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.

The Syntheses and Properties of Poly(L- Lactide)

Poly (L-lactide) was prepared by bulk polymerization ofL-lactide at 140°C in the presence of stannous octoate. The polymer products were characterized by number average molecular weight Mn, weight average molecular weight Mw and molecular weight distribution MWD (M w/M n) respectively. The results showed that stannous octoate was a high effective catalyst, and coordinated insertion mechanism of the reaction was proposed.

Poly(L-lactide)-Poly(ethylene glycol) Multiblock Copolymers: Synthesis and Properties

Poly (L-lactide)-poly(ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. These copolymers presented special properties, such as better miscibility between the two components, low crystallinity and better hydrophilicity, which can be modulated by adjusting the block lengths of the two components.

NON-ISOTHERMAL CRYSTALLIZATION OF POLY(L-LACTIDE)(PLLA) UNDER QUIESCENT AND STEADY SHEAR CONDITIONS

The non-isothermal crystallization of poly（L-lactide） （PLLA） under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy （POM） with a hot shear stage and wide-angle X-ray diffraction （WAXD）. The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s^-1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.

Different crystallinity of poly(d,l-lactide-co-p-dioxanone) copolymers acquired by control of chain microstructure

Poly（d,l-lactide-co-p-dioxanone） （P（LA-co-PDO）） copolymers with different chain microstructures were synthesized by onestep or two-step bulk ring-opening polymerizations of d,l-lactide （LA） and p-dioxanone （PDO） monomers using stannous octoate [Sn（Oct）2]/n-dodecanol as the initiating system. The average sequence lengths of the lactidyl （LLA） and dioxanyl （LpDo） units were calculated from the ^1H NMR spectra. It was found that both LLA and Lpoo values from the two-step syntheses were significantly longer than those from the corresponding one-step syntheses, indicating more blocky structure achieved for the twostep copolymers. Corresponding to this difference in microstructure, the two-step copolymers were semi-crystalline, while the one-step copolymers were completely amorphous. In conclusion, the crystallinity of P（LA-co-PDO） copolymers could be adjusted conveniently to meet specific applications by changing the microstructure of the copolymers via different polymerization routes.

Bioactivity of bioresorbable composite based on bioactive glass and poly-L-lactide

Bioactive and bioresorbable composite was fabricated by a solvent evaporation technique using poly-L-lactide(PLLA) and bioactive glass (average particle size: 6.8 μm). Bioactive glass granules are homogeneously distributed in the composite with microcrack structure. The formation of hydroxyapatite(HA) on the composite in simulated body fluid(SBF) was analyzed by scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), and Raman spectra. Rod-like HA crystals deposit on the surface of PLLA/bioactive glass composite after soaking for 3 d. Both rod-like crystals and HA layer form on the surface for 14 d in SBF. The high bioactivity of PLLA/bioactive glass composite indicates the potential of materials for integration with bone.

Preparation of poly(lactide-co-glycolide)microspheres and evaluation of pharmacokinetics and tissue distribution of BDMC-PLGA-MS in rats

The aim of the present study was to develop a novel long-acting Poly(lactic-co-glycolic acid)(PLGA)-based microspheres formulation of Bisdemethoxycurcum(BDMC) by emulsionsolvent evaporation method. Meanwhile, the effects of the volume ratio of the dispersed phase and continuous phase, the concentration of PLGA and PVA, the theoretical drug loading and stirring speed were investigated. The mean diameter of the microspheres was 8.5 μm and the size distribution was narrow. The encapsulation efficiency(EE) and drug loading efficiency(DLE) of BDME loaded PLGA microspheres(BDMC-PLGA-MS) was 94.18% and 8.14%,respectively. In an in vitro study of drug release, it can be concluded that the BDMC-PLGAMS exhibited sustained and long-term release properties for 96 h. Stability studies suggested that the microspheres we prepared had a very good stability. Furthermore, the results of an in vivo study indicated that the BDMC-PLGA-MS had sustained release effect and was mainly distributed in the lung tissue, and less distribution in other tissues, which indicated that microspheres could be an effective parenteral carrier for the delivery of BDMC in lung cancer treatment.

Microwave-assisted Polymerization of D,L-Lactide with Stannous Octanoate as Catalyst

Poly (lactic acid) (PLA) was synthesized by microwave-assisted ring-opening polymerization of D, L-lactide with stannous octanoate (SnOct(2)) as catalyst. Its weight-average molar mass (M-w) ranged from 39000 to 67000 and the polydispersity index from 1.3 to 1.7. The polymerization rate was much faster than that of the conventional thermal polymerization. A degradation of newly formed PLA in reaction mixture by microwave irradiation was observed.

