Pullulan dialdehyde crosslinked gelatin hydrogels with high strength for biomedical applications

Crosslinking of gelatin Schiff base hydrogels with different structural dialdehyde polysaccharides as novel crosslinkers: Characterization and performance comparison

Few studies have been conducted on the relationship between the crosslinking ability of dialdehyde polysaccharides (DPs) with different structures and the structure and properties of hydrogels. Herein, the effects of dialdehyde sodium alginate (DSA), dialdehyde guar gum (DGG), and dialdehyde dextran (DDE) as crosslinking agents for gelatin (GE)-based hydrogels were comparatively studied. First, the structure and aldehyde content of DPs were evaluated. Subsequently, the structure, crosslinking degree, and physicochemical properties of GE/DP hydrogels were characterized. Compared with pure GE hydrogels, GE/DP hydrogels had higher thermal stability and mechanical properties. Moreover, the aldehyde content of DPs was ordered as follows: DSA < DGG < DDE. The higher crosslinking degree of the hydrogels formed by DPs with a higher aldehyde content resulted in smaller hydrogel pores, higher mechanical strength, and a lower equilibrium swelling rate. These observations provide a theoretical basis for selecting crosslinking candidates for hydrogel-specific applications.

Degradable Cell-Adhesive Hybrid Hydrogels by Cross-Linking of Gelatin with Poly(2-isopropenyl-2-oxazoline)

This study focused on the cross-linking of poly(2-isopropenyl-2-oxazoline) (PiPOx) with gelatin to obtain strong, degradable hybrid hydrogels with good cell adhesion. The molecular weight and concentration of PiPOx and the PiPOx-to-gelatin ratio were varied to adjust the mechanical and swelling properties of the hybrid hydrogels. The swelling degree of PiPOx-gelatin hydrogels in water ranged between 1260 and 810%, with the corresponding Young's compressive moduli ranging from 77 to 215 kPa. Rheological measurements demonstrated the mechanical stability of the hydrogels. The hydrogels exhibited substantial degradation in Dulbecco's phosphate-buffered saline (DPBS) and cell culture medium within several weeks, indicating their degradability and responsiveness. The cell adhesion assay with primary human foreskin fibroblasts revealed the hybrid hydrogels are noncytotoxic and support cell attachment and proliferation. These strong hydrogels thus show excellent potential as biomedical cell scaffolds, combining the tunability and strength of PiPOx hydrogels with gelatin's cell-interactive properties while the ester-containing cross-links provide tunable degradability.

Tough, conductive hydrogels based on gelatin and oxidized sodium carboxymethyl cellulose as flexible sensors

Natural polymer-based hydrogels have been wildly used in electronic skin, health monitoring and human motion sensing. However, the construction of hydrogel with excellent mechanical strength and electrical conductivity totally using natural polymers still faces many challenges. In this paper, gelatin and oxidized sodium carboxymethylcellulose were used to synthesize a double-network hydrogel through the dynamic Schiff base bonds. Then, the mechanical strength of the hydrogel was further enhanced by immersing it in an ammonium sulfate solution based on the Hofmeister effect between gelatin and salt. Finally, the gelatin/oxidized sodium carboxymethylcellulose hydrogel exhibited high tensile properties (614 %), tensile fracture strength (2.6 MPa), excellent compressive fracture strength (64 MPa), and compressive toughness (4.28 MJ/m3). Also, the electrical conductivity reached 3.94 S/m. The hydrogel after salt soaked was fabricated as strain sensors, which could accurately monitor the movement of many joints in the human body, such as fingers, wrists, elbows, neck, and throat. Therefore, the designed hydrogel fully originated from natural polymers and has great application potential in motion detection and information recording.

Electric-field-sensitive hydrogel based on pineapple peel oxidized hydroxyethyl cellulose/gelatin/Hericium erinaceus residues chitosan and its study in curcumin delivery

This study focused on synthesis of innovative hydrogels with electric field response from modified pineapple peel cellulose and hericium erinaceus chitosan and gelatin based on Schiff base reaction. A series of hydrogels were prepared by oxidized hydroxyethyl cellulose, gelatin and chitosan at different deacetylation degree via mild Schiff base reaction. Subsequently experiments towards the characterization of oxidized hydroxyethyl cellulose/gelatin/chitosan (OHGCS) hydrogel polymers were carried out by FTIR/XRD/XPS, swelling performances and electric response properties. The prepared hydrogels exhibited stable and reversible bending behaviors under repeated on-off switching of electric fields, affected by ionic strength, electric voltage and pH changes. The swelling ratio of OHGCS hydrogels was found reduced as deacetylation degree increasing and reached the maximum ratio ∼ 2250 % for OHGCS-1. In vitro drug releasing study showed the both curcumin loading capacity and release amount of Cur-OHGCS hydrogels arrived about 90 % during 6 h. Antioxidation assessments showed that the curcumin-loaded hydrogels had good antioxidation activities, in which, 10 mg Cur-OHGCS-1 hydrogel could reach to the maximum of about 90 % DPPH scavenging ratio. These results indicate the OHGCS hydrogels have potentials in sensor and drug delivery system.

Formation of Stable Vascular Networks by 3D Coaxial Printing and Schiff-Based Reaction

Vascularized organs hold potential for various applications, such as organ transplantation, drug screening, and pathological model establishment. Nevertheless, the in vitro construction of such organs encounters many challenges, including the incorporation of intricate vascular networks, the regulation of blood vessel connectivity, and the degree of endothelialization within the inner cavities. Natural polymeric hydrogels, such as gelatin and alginate, have been widely used in three-dimensional (3D) bioprinting since 2005. However, a significant disparity exists between the mechanical properties of the hydrogel materials and those of human soft tissues, necessitating the enhancement of their mechanical properties through modifications or crosslinking. In this study, we aim to enhance the structural stability of gelatin-alginate hydrogels by crosslinking gelatin molecules with oxidized pullulan (i.e., a polysaccharide) and alginate molecules with calcium chloride (CaCl2). A continuous small-diameter vascular network with an average outer diameter of 1 mm and an endothelialized inner surface is constructed by printing the cell-laden hydrogels as bioinks using a coaxial 3D bioprinter. The findings demonstrate that the single oxidized pullulan crosslinked gelatin and oxidized pullulan/CaCl2 double-crosslinked gelatin-alginate hydrogels both exhibit a superior structural stability compared to their origins and CaCl2 solely crosslinked gelatin-alginate hydrogels. Moreover, the innovative gelatin and gelatin-alginate hydrogels, which have excellent biocompatibilities and very low prices compared with other hydrogels, can be used directly for tissue/organ construction, tissue/organ repairment, and cell/drug transportation.

