Synthesis and characterization of photo-cross-linked hydrogels based on biodegradable polyphosphoesters and poly(ethylene glycol) copolymers

Novel biodegradable hydrogels by photo-cross-linking macromers based on polyphosphoesters and poly(ethylene glycol) (PEG) are reported. Photo-cross-linkable macromers were synthesized by ring-opening polymerization of the cyclic phosphoester monomer 2-(2-oxo-1,3,2-dioxaphospholoyloxy) ethyl methacrylate (OPEMA) using PEG as the initiator and stannous octoate as the catalyst. The macrorners were characterized by H-1 NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography measurements. The content of polyphosphoester in the macromer was controlled by varying the feed ratio of OPEMA to PEG. Hydrogels were fabricated by exposing aqueous solutions of macromers with 0.05% (w/w) photoinitiator to UV light irradiation, and their swelling kinetics as well as degradation behaviors were evaluated. The results demonstrated that cross-linking density and pH values strongly affected the degradation rates. The macromers was compatible to osteoblast cells, not exhibiting significant cytotoxicity up to 0.5 mg/mL. "Live/dead" cell staining assay also demonstrated that a large majority of the osteoblast cells remained viable after encapsulation into the hydrogel constructs, showing their potential as tissue engineering scaffolds.

Biodegradable amphiphilic triblock copolymer bearing pendant glucose residues: Preparation and specific interaction with Concanavalin A molecules

A novel biodegradable amphiphilic block copolymer PLGG-PEG-PLGG bearing pendant glucose residues is successfully prepared by the coupling reaction of 3-(2-aminoethylthio) propyl-R-D-glucopyranoside with the pendant carboxyl groups of PLGG-PEG-PLGG in the presence of N,N'-carbonyldiimidazole. The polymer PLGG-PEG-PLGG, i.e., poly {(lactic acid)-co-[(glycolic acid)-alt-(L-glutamic acid)]}-block-poly(ethylene glycol)-block-poly{( lactic acid)-co-[( glycolic acid)-alt-(L-glutamic acid)]}, is prepared by ring-opening copolymerization of L-lactide (LLA) with (3s)-benzoxylcarbonylethylmorpholine-2,5-dione (BEMD) in the presence of dihydroxyl PEG with molecular weight of 2000 as macroinitiator and Sn(Oct)(2) as catalyst, and then by catalytic hydrogenation. The glucose-grafted copolymer shows a lower degree of cytotoxicity to ECV-304 cells and improved specific recognition and binding with Concanavalin A (Con A). Therefore, this kind of glucose-grafted copolymer may find biomedical applications.

Synthesis and characterization of a novel biodegradable, thermoplastic polyurethane elastomer

A series of biodegradable, thermoplastic polyurethane elastomers poly (epsilon-caprolactone-co-lactide)polyurethane [PCLA-PU] were synthesized from a random copolymer Of L-lactide (LA) and epsilon-caprolactone (CL), hexamethylene diisocyanate, and 1,4-butanediol. The effects of the LA/CL monomer ratio and hard-segment content on the thermal and mechanical properties of PCLA-PUs were investigated. Gel permeation chromatography, IR, C-13 NMR, and X-ray diffraction were used to confirm the formation and structure of PCLA-PUs. Through differential scanning calorimetry, tensile testing, and tensile-recovery testing, their thermal and mechanical properties were characterized. Their glass-transition temperatures were below -8 degrees C, and their soft domains became amorphous as the LA content increased. They displayed excellent mechanical properties, such as a tensile strength as high as 38 MPa, a tensile modulus as low as 10 MPa, and an elongation at break of 1300%. Therefore, they could find applications in biomedical fields, such as soft-tissue engineering and artificial skin.

Synthesis and characterization of the biodegradable polycaprolactone-graft-chitosan amphiphilic copolymers

A novel synthetic approach to biodegradable amphiphilic copolymers based on poly (epsilon-caprolactone) (PCL) and chitosan was presented, and the prepared copolymers were used to prepare nanoparticles successfully. The PCL-graft-chitosan copolymers were synthesized by coupling the hydroxyl end-groups on preformed PCL chains and the amino groups present on 6-O-triphenylmethyl chitosan and by removing the protective 6-O-triphenylmethyl groups in acidic aqueous solution. The PCL content in the copolymers can be controlled in the range of 10-90 wt %. The graft copolymers were thoroughly characterized by H-1 NAM, C-13 NMR, FT-IR and DSC. The nanoparticles made from the graft copolymers were investigated by H-1 NMR, DLS, AFM and SEM measurements. It was found that the copolymers could form spherical or elliptic nanoparticles it? water. The amount of available primary amines on the surface of the prepared nanoparticles was evaluated by ninhydrin assail, and it can be controlled by the grafting degree of PCL.

