Gelatin Methacryloyl Hydrogels Control the Localized Delivery of Albumin-Bound Paclitaxel

Optimised GelMA/tragacanth gum hydrogel loaded with vanillic acid for biomedical applications

In this study a hybrid hydrogel based on GelMA incorporated with Tragacanth gum that can improve compressive properties and swelling of the GelMA and provide a sustained release of vanillic acid is developed and thoroughly evaluated. This hydrogel hybrid system undergoes gelation through UV crosslinking. The presence of Tragacanth was found to increase the swelling of the hydrogel system from 500 to 1200 times and the compressive strength from 15 ± 1 kPa to 49 ± 3 kPa. Also, rheological and injectability investigations confirmed that the proposed hydrogel system is suitable for use as an injectable hydrogel. In addition, the drug loading and release profile of vanillic acid, used as a model drug, was investigated. The results revealed sustained release behavior that follows the Korsmeyer-Peppas model and non-Fickian diffusion mechanism. The results demonstrate the synergistic effects of the GelMA/tragacanth gum hybrid system, highlighting the potential of this degradable and non-toxic composite hydrogel for advanced biomedical applications such as controlled drug delivery systems and wound healing.

Tuneable gelatin methacryloyl (GelMA) hydrogels for the directed specification of renal cell types for hiPSC-derived kidney organoid maturation

Diabetic Kidney Disease (DKD) represents a significant global health burden and is recognised as the leading cause of end-stage renal disease. Kidney organoids derived from human induced Pluripotent Stem Cells (hiPSCs) have the potential to transform how we model renal disease and may provide personalised replacement tissues for patients with renal failure. However, kidney organoids remain poorly reproducible, and are structurally and functionally immature. Three-dimensional cultures that more appropriately mimic the complexity of the in vivo microenvironment are required to improve organoid maturation and structural authenticity. Here, we describe the application of semi-synthetic Gelatin Methacryloyl (GelMA) hydrogels as extracellular support matrices for the differentiation of hiPSC-derived kidney organoids. Hydrogels of defined mechanical strengths were generated by varying the concentration of GelMA solution in the presence of low concentration photo-initiator. After confirming a high level of mechanical stability of the hydrogels over extended culture periods, their effect on kidney organoid maturation was investigated. Organoids differentiated within GelMA hydrogels generated typical renal cell types including podocytes, tubular epithelia, renal interstitial cells, and some nascent vascularisation. Interestingly, kidney organoids derived within hydrogels that closely approximate the stiffness of the adult human kidney (∼5000-10,000 Pa) demonstrated improved podocyte maturation and were shown to upregulate renal vesicle-associated genes at an earlier stage following encapsulation when compared to organoids derived within softer hydrogels (∼400 Pa). A model of TGFβ-induced injury was also developed to investigate the influence of the mechanical environment in propagating early, fibrotic-like features of DKD within organoids. Growth within the softer matrix was shown to reduce pSMAD3 expression following TGFβ1 treatment, and accordingly ameliorate the expression of the myofibroblast marker α-Smooth Muscle Actin (α-SMA). This work demonstrates the suitability of GelMA hydrogels as mechanically-stable, highly-tuneable, batch-to-batch reproducible three-dimensional supports for hiPSC-derived kidney organoid growth and differentiation, and further substantiates the role of the biophysical environment in guiding processes of cell fate determination and organoid maturation.

3D Printed GelMA/CHIMA Cross-Linked Network Hydrogel for Angiogenesis

Vascularization is a key issue facing the construction of functional three-dimensional (3D) tissues, which is critical for the long-term survival and stability of tissue construct transplantation. In this study, a photocurable hydrogel material carboxymethyl chitosan (CHIMA) was successfully prepared and integrated with methacryloyl gelatin (GelMA) to construct the bioink GelMA/CHIMA, which was subsequently used 3D printing technology to prepared a bioactive scaffold with angiogenesis-inducing functionality. The results showed that the cross-linked GelMA/CHIMA bioink had a porous structure that supported cell growth and metabolism. The incorporation of CHIMA could significantly improve the hydrophilicity, swelling rate, pressure resistance and mechanical strength of the bioink. GelMA/CHIMA bioink supported the survival and continued proliferation of human umbilical vein endothelial cells (HUVECs) in the scaffold. In particular, the bioink composed of 8 wt% GelMA and 2 wt% CHIMA could stimulate the expression of angiogenesis genes. 3D printed bioactive scaffolds supported the survival of HUVECs and had abundant protein deposition including CD31 and VEGF. Therefore, this study constructed a bioactive scaffold with angiogenesis induction function, which provides a feasible strategy for the construction of vascularized complex tissues.

Implantable Polymer Scaffolds Loaded with Paclitaxel-Cyclodextrin Complexes for Post-Breast Cancer Tissue Reconstruction

The side effects associated with the chemotherapy of triple-negative breast cancer (TNBC), such as nucleotide-binding oligomerization domain (NOD)-like receptor family (NLR), pyrin domain containing 3 (NLRP3) inflammasome activity, are responsible for the treatment failure and high mortality rates. Therefore, advanced delivery systems have been developed to improve the transport and targeted administration of anti-tumor agents at the tumor sites using tissue engineering approaches. Implantable delivery systems based on biodegradable polymers are an effective alternative due high biocompatibility, porosity, and mechanical strength. Moreover, the use of paclitaxel (PTX)-cyclodextrin complexes increases the solubility and permeability of PTX, enhancing the bioavailability and efficacy of the drug. All of these properties contribute to the efficient encapsulation and controlled release of drugs, preventing the damage of healthy tissues. In the current study, we detailed the synthesis process and evaluation of 3D scaffolds based on gelatin functionalized with methacryloyl groups (GelMA) and pectin loaded with PTX-cyclodextrin inclusion complexes on TNBC pathogenesis in vitro and in vivo. Bio-physio-chemical analysis of the proposed scaffolds revealed favorable mechanical and biological properties for the cellular component. To improve the drug solubility, a host-guest interaction was performed by the complexation of PTX with a cyclodextrin derivative prior to scaffold synthesis. The presence of PTX suppressed the growth of breast tumor cells and promoted caspase-1 activity, the release of interleukin (IL)-1β, and the production of reactive oxygen species (ROS), conditioning the expression levels of the genes and proteins associated with breast tumorigenesis and NLRP3 inflammasome. The in vivo experiments suggested the activation of pyroptosis tumor cell death, confirming the in vitro experiments. In conclusion, the bio-mechanical properties of the GelMA and pectin-based scaffolds as well as the addition of the PTX-cyclodextrin complexes allow for the targeted and efficient delivery of PTX, suppressing the viability of the breast tumor cells via pyroptosis cell death initiation.

Preventing postsurgical colorectal cancer relapse: A hemostatic hydrogel loaded with METTL3 inhibitor for CAR-NK cell therapy

Colorectal cancer (CRC) recurrence post-surgery remains a major challenge. While Chimeric Antigen Receptor (CAR)-engineered natural killer (NK) cells hold immense therapeutic potential, their intratumoral infiltration ability remains limited, hampering efficacy. Building upon prior research suggesting that chemokines like C-X-C motif chemokine ligand 9 (CXCL9) and C-X-C motif chemokine ligand 10 (CXCL10) recruit CAR-NK cells, we hypothesized that tumor cell m6A methylation, regulated by Methyltransferase-like 3 (METTL3), influences chemokine secretion. This study aims to elucidate the underlying mechanisms and improve METTL3 inhibition efficiency. We designed an adhesive hemostasis hydrogel loaded with STM2457, a METTL3 inhibitor, aimed at sustained release in the acidic tumor microenvironment. In vitro, the hydrogel promoted CAR-NK cell recruitment and tumor killing via sustained METTL3 inhibition. The hydrogel's Schiff base bonds further enabled intestinal adhesion and hemostasis in an incomplete tumor resection model of CRC. Combining the hydrogel with CAR-NK cell therapy significantly reduced CRC recurrence in vivo. Overall, our study reveals the crucial role of METTL3 in CRC recurrence and proposes a promising, multimodal strategy using STM2457-loaded hydrogel and CAR-NK cells for enhanced therapeutic efficacy.

