Controlled gelation temperature, pore diameter and degradation of a highly porous chitosan-based hydrogel

Strong, elastic and degradation-tolerated hydrogels composed of chitosan, silk fibroin and bioglass nanoparticles with factor-bestowed activity for bone tissue engineering

Polymer hydrogels intended for use in bone repair need to be strong, elastic, and capable of enduring degradation. However, many natural polymer hydrogels lack these essential properties and thus, are unsuitable for bone repair applications. Here, a new type of multi-network hydrogel with improved mechanical and degradation-resistant properties has been developed for use in bone repair. The hydrogel is composed of thiolated chitosan (TCH), silk fibroin (SF), and thiolated bioglass (TBG) nanoparticles (NPs). The multi-networks are built through sulfhydryl self-crosslinking, diepoxide crosslinker-involved linkages of amino or hydroxyl groups, and enzyme-mediated phenol hydroxyl crosslinking. Additionally, mesoporous TBG NPs serve as a vehicle for loading stromal cell-derived factor-1 (SDF-1) to provide the gel with cell-recruiting activity. The formulated TCH/SF/TBG hydrogels exhibit remarkably enhanced strength, elasticity, and improved degradation tolerance compared to some gels made from only TCH or SF. Furthermore, TCH/SF/TBG gels can support the growth of seeded cells and the deposition of matrix components. Some TCH/SF/TBG gels also demonstrate the ability to release SDF-1 in an approximately linear manner for a few weeks while retaining the chemotactic properties of the released SDF-1. Overall, the multi-network hydrogel has the potential as an in situ forming material for cell-recruiting bone repair and regeneration.

β-Tricalcium Phosphate-Loaded Chitosan-Based Thermosensitive Hydrogel for Periodontal Regeneration

The current treatment for periodontitis is aimed at resolving gingival inflammation, whilst complete periodontal tissue regeneration is not predictable, and it represents a therapeutic challenge. Injectable biomaterials hold tremendous potential in dental tissue regeneration. This study aimed to investigate the ability of an injectable thermosensitive β-tricalcium phosphate (β-TCP) and chitosan-based hydrogel to carry cells and promote periodontal tissue regeneration. In this study, different concentrations of β-TCP-loaded chitosan hydrogels were prepared (0%, 2%, 4%, or 6% β-TCP, 10% β-glycerol phosphate, and 1.5% chitosan). The characteristics of the hydrogels were tested using rheology, a scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), degradation, and biological analyses. The new biomaterial showed a sol-gel transformation ability at body temperature and exhibited excellent chemical and physical characteristics, whilst the existence of β-TCP enhanced the structure and the properties of the hydrogels. The SEM confirmed the three-dimensional networks of the hydrogels, and the typical rheological properties of strong gel were observed. The EDX and XRD validated the successful incorporation of β-TCP, and similar patterns between different groups were found in terms of the FTIR spectra. The stable structure of the hydrogels under 100 °C was confirmed via DSC. Biological tests such as Alamar Blue assay and Live/Dead staining confirmed the remarkable biocompatibility of the hydrogels with pre-osteoblast MC3T3-E1 and human gingival fibroblast (HGF) cells for 14 days, and the results were validated with confocal imaging. This preliminary study shows great promise for the application of the β-TCP-loaded thermosensitive chitosan hydrogels as a scaffold in periodontal bone and soft tissue repair.

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.

An all-in-one CO gas therapy-based hydrogel dressing with sustained insulin release, anti-oxidative stress, antibacterial, and anti-inflammatory capabilities for infected diabetic wounds

