Preparation and characterization of temperature and pH-sensitive chitosan material and its controlled release on coenzyme A

Multi-responsive Pickering emulsifiers: a comprehensive study on the emulsification-demulsification behavior of modified chitosan-coated Fe3O4 nanocomposites

The surface characteristics of stimuli-responsive Pickering emulsifiers can be modified by external environmental triggers, making them highly versatile in various applications. In this study, we report three novel organic-inorganic composite structure emulsifiers. These emulsifiers were designed with a core of magnetic Fe3O4 particles, surrounded by a protective silica layer, and coated on the exterior with three distinct types of modified chitosan (CS). Experimental results demonstrate that these emulsifiers can stabilize emulsion systems consisting of liquid paraffin and deionized water at a concentration of 0.5 wt%. The unique properties of the modified CS coatings allowed for the controlled demulsification of two types of emulsions by adjusting the proton concentration. Additionally, these emulsifiers exhibited magnetic-responsive demulsification under the control of an external magnetic field. The findings of this study provide valuable insights into the design and construction of multi-responsive chitosan-based magnetic Pickering emulsifiers with controllable properties.

Advances in Injectable and Self-healing Polysaccharide Hydrogel Based on the Schiff Base Reaction

Injectable hydrogel possesses great application potential in disease treatment and tissue engineering, but damage to gel often occurs due to the squeezing pressure from injection devices and the mechanical forces from limb movement, and leads to the rapid degradation of gel matrix and the leakage of the load material. The self-healing injectable hydrogels can overcome these drawbacks via automatically repairing gel structural defects and restoring gel function. The polysaccharide hydrogels constructed through the Schiff base reaction own advantages including simple fabrication, injectability, and self-healing under physiological conditions, and therefore have drawn extensive attention and investigation recently. In this short review, the preparation and self-healing properties of the polysaccharide hydrogels that is established on the Schiff base reaction are focused on and their biological applications in drug delivery and cell therapy are discussed.

Biomimetic phosphorylcholine strategy to improve the hemocompatibility of pH-responsive micelles containing tertiary amino groups

pH-responsive nanocarriers such as polymeric micelles that self-assemble from amphiphilic copolymers containing amino groups have been limited by their significant effects on the blood and thus compromise of their hemocompatibility due to the amino group-induced positive charges. Here we report a biomimetic phosphorylcholine strategy to improve the hemocompatibility of the pH-responsive micelles with positive charges. Amphiphilic copolymers containing different number of tertiary amino groups were synthesized in five steps through ring opening polymerization, azide reaction, thio-bromo "Click" chemistry, and atom transfer radical polymerization to self-assemble biomimetic phosphorylcholine micelles with pH-responsiveness, which shown no significant effects on red blood cells, coagulation, and platelet activation. Moreover, albumin adsorption on the micelles was significantly lower than that of polycaprolactone-methoxypolyethylene glycol (PCL-mPEG) control, and in terms of immune cells, the micelles showed controllable phagocytosis that dependent on the number of tertiary amino groups, in which the one containing four tertiary amino groups in its corresponding copolymer remains had a lower phagocytosis by whole blood leukocyte than that of PCL-mPEG. Based on these results, the hemocompatibility related mechanism of the micelles was discussed and proposed. Our findings demonstrated that this biomimetic phosphorylcholine is a promising strategy to improve the hemocompatibility of the positively charged nanocarriers.

