Rheological study of chitosan/polyol-phosphate systems: influence of the polyol part on the thermo-induced gelation mechanism

Modulating the Thermoresponsive Characteristics of PLGA-PEG-PLGA Hydrogels via Manipulation of PLGA Monomer Sequences

Hydrogels are promising materials for biomedical applications, particularly in drug delivery and tissue engineering. This study highlights thermoresponsive hydrogels, specifically poly(lactic-co-glycolic acid) (PLGA)-poly(ethylene glycol) (PEG)-PLGA triblock copolymers, and introduces a feed rate-controlled polymerization (FRCP) method. By utilizing an organic catalyst and regulating the monomer feed rate, the sequence distribution of PLGA within the triblock copolymer is controlled. Various analyses, including 13C NMR and rheological measurements, were conducted to investigate the impact of sequence distribution. Results show that altering sequence distribution significantly influences the sol-gel transition, hydrophobicity-hydrophilicity balance, and drug release profile. Increased sequence uniformity lowers the glass transition temperature, raises the sol-gel transition temperature due to enhanced hydrophilicity, and promotes a more uniform drug (curcumin) distribution within the PLGA domain, resulting in a slower release rate. This study emphasizes the importance of PLGA sequence distribution in biomedical applications and the potential of FRCP to tailor thermoresponsive hydrogels for biomedical advancements.

Chitosan-Based Thermogelling System for Nose-to-Brain Donepezil Delivery: Optimising Formulation Properties and Nasal Deposition Profile

Donepezil nasal delivery strategies are being continuously investigated for advancing therapy in Alzheimer's disease. The aim of this study was to develop a chitosan-based, donepezil-loaded thermogelling formulation tailored to meet all the requirements for efficient nose-to-brain delivery. A statistical design of the experiments was implemented for the optimisation of the formulation and/or administration parameters, with regard to formulation viscosity, gelling and spray properties, as well as its targeted nasal deposition within the 3D-printed nasal cavity model. The optimised formulation was further characterised in terms of stability, in vitro release, in vitro biocompatibility and permeability (using Calu-3 cells), ex vivo mucoadhesion (using porcine nasal mucosa), and in vivo irritability (using slug mucosal irritation assay). The applied research design resulted in the development of a sprayable donepezil delivery platform characterised by instant gelation at 34 °C and olfactory deposition reaching a remarkably high 71.8% of the applied dose. The optimised formulation showed prolonged drug release (t_1/2 about 90 min), mucoadhesive behaviour, and reversible permeation enhancement, with a 20-fold increase in adhesion and a 1.5-fold increase in the apparent permeability coefficient in relation to the corresponding donepezil solution. The slug mucosal irritation assay demonstrated an acceptable irritability profile, indicating its potential for safe nasal delivery. It can be concluded that the developed thermogelling formulation showed great promise as an efficient donepezil brain-targeted delivery system. Furthermore, the formulation is worth investigating in vivo for final feasibility confirmation.

Optimization of thermoresponsive chitosan/β-glycerophosphate hydrogels for injectable neural tissue engineering application

Regeneration of neural tissue and recovery of lost functions following an accident or disease to the central nervous system remains a major challenge worldwide, with limited treatment options available. The main reason for the failure of conventional therapeutic techniques to regenerate neural tissue is the presence of blood-brain barrier separating nervous system from systemic circulation and the limited capacity of self-regeneration of the nervous system. Injectable hydrogels have shown great promise for neural tissue engineering given their suitability for minimally invasive in situ delivery and tunable mechanical and biological properties. Chitosan (CS)/β-glycerophosphate (β-GP) hydrogels have been extensively investigated and shown regenerative potential in a wide variety of tissues such as bone and cartilage tissue engineering. However, the potential of CS/β-GP hydrogels has never been tested for injectable neural tissue engineering applications. In the present study, CS/β-GP hydrogels, consisting of 0.5-2% CS and 2-3% β-GP, were prepared and characterized to investigate their suitability for injectable neural tissue engineering applications. The resulting CS/β-GP-hydrogels showed a varying range of properties depending on the CS/β-GP blend ratio. In particular, the 0.5%:3% and 0.75%:3% CS/β-GP hydrogels underwent rapid gelation (3 min and 5 min, respectively) at physiological temperature (37 °C) and pH (7.4). They also had suitable porosity, osmolality, swelling behavior and biodegradation for tissue engineering. The biocompatibility of hydrogels was determined in vitro using PC12 cells, an immortalized cell line with neuronal cell-like properties, revealing that these hydrogels supported cell growth and proliferation. In conclusion, the thermoresponsive 0.5%:3% and 0.75%:3% CS/β-GP hydrogels had the greatest potential for neural tissue engineering.

