Development of thermosensitive hydrogels of chitosan, sodium and magnesium glycerophosphate for bone regeneration applications

Chitosan-Based Biomaterials for Bone Tissue Engineering Applications: A Short Review

Natural bone tissue is composed of calcium-deficient carbonated hydroxyapatite as the inorganic phase and collagen type I as the main organic phase. The biomimetic approach of scaffold development for bone tissue engineering application is focused on mimicking complex bone characteristics. Calcium phosphates are used in numerous studies as bioactive phases to mimic natural bone mineral. In order to mimic the organic phase, synthetic (e.g., poly(ε-caprolactone), polylactic acid, poly(lactide-co-glycolide acid)) and natural (e.g., alginate, chitosan, collagen, gelatin, silk) biodegradable polymers are used. However, as materials obtained from natural sources are accepted better by the human organism, natural polymers have attracted increasing attention. Over the last three decades, chitosan was extensively studied as a natural polymer suitable for biomimetic scaffold development for bone tissue engineering applications. Different types of chitosan-based biomaterials (e.g., molded macroporous, fiber-based, hydrogel, microspheres and 3D-printed) with specific properties for different regenerative applications were developed due to chitosan's unique properties. This review summarizes the state-of-the-art of biomaterials for bone regeneration and relevant studies on chitosan-based materials and composites.

Chitosan/Sodium Alginate/Velvet Antler Blood Peptides Hydrogel Promoted Wound Healing by Regulating PI3K/AKT/mTOR and SIRT1/NF-κB Pathways

Skin wound healing is a principal clinical challenge, and it is necessary to develop effective alternative treatments. Excessive inflammatory response is linked to delayed healing. This study was the first to report a multi-functional chitosan/sodium alginate/velvet antler blood peptides (VBPs) hydrogel (CAVBPH) and explore its potential mechanism to promote wound healing. The results showed that CAVBPH possessed desirable characteristics including thermo-sensitivity, antioxidation, antibacterial activity, biosafety, VBPs release behavior, etc., and significantly accelerated skin wound healing in mice. Specifically, the CAVBPH treatment enhanced cell proliferation, angiogenesis, and extracellular matrix (ECM) secretion, and also relieved inflammation at the wound site compared to the PBS-treated group and blank hydrogel scaffold-treated group. Mechanistically, the efficacy of CAVBPH might be related to the activation of the PI3K/AKT/mTOR and SIRT1/NF-κB pathways. Overall, CAVBPH seems to be a promising therapy for skin repair, probably relying on the abundant short-chain peptides in VBPs.

Methods for crosslinking and stabilization of chitosan structures for potential medical applications

Chitosan is a well-known polymer widely used in tissue engineering and regenerative medicine. It is biocompatible, biodegradable, non-toxic, has antibacterial and osteoconductive properties. Chitosan is often used in the form of composites (with the participation of ceramic particles), membranes, hydrogels or nanoparticles. The problem with biomaterials is their low durability, rapid degradation, poor mechanical properties and cytotoxicity. Cross-linking or stabilization of such materials allows for solving these problems. It is important that the compounds used for this purpose exhibit limited or no toxicity. The presented article is a review and presents some methods of cross-linking/stabilization of chitosan structures. The analysis concerns low or non-cytotoxic cross-linking/stabilization methods. The discussed compounds used for the purpose of chitosan structure fixation are: cinnamaldehyde, genipin, L-aspartic acid, vanillin, sodium carbonate, sodium alginate, BGP, ethanol and TPP. There is discussed also a hydrothermal/dehydrothermal method which seems to be promising as it is more advantageous since no additional compounds are introduced into the structure.

Bioactive Chitosan-Based Organometallic Scaffolds for Tissue Engineering and Regeneration

Captivating achievements in developing advanced hybrid biostructures through integrating natural biopolymers with inorganic materials (e.g., metals and metalloids) have paved the way towards the application of bioactive organometallic scaffolds (OMSs) in tissue engineering and regenerative medicine (TERM). Of various biopolymers, chitosan (CS) has been used widely for the development of bioactive OMSs, in large part due to its unique characteristics (e.g., biocompatibility, biodegradability, surface chemistry, and functionalization potential). In integration with inorganic elements, CS has been used to engineer advanced biomimetic matrices to accommodate both embedded cells and drug molecules and serve as scaffolds in TERM. The use of the CS-based OMSs is envisioned to provide a new pragmatic potential in TERM and even in precision medicine. In this review, we aim to elaborate on recent achievements in a variety of CS/metal, CS/metalloid hybrid scaffolds, and discuss their applications in TERM. We also provide comprehensive insights into the formulation, surface modification, characterization, biocompatibility, and cytotoxicity of different types of CS-based OMSs.

