslinked polymer walls, macroporous structures, and often improved properties. Recently, one biomaterial that has garnered a lot of interest for cryogel fabrication is silk and its derivatives. In this review, we provide a brief overview of silk-based biomaterials and how cryogelation can be used for novel scaffold design. We discuss how various parameters and fabrication strategies can be used to tune the properties of silk-based biomaterials. Finally, we discuss specific biomedical applications of silk-based biomaterials. Ultimately, we aim to demonstrate how the latest advances in silk-based cryogel scaffolds can be used to address challenges in numerous bioengineering disciplines.

Impact of Crosslinking on the Characteristics of Pectin Monolith Cryogels

In this research, the pectin monoliths were prepared via the sol-gel process through different routes of crosslinking and additional freeze-drying. The crosslinking reaction was induced by the use of calcium ions in aqueous solutions and in alcohol/water solutions. The resulting pectin monoliths obtained by freeze-drying were macroporous with open cells, limited specific surface area, moderate mechanical stability and moderate biodegradation rate. The presence of alcohol in crosslinking solution significantly changed the morphology of final pectin monoliths, which was evidenced by the reduction of their pore size for one order. The specific surface area of pectin monoliths obtained through the calcium-water-alcohol route was 25.7 m²/g, the Young compressive modulus was 0.52 MPa, and the biodegradation rate was 45% after 30 days of immersion in compost media. Considering that pectin can be obtained from food waste, and its physical properties could be tailored by different crosslinking routes, the pectin monoliths could find wide application in the pharmaceutical, agricultural, medical and food industries, providing sustainable development concepts.

Chitosan versus Carboxymethyl Chitosan Cryogels: Bacterial Colonization, Human Embryonic Kidney 293T Cell Culturing and Co-Culturing

The potential of chitosan and carboxymethyl chitosan (CMC) cryogels cross-linked with diglycidyl ether of 1,4-butandiol (BDDGE) and poly(ethylene glycol) (PEGDGE) have been compared in terms of 3D culturing HEK-293T cell line and preventing the bacterial colonization of the scaffolds. The first attempts to apply cryogels for the 3D co-culturing of bacteria and human cells have been undertaken toward the development of new models of host-pathogen interactions and bioimplant-associated infections. Using a combination of scanning electron microscopy, confocal laser scanning microscopy, and flow cytometry, we have demonstrated that CMC cryogels provided microenvironment stimulating cell-cell interactions and the growth of tightly packed multicellular spheroids, while cell-substrate interactions dominated in both chitosan cryogels, despite a significant difference in swelling capacities and Young's modulus of BDDGE- and PEGDGE-cross-linked scaffolds. Chitosan cryogels demonstrated only mild antimicrobial properties against Pseudomonas fluorescence, and could not prevent the formation of Staphylococcus aureus biofilm in DMEM media. CMC cryogels were more efficient in preventing the adhesion and colonization of both P. fluorescence and S. aureus on the surface, demonstrating antifouling properties rather than the ability to kill bacteria. The application of CMC cryogels to 3D co-culture HEK-293T spheroids with P. fluorescence revealed a higher resistance of human cells to bacterial toxins than in the 2D co-culture.

Facile Fabrication of Transparent and Opaque Albumin Methacryloyl Gels with Highly Improved Mechanical Properties and Controlled Pore Structures

For porous protein scaffolds to be employed in tissue-engineered structures, the development of cost-effective, macroporous, and mechanically improved protein-based hydrogels, without compromising the original properties of native protein, is crucial. Here, we introduced a facile method of albumin methacryloyl transparent hydrogels and opaque cryogels with adjustable porosity and improved mechanical characteristics via controlling polymerization temperatures (room temperature and −80 °C). The structural, morphological, mechanical, and physical characteristics of both porous albumin methacryloyl biomaterials were investigated using FTIR, CD, SEM, XRD, compression tests, TGA, and swelling behavior. The biodegradation and biocompatibility of the various gels were also carefully examined. Albumin methacryloyl opaque cryogels outperformed their counterpart transparent hydrogels in terms of mechanical characteristics and interconnecting macropores. Both materials demonstrated high mineralization potential as well as good cell compatibility. The solvation and phase separation owing to ice crystal formation during polymerization are attributed to the transparency of hydrogels and opacity of cryogels, respectively, suggesting that two fully protein-based hydrogels could be used as visible detectors/sensors in medical devices or bone regeneration scaffolds in the future.