To effectively treat diabetic wounds, the development of versatile medical dressings that can long-term regulate blood glucose and highly effective anti-oxidative stress, antibacterial and anti-inflammatory are critical. Here, an all-in-one CO gas-therapy-based versatile hydrogel dressing (ICOQF) was developed via the dynamic Schiff base reaction between the amino groups on quaternized chitosan (QCS) and the aldehyde groups on benzaldehyde-terminated F108 (F108-CHO) micelles. CORM-401 (an oxidant-sensitive CO-releasing molecules) was encapsulated in the hydrophobic core of F108-CHO micelles and insulin was loaded in the three-dimensional network structure of ICOQF. The dynamic Schiff base bonds not only endowed ICOQF with good tissue adhesion, injectability and self-healing, but also gave it sustained and controllable insulin release ability. In addition, ICOQF could quickly generate CO in inflamed wound tissue by consuming reactive oxygen species. The generated CO could effectively anti-oxidative stress by activating the expression of heme oxygenase; antibacterial by inducing the rupture of bacterial cell membranes and mitochondrial dysfunction and inhibiting the synthesis of adenosine triphosphate; and anti-inflammatory by inhibiting the proliferation of activated macrophages and promoting the polarization of the M1 phenotype to the M2 phenotype. Due to these outstanding properties, ICOQF significantly promoted the healing of STZ-induced MRSA-infected diabetic wounds accompanied by good biocompatibility. This study clearly shows that ICOQF is a versatile hydrogel dressing with great application potential for the management of diabetic wounds. STATEMENT OF SIGNIFICANCE: The development of some versatile hydrogel dressings that can not only provide a prolonged and controlled insulin release property but also utilize a non-antibiotic treatment modality for highly effective antibacterial, anti-inflammatory, and anti-oxidative stress effects is vital for the successful treatment of diabetic wounds. Herein, we developed an all-in-one CO gas-therapy-based versatile hydrogel dressing (ICOQF) with sustained and controllable insulin release abilities. Moreover, ICOQF could not only quickly release CO in the inflamed wound tissue by consumption of reactive oxygen species but also utilize the generated CO to highly effectively anti-oxidative stress, antibacterial, and anti-inflammatory. ICOQF therapy substantially promoted the healing of STZ-induced MRSA-infected diabetic wounds. Overall, this work provides a multifunctional hydrogel dressing for the management of diabetic wounds.

Injectable Thermosensitive Chitosan-Collagen Hydrogel as A Delivery System for Marine Polysaccharide Fucoidan

Fucoidans, sulfated polysaccharides from brown algae, possess multiple bioactivities in regard to osteogenesis, angiogenesis, and inflammation, all representing key molecular processes for successful bone regeneration. To utilize fucoidans in regenerative medicine, a delivery system is needed which temporarily immobilizes the polysaccharide at the injured site. Hydrogels have become increasingly interesting biomaterials for the support of bone regeneration. Their structural resemblance with the extracellular matrix, their flexible shape, and capacity to deliver bioactive compounds or stem cells into the affected tissue make them promising materials for the support of healing processes. Especially injectable hydrogels stand out due to their minimal invasive application. In the current study, we developed an injectable thermosensitive hydrogel for the delivery of fucoidan based on chitosan, collagen, and β-glycerophosphate (β-GP). Physicochemical parameters such as gelation time, gelation temperature, swelling capacity, pH, and internal microstructure were studied. Further, human bone-derived mesenchymal stem cells (MSC) and human outgrowth endothelial cells (OEC) were cultured on top (2D) or inside the hydrogels (3D) to assess the biocompatibility. We found that the sol-gel transition occurred after approximately 1 min at 37 °C. Fucoidan integration into the hydrogel had no or only a minor impact on the mentioned physicochemical parameters compared to hydrogels which did not contain fucoidan. Release assays showed that 60% and 80% of the fucoidan was released from the hydrogel after two and six days, respectively. The hydrogel was biocompatible with MSC and OEC with a limitation for OEC encapsulation. This study demonstrates the potential of thermosensitive chitosan-collagen hydrogels as a delivery system for fucoidan and MSC for the use in regenerative medicine.

