In situ photocrosslinked hyaluronic acid and poly (γ-glutamic acid) hydrogels as injectable drug carriers for load-bearing tissue application

Harnessing the potential of hyaluronic acid methacrylate (HAMA) hydrogel for clinical applications in orthopaedic diseases

The treatment of orthopaedic diseases, such as fractures and osteoarthritis, remains a significant challenge due to the complex requirements for mechanical strength and tissue repair. Hydrogels based on hyaluronic acid methacrylate (HAMA) show promise as tissue engineering materials for these conditions. Hyaluronic acid (HA) is a natural component of the extracellular matrix, known for its good compatibility. The mechanical strength of HAMA-based hydrogels can be adjusted through crosslinking and by combining them with other materials. This review provides an overview of recent research on HAMA-based hydrogels for tissue engineering applications in orthopaedic diseases. First, we summarize the techniques for the preparation and characterization of HAMA hydrogels. Next, we offer a detailed review of the use of HAMA-based hydrogels in treating conditions such as cartilage injuries, bone defects, and meniscus injuries. Additionally, we discuss the applications of HAMA-based hydrogels in other diseases related to orthopaedics. Finally, we point out the challenges and propose future directions for the clinical translation of HAMA-based hydrogels.

Translational potential statement

HAMA-based hydrogels show strong translational potential in orthopaedics due to their biocompatibility, adjustable mechanical properties, and regenerative capabilities. With ongoing research, these hydrogels are well-positioned for clinical applications, particularly in cartilage repair, meniscus injuries, and osteoarthritis treatment.

Advances in stimuli-responsive injectable hydrogels for biomedical applications

Injectable hydrogels, as a class of highly hydrated soft materials, are of interest for biomedicine due to their precise implantation and minimally invasive local drug delivery at the implantation site. The combination of in situ gelation ability and versatile therapeutic agent/cell loading capabilities makes injectable hydrogels ideal materials for drug delivery, tissue engineering, wound dressing and tumor treatment. In particular, the stimuli-responsive injectable hydrogels that can respond to different stimuli in and out of the body (e.g., temperature, pH, redox conditions, light, magnetic fields, etc.) have significant advantages in biomedicine. Here, we summarize the design strategies, advantages, and recent developments of stimuli-responsive injectable hydrogels in different biomedical fields. Challenges and future perspectives of stimuli-responsive injectable hydrogels are also discussed and the future steps necessary to fulfill the potential of these promising materials are highlighted.

A novel injectable boron doped-mesoporous nano bioactive glass loaded-alginate composite hydrogel as a pulpotomy filling biomaterial for dentin regeneration

BACKGROUND

Different materials have been used as wound dressings after vital pulp therapies. Some of them have limitations such as delayed setting, difficult administration, slight degree of cytotoxicity, crown discoloration and high cost. Therefore, to overcome these disadvantages, composite scaffolds have been used in regenerative dentistry. This study aims to construct and characterize the physicochemical behavior of a novel injectable alginate hydrogel loaded with different bioactive glass nanoparticles in various concentrations as a regenerative pulpotomy filling material.

METHODS

Alginate hydrogels were prepared by dissolving alginate powder in alcoholic distilled water containing mesoporous bioactive glass nanoparticles (MBG NPs) or boron-doped MBG NPs (BMBG NPs) at 10 and 20 wt% concentrations. The mixture was stirred and incubated overnight in a water bath at 50 0 C to ensure complete solubility. A sterile dual-syringe system was used to mix the alginate solution with 20 wt% calcium chloride solution, forming the hydrogel upon extrusion. Then, constructed hydrogel specimens from all groups were characterized by FTIR, SEM, water uptake percentage (WA%), bioactivity and ion release, and cytotoxicity. Statistical analysis was done using One-Way ANOVA test for comparisons between groups, followed by multiple pairwise comparisons using Bonferroni adjusted significance level (p < 0.05).