Degradable biomedical elastomers: paving the future of tissue repair and regenerative medicine

Degradable biomedical elastomers (DBE), characterized by controlled biodegradability, excellent biocompatibility, tailored elasticity, and favorable network design and processability, have become indispensable in tissue repair. This review critically examines the recent advances of biodegradable elastomers for tissue repair, focusing mainly on degradation mechanisms and evaluation, synthesis and crosslinking methods, microstructure design, processing techniques, and tissue repair applications. The review explores the material composition and cross-linking methods of elastomers used in tissue repair, addressing chemistry-related challenges and structural design considerations. In addition, this review focuses on the processing methods of two- and three-dimensional structures of elastomers, and systematically discusses the contribution of processing methods such as solvent casting, electrostatic spinning, and three-/four-dimensional printing of DBE. Furthermore, we describe recent advances in tissue repair using DBE, and include advances achieved in regenerating different tissues, including nerves, tendons, muscle, cardiac, and bone, highlighting their efficacy and versatility. The review concludes by discussing the current challenges in material selection, biodegradation, bioactivation, and manufacturing in tissue repair, and suggests future research directions. This concise yet comprehensive analysis aims to provide valuable insights and technical guidance for advances in DBE for tissue engineering.

Citric Acid Cross-Linked Gelatin-Based Composites with Improved Microhardness

The aim of this study is to investigate the influence of cross-linking and reinforcements in gelatin on the physico-mechanical properties of obtained composites. The gelatin-based composites cross-linked with citric acid (CA) were prepared: gelatin type B (GB) and β-tricalcium phosphate (β-TCP) and novel hybrid composite GB with β-TCP and hydroxyapatite (HAp) particles, and their structure, thermal, and mechanical properties were compared with pure gelatin B samples. FTIR analysis revealed that no chemical interaction between the reinforcements and gelatin matrix was established during the processing of hybrid composites by the solution casting method, proving the particles had no influence on GB cross-linking. The morphological investigation of hybrid composites revealed that cross-linking with CA improved the dispersion of particles, which further led to an increase in mechanical performance. The microindentation test showed that the hardness value was increased by up to 449%, which shows the high potential of β-TCP and HAp particle reinforcement combined with CA as a cross-linking agent. Furthermore, the reduced modulus of elasticity was increased by up to 288%. Results of the MTT assay on L929 cells have revealed that the hybrid composite GB-TCP-HA-CA was not cytotoxic. These results showed that GB cross-linked with CA and reinforced with different calcium phosphates presents a valuable novel material with potential applications in dentistry.

Progress in the Use of Hydrogels for Antioxidant Delivery in Skin Wounds

The skin is the largest organ of the body, and it acts as a protective barrier against external factors. Chronic wounds affect millions of people worldwide and are associated with significant morbidity and reduced quality of life. One of the main factors involved in delayed wound healing is oxidative injury, which is triggered by the overproduction of reactive oxygen species. Oxidative stress has been implicated in the pathogenesis of chronic wounds, where it is known to impair wound healing by causing damage to cellular components, delaying the inflammatory phase of healing, and inhibiting the formation of new blood vessels. Thereby, the treatment of chronic wounds requires a multidisciplinary approach that addresses the underlying causes of the wound, provides optimal wound care, and promotes wound healing. Among the promising approaches to taking care of chronic wounds, antioxidants are gaining interest since they offer multiple benefits related to skin health. Therefore, in this review, we will highlight the latest advances in the use of natural polymers with antioxidants to generate tissue regeneration microenvironments for skin wound healing.

Rhizobial oxidized 3-hydroxylbutanoyl glycan-based gelatin hydrogels with enhanced physiochemical properties for pH-responsive drug delivery

Rhizobial exopolysaccharide (EPS) is an acidic polysaccharide involved in nitrogen fixation-related signal transduction in the rhizosphere, serving as a structural support for biofilms, and protecting against various external environmental stresses. Rhizobial EPS as a hydrogel biomaterial was used for a pH-responsive drug delivery system combing with gelatins. Pure gelatin (GA) hydrogels have limited practical applications due to their poor mechanical strength and poor thermal stability. We developed new GA hydrogels using oxidized 3-hydroxylbutanoyl glycan (OHbG) as a polymer cross-linking agent to overcome these limitations. OHbG was synthesized from sodium periodate oxidation of 3-hydroxylbutanoyl glycan directly isolated from Rhizobium leguminosarum bv. viciae VF39. The newly fabricated OHbG/GA hydrogels exhibited 21-fold higher compressive stress and 4.7-fold higher storage modulus (G') than GA at the same strain. This result suggested that OHbG provided mechanical improvement. In addition, these OHbG/GA hydrogels showed effective pH-controlled drug release for 5-fluorouracil, self-healable, and self-antioxidant capacity by uronic acids of OHbG. Cell viability tests using HEK-293 cells in vitro also showed that the OHbG/GA hydrogels were non-toxic. This suggests that the new OHbG/GA hydrogels can be used as a potentially novel biomaterial for drug delivery based on its self-healing ability, antioxidant capacity, and pH-responsive drug delivery.

Polyvinyl alcohol/collagen composite scaffold reinforced with biodegradable polyesters/gelatin nanofibers for adipose tissue engineering

Breast cancer has become the most diagnosed cancer type, endangering the health of women. Patients with breast resection are likely to suffer serious physical and mental trauma. Therefore, breast reconstruction becomes an important means of postoperative patient rehabilitation. Polyvinyl alcohol hydrogel has great potential in adipose tissue engineering for breast reconstruction. However, its application is limited because of the lack of bioactive factors and poor structural stability. In this study, we prepared biodegradable polylactic acid-glycolic acid copolymer/polycaprolactone/gelatin (PPG) nanofibers. We then combined them with polyvinyl alcohol/collagen to create tissue engineering scaffolds to overcome limitations. We found that PPG fibers formed amide bonds with polyvinyl alcohol/collagen scaffolds. After chemical crosslinking, the number of amide bonds increased, leading to a significant improvement in their mechanical properties and thermal stability. The results showed that compared with pure PVA scaffolds, the maximum compressive stress of the scaffold doped with 0.9 g nanofibers increased by 500 %, and the stress loss rate decreased by 40.6 % after 10 cycles of compression. The presence of natural macromolecular gelatin and the changes in the pore structure caused by nanofibers provide cells with richer and more three-dimensional adsorption sites, allowing them to grow in three dimensions on the scaffold. So, the hydrogel scaffold by reinforcing polyvinyl alcohol hydrogel with PPG fibers is a promising breast reconstruction method.

