Intelligent Metal-Phenolic Metallogels as Dressings for Infected Wounds

In this study, we report a metallogel developed based on metal-phenolic coordination of natural low-cost polyphenolic molecule and metal ions. Gelation occurs by mixing tannic acid (TA) and group (IV) titanium ions (Ti^IV) to form TA-Ti^IV gel. The TA-Ti^IV gel exhibits good capability to incorporate diverse metal ions by in situ co-gelation. Herein, five antimicrobial metal ions, i.e. ferric (Fe^III), copper (Cu^II), zinc (Zn^II), cobalt (Co^II) and nickel (Ni^II) ions, were employed to include in TA-Ti^IV gels for developing intelligent dressings for infected wounds. The chemical and coordinative structures of TA-Ti^IV metallogels were characterized by UV-Vis and Fourier-transform infrared (FT-IR) spectroscopies. Cytotoxicity of antimicrobial metallogels was explored by MTT assay with NIH 3T3 fibroblasts. The release of metal ions was evaluated by inductively coupled plasma mass spectrometry (ICP-MS), indicating the different releasing profiles upon the coordinative interactions of metal ions with TA. The formation and disassembly of metallogels are sensitive to the presence of acid and an oxidizer, H₂O₂, which are substances spontaneously generated in infected wounds due to the metabolic activity of bacteria and the intrinsic immune response. The Cu^II releasing rates of TA-Ti^IV-Cu^II metallogels at different pH values of 5.5, 7.4 and 8.5 have been studied. In addition, addition of H₂O₂ trigger fast release of Cu^II as a result of oxidation of galloyl groups in TA. Consequently, the antimicrobial potency of TA-Ti^IV-Cu^II metallogels can be simultaneously activated while the wounds are infected and healing. The antimicrobial property of metallogels against Gram-negative Escherichia coli, and Gram-positive Methicillin-Resistant Staphylococcus aureus (USA300) and Staphylococcus epidermidis has been investigated by agar diffusion test. In an animal model, the TA-Ti^IV-Cu^II metallogels were applied as dressings for infected wounds, indicating faster recovery in the wound area and extremely lower amount of bacteria around the wounds, compared to TA-Ti^IV gels and gauze. Accordingly, the intelligent nature derived metallogels is a promising and potential materials for medical applications.

Thermo-triggered drug delivery from polymeric micelles of poly(N-isopropylacrylamide-co-acrylamide)-b-poly(n-butyl methacrylate) for tumor targeting

Novel temperature-sensitive micelles, possessing a core-shell structure, were successfully fabricated and evaluated as possible systems for targeting anticancer drugs to solid tumors. The amphiphilic block copolymer poly( N-isopropylacrylamide- co-acrylamide)-b-poly( n-butyl methacrylate) was used to achieve a stimuli-responsive on/off release and spatial specificity. The anticancer drug methotrexate, which is poorly water soluble, was used as the model. Fourier transform–infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, gel-permeation chromatography, and critical micelle concentration were used to evaluate the successful synthesis of block copolymers with a lower critical solution temperature ~40°C. Based on transmission electron microscope images, the micelles are spherical particles with narrow size distribution. The thermally triggered release of methotrexate was observed in vitro. Quartz crystal microbalance with dissipation was used to investigate the interactions of the polymeric micelles with bovine serum albumin, to illustrate protein adsorption and cell attachment. Cytotoxicity studies were conducted on Lewis lung carcinoma cells, and the anticancer activity of methotrexate-loaded micelles was significantly enhanced in combination with hyperthermia. The thermo-sensitive characteristics of the micelles make them applicable as smart drug delivery systems, when combined with localized hyperthermia.

Thermosensitive poly(N-isopropyl acrylamide-co-N,N-dimethyl acryl amide)-block-poly(d,l-lactide) amphiphilic block copolymer micelles for prednisone drug release

Novel amphiphilic block copolymers consisting of hydrophobic poly(D,L-lactide) segments and hydrophilic poly( N-isopropylacrylamide- co- N, N-dimethylacrylamide) blocks were designed and synthesized through a simple free radical copolymerization route based on a bifunctional initiator, followed by the ring-opening polymerization of D,L-lactide. The copolymers self-assembled into thermosensitive spherical-nanosized core–shell micelles in aqueous solution in the presence or the absence of the model drug prednisone. The chemical and physical characterizations of drug-loaded and unloaded micelles revealed a lower critical solution temperature of 40°C–47°C, and a critical micelle concentration less than 7.20 mg L−1, a transmission electron microscope mean particle size from 50 to 75 nm, and a narrow dynamic light scattering diameter below 180 nm. The prepared blank and drug-loaded micellar nanoparticles were thermodynamically stabile and employed in targeted drug delivery by responding to the higher temperature of the local microenvironment. Based on prednisone release kinetic studies, structural changes of the self-assembled micelles as well as temperature- or environment-induced diffusion controlled drug release and improved bioavailability. The copolymer micelles exhibited good biocompatibility as established by the MTT cytotoxicity assay. Therefore, an effective target therapy against lesion tissues is feasible using these polymeric micelles.