Chitosan-Based Biomaterials: Insights into Chemistry, Properties, Devices, and Their Biomedical Applications

Chitosan is a marine-origin polysaccharide obtained from the deacetylation of chitin, the main component of crustaceans’ exoskeleton, and the second most abundant in nature. Although this biopolymer has received limited attention for several decades right after its discovery, since the new millennium chitosan has emerged owing to its physicochemical, structural and biological properties, multifunctionalities and applications in several sectors. This review aims at providing an overview of chitosan properties, chemical functionalization, and the innovative biomaterials obtained thereof. Firstly, the chemical functionalization of chitosan backbone in the amino and hydroxyl groups will be addressed. Then, the review will focus on the bottom-up strategies to process a wide array of chitosan-based biomaterials. In particular, the preparation of chitosan-based hydrogels, organic–inorganic hybrids, layer-by-layer assemblies, (bio)inks and their use in the biomedical field will be covered aiming to elucidate and inspire the community to keep on exploring the unique features and properties imparted by chitosan to develop advanced biomedical devices. Given the wide body of literature that has appeared in past years, this review is far from being exhaustive. Selected works in the last 10 years will be considered.

A Thermosensitive, Chitosan-Based Hydrogel as Delivery System for Antibacterial Liposomes to Surgical Site Infections

Prophylaxis and the treatment of surgical site infections (SSIs) with antibiotics frequently fail due to the antibiotic resistance of bacteria and the ability of bacteria to reside in biofilms (i.e., bacterial clusters in a protective matrix). Therefore, alternative antibacterial treatments are required to combat biofilm infections. The combination of diethyldithiocarbamate (DDC^-) and copper ions (Cu²⁺) exhibited antibiofilm activity against the staphylococci species associated with SSIs; however, the formation of a water-insoluble Cu(DDC)₂ complex limits its application to SSIs. Here, we describe the development and antibiofilm activity of an injectable gel containing a liposomal formulation of Cu(DDC)₂ and Cu²⁺ (lipogel). Lyophilized liposomes were incorporated into a mixture of chitosan (CS) and beta-glycerophosphate (βGP), and the thermosensitive gelling properties of CS-βGP and the lipogel were determined. The liposomes remained stable after lyophilization over six months at 4-6 °C and -20 °C. The sol-gel transition of the gel and lipogel occurred between 33 and 39 °C, independently of sterilization or storage at -20 °C. CS-βGP is biocompatible and the liposomes were released over time. The lipogel prevented biofilm formation over 2 days and killed 98.7% of the methicillin-resistant Staphylococcus aureus and 99.9% of the Staphylococcus epidermidis biofilms. Therefore, the lipogel is a promising new prophylaxis and treatment strategy for local application to SSIs.

Aggressive strategies for regenerating intervertebral discs: stimulus-responsive composite hydrogels from single to multiscale delivery systems

As our research on the physiopathology of intervertebral disc degeneration (IVD degeneration, IVDD) has advanced and tissue engineering has rapidly evolved, cell-, biomolecule- and nucleic acid-based hydrogel grafting strategies have been widely investigated for their ability to overcome the harsh microenvironment of IVDD. However, such single delivery systems suffer from excessive external dimensions, difficult performance control, the need for surgical implantation, and difficulty in eliminating degradation products. Stimulus-responsive composite hydrogels have good biocompatibility and controllable mechanical properties and can undergo solution-gel phase transition under certain conditions. Their combination with ready-to-use particles to form a multiscale delivery system may be a breakthrough for regenerative IVD strategies. In this paper, we focus on summarizing the progress of research on the stimulus response mechanisms of regenerative IVD-related biomaterials and their design as macro-, micro- and nanoparticles. Finally, we discuss multi-scale delivery systems as bioinks for bio-3D printing technology for customizing personalized artificial IVDs, which promises to take IVD regenerative strategies to new heights.

