Degradation rate is an important index for evaluating biomaterials. The authors' aim was to determine whether the degradation rate of biomaterials is different in distinct tissues and to clarify the underlying mechanism of degradation. The collagen-chitosan (CG-CS) composite scaffolds were prepared using freeze-drying technology. The porosity, water absorption and swelling ratio of the scaffolds were tested in vitro. The scaffolds were implanted into the subcutis, spinal cord and brain tissues of SD rats, the rate of degradation was assessed by continuous monitoring of weight loss, the pathological changes of target areas were observed by histological staining, and matrix metalloproteinase 9 (MMP-9) and lysozyme were detected at the rapid stage of degradation of the scaffolds. Physical and chemical property testing confirmed that CG-CS composite scaffold components can meet the biological requirements of in vivo transplantation. The in vivo experimental results showed that the scaffolds were completely absorbed in the subcutis at 12 days, the scaffolds in the spinal cord and brain groups exhibited progressive mass loss starting from the 3rd week, and a substantial fraction of the scaffold was degraded at 12 weeks. HE staining found that compared with the spinal cord and brain groups, macrophages and capillaries appeared earlier in the subcutis group, and the number was significantly higher (P < 0.05). Western blot analysis showed that the MMP-9 and lysozyme levels in the subcutis were higher than those in the spinal cord and brain (P < 0.05). The results of in vivo experiments demonstrated that the CG-CS scaffold has good biocompatibility and biodegradability, while the rate of degradation was significantly different between the three tissues at the same time point. Macrophage behavior and vascularization in different parts of the body may result in control over the balance of degradation and reconstruction.

Conventional fabrication methods lack the ability to control both macro- and micro-structures of generated scaffolds. Three-dimensional printing is a solid free-form fabrication method that provides novel ways to create customized scaffolds with high precision and accuracy. In this study, an electrically controlled cortical impactor was used to induce randomized brain tissue defects. The overall shape of scaffolds was designed using rat-specific anatomical data obtained from magnetic resonance imaging, and the internal structure was created by computer-aided design. As the result of limitations arising from insufficient resolution of the manufacturing process, we magnified the size of the cavity model prototype five-fold to successfully fabricate customized collagen-chitosan scaffolds using three-dimensional printing. Results demonstrated that scaffolds have three-dimensional porous structures, high porosity, highly specific surface areas, pore connectivity and good internal characteristics. Neural stem cells co-cultured with scaffolds showed good viability, indicating good biocompatibility and biodegradability. This technique may be a promising new strategy for regenerating complex damaged brain tissues, and helps pave the way toward personalized medicine.

BACKGROUND:Biological scaffolds should be gradually degraded with the formation of new tissues, so the degradation rate is an important index for evaluating scaffold materials. Conventional testing methods make an impact on the assessment of the scaffold degradation rate at different sites due to some limitations. OBJECTIVE:To evaluate the degradation rate of col agen-chitosan (CG-CS) composite implanted into the subcutaneous, spinal cord and brain tissues of Sprague-Dawley rats and to explore the underlying mechanism. METHODS:A 3 mm×3 mm disc-shaped CG-CS composite scaffold was prepared, and its microstructure was observed under scanning electron microscope. Nerve stem cel s were co-cultured with CG-CS scaffold, and then the cel viability was detected through cel counting kit-8 assay to assess the biocompatibility. Sprague-Dawley rats were randomly divided into three groups:cortex, spinal cord, and subcutaneous groups. The CG-CS scaffold was implanted into cortex, spinal cord T9, or back T9, respectively. The rats were sacrificed at different time points, and three rats in each group were subjected to the scaffold removal to evaluate the scaffold degradation rate. The resting rats were used to prepare the tissue sections for histological observation of the scaffold and the surrounding tissues. RESULTS AND CONCLUSION:Scanning electron microscope revealed that the CG-CS composite scaffold had a three-dimensional porous structure with a pore size that met the biological requirements of in vivo transplantation. The in vivo experiments showed that no graft rejection occurred, suggesting that the scaffold has good biocompatibility. The degradation rate was fastest in the subcutaneous group, and the scaffold was degraded completely with 12 days, which was significantly higher than that in the spinal cord and brain groups (P<0.05). The degradation rate in the spinal cord group was significantly higher than that in the brain group since the 3rd week (P<0.05);the scaffold degraded completely in the spinal cord group, while the partial scaffold could still be found in the brain group. The number of blood vessels and the scores of macrophage infiltration were as fol ows:subcutaneous group>spinal cord group>brain group (P<0.05). Our findings suggest that the CG-CS scaffold holds a good biocompatibility and its degradation rate differs significantly among groups. In the field of tissue engineering, the complex microenvironment of target tissues and the host response after stent implantation should have effects on the balance between the biodegradation rate and reconstitution rate of the organism.