A cryo-shocked M2 macrophages based treatment strategy promoting repair of spinal cord injury via immunomodulation and axonal regeneration effects

Recovery from spinal cord injury (SCI) is often impeded by neuroinflammation, scar formation, and limited axonal regeneration. To tackle these issues, we developed an innovative biomimetic drug delivery system using liquid nitrogen-treated M2 macrophages (LNT M2) which internalized paclitaxel (PTX) nanoparticles beforehand. These were incorporated into a gelatin methacryloyl (GelMA) scaffold, creating a multifunctional, injectable treatment for single-dose administration. The LNT M2 inherited the inflammatory factor/chemokine receptors from the living M2 macrophages and thus possessing significant inflammatory neutralizing effect. In addition, the scaffold provides slow, sustained release of PTX, promoting axonal regeneration and suppressing scar formation in SCI rats. The LNT M2-based dual-functional scaffold significantly enhances motor function, reduces neuroinflammation, and accelerates axonal regeneration by modulating the inflammatory microenvironment and preventing the formation of glial and fibrotic scars. This approach combines the regenerative effects of low-dose PTX with the immunoregulatory properties of LNT M2, leading to remarkable neurological recovery in SCI rats. Moreover, the scaffold's straightforward preparation, ease of standardization, and "ready-to-use" nature make it a promising candidate for acute SCI intervention and future clinical applications.

Co-culturing neural and bone mesenchymal stem cells in photosensitive hydrogel enhances spinal cord injury repair

In mammalian species, neural tissues cannot regenerate following severe spinal cord injury (SCI), for which stem cell transplantation is a promising treatment. Neural stem cells (NSCs) have the potential to repair SCI; however, in unfavourable microenvironments, transplanted NSCs mainly differentiate into astrocytes rather than neurons. In contrast, bone mesenchymal stem cells (BMSCs) promote the differentiation of NSCs into neurons and regulate inflammatory responses. Owing to their easily controllable mechanical properties and similarities to neural tissue, gelatin methacrylate (GelMA) hydrogels offer remarkable cell biocompatibility and regulate the differentiation of NSCs. Therefore, in this study, we propose co-culturing NSCs and BMSCs within low-modulus GelMA hydrogel scaffolds to promote regeneration following SCI. In vitro comparisons revealed that the viability, proliferation, migration, and neuron differentiation capacity of cells in these low-modulus scaffolds exhibit substantially superior performance compared to those in high-modulus hydrogel scaffolds. To the best of our knowledge, this study is the first to report that NSCs/BMSCs co-culture implants can remarkably enhance motor function recovery in SCI rats, reduce the area of spinal cord cavities, stimulate neuron regeneration, and suppress scar tissue formation. Thus, this hydrogel system loaded with co-cultured cells represents a promising therapeutic approach for SCI repair.

Development and In-Vitro Evaluation of Doxorubicin-Loaded Methacrylate Gelatin (GelMa)-Acrylamide Hydrogels for the Treatment of Malignant Pleural Mesothelioma

OBJECTIVE

Malignant pleural mesothelioma (MPM) is the most prevalent subtype of malignant mesothelioma that affects the pleural lining of the lungs. Conventionally, chemotherapy via systemic injections has shown limited efficacy due to off-target effects, and inefficacious deposition at the disease site. In our previous study, we reported the development and optimization of UV-initiated methacrylate gelatin (GelMa)-acrylamide based hydrogel formulation for local intracavitary administration of therapies. The current study utilizes a pre-established GelMa formulation for delivering a small molecule chemotherapeutic agent, Doxorubicin (Dox), against in-vitro MPM models.

METHODS

Dox-loaded hydrogel (DLH) precursor solution was prepared by dissolving Dox in the precursor solution. The gels were characterized for physical properties such as gelling time, swelling index, bio adhesion, and injectability and were compared to blank hydrogels. Dox-loaded hydrogels were also tested for therapeutic efficacy in MPM cells in various 2D and 3D cell culture models.

RESULTS

It was revealed that Dox-loaded hydrogels retained similar physical properties, including gelling time (< 25 s), swelling index (~ 1,200%), bio-adhesion (> 20 g detachment force), and injectability (< 2N force for injecting precursor), compared to blank hydrogels. Moreover, the gel formulation effectively sustained the release of hydrophilic Dox HCl over a period of 12 days by increasing the degree of crosslinking between GelMa and its crosslinkers. Further, the therapeutic efficacy of Dox was retained even after loading into hydrogels, indicating that no chemical interactions took place between gel excipients and the drug. Studies in MPM cell-based models revealed that DLH showed excellent potential in inhibiting 2D and 3D cell growth, with DLH being more effective than plain Dox in suppressing tumor growth in 3D spheroid models.

CONCLUSIONS

Overall, the results of the present study suggest that Dox-loaded hydrogels (DLH) may be a good candidate for efficacy study in preclinical mesothelioma models, with strong potential for clinical translation.

Synthesis of Amphiphilic Amino Poly-Amido-Saccharide and Poly(lactic) Acid Block Copolymers and Fabrication of Paclitaxel-Loaded Mucoadhesive Nanoparticles

Drug delivery to the esophagus through systemic administration remains challenging, as minimal drug reaches the desired target. Local delivery offers the potential for improved efficacy while minimizing off-target toxicities but necessitates bioadhesive properties for mucosal delivery. Herein, we describe the synthesis of two new mucoadhesive amphiphilic copolymers prepared by sequential ring-opening copolymerization or postpolymerization click conjugation. Both strategies yield block copolymers containing a hydrophilic amine-functionalized poly-amido-saccharide and either a hydrophobic alkyl derivatized poly-amido-saccharide or poly(lactic acid), respectively. The latter resulting copolymers readily self-assemble into spherical, ≈200 nm diameter, positively charged mucoadhesive nanoparticles. The NPs entrap ultrahigh levels of paclitaxel via encapsulation of free paclitaxel and paclitaxel conjugated to a biodegradable, biocompatible poly(1,2-glycerol carbonate). Paclitaxel-loaded NPs rapidly enter cells, release paclitaxel, are cytotoxic to esophageal OE33 and OE19 tumor cells in vitro, and, importantly, demonstrate improved mucoadhesion compared to conventional poly(ethylene glycol)-poly(lactic acid) nanoparticles to ex vivo esophageal tissue.

Synthesis of Gelatin Methacryloyl Analogs and Their Use in the Fabrication of pH-Responsive Microspheres

pH-responsive hydrogels have numerous applications in tissue engineering, drug delivery systems, and diagnostics. Gelatin methacryloyl (GelMA) is a biocompatible, semi-synthetic polymer prepared from gelatin. When combined with aqueous solvents, GelMA forms hydrogels that have extensive applications in biomedical engineering. GelMA can be produced with different degrees of methacryloyl substitution; however, the synthesis of this polymer has not been tuned towards producing selectively modified materials for single-component pH-responsive hydrogels. In this work, we have explored two different synthetic routes targeting different gelatin functional groups (amine, hydroxyl, and/or carboxyl) to produce two GelMA analogs: gelatin A methacryloyl glycerylester (polymer A) and gelatin B methacrylamide (polymer B). Polymers A and B were used to fabricate pH-responsive hydrogel microspheres in a flow-focusing microfluidic device. At neutral pH, polymer A and B microspheres displayed an average diameter of ~40 µm. At pH 6, microspheres from polymer A showed a swelling ratio of 159.1 ± 11.5%, while at pH 10, a 288.6 ± 11.6% swelling ratio was recorded for polymer B particles.

Unveiling the versatility of gelatin methacryloyl hydrogels: a comprehensive journey into biomedical applications

Gelatin methacryloyl (GelMA) hydrogels have gained significant recognition as versatile biomaterials in the biomedical domain. GelMA hydrogels emulate vital characteristics of the innate extracellular matrix by integrating cell-adhering and matrix metalloproteinase-responsive peptide motifs. These features enable cellular proliferation and spreading within GelMA-based hydrogel scaffolds. Moreover, GelMA displays flexibility in processing, as it experiences crosslinking when exposed to light irradiation, supporting the development of hydrogels with adjustable mechanical characteristics. The drug delivery landscape has been reshaped by GelMA hydrogels, offering a favorable platform for the controlled and sustained release of therapeutic actives. The tunable physicochemical characteristics of GelMA enable precise modulation of the kinetics of drug release, ensuring optimal therapeutic effectiveness. In tissue engineering, GelMA hydrogels perform an essential role in the design of the scaffold, providing a biomimetic environment conducive to cell adhesion, proliferation, and differentiation. Incorporating GelMA in three-dimensional printing further improves its applicability in drug delivery and developing complicated tissue constructs with spatial precision. Wound healing applications showcase GelMA hydrogels as bioactive dressings, fostering a conducive microenvironment for tissue regeneration. The inherent biocompatibility and tunable mechanical characteristics of GelMA provide its efficiency in the closure of wounds and tissue repair. GelMA hydrogels stand at the forefront of biomedical innovation, offering a versatile platform for addressing diverse challenges in drug delivery, tissue engineering, and wound healing. This review provides a comprehensive overview, fostering an in-depth understanding of GelMA hydrogel's potential impact on progressing biomedical sciences.