Microcin C7-laden modified gelatin based biocomposite hydrogel for the treatment of periodontitis

Periodontitis is an oral disease with the highest incidence globally, and plaque control is the key to its treatment. In this study, Microcin C7 was used to treat periodontitis, and a novel injectable temperature-sensitive sustained-release hydrogel was synthesized as an environmentally sensitive carrier for drug delivery. First, modified gelatin was formed from gelatin and glycidyl methacrylate. Then, Microcin C7-laden hydrogel was formed from cross-linking with double bonds between modified gelatin, N-isopropyl acrylamide, and 2-Methacryloyloxyethyl phosphorylcholine through radical polymerization, and the model drug Microcin C7 was loaded by electrostatic adsorption. The hydrogel has good temperature sensitivity, self-healing, and injectable properties. In vitro results showed that the hydrogel could slowly and continuously release Microcin C7 with good biocompatibility and biodegradability, with a remarkable antibacterial effect on Porphyromonas gingivalis. It also confirmed the antibacterial and anti-inflammatory effects of Microcin C7-laden hydrogel in a periodontitis rat model. The results showed that Microcin C7-laden hydrogel is a promising candidate for local drug delivery systems in periodontitis.

Construction and properties of a carbon dots-decorated gelatin-dialdehyde starch hydrogel with pH response release and antibacterial activity

An antibacterial carbon dot hydrogel (GDSS-PCD) was constructed based on gelatin, dialdehyde starch (DS) and carbon dots (S-PCDs). The formation mechanism of GDSS-PCD hydrogels was attributed to the synergistic cross-linking of hydrogen bonds and dynamic covalent bonds. With increasing S-PCD content, the mechanical and rheological properties of GDSS-PCD hydrogels can be improved, and the micropore size becomes denser. GDSS-PCD hydrogels had pH-dependent swelling and degradation behavior, with a high swelling rate under acidic conditions and relatively low swelling under neutral and alkaline conditions. The cumulative release of S-PCDs from the same hydrogel in an acidic environment was higher than that in an alkaline environment, indicating that the GDSS-PCD hydrogel had a pH-dependent controlled release ability. The release behavior of S-PCDs conformed to the first-order kinetic release model (R2 > 0.95), and the release mechanism was related to Fickian diffusion. The synergistic antibacterial mechanism of GDSS-PCD hydrogels against Staphylococcus aureus suggested that bacterial metabolism leads to an acidic culture environment, which releases S-PCDs and destroys the bacterial cell membrane for antibacterial purposes. In GDSS-PCD hydrogels, S-PCDs play the main antibacterial role, and the hydrogel plays a synergistic role in trapping bacteria. Carbon dot hydrogels are promising materials to fulfil the functions of antibacterial and controlled release in the food and biomedical fields.

Advancements in gelatin-based hydrogel systems for biomedical applications: A state-of-the-art review

A gelatin-based hydrogel system is a stimulus-responsive, biocompatible, and biodegradable polymeric system with solid-like rheology that entangles moisture in its porous network that gradually protrudes to assemble a hierarchical crosslinked arrangement. The hydrolysis of collagen directs gelatin construction, which retains arginyl glycyl aspartic acid and matrix metalloproteinase-sensitive degeneration sites, further confining access to chemicals entangled within the gel (e.g., cell encapsulation), modulating the release of encapsulated payloads and providing mechanical signals to the adjoining cells. The utilization of various types of functional tunable biopolymers as scaffold materials in hydrogels has become highly attractive due to their higher porosity and mechanical ability; thus, higher loading of proteins, peptides, therapeutic molecules, etc., can be further modulated. Furthermore, a stimulus-mediated gelatin-based hydrogel with an impaired concentration of gellan demonstrated great shear thinning and self-recovering characteristics in biomedical and tissue engineering applications. Therefore, this contemporary review presents a concise version of the gelatin-based hydrogel as a conceivable biomaterial for various biomedical applications. In addition, the article has recapped the multiple sources of gelatin and their structural characteristics concerning stimulating hydrogel development and delivery approaches of therapeutic molecules (e.g., proteins, peptides, genes, drugs, etc.), existing challenges, and overcoming designs, particularly from drug delivery perspectives.

Hydrogels dressings based on guar gum and chitosan: Inherent action against resistant bacteria and fast wound closure

Hydrogels made with depolymerized guar gum, oxidized with theoretical oxidation degrees of 20, 35 and 50 %, were obtained via Schiff's base reaction with N-succinyl chitosan. The materials obtained were subjected to characterization by FT-IR, rheology, swelling, degradation, and morphology. Additionally, their gelation time categorized all three hydrogels as injectable. The materials' swelling degrees in Phosphate-Buffered Saline (PBS) were in the range of 26-35 g of fluid/g gel and their pore size distribution was heterogeneous, with pores varying from 67 to 93 μm. All hydrogels degraded in PBS solution, but maintained around 40 % of their initial mass after 28 days, which was more than enough time for wound healing. The biomaterials were also flexible, self-repairing, adhesive and cytocompatible and presented intrinsic actions, regardless of the presence of additives or antibiotics, against gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and gram-negative bacteria (Escherichia coli). However, the most pronounced bactericidal effect was against resistant Staphylococcus aureus - MRSA. In vivo assays, performed with 50 % oxidized gum gel, demonstrated that this material exerted anti-inflammatory effects, accelerating the healing process and restoring tissues by approximately 99 % within 14 days. In conclusion, these hydrogels have unique characteristics, making them excellent candidates for wound-healing dressings.

Construction of protein-, polysaccharide- and polyphenol-based conjugates as delivery systems

Natural polymers, such as polysaccharides and proteins, have been used to prepare several delivery systems owing to their abundance, bioactivity, and biodegradability. They are usually modified or combined with small molecules to form the delivery systems needed to meet different needs in food systems. This paper reviews the interactions of proteins, polysaccharides, and polyphenols in the bulk phase and discusses the design strategies, coupling techniques, and their applications as conjugates in emulsion delivery systems, including traditional, Pickering, multilayer, and high internal-phase emulsions. Furthermore, it explores the prospects of the application of conjugates in food preservation, food development, and nanocarrier development. Currently, there are seven methods for composite delivery systems including the Maillard reaction, carbodiimide cross-linking, alkali treatment, enzymatic cross-linking, free radical induction, genipin cross-linking, and Schiff base chemical cross-linking to prepare binary and ternary conjugates of proteins, polysaccharides, and polyphenols. To design an effective target complex and its delivery system, it is helpful to understand the physicochemical properties of these biomolecules and their interactions in the bulk phase. This review summarizes the knowledge on the interaction of biological complexes in the bulk phase, preparation methods, and the preparation of stable emulsion delivery system.

Dialdehyde carbohydrates - Advanced functional materials for biomedical applications

Dialdehyde carbohydrates (DCs) have found applications in a wide range of biomedical field due to their great versatility, biocompatibility/biodegradability, biological properties, and controllable chemical/physical characteristics. The presence of dialdehyde groups in carbohydrate structure allows cross-linking of DCs to form versatile architectures serving as interesting matrices for biomedical applications (e.g., drug delivery, tissue engineering, and regenerative medicine). Recently, DCs have noticeably contributed to the development of diverse physical forms of advanced functional biomaterials i.e., bulk architectures (hydrogels, films/coatings, or scaffolds) and nano/-micro formulations. We underline here the current scientific knowledge on DCs, and demonstrate their potential and newly developed biomedical applications. Specifically, an update on the synthesis approach and functional/bioactive attributes is provided, and the selected in vitro/in vivo studies are reviewed comprehensively as examples of the latest progress in the field. Moreover, safety concerns, challenges, and perspectives towards the application of DCs are deliberated.

