A STUDY OF STRUCTURE AND PROPERTY CHANGES OF BIODEGRADABLE POLYGLYCOLIDE AND POLY(GLYCOLIDE-co-LACTIDE)FIBERS DURING PROCESSING AND IN VITRO DEGRADATION

Structure and properties of bioabsorbable polyglycolide (PGA) and poly(glycolide-co-lactide) (PGA-co-PLA)fibers were investigated during several industrial processing stages and in vitro degradation by means of wide-angle X-raydiffraction (WAXD), dynamic mechanical analysis (DMA) and mechanical property tests. In the orientation stage, the PGAfibers were found to have higher degrees of crystallinity than corresponding PGA-co-PLA samples produced under similarconditions. In the hot-stretching and post-annealing stages, after fibers were braided, PGA samples were found to gain morecrystallinity and higher T_g than PGA-co-PLA samples. The higher crystallinity in PGA fibers resulted in a slower rate ofdegradation. DMA results showed that a great deal of internal stress that was built during orientation and hot-stretchingstages was released in the post-annealing stage for a1l PGA and PGA-co-PLA samples. During earlier stages of in vitrodegradation, both PGA and PGA-co-PLA samples exhibited the typical cleavage-induced crystallization mechanism. Theheat shrinkage in the glass transition area was found to disappear after 6-8 days of degradation for all PGA and PGA-co-PLAsamples, indicating the amorphous portions of the polymers lost orientation after a short period in the buffer solution, mostlikely due to relaxation of the cleaved chains.

Thermal degradation and isothermal crystalline behavior of poly(trimethylene terephthalate)

Poly（trimethylene terephthalate） （PTT） is an excellent fiber material. Its thermal degradation and isothermal crystalline behaviors were in this study investigated using thermogravimetric analysis （TGA）, thermogravimetric analysis-Fourier transform infrared spectroscopy （TGA-FTIR） analysis, differential scanning calorimetry （DSC） and X-ray diffraction （XRD）. The thermal degradation mechanism of PTT follows Mclafferty rearrangement principle. The PTTwithintrinsicviscosity（IV） of 0.74 dL/g has a maximum crystallinity of about 55% at 190 ℃, as demonstrated by DSC and XRD measurements consistently.

Mathematical modeling of drug release from biodegradable polymeric microneedles

Transdermal drug delivery systems have overcome many limitations of other drug administration routes,such as injection pain and first-pass metabolism following oral route,although transdermal drug delivery systems are limited to drugs with low molecular weight.Hence,new emerging technology allowing high molecular weight drug delivery across the skin—known as‘microneedles’—has been developed,which creates microchannels that facilitate drug delivery.In this report,drug-loaded degradable conic microneedles are modeled to characterize the degradation rate and drug release profile.Since a lot of data are available for polylactic acid-co-glycolic acid(PLGA)degradation in the literature,PLGA of various molecular weights-as a biodegradable polymer in the polyester family-is used for modeling and verification of the drug delivery in themicroneedles.The main reaction occurring during polyester degradation is hydrolysis of steric bonds,leading to molecular weight reduction.The acid produced in the degradation has a catalytic effect on the reaction.Changes in water,acid and steric bond concentrations over time and for different radii of microneedles are investigated.To solve the partial and ordinary differential equations simultaneously,finite difference and Runge–Kutta methods are employed,respectively,with the aid of MATLAB.Correlation of the polymer degradation rate with its molecular weight and molecular weight changes versus time are illustrated.Also,drug diffusivity is related to matrix molecular weight.The molecular weight reduction and accumulative drug release within the system are predicted.In order to validate and assess the proposed model,data series of the hydrolytic degradation of aspirin(180.16 Da)-and albumin(66,000 Da)-loaded PLGA(1:1 molar ratio)are used for comparison.The proposed model is in good agreement with experimental data from the literature.Considering diffusion as themain phenomena and autocatalytic effects in the reaction,the drug release profile is predicted.Based on our results for a microneedle containing drug,we are able to estimate drug release rates before fabrication.