Degradable conductive self-healing hydrogels based on dextran-graft-tetraaniline and N-carboxyethyl chitosan as injectable carriers for myoblast cell therapy and muscle regeneration

Injectable conductive hydrogels have great potential as tissue engineering scaffolds and delivery vehicles for electrical signal sensitive cell therapy. In this work, we present the synthesis of a series of injectable electroactive degradable hydrogels with rapid self-healing ability and their potential application as cell delivery vehicles for skeletal muscle regeneration. Self-healable conductive injectable hydrogels based on dextran-graft-aniline tetramer-graft-4-formylbenzoic acid and N-carboxyethyl chitosan were synthesized at physiological conditions. The dynamic Schiff base bonds between the formylbenzoic acid and amine group from N-carboxyethyl chitosan endowed the hydrogels with rapid self-healing ability, which was verified by rheological test. Equilibrated swelling ratio, morphology, mechanical strength, electrochemistry and conductivity of the injectable hydrogels were fully investigated. The self-healable conductive hydrogels showed an in vivo injectability and a linear-like degradation behavior. Two different kinds of cells (C2C12 myoblasts and human umbilical vein endothelial cells (HUVEC)) were encapsulated in the hydrogels by self-healing effect. The L929 fibroblast cell culture results indicated the biocompatibility of the hydrogels. Moreover, the C2C12 myoblast cells were released from the conductive hydrogels with a linear-like profile. The in vivo skeletal muscle regeneration was also studied in a volumetric muscle loss injury model. All these data indicated that these biodegradable self-healing conductive hydrogels are potential candidates as cell delivery vehicles and scaffolds for skeletal muscle repair. STATEMENT OF SIGNIFICANCE: Injectable hydrogels with self-healing and electrical conductivity properties are excellent candidates as tissue-engineered scaffolds for myoblast cell therapy and skeletal muscle regeneration. The self-healing property of these hydrogels can prolong their lifespan. However, most of the reported conductive hydrogels are not degradable or do not have the self-healing ability. Herein, we synthesized antibacterial conductive self-healing hydrogels as a cell delivery carrier for cardiac cell therapy based on chitosan-grafted-tetraaniline hydrogels synthesized in our previous work. However, an acid solution was used to dissolve the polymers in that study, which may induce toxicity to cells. In this work, we synthesized a series of injectable electroactive biodegradable hydrogels with rapid self-healing ability composed of N-carboxyethyl chitosan (CECS) and dextran-graft-aniline oligomers, and these hydrogel precusor can dissolve in PBS solution of pH 7.4; we further demonstrated their potential application as cell delivery vehicles for skeletal muscle regeneration.

Conducting Polymers for Tissue Engineering

Electrically conducting polymers such as polyaniline, polypyrrole, polythiophene, and their derivatives (mainly aniline oligomer and poly(3,4-ethylenedioxythiophene)) with good biocompatibility find wide applications in biomedical fields including bioactuators, biosensors, neural implants, drug delivery systems, and tissue engineering scaffolds. This review focuses on these conductive polymers for tissue engineering applications. Conductive polymers exhibit promising conductivity as bioactive scaffolds for tissue regeneration, and their conductive nature allows cells or tissue cultured on them to be stimulated by electrical signals. However, their mechanical brittleness and poor processability restrict their application. Therefore, conductive polymeric composites based on conductive polymers and biocompatible biodegradable polymers (natural or synthetic) were developed. The major objective of this review is to summarize the conductive biomaterials used in tissue engineering including conductive composite films, conductive nanofibers, conductive hydrogels, and conductive composite scaffolds fabricated by various methods such as electrospinning, coating, or deposition by in situ polymerization. Furthermore, recent progress in tissue engineering applications using these conductive biomaterials including bone tissue engineering, muscle tissue engineering, nerve tissue engineering, cardiac tissue engineering, and wound healing application are discussed in detail.