Antibacterial Sericin Cryogels Promote Hemostasis by Facilitating the Activation of Coagulation Pathway and Platelets

Cryogels, with high water/blood absorption, have great potential for rapid hemostasis. In this study, a hemostatic and antibacterial sericin-methacryloyl/Ag cryogel (SMC@Ag) based on freeze polymerization of methacryloyl-modified sericin and in situ reduction of silver ions is developed. The combination of interconnected micropores and Ag NPs endows the cryogel with high water/blood absorption, and outstanding hemostatic and antibacterial performance. SMC@Ag shows much better hemostatic performance than the commercial gelatin sponge in rat liver injury, tail amputation, and femoral artery injury models. Furthermore, the excellent hemostatic activity of SMC@Ag is due to facilitating the coagulation pathway activation and enhancing the platelets adhesion during coagulation process. Overall, SMC@Ag cryogel with excellent hemostatic and antibacterial performance is a suitable candidate for traumatic hemorrhage and wound healing.

Cryogel Scaffold-Mediated Delivery of Adipose-Derived Stem Cells Promotes Healing in Murine Model of Atrophic Non-Union

Non-union is defined as the permanent failure of a bone to heal and occurs clinically in 5% of fractures. Atrophic non-unions, characterized by absent/minimal callus formation, are poorly understood and difficult to treat. We recently demonstrated a novel murine model of atrophic non-union in the 3.6Col1A1-tk (Col1-tk) mouse, wherein dosing with the nucleoside analog ganciclovir (GCV) was used to deplete proliferating osteoprogenitor cells, leading to a radiographic and biomechanical non-union after the mid-shaft femur fracture. Using this Col1-tk atrophic non-union model, we hypothesized that the scaffold-mediated lentiviral delivery of doxycycline-inducible BMP-2 transgenes would induce osteogenesis at the fracture site. Cryogel scaffolds were used as a vehicle for GFP+ and BMP-2+ cell delivery to the site of non-union. Cryogel scaffolds were biofabricated through the cross-linking of a chitosan-gelatin polymer solution at subzero temperatures, which results in a macroporous, spongy structure that may be advantageous for a bone regeneration application. Murine adipose-derived stem cells were seeded onto the cryogel scaffolds, where they underwent lentiviral transduction. Following the establishment of atrophic non-unions in the femurs of Col1-tk mice (4 weeks post-fracture), transduced, seeded scaffolds were surgically placed around the site of non-union, and the animals were given doxycycline water to induce BMP-2 production. Controls included GFP+ cells on the cryogel scaffolds, acellular scaffolds, and sham (no scaffold). Weekly radiographs were taken, and endpoint analysis included micro-CT and histological staining. After 2 weeks of implantation, the BMP-2+ scaffolds were infiltrated with cartilage and woven bone at the non-union site, while GFP+ scaffolds had woven bone formation. Later, timepoints of 8 weeks had woven bone and vessel formation within the BMP-2+ and GFP + scaffolds with cortical bridging of the original fracture site in both groups. Overall, the cell-seeded cryogels promoted osseous healing. However, while the addition of BMP-2 promoted the endochondral ossification, it may provide a slower route to healing. This proof-of-concept study demonstrates the potential for cellularized cryogel scaffolds to enhance the healing of non-unions.

Facile Preparation of Mechanically Robust and Functional Silica/Cellulose Nanofiber Gels Reinforced with Soluble Polysaccharides

Nanoporous silica gels feature extremely large specific surface areas and high porosities and are ideal candidates for adsorption-related processes, although they are commonly rather fragile. To overcome this obstacle, we developed a novel, completely solvent-free process to prepare mechanically robust CNF-reinforced silica nanocomposites via the incorporation of methylcellulose and starch. Significantly, the addition of starch was very promising and substantially increased the compressive strength while preserving the specific surface area of the gels. Moreover, different silanes were added to the sol/gel process to introduce in situ functionality to the CNF/silica hydrogels. Thereby, CNF/silica hydrogels bearing carboxyl groups and thiol groups were produced and tested as adsorber materials for heavy metals and dyes. The developed solvent-free sol/gel process yielded shapable 3D CNF/silica hydrogels with high mechanical strength; moreover, the introduction of chemical functionalities further widens the application scope of such materials.