Design and Fabrication of PLGA Sandwiched Cell/Fibrin Constructs for Complex Organ Regeneration

A poly(DL-lactic-co-glycolic acid) (PLGA) sandwich fibrinogen/ adipose stem cell (ADSC) construct was fabricated to generate smooth muscle tissue. The mechanical properties and ADSC compatibility of PLGA, poly(ethylene glycol-1,6-hexamethyl diisocyanate-caprolactone) i.e. polyurethane (PU), gelatin, alginate, and fibrin composites were evaluated for vascular smooth muscle tissue generation. Synthetic PLGA and PU combined with natural gelatin, alginate, and fibrin for strength and cell compatibility were found to be effective. A trilayer construct was designed and built with a microporous inner PLGA layer to provide nutrient, oxygen, and metabolite transfer while the outer PLGA layer with no pores prevented leakage during in vitro culture and in vivo implantation. The fibrin layer suitably accommodated ADSC growth, migration, proliferation, and differentiation inside the construct. This design has the potential for wide use in tissue engineering and complex organ construction.

In situ crosslinkable hydrogel formed from a polysaccharide-based hydrogelator

In situ crosslinkable hydrogel formed from an amphiphilic amylopectin-based hydrogelator in aqueous solution was investigated with respect to its viscoelasticity, structure as well as protein encapsulation and release. Different from the physical hydrogel formed from an aqueous amylopectin system of sufficiently high concentration, such a hydrogel could be formed rapidly at room temperature and exhibit enhanced viscoelastic properties, mechanical strength, and shear thinning behavior. In addition, it has a more complex network structure with a higher fractal dimension due to intermolecular hydrophobic interactions and macromolecular chain entanglements. By circular dichroism analyses and in vitro release experiments, this hydrogel material was found to have a great potential as new matrix for the entrapment and sustained release of bovine serum albumin.

In Vitro Angiogenesis of 3D Tissue Engineered Adipose Tissue

Using a cell assembly device developed in this laboratory, we coextruded adipose derived stem cells (ADSC) and gelatin/alginate hydrogel to form cubic 3D constructions (10 × 10 × 10 mm3) with regular distributed go-through pores. The ADSC grew, proliferated, and differentiated within these constructions. With the addition of basic fibroblast growth factor (bFGF), cells located on the scaffold walls differentiated into endothelial like cells while cells embedded in the hydrogel differentiated into adipose like cells. The integrity of the constructions remained for more than 60 days. This new technology enables us to construct 3D adipose tissue with blood vessel-like structures in vitro which is a significant enhancement in adipose tissue engineering and provides a better biomimic 3D model for studying cell—cell interaction, stem cell differentiation conditions and cell organization mechanisms.

Synthesis of Novel Chitosan Derivatives for Micellar Solubilization of Cyclosporine A

In this study, the solubilization of poor water-soluble drugs using N-acyl, O-acyl-N-trimethyl chitosan chloride (ATMC) micelles as a carrier system was investigated. Three series ofATMCs were synthesized by N-trimethyl chitosan chloride (TMC) with substitutions of 21.3, 44.8, and 45.2% as start material grafting five different long-chain saturated fatty acids (C10—C 18), and characterized by 1H-NMR, 13C-NMR, and FT-IR spectra, respectively. The degree of long-chain acyl group of ATMC was ~8.1%. These ATMC micelles self-assemble and were used to encapsulate the poorly soluble drug, Cyclosporine A. These assemblies were prepared by a dialysis, wherein the drug loading capacity of the ATMC micelles ranged from 9.6% to 17.1% and encapsulation capacity ranged from 35.8% to 69.8%, with the mean micellar particle size of 288 nm. The critical micellar concentrations of the 70,000 Mw ATMC2 were 0.028—0.038 mg/mL. Nanoscale near-spherical ATMC micelles were observed by transmission electron microscopy. Additionally, the chitosan derivatives with a high methylation degree, medium-sized long-chain acyl groups (C14) and large molecular weight had the most effective capacity for loading Cyclosporine A. These ATMC micelles are being investigated as carriers to improve oral administration absorption of poorly permeable drugs.

A Polyurethane-Gelatin Hybrid Construct for Manufacturing Implantable Bioartificial Livers

A novel 3D hybrid construct was developed for liver manufacturing by depositing biodegradable polyurethane (PU) and a naturally derived polymer gelatin simultaneously via a double nozzle rapid prototyping (RP) technique. A grid object was produced by precisely and simultaneously dispersing the PU and gelatin to form 3D constructs with interconnected macro-channels at a low temperature (-28°C). Micro-pores were formed by freeze-drying the constructs. The PU polymer provided mechanical support while gelatin provided accommodation for implant cells. The hydrophilicity of the hybrid constructs was between the pure PU and pure gelatin structures. The interconnected channels allow nutrients and oxygen to be supplied throughout the construct as well as provide space for the attachment of cells. The design and fabrication strategies, used to create complex physical objects directly from computer aided design (CAD) models, represent a promising technique for implantable bioartificial livers. It is anticipated that these PU-gelatin hybrid constructs will serve as a useful model for bioartificial liver manufacturing.