Ruan Jianming

Review – recent development of ring-opening polymerization of cyclic esters using aluminum complexes

With the development of the technology of ring-opening polymerization (ROP) rapidly, many novel aluminum complexes have been designed, synthesized, and applied in initiating ROP of cyclic esters and new stereoregular polymerization mechanism of lactide polymerization have been reported. In this review, the mechanism for ROP of cyclic ester, synthesis of aluminum complexes containing tetradendete ligand, tridentate ligand, bidentate ligand, and bimetallic complexes containing aluminum were reviewed. We hope to give some helpful information for designing aluminum complexes, improving activity, and stereoregularity of aluminum complexes.

Effects of Surface Modification on the Properties of Poly(lactide-co-glycolide) Composite Materials

HA/PLGA composites with and without APS-modification were successfully prepared via solution dispersion method. The mechanical test of composites was performed by the three-point-bending test and the micrographs of materials were observed using SEM. The results indicate that by surface modification, uniform HA particles without agglomeration were obtained. Furthermore, the bending strengths and moduli of APS-HA/PLGA composites are higher than those of unmodified composites, which both first increased and then significantly decreased with increasing the HA content. The biocompatibility results show that modified HA/PLGA composite are more favorable biomaterials for cell adhesion, differentiation and proliferation than unmodified composites.

The Kinetics of Melting Crystallization of Poly-L-Lactide

The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of poly-L-lactide (PLLA) were investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM) and x-ray diffraction (XRD). Crystallization performed at lower cooling rates (2°C·min−1) is accompanied by a variation of the kinetics around 118°C. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10°C·min−1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90°C to 140°C. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118°C, and the value of Kg(II)/Kg(III) is 2.17 [Kg(II) = 6.025 × 105K2, Kg(III) = 1.307 × 106 K2].

Preparation and Properties of Bioactive Composite Based on Bioactive Glass and Poly-L-Lactide

Bioactive and bioresorbable composite was fabricated based on poly-L-lactide (PLLA) and bioactive glass (average particle size: 4.24 µm) by the combination of solvent evaporation technique and hot pressing. Bioactive glass granules are distributed homogeneously in the composite. With the increasing of the amount of bioactive glass, the bending strength and shearing strength of composite decrease while the bending modulus increases. PLLA/bioactive glass composites present a typical morphology of brittle failure with a smooth fracture surface. The biocompatibility test shows that the bioactive glass existing in the composite facilitates both adhesion and proliferation of rat fibroblast on the PLLA/bioactive glass composite film.

Rheological behavior of fumed silica suspension in polyethylene glycol

The rheological behavior of fumed silica suspensions in polyethylene glycol(PEG) was studied at steady and oscillatory shear stress using AR 2000 stress controlled rheometer. The systems show reversible shear thickening behavior and the shear-thickening behavior can be explained by the clustering mechanism. The viscosity and the degree of shear-thickening of the systems strongly depend on the mass fraction of the silica, the molecular weigh of PEG and the frequency used in the rheological measurement. The silica volume fraction of the systems is 1.16%–3.62%, corresponding to the mass fraction of 4%–9%. The shear-thickening taking place in the low volume fraction may contribute to the fractal nature of the silica. At oscillatory shear stress, when the shear stress is less than the critical stress, the storage modulus decreases significantly, meanwhile the loss modulus and the complex viscosity almost remain unchanged; when the shear stress is larger than the critical stress, the storage modulus, the loss modulus and the complex viscosity increase with the increase of shear stress. The loss modulus is larger than the storage modulus in the range of stress studied and both moduli depend on frequency.

Preparation of high viscosity average molecular mass poly-L-lactide

Poly-L-lactide(PLLA) was synthesized by ring-opening polymerization from high purity L-lactide with tin octoate as initiator, and characterized by means of infrared, and 1H-nuclear magnetic resonance. The influences of initiator concentration, polymerization temperature and polymerization time on the viscosity average molecular mass of PLLA were investigated. The effects of different purification methods on the concentration of initiator and viscosity average molecular mass were also studied. PLLA with a viscosity average molecular mass of about 50.5×104 was obtained when polymerization was conducted for 24 h at 140 °C with the molar ratio of monomer to purification initator being 12 000. After purification, the concentration of tin octoate decreases; however, the effect of different purification methods on the viscosity average molecular mass of PLLA is different, and the obtained PLLA is a typical amorphous polymeric material. The crystallinity of PLLA decreases with the increase of viscosity average molecular mass.

Preparation and Properties of Poly(lactide-co-glycolide)/Bone Meals Composite Materials

Poly(lactide-co-glycolide)/bone meals composites using poly(lactide-co-glycolide) (PLGA) and bone meals (BM) as the starting materials were successfully prepared via solution dispersion method. Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction and BET were used to characterize the resulting PLGA and bone meals. The mechanical properties of composites were carried out by the three-point-bending test, and the micrographs of cross-section of composites were observed using SEM. The results indicate that both the bending strength and modulus of PLGA/BM composites increased with bone meals increasing up to 10 wt%, then decreased with bone meals content, indicating that the fracture feature of PLGA/BM composites changed from typical brittle to ductile fracture when the bone meals content changed from 0 to 10 wt% and from ductile to brittle facture while bone meals content ranging from 10 to 20 wt%. It was further confirmed by SEM images of composites. The biocompatibility results show that resulted PLGA/BM composites are favorable biomaterials for cell adhesion, differentiation and proliferation. PLGA/BM composite has shown great potential for biomedical applications as biodegradable polymers.

Synthesis and structural characterization of macroporous bioactive glass

Porous sol-gel glass of CaO-SiO2-P2O5 system with macropores larger than 100 μm was prepared by adding stearic acid as pore former when the sintering was carried out at 700 °C for 3 h. The sol-gel porous glass shows an amorphous structure. The diameter of the pore created by pore former varies from 100 to 300 μm, and macroporous glass has a narrow and small pore size distribution in mesoporous scale. The porosity and pore size of macroporous bioactive glass can be controlled.

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.

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 °C. 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 L-lactide has great influence on the relative molecular mass of poly(L-lactide).