Carbon Dot-Based Photo-Cross-Linked Gelatin Methacryloyl Hydrogel Enables Dental Pulp Regeneration: A Preliminary Study

An essential factor in tooth nutritional deficits and aberrant root growth is pulp necrosis. Removing inflammatory or necrotic pulp tissue and replacing it with an inert material are the most widely used therapeutic concepts of endodontic treatment. However, pulp loss can lead to discoloration, increased fracture risk, and the reinfection of the damaged tooth. It is now anticipated that the pulp-dentin complex will regenerate through a variety of application methods based on human dental pulp stem cells (hDPSC). In order to create a photo-cross-linked gelatinized methacrylate hydrogel, GelMA/EUO-CDs-E (ECE), that is biodegradable and injectable for application, we created a novel nanoassembly of ECE based on eucommia carbon dots (EUO-CDs) and epigallocatechin gallate (EGCG). We then loaded it onto gelatin methacryloyl (GelMA) hydrogel. We have evaluated the material and examined its in vivo and in vitro angiogenesis-promoting potential as well as its dentin differentiation-enabling characteristics. The outcomes of the experiment demonstrated that GelMA/ECE was favorable to cell proliferation and enhanced hDPSC's capacity for angiogenesis and dentin differentiation. The regeneration of vascular-rich pulp-like tissues was found to occur in vivo when hDPSC-containing GelMA/ECE was injected into cleaned human root segments (RS) for subcutaneous implantation in nude mice. This suggests that the injectable bioscaffold is appropriate for clinical use in pulp regenerative medicine.

Fabrication of silicon-based nickel nanoflower-encapsulated gelatin microspheres as an active antimicrobial carrier

Local antibiotic application might mitigate the burgeoning problem of rapid emergence of antibiotic resistance in pathogenic microbes. To accomplish this, delivery systems must be engineered. Hydrogels have a wide range of physicochemical properties and can mimic the extracellular matrix, rendering them promising materials for local antibacterial agent application. Here, we synthesized antibacterial silicon (Si)-based nickel (Ni) nanoflowers (Si@Ni) and encapsulated them in gelatin methacryloyl (GelMA) using microfluidic and photo-crosslink technology, constructing uniform micro-sized hydrogel spheres (Si@Ni-GelMA). Si@Ni and Si@Ni-GelMA were characterized using X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Injectable Si@Ni-GelMA exhibited excellent antibacterial activities owing to the antibiotic effect of Ni against Pseudomonas aeruginosa, Klebsiella pneumoniae, and methicillin-resistant Staphylococcus aureus, while showing negligible cytotoxicity. Therefore, the Si@Ni-GelMA system can be used as drug carriers owing to their injectability, visible light-mediated crosslinking, degradation, biosafety, and superior antibacterial properties.

Addition of Laponite to gelatin methacryloyl bioinks improves the rheological properties and printability to create mechanically tailorable cell culture matrices

Extrusion-based bioprinting has gained widespread popularity in biofabrication due to its ability to assemble cells and biomaterials in precise patterns and form tissue-like constructs. To achieve this, bioinks must have rheological properties suitable for printing while maintaining cytocompatibility. However, many commonly used biomaterials do not meet the rheological requirements and therefore require modification for bioprinting applications. This study demonstrates the incorporation of Laponite-RD (LPN) into gelatin methacryloyl (GelMA) to produce highly customizable bioinks with desired rheological and mechanical properties for extrusion-based bioprinting. Bioink formulations were based on GelMA (5%-15% w/v) and LPN (0%-4% w/v), and a comprehensive rheological design was applied to evaluate key rheological properties necessary for extrusion-based bioprinting. The results showed that GelMA bioinks with LPN (1%-4% w/v) exhibited pronounced shear thinning and viscoelastic behavior, as well as improved thermal stability. Furthermore, a concentration window of 1%-2% (w/v) LPN to 5%-15% GelMA demonstrated enhanced rheological properties and printability required for extrusion-based bioprinting. Construct mechanical properties were highly tunable by varying polymer concentration and photocrosslinking parameters, with Young's moduli ranging from ∼0.2 to 75 kPa. Interestingly, at higher Laponite concentrations, GelMA cross-linking was inhibited, resulting in softer hydrogels. High viability of MCF-7 breast cancer cells was maintained in both free-swelling droplets and printed hydrogels, and metabolically active spheroids formed over 7 days of culture in all conditions. In summary, the addition of 1%-2% (w/v) LPN to gelatin-based bioinks significantly enhanced rheological properties and retained cell viability and proliferation, suggesting its suitability for extrusion-based bioprinting.

Preparation and characterization of 3D bioprinted gelatin methacrylate hydrogel incorporated with curcumin loaded chitosan nanoparticles for in vivo wound healing application

This study developed a biomimetic composite bioink consisting of gelatin methacrylate (GelMA) /chitosan nanoparticles (CSNPs) for extrusion-based 3D bioprinting. Additionally, curcumin(Cur)-loaded nanoparticles were incorporated which increased the proliferation and antibacterial activity of biomimetic skin constructs. The hydrogel, curcumin-loaded NPs, and the biocomposite was characterized chemically and physically. The results indicated proper modified gelatin with tunable physical characteristics, e.g., swelling ratio and biodegradability up to 1200 % and 25 days, respectively. In addition, the characterized CSNPs showed good distribution with a size of 370 nm and a zeta potential of 41.1 mV. We investigated the mechanical and cytocompatibility properties of chitosan nanoparticles encapsulated in hydrogel for emulating an extracellular matrix suitable for skin tissue engineering. CSNPs entrapped in GelMA (15 % w/v) exhibited controlled drug release during 5 days, which was fitted into various kinetic models to study the mass transfer mechanism behavior. Also, the composite hydrogels were effective as a barrier against both gram-positive and gram-negative bacteria at a concentration of 50 μg/ml nanoparticles in GelMA 15 %. Furthermore, the biocomposite was applied on Wistar rats for wound healing. As a result, this study provides a GelMA-NP50-Cur3 scaffold that promotes cell proliferation and decreases microbial infections in wounds.

An In Vitro and Ex Vivo Analysis of the Potential of GelMA Hydrogels as a Therapeutic Platform for Preclinical Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition with no curative therapy currently available. Immunomodulation can be applied as a therapeutic strategy to drive alternative immune cell activation and promote a proregenerative injury microenvironment. Locally injected hydrogels carrying immunotherapeutic cargo directly to injured tissue offer an encouraging treatment approach from an immunopharmacological perspective. Gelatin methacrylate (GelMA) hydrogels are promising in this regard, however, detailed analysis on the immunogenicity of GelMA in the specific context of the SCI microenvironment is lacking. Here, the immunogenicity of GelMA hydrogels formulated with a translationally relevant photoinitiator is analyzed in vitro and ex vivo. 3% (w/v) GelMA, synthesized from gelatin type-A, is first identified as the optimal hydrogel formulation based on mechanical properties and cytocompatibility. Additionally, 3% GelMA-A does not alter the expression profile of key polarization markers in BV2 microglia or RAW264.7 macrophages after 48 h. Finally, it is shown for the first time that 3% GelMA-A can support the ex vivo culture of primary murine organotypic spinal cord slices for 14 days with no direct effect on glial fibrillary acidic protein (GFAP+ ) astrocyte or ionized calcium-binding adaptor molecule 1 (Iba-1+ ) microglia reactivity. This provides evidence that GelMA hydrogels can act as an immunotherapeutic hydrogel-based platform for preclinical SCI.