Bioinspired self-healing injectable nanocomposite hydrogels based on oxidized dextran and gelatin for growth-factor-free bone regeneration

Hydrogels with great biocompatibility, biodegradability, and mechanical properties, combined with osteoconductivity, osteoinductivity, and osteointegration as biomaterials for bone regeneration without adding exogenous growth factors and cells are highly appealing but challenging. Here, inspired by organic-inorganic analogues of natural bone tissue and the adhesion chemistry of mussels, nanocomposite hydrogels with self-healing, injectable, adhesive, antioxidant, and osteoinductive properties (termed GO-PHA-CPs) were constructed by Schiff base cross-linking between dopamine-modified gelatin (Gel-DA) and oxidized dextran (ODex). Furthermore, the hydrogel network was enhanced by the introduction of polydopamine-functionalized nanohydroxyapatite (PHA) by improving the interfacial compatibility between the rigid inorganic particles and the flexible hydrogel matrix. Bioactive cod peptides (CPs) with osteogenic activity from Atlantic cod were further incorporated into the nanocomposite hydrogel. As a result, the multicomponent nanocomposite hydrogel favored the adhesion and spreading of MC3T3-E1 cells. The increased ALP activity suggested that GO-PHA-CPs hydrogels contributed to the osteogenic differentiation of MC3T3-E1 cells. The suitability of GO-PHA-CPs hydrogels for enhancing bone regeneration in vivo was further confirmed by the rat femoral defect model. Our results indicate that the multifunctional GO-PHA-CPs nanocomposite hydrogels without growth factors are a promising and effective candidate material for bone regeneration.

Tailoring the Swelling-Shrinkable Behavior of Hydrogels for Biomedical Applications

Hydrogels with tailor-made swelling-shrinkable properties have aroused considerable interest in numerous biomedical domains. For example, as swelling is a key issue for blood and wound extrudates absorption, the transference of nutrients and metabolites, as well as drug diffusion and release, hydrogels with high swelling capacity have been widely applicated in full-thickness skin wound healing and tissue regeneration, and drug delivery. Nevertheless, in the fields of tissue adhesives and internal soft-tissue wound healing, and bioelectronics, non-swelling hydrogels play very important functions owing to their stable macroscopic dimension and physical performance in physiological environment. Moreover, the negative swelling behavior (i.e., shrinkage) of hydrogels can be exploited to drive noninvasive wound closure, and achieve resolution enhancement of hydrogel scaffolds. In addition, it can help push out the entrapped drugs, thus promote drug release. However, there still has not been a general review of the constructions and biomedical applications of hydrogels from the viewpoint of swelling-shrinkable properties. Therefore, this review summarizes the tactics employed so far in tailoring the swelling-shrinkable properties of hydrogels and their biomedical applications. And a relatively comprehensive understanding of the current progress and future challenge of the hydrogels with different swelling-shrinkable features is provided for potential clinical translations.

Oxidized pullulan exhibits potent antibacterial activity against S. aureus by disrupting its membrane integrity

The capability of bacteria to withstand the misuse of antibiotics leads to the generation of multi-drug resistant strains, posing a new challenge to curb wound infections. The biological macromolecules, due to their biocompatibility, biodegradability, and antimicrobial properties, have been explored for a variety of antimicrobial and therapeutic purposes. This work reports that a single-step oxidation of pullulan polymer leads to the formation of oxidized pullulan (o-pullulan), which shows striking antibacterial and antibiofilm activities against the Gram-positive bacteria, Staphylococcus aureus, implicated in wound-related infections. Oxidation of pullulan generates 28 % aldehyde groups (3.462 mmol/g) which exerted 97 % bactericidal activity against S. aureus by targeting cell wall-associated membrane protein SpA (Staphylococcal protein A). The molecular docking, gene silencing, and fluorescence quenching studies revealed a direct binding of o-pullulan with the B and C domains of SpA, which alters the membrane potential and inhibits Ca2+-Mg2+-ATPase pumps. O-pullulan also exhibited scavenging activity against intracellular reactive oxygen species (ROS), and non-immunotoxic activity and was found to be non-toxic to mammalian cells. Thus, o-pullulan shows great promise as an antimicrobial polymer against S. aureus for chronic wound management.

Novel electrospun nanofibers based on gelatin/oxidized xanthan gum containing propolis reinforced by Schiff base cross-linking for food packaging

Gelatin-based electrospun fibers are promising materials for food packaging but suffer from high hydrophilicity and weak mechanical properties. To overcome these limitations, in the current study, gelatin-based nanofibers were reinforced by using oxidized xanthan gum (OXG) as a crosslinking agent. The nanofibers' morphology was investigated through SEM, and the observations showed that the fibers' diameter was decreased by enhancing OXG content. The resultant fibers with more OXG content exhibited high tensile stress so the optimal sample obtained showed a tensile stress of 13.24 ± 0.76 MPa, which is up to 10 times more than neat gelatin fiber. Adding OXG to gelatin fibers reduced water vapor permeability, water solubility, and moisture content properties while increasing thermal stability and porosity. Additionally, the nanofibers containing propolis displayed a homogenous morphology with high antioxidant and antibacterial activities. In general, the findings suggested that the designed fibers could be used as a matrix for active food packaging.

Diversity of Bioinspired Hydrogels: From Structure to Applications

Hydrogels are three-dimensional networks with a variety of structures and functions that have a remarkable ability to absorb huge amounts of water or biological fluids. They can incorporate active compounds and release them in a controlled manner. Hydrogels can also be designed to be sensitive to external stimuli: temperature, pH, ionic strength, electrical or magnetic stimuli, specific molecules, etc. Alternative methods for the development of various hydrogels have been outlined in the literature over time. Some hydrogels are toxic and therefore are avoided when obtaining biomaterials, pharmaceuticals, or therapeutic products. Nature is a permanent source of inspiration for new structures and new functionalities of more and more competitive materials. Natural compounds present a series of physico-chemical and biological characteristics suitable for biomaterials, such as biocompatibility, antimicrobial properties, biodegradability, and nontoxicity. Thus, they can generate microenvironments comparable to the intracellular or extracellular matrices in the human body. This paper discusses the main advantages of the presence of biomolecules (polysaccharides, proteins, and polypeptides) in hydrogels. Structural aspects induced by natural compounds and their specific properties are emphasized. The most suitable applications will be highlighted, including drug delivery, self-healing materials for regenerative medicine, cell culture, wound dressings, 3D bioprinting, foods, etc.

