Jianzhong Bei

Enhanced cell affinity of poly (D,L-lactide) by combining plasma treatment with collagen anchorage.

Surface properties of poly (D,L-lactide) (PDLLA) were modified by combining plasma treatment and collagen modification. The changes of surface properties were characterized by contact angles, surface energy, X-ray photoelectron spectra and scanning electron microscopy. The mouse 3T3 fibroblasts were used as model cells to evaluate the cell affinity of PDLLA before and after modification. Effects of different modification methods including plasma treatment, collagen coating and combining plasma treatment with collagen anchorage were investigated and compared. The results showed that the hydrophilicity and surface-free energy were improved and reduced, respectively, after each modification. Plasma pre-treatment could improve the roughness as it incorporated the polar groups and positively charged groups onto the sample surface; so the plasma pre-treated surface would benefit in anchoring more collagen tightly. As a result, cell affinity of PDLLA modified by combining plasma treatment with collagen anchorage was greatly improved. The modified materials could endure rinsing by PBS, which would facilitate further application when the modified materials were used as cells scaffold in tissue engineering.

A novel porous cells scaffold made of polylactide–dextran blend by combining phase-separation and particle-leaching techniques

In this study, a kind of biodegradable material was developed by blending polylactide (PLA) with natural biodegradable dextran, and a novel sponge-like scaffold made of it was fabricated thereof using solvent-casting and particle-leaching technique. To obtain a uniform blend of PLA and dextran by simple solvent-casting method, hydroxyls of dextran should be protected via trimethylsilyl (TMS) groups to make dextran soluble in organic solvents. Benzene was found among the few solvents that could dissolve this TMS-protected dextran (TMSD) well, however, it was not a good solvent for PLA. Therefore, a homogeneous mixed solution of PLA and TMSD could be obtained when a mixture of dichloroform (DCM) and benzene (v/v = 6/4) was used. By this technique, PLA-dextran blend films and even PLA films were observed a microporous structure (pore size around 5-10 microm) formation throughout the films under scanning electron microscope (SEM). Scaffolds that were prepared by dissolving PLA and TMSD in mixed solvent of DCM and benzene and using salt as porogen, were observed the formation of micropores (pore size around 5-10 microm) in the cellular walls of macropores (pore size around 100-200 microm). This microporous structure was closely related to the phase separation occurring during films or foams formation, which was mainly due to the different solubility of PLA and TMSD in benzene, as well as the different evaporation rates of DCM and benzene. In comparison with PLA, the surface and bulk hydrophilicity of PLA-dextran blend films or foams were significantly improved after the TMS groups were removed in methanol, and the results of cell culture on these polymeric substrates exhibited an enhancement on cell attachment and proliferation.

Cell adhesion on gaseous plasma modified poly-(l-lactide) surface under shear stress field

A series of gases were used for plasma treatment of poly-(L-lactide) (PLLA) under various conditions such as atmosphere, electric power, pressure and time. The NH(3) was preferably selected for modifying the surface of PLLA because it can obtain appropriate hydrophilicity and surface energy with high polar component compared to other gases. Subsequently, cells were seeded onto NH(3) modified surface and exposed to 29.5N/m(2) of shear stress field by means of a parallel plate flow chamber in order to get good insight into the influence of N-containing incorporation on cell retention, cell morphology, and cell shape factor. The results showed that cell retention on the modified PLLA was much higher than that on the unmodified one. The NH(3) plasma modified PLLA with high cell affinity and resistance to shear stress was gained. Surface hydrophilicity, surface energy with high polar component and N-containing groups may play an important role in enhancing cell resistance to shear stress. It revealed that the parallel plate flow chamber is an effective device for evaluating the effects of surface modification on the cell affinity of a material.

Biodegradable poly(L-lactide)-poly(ethylene glycol) multiblock copolymer: synthesis and evaluation of cell affinity.

