Gellan gum based physical hydrogels incorporating highly valuable endogen molecules and associating BMP-2 as bone formation platforms

Hydrogel-Based Growth Factor Delivery Platforms: Strategies and Recent Advances

Growth factors play a crucial role in regulating a broad variety of biological processes and are regarded as powerful therapeutic agents in tissue engineering and regenerative medicine in the past decades. However, their application is limited by their short half-lives and potential side effects in physiological environments. Hydrogels are identified as having the promising potential to prolong the half-lives of growth factors and mitigate their adverse effects by restricting them within the matrix to reduce their rapid proteolysis, burst release, and unwanted diffusion. This review discusses recent progress in the development of growth factor-containing hydrogels for various biomedical applications, including wound healing, brain tissue repair, cartilage and bone regeneration, and spinal cord injury repair. In addition, the review introduces strategies for optimizing growth factor release including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cellular system-based delivery. Finally, the review presents current limitations and future research directions for growth factor-delivering hydrogels.

Sequential deacetylation/self-gelling chitin hydrogels and scaffolds functionalized with fucoidan for enhanced BMP-2 loading and sustained release

Bone morphogenetic protein 2 (BMP-2) is a potent osteoinductive factor that promotes bone formation. A major obstacle to the clinical application of BMP-2 is its inherent instability and complications caused by its rapid release from implants. Chitin based materials have excellent biocompatibility and mechanical properties, making them ideal for bone tissue engineering applications. In this study, a simple and easy method was developed to spontaneously form deacetylated β-chitin (DAC-β-chitin) gels at room temperature through a sequential deacetylation/self-gelation process. The structural transformation of β-chitin to DAC-β-chitin leads to the formation of self-gelling DAC-β-chitin, from which hydrogels and scaffolds were prepared. Gelatin (GLT) accelerated the self-gelation of DAC-β-chitin and increased the pore size and porosity of the DAC-β-chitin scaffold. The DAC-β-chitin scaffolds were then functionalized with a BMP-2-binding sulfate polysaccharide, fucoidan (FD). Compared with β-chitin scaffolds, FD-functionalized DAC-β-chitin scaffolds showed higher BMP-2 loading capacity and more sustainable release of BMP-2, and thus had better osteogenic activity for bone regeneration.

Preparation of gum tragacanth/poly (vinyl alcohol)/halloysite hydrogel using electron beam irradiation with potential for bone tissue engineering

Nanocomposite hydrogels based on tyramine conjugated gum tragacanth, poly (vinyl alcohol) (PVA), and halloysite nanotubes (HNTs) were prepared by electron beam irradiation and characterized. The FTIR, ¹H NMR, and TGA results confirmed the chemical incorporation of HNTs into gum tragacanth. Gel content and swelling of hydrogels decreased with HNTs loading up to 20 % wt. The mechanical strength of hydrogels increased by increasing HNTs content up to 10 % with 371 kPa fracture stress at 0.95 fracture strain, compared to 312 kPa stress at 0.79 strain for gum tragacanth/PVA hydrogel. Hydrogel's biocompatibility and osteogenic activity were tested by seeding rabbit bone marrow mesenchymal stem cells. The cell viability was >85 % after 7 days of culture. In vitro secretion of ALP and calcium deposition on hydrogels in alizarin red assay after 21 days of culture indicated hydrogel potential for bone tissue engineering.

Spermidine Crosslinked Gellan Gum-Based “Hydrogel Nanofibers” as Potential Tool for the Treatment of Nervous Tissue Injuries: A Formulation Study

Purpose

Aim of the work was to develop a potential neural scaffold, endowed with neuroprotective and neuroregenerative potential, to be applied at the site of nervous tissue injuries: nanofibers, consisting of gellan gum (GG), spermidine (SP) and gelatin (GL), were prepared via electrospinning. SP was selected for its neuroprotective activity and cationic nature that makes it an ideal GG cross-linking agent. GL was added to improve the scaffold bioactivity.

Methods

Mixtures, containing 1.5% w/w GG and increasing SP concentrations (0–0.125% w/w), were prepared to investigate GG/SP interaction and, thus, to find the best mixture to be electrospun. Mixture rheological and mechanical properties were assessed. The addition of 0.1% w/w GL was also investigated. The most promising GG/SP/GL mixtures were added with poly(ethylene oxide) (PEO) and poloxamer (P407) and, then, electrospun. The resulting fibers were characterized in terms of size and mechanical properties and fiber morphology was observed after soaking in water for 24 hours. Nanofiber biocompatibility was assessed on Schwann cells.