Hydrogel-based treatments for spinal cord injuries

Spinal cord injury (SCI) is characterized by damage resulting in dysfunction of the spinal cord. Hydrogels are common biomaterials that play an important role in the treatment of SCI. Hydrogels are biocompatible, and some have electrical conductivity that are compatible with spinal cord tissues. Hydrogels have a high drug-carrying capacity, allowing them to be used for SCI treatment through the loading of various types of active substances, drugs, or cells. We first discuss the basic anatomy and physiology of the human spinal cord and briefly discuss SCI and its treatment. Then, we describe different treatment strategies for SCI. We further discuss the crosslinking methods and classification of hydrogels and detail hydrogel biomaterials prepared using different processing methods for the treatment of SCI. Finally, we analyze the future applications and limitations of hydrogels for SCI. The development of biomaterials opens up new possibilities and options for the treatment of SCI. Thus, our findings will inspire scholars in related fields and promote the development of hydrogel therapy for SCI.

Photocrosslinked methacrylated natural macromolecular hydrogels for tissue engineering: A review

A hydrogel is a three-dimensional (3D) network structure formed through polymer crosslinking, and these have emerged as a popular research topic in recent years. Hydrogel crosslinking can be classified as physical, chemical, or enzymatic, and photocrosslinking is a branch of chemical crosslinking. Compared with other methods, photocrosslinking can control the hydrogel crosslinking initiation, crosslinking time, and crosslinking strength using light. Owing to these properties, photocrosslinked hydrogels have important research prospects in tissue engineering, in situ gel formation, 3D bioprinting, and drug delivery. Methacrylic anhydride modification is a common method for imparting photocrosslinking properties to polymers, and graft-substituted polymers can be photocrosslinked under UV irradiation. In this review, we first introduce the characteristics of common natural polysaccharide- and protein-based hydrogels and the processes used for methacrylate group modification. Next, we discuss the applications of methacrylated natural hydrogels in tissue engineering. Finally, we summarize and discuss existing methacrylated natural hydrogels in terms of limitations and future developments. We expect that this review will help researchers in this field to better understand the synthesis of methacrylate-modified natural hydrogels and their applications in tissue engineering.

Effects of Adding Chitosan on Drug Entrapment Efficiency and Release Duration for Paclitaxel-Loaded Hydroxyapatite-Gelatin Composite Microspheres

Hydroxyapatite-gelatin microspheres with cone-like pores were synthesized via the wet-chemical method using ammonium dihydrogen phosphate ((NH4)H2PO4) and calcium nitrate (Ca(NO3)2·4H2O) as a source of calcium and phosphate ions with the addition of gelatin, which proved to be more osteoconductive than commercial products, such as fibrin glue and Osteoset® Bone Graft Substitute. Following the method of the previous study for loading paclitaxel (PTX), a drug entrapment efficiency of around 58% was achieved, which is much lower than that of the doxorubicin (DOX)-loaded one. Since PTX is hydrophobic while DOX is hydrophilic, the order of chitosan processing and addition of the solvent were tuned in this study, finally leading to an increase in drug entrapment efficiency of 94%. Additionally, the release duration of PTX exceeded six months. The MTT assay indicated that the effect of drug release on the suppression of cancer cells reached more than 40% after one week, thereby showcasing PTX's capacity to carry out its medicinal functions without being affected by the loading procedures.

From Grape By-Products to Enriched Yogurt Containing Pomace Extract Loaded in Nanotechnological Nutriosomes Tailored for Promoting Gastro-Intestinal Wellness

Grape pomace is the main by-product generated during the winemaking process; since it is still rich in bioactive molecules, especially phenolic compounds with high antioxidant power, its transformation in beneficial and health-promoting foods is an innovative challenge to extend the grape life cycle. Hence, in this work, the phytochemicals still contained in the grape pomace were recovered by an enhanced ultrasound assisted extraction. The extract was incorporated in liposomes prepared with soy lecithin and in nutriosomes obtained combining soy lecithin and Nutriose FM06^®, which were further enriched with gelatin (gelatin-liposomes and gelatin-nutriosomes) to increase the samples' stability in modulated pH values, as they were designed for yogurt fortification. The vesicles were sized ~100 nm, homogeneously dispersed (polydispersity index < 0.2) and maintained their characteristics when dispersed in fluids at different pH values (6.75, 1.20 and 7.00), simulating salivary, gastric and intestinal environments. The extract loaded vesicles were biocompatible and effectively protected Caco-2 cells against oxidative stress caused by hydrogen peroxide, to a better extent than the free extract in dispersion. The structural integrity of gelatin-nutriosomes, after dilution with milk whey was confirmed, and the addition of vesicles to the yogurt did not modify its appearance. The results pointed out the promising suitability of vesicles loading the phytocomplex obtained from the grape by-product to enrich the yogurt, offering a new and easy strategy for healthy and nutritional food development.

Encapsulation of Thymol in Gelatin Methacryloyl (GelMa)-Based Nanoniosome Enables Enhanced Antibiofilm Activity and Wound Healing

Non-healing wounds impose huge cost on patients, healthcare, and society, which are further fortified by biofilm formation and antimicrobial resistance (AMR) problems. Here, Thymol, an herbal antimicrobial agent, is utilized to combat AMR. For efficient delivery of Thymol gelatin methacryloyl (GelMa), a hydrophilic polymeric hydrogel with excellent biocompatibility combined with niosome was used to encapsulate Thymol. After optimization of the niosomal Thymol (Nio-Thymol) in the company of GelMa (Nio-Thymol@GelMa) to achieve maximum entrapment efficiency, minimum size, and low polydispersity index, the Thymol release peaked at 60% and 42% from Nio-Thymol@GelMa in medium with pH values of 6.5 and 7.4 after 72 h, respectively. Furthermore, Nio-Thymol@GelMa demonstrated higher antibacterial and anti-biofilm activity than Nio-Thymol and free Thymol against both Gram-negative and Gram-positive bacteria. Interestingly, compared with other obtained formulations, Nio-Thymol@GelMa also led to greater enhancement of migration of human dermal fibroblasts in vitro, and higher upregulation of the expression of certain growth factors such as FGF-1, and matrix metalloproteinases such as MMP-2 and MMP-13. These results suggest that Nio-Thymol@GelMa can represent a potential drug preparation for Thymol to enhance the wound healing process and antibacterial efficacy.

New Methacrylated Biopolymer-Based Hydrogels as Localized Drug Delivery Systems in Skin Cancer Therapy

The aim of the present work was to obtain drug-loaded hydrogels based on combinations of dextran, chitosan/gelatin/xanthan, and poly (acrylamide) as a sustained and controlled release vehicle of Doxorubicin, a drug used in skin cancer therapy that is associated with severe side effects. Hydrogels for use as 3D hydrophilic networks with good manipulation characteristics were produced using methacrylated biopolymer derivatives and the methacrylate group's polymerization with synthetic monomers in the presence of a photo-initiator, under UV light stimulation (365 nm). Transformed infrared spectroscopy analysis (FT-IR) confirmed the hydrogels' network structure (natural-synthetic composition and photocrosslinking), while scanning electron microscopy (SEM) analysis confirmed the microporous morphology. The hydrogels are swellable in simulated biological fluids and the material's morphology regulates the swelling properties: the maximum swelling degree was obtained for dextran-chitosan-based hydrogels because of their higher porosity and pore distribution. The hydrogels are bioadhesive on a biological simulating membrane, and values for the force of detachment and work of adhesion are recommended for applications on skin tissue. The Doxorubicin was loaded into the hydrogels and the drug was released by diffusion for all the resulting hydrogels, with small contributions from the hydrogel networks' relaxation. Doxorubicin-loaded hydrogels are efficient on keratinocytes tumor cells, the sustained released drug interrupting the cells' division and inducing cell apoptosis; we recommend the obtained materials for the topical treatment of cutaneous squamous cell carcinoma.

