Study On Cellular 3-Dimensional (3-D) Cultivation In Bone Tissue Engineering And The Mechanical Micro-circumstance

Objective To establish a biological model in a non-invasive way using a high-resolution micro-Computed Tomography(micro-CT) system and Finite Element Analysis(FEA) to mimic the microscopic mechanical environment of cell seeding in scaffold for bone tissue engineering. To investigate the local strain of cell/scaffold complex.Bovine cancellous bone was selected aiming to prepare scaffold for tissue engineering.Osteoblast was aimed to seeded in scaffold and cultured in three-dimension(3D).To explore biological responses and potential mechanism under physiological mechanic strain of the osteoblast to verify the data gained from computed model.Apparent compress strain at 1000μεand 2000μεwas applied dynamically.To study the feasibility of research on microscopic mechanical environment and corresponding biological responses by engineering modeling and analysis.Methods Mechanical response of bone is representative of bone remodeling and modeling,which indicates a significant impact of mechanical loading during the cultivation of complex in bone tissue engineering.Effects has been taken on cellular proliferation,migration, extra-cellular matrix synthesis,secretion and differentiation of Mesenchymal Stem Cells(MSC) etc.Therefore mechanical micro-circumstance of cellular 3D cultivation in bone tissue engineering plays a crucial role in extensive investigation.Especially the introduction of finite element method in combination with such nontraditional imaging technology of high resolution as Micro-CT has already been used for visualization and quantification of microscopic stress/strain environment in different scaffolds.The xenogeneic cancellous bone harvested from bovine ilium was scanned by the micro-CT after a set of physicochemical treatment.The structural parameters obtained from micro-CT were analyzed to evaluate biomechanical properties of the xenogeneic cancellous bone used as the scaffold in bone tissue engineering. The bone volume fraction(BV/TV),degree of anisotropy(DA),Euler Number,trabecular thickness(Tb.Th),and the three radii of the mean intercept length(MIL) ellipsoid(al,a2,and a3) were recorded.A non-invasive visualization and measurement was explored by combining micro-CT as a novel imaging technology with Finite Element(FE) method.The surface meshes generated in medical image processing software MIMICS based on micro-CT images were converted into finite element models which were assigned material properties according to the Gray Value.All the FE models of samples were ultimately subjected to physiological apparent strain using FE analysis software ANSYS to figure out the local strain.The macro-structure and surface observation was detected by scanning electron microscope(SEM).Apparent compress strain ranged from1000μεto 2000μεwas applied for 5 days at 8 rain,3Hz per day when osteoblasts were seeded.The cell proliferation was examined by MTT colorimetry.Expression of alkaline phosphatase(ALP),bone glaprotein(BGP) collagen-Ⅰwas estimated compared with the expression under no mechanical strain.Results The four microstructural parameters in both strain groups were in normal distribution and homogeneity of variance,except for Euler Number,and no statistically significant change in both different load groups could be detected.There were stress concentration existed on local surface of trabacular bone within each bone column.More than 80%elements bore 800μεand below when subjected to apparent displacement of 1000μεapplied on both the top surface and the bottom,While 2000μεapplied,less than 1500μεwas figured in 75%elements.The number of elements decreased when corresponding strain was on decrease.Conclusion A non-invasive visualization and measurement was explored effectively and this approach also shed light on the correlation between strain and stress about the specific scaffold material,for an accurate prediction of the mechanical properties of the xenogeneic cancellous bone,it was more reasonable that bone mineral density was made correlate with the Gray Value of segmented 3D images,which were better than those studies based on the isotropy hypothesis.