Synthesis and characterization of biodegradable polymer:Poly (ethene maleic acid ester-co-D,L-lactide acid)

A novel biodegradable polymer--poly （ethene maleic acid ester-co-D,L-lactide acid） was synthesized by copolymerizing lactide and prepolymer, which was prepared by the condensation of maleic anhydride and glycol, using p-toluene sulphonic acid as a catalyst, attempting to improve the hydrophilicity, increase flexibility and modulate the degradation rate. FTIR,^1H NMR, MALLS and DSC were employed to characterize these polymers.

Preparation of monomer of degradable biomaterial poly(L-lactide)

L-lactide was prepared from L-lactic acid with stannous octoate as the catalyst. The effects of reaction temperature and pressure on the ingredient of crude lactide were investigated. The results show that the mass fraction of meso-lactide increases with the increasing reaction temperature. Crude lactide containing 85.4% L-lactide is obtained when the reaction temperature is 200 ℃. High purity of L-lactide with a yield of 40.6 % is obtained by synthetic purifying method. The properties of L-lactide are characterized by optical purity, infrared spectrum and gas chromatogram/mass spectrum. The L-lactide samples purified by recrystallization and synthetic purifying methods are polymerized with the catalyst of stannous octoate, and the corresponding viscosity average relative molecular masses of poly(L-lactide) are 2.85 × 105 and 5.05 × 105 , respectively. This indicates that the optical purity of Llactide has great influence on the relative molecular mass of poly(L-lactide).

Preparation and characterization of poly(D,L-lactide) and its porous biomaterials

Poly(D,L-lactide) was synthesized by indirect method from D,L-lactic acid and characterized by infrared spectrum and proton nuclear magnetic resonance. The influences of monomer purity, initiator concentration, polymerization temperature and polymerization time on the relative molecular mass of poly(D, L-lactide) were investigated. The polylactide was made into porous materials by using solvent-casting particulate-leaching method. Under the optimized conditions, polylactides with a viscosity average molecular mass up to 1.82×105 are obtained and the results are fairly reproducible. Scanning electron microscope observation indicates that the sample is highly porous and well-distributed with good interconnections between pores and the pore size of porous materials is in the range from 200 μm to 500 μm and it can be used as scaffold for bone tissue engineering.

RING-OPENING COPOLYMERIZATION OF DL-LACTIDE AND POLY(ETHYLENE GLYCOL) INITIATED BY LANTHANUM ACETATE AND APPLICATION OF THE COPOLYMER AS MATRIX OF MICROSPHERES CONTAINING VIBRIO CHOLERA ANTIGENS

Poly-dl-lactide-poly(ethylene glycol) (PELA) triblock copolymers were synthesized with lanthanum acetate as the initiator. PELA microspheres with entrapped Vibrio Cholera antigen and outer membrane protein (OMP) were prepared by a double emulsion W/O/W based on solvent extraction methods. The obtained microspheres showed smooth and spherical surface and their size varied between 0.5 and 5.0 mu m, which are suitable for oral targeting delivery system. The distribution tests in rabbits and mice through scanning electronic micrography and fluorescence microscope indicated that microspheres have successfully reached the immunization-related tissues, such as the liver, spleen and intestinal peyer's patches, following oral administration. The PELA microspheres were also evaluated as an efficient antigen delivery system by enhancing a higher protective ratio against live Vibrios Cholera.

The Ring-opening Polymerization of D, L-Lactide Initiated with Stannous Octoate

The ring-opening polymerization of D, L-lactide in the melt was systematically investigated by using stannous octoate as the initiator. The molecular weight of poly (D, L-lactide) was characterized with M,. Mn and Mw respectively. The results indicated that five variables, namely purity of monomer, initiator to monomer ratio, vacuum level, polymerization temperature and polymerization time had different influences on the molecular weight and molecular weight distribution of poly(D. L-lactide).

Silk Fibroin/Poly-L-lactide Lactone Bi-layered Membranes for Guided Bone Regeneration

After removal of the caries or diseased teeth,the alveolar ridge will undergo absorption and atrophy.When the amount of alveolar bone is insufficient,it will cause an inability to perform effective dental implant restoration.In order to control the absorption and promote the repair and regeneration of alveolar ridge,a method of implanting guided bone regeneration(GBR)membranes at the extraction site is often used.In this study,silk fibroin(SF)and poly-L-lactide lactone(PLCL)were used to prepare bilayered guided bone regeneration membranes,and its morphology,hydrophilicity,surface roughness and mechanical properties were studied.At the same time,the drug release behaviors and cell compatibility of the bilayered membranes were studied.The results showed that SF/PLCL bi-layered membranes had good mechanical properties and surface hydrophilicity,and the drug-loaded bi-layered membranes had good cell compatibility.The bilayered membranes fabricated in this study are of potential for applying in the oral health field to promote bone regeneration.