Understanding the Molecular Conformation and Viscoelasticity of Low Sol-Gel Transition Temperature Gelatin Methacryloyl Suspensions

For biomedical applications, gelatin is usually modified with methacryloyl groups to obtain gelatin methacryloyl (GelMA), which can be crosslinked by a radical reaction induced by low wavelength light to form mechanically stable hydrogels. The potential of GelMA hydrogels for tissue engineering has been well established, however, one of the main disadvantages of mammalian-origin gelatins is that their sol-gel transitions are close to room temperature, resulting in significant variations in viscosity that can be a problem for biofabrication applications. For these applications, cold-water fish-derived gelatins, such as salmon gelatin, are a good alternative due to their lower viscosity, viscoelastic and mechanical properties, as well as lower sol-gel transition temperatures, when compared with mammalian gelatins. However, information regarding GelMA (with special focus on salmon GelMA as a model for cold-water species) molecular conformation and the effect of pH prior to crosslinking, which is key for fabrication purposes since it will determine final hydrogel's structure, remains scarce. The aim of this work is to characterize salmon gelatin (SGel) and salmon methacryloyl gelatin (SGelMA) molecular configuration at two different acidic pHs (3.6 and 4.8) and to compare them to commercial porcine gelatin (PGel) and methacryloyl porcine gelatin (PGelMA), usually used for biomedical applications. Specifically, we evaluated gelatin and GelMA samples' molecular weight, isoelectric point (IEP), their molecular configuration by circular dichroism (CD), and determined their rheological and thermophysical properties. Results showed that functionalization affected gelatin molecular weight and IEP. Additionally, functionalization and pH affected gelatin molecular structure and rheological and thermal properties. Interestingly, the SGel and SGelMA molecular structure was more sensitive to pH changes, showing differences in gelation temperatures and triple helix formation than PGelMA. This work suggests that SGelMA presents high tunability as a biomaterial for biofabrication, highlighting the importance of a proper GelMA molecular configuration characterization prior to hydrogel fabrication.

In Situ Formation of Injectable Gelatin Methacryloyl (GelMA) Hydrogels for Effective Intraocular Delivery of Triamcinolone Acetonide

A novel drug delivery system designed for intraocular injection, gelatin methacryloyl (GelMA), has attracted much attention due to its sustained-release character and low cytotoxicity. We aimed to explore the sustained drug effect of GelMA hydrogels coupled with triamcinolone acetonide (TA) after injection into the vitreous cavity. The GelMA hydrogel formulations were characterized using scanning electron microscopy, swelling measurements, biodegradation, and release studies. The biological safety effect of GelMA on human retinal pigment epithelial cells and retinal conditions was verified by in vitro and in vivo experiments. The hydrogel exhibited a low swelling ratio, resistance to enzymatic degradation, and excellent biocompatibility. The swelling properties and in vitro biodegradation characteristics were related to the gel concentration. Rapid gel formation was observed after injection, and the in vitro release study confirmed that TA-hydrogels have slower and more prolonged release kinetics than TA suspensions. In vivo fundus imaging, optical coherence tomography measurements of retinal and choroid thickness, and immunohistochemistry did not reveal any apparent abnormalities of retinal or anterior chamber angle, and ERG indicated that the hydrogel had no impact on retinal function. The GelMA hydrogel implantable intraocular device exhibited an extended duration, in situ polymerization, and support cell viability, making it an attractive, safe, and well-controlled platform for treating the posterior segment diseases of the eye.

An experimental and theoretical approach to understand the interaction between particles and mucosal tissues

Nanonization of poorly water-soluble drugs has shown great potential in improving their oral bioavailability by increasing drug dissolution rate and adhesion to the gastrointestinal mucus. However, the fundamental features that govern the particle-mucus interactions have not been investigated in a systematic way before. In this work, we synthesize mucin hydrogels that mimic those of freshly excised porcine mucin. By using fluorescent pure curcumin particles, we characterize the effect of particle size (200 nm, and 1.2 and 1.3 μm), concentration (18, 35, and 71 μg mL^-1), and hydrogel crosslinking density on the diffusion-driven particle penetration in vitro. Next, we derive a phenomenological model that describes the physics behind the diffusion-derived penetration and considers the contributions of the key parameters assessed in vitro. Finally, we challenge our model by assessing the oral pharmacokinetics of an anti-cancer model drug, namely dasatinib, in pristine and nanonized forms and two clinically relevant doses in rats. For a dose of 10 mg kg^-1, drug nanonization leads to a significant ∼8- and ∼21-fold increase of the drug oral bioavailability and half-life, respectively, with respect to the unprocessed drug. When the dose of the nanoparticles was increased to 15 mg kg^-1, the oral bioavailability increased though not significantly, suggesting the saturation of the mucus penetration sites, as demonstrated by the in vitro model. Our overall results reveal the potential of this approach to pave the way for the development of tools that enable a more rational design of nano-drug delivery systems for mucosal administration. STATEMENT OF SIGNIFICANCE: The development of experimental-theoretical tools to understand and predict the diffusion-driven penetration of particles into mucus is crucial not only to rationalize the design of nanomedicines for mucosal administration but also to anticipate the risks of the exposure of the body to nano-pollutants. However, a systematic study of such tools is still lacking. Here we introduce an experimental-theoretical approach to predict the diffusion-driven penetration of particles into mucus and investigate the effect of three key parameters on this interaction. Then, we challenge the model in a preliminary oral pharmacokinetics study in rats which shows a very good correlation with in vitro results. Overall, this work represents a robust platform for the modelling of the interaction of particles with mucosae under dynamic conditions.

Enzymatically-Crosslinked Gelatin Hydrogels with Nanostructured Architecture and Self-Healing Performance for Potential Use as Wound Dressings

Development of natural protein-based hydrogels with self-healing performance and tunable physical properties has attracted increased attention owing to their wide potential not only in the pharmaceutical field, but also in wounds management. This work reports the development of a versatile hydrogel based on enzymatically-crosslinked gelatin and nanogels loaded with amoxicillin (Amox), an antibiotic used in wound infections. The transglutaminase (TGase)-crosslinked hydrogels and encapsulating nanogels were formed rapidly through enzymatic crosslinking and self-assembly interactions in mild conditions. The nanogels formed through the self-assemble of maleoyl-chitosan (MAC5) and polyaspartic acid (PAS) may have positive influence on the self-healing capacity and drug distribution within the hydrogel network through the interactions established between gelatin and gel-like nanocarriers. The physicochemical properties of the enzymatically-crosslinked hydrogels, such as internal structure, swelling and degradation behavior, were studied. In addition, the Amox release studies indicated a rapid release when the pH of the medium decreased, which represents a favorable characteristic for use in the healing of infected wounds. It was further observed through the in vitro and in vivo biocompatibility assays that the optimized scaffolds have great potential to be used as wound dressings.

Pyroptosis in bone loss

Pyroptosis could be responsible for the bone loss from bone metabolic diseases, leading to the negative impact on people's health and life. It has been shown that osteoclasts, osteoblasts, macrophages, chondrocytes, periodontal and gingival cells may be involved in bone loss linked with pyroptosis. So far, the involved mechanisms have not been fully elucidated. In this review, we introduced the related cells involved in the pyroptosis associated with bone loss and summarized the role of these cells in the bone metabolism during the process of pyroptosis. We also discuss the clinical potential of targeting mechanisms in the osteoclasts, osteoblasts, macrophages, chondrocytes, periodontal and gingival cells touched upon pyroptosis to treat bone loss from bone metabolic diseases as well as the challenges of avoiding potential side effects and producing efficient treatment methods.

GelMA, Click-Chemistry Gelatin and Bioprinted Polyethylene Glycol-Based Hydrogels as 3D Ex Vivo Drug Testing Platforms for Patient-Derived Breast Cancer Organoids

3D organoid model technologies have led to the development of innovative tools for cancer precision medicine. Yet, the gold standard culture system (Matrigel®) lacks the ability for extensive biophysical manipulation needed to model various cancer microenvironments and has inherent batch-to-batch variability. Tunable hydrogel matrices provide enhanced capability for drug testing in breast cancer (BCa), by better mimicking key physicochemical characteristics of this disease’s extracellular matrix. Here, we encapsulated patient-derived breast cancer cells in bioprinted polyethylene glycol-derived hydrogels (PEG), functionalized with adhesion peptides (RGD, GFOGER and DYIGSR) and gelatin-derived hydrogels (gelatin methacryloyl; GelMA and thiolated-gelatin crosslinked with PEG-4MAL; GelSH). Within ranges of BCa stiffnesses (1−6 kPa), GelMA, GelSH and PEG-based hydrogels successfully supported the growth and organoid formation of HR+,−/HER2+,− primary cancer cells for at least 2−3 weeks, with superior organoid formation within the GelSH biomaterial (up to 268% growth after 15 days). BCa organoids responded to doxorubicin, EP31670 and paclitaxel treatments with increased IC50 concentrations on organoids compared to 2D cultures, and highest IC50 for organoids in GelSH. Cell viability after doxorubicin treatment (1 µM) remained >2-fold higher in the 3D gels compared to 2D and doxorubicin/paclitaxel (both 5 µM) were ~2.75−3-fold less potent in GelSH compared to PEG hydrogels. The data demonstrate the potential of hydrogel matrices as easy-to-use and effective preclinical tools for therapy assessment in patient-derived breast cancer organoids.