Synthesis, Characterization and in vitro Degradation Properties of Poly(Propylene Fumarate-co-Propylene Sebacate) Networks

Poly（propylene fumarate-co-propylene sebacate） （P（PF-co-PS）） was crosslinked with Nvinyl pyrrolidone （N-VP） to form networks. It was investigated as biodegradable bone cement. In this paper, P（PF-co-PS） was synthesized and characterized by ^1H-NMR, FTIR and GPC. The effects of the amount of sebacate segments in P（PF-co-PS） main chains and the quantity of N-vinyl pyrrolidone on the in vitro degradation of the polymer networks were examined. Cylindrical specimens were submerged in phosphate buffered saline （PBS） at 37 ℃ and the pH value of PBS is 7.4 for 10 weeks. The gravimetry and compressive mechanical properties were tested over the degradation period. Networks formed by P（PF-oo-PS）8020/N-VP exhibited higher weight loss and better mechanical properties when compared with poly（propylene fumarate）/N-VP networks. The mechanical properties of P（PF-co-PS）/N-VP can be maintained for a very long time, even for 70 days, the yield strength, fracture strength and compressive modulus are （51.78 ± 2.01） MPa, （52.331 ± 1.84） MPa and （957.78 ± 24.40） MPa, respectively. The results demonstrate that the compressive mechanical properties and degradation velocity can be modulated by the amount of crosslinking agents and sebacate segments along the main chains of copolymers.

Preparation and Degradation Characteristics of Poly(d,1-laetide) Composite Films

PDLLA/CHI/β-TCP/NGF composite films were prepared by a solvent evaporation method. The degradation characteristics of the poly （d, l-lactide） composite films were studied in vitro and in vivo. The acidity produced by poly （d, l-lactide） materials was not obvious. Adding chitosan and β-TCP can relieve the acidity problem and improve strength performance of films. The NGF has influences on the degradation characteristics of films. It is verified that PDLLA/CHI/β-TCP/NGF composite films prepared by solvent evaporation method have excellent degradation characteristics. It can be used as a perfect biomaterial for repairing nerve injuries.

The interphasial degradation of 4.2 V-class poly(ethylene oxide)-based solid batteries beyond electrochemical voltage limit

Solid-state polymer electrolytes(SPEs)have attracted increasing attention due to good interfacial contact,light weight,and easy manufacturing.However,the practical application of SPEs such as the most widely studied poly(ethylene oxide)(PEO)in high-energy solid polymer batteries is still challenging,and the reasons are yet elusive.Here,it is found that the mismatch between PEO and 4.2 V-class cathodes is beyond the limited electrochemical window of PEO in the solid Li Ni_(1/3)Mn_(1/3)Co_(1/3)O_(2)(NMC)-PEO batteries.The initial oxidation of PEO initiates remarkable surface reconstruction of NMC grains in solid batteries that are different from the situation in liquid electrolytes.Well-aligned nanovoids are observed in NMC grains during the diffusion of surface reconstruction layers towards the bulk in solid batteries.The substantial interphasial degradation,therefore,blocks smooth Li+transport across the NMC-PEO interface and causes performance degradation.A thin yet effective Li F-containing protection layer on NMC can effectively stabilize the NMC-PEO interface with a greatly improved lifespan of NMC|PEO|Li batteries.This work deepens the understanding of degradations in high-voltage solid-state polymer batteries.

Fabrication, Crosslinking and in vitro Biocompatibility of a Novel Degradable Nano-structure Urethral Tubular Scaffold

A degradable poly（lactic-co-glycolic acid, LA：GA=80：20）（PLGA） urethral tubular scaffold was fabricated by electrospinning. In order to enhance the mechanical properties, the scaffold was crosslinked with glutaraldehyde. The structure and properties of the crosslinked scaffolds were investigated by the mechanical property testing, scanning electron microscopy（SEM）, degradability test in vitro and 3-（4,5）-dimethylthiahiazo（-z-yl）-3,5-diphenytetrazo- liumromide（MTT）. The results show that the scaffold has the nano-structure. The pore size and the porosity are suitable for cell seeding, growth and extracellular matrix production. Although influenced by the crosslinking slightly, the pore size and the porosity could still support cell proliferation and tissuse formation. The mechanical properties are remarkably increased by the crosslinking of glutaraldehyde, and it could meet the demands of a urethral stent. The scaffold could completely collapse within 70 d. The results of the biocompatibility test show that the PLGA scaffold had no cytotoxicity.