A self-healing hydrogel and injectable cryogel of gelatin methacryloyl-polyurethane double network for 3D printing

Three-dimensional (3D) printing of soft biomaterials facilitates the progress of personalized medicine. The development for different forms of 3D-printable biomaterials can promotes the potential manufacturing for artificial organs and provides biomaterials with the required properties. In this study, gelatin methacryloyl (GelMA) and dialdehyde-functionalized polyurethane (DFPU) were combined to create a double crosslinking system and develop 3D-printable GelMA-PU biodegradable hydrogel and cryogel. The GelMA-PU system demonstrates a combination of self-healing ability and 3D printability and provides two distinct forms of 3D-printable biomaterials with smart functions, high printing resolution, and biocompatibility. The hydrogel was printed into individual modules through an 80 µm or larger nozzle and further assembled into complex structures through adhesive and self-healing abilities, which could be stabilized by secondary photocrosslinking. The 3D-printed hydrogel was adhesive, light transmittable, and could embed a light emitting diode (LED). Furthermore, the hydrogel laden with human mesenchymal stem cells (hMSCs) was successfully printed and showed cell proliferation. Meanwhile, 3D-printed cryogel was achieved by printing on a subzero temperature platform through a 210 µm nozzle. After secondary photocrosslinking and drying, the cryogel was deliverable through a 16-gauge (1194 µm) syringe needle and can promote the proliferation of hMSCs. The GelMA-PU system extends the ink pool for 3D printing of biomaterials and has potential applications in tissue engineering scaffolds, minimally invasive surgery devices, and electronic wound dressings. STATEMENT OF SIGNIFICANCE: The 3D-printable biomaterials developed in this work are GelMA-based ink with smart funcitons and have potentials for various customized medical applications. The synthesized GelMA-polyurethane double network hydrogel can be 3D-printed into individual modules (e.g., 11 × 11 × 5 mm³) through an 80 μm or larger size nozzle, which are then assembled into a taller structure over five times of the initial height by self-healing and secondary photocrosslinking. The hydrogel is adhesive, light transmittable, and biocompatible that can either carry human mesenchymal stem cells (hMSCs) as bioink or embed a red light LED (620 nm) with potential applications in electronic skin dressing. Meanwhile, the 3D-printed highly compressible cryogel (e.g., 6 × 6 × 1 mm³) is deliverable by a 16-gauge (1194 μm) syringe needle and supports the proliferation of hMSCs also.

Gelatin hydrogel reinforced with mussel-inspired polydopamine-functionalized nanohydroxyapatite for bone regeneration

Developing high-strength hydrogels with biocompatibility and bone conductibility is still desirable for bone regeneration. The nanohydroxyapatite (nHA) was incorporated into a dopamine-modified gelatin (Gel-DA) hydrogel system to create a highly biomimetic native bone tissue microenvironment. In addition, to further increase the cross-linking density between nHA and Gel-DA, nHA was functionalized by mussel-inspired polydopamine (PDA). Compared with nHA, adding polydopamine functionalized nHA (PHA) increased the compressive strength of Gel-Da hydrogel from 449.54 ± 180.32 kPa to 611.18 ± 211.86 kPa without affecting its microstructure. Besides, the gelation time of Gel-DA hydrogels with PHA incorporation (GD-PHA) was controllable from 49.47 ± 7.93 to 88.11 ± 31.18 s, contributing to its injectable ability in clinical applications. In addition, the abundant phenolic hydroxyl group of PHA was beneficial to the cell adhesion and proliferation of Gel-DA hydrogels, leading to the excellent biocompatibility of Gel-PHA hydrogels. Notably, the GD-PHA hydrogels could accelerate the bone repair efficiency in the rat model of the femoral defect. In conclusion, our results suggest the Gel-PHA hydrogel with osteoconductivity, biocompatibility, and enhanced mechanical properties is a potential bone repair material.

Controlled release of curcumin from gelatin hydrogels by the molecular-weight modulation of an oxidized dextran cross-linker

Controlled drug delivery could minimize side effects while maintaining a high local dose. Herein, a hydrogel carrier was prepared by forming dynamic imine bonds between gelatin and oxidized dextran (ODex) of different molecular weights (Mw = 10, 70, and 150 kDa). The morphology, thermal stability, rheology, mechanical properties, and swelling properties of the hydrogels and the controlled release of curcumin were characterized. When dextran with a higher Mw was used, the ODex contained more aldehyde groups, which led to a higher degree of cross-linking, considerably shorter gel time, decreased hydrogel porosity, and well-controlled release of curcumin. In addition, the cross-linked hydrogels exhibited not only high thermal stability but also excellent mechanical properties. However, because the matrix was hydrophilic, the swelling properties of the hydrogels were not significantly affected by the Mw of ODex. These observations suggest an approach for designing nutrient delivery carriers with improved controlled release.

Targeting active sites of inflammation using inherent properties of tissue-resident mast cells

Mast cells play a pivotal role in initiating and directing host's immune response. They reside in tissues that primarily interface with the external environment. Activated mast cells respond to environmental cues throughout acute and chronic inflammation through releasing immune mediators via rapid degranulation, or long-term de novo expression. Mast cell activation results in the rapid release of a variety of unique enzymes and reactive oxygen species. Furthermore, the increased density of mast cell unique receptors like mas related G protein-coupled receptor X2 also characterizes the inflamed tissues. The presence of these molecules (either released mediators or surface receptors) are particular to the sites of active inflammation, and are a result of mast cell activation. Herein, the molecular design principles for capitalizing on these novel mast cell properties is discussed with the goal of manipulating localized inflammation. STATEMENT OF SIGNIFICANCE: Mast cells are immune regulating cells that play a crucial role in both innate and adaptive immune responses. The activation of mast cells causes the release of multiple unique profiles of biomolecules, which are specific to both tissue and disease. These unique characteristics are tightly regulated and afford a localized stimulus for targeting inflammatory diseases. Herein, these important mast cell attributes are discussed in the frame of highlighting strategies for the design of bioresponsive functional materials to target regions of inflammations.

Pullulan-Based Hydrogels in Wound Healing and Skin Tissue Engineering Applications: A Review

Wound healing is a complex process of overlapping phases with the primary aim of the creation of new tissues and restoring their anatomical functions. Wound dressings are fabricated to protect the wound and accelerate the healing process. Biomaterials used to design dressing of wounds could be natural or synthetic as well as the combination of both materials. Polysaccharide polymers have been used to fabricate wound dressings. The applications of biopolymers, such as chitin, gelatin, pullulan, and chitosan, have greatly expanded in the biomedical field due to their non-toxic, antibacterial, biocompatible, hemostatic, and nonimmunogenic properties. Most of these polymers have been used in the form of foams, films, sponges, and fibers in drug carrier devices, skin tissue scaffolds, and wound dressings. Currently, special focus has been directed towards the fabrication of wound dressings based on synthesized hydrogels using natural polymers. The high-water retention capacity of hydrogels makes them potent candidates for wound dressings as they provide a moist environment in the wound and remove excess wound fluid, thereby accelerating wound healing. The incorporation of pullulan with different, naturally occurring polymers, such as chitosan, in wound dressings is currently attracting much attention due to the antimicrobial, antioxidant and nonimmunogenic properties. Despite the valuable properties of pullulan, it also has some limitations, such as poor mechanical properties and high cost. However, these properties are improved by blending it with different polymers. Additionally, more investigations are required to obtain pullulan derivatives with suitable properties in high quality wound dressings and tissue engineering applications. This review summarizes the properties and wound dressing applications of naturally occurring pullulan, then examines it in combination with other biocompatible polymers, such chitosan and gelatin, and discusses the facile approaches for oxidative modification of pullulan.