RESULTS

Alginate/BMBG loaded groups exhibited remarkable increase in porosity and pore size diameter [IIB1 (168), IIB2 (183) (µm)]. Similarly, WA% increased (~ 800%) which was statistically significant (p < 0.05). Alginate/BMBG loaded groups exhibited the strongest bioactive capability displaying prominent clusters of hydroxyapatite precipitates on hydrogel surfaces. Ca/P ratio of precipitates in IIA2 and IIB1 (1.6) were like Ca/P ratio for stoichiometric pure hydroxyapatite (1.67). MTT assay data revealed that the cell viability % of human gingival fibroblast cells have declined with increasing the concentration of both powders and hydrogel extracts in all groups after 24 and 48 h but still higher than the accepted cell viability % of (˃70%).

CONCLUSIONS

The outstanding laboratory performance of the injectable alginate/BMBGNPs (20 wt%) composite hydrogel suggested it as promising candidate for pulpotomy filling material potentially enhancing dentin regeneration in clinical applications.

Exploring the Formulation and Approaches of Injectable Hydrogels Utilizing Hyaluronic Acid in Biomedical Uses

The characteristics of injectable hydrogels make them a prime contender for various biomedical applications. Hyaluronic acid is an essential component of the matrix surrounding the cells; moreover, hyaluronic acid's structural and biochemical characteristics entice researchers to develop injectable hydrogels for various applications. However, due to its poor mechanical properties, several strategies are used to produce injectable hyaluronic acid hydrogel. This review summarizes published studies on the production of injectable hydrogels based on hyaluronic acid polysaccharide polymers and the biomedical field's applications for these hydrogel systems. Hyaluronic acid-based hydrogels are divided into two categories based on their injectability mechanisms: in situ-forming injectable hydrogels and shear-thinning injectable hydrogels. Many crosslinking methods are used to create injectable hydrogels; chemical crosslinking techniques are the most frequently investigated technique. Hybrid injectable hydrogel systems are widely investigated by blending hyaluronic acid with other polymers or nanoparticulate systems. Injectable hyaluronic acid hydrogels were thoroughly investigated and proven to demonstrate potential in various medical fields, including delivering drugs and cells, tissue repair, and wound dressings.

Poly (γ) glutamic acid: a unique microbial biopolymer with diverse commercial applicability

Microbial biopolymers have emerged as promising solutions for environmental pollution-related human health issues. Poly-γ-glutamic acid (γ-PGA), a natural anionic polymeric compound, is composed of highly viscous homo-polyamide of D and L-glutamic acid units. The extracellular water solubility of PGA biopolymer facilitates its complete biodegradation and makes it safe for humans. The unique properties have enabled its applications in healthcare, pharmaceuticals, water treatment, foods, and other domains. It is applied as a thickener, taste-masking agent, stabilizer, texture modifier, moisturizer, bitterness-reducing agent, probiotics cryoprotectant, and protein crystallization agent in food industries. γ-PGA is employed as a biological adhesive, drug carrier, and non-viral vector for safe gene delivery in tissue engineering, pharmaceuticals, and medicine. It is also used as a moisturizer to improve the quality of hair care and skincare cosmetic products. In agriculture, it serves as an ideal stabilizer, environment-friendly fertilizer synergist, plant-growth promoter, metal biosorbent in soil washing, and animal feed additive to reduce body fat and enhance egg-shell strength.

Synthesis of Poly-γ-Glutamic Acid and Its Application in Biomedical Materials

Poly-γ-glutamic acid (γ-PGA) is a natural polymer composed of glutamic acid monomer and it has garnered substantial attention in both the fields of material science and biomedicine. Its remarkable cell compatibility, degradability, and other advantageous characteristics have made it a vital component in the medical field. In this comprehensive review, we delve into the production methods, primary application forms, and medical applications of γ-PGA, drawing from numerous prior studies. Among the four production methods for PGA, microbial fermentation currently stands as the most widely employed. This method has seen various optimization strategies, which we summarize here. From drug delivery systems to tissue engineering and wound healing, γ-PGA's versatility and unique properties have facilitated its successful integration into diverse medical applications, underlining its potential to enhance healthcare outcomes. The objective of this review is to establish a foundational knowledge base for further research in this field.