Results

More and more structured GG/SP mixtures were obtained by increasing SP concentration, proving its cross-linking potential. After blending with PEO and P407, the mixture consisting of 1.5% w/w GG, 0.05% w/w SP and 0.1% w/w GL was electrospun. The resulting nanofibers appeared homogenous and characterized by a plastic behavior, suggesting a good mechanical resistance when applied at the injury site. Nanofibers were insoluble in aqueous media and able to form a thin gel layer after hydration. GG/SP/GL nanofibers showed a higher compatibility with Schwann cells than GG/SP ones.

Conclusion

SP and GL allowed the production of homogenous GG-based nanofibers, which preserved their structure after contact with aqueous media and showed a good compatibility with a neural cell line. After local application at the injury site, nanofibers should support and guide axonal outgrowth, releasing SP in a controlled manner.

Gum Tragacanth (GT): A Versatile Biocompatible Material beyond Borders

The use of naturally occurring materials in biomedicine has been increasingly attracting the researchers’ interest and, in this regard, gum tragacanth (GT) is recently showing great promise as a therapeutic substance in tissue engineering and regenerative medicine. As a polysaccharide, GT can be easily extracted from the stems and branches of various species of Astragalus. This anionic polymer is known to be a biodegradable, non-allergenic, non-toxic, and non-carcinogenic material. The stability against microbial, heat and acid degradation has made GT an attractive material not only in industrial settings (e.g., food packaging) but also in biomedical approaches (e.g., drug delivery). Over time, GT has been shown to be a useful reagent in the formation and stabilization of metal nanoparticles in the context of green chemistry. With the advent of tissue engineering, GT has also been utilized for the fabrication of three-dimensional (3D) scaffolds applied for both hard and soft tissue healing strategies. However, more research is needed for defining GT applicability in the future of biomedical engineering. On this object, the present review aims to provide a state-of-the-art overview of GT in biomedicine and tries to open new horizons in the field based on its inherent characteristics.

Advanced gellan gum-based glycol chitosan hydrogel for cartilage tissue engineering biomaterial

Gellan gum (GG), a nature-derived polysaccharide, is one of the materials widely used in cartilage tissue engineering (TE). Glycol chitosan (GC), a derivative of chitosan, is a water-soluble natural polymer that has excellent biocompatibility and biodegradability as well as cell adhesion. Herein, GG was physically blended with GC to enhance the mechanical properties and microenvironment of the GG to apply in cartilage TE. The study was conducted with a hydrogel model which is similar to the extracellular matrix (ECM) of cartilage tissue. The physicochemical studies were carried out with morphological study, swelling ratio, weight loss, and sol fraction. The mechanical characterization was conducted with compression test and rheological study to confirm availability in cartilage TE material. Furthermore, in vitro studies such as morphology investigation, viability assay, GAG content, qRT-PCR, and histological study were performed to verify biocompatibility and chondrogenesis of the material. The mechanical and biological properties improved with a proper amount of GC. Overall results verify the potential of the material and can be further used for the cartilage TE.

Printing bone in a gel: using nanocomposite bioink to print functionalised bone scaffolds

Free-form printing offers a novel biofabrication approach to generate complex shapes by depositing hydrogel materials within a temporary supportive environment. However, printed hydrogels typically lack the requisite mechanical properties and functionality of the desired tissue, limiting application and, more importantly, safety and efficacy of the implant. The study authors have developed an innovative nanoclay-based bioink to print high shape fidelity functional constructs for potential skeletal application. Laponite® (LAP) nanoclay was combined with gellan gum (GG) to generate a printable hydrogel that was highly stable in vitro, displayed limited swelling ability compared with the silicate-free control and remained stable over time. An agarose fluid gel was found to provide the requisite support for the deposition of the material ink and preservation of the printed structure before crosslinking. Printed C2C12 myoblasts remained viable and displayed extensive proliferation over 21 days in culture. Cell-laden scaffolds demonstrated functionality within 1 day of culture in vitro and that was preserved over 3 weeks. Analysis of absorption and release mechanisms from LAP-GG using model proteins (lysozyme and bovine serum albumin) demonstrated the retention capability of the clay-based materials for compound localisation and absence of burst release. Vascular endothelial growth factor ​was loaded within the agarose fluid gel and absorbed by the material ink via absorption during deposition. The 3D-printed constructs were implanted on the chorioallantoic membrane of a 10-day-old developing chick. Extensive and preferential vasculature infiltration was observed in LAP-GG-loaded vascular endothelial growth factor constructs compared with controls (p<0.01 and p<0.0001) after only 7 days of incubation. The current studies demonstrate, for the first time, the application of innovative LAP-GG 3D constructs in the generation of growth factor-loaded 3D constructs for potential application in skeletal tissue repair.

