Chitin and chitosan based polyurethanes: A review of recent advances and prospective biomedical applications

Designing a castor oil-based polyurethane as bioadhesive

Based on the stealth behavior of castor oil and poly(ethylene glycol), we selected a polyurethane system to obtain an ideal surgical adhesive. The polyurethane adhesives with varying concentrations of castor oil were investigated by Fourier transform infrared spectrometer, differential scanning calorimetry, scanning electron microscopy, goniometer, and universal testing machine. Curing results show that a 7-min to 25-min room temperature curing can be achieved, providing one possibility of shortening the surgery time. In vitro biodegradation test demonstrates that a certain proportion of the polyurethane film will be hydrolyzed in a foregone manner after a period of time (7 weeks). The adhesion strengths of these adhesives show a strong bonding between pieces of tissue, which makes them qualified for application in a moist environment.

Selectivity of deproteinization and demineralization using natural deep eutectic solvents for production of insect chitin (Hermetia illucens)

Selectivity of deproteinization and demineralization using natural deep eutectic solvents for preparation of insect chitin (Hermetia illucens) was investigated. The relationships between the pH and pKa values of NADESs and demineralization, deproteinization and crystallinity indexes of the obtained chitin were discussed, respectively. It was found that the acidic NADESs consist of basic hydrogen bond acceptor (HBA) and acidic hydrogen bond donor (HBD), or the alkali NADESs composed of acid HBA and alkali HBD were better for chitin products. After reused for three times, demineralization and deproteinization abilities of NADESs were not significantly decreased. Mechanistic analysis indicated that H⁺ released from HBA or HBD was the main reason for demineralization, whereas intermolecular and intramolecular hydrogen bond in NADESs facilitates the removal of protein. Overall, this report provides a preliminary reference for design of the sustainable NADESs for preparation of chitin from natural resources.

Dietary chitosan-selenium nanoparticle (CTS-SeNP) enhance immunity and disease resistance in zebrafish

Selenium (Se) is an essential micronutrient for human and animals. It plays an important role in antioxidative stress, selenoenzymes regulation and immunomodulation. In this study, two common immunostimulants chitosan (CTS) and Se were used to synthesize nanoparticles (CTS-SeNP). Immunomodulation of CTS-SeNP were explored in wild-type zebrafish (Danio rerio). Dietary supplementation of CTS-SeNP enhanced lysozyme activity, phagocytic respiratory burst as well as splenocytes proliferation stimulated by LPS and ConA. CTS-SeNP showed immunomodulation effect from 5 to 20 μg/g but the best outcome was observed at 10 μg/g. Immunomodulation effect were rapidly induced after 3-9d and can sustain to 60. The zebrafish fed with 10 μg/g CTS-SeNP also showed 26.7% higher survival rate than the control after intraperitoneal injection of common bacterium Aeromonas hydrophila. Our results suggested that CTS-SeNP is an effective immunostimulant to fish and has potential application in aquaculture.

Amphiphilic hexadecyl-quaternized chitin micelles for doxorubicin delivery

A series of amphiphilic chitin derivatives were synthesized by conjugating hexadecyl groups (degree of substitute of hexadecyl groups (DS_H) = 0.11, 0.18, and 0.24) onto the backbone of quaternized chitins (degree of substitute of quaternary ammonium groups (DS_Q) = 0.36). The amphiphilic chitin derivatives could self-assemble into cationic micelles with hydrophobic alkyl side chain as core and hydrophilic quaternary ammonium groups as shell in deionized water. The biocompatible cationic micelles with an average particle size of 332.4-385.0 nm showed a drug loading content (DLC) of 10.2%-15.1%. The release behavior of DOX from micelles strongly depended on the DS_H values of chitin derivatives. DOX-loaded micelles effectively inhibited the growth of HepG2 cells through being internalized into HepG2 cells, and releasing DOX into the cytoplasm and nucleus. This work presented a novel chitin-based nanocarrier for potential chemotherapy.

Applications of cellulose and chitin/chitosan derivatives and composites as antibacterial materials: current state and perspectives

The bacterial infections have always a serious problem to public health. Scientists are developing new antibacterial materials to overcome this problem. Polysaccharides are promising biopolymers due to their diverse biological functions, low toxicity, and high biodegradability. Chitin and chitosan have antibacterial properties due to their cationic nature, while cellulose/bacterial cellulose does not possess any antibacterial activity. Moreover, the insolubility of chitin in common solvents, the poor solubility of chitosan in water, and the low mechanical properties of chitosan have restricted their biomedical applications. In order to solve these problems, chemical modifications such as quaternization, carboxymethylation, cationization, or surface modification of these polymers with different antimicrobial agents, including metal and metal oxide nanoparticles, are carried out to obtain new materials with improved physiochemical and biological properties. This mini review describes the recent progress in such derivatives and composites with potential antibacterial applications.