A series of poly(L-lactide)-poly(ethylene glycol) multiblock copolymers (Multi-PLE) with high molecular weight were synthesized and successfully used to fabricate three-dimensional scaffolds. Using mouse NIH 3T3 fibroblasts as model cells, the cell affinity of various Multi-PLE copolymers was evaluated and compared with that of poly(L-lactide) (PLLA) by means of cell attachment efficiency measurement, scanning electron microscopy observation and MTT assay. On one hand, the results showed that the cell attachment efficiency on Multi-PLE 4/1(4/1 refers to the molar ratio of lactidyl units to ethylene oxide units) films was close to that on PLLA film, however, the other Multi-PLE films exhibited much lower cell attachment efficiency than PLLA film, such as Multi-PLE 2/1 and Multi-PLE 1/1, which had higher PEG content. On the other hand, it was interesting to find that cell proliferation on Multi-PLE4/1 and Multi-PLE2/1 scaffolds was better than that on PLLA scaffold, which was closely related to the improved hydrophilicity of Multi-PLE copolymers due to the incorporation of PEG in comparison with pure PLLA. The Multi-PLE copolymer scaffolds with appropriate hydrophilicity were in favor of mass transportation, and then of cell proliferation and cell affinity. It meant that the cell proliferation would be much improved by increasing the hydrophilicity of the three-dimensional scaffolds, which even outweighed the disadvantages of the cell attachment efficiency reduction with the incorporation of PEG.

Cell affinity for bFGF immobilized heparin-containing poly(lactide-co-glycolide) scaffolds.

In order to effectively and uniformly immobilize basic fibroblast growth factor (bFGF) to thick PLGA scaffold, the heparin-conjugated PLGA (H-PLGA) was synthesized at the first by reaction between heparin and a low molecular weight PLGA. Then heparin-containing PLGA (H-PLGA/PLGA) scaffold was fabricated by blending the H-PLGA with a high molecular weight PLGA. Finally, bFGF was immobilized on the H-PLGA/PLGA scaffold mainly by static electricity action between them. The effect of H-PLGA content on bFGF binding efficiency of the H-PLGA/PLGA scaffolds was investigated. It was found that bFGF binding efficiency increased with increasing H-PLGA content. The bound bFGF can release in vitro slowly from the H-PLGA/PLGA scaffolds and last over two weeks. The released bFGF has still preserved its bioactivity. The attachment and growth of mouse 3T3 fibroblasts on the H-PLGA/PLGA scaffolds were better than that on the PLGA scaffold, however bFGF immobilized H-PLGA/PLGA scaffolds showed much better cell affinity. Therefore, the method to use the H-PLGA/PLGA scaffold for immobilizing bFGF is not only effective for slow delivering bFGF with bioactivity, but also can be used for fabricating thick scaffold where bFGF could be combined and uniformly distributed.

Morphology and biodegradation of microspheres of polyester–polyether block copolymer based on polycaprolactone/polylactide/poly(ethylene oxide)

Porous microspheres of polyester–polyether block copolymer based on polycaprolactone/polylactide/poly(ethylene oxide) (PCEL) were prepared by an emulsification–solvent evaporation technique. The effect of hydrophilicity/hydrophobicity of the polymer on the morphology of the PCEL microspheres was studied and compared with that of polycaprolactone (PCL) and polycaprolactone/poly(ethylene oxide) block copolymer (PCE) microspheres. It was demonstrated by X-ray photoelectron spectroscopy (XPS) that the enrichment of PEO segments on the surface of the microspheres occurred during solvent evaporation of the microdrops and lead to porous structure of the microspheres. The effects of the content and length of PEO segments of the PCEL polymer on the morphology of the microspheres were studied. The degradation behaviour of film-like and microsphere-like PCEL was investigated at pH 7.4 and 37u2009±u20091u2009°C. The shape of the PCEL samples had no obvious effect on the degradation rate of the material and homogeneous degradation was a main process. The degradation rate of PCEL microspheres was enhanced in the presence of the enzyme lipase. 1H NMR measurements revealed that the PEO content reduced with degradation time because the PEO segment was broken down and dissolved in the medium during degradation. n n n n© 2000 Society of Chemical Industry

