Advanced Materials Research Vols. 47-50

Abstract: Porous calcium phosphate cement (CPC) scaffolds were successfully fabricated utilizing particle-leaching method. Mesenchymal stem cells (MSCs) were cultured, expanded and seeded on the scaffolds and the proliferation and differentiation of MSCs into osteoblastic phenotype were determined using MTT assay, ALP activity and ESEM. The results revealed that the CPC scaffolds were biocompatible and had no negative effects on the MSCs in vitro. The in vivo biocompatibility and osteogenicity of the scaffolds were investigated. Both pure scaffolds and MSCs/scaffold constructs were implanted in rabbit mandibles and studied histologically. The results showed that CPC scaffolds exhibited good biocompatibility and osteoconductivity. Moreover, the introduction of MSCs into the scaffolds dramatically enhanced the efficiency of new bone formation initially.

Abstract: Percutaneous type of orthopedic and dental implants requires not only a good adhesion with bone, but also the ability to form good attachment and seal with connective tissues and skins. Currently, the skin-seal of such implants still remains as a problem to be resolved. Electrochemical processing was used to modify the surface of titanium implants in order to improve the ability of anti-bacteria infection and skin seal around the implants by synthesizing a fluoridated calcium phosphate thin film on titanium substrate. The surface of titanium was cathodically treated in an electrochemical cell. A thin film of about 80 nm thickness was deposited on the titanium surface by controlling the treatment parameters. The dense and gel-like film was composed of calcium phosphate and fluorine ions. Fluorine ion has the anti-bacteria property and could help to improve the skin seal around the percutaneous device. The electrochemical method of fluoridated calcium phosphate thin film synthesis will provide an alternative method for surface treatment of orthopedic and dental implants.

Abstract: By mimicking the microstructure of human cortical bone, a variety of bioactive particle reinforced polymer composites have been developed for hard tissue repair. Apart from biological assessments, these composites must be fully evaluated in terms of their mechanical performance before they can be used in patients. The bioactive particles in these composites are normally hard (relative to matrix materials) and brittle bioceramics such as hydroxyapatite (HA), tricalcium phosphate (TCP), Bioglass, etc. The matrices can be either “biostable” polymers such as high density polyethylene (HDPE) and polysulfone (PSU) or biodegradable polymers such as polyhydroxybutyrate (PHB) and poly(L-lactide) (PLLA). These polymers on their own possess different mechanical properties and display different deformation behaviours. With the incorporation of various amounts of particulate HA, TCP or Bioglass, the bone analogue polymeric composites exhibit a spectrum of deformation and fracture characteristics. In our systematic studies of HA/HDPE, Bioglass/HDPE, HA/PSU, HA/PHB, TCP/PHB and a few other bone analogues biomaterials over the past fifteen years, mechanical tests were conducted under a variety of loading conditions (tension, compression, bending, torsion, etc.). Comparisons of deformation and fracture behaviours of these composites were made and presented. The insights that have been gained are important for developing other bioactive ceramic-polymer composites.

Abstract: Totally biodegradable and osteoconductive composite material consisting of polyhydroxybutyrate (PHB) and β-tricalcium phosphate (β-TCP) was manufactured for bone tissue repair. The composite production process was optimized with the help of differential scanning calorimetry (DSC) analyses. Thermogravimetric analyses (TGA) indicated that intended compositions for TCP/PHB composite could be achieved through this manufacturing route. Scanning electron microscopic (SEM) examinations revealed that TCP/PHB composite containing up to 40 vol.% of β-TCP had satisfactory distribution of micron-sized TCP particles in the composite. The good-quality composite will be further investigated in in vitro and in vivo experiments.