Rational formulation design of injectable thermosensitive chitosan-based hydrogels for cell encapsulation and delivery

This work reports a rational design of injectable thermosensitive chitosan systems for cell encapsulation and delivery. Using mixtures of two phosphate salts, beta-glycerophosphate and ammonium hydrogen phosphate, we demonstrate that the pH and the osmolarity can be adjusted separately by varying the molar ratios between the salts and the d-glucosamine monomers. We found the existence of a critical temperature above which gelation time decays following a power-law. This gelation kinetics can be finely tuned through the pH and salt-glucosamine ratios. Formulations having physiological pH and osmolarity were produced for chitosan concentrations ranging from 0.4 to 0.9 wt%. They remain liquid for more than 2 h at 20 °C and form a macroporous gel within 2 min at 37 °C. In vitro encapsulation of pre-osteoblastic cells and gingival fibroblasts showed homogeneous cell distribution and good cell viability up to 24 h. Such an approach provides a valuable platform to design thermosensitive cell-laden systems.

Controlled Liposome Delivery from Chitosan-Based Thermosensitive Hydrogel for Regenerative Medicine

This work describes the development of an injectable nanocomposite system based on a chitosan thermosensitive hydrogel combined with liposomes for regenerative medicine applications. Liposomes with good physicochemical properties are prepared and embedded within the chitosan network. The resulting nanocomposite hydrogel is able to provide a controlled release of the content from liposomes, which are able to interact with cells and be internalized. The cellular uptake is enhanced by the presence of a chitosan coating, and cells incubated with liposomes embedded within thermosensitive hydrogels displayed a higher cell uptake compared to cells incubated with liposomes alone. Furthermore, the gelation temperature of the system resulted to be equal to 32.6 °C; thus, the system can be easily injected in the target site to form a hydrogel at physiological temperature. Given the peculiar performance of the selected systems, the resulting thermosensitive hydrogels are a versatile platform and display potential applications as controlled delivery systems of liposomes for tissue regeneration.

Influence of Injection Application on the Sol-Gel Phase Transition Conditions of Polysaccharide-Based Hydrogels

Polysaccharide matrices formed via thermoinduced sol-gel phase transition are promising systems used as drug carriers and minimally invasiveness scaffolds in tissue engineering. The strong shear field generated during injection may lead to changes in the conformation of polymer molecules and, consequently, affect the gelation conditions that have not been studied so far. Chitosan (CS) and hydroxypropyl cellulose (HPC) sols were injected through injection needles (14 G-25 G) or sheared directly in the rheometer measuring system. Then the sol-gel phase transition conditions were determined at 37 °C using rheometric, turbidimetric, and rheo-optical techniques. It was found that the use of low, respecting injection, shear rates accelerate the gelation, its increase extends the gelation time; applying the highest shear rates may significantly slow down (HPC) or accelerate gelation (CS) depending on thixotropic properties. From a practical point of view, the conducted research indicates that the use of thin needles without preliminary tests may lead to an extension of the gelation time and consequently the spilling of the polymeric carrier before gelation. Finally, an interpretation of the influence of an intensive shear field on the conformation of the molecules on a molecular scale was proposed.

A thermo-sensitive chitosan/pectin hydrogel for long-term tumor spheroid culture

Hydrogels represent a key element in the development of in vitro tumor models, by mimicking the typical 3D tumor architecture in a physicochemical manner and allowing the study of tumor mechanisms. Here we developed a thermo-sensitive, natural polymer-based hydrogel, where chitosan and pectin were mixed and, after a weak base-induced chitosan gelation, a stable semi-Interpenetrating Polymer Network formed. This resulted thermo-responsive at 37 °C, injectable at room temperature, stable up to 6 weeks in vitro, permeable to small/medium-sized molecules (3 to 70 kDa) and suitable for cell-encapsulation. Tunable mechanical and permeability properties were obtained by varying the polymer content. Optimized formulations successfully supported the formation and growth of human colorectal cancer spheroids up to 44 days of culture. The spheroid dimension and density were influenced by the semi-IPN stiffness and permeability. These encouraging results would allow the implementation of faithful tumor models for the study and development of personalized oncological treatments.