Candidate Polyurethanes Based on Castor Oil (Ricinus communis), with Polycaprolactone Diol and Chitosan Additions, for Use in Biomedical Applications

Polyurethanes are widely used in the development of medical devices due to their biocompatibility, degradability, non-toxicity and chemical versatility. Polyurethanes were obtained from polyols derived from castor oil, and isophorone diisocyanate, with the incorporation of polycaprolactone-diol (15% w/w) and chitosan (3% w/w). The objective of this research was to evaluate the effect of the type of polyol and the incorporation of polycaprolactone-diol and chitosan on the mechanical and biological properties of the polyurethanes to identify the optimal ones for applications such as wound dressings or tissue engineering. Polyurethanes were characterized by stress-strain, contact angle by sessile drop method, thermogravimetric analysis, differential scanning calorimetry, water uptake and in vitro degradation by enzymatic processes. In vitro biological properties were evaluated by a 24 h cytotoxicity test using the colorimetric assay MTT and the LIVE/DEAD kit with cell line L-929 (mouse embryonic fibroblasts). In vitro evaluation of the possible inflammatory effect of polyurethane-based materials was evaluated by means of the expression of anti-inflammatory and proinflammatory cytokines expressed in a cellular model such as THP-1 cells by means of the MILLIPLEX® MAP kit. The modification of polyols derived from castor oil increases the mechanical properties of interest for a wide range of applications. The polyurethanes evaluated did not generate a cytotoxic effect on the evaluated cell line. The assessed polyurethanes are suggested as possible candidate biomaterials for wound dressings due to their improved mechanical properties and biocompatibility.

En route to CO2-containing renewable materials: catalytic synthesis of polycarbonates and non-isocyanate polyhydroxyurethanes derived from cyclic carbonates

The strategies and challenges in the preparation of fully renewable materials prepared from CO₂ and biomass enabled by catalysis are presented.

Bio-Based Electrospun Nanofiber of Polyhydroxyalkanoate Modified with Black Soldier Fly's Pupa Shell with Antibacterial and Cytocompatibility Properties

We report on the antibacterial and cytocompatibility properties of a bio-based electrospun polyhydroxyalkanoate (PHA) nanofiber modified with Black Soldier Fly (BSF) pupa shell. A 5-50 μm chitosan powder (CSP) was made by grinding BSF pupa shell in water, acid, alkali. CSP was combined with PHA in an electrospinning machine using a biaxial feed method and manufactured into a 50-500 nm antibacterial nanofiber. We studied the morphology, mechanical properties, water absorption, and antibacterial properties of the electrospun PHA/CSP nanofiber. To improve the fiber's compatibility and functionality, acrylic acid (AA) was grafted onto PHA. The resulting tensile properties and morphological characterizations indicated enhanced adhesion between CSP and PHA- g-AA nanofiber, as well as an improvement in its water resistance and tensile strength, compared with the PHA/CSP nanofiber. To study the cytocompatibility of the material, human foreskin fibroblasts were seeded onto the nanofiber specimens with 3.0 and 6.0 wt % CSP. Increasing the CSP content in PHA/CSP and PHA- g-AA/CSP nanofibers enhanced cell proliferation; additionally, the nanofibers with CSP showed strong inhibition of bacteria. The enhanced antibacterial and biodegradable properties of PHA- g-AA/CSP and PHA/CSP nanofibers demonstrate their potential for biomedical material applications.

Preparation Method of Porous Dressing Materials Based on Butyric-Acetic Chitin Co-Polyesters

A method for obtaining highly porous materials in the form of film, based on the butyric-acetic chitin co-polyesters, containing 90% of butyryl and 10% of acetyl groups, was developed. The highly porous films, with thickness up to 0.11 mm, were obtained by two methods: (a) pouring 5% BAC 90/10 solution in ethanol on the layer of solid salts (porophor agent) which after solidification was eluted with water; (b) application of the suspension of porophor agent in BAC 90/10 solution in the solvent mixture with density similar to bulk porophor agent. In the final stage, the materials were obtained with porosity up to 95⁻99% and tensile strength 5 cN, which can be used as an active layer of medical dressings. The optimised procedure was used in the production of porous medical dressings (Medisorb) on an industrial scale. In the industrial method, NaCl was used as a porophor agent in the solid form and as a 3% solution in polymer. The final materials were characterised by porosity and other functional parameters at the level recommended for medical dressings. Medisorb series materials do not show in vitro cytotoxic activity.

