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The aims of the present study were to fabricate a novel porous polylactic acid (PLLA) composite scaffold and evaluate the capacity of the scaffold in carrying recombinant bone morphogenetic protein 2 (rhBMP2) for engineering bone formation. The structures of the PLLA scaffolds were evaluated by SEM and the controlled release of rhBMP2 from the composite scaffolds was assayed by ELISA. Bone induction by the scaffolds loaded with or without rhBMP2 was performed in the calf muscle of twenty Wistar rats for 3, 7, 10, 14, and 28 days. Tissue specimens were examined by Masson's trichrome and von Kossa stainings, and immunohistochemistry of bone proteins. Our results indicated that a moderate foreign body reaction was found in control scaffolds, which lasted for 4 weeks. The addition of rhBMP2 to this novel scaffold dramatically alleviated the adverse responses to PLLA. Enhanced deposition of collagen matrix and endochondral formation were observed in rhBMP2-PLLA scaffolds at 7-10 days, compatible with an early release of rhBMP2 in the composite scaffolds. Bone sialoprotein and osteopontin were demonstrated simultaneously. Von Kossa staining was observed in the test group at 10-14 days. In conclusion, the PLLA scaffolds exhibited the capability of carrying rhBMP2 for inducing bone formation within 2 weeks. These results suggest that rhBMP2-PLLA scaffold may be applicable in tissue engineering., ((c) 2007 Wiley Periodicals, Inc.)

In the present work, RGDS (Arg-Gly-Asp-Ser) was immobilized on PLLA scaffolds with plasma treatment. The amount of immobilization, determined by HPLC, was confirmed to be in the effective order. Results from the culture of rat osteosarcoma (ROS), osteoblastic-like cells, demonstrate that the immobilization of RGDS could effectively enhance the attachment of ROS cells on PLLA and increase the cell density in PLLA scaffolds. In addition, experiments of in vitro mineralization indicate that there were more cells and mineralization focci in the RGDS-immobilized scaffolds, suggesting a tendency to form bone-like tissues, compared with the unmodified PLLA scaffold. On the other hand, the PLLA scaffolds immobilized with RGES (Arg-Gly-Glu-Ser) were much less effective in promotion of ROS attachment, suggesting that the enhancement on cell attachment was mainly due to the recognition of RGDS by the adhesion receptors on the cell membrane. The results presented in this work demonstrate that RGDS could be successfully immobilized on PLLA scaffolds with plasma treatment and such modification can make PLLA scaffolds more suitable for culture of osteoblast-like cells and for generation of bone-like tissues.

Gamma-poly(glutamic acid) (gamma-PGA), a hydrophilic and biodegradable polymer, was chosen to modify chitosan matrices to produce a gamma-PGA/chitosan composite biomaterial. Three types of both dense and porous composite matrices containing different amounts of gamma-PGA were fabricated. Chitosan and gamma-PGA matrices were also prepared as controls. Fluorescence staining indicated that chitosan and gamma-PGA were evenly distributed in the composite matrices. SEM micrographs showed that an interconnected porous structure with a pore size of 30-100 microm was present in all porous matrices except the gamma-PGA ones. By increasing the percentage of gamma-PGA from 0% to 20%, the swelling ratio of the matrices was enhanced from 1.6 to 3.2. Similarly, the contact angle of the matrices decreased from 113 degrees to 94 degrees . These data suggested that the surface hydrophilicity, water absorption rate, and swelling ratio were improved by adding gamma-PGA to the matrices. Additionally, the mechanical strength of the porous gamma-PGA/chitosan matrices was about 25-50%, higher than that of the unmodified chitosan matrices. The composite matrices were also examined and found to be an appropriate environment for cell attachment and proliferation. The cell density on the 20% gamma-PGA-modified matrices was almost triple that on the unmodified chitosan matrices on day 5. In summary, the gamma-PGA/chitosan composite matrices, due to their better hydrophilic, cytocompatible, and mechanical properties, are very promising biomaterials for tissue engineering applications.

Freeze-fixation and freeze-gelation methods are presented in this paper which can be used to prepare highly porous scaffolds without using the time and energy consuming freeze-drying process. The porous structure was generated during the freeze of a polymer solution, following which either the solvent was extracted by a non-solvent or the polymer was gelled under the freezing condition; thus, the porous structure would not be destructed during the subsequent drying stage. Compared with the freeze-drying method, the presented methods are time and energy-saving, with less residual solvent, and easier to be scaled up. Besides, the problem of formation of surface skin can be resolved and the limitation of using solvent with low boiling point can be lifted by the presented methods. With the freeze-extraction and freeze-gelation methods, porous PLLA, PLGA, chitosan and alginate scaffolds were successfully fabricated. In addition to the presentation of the morphologies of the fabricated scaffolds, preliminary data of cell culture on them are as well included in the present work.

Abstract: Chitosan scaffolds were modified with RGDS (Arg–Gly–Asp–Ser) in the present work via an imide-bond forming reaction between amino groups in chitosan and carboxyl groups in peptides. Successful immobilization was verified with FTIR spectroscopy, and the immobilized amount was determined to be on the order of 10-12mol/cm2 through analysis of the immobilized amino acids. Results of experiments of cell culture with rat osteosarcoma (ROS) cells demonstrated that RGDS immobilization could enhance the attachment of ROS cells onto the chitosan, resulting in higher cell density attached to the RGDS-modified scaffold than to the unmodified scaffold. It should be noted that only RGDS, but not other peptide such as RGES, is effective in enhancing cell attachment and possible proliferation. Experiments of in vitro mineralization indicated that there were more cells on the RGDS-modified scaffold than on the unmodified scaffold, which tended to form bone-like tissues. The results presented in this work suggest that immobilization of RGDS can make chitosan scaffolds more compatible for the culture of osteoblast-like cells and the regeneration of bone-like tissues. [Copyright &y& Elsevier]

Polyglycolide (PGA) and chitosan mixture solution was prepared using solvents of low toxicity to create novel, porous, biocompatible, degradable, and modifiable hybrid matrices for biomedical applications. The porosity of these PGA-chitosan hybrid matrices (P/C matrices) was created by a thermally induced phase separation method. Two types of the P/C hybrid matrices containing 70 wt% PGA (P/C-1 matrix) and 30 wt% PGA (P/C-2 matrix) were fabricated. Chitosan matrix was also prepared for comparison. A 35-day in vitro degradation revealed that the weight losses for the P/C-1 and P/C-2 matrices were similar (∼61%), but the releases of glycolic acid from the P/C-1 and P/C-2 matrices were 95% and 60%, respectively. The P/C-1 matrix had higher porosity and higher mechanical strength than the P/C-2 and chitosan matrices. Fibroblast cells cultivated in these matrices proliferated well and the cell density was the highest in the P/C-1 matrix, followed by the chitosan and P/C-2 matrices, suggesting good biocompatibility for the P/C-1 matrix. We thereby concluded that the P/C-1 matrix, due to its high strength, porosity, biocompatibility and degradability, is a promising biomaterial. The presence of chitosan in the P/C matrices provides many amino groups for further modifications such as biomolecule conjugation and thus enhances the application potential of the P/C hybrid matrices in tissue engineering. [Copyright &y& Elsevier]