Photocrosslinked Fish Collagen Peptide/Chitin Nanofiber Composite Hydrogels from Marine Resources: Preparation, Mechanical Properties, and an In Vitro Study

Fish collagen peptide (FCP) is a water-soluble polymer with easy accessibility, bioactivity, and reactivity due to its solubility. The gelation of FCP can be carried out by chemical crosslinking, but the mechanical strength of FCP hydrogel is very low because of its intrinsically low molecular weight. Therefore, the mechanical properties of FCP gel should be improved for its wider application as a biomaterial. In this study, we investigated the mechanical properties of M-FCP gel in the context of understanding the influence of chitin nanofibers (CHNFs) on FCP hydrogels. FCP with a number average molecular weight (M_n) of ca. 5000 was reacted with glycidyl methacrylate (GMA) and used for the preparation of photocrosslinked hydrogels. Subsequently, composite hydrogels of methacrylate-modified FCP (M-FCP) and CHNF were prepared by the photoirradiation of a solution of M-FCP containing dispersed CHNF at an intensity of ~60 mW/cm² for 450 s in the presence of 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959) as a photoinitiator. Compression and tensile tests of the FCP hydrogels were carried out using a universal tester. The compression and tensile strength of the hydrogel increased 10-fold and 4-fold, respectively, by the addition of 0.6% CHNF (20% M-FCP), and Young's modulus increased 2.5-fold (20% M-FCP). The highest compression strength of the M-FCP/CHNF hydrogel was ~300 kPa. Cell proliferation tests using fibroblast cells revealed that the hydrogel with CHNF showed good cell compatibility. The cells showed good adhesion on the M-FCP gel with CHNF, and the growth of fibroblast cells after 7 days was higher on the M-FCP/CHNF gel than on the M-FCP gel without CHNF. In conclusion, we found that CHNF improved the mechanical properties as well as the fibroblast cell compatibility, indicating that M-FCP hydrogels reinforced with CHNF are useful as scaffolds and wound-dressing materials.

Removal of Methylene Blue Dye from Aqueous Solutions by Pullulan Polysaccharide/Polyacrylamide/Activated Carbon Complex Hydrogel Adsorption

In this study, composite hydrogels were prepared using a simple synthetic technique to adsorb methylene blue (MB) from water. The hydrogel comprised potassium persulfate (KPS) as the initiator, N,N'-methylene bisacrylamide as the crosslinking agent, and sodium hydroxide (NaOH) as the activator. It was employed to adsorb MB at different concentrations from water. The morphology and properties of PUL/PAM/GO composites were characterized through thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. Moreover, the adsorption properties, adsorption isotherms, adsorption kinetics, adsorption thermodynamics, and swelling properties of the hydrogel for MB were investigated. The optimal ratio of PUL to AC was obtained as 6:1 by fixing the amount of PUL and loading AC of different masses. The maximum adsorption capacity was obtained as 591.4 mg/g. It also exhibited certain mechanical strength. The adsorption of MB conforms to pseudo-first-order kinetics and Langmuir isotherms. In this study, an environment-friendly, cheap, simple, and efficient way was presented for the composite hydrogel in the direction of water treatment.

Bioactive functional collagen-oxidized pullulan scaffold loaded with polydatin for treating chronic wounds

Prolonged inflammation, elevated matrix metalloproteinases, hypoxia, decreased vascularization, increased oxidative stress, and bacterial infection are typical signs of chronic non-healing diabetic wounds. Any agent that improves one or all factors could offer enhanced opportunities for better healing of diabetic wounds. In this study, a polyphenol (polydatin) incorporated collagen scaffold was prepared using a biocompatible crosslinker, oxidized pullulan (Col-OxP3-Po), to treat diabetic wounds. The scaffolds were characterized using SEM, FTIR, antioxidant activity, in vitro and in vivo wound healing assay, gene expression, and immunohistopathological studies. Polydatin incorporated scaffold exhibited 75 % antioxidant activity, hemostatic and erythrocyte adhesion properties. FTIR results proved the incorporation of polydatin in the Col-OxP3-Po scaffold. They were also non-toxic to the 3 T3 fibroblasts with a viability of 93 % and good cell attachment. In vivo, normal and diabetic wound healing studies showed that the Col-OxP3-Po scaffold treated group healed on days 16 and 21. The histological and immunohistochemistry analyses of the granulation tissues showed improved epithelialization, angiogenesis and enhanced collagen deposition by modulating TGF-β3 and MMP - 9 gene expressions favorable for better healing. Thus, this scaffold could be a newer treatment strategy for chronic non-healing wounds.

Preparation, properties, and applications of gelatin-based hydrogels (GHs) in the environmental, technological, and biomedical sectors

Gelatin's versatile functionalization offers prospects of facile and effective crosslinking as well as combining with other materials (e.g., metal nanoparticles, carbonaceous, minerals, and polymeric materials exhibiting desired functional properties) to form hybrid materials of improved thermo-mechanical, physio-chemical and biological characteristics. Gelatin-based hydrogels (GHs) and (nano)composite hydrogels possess unique functional features that make them appropriate for a wide range of environmental, technical, and biomedical applications. The properties of GHs could be balanced by optimizing the hydrogel design. The current review explores the various crosslinking techniques of GHs, their properties, composite types, and ultimately their end-use applications. GH's ability to absorb a large volume of water within the gel network via hydrogen bonding is frequently used for water retention (e.g., agricultural additives), and absorbency towards targeted chemicals from the environment (e.g., as wound dressings for absorbing exudates and in water treatment for absorbing pollutants). GH's controllable porosity makes its way to be used to restrict access to chemicals entrapped within the gel phase (e.g., cell encapsulation), regulate the release of encapsulated cargoes within the GH (e.g., drug delivery, agrochemicals release). GH's soft mechanics closely resembling biological tissues, make its use in tissue engineering to deliver suitable mechanical signals to neighboring cells. This review discussed the GHs as potential materials for the creation of biosensors, drug delivery systems, antimicrobials, modified electrodes, water adsorbents, fertilizers and packaging systems, among many others. The future research outlooks are also highlighted.

