Hydroxyapatite-Integrated, Heparin- and Glycerol-Functionalized Chitosan-Based Injectable Hydrogels with Improved Mechanical and Proangiogenic Performance

Injecting hope: chitosan hydrogels as bone regeneration innovators

Spontaneous bone regeneration encounters substantial restrictions in cases of bone defects, demanding external intervention to improve the repair and regeneration procedure. The field of bone tissue engineering (BTE), which embraces a range of disciplines, offers compelling replacements for conventional strategies like autografts, allografts, and xenografts. Among the diverse scaffolding materials utilized in BTE applications, hydrogels have demonstrated great promise as templates for the regeneration of bone owing to their resemblance to the innate extracellular matrix. In spite of the advancement of several biomaterials, chitosan (CS), a natural biopolymer, has garnered significant attention in recent years as a beneficial graft material for producing injectable hydrogels. Injectable hydrogels based on CS formulations provide numerous advantages, including their capacity to absorb and preserve a significant amount of water, their minimally invasive character, the existence of porous structures, and their capability to adapt accurately to irregular defects. Moreover, combining CS with other naturally derived or synthetic polymers and bioactive materials has displayed its effectiveness as a feasible substitute for traditional grafts. We aim to spotlight the composition, production, and physicochemical characteristics and practical utilization of CS-based injectable hydrogels, explicitly focusing on their potential implementations in bone regeneration. We consider this review a fundamental resource and a source of inspiration for future research attempts to pioneer the next era of tissue-engineering scaffold materials.

Chitosan/Virgin Coconut Oil-Based Emulsions Doped with Photosensitive Curcumin Loaded Capsules: A Functional Carrier to Topical Treatment

In recent years, there has been a growing interest in developing smart drug delivery systems based on natural resources combined with stimulus-sensitive elements. This trend aims to formulate innovative and sustainable delivery platforms tailored for topical applications. This work proposed the use of layer-by-layer (LbL) methodology to fabricate biocompatible photo-responsive multilayer systems. These systems are composed of a polyoxometalate inorganic salt (POM) ([NaP5W30O110]14-) and a natural origin polymer, chitosan (CHT). Curcumin (CUR), a natural bioactive compound, was incorporated to enhance the functionality of these systems during the formation of hollow capsules. The capsules produced, with sizes between 2-5µm (SEM), were further dispersed into CHT/VCO (virgin coconut oil) emulsion solutions that were casted into molds and dried at 37 °C for 48 h. The system presented a higher water uptake in PBS than in acidic conditions, still significantly lower than that earlier reported to other CHT/VCO-based systems. The drug release profile is not significantly influenced by the medium pH reaching a maximum of 37% ± 1% after 48 h. The antioxidant performance of the designed structures was further studied, suggesting a synergistic beneficial effect resulting from CUR, POM, and VCO individual bioactivities. The increased amount of those excipients released to the media over time promoted an increase in the antioxidant activity of the system, reaching a maximum of 38.1% ± 0.1% after 48 h. This work represents a promising step towards developing advanced, sustainable drug delivery systems for topical applications.

Bilayer wound dressing composed of asymmetric polycaprolactone membrane and chitosan-carrageenan hydrogel incorporating storax balsam

A comprehensive approach is needed to develop multifunctional wound dressing that is simple yet efficient. In this work, Liquidambar orientalis Mill. storax loaded hydroxyethyl chitosan (HECS)-carrageenan (kC) based hydrogel (HECS-kC) and polydopamine coated asymmetric polycaprolactone membrane (PCL-DOP) were used to develop a multifunctional and modular bilayer wound dressing. Asymmetric PCL-DOP membrane was prepared by non-solvent induced phase separation (NIPS) followed by polydopamine coating and demonstrated an excellent barrier against bacteria while allowing permeability for 5.45 ppm dissolved‑oxygen and 2130 g/m2 water vapor transmission in 24 h in addition to 805 kPa tensile strength. Storax loaded HECS-kC hydrogel, on the other hand, demonstrated a pH-responsive degradation and swelling to provide necessary conditions to facilitate wound healing. The hydrogels showed stretchability above 140 %, mild adhesive strength on sheep skin and PCL-DOP membrane, while the storax incorporation enhanced antibacterial and antioxidant activity. Furthermore, rat full-thickness skin defect model showed that the developed bilayer wound dressing could significantly facilitate wound healing compared to Tegaderm™ and control groups. This study shows that the bilayered wound dressing has the potential to be used as a simple and effective wound care system.