Hydrophobization of chitosan films by surface grafting with fluorinated polymer brushes

Chitosan with its surface-properties and biodegradability is a promising biomaterial for green packaging applications. Till now, this application is still limited due to chitosan high sensitivity to water. Some existing studies deal with the incorporation of hydrophobic additives to enhance water-proof performances of chitosan films. As these additives may impair the film properties, our study focuses on chitosan efficient hydrophobization by means of simple and successful surface grafting reactions. Chitosan films prepared by solvent casting were modified by means of surface-initiated activators regenerated by electron transfer atom radical polymerization (SI-ARGET-ATRP) of 2-hydroxyethyl methacrylate (HEMA) followed by esterification reaction with fluorinated acyl compound. X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) highlighted the surface chemical changes after each step. Surface properties were investigated by contact angle measurements and surface energy calculations. Hydrophobic surfaces with low surface energy and good water-repellent properties were obtained using a simple handling polymerization procedure. This is the first study in applying ARGET ATRP to prepare hydrophobic biopolymer films offering potential applications in packaging.

Analysis of structure and properties of antibacterial vascular patch used in abdominal aorta aneurysm surgeries

BACKGROUND

Biocompatible materials are used for treatment of blood circulatory system diseases, especially abdominal aortic aneurysms. The most popular and often used are knitted and polymer vascular patches. The aim of this study was to optimize the manufacturing process of implantable materials, ensuring antibacterial activity useful for treating abdominal aorta aneurysms.

METHODS

The vascular patch was manufactured from Trevira® yarn. The parameters of the intermediate product and vascular patch were tested according to standard procedures.

RESULTS

The vascular patch, manufactured from microsilver-containing yarn, with crimps on the surface of the patch, has been found useful for treatment of abdominal aorta aneurysms. Introducing crimps on the surface of the patch resulted in reduction of water permeability and enabled cutting of the graft at various angles without fraying at the cut ends of the biomaterial. The final vascular patch was marked by a gradual release of silver within 48 hours.

CONCLUSIONS

On the basis of the performed test, it has been demonstrated that an implantable material for the treatment of abdominal aorta aneurysms was obtained, and that it can be considered as an alternative for currently used vascular patches. The final vascular patch was marked by a gradual release of silver during the first period of incubation. The antibacterial properties of the final product were confirmed by observation of a significant reduction in the number of Staphylococcus aureus and Klebsiella pneumoniae bacterial colonies.

Chitosan/polyethylene glycol fumarate blend films for wound dressing application: in vitro biocompatibility and biodegradability assays

Blending is one of the effective approaches in preparing tailored materials with a wide range of properties. Thus, chitosan-based polymers have been fabricated and used as wound dressings since they possess better properties than those of the constituent materials. The objective of this work was to evaluate the biocompatibility and biodegradability of biodegradable blend films based on polyethylene glycol-co-fumarate (PEGF) and chitosan (Ch). The blend films of Ch/PEGF were prepared by solution casting/solvent evaporation method. Degradation behavior of these blend films was evaluated in a simulated fluid at physiological pH supplemented with lysozyme at a concentration similar to that in human serum by weight loss of the films and changes in the pH of media. When the pH of incubation media was analyzed, with an increase of PEGF content in the blend films, the degradation rate increased accordingly. The pH of the media of samples was not significantly changed at any measured time point and all films kept their integrities during 28 days. The biocompatibility of the films and cell behavior on the surface of these films were investigated by in vitro tests. Biological assessment using mouse fibroblast cell line L929 on the blend films of Ch/PEGF indicated that films supported the attachment, spreading and proliferation of cells. Since the Ch/PEGF films are biocompatible with the tailored biodegradation rate, they might have a great prospective position in the application of wound dressings.