Considerations on the Controlled Delivery of Bioactive Compounds through Hyaluronic Acid Membrane

(1) Background: The standard treatment for periodontal disease, a chronic inflammatory state caused by the interaction between biofilms generated by organized oral bacteria and the local host defense response, consists of calculus and biofilm removal through mechanical debridement, associated with antimicrobial therapy that could be delivered either systemically or locally. The present study aimed to determine the effectiveness of a hyaluronic acid membrane matrix as a carrier for the controlled release of the active compounds of a formulation proposed as a topical treatment for periodontal disease, and the influence of pH on the complex system’s stability. (2) Methods: The obtained hyaluronic acid (HA) hydrogel membrane with dispersed melatonin (MEL), metronidazole (MZ), and tetracycline (T) was completely characterized through FTIR, XRD, thermal analysis, UV-Vis and fluorescence spectroscopy, fluorescence microscopy, zeta potential and dielectric analysis. The MTT viability test was applied to check the cytotoxicity of the obtained membranes, while the microbiological assessment was performed against strains of Staphylococcus spp. and Streptococcus spp. The spectrophotometric investigations allowed to follow up the release profile from the HA matrix for MEL, MZ, and T present in the topical treatment considered. We studied the behavior of the active compounds against the pH of the generated environment, and the release profile of the bioactive formulation based on the specific comportment towards pH variation. The controlled delivery of the bioactive compounds using HA as a supportive matrix was modeled applying Korsmeyer–Peppas, Higuchi, first-order kinetic models, and a newly proposed pseudo-first-order kinetic model. (3) Results: It was observed that MZ and T were released at higher active concentrations than MEL when the pH was increased from 6.75, specific for patients with periodontitis, to a pH of 7.10, characterizing the healthy patients. Additionally, it was shown that for MZ, there is a burst delivery up to 2.40 × 10⁻⁵ mol/L followed by a release decrease, while for MEL and T a short release plateau was recorded up to a concentration of 1.80 × 10⁻⁵ mol/L for MEL and 0.90 × 10⁻⁵ mol/L for T, followed by a continuous release; (4) Conclusions: The results are encouraging for the usage of the HA membrane matrix as releasing vehicle for the active components of the proposed topical treatment at a physiological pH.

Preparation of pH-Responsive Poly(γ-glutamic acid) Hydrogels by Enzymatic Cross-Linking

pH-responsive hydrogels are important for oral drug release applications, and they are increasingly demanded to reduce the adverse side effects of drug release and improve drug absorption. In this study, a new type of pH-responsive hydrogel comprised of poly(γ-glutamic acid) modified with tyramine (PGA-Tyr) was developed through enzymatic cross-linking in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂). The gelation rate, stiffness, swelling behavior, and pore size of the resulting hydrogels were tuned by changing the concentrations of HRP and H₂O₂ or the degree of substitution (DS) of PGA-Tyr. The pH responsiveness of the hydrogels was evaluated by the swelling ratio in solutions with various pH values, and their pH responsiveness exhibited a good reversibility in pH 2.0 and 7.0 solutions. The degradation rate of the hydrogels in simulated intestinal fluid (SIF) was faster than that in simulated gastric fluid (SGF). Moreover, indomethacin (IM), a hydrophobic drug model, was encapsulated in the hydrogels by rapid in situ gelation, and the pH-dependent drug release of IM-loaded hydrogels was achieved in SGF and SIF. Importantly, when IM was entrapped in pluronic F-127 to form drug micelles, the burst release of the IM-micelle-loaded hydrogels with a high DS of PGA-Tyr was remarkably decreased in SGF, and sustained drug release was presented in SIF. Thus, pH-responsive PGA-based hydrogels have tremendous promise for biomedical applications, especially oral drug delivery.