Recent Developments in Hyaluronic Acid-Based Hydrogels for Cartilage Tissue Engineering Applications

Articular cartilage lesions resulting from injurious impact, recurring loading, joint malalignment, etc., are very common and encompass the risk of evolving to serious cartilage diseases such as osteoarthritis. To date, cartilage injuries are typically treated via operative procedures such as autologous chondrocyte implantation (ACI), matrix-associated autologous chondrocyte implantation (MACI) and microfracture, which are characterized by low patient compliance. Accordingly, cartilage tissue engineering (CTE) has received a lot of interest. Cell-laden hydrogels are favorable candidates for cartilage repair since they resemble the native tissue environment and promote the formation of extracellular matrix. Various types of hydrogels have been developed so far for CTE applications based on both natural and synthetic biomaterials. Among these materials, hyaluronic acid (HA), a principal component of the cartilage tissue which can be easily modified and biofunctionalized, has been favored for the development of hydrogels since it interacts with cell surface receptors, supports the growth of chondrocytes and promotes the differentiation of mesenchymal stem cells to chondrocytes. The present work reviews the various types of HA-based hydrogels (e.g., in situ forming hydrogels, cryogels, microgels and three-dimensional (3D)-bioprinted hydrogel constructs) that have been used for cartilage repair, specially focusing on the results of their preclinical and clinical assessment.

Versatile Route for Multifunctional Aerogels Including Flaxseed Mucilage and Nanocrystals

Preparation of low density monolithic and free-standing organic-inorganic hybrid aerogels of various properties is demonstrated using green chemistry from a biosafe natural source (flaxseed mucilage) and freeze-casting and subsequent freeze drying. Bio-aerogels, luminescent aerogels and magneto-responsive aerogels were obtained by combination of the flaxseed mucilage with different types of nanoparticles. Moreover, the aerogels are investigated as possible drug release system using curcumin as a model. Various characterization techniques like thermogravimetric analysis, nitrogen physisorption, electron microscopy, UV/Vis absorption and emission spectroscopy, bulk density and mechanical measurements as well as in vitro release profile measurements are employed to investigate the obtained materials. The flaxseed-inspired organic-inorganic hybrid aerogels exhibit ultra-low densities of as low as 5.6 mg/cm³ for 0.5% (w/v) mucilage polymer, a specific surface area of 4 to 20 m² /g, high oil absorption capacity (23 g/g) and prominent compressibility. The natural biopolymer technique leads to low cost and biocompatible functional lightweight materials with tunable properties (physicochemical and mechanical) and significant potential for applications as supporting or stimuli responsive materials, carriers, reactors, microwave, and electromagnetic radiation protective (absorbing) material as well as in drug delivery and oil absorption. This article is protected by copyright. All rights reserved.

New horizons of biomaterials in treatment of nerve damage in diabetes mellitus: A translational prospective review

BACKGROUND

Peripheral nerve injury is a serious concern that leads to loss of neuronal communication that impairs the quality of life and, in adverse conditions, causes permanent disability. The limited availability of autografts with associated demerits shifts the paradigm of researchers to use biomaterials as an alternative treatment approach to recover nerve damage.

PURPOSE

The purpose of this study is to explore the role of biomaterials in translational treatment approaches in diabetic neuropathy.

STUDY DESIGN

The present study is a prospective review study.

METHODS

Published literature on the role of biomaterials in therapeutics was searched for.

RESULTS

Biomaterials can be implemented with desired characteristics to overcome the problem of nerve regeneration. Biomaterials can be further exploited in the treatment of nerve damage especially associated with PDN. These can be modified, customized, and engineered as scaffolds with the potential of mimicking the extracellular matrix of nerve tissue along with axonal regeneration. Due to their beneficial biological deeds, they can expedite tissue repair and serve as carriers of cellular and pharmacological treatments. Therefore, the emerging research area of biomaterials-mediated treatment of nerve damage provides opportunities to explore them as translational biomedical treatment approaches.

CONCLUSIONS

Pre-clinical and clinical trials in this direction are needed to establish the effective role of several biomaterials in the treatment of other human diseases.