Thermosensitive injectable dual drug-loaded chitosan-based hybrid hydrogel for treatment of orthopedic implant infections

A myriad of therapeutic agents and drug delivery systems are available to the surgeons for treating orthopedic implant-associated infections (OIAI), but only very few have demonstrated their effectiveness in preventing bacteria colonization and biofilm formation due to challenges in the local and sustainable therapeutic release. To address this issue, in this work, a thermosensitive injectable hydrogel based on chitosan (CH)-integrated hydroxyapatite nanoparticles (HAP NPs) containing vancomycin (Van) and quercetin (QC)-loaded in F127 micelles (CH-HAP-FQ-Van hydrogel) was fabricated with potential application in the treatment of OIAI. This dual drug delivery system demonstrated a pH-sensitive drug release pattern. In addition, 100 % growth inhibition of Staphylococcus aureus for a duration of 14 days was observed. Apart from the strong antioxidant activities owing to the co-administration of QC even after 432 h, this composite hydrogel revealed 95.88 ± 2.8 % S. aureus biofilm eradication. By consideration of degradation stability (53.52 ± 4.24 %) during 60 days along with smart gelation within 10 min at 37 °C and easy injectability, CH-HAP-FQ-Van hydrogel could be used as a promising ideal local drug delivery system for implant-related infections.

The effect of conductive aligned fibers in an injectable hydrogel on nerve tissue regeneration

Injectable hydrogels are a promising treatment option for nervous system injuries due to the difficulty to replace lost cells and nervous factors but research on injectable conductive hydrogels is limited and these scaffolds have poor electromechanical properties. This study developed a chitosan/beta-glycerophosphate/salt hydrogel and added conductive aligned nanofibers (polycaprolactone/gelatin/single-wall carbon nanotube (SWCNT)) for the first time and inspired by natural nerve tissue to improve their biochemical and biophysical properties. The results showed that the degradation rate of hydrogels is proportional to the regrowth of axons and these hydrogels' mechanical (hydrogels without nanofibers or SWCNTs and hydrogels containing these additions have the same Young's modulus as the brain and spinal cord or peripheral nerves, respectively) and electrical properties, and the interconnective structure of the scaffolds have the ability to support cells.

Genipin versus Ferric Chloride cross-linked unmodified Gum Arabic/Chitosan/nano-Hydroxyapatite nanocomposite hydrogels as potential scaffolds for bone regeneration

Ferric chloride (FeCl3) and Genipin were utilized as cross-linkers to create two types of nanocomposite hydrogels through physical and covalent cross-linking methods, respectively. The hydrogels were composed of unmodified Gum Arabic (GA), Chitosan (Ch), and natural nano-Hydroxyapatite (nHA) using an acrylic acid solvent. Both the natural nHA and the FeCl3 vs. genipin cross-linked GA/Ch/nHA nano-composite hydrogels were prepared and characterized using various in vitro and in vivo analysis techniques. The use of FeCl3 and genipin cross-linkers resulted in the formation of novel hydrogels with compressive strengths of (15.43-22.20 MPa), which are comparable to those of natural cortical bone. In vivo evaluation was conducted by creating calvarial defects (6 mm) in Sprague-Dawley male rats. The results showed the formation of new, full-thickness bone at the implantation sites in all groups, as evidenced by digital planar tomography and histological staining with Hematoxylin and Eosin stain (H & E). Additionally, the use of genipin as a cross-linker positively affected the hydrogel's hydrophilicity and porosity. These findings justify further investigation into the potential of these nanocomposite hydrogels for bone regeneration applications.