Mechanoadaptive injectable hydrogel based on poly(γ-glutamic acid) and hyaluronic acid regulates fibroblast migration for wound healing

Injectable hydrogels have shown therapeutic effects on wound repair, but most of them exhibit poor mechanical strength. The impacts of stiff injectable hydrogels on cell behavior and wound healing remain unclear. Herein, an injectable hydrogel was developed based on thiolated poly(γ-glutamic acid) (γ-PGA-SH) and glycidyl methacrylate-conjuated oxidized hyaluronic acid (OHA-GMA). Thiol-methacrylate Michael chemistry-mediated post-stabilization and increase of polymer concentration were found to improve the mechanical strength of γ-PGA-SH/OHA-GMA hydrogel. Moreover, in vitro studies confirmed its biodegradability, biocompatibility, and self-healing property. Using the mechanically-tunable hydrogel, it further showed that fibroblasts migrated faster on the surface of stiffer hydrogel, but infiltrated slowly inside it compared with softer hydrogel. In animal experiments, the injectable hydrogel could promote wound healing by increasing collagen deposition and vascularization. In summary, γ-PGA-SH/OHA-GMA hydrogel is able to regulate migration and infiltration of fibroblasts by altering stiffness and offers effective in situ forming scaffolds towards skin tissue regeneration.

Bioactive potential of natural biomaterials: identification, retention and assessment of biological properties

Biomaterials have had an increasingly important role in recent decades, in biomedical device design and the development of tissue engineering solutions for cell delivery, drug delivery, device integration, tissue replacement, and more. There is an increasing trend in tissue engineering to use natural substrates, such as macromolecules native to plants and animals to improve the biocompatibility and biodegradability of delivered materials. At the same time, these materials have favourable mechanical properties and often considered to be biologically inert. More importantly, these macromolecules possess innate functions and properties due to their unique chemical composition and structure, which increase their bioactivity and therapeutic potential in a wide range of applications. While much focus has been on integrating these materials into these devices via a spectrum of cross-linking mechanisms, little attention is drawn to residual bioactivity that is often hampered during isolation, purification, and production processes. Herein, we discuss methods of initial material characterisation to determine innate bioactivity, means of material processing including cross-linking, decellularisation, and purification techniques and finally, a biological assessment of retained bioactivity of a final product. This review aims to address considerations for biomaterials design from natural polymers, through the optimisation and preservation of bioactive components that maximise the inherent bioactive potency of the substrate to promote tissue regeneration.

Glucose-responsive hydrogel enhances the preventive effect of insulin and liraglutide on diabetic nephropathy of rats

Diabetic nephropathy (DN) is one of the most serious complications of diabetes mellitus. The combination of insulin (Ins) with liraglutide (Lir) has a greater potential for preventing DN than monotherapy. However, the renal protective effect of the combined Ins/Lir therapy is largely compromised due to their short half-lives after subcutaneous injection. Herein, a glucose-responsive hydrogel was designed in situ forming the dynamic boronic esters bonds between phenylboronic acid-grafted γ-Polyglutamic acid (PBA-PGA) and konjac glucomannan (KGM). It was hypothesized that the KGM/PBA-PGA hydrogel as the delivery vehicle of Ins/Lir would enhance the combinational effect of the latter on preventing the DN progress. Scan electronic microscopy and rheological studies showed that KGM/PBA-PGA hydrogel displayed good glucose-responsive property. Besides, the glucose-sensitive release profile of either Ins or Lir from KGM/PBA-PGA hydrogel was uniformly displayed at hyperglycemic level. Furthermore, the preventive efficacy of KGM/PBA-PGA hydrogel incorporating insulin and liraglutide (Ins/Lir-H) on DN progress was evaluated on streptozotocin-induced rats with diabetic mellitus (DM). At 6 weeks after subcutaneous injection of Ins/Lir-H, not only the morphology of kidneys was obviously recovered as shown by ultrasonography, but also the renal hemodynamics was significantly improved. Meanwhile, the 24-h urinary protein and albumin/creatinine ratio were well modulated. Inflammation and fibrosis were also largely inhibited. Besides, the glomerular NPHS-2 was obviously elevated after treatment with Ins/Lir-H. The therapeutic mechanism of Ins/Lir-H was highly associated with the alleviation of oxidative stress and activation of autophagy. Conclusively, the better preventive effect of the combined Ins/Lir via KGM/PBA-PGA hydrogel on DN progress was demonstrated as compared with their mixed solution, suggesting KGM/PBA-PGA hydrogel might be a potential vehicle of Ins/Lir to combat the progression of DN.