Characterization and properties of biodegradable poly(hydroxyalkanoates) and 4,4-dihydroxydiphenylpropane blends: Intermolecular hydrogen bonds, miscibility and crystallization

Intermolecular hydrogen bonds, miscibility, crystallization and thermal stability of the blends of biodegradable poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-3HHx)] with 4,4-dihydroxydiphenylpropane (DOH2) were investigated by FTIR, C-13 Solid state NMR, DSC, WAXD and TGA. Intermolecular hydrogen bonds were found in both blend systems, which resulted from the carbonyl groups in the amorphous phase of both polyesters and the hydroxyl groups of DOH2. The intermolecular interaction between P(3HB-3HHx) and DOH2 is weaker than that between PHB and DOH2 owing to the steric hindrance of longer 3HHx side chains. Because of the effect of the hydrogen bonds, the chain mobility of both PHB and P(3HB-3HHx) components was limited after blending with DOH2 molecules. Single glass transition temperature depending on the composition was observed in all blends, indicating that those blends were miscible in the melt. The addition of DOH2 suppressed the crystallization of PHB and P(3HB-3HHx) components. Moreover, the crystallinity of PHB and P(3HB-3HHx) components also decreased with increasing DOH2 content in the blends.

Biodegradable electrospun poly(L-lactide) fibers containing antibacterial silver nanoparticles

Biodegradable poly(L-lactide) (PLA) ultrafine fibers containing nanosilver particles were prepared via electrospinning. Morphology of the Ag/PLA fibers and distribution of the silver nanoparticles were characterized. The release of silver ions from the Ag/PLA fibers and their antibacterial activities were investigated. These fibers showed antibacterial activities (microorganism reduction) of 98.5% and 94.2% against Staphylococcus aureus and Escherichia coli, respectively, because of the presence of the silver nanoparticles.

Characterization of Full-Biodegradable Starch-PVA-Polyester Film

IntroductionConventional polymers such as polyethyleneand polypropylene persistfor many years after landdisposal.Furthermore,plastics are often soiled byfood and other biological substances,making phys-ical recycling of those materials impractical andgenerally undesirable. In contrast,biodegradablepolymers disposed in bioactive environment are de-graded by the enzymatic action of microorganismssuch as bacteria,fungi,and algae.The worldwideconsumption of biodegradable polymers increasedfrom1.4×107kg in ...

Studies on Mechanical Properties of Full-Biodegradable Starch-PVA-Polyester Films

A kind of full-biodegradable film material is discussed in this article. The film material is composed of starch, PVA, degradable polyesters(PHB, PHB-V, PCL) with built plasticizer, a cross-linking reinforcing agent and a wet strengthening agent. It contains a high percentage of starch, costs cheap and is excellent in weather fastness, temperature resistance and waterproof and it could be completely biodegraded. The present paper deals mainly with a new technical route using a new type of electromagnetic dynamic blow molding extruder and some effects on mechanical properties of the system.

Biodegradable electrospun fibers for drug delivery

The influences of surfactants and medical drugs on the diameter size and uniformity of electrospun poly(L-lactic acid) (PLLA) fibers were examined by adding various surfactants (cationic, anionic, and nonionic) and typical drugs into the PLLA solution. Significant diameter reduction and uniformity improvement were observed. It was shown that the drugs were capsulated inside of the fibers and the drug release in the presence of proteinase K followed nearly zero-order kinetics due to the degradation of the PLLA fibers. Such ultrafine fiber mats containing drugs may find clinical applications in the future.

Ultrafine fibers electrospun from biodegradable polymers

Biodegradable poly(I-lactide) (PLLA) and poly(e-caprolactone) (PCL) were electrospun into ultrafine fibers. The technological parameters influencing the spinning process and morphology of the fibers obtained were examined. These parameters included solvent composition, addition of certain organic salts, molecular weight and concentration of the polymers, capillary diameter, air ventilation, and pressure imposed on the surface of the solution as well as electrostatic field. By properly choosing and adjusting these parameters, submicron PLLA and PCL fibers with a narrow diameter distribution were prepared. Scanning electronic microscopy was used to observe the morphology and diameter size of the fibers.