THERMAL DEGRADATION OF POLY(ARYLENE SULFIDE SULFONE)/NMETHYLPYRROLIDONE CRYSTAL SOLVATE

The thermal degradation of poly（arylene sulfide sulfone）/N-methylpyrrolidone （PASS/NMP） crystal solvate was studied by thermogravimetric analysis （TGA） and was compared with pure PASS in order to determine the way in which the formation of the crystal solvate affected the thermal properties of the polymer. The activation energy of the solid state process was determined using Kissinger＇s method, which does not require knowledge of the reaction mechanism （RM）, to be 174.18 kJ/mol which was lower than that for pure PASS （E = 214 kJ/mol）. The study of master curves together with interpretation of integral methods, allows confirmation that the thermal degradation mechanism for PASS in the crystal solvate system is a decelerated Rn type, which is a solid-state process based on a phase boundary controlled reaction, in the conversion range considered. Whereas, the pure PASS follows a decelerated Dn thermodegradation mechanism in the same conversion range.

The Green Composites: Millet Husk Fiber (MHF) Filled Poly Lactic Acid (PLA) and Degradability Effects on Environment

This study provides an overview on green composites degradability. Practically, the main drawbacks of using natural fibers are their poor dimensional stability, degradability and high degree of moisture absorption. While, end use of product from natural fiber filled or reinforced composites has become subject of concern to material engineers and scientist. The major properties of natural fiber reinforced polymer composites are greatly dependent on the hydrophilic tendency and dimensional stability of the fibers used, morphology aspect ratio for long fiber, while voids for powder fibers. The effects of chemical treatments on cellulosic fibers that are used as reinforcements for thermoplastics were studied. The chemical source for the treatments is alkalization. The significance of chemically-treated natural fibers is seen through the improvement of mechanical properties. The untreated fiber composites degrade faster in municipal soil compared to treated fiber composites.

Construction and evaluation of co-electrospun poly (butylene succinate)/gelatin materials as potential vascular grafts

In this study,a series of poly(butylene succinate)(PBSU)/gelatin composites were prepared by electrospinning.The morphology,physicochemical analysis,biomechanical properties,biocompatibility,and biodegradability of the materials were evaluated.The results showed that the ultimate tensile stress of the vascular PBSU/gelatin grafts at(95/5),(90/10),(85/15),and(80/20)was(4.17±0.54)MPa,(3.81±0.44)MPa,2.94±0.69 MPa and 2.11±0.72 MPa respectively,and the burst pressure was(282.7±22.3)kPa,(295.3±3.9)kPa,(306.8±13.9)kPa and(307.6±9.0)kPa respectively,which met the requirements of tissue-engineered blood vessels.Furthermore,the addition of gelatin improved the hydrophilicity and degradation properties of PBSU,thus enhancing cell adhesion and promoting the inward growth of vascular smooth muscle cells.In summary,the research in this paper provides a useful reference for the preparation and optimization of vascular scaffolds.

Synthesis and Characterization of Poly(L-lactide-co-glycolide)

Poly （ l- lactide- co-glycolide ） （ PLGA ） with different compositions was prepared using stannous octaoate as catalyst by bulk ring-opening copolymerization of l-lactide and glycolide. The structure and properties of the PLGA copolymers were cbaracterized by means of attenuated total reflectance-Fourier transform infrared （ATR-FTIR）, ^1H NMR, differential scanning calorimeter （ DSC and X-ray diffraction （XRD） methods, The experimented results indicate that the synthetic conditions and the composition of copolymers have art obvious influence on the structure of PLGA copolymers, The degradation rate of eopolymers increased with the increasing of the glycolide component in the copolymers.

pH-Compensation Effect of Lysine on the Acidic Degradation of Electrospun Poly( lactide-co-glycolide) Fibers in PBS

Electrospun aligned ultrafine fibers of poly( lactide-coglycolide)( PLGA) can be used to construct biomimetic scaffolds for engineering those structurally anisotropic and dense tissues( e. g.,tendon,ligament,etc.). But the acidic degradation products of the PLGA could result in p H decrease in the vicinity of the scaffolds,which may give rise to biocompatibility concerns. To address the noted problem, this study was designed to evaluate the p Hcompensation capacity of using Lysine( Lys) —a kind of basic amino acid on the acidic degradation products of PLGA. Ultrafine PLGA( 50∶ 50) fibers with 0,10%,20%,and 30% by weight of Lys loadings were prepared by a stable jet electrospinning( SJES)approach. The morphology,structure,and mechanical properties of the electrospun aligned fibrous mats of Lys-incorporated PLGA( 50∶50) were characterized by scanning electron microscope( SEM),Fourier transform infrared spectroscopy( FTIR),and tensile testing,respectively. Thereafter,the fibrous PLGA( 50 ∶50) scaffolds were subjected to degradation by being immersed in phosphate buffered saline( PBS,p H 6. 86) solution at 37 ℃ for 5weeks. Our results show that the formed Lys / PLGA composite ultrafine fibers have a well-aligned and uniform morphology with a fineness of ca. 1 #m in diameter. Introduction of Lys led to increased mechanical performance; that is,when the Lys loading is less than 30%,tensile strength and Young's modulus of the aligned Lys / PLGA fibers reached up to the impressive values of 84. 5 MPa and 2. 4 GPa,respectively. Degradation results show that the p H of the PLGA group fell to 5. 6 in 5 weeks while the p H of the Lys /PLGA groups with 10%,20%, and 30% of Lys loadings was maintained at 6. 3, 6. 5 and 6. 7, respectively. This work demonstrated that incorporation of Lys into electrospun PLGA fibers could be an effective approach in mediating the p H decrease caused by the acidic degradation products of the PLGA.