Development and in vitro assessment of a bi-layered chitosan-nano-hydroxyapatite osteochondral scaffold

An innovative approach was developed to engineer a multi-layered chitosan scaffold for osteochondral defect repair. A combination of freeze drying and porogen-leaching out methods produced a porous, bioresorbable scaffold with a distinct gradient of pore size (mean = 160-275 μm). Incorporation of 70 wt% nano-hydroxyapatite (nHA) provided additional strength to the bone-like layer. The scaffold showed instantaneous mechanical recovery under compressive loading and did not delaminate under tensile loading. The scaffold supported the attachment and proliferation of human mesenchymal stem cells (MSCs), with typical adherent cell morphology found on the bone layer compared to a rounded cell morphology on the chondrogenic layer. Osteogenic and chondrogenic differentiation of MSCs preferentially occurred in selected layers of the scaffold in vitro, driven by the distinct pore gradient and material composition. This scaffold is a suitable candidate for minimally invasive arthroscopic delivery in the clinic with potential to regenerate damaged cartilage and bone.

Injectable chitosan/collagen hydrogels nano-engineered with functionalized single wall carbon nanotubes for minimally invasive applications in bone

Mechanical robustness is an essential consideration in the development of hydrogel platforms for bone regeneration, and despite significant advances in the field of injectable hydrogels, many fail in this regard. Inspired by the mechanical properties of carboxylated single wall carbon nanotubes (COOH-SWCNTs) and the biological advantages of natural polymers, COOH-SWCNTs were integrated into chitosan and collagen to formulate mechanically robust, injectable and thermoresponsive hydrogels with interconnected molecular structure for load-bearing applications. This study presents a complete characterisation of the structural and biological properties, and mechanism of gelation of these novel formulated hydrogels. Results demonstrate that β-glycerophosphate (β-GP) and temperature play important roles in attaining gelation at physiological conditions, and the integration with COOH-SWCNTs significantly changed the structural morphology of the hydrogels to a more porous and aligned network. This led to a crystalline structure and significantly increased the mechanical strength of the hydrogels from kPa to MPa, which is closer to the mechanical strength of the bone. Moreover, increased osteoblast proliferation and rapid adsorption of hydroxyapatite on the surface of the hydrogels indicates increased bioactivity with addition of COOH-SWCNTs. Therefore, these nano-engineered hydrogels are expected to have wide utility in the area of bone tissue engineering and regenerative medicine.

Optimization of a floating poloxamer 407-based hydrogel using the Box-Behnken design: in vitro characterization and in vivo buoyancy evaluation for intravesical instillation

Intravesical instillation of a poloxamer 407 (PLX)-based hydrogel offers advantages such as thermo-sensitivity and sol-to-gel transition, but its utility is limited by urinary obstruction and insufficient bladder residence time. To overcome these obstacles, a floating PLX-hydrogel (FPH) was developed using sodium bicarbonate (BC) as a floating agent and hyaluronic acid (HA) as a gel strength modulator. The FPH composition was optimized using the Box-Behnken design with three independent variables: X₁ [PLX concentration, 23.91%], X₂ [BC concentration, 5.15%], and X₃ [HA concentration, 3.49%]. The quadratic model was the best fit (desirability function, 0.623), resulting in response parameters of Y₁ [floating time, 53.7 s], Y₂ [gelation temperature gap, 20.3°C], and Y₃ [duration time of gel, 396.7 min]. Rheological observations revealed the mechanical rigidity (storage modulus > loss modulus at elevated temperature) of the optimized FPH (phase transition temperature, 15.08°C). Gel erosion and drug release studies were performed using the gravimetric method; the remaining FPH fraction decreased exponentially with time, and gemcitabine release was biphasic and surface erosion-controlled. In vivo buoyancy was evaluated in rats using ultrasonography; these results were similar to those of the in vitro floating behavior. Thus, optimized FPH for intravesical instillation is a prospective option for bladder cancer treatment.

Cell encapsulated and microenvironment modulating microbeads containing alginate hydrogel system for bone tissue engineering