Montmorillonite/Poly(L-Lactide)microcomposite spheres as reservoirs of antidepressant drugs and their controlled release property

This work evaluates intercalation of Nortriptyline(NT)and Venlafaxine(VFX)in an interlayer gallery of Na^(+)-MMT(Montmorillonite),which was further compounded with Poly(LLactide)(PLLA)to form microcomposite spheres(MPs)for oral controlled drug delivery.The XRD patterns,thermal and spectroscopic analyses indicated intercalation of drugs into the MMT interlayer that was stabilized by electrostatic interaction.No significant changes in structural and functional properties of drugs were found in the MMT layers.In vitro drug release studies showed controlled release pattern.

Biodegradation of Absorbable Hydroxyapatite/Poly-DL-lactide Composites in Different Environment

To develop a new generation of absorbable fracture fixation devices with enhanced biocompatibility, the biodegradation mechanism and its influence on the cellular response at the tissue/implant interface of hydroxyapatite/ poly DL lactide (HA/PDLLA) composites were investigated in vitro and in vivo.HA/PDLLA rods were immersed in phosphate buffered saline,or implanted in muscle and bony tissue for 52 weeks.Scanning electron microscopic and histological studies were done.The degradation rate was the slowest in vitro,slower in muscle tissue and fast in bone.In vitro, the composites degraded heterogeneously and a hollow structure was formed.In bone,the limited clearing capacity leads to the accumulation of oligomeric debris,which contribute totally to the autocatalytic effect.So,the fastest degradation and intense tissue response were seen.In muscle tissue,oligomeric debris migrated into vicinal fibers over a long distance from the original implant cavity and the tissue reactions were,however, quite moderate.For the same size organic/inorganic composite,the environment where it was placed is the major factor in determining its biodegradation process and cellular reaction.In living tissue,factors such as cells,enzymes and mechanical stress have an obvious influence on the biodegradation and biological process at the tissue/implant interface.The biocompatibility of the HA/PDLLA composites is enhanced with the incorporating of the resorbable HA microparticles.

Improving Polylactide Toughness by Plasticizing with Low Molecular Weight Polylactide-Poly(Butylene Succinate)Copolymer

A low-molecular-weight polylactide-poly(butylene succinate)(PLA-PBS)copolymer was synthesized and incorporated into polylactide(PLA)as a novel toughening agent by solvent casting.The copolymer had the same chemical structure and function as PLA and it was used as a plasticizer to PLA.The copolymer was blended with PLA at a weight ratio from 2 to 10 wt%.Phase separation between PLA and PLA-PBS was not observed from their scanning electron microscopy(SEM)images and the crystal structure of PLA almost remained unchanged based on the X-ray diffraction(XRD)measurement.The melt flow index(MFI)of the blends was higher as the amount of PLA-PBS increased,indicating that the block copolymer did improve the mobility of the PLA chains.Moreover,tensile tests revealed that PLA with greater PLA-PBS copolymer exhibited higher elongation at break and it reached the maximum at 8 wt%of PLA-PBS in PLA,which was around 6 times higher than that of pure PLA.Furthermore,the glass transition temperature,measured by differential scanning calorimetry(DSC),markedly decreased with an increasing amount of the copolymer as it decreased from 61.2℃ for pure PLA to 41.3℃when it was blended with 10 wt%PLA-PBS copolymer.Therefore,the PLA-PBS copolymer was shown to be a promising plasticizer for fully biobased and toughened PLA.

Poly (L-lactide-co-e-caprolactone)/Functionalized CNTs Nanocomposite,Thermal and Mechanical Properties

Multiwalled carbon nanotubes(MWCNTs) grafted with poly(L-lactide-e-caprolactone)(PCLA) were synthesized by ring opening polymerization reaction and used as a reinforcement for neat PCLA.Scanning electron microscopy(SEM) revealed that the applied tensile load on the composite was transferred to the MWNT-OH-g-PCLA,loading to a strain failure of the MWCNTs rather than an adhesive failure between the MWCNTs and the matrix.

NOVEL COMPOSITES OF POLY(L-LACTIDE)AND SURFACE MODIFIED BIOACTIVE SiO_2-CaO-P_2O_5 GEL NANOPARTICLES:MECHANICAL AND BIOLOGICAL PROPERTIES

Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite. All these results showed that the mBAG/PLLA composite would be a promising material for bone tissues regeneration.

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.