In Vitro Wound Dressing Stack Model as a First Step to Evaluate the Behavior of Dressing Materials in Wound Bed-An Assessment of Mass Transport Phenomena in Hydrogel Wound Dressings

Wound dressings when applied are in contact with wound exudates in vivo or with acceptor fluid when testing drug release from wound dressing in vitro. Therefore, the assessment of bidirectional mass transport phenomena in dressing after application on the substrate is important but has never been addressed in this context. For this reason, an in vitro wound dressing stack model was developed and implemented in the 3D printed holder. The stack was imaged using magnetic resonance imaging, i.e., relaxometric imaging was performed by means of T2 relaxation time and signal amplitude 1D profiles across the wound stack. As a substrate, fetal bovine serum or propylene glycol were used to simulate in vivo or in vitro cases. Multi-exponential analysis of the spatially resolved magnetic resonance signal enabled to distinguish components originating from water and propylene glycol in various environments. The spatiotemporal evolution of these components was assessed. The components were related to mass transport (water, propylene glycol) in the dressing/substrate system and subsequent changes of physicochemical properties of the dressing and adjacent substrate. Sharp changes in spatial profiles were detected and identified as moving fronts. It can be concluded that: (1) An attempt to assess mass transport phenomena was carried out revealing the spatial structure of the wound dressing in terms of moving fronts and corresponding layers; (2) Moving fronts, layers and their temporal evolution originated from bidirectional mass transport between wound dressing and substrate. The setup can be further applied to dressings containing drugs.

Polysaccharide Cryogels Containing β-Cyclodextrin for the Delivery of Cannabidiol

Cannabidiol (CBD) has attracted increasing interest due to its therapeutic potential for treating numerous diseases. However, CBD is very lipophilic and has very unfavorable pharmacokinetics and low bioavailability. Efforts are focused on developing drug delivery systems for enhanced solubilization and therapeutic activity of CBD. Here, we report the preparation of original super-macroporous cryogels from 2-hydroxyethyl cellulose (HEC) and β-cyclodextrin (β-CD) designed for the topical delivery of CBD. The cryogels were synthesized by photochemical crosslinking in a frozen aqueous system, purified, and then loaded with CBD. The effect of HEC/β-CD mass ratio (100:0; 50:50; 40:60 and 20:80) in the reaction mixture on the reaction efficiency, physico-mechanical properties of cryogels, drug release profile, and antineoplastic potential were evaluated in detail. The cryogels showed a bi-phasic release behavior: initial burst release in the first 3 hours followed by slower drug release which can be beneficial in the treatment of cutaneous neoplastic diseases.

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.

Cryogels: recent applications in 3D-bioprinting, injectable cryogels, drug delivery, and wound healing

Cryogels are macroporous polymeric structures formed from the cryogelation of monomers/polymers in a solvent below freezing temperature. Due to their inherent interconnected macroporosity, ease of preparation, and biocompatibility, they are increasingly being investigated for use in biomedical applications such as 3D-bioprinting, drug delivery, wound healing, and as injectable therapeutics. This review highlights the fundamentals of macroporous cryogel preparation, cryogel properties that can be useful in the highlighted biomedical applications, followed by a comprehensive review of recent studies in these areas. Research evaluated includes the use of cryogels to combat various types of cancer, for implantation without surgical incision, and use as highly effective wound dressings. Furthermore, conclusions and outlooks are discussed for the use of these promising and durable macroporous cryogels.

Water Uptake as a Crucial Factor on the Properties of Cryogels of Gelatine Cross-Linked by Dextran Dialdehyde

We investigated the water sorption properties of macroporous cryogels of gelatine (Gel) and dextran dialdehyde (DDA) prepared via cryogelation at 260 K and following the freeze drying processes. Water vapour sorption isotherms for aerogels were studied at 293 K by two independent methods: static-gravimetric and dynamic vapour sorption (DVS) over a water activity range of 0.11-1.0. Experimental data were fitted by use of the Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models. The BET model (for a water activity range of 0.1 ≤ p/po ≤ 0.5) was used to calculate the sorption parameters of the studied cryogels (the monolayer capacity, surface area and energy of interaction). In comparison with BET, the GAB model can be applied for the whole range of water activities (0.1 ≤ p/po ≤ 0.95). This model gave an almost perfect correlation between the experimental and calculated sorption isotherms using nonlinear least squares fitting (NLSF). Confocal Laser Scanning Microscopy (CLSM) was used to confirm the structural differences between various DDA:Gel cryogel compositions. Thermogravimetric analysis and DSC data for aerogels DDA:Gel provided information regarding the bonded water loss, relative remaining water content of the material and the temperature of decomposition. Estimation of the amount of bound water in the cryogels after the freeze drying process as well as after the cycle of treatment of cryogels with high humidity and drying was performed using DSC. The results of the DSC determinations showed that cryogels with higher gelatin content had higher levels of bonded water.