STUDIES ON ULTRASONIC DEGRADATION AND BLOCK COPOLYMERIZATION OF POLYACRYLAMIDE AND POLY(ETHYLENE OXIDE)

The kinetics of ultrasonic degradation of aqueous solution of polyacrylamide（PAM）and poly（ethyleneoxide）（PEO）as well as ultrasonic block copolymerization of aqueous solution of the mixture of PAM/PEOwere studied respectively.The degradation reaction of PEO follows a linear relationship between（P1-P∞）-1and irradiation time,while that of PAM follows a linear relationship between（P1-P∞）-1/2and irradiation time.The structure of the copolymer was identified by IR,NMR and DTA,and the copolymer prepared is a blockone.The copolymer formed by irradiating 1% aqueous solution of PEO/PAM mixture（1:1）for a period of40min.at 18.2 kHz with a sonic intensity corresponding to 2.OA input current on the reversed main circuitamounts to 61.8%.

Comparison of Photochemical and Thermal Degradation of Poly （Lactic Acid） Doped by Nanosilver

A comparison of thermal and photochemical degradation of poly （lactic acid） film materials （10/am） containing nanosilver are studied by FTlR （Fourier transform infrared） spectroscopy and DSC （differential scanning calorimetry）. Rates of thermal and photochemical degradation are determined by measuring the relative changes of absorbance （A/Ao） of selected bands in PLA （polylactic acid） spectra. Comparison of the effect of both degradation on PLA structure showed that nanosilver act as a stabilizer for photodegradation at 254 nm. As oppose, thermal degradation at 80 ~C indicate, that nanosilver accelerates PLA degradation at the temperature. Glass transition and crystallization/melting processes occurring in PLA and PLA/Ag nanocomposites during both degradation processes were also compared.

Preparation and Characterization of Poly(β-Amino Ester) Capsules for Slow Release of Bioactive Material

Network structures from poly(β-amino ester) (PAE) were synthesized for applying as drug delivery matrix via a simplified addition polymerization method. It can hold an active organic compound (drug) that has an effect as antitumor activity in order to control its release. PAE was prepared from piperazine and 1,4-butandiol diacrylate with different molar ratios. The active compound was mixed with the prepared polymer while warming for 15 minutes to obtain the capsule product. The resulting polymer structures and the surface morphology of the PAE capsules before and after encapsulation with the active drug were characterized by FT-IR and SEM, respectively. Swelling and degradation behavior of PAE were studied. The characterization showed that the obtained network structure of PAE depends on the molar ratio between the reactants. The optimum ratio of the reactants was found to be 1:1. Therefore, stable and white product as well as good holding capability for drug produced. The SEM studies illustrate good dispersion and holding properties of the drug into the network structure of the prepared polymer. In vitro, the release results of the drug from the PAE capsules indicated that the capsules were able to give sustained release of drug in DMF up to 10 days at 25°C.

Poly(lactic acid)-aspirin microspheres prepared via the traditional and improved solvent evaporation methods and its application performances

Drug-loaded microspheres are significant for the development of modern pharmaceutical products. It is well known that the taken of aspirin for long-term increases the risk of serious gastrointestinal complications, therefore a controllable delivery of aspirin is of importance to lighten those side effects. In this work, poly(lactic acid)(PLA) was chosen as the carrier to prepare PLA-aspirin microspheres by using the traditional and the improved solvent evaporation methods. It was found that no matter which experimental condition was, the encapsulation efficiency of aspirin was higher by using the improved method than that of the traditional method. Specifically, when the concentration of polyvinyl alcohol = 1%(mass),the polymer concentration = 1:20, the oil/water rate = 1:2.5, PLA-aspirin microspheres were obtained via the improved method with a high yield of 82.83%(mass) and an encapsulation efficiency of 44.09%. PLAaspirin microspheres were then prepared continuously using the improved method, which further enhanced the encapsulation efficiency to 54.56%. Approximate 85% aspirin released from microspheres within 7 days. Obvious degradation which was represented by reduction on hardness was observed by soaking microspheres in PBS for 60 days. This work is of interest because it provides a continuous route to prepare PLA-aspirin microspheres continuously with a high drug encapsulation efficiency.