Functional tissue regeneration using synthetic biomaterials requires proliferation and heterotypic differentiation of stem/progenitor cells within a specialized heterogeneous (biophysical-biochemical) microenvironment. The current techniques have limitations to develop synthetic hydrogels, mimicking native extracellular matrix porosity along with heterogeneous microenvironmental cues of matrix mechanics, degradability, microstructure and cell-cell interactions. Here, we have developed a microenvironment modulating system to fabricate in situ porous hydrogel matrix with two or more distinct tailored microenvironmental niches within microbeads and the hydrogel matrix for multicellular tissue regeneration. Electrosprayed pectin-gelatin blended microbeads and crosslinked alginate hydrogel system help to tailor microenvironmental niches of encapsulated cells where two different cells are surrounded by a specific microenvironment. The effect of different microenvironmental parameters associated with the microbead/hydrogel matrix was evaluated using human umbilical-cord mesenchymal stem cells (hUCMSCs). The osteogenic differentiation of hUCMSCs in the hydrogel matrix was evaluated for bone tissue regeneration. This will be the first report on microenvironment modulating microbead-hydrogel system to encapsulate two/more types of cells in a hydrogel, where each cell is surrounded with distinct niches for heterogeneous tissue regeneration.

Thermo-responsive chitosan/silk fibroin/amino-functionalized mesoporous silica hydrogels with strong and elastic characteristics for bone tissue engineering

Amino-functionalized mesoporous silica nanoparticles with radially porous architecture were optimally synthesized, and they were used together with silk fibroin and chitosan to produce a type of covalently crosslinked composite hydrogel using genipin as a crosslinker. The optimally achieved composite gels were found to be thermo-responsive at physiological temperature and pH with well-defined injectability. They were also detected to have mechanically strong and elastic characteristics. In addition, these gels showed the ability to release bioactive Si ions suited to an effective dose range in approximately linear manners for a few weeks. Studies on the cell-gel constructs revealed that the composite gels well supported the growth of seeded MC3T3-E1 cells, and the deposition of matrix components. Results obtained from the detection of alkaline phosphatase activity and the matrix mineralization in the cell-gel constructs confirmed that these composite gels had certain osteogenic capacity. The obtained results suggest that these composite gels have promising potential in bone repair and regeneration.

Development of macroscopically ordered liquid crystalline hydrogels from biopolymers with robust antibacterial activity for controlled drug delivery applications

Macroscopically ordered liquid crystalline hydrogel with antibacterial activity for controlled drug delivery applications.

Nanoscale Thermosensitive Hydrogel Scaffolds Promote the Chondrogenic Differentiation of Dental Pulp Stem and Progenitor Cells: A Minimally Invasive Approach for Cartilage Regeneration

Purpose

Several scaffolds and cell sources are being investigated for cartilage regeneration. The aim of the study was to prepare nanocellulose-based thermosensitive injectable hydrogel scaffolds and assess their potential as 3D scaffolds allowing the chondrogenic differentiation of embedded human dental pulp stem and progenitor cells (hDPSCs).

Materials and Methods

The hydrogel-forming solutions were prepared by adding β-glycerophosphate (GP) to chitosan (CS) at different ratios. Nanocellulose (NC) suspension was produced from hemp hurd then added dropwise to the CS/GP mixture. In vitro characterization of the prepared hydrogels involved optimizing gelation and degradation time, mass-swelling ratio, and rheological properties. The hydrogel with optimal characteristics, NC-CS/GP-21, was selected for further investigation including assessment of biocompatibility. The chondrogenesis ability of hDPSCs embedded in NC-CS/GP-21 hydrogel was investigated in vitro and compared to that of bone marrow-derived mesenchymal stem cells (BMSCs), then was confirmed in vivo in 12 adult Sprague Dawley rats.

Results

The selected hydrogel showed stability in culture media, had a gelation time of 2.8 minutes, showed a highly porous microstructure by scanning electron microscope, and was morphologically intact in vivo for 14 days after injection. Histological and immunohistochemical analyses and real-time PCR confirmed the chondrogenesis ability of hDPSCs embedded in NC-CS/GP-21 hydrogel.

Conclusion

Our results suggest that nanocellulose–chitosan thermosensitive hydrogel is a biocompatible, injectable, mechanically stable and slowly degradable scaffold. hDPSCs embedded in NC-CS/GP-21 hydrogel is a promising, minimally invasive, stem cell-based strategy for cartilage regeneration.