Semi-Synthetic Click-Gelatin Hydrogels as Tunable Platforms for 3D Cancer Cell Culture

Basement membrane extracts (BME) derived from Engelbreth-Holm-Swarm (EHS) mouse sarcomas such as Matrigel^® remain the gold standard extracellular matrix (ECM) for three-dimensional (3D) cell culture in cancer research. Yet, BMEs suffer from substantial batch-to-batch variation, ill-defined composition, and lack the ability for physichochemical manipulation. Here, we developed a novel 3D cell culture system based on thiolated gelatin (Gel-SH), an inexpensive and highly controlled raw material capable of forming hydrogels with a high level of biophysical control and cell-instructive bioactivity. We demonstrate the successful thiolation of gelatin raw materials to enable rapid covalent crosslinking upon mixing with a synthetic poly(ethylene glycol) (PEG)-based crosslinker. The mechanical properties of the resulting gelatin-based hydrogels were readily tuned by varying precursor material concentrations, with Young's moduli ranging from ~2.5 to 5.8 kPa. All hydrogels of varying stiffnesses supported the viability and proliferation of MDA-MB-231 and MCF-7 breast cancer cell lines for 14 and 21 days of cell culture, respectively. Additionally, the gelatin-based hydrogels supported the growth, viability, and osteogenic differentiation of patient-derived preosteoblasts over 28 days of culture. Collectively, our data demonstrate that gelatin-based biomaterials provide an inexpensive and tunable 3D cell culture platform that may overcome the limitations of traditional BMEs.

Pulsed Laser Photo-Crosslinking of Gelatin Methacryloyl Hydrogels for the Controlled Delivery of Chlorpromazine to Combat Antimicrobial Resistance

Hydrogels are ideal candidates for the sustained local administration of antimicrobial drugs because they have customizable physicochemical properties that allow drug release kinetics to be controlled and potentially address the issue of systemic side effects. Consequently, the purpose of this study was to use 266 nm-pulsed laser beams to photo-crosslink gelatin methacryloyl hydrogels using Irgacure 2959 as a photo-initiator to reduce the curing time and to have an online method to monitor the process, such as laser-induced fluorescence. Additionally, irradiated chlorpromazine was loaded into the hydrogels to obtain a drug delivery system with antimicrobial activity. These hydrogels were investigated by UV–Vis and FTIR absorption spectroscopy, scanning electron microscopy, and laser-induced fluorescence spectroscopy and their structural and morphological characteristics, swelling behavior, and drug release profile were obtained. As a result the morphology, swelling behavior, and drug release profile were influenced by both the energy of the laser beam and the exposure time. The optimal hydrogel was obtained after 1 min of laser irradiation for Irgacure 2959 at 0.05% w/v concentration and gelatin methacryloyl at 10% w/v concentration. The hydrogels loaded with irradiated chlorpromazine show significant antimicrobial activity against Staphylococcus aureus and MRSA bacteria and a non-cytotoxic effect against L929 fibroblast cell lines.

Progress of Research in In Situ Smart Hydrogels for Local Antitumor Therapy: A Review

Cancer seriously threatens human health. Surgery, radiotherapy and chemotherapy are the three pillars of traditional cancer treatment, with targeted therapy and immunotherapy emerging over recent decades. Standard drug regimens are mostly executed via intravenous injection (IV), especially for chemotherapy agents. However, these treatments pose severe risks, including off-target toxic side effects, low drug accumulation and penetration at the tumor site, repeated administration, etc., leading to inadequate treatment and failure to meet patients’ needs. Arising from these challenges, a local regional anticancer strategy has been proposed to enhance therapeutic efficacy and concomitantly reduce systemic toxicity. With the advances in biomaterials and our understanding of the tumor microenvironment, in situ stimulus-responsive hydrogels, also called smart hydrogels, have been extensively investigated for local anticancer therapy due to their injectability, compatibility and responsiveness to various stimuli (pH, enzyme, heat, light, magnetic fields, electric fields etc.). Herein, we focus on the latest progress regarding various stimuli that cause phase transition and drug release from smart hydrogels in local regional anticancer therapy. Additionally, the challenges and future trends of the reviewed in situ smart hydrogels for local drug delivery are summarized and proposed.

An Injectable Epigenetic Autophagic Modulatory Hydrogel for Boosting Umbilical Cord Blood NK Cell Therapy Prevents Postsurgical Relapse of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) exhibits resistance to conventional treatments due to the presence of cancer stem cells (CSCs), causing postsurgical relapse and a dismal prognosis. Umbilical cord blood natural killer (UCB-NK) cell-based immunotherapy represents a promising strategy for cancer treatment. However, its therapeutic efficacy is greatly restrained by downregulation of the NK cell activation ligand MHC class I-related chain A/B (MICA/B) and autophagy-mediated degradation of NK cell-derived granzyme B (GZMB) in CSCs. Herein, it is demonstrated that suberoylanilide hydroxamic acid (SAHA) epigenetically downregulates let-7e-5p and miR-615-3p to increase MICA/B expression and that 3-methyl adenine (3MA) inhibits autophagy-mediated GZMB degradation, thereby sensitizing breast CSCs to UCB-NK cells. Then, an injectable hydrogel is designed to codeliver SAHA and 3MA to enhance UCB-NK cell infusion efficacy in TNBC. The hydrogel precursors can be smoothly injected into the tumor resection bed and form a stable gel in situ, allowing for a pH-sensitive sustained release of SAHA and 3MA. Moreover, UCB-NK cell infusion in combination with the hydrogel efficiently controls postsurgical relapse of TNBC. In addition, the hydrogel exhibits good hemostasis and wound-healing functions. Therefore, the work provides proof of concept that an injectable epigenetic autophagic modulatory hydrogel augments UCB-NK cell therapy to combat postsurgical relapse of TNBC.

Immunomodulatory Microgels Support Proregenerative Macrophage Activation and Attenuate Fibroblast Collagen Synthesis

Scars composed of fibrous connective tissues are natural consequences of injury upon incisional wound healing in soft tissues.  Hydrogels that feature a sustained presentation of immunomodulatory cytokines are known to modulate wound healing. However, existing immunomodulatory hydrogels lack interconnected micropores to promote cell ingrowth. Other limitations include invasive delivery procedures and harsh synthesis conditions that are incompatible with drug molecules. Here, hybrid nanocomposite microgels containing interleukin-10 (IL-10) are reported to modulate tissue macrophage phenotype during wound healing. The intercalation of laponite nanoparticles in the polymer network yields microgels with tissue-mimetic elasticity (Young's modulus in the range of 2-6 kPa) and allows the sustained release of IL-10 to promote the differentiation of macrophages toward proregenerative phenotypes. The porous interstitial spaces between microgels promote fibroblast proliferation and fast trafficking (an average speed of ≈14.4 µm h^-1 ). The incorporation of hyaluronic acid further enhances macrophage infiltration. The coculture of macrophages and fibroblasts treated with transforming growth factor-beta 1 resulted in a twofold reduction in collagen-I production for microgels releasing IL-10 compared to the IL-10 free group. The new microgels show potential toward regenerative healing by harnessing the antifibrotic behavior of host macrophages.

Sustained released of bioactive mesenchymal stromal cell-derived extracellular vesicles from 3D-printed gelatin methacrylate hydrogels

Extracellular vesicles (EVs) represent an emerging class of therapeutics with significant potential and broad applicability. However, a general limitation is their rapid clearance after administration. Thus, methods to enable sustained EV release are of great potential value. Here, we demonstrate that EVs from mesenchymal stem/stromal cells (MSCs) can be incorporated into 3D-printed gelatin methacrylate (GelMA) hydrogel bioink, and that the initial burst release of EVs can be reduced by increasing the concentration of crosslinker during gelation. Further, the data show that MSC EV bioactivity in an endothelial gap closure assay is retained after the 3D printing and photocrosslinking processes. Our group previously showed that MSC EV bioactivity in this assay correlates with pro-angiogenic bioactivity in vivo, thus these results indicate the therapeutic potential of MSC EV-laden GelMA bioinks.