Evaluation of Inflammatory Response Due to Use of Controlled Release Drug Delivery System of Chitosan Hydrogel Loaded with Buprenorphine and Ketorolac in Rat with Experimental Proximal Tibial Epiphysis Defect

Aims:A controlled release drug delivery system loaded with buprenorphine and ketorolac was synthesized and used in the experimental model of bone defect and while evaluating the inflammatory response, the repair process in the defects was investigated.Materials and methods:To determine the effectiveness of the synthesized the mentioned systems, 5 groups were defined; the control group, the chitosan hydrogel receiving group (chitosan group), the ketorolac-loaded chitosan hydrogel group (ketorolac group), the buprenorphine-loaded chitosan hydrogel receiving group (buprenorphine group), and the chitosan hydrogel-loading group loaded with a combination of ketorolac and buprenorphine (ketorolac-buprenorphine group).Results:The results showed that the population of leukocytes (tWBC) and neutrophils on different days of the study in the control group compared to other groups had a significant increase (P < 0.05) while on day 7 of the study in the ketorolac group these parameters decreased significantly compared to other groups (P < 0.05). While examining the histological changes in the experimental defect created in the proximal tibia of rats at different times, some inflammatory indices such as total and differential leukocyte population, plasma concentrations of TNF-α and IL-6 were compared in different groups (P < 0.05). The various evaluated data showed that among the different groups, in the control and ketorolac-buprenorphine groups, there was the lowest and highest control of inflammatory response and bone repair, respectively.Conclusion:In the ketorolac group due to the impact of ketorolac on leukocyte populations the best bone healing can be expected among the different treatment groups.

3D printable self-healing hyaluronic acid/chitosan polycomplex hydrogels with drug release capability

Multifunctional printable biomaterials are at the base of advanced biomedical applications. Chitosan (CHI) and hyaluronic acid (HA) allow the development of polycomplex hydrogels with tailorable properties, including self-healing and controlled drug release. This work correlates and optimizes the mucoadhesive, swelling, biodegradation, mechanical and rheological properties of HA/CHI polycomplex hydrogels with synthesis parameters such as polysaccharide content and complexation time, according to the interaction forces established between both polyelectrolytes. Related to these dynamic forces, the self-healing ability of the hydrogels was investigated together with the potential of the HA/CHI polycomplex hydrogels for 3D printing. Finally, their capability to modulate and promote controlled release of a variety of drugs (anionic and anti-inflammatory sodium diclofenac and the neutral antibiotic rifampicin) was demonstrated. Thus, the reported tunable properties, self-repair ability, printability and drug release properties, demonstrate the suitability of HA/CHI hydrogels for advanced biomedical applications.

Injectable Thermosensitive Chitosan Solution with β-Glycerophosphate as an Optimal Submucosal Fluid Cushion for Endoscopic Submucosal Dissection

Endoscopic submucosal dissection (ESD) is a surgical procedure to remove early neoplastic lesions in the gastrointestinal tract with the critical issue of perforation. A submucosal fluid cushion, such as normal saline, is used as a cushioning agent to prevent perforation; however, its cushioning maintenance is insufficient for surgery. In this study, we introduce an injectable thermosensitive chitosan solution (CS) with β-glycerophosphate (β-GP) as a submucosal injection agent for ESD. The CS/β-GP system with optimal β-GP concentration showed drastic viscosity change near body temperature while other commercial products did not. Additionally, the injectability of the solution was similar to or greater than other commercial products. The solution with low β-GP concentration showed low cytotoxicity similar to other products. An in vivo preclinical study illustrated maintenance of the high cushioning of the thermosensitive solutions. These results indicate that a CS/β-GP system with optimal β-GP concentration might be used as a submucosal injection agent in ESD, and further studies are needed to validate the effectiveness of the solutions in vivo.

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.

Recent advances in thermo-sensitive hydrogels for drug delivery

Thermo-sensitive hydrogels based on different polymers have been broadly used in the pharmaceutical fields. In this review, the state-of-the-art thermo-sensitive hydrogels for drug delivery are elaborated

Thermoinduced aggegation of chitosan systems in perikinetic and orthokinetic regimes

Thermoresponsive colloidal chitosan systems forming the polymer structure in situ are an example of promising solutions in tissue engineering as an injectable scaffolds or drug carriers. Their application method, and thus shearing, may affect the aggregation process in accordance with the colloidal engineering approach. The aim of the study is to compare the kinetics of chitosan aggregation in the perikinetic regime (limited by Brownian motions) with the orthokinetic process carried out under the influence of an external shear field. The research was carried out using static multiple light scattering (S-MLS) and rheometric measurement techniques coupled with small-angle light scattering (Rheo-SALS). It has been found that the introduction of an external shear field (orthokinetic regime) accelerates the aggregation of chitosan systems. Simultaneously, the rotational measurements can even lead to spontaneous gelation, most likely caused by changes in the conformation of chitosan molecules, their deformation and ordering along the shear field.