Synthesis and characterization of polycaprolactone (B)–poly(lactide‐co‐glycolide) (A) ABA block copolymer

Novel poly(lactide-co-glycolide) (PLGA)/polycaprolactone (PCL) ABA block copolymers were synthesized by bulk copolymerization of glycolide and lactide with PCL diols prepolymer using stannous octoate as catalyst. The resulting copolymers were characterized by various analytical techniques including gel permeation chromatography, IR, 1H nuclear magnetic resonance, differential scanning calorimeter and X-ray diffractometry. Mechanical properties and hydrophilicity of the copolymers were also studied. Data showed that the copolymers presented a part-regular structure, containing both PCL crystalline and amorphous PLGA domains. The properties of these copolymers can be adjusted by changing the compositions of the copolymers. Copyright

Polycaprolactone-poly(ethylene-glycol) block copolymer. IV: Biodegradation behaviorin vitro andin vivo

The biodegration behavior of polycaprolactone–poly(ethylene glycol) block copolymer (PCL–b–PEG) was identified by degradation tests in vitro and in vivo. The tests in vitro and in vivo were carried out by immersing samples in pH 5.0, 7.2 and 9.0 buffer solutions with or without lipase at 25.0, 37.0 and 50.0±°C, and implanting samples in the back or small intestine of rats. It was found that the degradation rate of the PCL–b–PEG was increased with increasing PEG content, temperature, acidity or alkalinity, and it was accelerated by the presence of enzyme. The fastest degradation rate was observed in the physiological condition of the sample being implanted in the body of animals. It has been shown that the PCL–b–PEG copolymer is a possible biodegradable polymer.

Hydrolytic degradation of polyester–polyether block copolymer based on polycaprolactone/poly(ethylene glycol)/polylactide

Polyester–polyether block copolymers based on polycaprolactone/poly(ethylene glycol)/polylactide (PCEL) with various compositions were synthesized by direct copolymerization of ϵ-caprolactone, L-lactide and PEG (6000) in the presence of stannous octoate at 130u2009°C for 56u2009hr. The degradation behavior of the copolymers was investigated in a pH 7.4 phosphate buffer solution at 37 ±1u2009°C. Various techniques such as weight, gel permeation chromatography, 1H nuclear magnetic resonance, differential scanning calorimetry and X-ray diffractometry were used to monitor the changes in water absorption, weight loss, molar mass, molar mass distribution, thermal properties and compositions. The results show that the hydrophilicity of copolymer was enhanced with increasing poly(ethylene oxide) content, which led to the PEG sequences fast release and an increase in weight loss of the copolymer. Bimodal chromatograms were detected in the degradation, which were attributed to the degradation mechanism of the partial crystalline polymer proceeding predominantly in amorphous zones. Copyright

Tissue engineering and peripheral nerve regeneration (III)

The biodegradation rate and biocompatibility of poly (d, / -lactide) (PDLLA)in vivo were evaluated. The aim of this study was to establish a nerve guide constructed by the PDLLA with 3-D microenvironment and to repair a 10 mm of sciatic nerve gap in rats. The process of the nerve regeneration was investigated by histological assessment, electrophysiological examination, and determination of wet weight recovery rate of the gastrocnemius muscle. After 3 weeks, the nerve guide had changed from a transparent to an opaque status. The conduit was degraded and absorbed partly and had lost their strength with breakage at the 9th week of postoperation. At the conclusion of 12 weeks, proximal and distal end of nerves were anastomosed by nerve regeneration and the conduit vanished completely. The results suggest that PDLLA conduits may serve for peripheral nerve regeneration and PDLLA is a sort of hopeful candidate for tissue engineering.