UV-Cured Chitosan and Gelatin Hydrogels for the Removal of As(V) and Pb(II) from Water

In this study, new photocurable biobased hydrogels deriving from chitosan and gelatin are designed and tested as sorbents for As(V) and Pb(II) removal from water. Those renewable materials were modified by a simple methacrylation reaction in order to make them light processable. The success of the reaction was evaluated by both 1H-NMR and FTIR spectroscopy. The reactivity of those formulations was subsequently investigated by a real-time photorheology test. The obtained hydrogels showed high swelling capability reaching up to 1200% in the case of methacrylated gelatin (GelMA). Subsequently, the Z-potential of the methacrylated chitosan (MCH) and GelMA was measured to correlate their electrostatic surface characteristics with their adsorption properties for As(V) and Pb(II). The pH of the solutions proved to have a huge influence on the As(V) and Pb(II) adsorption capacity of the obtained hydrogels. Furthermore, the effect of As(V) and Pb(II) initial concentration and contact time on the adsorption capability of MCH and GelMA were investigated and discussed. The MCH and GelMA hydrogels demonstrated to be promising sorbents for the removal of heavy metals from polluted waters.

Antimicrobial Activity of Silver, Copper, and Zinc Ions/Poly(Acrylate/Itaconic Acid) Hydrogel Matrices

The design and use of new potent and specific antimicrobial systems are of crucial importance in the medical field. This will help relieve, fight, and eradicate infections and thus improve human health. The use of metals in various forms as antimicrobial therapeutics has been known since ancient times. In this sense, polymeric hydrogel matrices as multifunctional materials and in combination with various metal forms can be a great alternative to conventional treatments for infections. Hydrogels possess high hydrophilicity, specific three-dimensional networks, fine biocompatibility, and cell adhesion and are therefore suitable as materials for the loading of active antimicrobial agents and acting in antimicrobial areas. The biocompatible nature of hydrogels’ matrices makes them a convenient starting platform to develop biocompatible, selective, active controlled-release antimicrobial materials. Hydrogels based on acrylate and itaconic acid were synthesized and loaded with silver (Ag+), copper (Cu2+), and zinc (Zn2+) ions as a controlled release and antimicrobial system to test release properties and antimicrobial activity in contact with microbes. The metal ions/hydrogel systems exhibited favorable biocompatibility, release profiles, and antimicrobial activity against methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus aureus, Escherichia coli, and Candida albicans microbes, and have shown that they have the capacity to “fight” with the life-threatening infections. Antimicrobial activity depends on types of metal ions, the composition of polymeric matrices, as well as the types of microbes. Designed metal ions/poly(acrylate/itaconic acid) antimicrobial systems have shown to have good potential as antimicrobial therapeutics and suitable biomaterials for medical applications.

Development of Gelatin Methacrylate (GelMa) Hydrogels for Versatile Intracavitary Applications: In-vitro Characterization and Ex-vivo Performance Assessment

Applicability of hydrogels as drug delivery systems is on the rise due to their highly tunable degree of polymeric crosslinking to attain varying rates of payload release. Sustaining the release...

Mechanically robust hybrid hydrogels of photo-crosslinkable gelatin and laminin-mimetic peptide amphiphiles for neural induction

Self-assembling bio-instructive materials that can provide a biomimetic tissue microenvironment with the capability to regulate cellular behaviors represent an attractive platform in regenerative medicine. Herein, we develop a hybrid neuro-instructive hydrogel that combines the properties of a photo-crosslinkable gelatin methacrylate (GelMA) and self-assembling peptide amphiphiles (PAs) bearing a laminin-derived neuro-inductive epitope (PA-GSR). Electrostatic interaction and ultraviolet light crosslinking mechanisms were combined to create dual-crosslinked hybrid hydrogels with tunable stiffness. Spectroscopic, microscopic and theoretical techniques show that the cationic PA-GSR(+) electrostatically co-assembles with the negatively charged GelMA to create weak hydrogels with hierarchically ordered microstructures, which were further photo-crosslinked to create mechanically robust hydrogels. Dynamic oscillatory rheology and micromechanical testing show that photo-crosslinking of the co-assembled GelMA and PA-GSR(+) hydrogel results in robust hydrogels displaying improved stiffness. Gene expression analysis was used to show that GelMA/PA-GSR(+) hydrogels can induce human mesenchymal stem cells (hMSCs) into neural-lineage cells and supports neural-lineage specification of neuroblast-like cells (SH-SY5Y) in a growth-factor-free manner. Also, metabolomics analysis suggests that the hydrogel alters the metabolite profiles in the cells by affecting multiple molecular pathways. This work highlights a new approach for the design of PA-based hybrid hydrogels with robust mechanical properties and biological functionalities for nerve tissue regeneration.

Gelatin Methacryloyl Hydrogels for the Localized Delivery of Cefazolin

The tuneability of hydrogels renders them promising candidates for local drug delivery to prevent and treat local surgical site infection (SSI) while avoiding the systemic side-effects of intravenous antibiotic injections. Here, we present a newly developed gelatin methacryloyl (GelMA)-based hydrogel drug delivery system (GelMA-DDS) to locally deliver the broad-spectrum antibiotic cefazolin for SSI prophylaxis and treatment. Antibiotic doses from 3 µg to 90 µg were loaded in photocrosslinked GelMA hydrogel discs with 5 to 15% w/v polymer concentration and drug encapsulation efficiencies, mechanical properties, crosslinking and release kinetics, as well as bacterial growth inhibition were assessed. Our results demonstrate that all GelMA groups supported excellent drug encapsulation efficiencies of up to 99%. Mechanical properties of the GelMA-DDS were highly tuneable and unaffected by the loading of small to medium doses of cefazolin. The diffusive and the proteolytic in vitro drug delivery of all investigated cefazolin doses was characterized by a burst release, and the delivered cefazolin amount was directly proportional to the encapsulated dose. Accelerated enzymatic degradation of the GelMA-DDS followed zero-order kinetics and was dependent on both the cefazolin dose and GelMA concentration (3-13 h). Finally, we demonstrate that cefazolin delivered from GelMA induced a dose-dependent antibacterial efficacy against S. aureus, in both a broth and a diffusive assay. The cefazolin-loaded GelMA-DDS presented here provides a highly tuneable and easy-to-use local delivery system for the prophylaxis and treatment of SSI.

Long-Term Sustained Drug Delivery via 3D Printed Masks for the Development of a Heparin-Loaded Interlayer in Vascular Tissue Engineering Applications

Current approaches in small-diameter vascular grafts for coronary artery bypass surgeries fail to address physiological variations along the graft that contribute to thrombus formation and ultimately graft failure. We present an innovative interlayer drug delivery system that can be utilized for the sustained delivery of heparin through a graft with a high degree of temporal and spatial control. A heparin-loaded gelatin methacrylate (gelMA) interlayer sits within a biohybrid composed of decellularized bovine pericardium (dECM) and poly(propylene fumarate) (PPF), and its UV crosslinking is controlled via three-dimensional (3D) printed shadow masks. The masks can be readily designed to modulate the incident light intensity on the graft, enabling us to control the resultant gelMA crosslinking and properties. A high heparin loading efficiency was obtained in gelMA and was independent of crosslinking. We achieved sustained heparin release over the course of 2 weeks within the biohybrid material using the 3D printed mask patterns. High doses of heparin were observed to have detrimental effects on endothelial cell function. However, when exposed to heparin in a slower, more sustained manner consistent with the masks, endothelial cells behave similarly to untreated cells. Further, slower release profiles cause significantly more release of tissue factor pathway inhibitor, an anticoagulant, than a faster release profile. The heparin-loaded gelMA interlayer we have developed is a useful tool for the temporal and spatial control of heparin release that supports endothelial function and promotes an antithrombotic environment.