A novel bioartificial pancreas fabricated via islets microencapsulation in anti-adhesive core-shell microgels and macroencapsulation in a hydrogel scaffold prevascularized in vivo

Islets transplantation is a promising treatment for type 1 diabetes mellitus. However, severe host immune rejection and poor oxygen/nutrients supply due to the lack of surrounding capillary network often lead to transplantation failure. Herein, a novel bioartificial pancreas is constructed via islets microencapsulation in core-shell microgels and macroencapsulation in a hydrogel scaffold prevascularized in vivo. Specifically, a hydrogel scaffold containing methacrylated gelatin (GelMA), methacrylated heparin (HepMA) and vascular endothelial growth factor (VEGF) is fabricated, which can delivery VEGF in a sustained style and thus induce subcutaneous angiogenesis. In addition, islets-laden core-shell microgels using methacrylated hyaluronic acid (HAMA) as microgel core and poly(ethylene glycol) diacrylate (PEGDA)/carboxybetaine methacrylate (CBMA) as shell layer are prepared, which provide a favorable microenvironment for islets and simultaneously the inhibition of host immune rejection via anti-adhesion of proteins and immunocytes. As a result of the synergistic effect between anti-adhesive core-shell microgels and prevascularized hydrogel scaffold, the bioartificial pancreas can reverse the blood glucose levels of diabetic mice from hyperglycemia to normoglycemia for at least 90 days. We believe this bioartificial pancreas and relevant fabrication method provide a new strategy to treat type 1 diabetes, and also has broad potential applications in other cell therapies.

Injectable hydrogels for cartilage and bone tissue regeneration: A review

Annually, millions of patients suffer from irreversible injury owing to the loss or failure of an organ or tissue caused by accident, aging, or disease. The combination of injectable hydrogels and the science of stem cells have emerged to address this persistent issue in society by generating minimally invasive treatments to augment tissue function. Hydrogels are composed of a cross-linked network of polymers that exhibit a high-water retention capacity, thereby mimicking the wet environment of native cells. Due to their inherent mechanical softness, hydrogels can be used as needle-injectable stem cell carrier materials to mend tissue defects. Hydrogels are made of different natural or synthetic polymers, displaying a broad portfolio of eligible properties, which include biocompatibility, low cytotoxicity, shear-thinning properties as well as tunable biological and physicochemical properties. Presently, novel ongoing developments and native-like hydrogels are increasingly being used broadly to improve the quality of life of those with disabling tissue-related diseases. The present review outlines various future and in-vitro applications of injectable hydrogel-based biomaterials, focusing on the newest ongoing developments of in-situ forming injectable hydrogels for bone and cartilage tissue engineering purposes.

Chitosan/Virgin-Coconut-Oil-Based System Enriched with Cubosomes: A 3D Drug-Delivery Approach

Emulsion-based systems that combine natural polymers with vegetable oils have been identified as a promising research avenue for developing structures with potential for biomedical applications. Herein, chitosan (CHT), a natural polymer, and virgin coconut oil (VCO), a resource obtained from coconut kernels, were combined to create an emulsion system. Phytantriol-based cubosomes encapsulating sodium diclofenac, an anti-inflammatory drug, were further dispersed into CHT/VCO- based emulsion. Then, the emulsions were frozen and freeze-dried to produce scaffolds. The scaffolds had a porous structure ranging from 20.4 to 73.4 µm, a high swelling ability (up to 900%) in PBS, and adequate stiffness, notably in the presence of cubosomes. Moreover, a well-sustained release of the entrapped diclofenac in the cubosomes into the CHT/VCO-based system, with an accumulated release of 45 ± 2%, was confirmed in PBS, compared to free diclofenac dispersed (80 ± 4%) into CHT/VCO-based structures. Overall, the present approach opens up new avenues for designing porous biomaterials for drug delivery through a sustainable pathway.