Influence of Glycerophosphate Salt Solubility on the Gelation Mechanism of Colloidal Chitosan Systems

Recently, thermosensitive chitosan systems have attracted the interest of many researchers due to their growing application potential. Nevertheless, the mechanism of the sol-gel phase transition is still being discussed, and the glycerophosphate salt role is ambiguous. The aim of the work is to analyze the possibility of the exclusive use of a non-sodium glycerophosphate salt and to determine its impact on the gelation conditions determined by rheological and turbidimetric measurements as well as the stability of the systems by measuring changes in the Zeta potential value. It was found that ensuring the same proportions of glycerophosphate ions differing in cation to amino groups present in chitosan chains, leads to obtaining systems significantly different in viscoelastic properties and phase transition conditions. It was clearly shown that the systems with the calcium glycerophosphate, the insoluble form of which may constitute additional aggregation nuclei, undergo the gelation the fastest. The use of magnesium glycerophosphate salt delays the gelation due to the heat-induced dissolution of the salt. Thus, it was unequivocally demonstrated that the formulation of the gelation mechanism of thermosensitive chitosan systems based solely on the concentration of glycerophosphate without discussing its type is incorrect.

Catechol functionalized chitosan/active peptide microsphere hydrogel for skin wound healing

Chitosan-based thermosensitive hydrogels have been widely used in drug delivery and tissue engineering, but their poor bioactivity has limited their further applications. Integral active oyster peptide microspheres (OPM) with an average particle diameter of 3.9 μm were prepared with high encapsulation efficiency (72.8%) and loading capacity (11.9%), exhibiting desirable sustained release effects. Using catechol functionalized chitosan (CS-C) as the polymeric matrix, OPM as the filler, and β-sodium glycerophosphate (β-GP) as a thermal sensitizer, the thermosensitive hydrogel CS-C/OPM/β-GP was prepared. Besides, the application of the hydrogel on wound healing was studied, and its biosafety was evaluated. The results of cell migration in vitro showed that the cell migration rate of CS-C/OPM/β-GP reached 97.47 ± 5.41% within 48 h, indicating that the hydrogel accelerated the migration of L929 cells. As demonstrated in the mouse skin wound experiment, CS-C/OPM/β-GP hydrogel not only inhibited the aggregation of diversified inflammatory cells and accelerated the generation of collagen fibers and new blood vessels of the wound, but also enhanced the synthesis of total protein (TP) in granulation tissue, and up-regulated the expression of Ki-67 and VEGF in the injury, thereby achieving fast wound healing. Safety evaluation results showed that CS-C/OPM/β-GP hydrogel was not cytotoxic to L929 cells, and the hemolysis ratio was less than 5% within 1 mg/mL. In conclusion, CS-C/OPM/β-GP hydrogel is expected as a promising medical dressing for wound healing.

Application of a novel thermo-sensitive injectable hydrogel in therapy in situ for drug accurate controlled release

Local drug injection therapy for tumor site, as a neoadjuvant chemotherapy method, shows important significance in clinical application; however, it obtains unsatisfying therapeutic effect due to the serious toxic and side effect in normal tissues caused by drug diffusion or complexity of the preparation. In this article, the influence factors of the gelling time of traditional Chitosan (CTS) thermo-sensitive hydrogels were analyzed, and the gelling properties were improved significantly, and a thermo-sensitive hydrogel with precisely regulated gelling time was obtained through a green and simple preparation method, and the shortest gelling time (gelling time = 27 ± 2 s) of this hydrogel was 5% of that of the common CTS thermo-sensitive hydrogels. After loaded with different chemotherapy drugs with different pH values (gemctiabin hydrochloride, levofloxacin, and 5-foluorouracil), the hydrogels' gelling performance was not affected, while the gelling time could be shortened by 5-foluorouracil, effectively hindering the drug loss at the early stage of sustained release. in vitro and in vivo experiments proved that precise encapsulation toward tumors with different volumes was achieved by the hydrogels, with minimal damage to surrounding normal tissues and higher utilization of drugs in tumor sites, ultimately achieving better tumor therapeutic effect. In conclusion, the new thermo-sensitive hydrogels with precisely regulated gelling time showed great significance and potential for drug delivery and neoadjuvant chemotherapy.