Preparation, Physicochemical Properties and Hemocompatibility of Biodegradable Chitooligosaccharide-Based Polyurethane

The purpose of this study was to develop a process to achieve biodegradable chitooligosaccharide-based polyurethane (CPU) with improved hemocompatibility and mechanical properties. A series of CPUs with varying chitooligosaccharide (COS) content were prepared according to the conventional two-step method. First, the prepolymer was synthesized from poly(ε-caprolactone) (PCL) and uniform-size diurethane diisocyanates (HBH). Then, the prepolymer was chain-extended by COS in N,N-dimethylformamide (DMF) to obtain the weak-crosslinked CPU, and the corresponding films were obtained from the DMF solution by the solvent evaporation method. The uniform-size hard segments and slight crosslinking of CPU were beneficial for enhancing the mechanical properties, which were one of the essential requirements for long-term implant biomaterials. The chemical structure was characterized by FT-IR, and the influence of COS content in CPU on the physicochemical properties and hemocompatibility was extensively researched. The thermal stability studies indicated that the CPU films had lower initial decomposition temperature and higher maximum decomposition temperature than pure polyurethane (CPU-1.0) film. The ultimate stress, initial modulus, and surface hydrophilicity increased with the increment of COS content, while the strain at break and water absorption decreased, which was due to the increment of crosslinking density. The results of in vitro degradation signified that the degradation rate increased with the increasing content of COS in CPU, demonstrating that the degradation rate could be controlled by adjusting COS content. The surface hemocompatibility was examined by protein adsorption and platelet adhesion tests. It was found that the CPU films had improved resistance to protein adsorption and possessed good resistance to platelet adhesion. The slow degradation rate and good hemocompatibility of the CPUs showed great potential in blood-contacting devices. In addition, many active amino and hydroxyl groups contained in the structure of CPU could carry out further modification, which made it an excellent candidate for wide application in biomedical field.

Preparation and Characterization of Graphene Oxide-Modified Sapium sebiferum Oil-Based Polyurethane Composites with Improved Thermal and Mechanical Properties

Bio-based polyurethane (PU) composites with superior thermal and mechanical properties have received wide attention. This is due to the recent rapid developments in the PU industry. In the work reported here, novel nano-composites with graphene oxide (GO)-modified Sapium sebiferum oil (SSO)-based PU has been synthesized via in situ polymerization. GO, prepared using the improved Hummers method from natural graphene (NG), and SSO-based polyol with a hydroxyl value of 211 mg KOH/g, prepared by lipase hydrolysis, were used as raw materials. The microstructures and properties of GO and the nano-composites were both characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tensile tests. The results showed that GO with its nano-sheet structure possessed a significant number of oxygen-containing functional groups at the surface. The nano-composites containing 1 wt % GO in the PU matrix (PU1) exhibited excellent comprehensive properties. Compared with those for pure PU, the glass transition temperature (Tg) and initial decomposition temperature (IDT) of the PU1 were enhanced by 14.1 and 31.8 °C, respectively. In addition, the tensile strength and Young's modulus of the PU1 were also improved by 126% and 102%, respectively, compared to the pure PU. The significant improvement in both the thermal stability and mechanical properties for PU/GO composites was attributed to the homogeneous dispersion and good compatibility of GO with the PU matrix. The improvement in the properties upon the addition of GO may be attributable to the strong interfacial interaction between the reinforcing agent and the PU matrix.

Advances in Degradable Embolic Microspheres: A State of the Art Review

Considerable efforts have been placed on the development of degradable microspheres for use in transarterial embolization indications. Using the guidance of the U.S. Food and Drug Administration (FDA) special controls document for the preclinical evaluation of vascular embolization devices, this review consolidates all relevant data pertaining to novel degradable microsphere technologies for bland embolization into a single reference. This review emphasizes intended use, chemical composition, degradative mechanisms, and pre-clinical safety, efficacy, and performance, while summarizing the key advantages and disadvantages for each degradable technology that is currently under development for transarterial embolization. This review is intended to provide an inclusive reference for clinicians that may facilitate an understanding of clinical and technical concepts related to this field of interventional radiology. For materials scientists, this review highlights innovative devices and current evaluation methodologies (i.e., preclinical models), and is designed to be instructive in the development of innovative/new technologies and evaluation methodologies.

Mucoadhesive buccal film containing ornidazole and dexamethasone for oral ulcers: in vitro and in vivo studies

A bilayered mucoadhesive buccal film containing a combination of ornidazole (OD) and dexamethasone sodium phosphate (DEX) was prepared using solvent casting to treat oral ulcers. Films were systematically evaluated in vitro to obtain the optimum formulation. The therapeutic effects of these films were investigated in the rabbit oral ulcer model and the in vivo release of OD and DEX in the human oral cavity was also evaluated. The backing layer contained ethyl cellulose and an optimal mucoadhesive layer containing both OD and DEX was produced. Films from the optimum formulation were 0.427 ± 0.015 mm thick, weighed 55.89 ± 0.79 mg, and had a surface pH of 6.34 ± 0.01. The drug content of the optimum formulation approximated the theoretical value with good uniformity (2.959 ± 0.106 mg/cm² for OD and 0.877 ± 0.031 mg/cm² for DEX). The formulation showed favorable swelling characteristics and both drugs were released at >95% after 4 h. Moreover, the compound film had a statistically significant effect on mucosal repair and reduced ulcer inflammation without stimulating the human oral mucosa. C_max of OD in saliva was 37.04 μg/ml and that of DEX was 9.737 μg/ml. Given promising therapeutic effects, the compound film developed here could become a local drug delivery device for treating oral ulcers.

