Shenguo Wang

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.

The effect of composition of calcium phosphate composite scaffolds on the formation of tooth tissue from human dental pulp stem cells.

Different approaches towards making 3-dimensional (3-D) bioengineered tooth for future replacement therapy have been developed including scaffold-based tooth regeneration. However, selection of optimal scaffold for future clinical application remains a challenge. In the present study, we tested biocompatibility of four different types of 3-D scaffolds for tooth-tissue regeneration, including a pure poly(lactide-co-glycolide) (PLGA) (70/30, mol/mol) scaffold and three types of calcium phosphate contained composites scaffolds that were 50 wt% of PLGA combined with 50 wt% of hydroxyapatite (HA), tricalcium phosphate (TCP) or calcium carbonate hydroxyapatite (CDHA) respectively. These scaffolds were fabricated by the particle leaching in combination with phase separation technology. Surface modification of these scaffolds was further performed by an ammonia plasma treatment and anchorage of collagen technology. Effect of composition of the composite scaffolds on proliferation of human dental pulp stem cells (DPSCs) was accessed using in vitro MTT assay and in vivo BrdU labeling. Differentiation capability of the DPSCs in the scaffolds was analyzed by measurement of the levels of calcified tissue formation and ALP activity. Our results showed that while the calcium phosphate contained compound is able to support regeneration of tooth tissue effectively, the PLGA/TCP scaffold is more appropriate for the proliferation and differentiation of DPSCs. Furthermore, seeding of dissociated 4-dpn rat tooth bud cells on the PLGA/TCP scaffold generated dentin- and pulp-like tissues. Our results demonstrate that the PLGA/TCP scaffold is superior to the other three scaffolds for tooth-tissue regeneration, especially for dentin formation.

Responses of grassland ecosystems to precipitation and land use along the Northeast China Transect

Abstract The Northeast China Transect (NECT) has been used to study how water availability influences the composition of plant functional types, soil organic matter, net primary production, trace gas flux, and land-use patterns. We discuss relations of plant species number, soil C and N and above-ground biomass with a precipitation gradient and interactions with land-use practices (grassland fencing, mowing and grazing), on the basis of data from the west part of NECT. The results indicate: 1. The above-ground biomass of grassland communities has a linear relationship with precipitation under three land-use practices, while plant species number, soil C, and total soil N have linear relationships with precipitation under fencing and mowing; under grazing the relationships are non-linear. 2. Plant species number, soil C and total soil N have strong linear relationships with above-ground biomass under both fencing and mowing, while they seem to have non-linear relationships under grazing. 3. Land-use practices along the precipitation gradient result not only in changes in grassland communities but also in qualitative changes of their structure and function. 4. Grasslands are more vulnerable to changes in climate under mowing than under fencing, and are more capable to store C in soil and plants. 5. At a given precipitation level, number of plant species, above-ground biomass, and soil C are higher under low to medium intensity of human activities (mowing and grazing). A better understanding of how different intensities of human activities will affect the structure and function of grassland will require further research. Abbreviations: NECT = Northeast China Transect; NPP = Net primary production; GCTE = Global Change and Terrestrial Ecosystems; IGBP = International Geosphere-Biosphere Programme.

The impact of PLGA scaffold orientation on in vitro cartilage regeneration

The success of in vitro cartilage regeneration provides a promising approach for cartilage repair. However, the currently engineered cartilage in vitro is unsatisfactory for clinical application due to non-homogeneous structure, inadequate thickness, and poor mechanical property. It has been widely reported that orientation of scaffolds can promote cell migration and thus probably contributes to improving tissue regeneration. This study explored the impact of microtubular oriented scaffold on in vitro cartilage regeneration. Porcine articular chondrocytes were seeded into microtubule-oriented PLGA scaffolds and non-oriented scaffolds respectively. A long-term in vitro culture followed by a long-term in vivo implantation was performed to evaluate the influence of scaffold orientation on cartilage regeneration. The current results showed that the oriented scaffolds could efficiently promote cell migration towards the inner region of the constructs. After 12 weeks of in vitro culture, the chondrocyte-scaffold constructs in the oriented group formed thicker cartilage with more homogeneous structure, stronger mechanical property, and higher cartilage matrix content compared to the non-oriented group. Furthermore, the in vitro engineered cartilage based on oriented scaffolds showed better cartilage formation in terms of size, wet weight, and homogeneity after 12-week in vivo implantation in nude mice. These results indicated that the longitudinal microtubular orientation of scaffolds can efficiently improve the structure and function of in vitro engineered cartilage.

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.

Fabrication and cell affinity of biomimetic structured PLGA/articular cartilage ECM composite scaffold.

An ideal scaffold for cartilage tissue engineering should be biomimetic in not only mechanical property and biochemical composition, but also the morphological structure. In this research, we fabricated a composite scaffold with oriented structure to mimic cartilage physiological morphology, where natural nanofibrous articular cartilage extracellular matrix (ACECM) was used to mimic the biochemical composition, and synthetic PLGA was used to enhance the mechanical strength of ACECM. The composite scaffold has well oriented structure and more than 89% of porosity as well as about 107xa0μm of average pore diameter. The composite scaffold was compared with ACECM and PLGA scaffolds. Cell proliferation test showed that the number of MSCs in ACECM and composite scaffolds was noticeably bigger than that in PLGA scaffold, which was coincident with results of SEM observation and cell viability staining. The water absorption of ACECM and composite scaffolds were 22.1 and 10.2 times respectively, which was much higher than that of PLGA scaffolds (3.8 times). The compressive modulus of composite scaffold in hydrous status was 1.03xa0MPa, which was near 10 times higher than that of hydrous ACECM scaffold. The aforementioned results suggested that the composite scaffold has the potential for application in cartilage tissue engineering.

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