Hyaluronic acid and chondroitin sulfate (meth)acrylate-based hydrogels for tissue engineering: Synthesis, characteristics and pre-clinical evaluation

Hydrogels based on photocrosslinkable Hyaluronic Acid Methacrylate (HAMA) and Chondroitin Sulfate Methacrylate (CSMA) are presently under investigation for tissue engineering applications. HAMA and CSMA gels offer tunable characteristics such as tailorable mechanical properties, swelling characteristics, and enzymatic degradability. This review gives an overview of the scientific literature published regarding the pre-clinical development of covalently crosslinked hydrogels that (partially) are based on HAMA and/or CSMA. Throughout the review, recommendations for the next steps in clinical translation of hydrogels based on HAMA or CSMA are made and potential pitfalls are defined. Specifically, a myriad of different synthetic routes to obtain polymerizable hyaluronic acid and chondroitin sulfate derivatives are described. The effects of important parameters such as degree of (meth)acrylation and molecular weight of the synthesized polymers on the formed hydrogels are discussed and useful analytical techniques for their characterization are summarized. Furthermore, the characteristics of the formed hydrogels including their enzymatic degradability are discussed. Finally, a summary of several recent applications of these hydrogels in applied fields such as cartilage and cardiac regeneration and advanced tissue modelling is presented.

Hyaluronic acid as a bioactive component for bone tissue regeneration: Fabrication, modification, properties, and biological functions

Hyaluronic acid (HA) is widely distributed in the human body, and it is heavily involved in many physiological functions such as tissue hydration, wound repair, and cell migration. In recent years, HA and its derivatives have been widely used as advanced bioactive polymers for bone regeneration. Many medical products containing HA have been developed because this natural polymer has been proven to be nontoxic, noninflammatory, biodegradable, and biocompatible. Moreover, HA-based composite scaffolds have shown good potential for promoting osteogenesis and mineralization. Recently, many HA-based biomaterials have been fabricated for bone regeneration by combining with electrospinning and 3D printing technology. In this review, the polymer structures, processing, properties, and applications in bone tissue engineering are summarized. The challenges and prospects of HA polymers are also discussed.

Boron-assisted dual-crosslinked poly (γ-glutamic acid) hydrogels with high toughness for cartilage regeneration

Although mesenchymal stem cells (MSCs) encapsulated with bionic scaffolds have been widely used in treating trauma induced cartilage defects, challenges still persist for these hydrogel scaffolds to create suitable shelters for the MSCs and guide their behaviors. In this work, novel biomimetic hydrogel scaffolds were prepared by thiol-ene Michael addition between glycidyl methacrylate (GMA)-modified poly (γ-glutamic acid) (γ-PGA-GMA) and DL-1,4-Dithiothreitol (DTT) for cartilage tissue engineering. Sodium tetraborate decahydrate was added into the system to connect with DTT through hydrogen-bond interaction and served as catalyst for thiol-ene Michael addition to strengthen the intensity of the hydrogel. The hydrogels could be compressed to nearly a 90% strain, with 0.95 MPa compression stresses which was better than that of most hydrogels in mechanical property. Additionally, this hydrogel has other properties: fast and controlled gel-forming speed, adjustable swelling ration, suitable interior structure and so on. Above all, hydrogels have excellent cyto/tissue-compatibility. Cells cultured in hydrogels in vitro exhibited good proliferation and adhesion abilities and the hydrogels scaffolds contained stem cells immensely accelerated the regeneration of auricular cartilage of rabbits in vivo versus control group. The overall results approved that this bionic hydrogel may be a promising biomaterial for cartilage regeneration in the future.