Hydrogel of biodegradable cellulose derivatives. I. Radiation-induced crosslinking of CMC

Radiation crosslinking of carboxymethylcellulose (CMC) with a degree of substitution (DS) from 0.7 to 2.2 was the subject of the current investigation. CMC was irradiated in solid-state and aqueous solutions at various irradiation doses. The DS and the concentration of the aqueous solution had a remarkable affect on the crosslinking of CMC. Irradiation of CMC, even with a high DS, 2.2 in solid state, and a low DS, 0.7 in 10% aqueous solution, resulted in degradation. However, it was found that irradiation of CMC with a relatively high DS, 1.32, led to crosslinking in a 5% aqueous solution, and 20% CMC gave the highest gel fraction. CMC with a DS of 2.2 induced higher crosslinking than that with a DS of 1.32 at lower doses with the same concentration. Hence, it was apparent that a high DS and a high concentration in an aqueous solution were favorable for high crosslinking of CMC. It is assumed that; high radiation crosslinking of CMC was induced by the increased mobility of its molecules in water and by the formation of CMC radicals from the abstraction of H atoms from macromolecules in the intermediate products of water radiolysis. A preliminary biodegradation study confirmed that crosslinked CMC hydrogel can be digested by a cellulase enzyme. (C) 2000 John Wiley & Sons, Inc.

Radiation crosslinking of biodegradable poly(butylene succinate) and its heat distortion behavior

Poly(butylene succinate), (PBS1) was irradiated with Co-60-gamma radiation at various temperatures. The gel fraction of PBS I irradiated at molten state (100 degreesC) is higher than that of the samples irradiated at lower temperatures with the same dose. Two-step irradiation ( irradiation at room temperature and then irradiation at 100 degreesC) yielded the highest gel content as compared with other treatment conditions. It is due to the network structure formed by preirradiation at room temperature and further irradiation at molten state reduce degradation of PBS1. PBS1 prepared by the two-step irradiation was improved in heat distortion resistance because of its higher gel content. Unirradiated PBS1 sheets broke immediately at 110 degreesC. On the other hand, for samples (gel fraction 50%) irradiated by asing the two-step method, they did not break even at 130 degreesC for 200 min.

Radiation crosslinking of biodegradable poly(butylene succinate) at high temperature

Poly(butylene succinate), (PBS) with different molecular weight was gamma -irradiated at different temperatures and various doses. PBS with high molecular weight and smaller peak area of crystal melting gave the highest gel content at the same temperatures and dose. A two-step irradiation (irradiation in molten state after irradiation at room temperature) gave the highest gel content in different conditions. This is due to the formation of network structure by pre-irradiation at room temperature that leads to less degradation. PBS prepared by two step irradiation was effective for improvement of heat stability because of high gel content formation. Unirradiated PBS sheets broke immediately at 110 degrees, while the irradiated sample (gel fraction, 50%) by a two step-method did not break even up to 200 minutes at 130 degreesC. The PBS sheets are biodegradable even after crosslinking.

Electrocatalytic mechanism for formaldehyde oxidation on the highly dispersed gold microparticles and the surface characteristics of the electrode

Electrocatalytic mechanism for the electrochemical oxidation of formaldehyde (HCHO) on the highly dispersed Au microparticles electrodeposited on the surface of the glass carbon (GC) electrode in the alkaline Na2CO3/NaHCO3 solution and the surface characteristics of the Au microparticle-modified glass carbon (Au/GC) electrode were studied with in situ FTIR spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the final products of HCHO oxidation is HCOO- at the Au/GC electrode and CO2 at the bulk Au electrode. The difference may be ascribed to the different surface characteristics between the Au/GC electrode and the bulk Au electrode. (C) 1999 Elsevier Science B.V. All rights reserved.

Electrocatalytic oxidation of methanol at the titanium oxide electrode modified with Pt microparticles

The electrocatalytic oxidation of methanol at the Titanium oxide (TiOx, x<2) film modified with Pt microparticles has been studied. The results show that the modified electrodes exhibit a significant electrocatalytic activity and good stability for the oxidation of methanol. Under the optimal conditions, the peak current density at 0.58 V for the oxidation of methanol in the positive-going sweep is about 526 mA/cm(2) at the scan rate of 5 mV/s in 0.5 mol/L CH3OH and 0.5 mol/L H2SO4 solution and the over potential of the methanol oxidation at the modified electrode increases about 30 similar to 40 mV after 70 minutes at the current density of 100 mA/cm(2) and 50 mA/cm(2). The enhanced electrocatalytic activity and good stability are ascribed to the high dispersion of Pt microparticles in and on the TiOx film and the synergistic effect between Pt microparticles and TiOx.