Injectable Thermosensitive Chitosan/Pullulan-Based Hydrogels with Improved Mechanical Properties and Swelling Capacity

Thermosensitive chitosan/β-glycerophosphate (CS/BGP) systems have been developed as injectable hydrogels. However, the hydrogels exhibited poor mechanical properties due to their physically crosslinked networks. In this work, CS/BGP hydrogels were reinforced by covalent crosslinking using genipin (GE) and concomitantly semi-interpenetrating networks using pullulan (PL). Based on response surface methodology, the optimized formulation was composed of CS (1.05%, w/v), PL (1%, w/v), BGP (6%, w/v), and GE (70.79 mcg/mL). The optimized hydrogels exhibited Young's modulus of 92.65 ± 4.13 kPa and a percentage of equilibrium swelling ratio of 3259.09% ± 58.90%. Scanning electron micrographs revealed a highly porous structure with nanofibrous networks in the CS/PL/BGP/GE hydrogels. The chemical interactions between the compositions were investigated by Fourier-transform infrared spectroscopy. Rheological measurements illustrated that the optimized hydrogels displayed sol-gel transition within one minute at 37 °C, a lower critical solution temperature of about 31 °C, and viscoelastic behavior with high storage modulus. Furthermore, the optimized hydrogels demonstrated higher resistance to in vitro enzymatic degradation, compared to the hydrogels without GE. Our findings could suggest that the thermosensitive CS/PL/BGP/GE hydrogels with enhanced mechanical properties and swelling capacity demonstrate the potential for use as scaffolds and carriers for cartilage tissue engineering and drug delivery applications.

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.

On-line monitoring of the sol-gel transition temperature of thermosensitive chitosan/β-glycerophosphate hydrogels by low field NMR

A temperature controlled low field nuclear magnetic resonance (LF-NMR) T₂ relaxometry technique based on the mobility changes of water trapped in hydrogels, was successfully used for on-line determination of the sol-gel transition temperature for chitosan/β-glycerophosphate (CS/GP) hydrogels in real time. The LF-NMR results indicated that the gelation temperature decreased gradually with increasing GP concentration, and the results were supported by both thermogravimetric differential scanning calorimetry (DSC) and rheological findings; however, LF-NMR allows non-destructive monitoring of samples during continuous heating. Moreover, as the mobility of water molecules varies greatly during the sol-gel phase transition, the LF-NMR measurement was more sensitive and accurate (RSD ≤ 0.1 %, n = 5) compared with DSC (RSD: 1.2 %-3.7 %, n = 5) and rheology (RSD: 1.1 %-2.3 %, n = 5).

Advancing the stimuli response of polymer-based drug delivery systems for ocular disease treatment

Recent exploitations of stimuli-responsive polymers as ophthalmic drug delivery systems for the treatment of eye diseases are summarized and discussed.

Thermo-sensitive hydrogels for delivering biotherapeutic molecules: A review

To date, a variety of delivery systems based on organic or inorganic materials have been investigated. Among them, hydrogels have become one of the most promising field in drug delivery system due to their unique properties. Temperature-sensitive hydrogels, which gelation at physiological temperature, gift the delivery system with excellent spatial and temporal control, and have a widely application in drug delivery, tissue engineering, imaging, and wound dressing. This review provides a brief overview on the concept and classification of temperature-sensitive hydrogels, and covers the application of temperature-sensitive gel systems in delivery of biotherapeutic molecules.

Injectable and thermosensitive nanofibrous hydrogel for bone tissue engineering

The use of injectable hydrogels is currently restricted by the challenge of achieving fast gelation, good mechanical strength, and cytocompatibility. Polymeric self-assembly is a potent tool for generating functional materials that combine multiple characteristics and can react to external factors. In this study, we have developed fiber-reinforced composite hydrogels that exhibits significantly enhanced mechanical strength, reduced gelling time, and excellent cytocompatibility. The practicability of developing a chitosan-based thermogelling solution using hydroxyapatite and polyelectrolyte complex (PEC) self-assembled fibers were evaluated. The effect of βGP concentration on gelation time was studied by varying the concentration of βGP added to the chitosan solution. Various combinations were tested to create a suitable hydrogel environment for cell encapsulation, growth, and proliferation at physiological pH and temperature. Determination of Young modulus revealed that PEC fibers reinforced hydrogel was three times stiffer than chitosan-βGP gels. The gelation time was reduced to 3 min, and the hydrogels had porous structures and gels at physiological pH, temperature, and showed >80% viability for MTT assay to MG63 cells. Moreover, confocal imaging of PEC fiber reinforced hydrogels showed noticeable viability and proliferation. The molecular interactions between gelling agents, polyelectrolytes, and hydroxyapatite were studied using FTIR. We investigated interfacial bonding between PEC fibers with βGP, NaHCO_3, and HAp. The combination of hydroxyapatite and polymer self-assembly technique improved the efficiency of injectable hydrogels that are helpful in minimally invasive applications.