Injectability of Thermosensitive, Low-Concentrated Chitosan Colloids as Flow Phenomenon through the Capillary under High Shear Rate Conditions

Low-concentrated colloidal chitosan systems undergoing a thermally induced sol-gel phase transition are willingly studied due to their potential use as minimally invasive injectable scaffolds. Nevertheless, instrumental injectability tests to determine their clinical utility are rarely performed. The aim of this work was to analyze the flow phenomenon of thermosensitive chitosan systems with the addition of disodium β-glycerophosphate through hypodermic needles. Injectability tests were performed using a texture analyzer and hypodermic needles in the sizes 14G-25G. The rheological properties were determined by the flow curve, three-interval thixotropy test (3ITT), and Cox-Merz rule. It was found that reducing the needle diameter and increasing its length and the crosshead speed increased the injection forces. It was claimed that under the considered flow conditions, there was no need to take into account the viscoelastic properties of the medium, and the model used to predict the injection force, based solely on the shear-thinning nature of the experimental material, showed very good agreement with the experimental data in the shear rate range of 200-55,000 s-1. It was observed that the increase in the shear rate value led to macroscopic structural changes of the chitosan sol caused by the disentangling and ordering of the polysaccharide chains along the shear field.

In-Situ Forming pH and Thermosensitive Injectable Hydrogels to Stimulate Angiogenesis: Potential Candidates for Fast Bone Regeneration Applications

Biomaterials that promote angiogenesis are required for repair and regeneration of bone. In-situ formed injectable hydrogels functionalised with bioactive agents, facilitating angiogenesis have high demand for bone regeneration. In this study, pH and thermosensitive hydrogels based on chitosan (CS) and hydroxyapatite (HA) composite materials loaded with heparin (Hep) were investigated for their pro-angiogenic potential. Hydrogel formulations with varying Hep concentrations were prepared by sol-gel technique for these homogeneous solutions were neutralised with sodium bicarbonate (NaHCO3) at 4 °C. Solutions (CS/HA/Hep) constituted hydrogels setting at 37 °C which was initiated from surface in 5-10 minutes. Hydrogels were characterised by performing injectability, gelation, rheology, morphology, chemical and biological analyses. Hydrogel solutions facilitated manual dropwise injection from 21 Gauge which is highly used for orthopaedic and dental administrations, and the maximum injection force measured through 19 G needle (17.191 ± 2.296N) was convenient for manual injections. Angiogenesis tests were performed by an ex-ovo chick chorioallantoic membrane (CAM) assay by applying injectable solutions on CAM, which produced in situ hydrogels. Hydrogels induced microvascularity in CAM assay this was confirmed by histology analyses. Hydrogels with lower concentration of Hep showed more efficiency in pro-angiogenic response. Thereof, novel injectable hydrogels inducing angiogenesis (CS/HA/Hep) are potential candidates for bone regeneration and drug delivery applications.

Injectable Chitosan Scaffolds with Calcium β-Glycerophosphate as the Only Neutralizing Agent

The presented work describes the method of preparation of thermosensitive chitosan hydrogels using calcium β-glycerophosphate salt as the only pH neutralizing agent and supporting the crosslinking process. The presence of calcium ions instead of sodium ions is particularly important in the case of scaffolds in bone tissue engineering. Rheological and physicochemical properties of low concentrated chitosan solutions with the addition of calcium β-glycerophosphate were investigated using rotational rheometry techniques, Zeta potential (by electrophoresis), XPS, and SEM analysis together with an EDS detector. It was found to be possible to prepare colloidal solutions of chitosan containing only calcium β-glycerophosphate (without sodium ions) undergoing a sol-gel phase transition at the physiological temperature of the human body. It has also been shown that it is possible to further enrich the obtained cellular scaffolds with calcium ions. Using the addition of calcium carbonate, hydrogels with a physiological ratio of calcium to phosphorus (1.6–1.8):1 were obtained.

Alkaline Phosphatase Immobilization on New Chitosan Membranes with Mg2+ for Biomedical Applications

In this paper, we present the fabrication and characterization of new chitosan-based membranes while using a new biotechnology for immobilizing alkaline phosphatase (ALP). This technology involved metal ions incorporation to develop new biopolymeric supports. The chemical structure and morphological characteristics of proposed membranes were evaluated by infrared spectroscopy (FT-IR) and the scanning electron microscopy technique (SEM). The inductively coupled plasma mass spectrometry (ICP-MS) evidenced the metal ion release in time. Moreover, the effect of Mg²⁺ on the enzymatic activity and the antibacterial investigations while using Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria, hemolysis, and biocompatibility behavior were studied. Immobilizing ALP into the chitosan membranes composition followed by the incorporation of Mg²⁺ led to polymeric supports with enhanced cellular viability when comparing to chitosan-based membranes without Mg²⁺. The results obtained evidenced promising performance in biomedical applications for the new biopolymeric supports that are based on chitosan, ALP, and metal ions.