Development prospects of curable osteoplastic materials in dentistry and maxillofacial surgery

The article presents classification of the thermosetting materials for bone augmentation. The physical, mechanical, biological, and clinical properties of such materials are reviewed. There are two main types of curable osteoplastic materials: bone cements and hydrogels. Compared to hydrogels, bone cements have high strength features, but their biological properties are not ideal and must be improved. Hydrogels are biocompatible and closely mimic the extracellular matrix. They can be used as cytocompatible scaffolds for tissue engineering, as can protein- and nucleic acid-activated structures. Hydrogels may be impregnated with osteoinductors such as proteins and genetic vectors without conformational changes. However, the mechanical properties of hydrogels limit their use for load-bearing bone defects. Thus, improving the strength properties of hydrogels is one of the possible strategies to achieve the basis for an ideal osteoplastic material.

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.

Thermally triggered injectable chitosan/silk fibroin/bioactive glass nanoparticle hydrogels for in-situ bone formation in rat calvarial bone defects

Copper-containing bioactive glass nanoparticles (Cu-BG NPs) with designed compositions and sizes were synthesized and incorporated into chitosan (CH)/silk fibroin (SF)/glycerophosphate (GP) composites to prepare injectable hydrogels for cell-free bone repair. The resulting Cu-BG/CH/SF/GP gels were found to exhibit well-defined injectability and to undergo rapid gelation at physiological temperature and pH. They were highly porous and showed the ability to administer Si, Ca and Cu ions at their respective safe doses in a sustained and controlled manner. In vitro studies revealed that the gels supported the growth of seeded MC3T3-E1 and human umbilical vein endothelial cells, and effectively induced them toward osteogenesis and angiogenesis, respectively. In vivo bone repair based on a critical-size rat calvarial bone defect model demonstrated that the optimal Cu-BG/CH/SF/GP gel was able to fully restore the bone defect with formation of vascularized bone tissue and mineralized collagen deposition during a treatment period of 8 weeks without utilization of any cells and/or growth factors. The results suggest that the presently developed Cu-BG/CH/SF/GP composite hydrogels have great potential and translation ability for bone regeneration owing to their thermo-sensitive properties, cell-free bioactivity, and cost-effectiveness. STATEMENT OF SIGNIFICANCE: Hydrogels loaded with cells and/or growth factors exhibit potential in bone repair. However, they have been facing obstacles related to the clinic translation. Here, a novel type of hydrogel system consisting of copper-containing bioactive glass nanoparticles and chitosan/silk fibroin composite was developed. These gels showed injectability and thermally triggered in situ gelation properties and were able to administer the release of ions at safe but effective doses in a controlled manner while inducing the seeded cells toward osteogenesis and angiogenesis. The optimal gel showed the ability to fully repair critical-size rat calvarial bone defects without involving time consuming cell processing and/or the use of expensive growth factors, confirming that this novel hydrogel system has great potential for translation to the clinic.

Distilled pyroligneous liquor obtained from Eucalyptus grandis and chitosan: physicochemical properties of the solution and films

The pyroligneous liquor is a product obtained during the production of charcoal, with well-known antimicrobial activity. In this work, we characterized the physical chemistry properties of a formulation composed of distilled pyroligneous liquor (DPL), obtained from Eucalyptus grandis, and chitosan. A good interaction between the polymer and the solvent was observed. Auto-supported films were prepared with these systems and characterized with respect to their structure and photo-protection properties, water vapor permeability, and resistance to water and to thermal degradation. They present a semi-crystalline structure and are hygroscopic, but are stable under immersion for up to 7 days. The swelling degree in water is 300% in weight and the permeability to water vapor was between 30 and 45 g m^-1 h^-1 (for films with 80 to 10 μm, respectively). The obtained films are able to efficiently block the incident UVB and UVC radiation; the molar absorptivity decreases exponentially with increasing wavelength and is stable up to 300 °C. These properties confer desirable properties to the films, obtained from these precursors of a renewable source, to be used as coatings.