Glycosaminoglycan-Based Cryogels as Scaffolds for Cell Cultivation and Tissue Regeneration

Cryogels are a class of macroporous, interconnective hydrogels polymerized at sub-zero temperatures forming mechanically robust, elastic networks. In this review, latest advances of cryogels containing mainly glycosaminoglycans (GAGs) or composites of GAGs and other natural or synthetic polymers are presented. Cryogels produced in this way correspond to the native extracellular matrix (ECM) in terms of both composition and molecular structure. Due to their specific structural feature and in addition to an excellent biocompatibility, GAG-based cryogels have several advantages over traditional GAG-hydrogels. This includes macroporous, interconnective pore structure, robust, elastic, and shape-memory-like mechanical behavior, as well as injectability for many GAG-based cryogels. After addressing the cryogelation process, the fabrication of GAG-based cryogels and known principles of GAG monomer crosslinking are discussed. Finally, an overview of specific GAG-based cryogels in biomedicine, mainly as polymeric scaffold material in tissue regeneration and tissue engineering-related controlled release of bioactive molecules and cells, is provided.

Nanocellulose for peripheral nerve regeneration in rabbits using citric acid as crosslinker with chitosan and freeze/thawed PVA

This work investigates peripheral nerve regeneration using membranes consisting of pure chitosan (CHI), which was further blended with nanofibrillated cellulose, with citric acid as crosslinker, with posterior addition of polyvinyl alcohol, with subsequent freeze thawing. Nanocellulose improves the mechanical and thermal resistance, as well as flexibility of the film, which is ideal for the surgical procedure. The hydrogel presented a slow rate of swelling, which is adequate for cell and drug delivery. A series ofin vitrotests revealed to be non-toxic for neuronal Schwann cell from the peripheral nervous system of Rattus norvegicus, while there was a slight increase in toxicity if crosslink is performed-freeze-thaw. Thein vivoresults, using rabbits with a 5 mm gap nerve defect, revealed that even though pure CHI was able to regenerate the nerve, it did not present functional recovery with only the deep pain attribute being regenerated. When autologous implant was used jointly with the biomaterial membrane, as a covering agent, it revealed a functional recovery within 15 d when cellulose and the hydrogel were introduced, which was attributed to the film charge interaction that may help influence the neuronal axons growth into correct locations. Thus, indicating that this system presents ideal regeneration as nerve conduits.

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.

An Overview on Collagen and Gelatin-Based Cryogels: Fabrication, Classification, Properties and Biomedical Applications

Decades of research into cryogels have resulted in the development of many types of cryogels for various applications. Collagen and gelatin possess nontoxicity, intrinsic gel-forming ability and physicochemical properties, and excellent biocompatibility and biodegradability, making them very desirable candidates for the fabrication of cryogels. Collagen-based cryogels (CBCs) and gelatin-based cryogels (GBCs) have been successfully applied as three-dimensional substrates for cell culture and have shown promise for biomedical use. A key point in the development of CBCs and GBCs is the quantitative and precise characterization of their properties and their correlation with preparation process and parameters, enabling these cryogels to be tuned to match engineering requirements. Great efforts have been devoted to fabricating these types of cryogels and exploring their potential biomedical application. However, to the best of our knowledge, no comprehensive overviews focused on CBCs and GBCs have been reported currently. In this review, we attempt to provide insight into the recent advances on such kinds of cryogels, including their fabrication methods and structural properties, as well as potential biomedical applications.

Design and Assessment of Biodegradable Macroporous Cryogels as Advanced Tissue Engineering and Drug Carrying Materials

Cryogels obtained by the cryotropic gelation process are macroporous hydrogels with a well-developed system of interconnected pores and shape memory. There have been significant recent advancements in our understanding of the cryotropic gelation process, and in the relationship between components, their structure and the application of the cryogels obtained. As cryogels are one of the most promising hydrogel-based biomaterials, and this field has been advancing rapidly, this review focuses on the design of biodegradable cryogels as advanced biomaterials for drug delivery and tissue engineering. The selection of a biodegradable polymer is key to the development of modern biomaterials that mimic the biological environment and the properties of artificial tissue, and are at the same time capable of being safely degraded/metabolized without any side effects. The range of biodegradable polymers utilized for cryogel formation is overviewed, including biopolymers, synthetic polymers, polymer blends, and composites. The paper discusses a cryotropic gelation method as a tool for synthesis of hydrogel materials with large, interconnected pores and mechanical, physical, chemical and biological properties, adapted for targeted biomedical applications. The effect of the composition, cross-linker, freezing conditions, and the nature of the polymer on the morphology, mechanical properties and biodegradation of cryogels is discussed. The biodegradation of cryogels and its dependence on their production and composition is overviewed. Selected representative biomedical applications demonstrate how cryogel-based materials have been used in drug delivery, tissue engineering, regenerative medicine, cancer research, and sensing.