The Diamond Concept Enigma: Recent Trends of Its Implementation in Cross-linked Chitosan-Based Scaffolds for Bone Tissue Engineering

An increasing number of publications over the past ten years have focused on the development of chitosan-based cross-linked scaffolds to regenerate bone tissue. The design of biomaterials for bone tissue engineering applications relies heavily on the ideals set forth by a polytherapy approach called the "Diamond Concept". This methodology takes into consideration the mechanical environment, scaffold properties, osteogenic and angiogenic potential of cells, and benefits of osteoinductive mediator encapsulation. The following review presents a comprehensive summarization of recent trends in chitosan-based cross-linked scaffold development within the scope of the Diamond Concept, particularly for nonload-bearing bone repair. A standardized methodology for material characterization, along with assessment of in vitro and in vivo potential for bone regeneration, is presented based on approaches in the literature, and future directions of the field are discussed.

Synthesis, Characterization, Properties, and Biomedical Application of Chitosan-Based Hydrogels

The prospective applications of chitosan-based hydrogels (CBHs), a category of biocompatible and biodegradable materials, in biomedical disciplines such as tissue engineering, wound healing, drug delivery, and biosensing have garnered great interest. The synthesis and characterization processes used to create CBHs play a significant role in determining their characteristics and effectiveness. The qualities of CBHs might be greatly influenced by tailoring the manufacturing method to get certain traits, including porosity, swelling, mechanical strength, and bioactivity. Additionally, characterization methods aid in gaining access to the microstructures and properties of CBHs. Herein, this review provides a comprehensive assessment of the state-of-the-art with a focus on the affiliation between particular properties and domains in biomedicine. Moreover, this review highlights the beneficial properties and wide application of stimuli-responsive CBHs. The main obstacles and prospects for the future of CBH development for biomedical applications are also covered in this review.

Study of Hydroxypropyl β-Cyclodextrin and Puerarin Inclusion Complexes Encapsulated in Sodium Alginate-Grafted 2-Acrylamido-2-Methyl-1-Propane Sulfonic Acid Hydrogels for Oral Controlled Drug Delivery

Puerarin has been reported to have anti-inflammatory, antioxidant, immunity enhancement, neuroprotective, cardioprotective, antitumor, and antimicrobial effects. However, due to its poor pharmacokinetic profile (low oral bioavailability, rapid systemic clearance, and short half-life) and physicochemical properties (e.g., low aqueous solubility and poor stability) its therapeutic efficacy is limited. The hydrophobic nature of puerarin makes it difficult to load into hydrogels. Hence, hydroxypropyl-β-cyclodextrin (HP-βCD)-puerarin inclusion complexes (PIC) were first prepared to enhance solubility and stability; then, they were incorporated into sodium alginate-grafted 2-acrylamido-2-methyl-1-propane sulfonic acid (SA-g-AMPS) hydrogels for controlled drug release in order to increase bioavailability. The puerarin inclusion complexes and hydrogels were evaluated via FTIR, TGA, SEM, XRD, and DSC. Swelling ratio and drug release were both highest at pH 1.2 (36.38% swelling ratio and 86.17% drug release) versus pH 7.4 (27.50% swelling ratio and 73.25% drug release) after 48 h. The hydrogels exhibited high porosity (85%) and biodegradability (10% in 1 week in phosphate buffer saline). In addition, the in vitro antioxidative activity (DPPH (71%), ABTS (75%), and antibacterial activity (Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa) indicated the puerarin inclusion complex-loaded hydrogels had antioxidative and antibacterial capabilities. This study provides a basis for the successful encapsulation of hydrophobic drugs inside hydrogels for controlled drug release and other purposes.