An Overview of Injectable Thermo-Responsive Hydrogels and Advances in their Biomedical Applications

BACKGROUND

Injectable hydrogels are a thermo-responsive system based on biomaterials. Injectable hydrogels have been broadly investigated mainly as vehicles or scaffolds of therapeutic agents that include drugs, proteins, cells, and bioactive molecules among others, utilized in the treatment of diseases such as cancers and the repair and regeneration of tissues.

RESULTS

There are several studies that have described the multiple features of hydrogels. However, the main aspect that breaks the paradigm in the application of hydrogels is the thermoresponsiveness that some of them have, which is an abrupt modification in their properties in response to small variations in temperature. For that reason, the thermo-responsive hydrogels with the unique property of sol-gel transition have received special attention over the past decades. These hydrogels show phase transition near physiological human body temperature. This feature is key for being applied in promising areas of human health-related research.

CONCLUSION

The purpose of this study is the overview of injectable hydrogels and their latest advances in medical applications including bioactive compound delivery, tissue engineering, and regenerative medicine.

Injectable in situ dual-crosslinking hyaluronic acid and sodium alginate based hydrogels for drug release

A series of injectable in situ dual-crosslinking hydrogels (HA/ALG) based on oxidized sodium alginate (oxi-ALG) and hyaluronic acid modified with thiol and hydrazide (HA-SH/CDH) were prepared via hydrazone bonds and disulfide bonds. The chemical structures, morphologies, rheological properties, gelling time, swelling ratio, degradation rate and drug release behavior of hydrogels were investigated. HA/ALG hydrogels exhibited tunable gelling time, rheological properties, swelling ratio and degradation rate with varying precursor concentrations. The gelling time of HA/ALG hydrogels ranged from 157 s to 955 s, the values of yield stress of HA2/ALG2, HA3/ALG3 and HA4/ALG4 hydrogels were 1724, 4349 and 5306 Pa, and the degradation percentage of HA2/ALG2, HA3/ALG3 and HA4/ALG4 hydrogels were about 64%, 51% and 42% after incubating 35 days, respectively. Bovine serum albumin (BSA) was used as a model drug to investigate the drug controlled release properties, and the in vitro cumulative release percentage of BSA from HA2/ALG2, HA3/ALG3 and HA4/ALG4 drug-loaded hydrogels were about 79%, 72% and 69% after 20 days. The series of injectable in situ dual-crosslinking HA/ALG hydrogels could be an attractive candidate for drug delivery system, tissue engineering and regenerative medicine.

Dual-degradable and injectable hyaluronic acid hydrogel mimicking extracellular matrix for 3D culture of breast cancer MCF-7 cells

In tumor biology, it is widely recognized that 3D rather than 2D cell culture can recapitulate key features of solid tumors, including cell-extracellular matrix (ECM) interactions. In this study, to mimick the ECM of breast cancer, hyaluronic acid (HA) hydrogels were synthesized from two polyvalent HA derivatives through a hydrazone and photo dual crosslinking process. HA hydrogels could be formed within 120 s. The hydrogels had similar topography and mechanical properties to breast tumor and displayed glutathione and hyaluronidase dual-responsive degradation behavior. Biological studies demonstrated that HA hydrogel could support the proliferation and clustering of breast cancer MCF-7 cells. The expression levels of VEGF, IL-8 and bFGF in hydrogel-cultured cells were significantly greater than those in 2D culture. Moreover, cells from hydrogel culture exhibited greater migration/invasion abilities and tumorigenicity than 2D-cultured cells. Therefore, the HA hydrogels are a promising ECM-mimicking matrix for in vitro construction of breast cancer.