Microfiber-Reinforced Composite Hydrogels Loaded with Rat Adipose-Derived Stem Cells and BMP-2 for the Treatment of Medication-Related Osteonecrosis of the Jaw in a Rat Model

Severe adverse reactions of bisphosphonates and anti-resorptive or anti-angiogenic medications, termed medication-related osteonecrosis of the jaw (MRONJ), have been reported. MRONJ are difficult to completely cure and could cause great pain to patients. Recent studies have shown that mesenchymal stem cell (MSC) therapies are effective for treating MRONJ, but the method of intravenous injection is unstable and increases the risk of producing tumors. In the present study, low-acyl gellan gum (LAGG) hydrogels were modified with hemicellulose polysaccharide microfibers (PMs) to improve the performance of supporting three-dimensional (3D) cell growth. LAGG-PM composite hydrogels were found to be nontoxic to rat adipose-derived stem cells (rADSCs) in vitro. The hydrogels also promoted the secretion of angiogenic factors, induced osteoclastogenesis by conditioned medium, and supported osteogenic marker expression after the addition of human bone morphogenetic protein-2 (BMP-2). Due to its injectability, the LAGG-PM composite hydrogel incorporated with rADSCs and BMP-2 could be applied into the MRONJ lesion site, which promoted mucosal recovery, bone tissue reconstruction, and osteoclastogenesis. This study confirms the potential applications of LAGG-PM composite hydrogels as 3D cell culture platforms and delivery vehicles for the treatment of MRONJ in a rat model.

Recent progress in the industrial and biomedical applications of tragacanth gum: A review

Natural polymers have distinct advantages over synthetic polymers because of their abundance, biocompatibility, and biodegradability. Tragacanth gum, an anionic polysaccharide, is a natural polymer which is derived from renewable sources. As a biomaterial, tragacanth gum has been used in industrial settings such as food packaging and water treatment, as well as in the biomedical field as drug carriers and for wound healing purposes. The present review provides an overview on the state-of-the-art in the field of tragacanth gum applications. The structure, properties, cytotoxicity, and degradability as well as the recent advances in industrial and biomedical applications of tragacanth gum are reviewed to offer a backdrop for future research.

Photocrosslinked Dextran-Based Hydrogels as Carrier System for the Cells and Cytokines Induce Bone Regeneration in Critical Size Defects in Mice

Modified biomaterials have for years been the focus of research into establishing new bone substitutes. In our preceding in vitro study employing different cell cultures, we developed chemically and mechanically characterized hydrogels based on photocrosslinkable dextran derivatives and demonstrated their cytocompatibility and their beneficial effects on the proliferation of osteoblasts and endothelial cells. In the present in vivo study, we investigate photocrosslinked dextran-based hydrogels in critical size defects in mice to evaluate their potential as carrier systems for cells or for a specific angiogenesis enhancing cytokine to induce bone formation. We could demonstrate that, with optimized laboratory practice, the endotoxin content of hydrogels could be reduced below the Food and Drug Administration (FDA)-limit. Dextran-based hydrogels were either loaded with a monoculture of endothelial cells or a co-culture of human osteoblasts with endothelial cells, or with stromal-derived-growth factor (SDF-1). Scaffolds were implanted into a calvarial defect of critical size in mice and their impact on bone formation was assessed by µCt-analyses, histology and immunohistology. Our study demonstrates that promotion of angiogenesis either by SDF-1 or a monoculture of endothelial cells induces bone regeneration at a physiological level. These in vivo results indicate the potential of dextran-based hydrogel composites in bone regeneration to deliver cells and cytokines to the defect site.