Microenvironmental Control of MUC1 Aptamer-Guided Acid-Labile Nanoconjugate within Injectable Microporous Hydrogels

Although aptamers are well-known as cell-specific membrane biomarkers for tumor-targeted therapy, it is important to avoid their degradation by nucleases in vivo. In this study, we developed a MUC1 aptamer-doxorubicin nanoconjugate (APT-DOX) through an acid-labile linkage and embedded APT-DOX into a thermosensitive hydrogel for antitumor therapy. The hydrogels exhibit a sol-gel transition upon intratumoral injection, resulting in the protection and controlled release control of APT-DOX with the shielding of the gel network. Moreover, the released APT-DOX was prone to be enriched at the tumor cells due to specific intracellular transport by the overexpressing MUC1 protein; however, APT-DOX regained the free DOX form via the rupture of the linkage under tumor cells lysosome acidic conditions and achieved increased concentration in the nucleus for antitumor treatment.

Localized multidrug co-delivery by injectable self-crosslinking hydrogel for synergistic combinational chemotherapy

The multidrug co-loaded injectable hydrogels against tumor showed superiority and potential application values.

Development of a dual drug-loaded hydrogel delivery system for enhanced cancer therapy: in situ formation, degradation and synergistic antitumor efficiency

A stimuli-responsive, biodegradable, and dual drug-loaded hydrogel delivery system was formed in situ for combination drug therapy of cancer in vivo.

Controlled extended octenidine release from a bacterial nanocellulose/Poloxamer hybrid system

Although bacterial nanocellulose (BNC) has been widely investigated in the last 10years as drug delivery system, up to now no long-term controlled release of drugs could be realized. Therefore, the aim of the present work was the development of a BNC-based drug delivery system that provides prolonged retention time for the antiseptic octenidine up to one week with improved mechanical and antimicrobial properties as well as a high biocompatibility. BNC was modified by incorporation of differently concentrated Poloxamers 338 and 407 as micelles and gels that were extensively investigated regarding size, surface charge, and dynamic viscosity. Depending on type and concentration of the Poloxamer, a retarded octenidine release up to one week could be accomplished. Additionally, superior material properties such as high compression stability and water binding could be achieved. The antimicrobial activity of octenidine against Staphylococcus aureus and Pseudomonas aeruginosa was not changed by the use of Poloxamers. Excellent biocompatibility of the Poloxamer loaded BNC could be demonstrated after local administration in a shell-less hen's egg model. In conclusion, a long-term delivery system consisting of BNC and Poloxamer could be developed for octenidine as a ready-to-use system e.g. for long-term dermal wound treatment.

Development of thermosensitive chitosan/glicerophospate injectable in situ gelling solutions for potential application in intraoperative fluorescence imaging and local therapy of hepatocellular carcinoma: a preliminary study

OBJECTIVES

Thermosensitive chitosan/glycerophosphate (C/GP) solutions exhibiting sol-gel transition around body temperature were prepared to develop a class of injectable hydrogel platforms for the imaging and loco-regional treatment of hepatocellular carcinoma (HCC). Indocyanine green (ICG) was loaded in the thermosensitive solutions in order to assess their potential for the detection of tumor nodules by fluorescence.

METHODS

The gel formation of these formulations as well as their gelling time, injectability, compactness and resistance of gel structure, gelling temperature, storage conditions, biodegradability, and in vitro dye release behavior were investigated. Ex vivo studies were carried out for preliminary evaluation using an isolated bovine liver.

RESULTS

Gel strengths and gelation rates increased with the cross-link density between C and GP. These behaviors are more evident for C/GP solutions, which displayed a gel-like precipitation at 4°C. Furthermore, formulations with the lowest cross-link density between C and GP exhibited the best injectability due to a lower resistance to flow. The loading of the dye did not influence the gelation rate. ICG was not released from the hydrogels because of a strong electrostatic interaction between C and ICG. Ex vivo preliminary studies revealed that these injectable formulations remain in correspondence of the injected site.

CONCLUSIONS

The developed ICG-loaded hydrogels have the potential for intraoperative fluorescence imaging and local therapy of HCC as embolic agents. They form in situ compact gels and have a good potential for filling vessels and/or body cavities.