Advances in Biomaterials and Technologies for Vascular Embolization

Minimally invasive transcatheter embolization is a common nonsurgical procedure in interventional radiology used for the deliberate occlusion of blood vessels for the treatment of diseased or injured vasculature. A wide variety of embolic agents including metallic coils, calibrated microspheres, and liquids are available for clinical practice. Additionally, advances in biomaterials, such as shape-memory foams, biodegradable polymers, and in situ gelling solutions have led to the development of novel preclinical embolic agents. The aim here is to provide a comprehensive overview of current and emerging technologies in endovascular embolization with respect to devices, materials, mechanisms, and design guidelines. Limitations and challenges in embolic materials are also discussed to promote advancement in the field.

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.

Chitosan-based hydrogel to support the paracrine activity of mesenchymal stem cells in spinal cord injury treatment

Advanced therapies which combine cells with biomaterial-based carriers are recognized as an emerging and powerful method to treat challenging diseases, such as spinal cord injury (SCI). By enhancing transplanted cell survival and grafting, biomimetic hydrogels can be properly engineered to encapsulate cells and locate them at the injured site in a minimally invasive way. In this work, chitosan (CS) based hydrogels were developed to host mesenchymal stem cells (MSCs), since their paracrine action can therapeutically enhance the SC regeneration, limiting the formation of a glial scar and reducing cell death at the injured site. An injectable and highly permeable CS-based hydrogel was fabricated having a rapid gelation upon temperature increase from 0 to 37 °C. CS was selected as former material both for its high biocompatibility that guarantees the proper environment for MSCs survival and for its ability to provide anti-inflammatory and anti-oxidant cues. MSCs were mixed with the hydrogel solution prior to gelation. MSC viability was not affected by the CS hydrogel and encapsulated MSCs were able to release MSC-vesicles as well as to maintain their anti-oxidant features. Finally, preliminary in vivo tests on SCI mice revealed good handling of the CS solution loading MSCs during implantation and high encapsulated MSCs survival after 7 days.

Chitosan/β-glycerophosphate in situ gelling mucoadhesive systems for intravesical delivery of mitomycin-C

The development of mucoadhesive in situ gelling formulations for intravesical application may improve the therapeutic outcomes of bladder cancer patients. In this work, chitosan/β-glycerophosphate (CHIGP) thermosensitive formulations have been prepared using three different chitosan grades (62, 124 and 370 kDa). Their ability to form in situ gelling systems triggered by changes in temperature upon administration to urinary bladder were evaluated using vial inversion and rheological methods. Texture analysis was used to study their mucoadhesive properties as well as syringeability through the urethral catheter. The retention of CHIGP formulations, with fluorescein sodium as the model drug, was studied on porcine urinary bladder mucosa ex vivo using the flow-through technique and fluorescent microscopy. CHIGP formulations containing mitomycin-C were prepared and drug release was studied using in vitro dialysis method. It was established that the molecular weight of chitosan influenced the thermogelling, mucoadhesive and drug release behaviour of the in situ gelling delivery systems. Formulations prepared from chitosan with greatest molecular weight (370 kDa) were found to be the most promising for intravesical application due to their superior gelling properties and in vitro retention in the bladder.

The antitumor effect of cisplatin-loaded thermosensitive chitosan hydrogel combined with radiotherapy on nasopharyngeal carcinoma

Cisplatin-based chemo-radiotherapy (RT) is the most effective treatment in patients with loco-regionally advanced nasopharyngeal carcinoma (NPC). However, traditional chemotherapy drugs have low bioavailability and targeting ability, which reduce their antitumor effects. Therefore, we developed a chitosan/ cis-dichlorodiamineplatinum (CS/DDP) hydrogel-based drug delivery system for the in situ treatment of NPC in combination with RT, and investigated their synergistic antitumor efficacy and underlying mechanism of action. CS/DDP hydrogel remarkably prolonged the survival time (81 days) when combined with RT compared to the control group (P < 0.01). The main mechanism was likely the increase in cancer cell apoptosis (76.23 ± 1.13%, p < 0.01). Furthermore, the CS/DDP hydrogel in combination with RT also increased X-ray-induced DSBs and γ-H2AX foci, induced G2/M phase arrest, inhibited cell proliferation by blocking Ki-67, and decreased CD31+ micro-vessel density (MVD). These results underscore the therapeutic potential of the combination of CS/DDP hydrogel and RT for localized NPC.