Effect of Cryostructuring Treatment on Some Properties of Xanthan and Karaya Cryogels for Food Applications

Cryogels are novel materials because the manufacturing process known as cryostructuring allows biopolymers to change their properties as a result of repeated controlled freeze-thaw cycles. Hydrogels of xanthan and karaya gums were evaluated after undergoing up to four controlled freeze-thaw cycles in indirect contact with liquid nitrogen (up to -150 °C) to form cryogels. Changes in structural, molecular, rheological, and thermal properties were evaluated and compared to those of their respective hydrogels. Samples were also analyzed by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection (FTIR-ATR), Rotational Rheology (RR), Modulated Differential Scanning Calorimetry (MDSC) and zeta potential (ζ). In general, significant differences (p < 0.05) between the numbers of freeze-thaw cycles were found. Karaya cryogels were not stable to repeated cycles of cryostructuring such as the three-cycle xanthan cryogel, which has the best structural order (95.55%), molecular interactions, and thermal stability, which allows the generation of a novel material with improved thermal and structural properties that can be used as an alternative in food preservation.

Changes in Rat Bone Tissue at the Site of the Defect In Vivo under the Effect of a Cryogenically Structured Albumin Sponge Containing a Bioregulator

We performed a morphological study of the bone tissue after implantation of a cryogenically structured albumin sponge containing a bioregulator isolated from blood serum into an extensive experimental defect of the femur. By day 90, no complete reparation of the bone tissue was achieved in the control group (without implantation of 3D carrier), a loose spongy bone is formed at the site of the defect. After implantation of the 3D carrier without serum bioregulator, the defect was closed, but the formed bone was loose and contained no inflammation foci. After the defect was filed with the albumin sponge with the bioregulator, the repair pattern corresponded to the processes of epimorphic tissue regeneration. The results suggest that cryogenically structured protein material in combination with a serum bioregulator ensured complete restoration of the bone tissue.

Polymeric Materials Used for Immobilisation of Bacteria for the Bioremediation of Contaminants in Water

Bioremediation is a key process for reclaiming polluted soil and water by the use of biological agents. A commonly used approach aims to neutralise or remove harmful pollutants from contaminated areas using live microorganisms. Generally, immobilised microorganisms rather than planktonic cells have been used in bioremediation methods. Activated carbon, inorganic minerals (clays, metal oxides, zeolites), and agricultural waste products are acceptable substrates for the immobilisation of bacteria, although there are limitations with biomass loading and the issue with leaching of bacteria during the process. Various synthetic and natural polymers with different functional groups have been used successfully for the efficient immobilisation of microorganisms and cells. Promise has been shown using macroporous materials including cryogels with entrapped bacteria or cells in applications for water treatment and biotechnology. A cryogel is a macroporous polymeric gel formed at sub-zero temperatures through a process known as cryogelation. Macroporous hydrogels have been used to make scaffolds or supports for immobilising bacterial, viral, and other cells. The production of composite materials with immobilised cells possessing suitable mechanical and chemical stability, porosity, elasticity, and biocompatibility suggests that these materials are potential candidates for a range of applications within applied microbiology, biotechnology, and research. This review evaluates applications of macroporous cryogels as tools for the bioremediation of contaminants in wastewater.