Gelatin-lecithin-F127 gel mediated self-assembly of curcumin vesicles for enhanced wound healing

Curcumin, a principal component of Curcuma longa, has a long history of being used topically for wound healing. However, poor aqueous solubility of curcumin leads to poor topical absorption. Recently, gelatin based gel has been reported to overcome this issue. However, the release of curcumin from gelatin gel in the bioavailable or easily absorbable form is still a challenge. The present study reports the development of a composite gel prepared from gelatin, F127 and lecithin using temperature dependant gelation and loading of curcumin within it. Notably, the composite gel facilitated the release of curcumin entrapped within vesicles of ~400 nm size. Further, the composite gel exhibited increase in the storage modulus or gel strength, stability, pore size and hydrophobicity as compared to only gelatin gel. Finally, wound healing assay in murine model indicated that curcumin delivered through composite gel showed a significantly faster healing as compared to that delivered through organic solvent. This was also validated by histopathological and biochemical analysis showing better epithelization and collagen synthesis in the group dressed with curcumin containing composite gel. In conclusion, composite gel facilitated the release of bioavailable or easily absorbable curcumin which in turn enhanced the wound healing.

Self-Crosslinkable Oxidized Alginate-Carboxymethyl Chitosan Hydrogels as an Injectable Cell Carrier for In Vitro Dental Enamel Regeneration

Injectable hydrogels, as carriers, offer great potential to incorporate cells or growth factors for dental tissue regeneration. Notably, the development of injectable hydrogels with appropriate structures and properties has been a challenging task, leaving much to be desired in terms of cytocompatibility, antibacterial and self-healing properties, as well as the ability to support dental stem cell functions. This paper presents our study on the development of a novel self-cross-linkable hydrogel composed of oxidized alginate and carboxymethyl chitosan and its characterization as a cell carrier for dental enamel regeneration in vitro. Oxidized alginate was synthesized with 60% theoretical oxidation degree using periodate oxidation and characterized by Fourier Transform Infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and Ultraviolet-visible absorption spectroscopy. Then, hydrogels were prepared at three varying weight ratios of oxidized alginate to carboxymethyl chitosan (4:1, 3:1, and 2:1) through Schiff base reactions, which was confirmed by Fourier Transform Infrared spectroscopy. The hydrogels were characterized in terms of gelation time, swelling ratio, structure, injectability, self-healing, antibacterial properties, and in vitro characterization for enamel regeneration. The results demonstrated that, among the three hydrogels examined, the one with the highest ratio of oxidized alginate (i.e., 4:1) had the fastest gelation time and the lowest swelling ability, and that all hydrogels were formed with highly porous structures and were able to be injected through a 20-gauge needle without clogging. The injected hydrogels could be rapidly reformed with the self-healing property. The hydrogels also showed antibacterial properties against two cariogenic bacteria: Streptococcus mutans and Streptococcus sobrinus. For in vitro enamel regeneration, a dental epithelial cell line, HAT-7, was examined, demonstrating a high cell viability in the hydrogels during injection. Furthermore, HAT-7 cells encapsulated in the hydrogels showed alkaline phosphatase production and mineral deposition, as well as maintaining their round morphology, after 14 days of in vitro culture. Taken together, this study has provided evidence that the oxidized alginate-carboxymethyl chitosan hydrogels could be used as an injectable cell carrier for dental enamel tissue engineering applications.

Insight into the role and mechanism of polysaccharide in polymorphous magnesium oxide nanoparticle synthesis for arsenate removal

The low cost and non-toxic of magnesium oxides make it a potential eco-friendly material for arsenic removal. Polysaccharide is a kind of green modifier to obtain nanoscale MgO particles with a higher adsorption affinity. In this study, the impact of chain structures of polysaccharides on the morphology features and arsenate removal efficiency of MgO-NPs were investigated. Pullulan and starch facilitated the synthesis of flower-like MgO-NPs, and pectin facilitated the synthesis of plate-like ones. Although the two kinds of flower-like MgO-NPs undergone similar time to reach equilibrium, the one obtained from the starch-synthesis route showed a higher arsenate adsorption capacity (98 mg g^-1), due to that their bushy and smaller petals on the surface provide more active sites for arsenic adsorption. The pectin-synthesis route also produced MgO-NPs with higher arsenate adsorption capacity (101 mg g^-1), ascribed to stacking of nano-plates on their surfaces facilitated to form defect surfaces. However, due to their lower BET area, the plate-like MgO-NPs took twice times to reach equilibrium for arsenic adsorption compared with the others. In the stage for the hydrolysis of MgO, hydroxyl groups on the polymer chain provide active sites to physically trap or bond with MgO particles and then to produce hydrolyzed precursors. The poly chain containing inter- and intra-hydroxyl groups directed MgO molecular growing into hydroxide crystals with 3D frameworks during their nucleation and growth. However, pectin only provides inter-hydroxyl groups and directs to form hydroxides with 2D frameworks. Furthermore, the rapid-nucleation vs. slow-growth model in the stage of pyrolysis of hydroxide crystals successfully interprets the thinner petals and complex chemical phases of the final nanoparticles obtained from the pullulan-synthesis route. This work may provide direction and perspectives for the rational design of well-performing MgO materials for arsenate removal.

A self-healing, recyclable and conductive gelatin/nanofibrillated cellulose/Fe3+ hydrogel based on multi-dynamic interactions for a multifunctional strain sensor

Conductive hydrogels have emerged as promising material candidates for multifunctional strain sensors, attributed to their similarity to biological tissues, good wearability, and high accuracy of information acquisition. However, it is difficult to simultaneously manufacture conductive hydrogel-based multifunctional strain sensors with the synergistic properties of reliable healability for long-term usage and environmental degradability/recyclability for decreasing the electronic waste. This work reports a facile strategy to engineer a self-healing, recyclable and conductive strain sensor by virtue of molecular-level multi-dynamic interactions (MMDIs) including Schiff base complexes, hydrogen bonds, and coordination bonds, which were fabricated using a dialdehyde TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized nanofibrillated cellulose (DATNFC) pre-reinforced gelatin nanocomposite hydrogel (gelatin/DATNFC hydrogel, GDH) followed by dipping in an Fe³⁺ aqueous solution. The MMDI strategy allows synchronous regulation of both bulk and interfacial interactions to obtain exciting properties that outperform those of conventional hydrogels, including extraordinary compressive stress (1310 kPa), intriguing self-healing abilities, and remarkable electrical conductivity. With these outstanding merits, the as-prepared gelatin/DATNFC/Fe³⁺ hydrogel (GDIH) is developed to be a multifunctional strain sensor with appealing strain sensitivity (GF = 2.24 under 6% strain) and compressive sensitivity (S = 1.14 kPa^-1 under 15 kPa), which can be utilized to manufacture electronic skin and accurately discern subtle bodily motions, handwriting and personal signatures. Notably, this GDIH-based sensor also exhibited reliable self-healing properties for long-term usage, environmental degradability and complete recyclability for decreasing the electronic waste. In consideration of the extremely facile preparation process, biocompatibility, satisfactory functionalities, remarkable self-healing properties and recyclability, the emergence of the GDIH-based sensor is believed to propose a new strategy for the development of sustainable-multifunctional strain sensors and healthcare monitoring.