Phenol-Grafted Alginate Sulfate Hydrogel as an Injectable FGF-2 Carrier

In the field of tissue engineering, fibroblast growth factor-2 (FGF-2) effectively regenerates damaged tissue and restores its biological function. However, FGF-2 readily diffuses and degrades under physiological conditions. Therefore, methods for the sustained and localized delivery of FGF-2 are needed. Drug delivery systems using hydrogels as carriers have attracted significant interest. Injectable hydrogels with an affinity for FGF-2 are candidates for FGF-2 delivery systems. In this study, we fabricated a hydrogel from phenol-grafted alginate sulfate (AlgS-Ph) and investigated its application to the delivery of FGF-2. The hydrogel was prepared under mild conditions via horseradish peroxidase (HRP)-mediated cross-linking. Surface plasmon resonance (SPR) measurements show that the AlgS-Ph hydrogel has an affinity for FGF-2 in accordance with its degree of sulfation. Conditions for the preparation of the AlgS-Ph hydrogel, including HRP and H₂O₂ concentrations, are optimized so that the hydrogel can be used as an injectable drug carrier. The hydrogel shows no cytotoxicity when using 10T1/2 cells as a model cell line. The angiogenesis assay shows that FGF-2 released from the AlgS-Ph hydrogel promotes the formation of blood vessels. These results indicate that the AlgS-Ph hydrogel is a suitable candidate for the FGF-2 carrier.

Behavior of Calcium Phosphate-Chitosan-Collagen Composite Coating on AISI 304 for Orthopedic Applications

Calcium phosphate/chitosan/collagen composite coating on AISI 304 stainless steel was investigated. Coatings were realized by galvanic coupling that occurs without an external power supply because it begins with the coupling between two metals with different standard electrochemical potentials. The process consists of the co-deposition of the three components with the calcium phosphate crystals incorporated into the polymeric composite of chitosan and collagen. Physical-chemical characterizations of the samples were executed to evaluate morphology and chemical composition. Morphological analyses have shown that the surface of the stainless steel is covered by the deposit, which has a very rough surface. XRD, Raman, and FTIR characterizations highlighted the presence of both calcium phosphate compounds and polymers. The coatings undergo a profound variation after aging in simulated body fluid, both in terms of composition and structure. The tests, carried out in simulated body fluid to scrutinize the corrosion resistance, have shown the protective behavior of the coating. In particular, the corrosion potential moved toward higher values with respect to uncoated steel, while the corrosion current density decreased. This good behavior was further confirmed by the very low quantification of the metal ions (practically absent) released in simulated body fluid during aging. Cytotoxicity tests using a pre-osteoblasts MC3T3-E1 cell line were also performed that attest the biocompatibility of the coating.

Heparin-Loaded Alginate Hydrogels: Characterization and Molecular Mechanisms of Their Angiogenic and Anti-Microbial Potential

Background: Chronic wounds continue to be a global concern that demands substantial resources from the healthcare system. The process of cutaneous wound healing is complex, involving inflammation, blood clotting, angiogenesis, migration and remodeling. In the present study, commercially available alginate wound dressings were loaded with heparin. The purpose of the study was to enhance the angiogenic potential of alginate wound dressings and analyze the antibacterial activity, biocompatibility and other relevant properties. We also aimed to conduct some molecular and gene expression studies to elaborate on the mechanisms through which heparin induces angiogenesis. Methods: The physical properties of the hydrogels were evaluated by Fourier transform infrared spectroscopy (FTIR). Swelling ability was measured by soaking hydrogels in the Phosphate buffer at 37 °C, and cell studies were conducted to evaluate the cytotoxicity and biocompatibility of hydrogels in NIH3T3 (fibroblasts). Real-time PCR was conducted to check the molecular mechanisms of heparin/alginate-induced angiogenesis. The physical properties of the hydrogels were evaluated by Fourier transform infrared spectroscopy (FTIR). Results: FTIR confirmed the formation of heparin-loaded alginate wound dressing and the compatibility of both heparin and alginate. Among all, 10 µg/mL concentration of heparin showed the best antibacterial activity against E. coli. The swelling was considerably increased up to 1500% within 1 h. Alamar Blue assay revealed no cytotoxic effect on NIH3T3. Heparin showed good anti-microbial properties and inhibited the growth of E. coli in zones with a diameter of 18 mm. The expression analysis suggested that heparin probably exerts its pro-angiogenetic effect through VEGF and cPGE. Conclusions: We report that heparin-loaded alginate dressings are not cytotoxic and offer increased angiogenic and anti-bacterial potential. The angiogenesis is apparently taken through the VEGF pathway.