Chitosan-Based In Situ Gels for Ocular Delivery of Therapeutics: A State-of-the-Art Review

Ocular in situ gels are a promising alternative to overcome drawbacks of conventional eye drops because they associate the advantages of solutions such as accuracy and reproducibility of dosing, or ease of administration with prolonged contact time of ointments. Chitosan is a natural polymer suitable for use in ophthalmic formulations due to its biocompatibility, biodegradability, mucoadhesive character, antibacterial and antifungal properties, permeation enhancement and corneal wound healing effects. The combination of chitosan, pH-sensitive polymer, with other stimuli-responsive polymers leads to increased mechanical strength of formulations and an improved therapeutic effect due to prolonged ocular contact time. This review describes in situ gelling systems resulting from the association of chitosan with various stimuli-responsive polymers with emphasis on the mechanism of gel formation and application in ophthalmology. It also comprises the main techniques for evaluation of chitosan in situ gels, along with requirements of safety and ocular tolerability.

Comparison of Rheological, Drug Release, and Mucoadhesive Characteristics upon Storage between Hydrogels with Unmodified or Beta-Glycerophosphate-Crosslinked Chitosan

The physicochemical characteristics of beta-glycerophosphate-crosslinked chitosan hydrogels were investigated upon long-term storage at ambient, accelerated, and refrigerated conditions and compared to unmodified chitosan formulations. Additionally, the impact of chitosan modification on the ex vivo mucoadhesive performance in contact with porcine vaginal mucosa and on the drug release profile from hydrogels was evaluated. Viscosity and mechanical properties of formulations with unmodified chitosan decreased significantly upon storage regardless of tested conditions as a result of hydrolytic depolymerization. Introduction of ion crosslinker exerted stabilizing effect on physicochemical performance of chitosan hydrogels but only upon storage at refrigerated conditions. Beta-glycerophosphate-modified chitosan formulations preserved organoleptic, rheological behavior, and hydrogel structure up to 3-month storage at 4 ± 2°C. Viscosity variations upon storage influenced markedly mucoadhesive properties and drug release rate from hydrogels.

Concepts for Developing Physical Gels of Chitosan and of Chitosan Derivatives

Chitosan macro- and micro/nano-gels have gained increasing attention in recent years, especially in the biomedical field, given the well-documented low toxicity, degradability, and non-immunogenicity of this unique biopolymer. In this review we aim at recapitulating the recent gelling concepts for developing chitosan-based physical gels. Specifically, we describe how nowadays it is relatively simple to prepare networks endowed with different sizes and shapes simply by exploiting physical interactions, namely (i) hydrophobic effects and hydrogen bonds-mostly governed by chitosan chemical composition-and (ii) electrostatic interactions, mainly ensured by physical/chemical chitosan features, such as the degree of acetylation and molecular weight, and external parameters, such as pH and ionic strength. Particular emphasis is dedicated to potential applications of this set of materials, especially in tissue engineering and drug delivery sectors. Lastly, we report on chitosan derivatives and their ability to form gels. Additionally, we discuss the recent findings on a lactose-modified chitosan named Chitlac, which has proved to form attractive gels both at the macro- and at the nano-scale.

Influence of fish collagen on viscoelastic properties and sol-gel phase transition of chitosan solutions

The thermosensitive hydrogels are widely used in tissue engineering due to their non-invasive application. Special interest of researchers, due to the specific characteristics of both materials, is aimed at composites of natural origin obtained from chitosan hydrogels combined with collagen. The mechanical properties of the thermosensitive chitosan-fish collagen hydrogels and the sol-gel phase transition parameters were determined by the rotational rheometry measurement techniques. Based on comparison of the obtained storage modulus G' curves, it was found that the addition of collagen negatively affects the mechanical properties of composite scaffolds. The addition of this protein substance decreases their elasticity. Only the smallest concentration (0.25g collagen/1 g chitosan) of collagen improves the mechanical properties of composite hydrogels, from 56 kPa to 61 kPa. Conducted non-isothermal studies allowed to conclude that the addition of collagen causes an increasing temperature of sol-gel phase transition. However, the observed changes are not a monotone function of the biopolymer concentration.