Physical and degradation properties of PLGA scaffolds fabricated by salt fusion technique

Tissue engineering scaffolds require a controlled pore size and interconnected pore structures to support the host tissue growth. In the present study, three dimensional （3D） hybrid scaffolds of poly lactic acid （PLA） and poly glycolic acid （PGA） were fabricated using solvent casting/particulate leaching. In this case, partially fused NaCl particles were used as porogen （200-300μ） to improve the overall porosity （≥90%） and internal texture of scaffolds. Differential scanning calorimeter （DSC） analysis of these porous scaffolds revealed a gradual reduction in glass transition temperature （Tg） （from 48°C to 42.5°C） with increase in hydrophilic PGA content. The potential applications of these scaffolds as implants were further tested for their biocompatibility and biodegradability in four simulated body fluid （SBF） types in vitro. Whereas, simulated body fluid （SBF） Type1 with the optimal amount of HCO 3 ions was found to be more appropriate and sensible for testing the bioactivity of scaffolds. Among three combinations of polymer scaffolds, sample B with a ratio of 75：25 of PLA： PGA showed greater stability in body fluids （pH 7.2） with an optimum degradation rate （9% to 12% approx）. X-ray diffractogram also confirmed a thin layer of hydroxyapatite deposition over sample B with all SBF types in vitro.

Degradation of Mg-Zn-Y-Nd alloy intestinal stent and its effect on the growth of intestinal endothelial tissue in rabbit model

Biodegradable magnesium alloys have excellent properties with respect to biodegradability, biocompatibility, and biomechanics, which may indicate a possibility of its application in intestinal stents. Investigation of Mg-Zn-Y-Nd alloy’s application in intestinal stents has been performed. This study aims to investigate the degradation behavior of Mg-Zn-Y-Nd alloy intestinal stents coated with poly(L-lactide)/paclitaxel in the intestinal environment and its biocompatibility with intestinal tissue. In this paper, Mg-Zn-Y-Nd alloy’s corrosion properties were evaluated by the immersion test in human feces, SEM and XRD, and animal tests. In vitro results showed that when the Mg-Zn-Y-Nd alloy was immersed in human feces for two weeks, its corrosion resistance could be improved by micro arc oxidation(MAO) and poly-l-lactide(PLLA) dual coating. Additionally, this result was also confirmed in vivo experiments by rabbit model. And animal tests also demonstrated that the Mg-Zn-Y-Nd alloy with MAO/PLLA/paclitaxel dual coating drug-eluting stents could inhibit the proliferation of local intestinal tissue around the stents. However, in vivo studies illustrated that the intestinal stents gradually degraded in rabbit model within 12 days.Considering the degradation rate of the stent was faster than expected in rabbits, the support performance of the scaffold requires further improvement.

Synthesis and characterization of poly(p-dioxanone)-based degradable copolymers with enhanced thermal and hydrolytic stabilities

Herein, we presented a novel biodegradable copolymer via the chain extending reaction of poly(pdioxanone)-co-poly(2-(2-hydroxyethoxy) benzoate)(PPDO-co-PDHB) prepolymer with hexamethylene diisocyanate(HDI) as a chain extender. The structures and molecular weight of PPDO-co-PDHB prepolymer and PPDO-co-PDHB-PU chain-extended copolymer are characterized via hydrogen nuclear magnetic resonance spectroscopy(1 H NMR) and viscosity test. The relationship between the molecular structures and properties of the chain-extended copolymers is established. The PPDO-co-PDHB-PU copolymers possess a better thermal stability comparing with the PPDO homopolymer. The study of mechanical properties shows that the elongation-at-break of PPDO-co-PDHB-PU is much higher than that of PPDO. The investigation of hydrolytic degradation behaviors indicates the degradation rate of PPDO can be controlled by adjusting the PDHB compositions, and proves that chain-extended copolymers exhibit an excellent hydrolytic stability being better than that of PPDO.