Bioactive Composite for Orbital Floor Repair and Regeneration

In the maxillofacial area, specifically the orbital floor, injuries can cause bone deformities in the head and face that are difficult to repair or regenerate. Treatment methodologies include use of polymers, metal, ceramics on their own and in combinations mainly for repair purposes, but little attention has been paid to identify suitable materials for orbital floor regeneration. Polyurethane (PU) and hydroxyapatite (HA) micro- or nano- sized with different percentages (25%, 40% & 60%) were used to fabricate bioactive tissue engineering (TE) scaffolds using solvent casting and particulate leaching methods. Mechanical and physical characterisation of TE scaffolds was investigated by tensile tests and SEM respectively. Chemical and structural properties of PU and PU/HA scaffolds were evaluated by infrared (IR) spectroscopy and Surface properties of the bioactive scaffold were analysed using attenuated total reflectance (ATR) sampling accessory coupled with IR. Cell viability, collagen formed, VEGF protein amount and vascularisation of bioactive TE scaffold were studied. IR characterisation confirmed the integration of HA in composite scaffolds, while ATR confirmed the significant amount of HA present at the top surface of the scaffold, which was a primary objective. The SEM images confirmed the pores' interconnectivity. Increasing the content of HA up to 40% led to an improvement in mechanical properties, and the incorporation of nano-HA was more promising than that of micro-HA. Cell viability assays (using MG63) confirmed biocompatibility and CAM assays confirmed vascularization, demonstrating that HA enhances vascularization. These properties make the resulting biomaterials very useful for orbital floor repair and regeneration.

Suitability of Chitosan Scaffolds with Carbon Nanotubes for Bone Defects Treated with Photobiomodulation

Biomaterials have been investigated as an alternative for the treatment of bone defects, such as chitosan/carbon nanotubes scaffolds, which allow cell proliferation. However, bone regeneration can be accelerated by electrotherapeutic resources that act on bone metabolism, such as low-level laser therapy (LLLT). Thus, this study evaluated the regeneration of bone lesions grafted with chitosan/carbon nanotubes scaffolds and associated with LLLT. For this, a defect (3 mm) was created in the femur of thirty rats, which were divided into 6 groups: Control (G1/Control), LLLT (G2/Laser), Chitosan/Carbon Nanotubes (G3/C+CNTs), Chitosan/Carbon Nanotubes with LLLT (G4/C+CNTs+L), Mineralized Chitosan/Carbon Nanotubes (G5/C+CNTsM) and Mineralized Chitosan/Carbon Nanotubes with LLLT (G6/C+CNTsM+L). After 5 weeks, the biocompatibility of the chitosan/carbon nanotubes scaffolds was observed, with the absence of inflammatory infiltrates and fibrotic tissue. Bone neoformation was denser, thicker and voluminous in G6/C+CNTsM+L. Histomorphometric analyses showed that the relative percentage and standard deviations (mean ± SD) of new bone formation in groups G1 to G6 were 59.93 ± 3.04a (G1/Control), 70.83 ± 1.21b (G2/Laser), 70.09 ± 4.31b (G3/C+CNTs), 81.6 ± 5.74c (G4/C+CNTs+L), 81.4 ± 4.57c (G5/C+CNTsM) and 91.3 ± 4.81d (G6/C+CNTsM+L), respectively, with G6 showing a significant difference in relation to the other groups (a ≠ b ≠ c ≠ d; p < 0.05). Immunohistochemistry also revealed good expression of osteocalcin (OC), osteopontin (OP) and vascular endothelial growth factor (VEGF). It was concluded that chitosan-based carbon nanotube materials combined with LLLT effectively stimulated the bone healing process.