Environmental applications of chitosan and its derivatives

Chitosan originates from the seafood processing industry and is one of the most abundant of bio-waste materials. Chitosan is a by-product of the alkaline deacetylation process of chitin. Chemically, chitosan is a polysaccharide that is soluble in acidic solution and precipitates at higher pHs. It has great potential for certain environmental applications, such as remediation of organic and inorganic contaminants, including toxic metals and dyes in soil, sediment and water, and development of contaminant sensors. Traditionally, seafood waste has been the primary source of chitin. More recently, alternative sources have emerged such as fungal mycelium, mushroom and krill wastes, and these new sources of chitin and chitosan may overcome seasonal supply limitations that have existed. The production of chitosan from the above-mentioned waste streams not only reduces waste volume, but alleviates pressure on landfills to which the waste would otherwise go. Chitosan production involves four major steps, viz., deproteination, demineralization, bleaching and deacetylation. These four processes require excessive usage of strong alkali at different stages, and drives chitosan's production cost up, potentially making the application of high-grade chitosan for commercial remediation untenable. Alternate chitosan processing techniques, such as microbial or enzymatic processes, may become more cost-effective due to lower energy consumption and waste generation. Chitosan has proved to be versatile for so many environmental applications, because it possesses certain key functional groups, including - OH and -NH2 . However, the efficacy of chitosan is diminished at low pH because of its increased solubility and instability. These deficiencies can be overcome by modifying chitosan's structure via crosslinking. Such modification not only enhances the structural stability of chitosan under low pH conditions, but also improves its physicochemical characteristics, such as porosity, hydraulic conductivity, permeability, surface area and sorption capacity. Crosslinked chitosan is an excellent sorbent for trace metals especially because of the high flexibility of its structural stability. Sorption of trace metals by chitosan is selective and independent of the size and hardness of metal ions, or the physical form of chitosan (e.g., film, powder and solution). Both -OH and -NH2 groups in chitosan provide vital binding sites for complexing metal cations. At low pH, -NH3 + groups attract and coagulate negatively charged contaminants such as metal oxyanions, humic acids and dye molecules. Grafting certain functional molecules into the chitin structure improves sorption capacity and selectivity for remediating specific metal ions. For example, introducing sulfur and nitrogen donor ligands to chitosan alters the sorption preference for metals. Low molecular weight chitosan derivatives have been used to remediate metal contaminated soil and sediments. They have also been applied in permeable reactive barriers to remediate metals in soil and groundwater. Both chitosan and modified chitosan have been used to phytoremediate metals; however, the mechanisms by which they assist in mobilizing metals are not yet well understood. In addition, microbes have been used in combination with chitosan to remediate metals (e.g., Cu and Zn) in contaminated soils. Chitosan has also been used to remediate organic contaminants, such as oil-based wastewater, dyes, tannins, humic acids, phenols, bisphenoi-A, p-benzoquinone, organo-phosphorus insecticides, among others. Chitosan has also been utilized to develop optical and electrochemical sensors for in-situ detection of trace contaminants. In sensor technology, naturally-derived chitosan is used primarily as an immobilizing agent that results from its enzyme compatibility, and stabilizing effect on nanoparticles. Contaminant-sensing agents, such as enzymes, microbes and nanoparticles, have been homogeneously immobilized in chitosan gels by using coagulating (e.g., alginate, phosphate) or crosslinking agents (e.g., GA, ECH). Such immobilization maintains the stability of sensing elements in the chitosan gel phase, and prevents inactivation and loss of the sensing agent. In this review, we have shown that chitosan, an efficient by-product of a waste biomaterial, has great potential for many environmental applications. With certain limitations, chitosan and its derivatives can be used for remediating contaminated soil and wastewater. Notwithstanding, further research is needed to enhance the physicochemical properties of chitosan and mitigate its deficiencies.

