Key Engineering Materials Vols. 330-332

Abstract: Hydrogel biomaterials were synthesized by radical copolymerization of N-vinyl pyrrolidone (NVP) and 2-hydroxyethylmathacrylate (HEMA), with azobisisobutyronitrile (AIBN) as an initiator, reacting at 60~70°C for 24 hours, which were designed as contact lens due to the good chemical stability and high biocompatibility. The absorbency of bovine serum albumin (BSA) was measured by the ultraviolet spectrophotometer. The influence of pH, initial protein concentration and ionic strength were investigated in detail. The results showed that the absorption of protein on hydrogel biomaterials increased with the immersing time increasing, and was stable during 4 days. The absorption of protein on hydrogel increased with the equilibrium water content increasing. The protein absorption on hydrogels reduced the permeability of the oxygen of the biomaterials.

Abstract: Attempt to increase the mechanical properties of porous bioceramics, a dense/porous structured β-TCP bioceramics that mimic the characteristics of nature bone were fabricated. Experimental results show that the dense/porous structured β-TCP bioceramics demonstrated excellent mechanical properties with compressive strength up to 74 MPa and elastic modulus up to 960 MPa, which could be tailored by the dense/porous cross-sectional area ratio obeying the rule of exponential growth. The interface between the dense and porous bioceramics is connected compactly and tightly with some micropores distributed in the matrix of both porous and dense counterparts. The dense/porous structure of β-TCP bioceramics may provide an effective way to increase the mechanical properties of porous bioceramics for bone regeneration at weight bearing sites.

Abstract: Computerized X-ray micro tomography (micro CT) is a powerful technique for studying the structure and properties of porous scaffold. A variety of sample parameters can be studied using a single micro CT scan [1]. In general a segmented data set is a required for most quantitative analysis. However, segmentation of CT data can be difficult due to the artifacts in micro CT images such as blurred interfaces due to the machine contrast transfer function and the partial volume effect. Therefore the segmentation can be biased and prone to errors. Many methods have been developed to improve segmentation, however the interface problem has not been solved perfectly [2]. Porous scaffolds suffer from these effects because of their high surface to volume ratio and hence large interface. In this paper we discuss the interface problem in detail and demonstrate the effect of voxel size on the histograms of CT images of porous scaffold as well as a thresholding method based on 2 dimensional histogram is also presented. The potential of this method in more complicated scenarios such as 3-phase system is currently being investigated [3].

Abstract: Computerized X-ray microtomography (micro CT) is a powerful technique for imaging and quantification in biomedical materials research. Mapping of various tissue/implants in 3-dimension, which is not achievable with traditional histological slices, is particularly desirable in ex-vivo implant analysis. However, due to a variety of artifacts during image formation, especially the blurred interfaces due to the machine contrast transfer function and the partial volume effect, quantification based on traditional histograms is not accurate. In this work we propose a new 2-dimensional histogram and its application in the analysis of micro CT data of ex-vivo implants, which significantly improve the clarity of the definition of different phases and drastically reduced the artifacts of segmentation compared to conventional methods.

Abstract: In this study, the bioactive composites based on β-tricalcium phosphate (β-TCP), bioglass (BG) and poly lactic acid (PLA) were prepared. The microstructure, degradability and reaction products of the scaffold soaked in a simulated body fluid (SBF) at 36.5°C for different days were characterized through scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR) and induced coupled plasma spectroscopy (ICP). The weight loss and strength decrease with the time were tested. The results showed that at the same porosity, the degradability of the scaffold samples decreased as followed: β-TCP/BG/PLA>β－TCP/BG>β－TCP.The materials had highly bioactive response ability to the Simulate Body Fluid (SBF) and promptly induced a bone like HA layer on the surface of the scaffolds when immersed in the SBF.

Abstract: The surfaces of BC (bacterial cellulose) nanofibers are covered with homogeneous nano-sized precipitates upon exposure to SBF. The characteristics of the nanocompoiste scaffolds are characterized by XRD, FTIR, TEM and SEM. It is believed that the the HAp/BC nanocomposite scaffold are promising in applications of bone tissue engineering.

Abstract: Calcium phosphate compounds, in particular HA and β-TCP, are the principal synthetic materials used for bone substitutes. To assess the feasibility for further grafting of drug delivery systems, a pure HA was elaborated with specific internal material porosities and then tested on its biological effectiveness. The cell viability tests with L132 cells confirmed the excellent cytocompatibility of HA and the graphite powder. MC3T3-E1 osteoblasts were grown on HA conditioned with culture medium and FCS for 2h. All HA samples produced a higher proliferation and vitality rates than the TCPS controls; the micro-porous HA inducing the highest cell growth near 150%. The macro/meso-porous HA is easily colonized by MC3T3-E1 osteoblasts As to the cell morphology, no significant differences are observed between control cells and those grown on the HA samples. Cytochemical staining of osteoblasts revealed a well developed cytoskeleton with strong stress fibres oriented in the cells in their longitudinal direction. Labelling of the focal adhesion contacts with anti-vinculin showed a less developed adhesion process in the cells on the different HA substrates, which may explain the above mentioned increase of proliferation.

Abstract: Degradation of surface modified β-tricalcium phosphate (β-TCP) and poly L lactic acid (PLLA) composite scaffolds were investigated in vitro. Bending and compressive strengths were tested by electromechanical universal material testing machine. Molecular weight changes of lactic acid during degradation were measured by gel permeation chromatography (GPC). Phase composition of the surface after soaking was analyzed by Fourier transform infrared ray (FTIR). The surface and cross section of scaffold samples after degradation were observed by Scanning electron microscope (SEM).The results show that degradation speed can be controlled by adjusting the ratio of β-TCP to PLLA in the composite. PLLA can compound more closely with surface modified β-TCP than with non-modified one. The final compressive strength and bending strength of the scaffolds reach 7.11MPa and 2.20MPa respectively, which satisfies the need for bone tissue engineering scaffolds in clinic applications.

Abstract: In the present study, two methods for the production of three-dimensional scaffolds made of bioactive ceramics are presented. Depending on the method, the final product can be composed by pure hydroxyapatite or biphasic: hydroxiapatite + tricalcium phosphate. Bioactivity tests showed that all scaffolds are bioactive. Preliminary studies with adipose stem cells indicated biocompatibility of both scaffolds.

Abstract: The new type of bone tissue engineering scaffold composed of the sol-gel derived bioactive glass particles, type I collagen, hyaluronic acid and phosphatidylserine were prepared through cross-linking and freeze-drying techniques. SEM observation indicated that the scaffold possessed a 3-D interconnected porous structure and a high porosity. The properties of bio-mineralization and cells biocompatibility were investigated using SBF immersion and cells culture methods combined with SEM, XRD and FTIR techniques. The study revealed that this biomimetic scaffold possessed satisfactory functions of cells attachment, bio-mineralization, and cells biocompatibility. The porous structure and the surface of the scaffold which was covered by a bone-like HA crystal layer due to bio-mineralization were profitable for cells attachment and spread.