Investigation of Hybrid Materials Based on Polyurethane Modified with Aliphatic Side Chains Combined with Nano-TiO2

In this study, methylene diphenyl diisocyanate (MDI) and polytetrahydrofuran ether diol (PTMG) were used as the raw materials for the synthesis of polyurethane (PU). 1,4-Butanediol, glyceryl monostearate, d-sorbitol tetrastearate, or d-trehalose hexastearate, all containing different amounts of aliphatic side chains, were used as the chain extenders and to introduce C18 side chains into the hard segments of PU, and hybrid materials were then fabricated by mixing PUs with nano-titanium dioxide (nano-TiO2). The effects of the different chain extenders on the surface properties of PU coatings and the hybrid materials were investigated. All the materials were characterised by NMR and FT-IR spectroscopy, differential scanning calorimetry, polarising microscopy, atomic force microscopy, scanning electron microscopy, nanoindentation, and contact angle measurements. The results indicate that incremental changes in the number of side chains decrease the degree of microscale separation from the PU coating and increase the crystallinity of the aliphatic side chains. By introducing the aliphatic side chains, the surface coating presents many tiny protrusions, which enhance the surface roughness and the contact angle. Moreover, both the nano-TiO2 and aliphatic side chain content affect the contact angle of the hybrid materials. The as-obtained superhydrophobic materials exhibit contact angles above 150° with a sliding angle below 3° and present excellent mechanical properties such as hardness and Young’s modulus. The nano-TiO2 was chemically bonded to the molecular chains of PU, resulting in superhydrophobic materials with good acidic and alkaline resistance and anti-stripping properties.

Extraction and physicochemical characterization of chitin and chitosan from Zophobas morio larvae in varying sodium hydroxide concentration

Large amount of sodium hydroxide (NaOH) is consumed to remove the protein content in chitin biomass during deproteinization. However, excessive NaOH concentration used might lead to the reduction of cost effectiveness during chitin extraction. Hence, the present study aimed to extract and evaluate the physicochemical properties of chitin and chitosan isolated from superworm (Zophobas morio) larvae using 0.5M-2.0M of NaOH. The extracted chitin and chitosan were subjected to Fourier Transform Infrared Spectroscopy (FT-IR), elemental analysis, Scanning Electron Microscope (SEM), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and X-ray Diffraction (XRD). The 0.5M NaOH treatment resulted in the highest yield of chitin (5.43%), but produced the lowest yield (65.84%) of chitosan. The extracted chitin samples had relatively high degree of acetylation (DA) (82.39%-101.39%). Both chitin and chitosan showed smooth surface with tiny pores. The extracted chitin samples were confirmed as α-chitin based on the FT-IR and TGA. The chitin samples were amorphous with low degree of crystallinity. From TGA, the Chitosan 3 extracted was partially deacetylated. Both DPPH radical scavenging and ferric-chelating assay showed positive correlation with DD of chitosan isolates. However, the chitosan isolates were not fully dissolved, resulting in lower radical scavenging and ferric-chelating ability compared to commercial chitosan.

Thermal, structural and acetylation behavior of snail and periwinkle shells chitin

This article reports a successful removal of CaCO₃ from snail and periwinkle shells for the purpose of producing high quality chitin for possible application as bio-fillers in bone fixation materials. Experiment was designed with varying concentrations of acid and alkali for demineralization, deproteinization and deacetylation of the samples. Thermal characteristics, morphology, degree of de-acetylation, crystalline structure and hydrogen bonding characteristics of the extracted chitin were examined. Infra-red spectra, thermogravimetric analysis and X-ray diffraction patterns show that demineralization with 1.7 M HCl led to a successful removal of CaCO₃. Subsequent deproteinization and deacetylation with 1.2 M NaOH led to a development of chitosan having a degree of deacetylation of 77 and 60% for periwinkle and snail shells, respectively. Generally, all results show that different treatments led to different chitin structure and consequently different properties.

Biodegradable, pH-responsive chitosan aerogels for biomedical applications

Biodegradable chitosan aerogels with advanced properties for biomedical applications are obtained in a two-step process using biotolerant chemicals, MW irradiation and lyophilisation.