Glycerophosphate-based chitosan thermosensitive hydrogels and their biomedical applications

Chitosan is non-toxic, biocompatible and biodegradable polysaccharide composed of glucosamine and derived by deacetylation of chitin. Chitosan thermosensitive hydrogel has been developed to form a gel in situ, precluding the need for surgical implantation. In this review, the recent advances in chitosan thermosensitive hydrogels based on different glycerophosphate are summarized. The hydrogel is prepared with chitosan and β-glycerophosphate or αβ-glycerophosphate which is liquid at room temperature and transits into gel as temperature increases. The gelation mechanism may involve multiple interactions between chitosan, glycerophosphate, and water. The solution behavior, rheological and physicochemical properties, and gelation process of the hydrogel are affected not only by the molecule weight, deacetylation degree, and concentration of chitosan, but also by the kind and concentration of glycerophosphate. The properties and the three-dimensional networks of the hydrogel offer them wide applications in biomedical field including local drug delivery and tissue engineering.

A novel design of injectable porous hydrogels with in situ pore formation

The use of injectable porous hydrogels is of great interest in biomedical applications due to their excellent permeability and ease of integration into sites of surgical intervention. By implementing a method that enables the formation in situ of pores with controllable porosity and pore size, it is possible to synthesize bioactive hydrogels that are tailor-made for specific biomedical applications. An emulsion-templating technique was used to encapsulate oil droplets, which are subsequently leached out of the hydrogel to create the porous structure. Pore size and porosity were manipulated by changing oil-to-water ratios and the surfactant concentrations. Highly swellable porous hydrogels were obtained with control over mechanical strength and diffusive properties. The relationship between porosity, pore size, and the hydrogel's physical and mechanical characteristics was analyzed, and the potential of this material as a protein drug delivery system was demonstrated.

Injectable 3D hydrogel scaffold with tailorable porosity post-implantation

Since rates of tissue growth vary significantly between tissue types, and also between individuals due to differences in age, dietary intake, and lifestyle-related factors, engineering a scaffold system that is appropriate for personalized tissue engineering remains a significant challenge. In this study, a gelatin-hydroxyphenylpropionic acid/carboxylmethylcellulose-tyramine (Gtn-HPA/CMC-Tyr) porous hydrogel system that allows the pore structure of scaffolds to be altered in vivo after implantation is developed. Cross-linking of Gtn-HPA/CMC-Tyr hydrogels via horseradish peroxidase oxidative coupling is examined both in vitro and in vivo. Post-implantation, further alteration of the hydrogel structure is achieved by injecting cellulase enzyme to digest the CMC component of the scaffold; this treatment yields a structure with larger pores and higher porosity than hydrogels without cellulase injection. Using this approach, the pore sizes of scaffolds are altered in vivo from 32-87 μm to 74-181 μm in a user-controled manner. The hydrogel is biocompatible to COS-7 cells and has mechanical properties similar to those of soft tissues. The new hydrogel system developed in this work provides clinicians with the ability to tailor the structure of scaffolds post-implantation depending on the growth rate of a tissue or an individual's recovery rate, and could thus be ideal for personalized tissue engineering.

Thermosensitive chitosan/glycerophosphate-based hydrogel and its derivatives in pharmaceutical and biomedical applications

INTRODUCTION

Thermogelling chitosan (CS)/glycerophosphate (GP) solutions have been reported as a new type of parenteral in situ forming depot system. These free-flowing solutions at ambient temperature turn into semi-solid hydrogels after parenteral administration.

AREAS COVERED

Formulation parameters such as CS physico-chemical characteristics, CS/gelling agent ratio or pH of the system, were acknowledged as key parameters affecting the solution stability, the sol/gel transition behavior and/or the final hydrogel structure. We discuss also the use of the standard CS/GP thermogels for various biomedical applications, including drug delivery and tissue engineering. Furthermore, this manuscript reviews the different strategies implemented to improve the hydrogel characteristics such as combination with carrier particles, replacement of GP, addition of a second polymer and chemical modification of CS.

EXPERT OPINION

The recent advances in the formulation of CS-based thermogelling systems already overcame several challenges faced by the standard CS/GP system. Dispersion of drug-loaded carrier particles into the thermogels allowed achieving prolonged release profiles for low molecular weight drugs; incorporation of an additional polymer enabled to strengthen the network, while the use of chemically modified CS led to enhanced pH sensitivity or biodegradability of the matrix.