Surface Modification of Sponge-like Porous Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/Gelatine Blend Scaffolds for Potential Biomedical Applications

In this study, we described the preparation of sponge-like porous scaffolds that are feasible for medical applications. A porous structure provides a good microenvironment for cell attachment and proliferation. In this study, a biocompatible PHA, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) was blended with gelatine to improve the copolymer’s hydrophilicity, while structural porosity was introduced into the scaffold via a combination of solvent casting and freeze-drying techniques. Scanning electron microscopy results revealed that the blended scaffolds exhibited higher porosity when the 4HB compositions of P(3HB-co-4HB) ranged from 27 mol% to 50 mol%, but porosity decreased with a high 4HB monomer composition of 82 mol%. The pore size, water absorption capacity, and cell proliferation assay results showed significant improvement after the final weight of blend scaffolds was reduced by half from the initial 0.79 g to 0.4 g. The pore size of 0.79g-(P27mol%G10) increased three-fold while the water absorption capacity of 0.4g-(P50mol%G10) increased to 325%. Meanwhile, the cell proliferation and attachment of 0.4g-(P50mol%G10) and 0.4g-(P82mol%G7.5) increased as compared to the initial seeding number. Based on the overall data obtained, we can conclude that the introduction of a small amount of gelatine into P(3HB-co-4HB) improved the physical and biological properties of blend scaffolds, and the 0.4g-(P50mol%G10) shows great potential for medical applications considering its unique structure and properties.

In situ forming hydrogel recombination with tissue adhesion and antibacterial property for tissue adhesive

In situ forming hydrogels with strong adhesive strength and antibacterial activity are of great interest to serve as tissue adhesive in fields like wound dressing and mass hemorrhage. In this study, hybrid hydrogel (GOHA) based on gelatin and oxidized hyaluronic acid was developed and endowed with excellent mechanical strength and tissue adhesion. According to our results, GOHA hydrogel exhibits a fast gelation time of around 60 s, robust compression strength of 223.43 ± 24.28 kPa, and strong adhesion of 14.33 ± 0.78 kPa to porcine skin, which is much higher than that of commercial fibrin glue (around 1.00 kPa). Meanwhile, through the loading of levofloxacin, obvious antibacterial activity can be obtained for wider applications. Notably, it would not compromise the hemocompatibility and cytocompatibility in vitro. In summary, this kind of hybrid hydrogel shows great potential as tissue adhesive in biomedical fields.

High-Strength and Injectable Supramolecular Hydrogel Self-Assembled by Monomeric Nucleoside for Tooth-Extraction Wound Healing

Hydrogels with high mechanical strength and injectability have attracted extensive attention in biomedical and tissue engineering. However, endowing a hydrogel with both properties is challenging because they are generally inversely related. In this work, by constructing a multi-hydrogen-bonding system, a high-strength and injectable supramolecular hydrogel is successfully fabricated. It is constructed by the self-assembly of a monomeric nucleoside molecular gelator (2-amino-2'-fluoro-2'-deoxyadenosine (2-FA)) with distilled water/phosphate buffered saline as solvent. Its storage modulus reaches 1 MPa at a concentration of 5.0 wt%, which is the strongest supramolecular hydrogel comprising an ultralow-molecular-weight (MW < 300) gelator. Furthermore, it exhibits excellent shear-thinning injectability, and completes the sol-gel transition in seconds after injection at 37 °C. The multi-hydrogen-bonding system is essentially based on the synergistic interactions between the double NH₂ groups, water molecules, and 2'-F atoms. Furthermore, the 2-FA hydrogel exhibits excellent biocompatibility and antibacterial activity. When applied to rat molar extraction sockets, compared to natural healing and the commercial hemorrhage agent gelatin sponge, the 2-FA hydrogel exhibits faster degradation and induces less osteoclastic activity and inflammatory infiltration, resulting in more complete bone healing. In summary, this study provides ideas for proposing a multifunctional, high-strength, and injectable supramolecular hydrogel for various biomedical engineering applications.

Effect of Dialdehyde Carboxymethyl Cellulose Cross-Linking on the Porous Structure of the Collagen Matrix

Porous structures are essential for some collagen-based biomaterials and can be regulated by crosslinkers. Herein, dialdehyde carboxymethyl cellulose (DCMC) crosslinkers with similar size but different aldehyde group contents were prepared through periodate oxidation of sodium carboxymethyl cellulose with varying degrees of substitution (DS). They can penetrate into the hierarchy of fibril and form inter-molecular and intra-fibril cross-linking within the collagen matrix due to their nanoscale sizes and reactive aldehyde groups. The collagen matrices possessed higher porosity, significantly greater proportion of large pores (Φ > 10 μm), and shorter D-periodicity after cross-linking, showing greater potential for biomedical applications. In addition, the crosslinked collagen matrices showed satisfactory biocompatibility and biodegradation. The decreased DS of carboxymethyl cellulose, which led to the increased aldehyde content of corresponding DCMC, brought about an enhanced cross-linking degree, porosity, and proportion of large pores of the crosslinked collagen matrix. DCMC dosage of 6% was sufficient for cross-linking and pore formation. Excess DCMC would physically deposit in the matrix and decrease the porosity instead. Therefore, the desired pore properties of the collagen matrix could be obtained by regulating the structure of DCMC and thereby achieving the required functions of the biomaterial.

Morphology and Rheology of a Cool-Gel (Protein) Blended with a Thermo-Gel (Hydroxypropyl Methylcellulose)

This study investigates the morphological and rheological properties of blended gelatin (GA; a cooling-induced gel (cool-gel)) and hydroxypropyl methylcellulose (HPMC; a heating-induced gel (thermo-gel)) systems using a fluorescence microscope, small angle X-ray scattering (SAXS), and a rheometer. The results clearly indicate that the two biopolymers are immiscible and have low compatibility. Moreover, the rheological behavior and morphology of the GA/HPMC blends significantly depend on the blending ratio and concentration. Higher polysaccharide contents decrease the gelling temperature and improve the gel viscoelasticity character of GA/HPMC blended gels. The SAXS results reveal that the correlation length (ξ) of the blended gels decreases from 5.16 to 1.89 nm as the HPMC concentration increases from 1 to 6%, which suggests that much denser networks are formed in blended gels with higher HPMC concentrations. Overall, the data reported herein indicate that the gel properties of gelatin can be enhanced by blending with a heating-induced gel.