Poly(Vinyl Alcohol) Cryogel Membranes Loaded with Resveratrol as Potential Active Wound Dressings

Hydrogel wound dressings are highly effective in the therapy of wounds. Yet, most of them do not contain any active ingredient that could accelerate healing. The aim of this study was to prepare hydrophilic active dressings loaded with an anti-inflammatory compound - trans-resveratrol (RSV) of hydrophobic properties. A special attention was paid to select such a technological strategy that could both reduce the risk of irritation at the application site and ensure the homogeneity of the final hydrogel. RSV dissolved in Labrasol was combined with an aqueous sol of poly(vinyl) alcohol (PVA), containing propylene glycol (PG) as a plasticizer. This sol was transformed into a gel under six consecutive cycles of freezing (-80 °C) and thawing (RT). White, uniform and elastic membranes were successfully produced. Their critical features, namely microstructure, mechanical properties, water uptake and RSV release were studied using SEM, DSC, MRI, texture analyser and Franz-diffusion cells. The cryogels made of 8 % of PVA showed optimal tensile strength (0.22 MPa) and elasticity (0.082 MPa). The application of MRI enabled to elucidate mass transport related phenomena in this complex system at the molecular (detection of PG, confinement effects related to pore size) as well as at the macro level (swelling). The controlled release of RSV from membranes was observed for 48 h with mean dissolution time of 18 h and dissolution efficiency of 35 %. All in all, these cryogels could be considered as a promising new active wound dressings.

Semi-interpenetrating polymer network cryogels based on poly(ethylene glycol) diacrylate and collagen as potential off-the-shelf platforms for cancer cell research

In the present work, we investigated the potential of novel semi-interpenetrating polymer network (semi-IPN) cryogels, obtained through ultraviolet exposure of aqueous mixtures of poly(ethylene glycol) diacrylate and type I collagen, as tunable off-the-shelf platforms for 3D cancer cell research. We synthesized semi-IPN cryogels with variable collagen amounts (0.1% and 1% w/v) and assessed the effect of collagen on key cryogel properties for cell culture, for example, porosity, degradation rate and mechanical stiffness. Then, we investigated the ability of the cryogels to sustain the long-term growth of two pancreatic ductal adenocarcinoma (PDAC) cell populations, the parenchymal Panc1 cells and their derived cancer stem cells. Results revealed that both cell lines efficiently infiltrated, attached and expanded in the cryogels over a period of 14 days. However, only when grown in the cryogels with the highest collagen concentration, both cell lines reproduced their characteristic growth pattern previously observed in collagen-enriched organotypic cultures, biomimetic of the highly fibrotic PDAC stroma. Cellular preembedding in Matrigel, that is, the classical approach to develop/grow organoids, interfered with an efficient intra-scaffold migration and growth. Although preliminary, these findings highlight the potential of the proposed cryogels as reproducible and tunable cancer cell research platforms.

Removal of Cd2+ from Water by Use of Super-Macroporous Cryogels and Comparison to Commercial Adsorbents

In this study amphoteric cryogels were synthesized by the use of free-radical co-polymerization of acrylate-based precursors (methacrylic acid and 2-acrylamido-2-methyl-1-propansulfonic acid) with allylamine at different ratios. The physico-chemical characteristics of the cryogels were examined using SEM/EDX, FT-IR, XPS and zeta potential measurements. The cryogels were tested toward Cd²⁺ removal from aqueous solutions at various pH and initial concentrations. Equilibrium studies revealed a maximum sorption capacity in the range of 132-249 mg/g. Leaching experiments indicated the stability of Cd²⁺ in the cryogel structure. Based on kinetics, equilibrium and characterization results, possible removal mechanisms are proposed, indicating a combination of ion exchange and complexation of Cd²⁺ with the cryogels' surface functional groups. The cryogels were compared to commercially available adsorbents (zeolite Y and cation exchange resin) for the removal of Cd²⁺ from various water matrices (ultrapure water, tap water and river water) and the results showed that, under the experimental conditions used, the cryogels can be more effective adsorbents.

Cryostructuring of Polymeric Systems. 55. Retrospective View on the More than 40 Years of Studies Performed in the A.N.Nesmeyanov Institute of Organoelement Compounds with Respect of the Cryostructuring Processes in Polymeric Systems

The processes of cryostructuring in polymeric systems, the techniques of the preparation of diverse cryogels and cryostructurates, the physico-chemical mechanisms of their formation, and the applied potential of these advanced polymer materials are all of high scientific and practical interest in many countries. This review article describes and discusses the results of more than 40 years of studies in this field performed by the researchers from the A.N.Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences-one of the key centers, where such investigations are carried out. The review includes brief historical information, the description of the main effects and trends characteristic of the cryostructuring processes, the data on the morphological specifics inherent in the polymeric cryogels and cryostructurates, and examples of their implementation for solving certain applied tasks.