Injectable antibacterial conductive hydrogels with dual response to an electric field and pH for localized "smart" drug release

Injectable hydrogels with multistimuli responsiveness to electrical field and pH as a drug delivery system have been rarely reported. Herein, we developed a series of injectable conductive hydrogels as "smart" drug carrier with the properties of electro-responsiveness, pH-sensitivity, and inherent antibacterial activity. The hydrogels were prepared by mixing chitosan-graft-polyaniline (CP) copolymer and oxidized dextran (OD) as a cross-linker. The chemical structures, morphologies, electrochemical property, swelling ratio, conductivity, rheological property, in vitro and in vivo biodegradation, and gelation time of hydrogels were characterized. The pH-responsive behavior was verified by drug release from hydrogels in PBS solutions with different pH values (pH = 7.4 or 5.5) in an in vitro model. As drug carriers with electric-driven release, the release rate of the model drugs amoxicillin and ibuprofen loaded within CP/OD hydrogels dramatically increased when an increase in voltage was applied. Both chitosan and polyaniline with inherent antibacterial properties endowed the hydrogels with excellent antibacterial properties. Furthermore, cytotoxicity tests of the hydrogels using L929 cells confirmed their good cytocompatibility. The in vivo biocompatibility of the hydrogels was verified by H&E staining. Together, all these results suggest that these injectable pH-sensitive conductive hydrogels with antibacterial activity could be ideal candidates as smart drug delivery vehicles for precise doses of medicine to meet practical demand.

STATEMENT OF SIGNIFICANCE

Stimuli-responsive or "smart" hydrogels have attracted great attention in the field of biotechnology and biomedicine, especially on designing novel drug delivery systems. Compared with traditional implantable electronic delivery devices, the injectable hydrogels with electrical stimuli not only are easy to generate and control electrical field but also could avoid frequent invasive surgeries that offer a new avenue for chronic diseases. In addition, designing a drug carrier with pH-sensitive property could release drug efficiently in targeted acid environment, and it could reinforce the precise doses of medicine. Furthermore, caused by opportunistic microorganisms and rapid spread of antibiotic-resistant microbes, infection is still a serious threat for many clinical utilities. To overcome these barriers, we designed a series of injectable antibacterial conductive hydrogels based on chitosan-graft-polyaniline (CP) copolymer and oxidized dextran (OD), and we demonstrated their potential as "smart" delivery vehicles with electro-responsiveness and pH-responsive properties for triggered and localized release of drugs.

pH-responsive self-healing injectable hydrogel based on N-carboxyethyl chitosan for hepatocellular carcinoma therapy

Injectable hydrogels with pH-responsiveness and self-healing ability have great potential for anti-cancer drug delivery. Herein, we developed a series of polysaccharide-based self-healing hydrogels with pH-sensitivity as drug delivery vehicles for hepatocellular carcinoma therapy. The hydrogels were prepared by using N-carboxyethyl chitosan (CEC) synthesized via Michael reaction in aqueous solution and dibenzaldehyde-terminated poly(ethylene glycol) (PEGDA). Doxorubicin (Dox), as a model of water-soluble small molecule anti-cancer drug was encapsulated into the hydrogel in situ. Self-healing behavior of the hydrogels was investigated at microscopic and macroscopic levels, and the hydrogels showed rapid self-healing performance without any external stimulus owing to the dynamic covalent Schiff-base linkage between amine groups from CEC and benzaldehyde groups from PEGDA. The chemical structures, rheological property, in vitro gel degradation, morphology, gelation time and in vitro Dox release behavior from the hydrogels were characterized. Injectability was verified by in vitro injection and in vivo subcutaneous injection in a rat. pH-responsive behavior was verified by in vitro Dox release from hydrogels in PBS solutions with different pH values. Furthermore, the activity of Dox released from hydrogel matrix was evaluated by employing human hepatocellular liver carcinoma (HepG2). Cytotoxicity test of the hydrogels using L929 cells confirmed their good cytocompatibility. Together, these pH-responsive self-healing injectable hydrogels are excellent candidates as drug delivery vehicles for liver cancer treatment. STATEMENT OF SIGNIFICANCE: pH-responsive drug delivery system could release drug efficiently in targeted acid environment and minimalize the amount of drug release in normal physiological environment. pH-sensitive injectable hydrogels as smart anti-cancer drug delivery carriers show great potential application for cancer therapy. The hydrogels with self-healing property could prolong their lifetime during implantation and provide the advantage of minimally invasive surgery and high drug-loading ratio. This work reported the design of a series of pH-responsive self-healing injectable hydrogels based on N-carboxyethyl chitosan synthesized in aqueous solution and dibenzaldehyde-terminated poly(ethylene glycol) via a green approach, and demonstrated their potential as intelligent delivery vehicle of doxorubicin for hepatocellular carcinoma therapy via the pH-responsive nature of dynamic Schiff base.