Injectable and body temperature sensitive hydrogels based on chitosan and hyaluronic acid for pH sensitive drug release

Hydrogels based on chitosan/hyaluronic acid/β-sodium glycerophosphate demonstrate injectability, body temperature sensitivity, pH sensitive drug release and adhesion to cancer cell. The drug (doxorubicin) loaded hydrogel precursor solutions are injectable and turn to hydrogels when the temperature is increased to body temperature. The acidic condition (pH 4.00) can trigger the release of drug and the cancer cell (Hela) can adhere to the surface of the hydrogels, which will be beneficial for tumor site-specific administration of drug. The mechanical strength, the gelation temperature, and the drug release behavior can be tuned by varying hyaluronic acid content. The mechanisms were characterized using dynamic mechanical analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and fluorescence microscopy. The carboxyl group in hyaluronic acid can form the hydrogen bondings with the protonated amine in chitosan, which promotes the increase of mechanical strength of the hydrogels and depresses the initial burst release of drug from the hydrogel.

Injectable Polypeptide Thermogel as a Tissue Engineering System for Hepatogenic Differentiation of Tonsil-Derived Mesenchymal Stem Cells

A poly(ethylene glycol)-b-poly(l-alanine) (PEG-l-PA) hydrogel incorporating tonsil-derived mesenchymal stem cells (TMSCs), tauroursodeoxycholic acid (TUDCA), hepatocyte growth factor (HGF), and fibroblast growth factor 4 (FGF4) was prepared through thermal gelation of an aqueous polymer solution for an injectable tissue engineering application. The thermal gelation accompanied conformational changes of both PA and PEG blocks. The gel modulus at 37 °C was controlled to be 1000 Pa by using a 14.0 wt % aqueous polymer solution. The gel preserved its physical integrity during the 3D culture of the cells. TUDCA, HGF, and FGF4 were released from the PEG-l-PA hydrogel over 21 days of the 3D cell culture period. TMSCs initially exhibited a spherical shape, whereas some fibers protruded from the cells on days 14-21 of 3D culture. The injectable system exhibited pronounced expressions of the hepatic biomarkers at both mRNA and protein levels, which are significantly better than the commercially available hyaluronic acid gel. In particular, the hepatogenically differentiated cells from the TMSCs in the injectable system demonstrated hepatic biofunctions comparable to HepG2 cells for the uptakes of low density lipoproteins (52%) and indocyanine green (76%), and the production of albumin (40%) and urea (52%), which are also significantly better than the 3D-cultured cells in the commercially available hyaluronic acid gel. Our studies suggest that the PEG-l-PA thermogel incorporating TMSCs, TUDCA, and growth factors is highly promising as an in situ forming tissue engineering system.

Chitosan gel incorporated peptide-modified AuNPs for sustained drug delivery with smart pH responsiveness

Peptide-stabilized AuNPs incorporated into a CS hydrogel showed smart pH responsiveness in sustained drug delivery.

Exploration of the nature of a unique natural polymer-based thermosensitive hydrogel

The chitosan (CS)/β-glycerol phosphate (GP) system is a heat induced gelling system with a promising potential application, such as an injectable biomedical material. Unlike most thermosensitive gelling systems, the CS/GP system is only partially reversible. That is once the hydrogel is fully matured, it only softens but cannot go back to its initial liquid state when cooled down. Here, we perform both the small and large amplitude oscillatory shear (SAOS and LAOS) tests on the fully matured CS/GP hydrogel samples at a variety of temperatures within the cooling process. The purpose of such tests is to investigate the structural change of the hydrogel network and thus to understand the possible gelation mechanism of this unique thermosensitive hydrogel. From the LAOS results and the further analysis with the Chebyshev expansion method, it shows that the CS/GP hydrogel is composed of a colloidal network dominated by hydrophobic interactions at high temperature, and gradually turns into a flexible network dominated by hydrogen bonding when the temperature goes down. Therefore, we may conclude that LOAS is a powerful tool to study the nonlinear behaviour of a polymer system that is closely related to its structure, and as a practical example, we achieve a clearer vision on the gelation mechanism of the unique CS/GP thermosensitive hydrogel on the basis of considerable previous studies and assumptions in this laboratory and other research groups.