Adipose Tissue-Derived Stromal Cells Alter the Mechanical Stability and Viscoelastic Properties of Gelatine Methacryloyl Hydrogels

The extracellular matrix provides mechanical cues to cells within it, not just in terms of stiffness (elasticity) but also time-dependent responses to deformation (viscoelasticity). In this work, we determined the viscoelastic transformation of gelatine methacryloyl (GelMA) hydrogels caused by adipose tissue-derived stromal cells (ASCs) through mathematical modelling. GelMA-ASCs combination is of interest to model stem cell-driven repair and to understand cell-biomaterial interactions in 3D environments. Immortalised human ASCs were embedded in 5%, 10%, and 15% (w/v) GelMA hydrogels and evaluated for 14 d. GelMA had a concentration-dependent increase in stiffness, but cells decreased this stiffness over time, across concentrations. Viscoelastic changes in terms of stress relaxation increased progressively in 5% GelMA, while mathematical Maxwell analysis showed that the relative importance (R_i) of the fastest Maxwell elements increased proportionally. The 10% GelMA only showed differences at 7 d. In contrast, ASCs in 15% GelMA caused slower stress relaxation, increasing the R_i of the slowest Maxwell element. We conclude that GelMA concentration influenced the stiffness and number of Maxwell elements. ASCs changed the percentage stress relaxation and R_i of Maxwell elements transforming hydrogel viscoelasticity into a more fluid environment over time. Overall, 5% GelMA induced the most favourable ASC response.

MechAnalyze: An Algorithm for Standardization and Automation of Compression Test Analysis

The mechanical properties of hydrogels, as well as native and engineered tissues are key parameters frequently assessed in biomaterial science and tissue engineering research. However, a lack of standardized methods and user-independent data analysis has impacted the research community for many decades and contributes to poor reproducibility and comparability of datasets, representing a significant issue often neglected in publications. In this study, we provide a software package, MechAnalyze, facilitating the standardized and automated analysis of force-displacement data generated in unconfined compression tests. Using comparative studies of datasets analyzed manually and with MechAnalyze, we demonstrate that the software reliably determines the compressive moduli, failure stress and failure strain of hydrogels, as well as engineered and native tissues, while providing an intuitive user interface that requires minimal user input. MechAnalyze provides a fast and user-independent data analysis method and advances process standardization, reproducibility, and comparability of data for the mechanical characterization of biomaterials as well as native and engineered tissues. Impact statement Mechanical properties of hydrogels are crucial parameters in the development of new materials for tissue engineering. However, manual assessment is tedious, not standardized and suffers under user-to-user bias. Hence, the here presented stand-alone software package provides analysis and statistics of force-displacement and material geometry data to determine the compressive moduli, failure stress, and failure strain in a standardized, robust, and automated fashion. MechAnalyze will substantially support biomechanical testing of hydrogels as well as engineered and native tissues and will thus, be of appreciable value to a broad target group in regenerative medicine, tissue engineering, but also life sciences and biomedicine.

Deciphering the Molecular Mechanism of Water Interaction with Gelatin Methacryloyl Hydrogels: Role of Ionic Strength, pH, Drug Loading and Hydrogel Network Characteristics

Water plays a primary role in the functionality of biomedical polymers such as hydrogels. The state of water, defined as bound, intermediate, or free, and its molecular organization within hydrogels is an important factor governing biocompatibility and hemocompatibility. Here, we present a systematic study of water states in gelatin methacryloyl (GelMA) hydrogels designed for drug delivery and tissue engineering applications. We demonstrate that increasing ionic strength of the swelling media correlated with the proportion of non-freezable bound water. We attribute this to the capability of ions to create ion–dipole bonds with both the polymer and water, thereby reinforcing the first layer of polymer hydration. Both pH and ionic strength impacted the mesh size, having potential implications for drug delivery applications. The mechanical properties of GelMA hydrogels were largely unaffected by variations in ionic strength or pH. Loading of cefazolin, a small polar antibiotic molecule, led to a dose-dependent increase of non-freezable bound water, attributed to the drug’s capacity to form hydrogen bonds with water, which helped recruit water molecules in the hydrogels’ first hydration layer. This work enables a deeper understanding of water states and molecular arrangement at the hydrogel–polymer interface and how environmental cues influence them.

Exploring potential formulation strategies for chemoprevention of breast cancer: a localized delivery perspective

This review focuses on the various formulation approaches that have been explored to achieve localized delivery in breast cancer. The rationale behind the necessity of localized drug delivery has been extensively reviewed. The review also emphasizes the various possible routes for achieving localized drug delivery. Particularly, different types of nanoplatforms like lipid-based drug carriers, polymeric particles, hydrogels, drug conjugates and other formulation strategies like microneedles and drug-eluting implants, which have been used to increase tumor retention and subsequently halt tumor progression, have been deliberated here. In addition, the significant challenges that may be encountered in the delivery of anticancer drugs and the aspects that require careful evaluation for effective localized delivery of chemotherapeutic agents have been discussed.

Recent Advances of Taxol-Loaded Biocompatible Nanocarriers Embedded in Natural Polymer-Based Hydrogels

The discovery of paclitaxel (PTX) has been a milestone in anti-cancer therapy and has promoted the development and marketing of various formulations that have revolutionized the therapeutic approach towards several malignancies. Despite its peculiar anti-cancer activity, the physico-chemical properties of PTX compromise the administration of the compound in polar media. Because of this, since the development of the first Food and Drug Administration (FDA)-approved formulation (Taxol®), consistent efforts have been made to obtain suitable delivery systems able to preserve/increase PTX efficacy and to overcome the side effects correlated to the presence of some excipients. The exploitation of natural polymers as potential materials for drug delivery purposes has favored the modulation of the bioavailability and the pharmacokinetic profiles of the drug, and in this regard, several formulations have been developed that allow the controlled release of the active compound. In this mini-review, the recent advances concerning the design and applications of natural polymer-based hydrogels containing PTX-loaded biocompatible nanocarriers are discussed. The technological features of these formulations as well as the therapeutic outcome achieved following their administration will be described, demonstrating their potential role as innovative systems to be used in anti-tumor therapy.

Biomedical application of photo-crosslinked gelatin hydrogels

Abstract

During the past decades, photo-crosslinked gelatin hydrogel (methacrylated gelatin, GelMA) has gained a lot of attention due to its remarkable application in the biomedical field. It has been widely used in cell transplantation, cell culture and drug delivery, based on its crosslinking to form hydrogels with tunable mechanical properties and excellent bio-compatibility when exposed to light irradiation to mimic the micro-environment of native extracellular matrix (ECM). Because of its unique biofunctionality and mechanical tenability, it has also been widely applied in the repair and regeneration of bone, heart, cornea, epidermal tissue, cartilage, vascular, peripheral nerve, oral mucosa, and skeletal muscle et al. The purpose of this review is to summarize the recent application of GelMA in drug delivery and tissue engineering field. Moreover, this review article will briefly introduce both the development of GelMA and the characterization of GelMA. Finally, we discuss the challenges and future development prospects of GelMA as a tissue engineering material and drug or gene delivery carrier, hoping to contribute to accelerating the development of GelMA in the biomedical field.

Graphical abstract

Antitumor Effects of Self-Assembling Peptide-Emodin in situ Hydrogels in vitro and in vivo

PURPOSE

To study the in vitro and in vivo antitumor effects of the colloidal suspension-in situ hydrogel of emodin (EM) constructed with the self-assembling peptide RADA16-I and systematically evaluate the feasibility of the delivery system.

METHODS

The MTT and colony-formation assays were used to determine the viability of normal cells NCTC 1469 and tumor cells Hepa1-6. The uptake of EM in the RADA16-I-EM in situ hydrogel by tumor cells was analyzed by laser confocal microscope and flow cytometry. Flow cytometry was used to detect the cell apoptosis and cell cycle distribution. Transwell assay was used to detect the migration and invasion of tumor cells. The antitumor efficacy of the RADA16-I-EM in situ hydrogel and its toxic effects was further assessed in vivo on Hepa1-6 tumor-bearing C57 mice.

RESULTS

The results showed that the RADA16-I-EM in situ hydrogels could obviously reduce the toxicity of EM to normal cells and the survival of tumor cells. The uptake of EM by the cells from the hydrogels was obviously increased and could significantly induce apoptosis and arrest cell cycle in the G2/M phase, and reduce the migration, invasion and clone-formation ability of the cells. The RADA16-I-EM in situ hydrogel could also effectively inhibit the tumor growth and obviously decrease the toxic effects of EM on normal tissues in vivo.

CONCLUSION

Our results demonstrated that RADA16-I has the potential to be a carrier for the hydrophobic drug EM and can effectively improve the delivery of hydrophobic antitumor drugs with enhanced antitumor effects and reduced toxic effects of the drugs on normal cells and tissues.