pH- and Temperature-Responsive P(DMAEMA-GMA)-Alginate Semi-IPN Hydrogels Formed by Radical and Ring-Opening Polymerization for Aminophylline Release

A novel poly((2-dimethylamino) ethyl methacrylate-glycidyl methacrylate)-alginate (P(DMAEMA-GMA)alginate) semi-IPN hydrogel was synthesized via radical polymerization of the double bonds and ring-opening of the epoxy groups without using catalyst and cross-linker. (1)H-NMR, FT-IR and DSC data were consistent with the expected structures for the hydrogels. The interior morphology of the hydrogels was also investigated by SEM. The swelling ratio and compressive strength of the hydrogels were measured. The semi-IPN hydrogel had pH and temperature sensitivity, and pH-sensitive points of all hydrogels were found to be at pH 5.0. The release behavior of the model drug, aminophylline, was found to be dependent on the hydrogel composition and environment pH, which manifests that these materials have potential applications as intelligent drug carriers.

Synthesis and characterization of a biodegradable elastomer featuring a dual crosslinking mechanism

The need for advanced materials in emerging technologies such as tissue engineering has prompted increased research to produce novel biodegradable polymers elastic in nature and mechanically compliant with the host tissue. We have developed a soft biodegradable elastomeric platform biomaterial created from citric acid, maleic anhydride, and 1,8-octanediol, poly(octamethylene maleate (anhydride) citrate) (POMaC), which is able to closely mimic the mechanical properties of a wide range of soft biological tissues. POMaC features a dual crosslinking mechanism, which allows for the option of the crosslinking POMaC using UV irradiation and/or polycondensation to fit the needs of the intended application. The material properties, degradation profiles, and functionalities of POMaC thermoset networks can all be tuned through the monomer ratios and the dual crosslinking mechanism. POMaC polymers displayed an initial modulus between 0.03 and 1.54 MPa, and elongation at break between 48% and 534% strain. In vitro and in vivo evaluation using cell culture and subcutaneous implantation, respectively, confirmed cell and tissue biocompatibility. POMaC biodegradable polymers can also be combined with MEMS technology to fabricate soft and elastic 3D microchanneled scaffolds for tissue engineering applications. The introduction of POMaC will expand the choices of available biodegradable polymeric elastomers. The dual crosslinking mechanism for biodegradable elastomer design should contribute to biomaterials science.

Preparation, characterization and drug release behavior of polyion complex micelles

Double-hydrophilic block copolymer composed of poly(N-vinylpyrrolidone) (PVP) and poly(styrene-alter-maleic anhydride) (PSMA) has been synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Poly(N-vinylpyrrolidone)-block-poly(styrene-alter-maleic anhydride) (PVP-b-PSMA) thus formed was characterized by gel permeation chromatography (GPC), (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy and FTIR spectroscopy. In acid solution, this block copolymer spontaneously formed polyion complex (PIC) micelles with a cationic polyelectrolyte, chitosan. The PSMA/chitosan polyelectrolyte complex formed an inner core while PVP chains surrounded it as a shell. Transmission electron micrographs (TEMs) and dynamic light scattering (DLS) showed the PIC micelles to be spherically shaped, with mean hydrodynamic diameter around 146 nm. The model drug coenzyme A (CoA) was loaded into the micelles and the in vitro drug release behavior was investigated. We found that by manipulating the pH value and salt concentration of the release solution, it was possible to control the releasing rate of CoA.