Abstract: Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) was used to make composite scaffolds for bone tissue engineering in our previous studies. To control the degradation rate and process of composite scaffolds, PHBV was blended with poly(L-lactic acid) (PLLA), which has a much higher degradation rate than PHBV, and PHBV/PLLA blends were used as polymer matrices for composite scaffolds. Composite scaffolds based on these blends and containing nano-sized hydroxyapatite (nHA) were fabricated using an emulsion freezing / freeze-drying technique. Non-porous films of PHBV/PLLA blends were prepared using the solvent casting method. In vitro degradation tests of non-porous PHBV/PLLA blends and porous composite scaffolds were conducted by immersing samples in phosphate buffered saline (PBS) for various periods of time. It was found that the composition of polymer blends affected water uptake of films and scaffolds. For PHBV/PLLA-based scaffolds, the incorporated nHA particles also significantly increased water uptake within the initial immersion time. Both PHBV/PLLA blends and composite scaffolds underwent rapid weight losses within the first few weeks. The degradation of composite scaffolds arose from the dissolution of nHA particles and degradation of the PLLA component of polymer blends. Composite scaffolds exhibited enhanced adsorption of bovine serum albumin (BSA), a model protein, in the current study.

Abstract: To improve the biocompatibility and bioactivity of titanium and titanium alloys, a titanium oxide layer was synthesized on Ti, Ti-6Al-4V and NiTi shape memory alloy (SMA) using a H2O2-oxidation and hot water aging technique. The surface of these metals before and after the oxidation treatment was characterized using scanning electron microscopy and energy dispersive X-ray spectroscopy. Because of the synthetic titanium oxide surface layer, the Al and V contents on the surface of as-oxidized Ti-6Al-4V decreased significantly. Similarly, the Ni content on the surface of as-oxidized NiTi SMA was also significantly reduced. Potentiodynamic polarization curves indicated that the synthetic titania layer was more chemically stable than the spontaneous titania film on the metals. Among the three metals, the oxide layer on Ti was the most stable chemically. The in vitro bioactivity of as-oxidized metals was assessed through incubation in simulated body fluid (SBF). Compared to as-oxidized Ti-6Al-4V and NiTi SMA, as-oxidized Ti was the most bioactive.

Abstract: Si-N-O films have drawn researcher’s much attention recently due to their potential superiority in blood compatibility of biomaterials. In this paper, Si-N-O films were synthesized on <100> silicon substrates by pulsed reactive unbalanced magnetron sputtering a single crystal silicon target with high purity in a mixture atmosphere of Ar and N2. XPS and FTIR results showed the Si-N-O films synthesized at higher N2 flux could be described to random bonding model (RBM). In RBM, the Si2p existed in the form of a-Si3N4 and SiNνO4-ν (ν=0,1,2,3,4) components. Platelet adhesion behavior on Si-N-O films was assessed by platelet adhesion test and Lactate dehydrogenase (LDH) assay, qualitatively and quantitatively separately. The correlativity of film chemical structure and blood compatibility was investigated. The results of platelet adhesion and activation showed that the RBM film with higher N/O ratio exhibited favorable blood compatibility. It was shown that the Si-N-O film with specific composition and chemical bonding state was superior in blood compatibility compared to low temperature isotropic carbon (LTIC).

Abstract: This study deals with improving the cytocompatibility of titanium by a coating with heparin(hep), collagen(col) and CD34 antibody. Collagen and heparin molecules were adsorbed onto a titanium surface using a layer-by-layer (LBL) self-assembly technique. The col/hep coating were formed by alternating deposition of negatively charged heparin and positively charged collagen based on electrostatic interactions. Finally the CD34 antibody was absorbed onto the surface of col/hep coating by electrostatic interactions. The chemical composition and surface topography were investigated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The fluorescence microscopy images proved that the CD34 antibody was existed on the surface of the col/hep coating. The SEM results and the MTT test results showed that, compared to the surface of col/hep coating and the surface of titanium, the CD34 surface had better endothelial progenitor cells (EPCs) attachment and proliferation. The EPCs on the CD34 surface displayed the morphology of flat endothelium, and a confluent cell layer after cultured for 2d. This study suggested that this method maybe have good potential for surface modification of cardiovascular devices.

Abstract: In order to improve the abrasion property of polyoxymethylene (POM)，diamond like carbon (DLC) film was deposited on POM substrate by the method of magnetic filtered cathodic vacuum arc deposition (MFCVAD). X-ray photoelectron spectroscopy (XPS) showed that the sp3 fraction decreased with the negative bias voltages increased. According to the result of the nano-indenter, the hardness of POM plates coated with DLC films was significantly harder than POM substrate. The results of ball-on-disc tribological testing demonstrated that the hardest DLC film had the lowest friction coefficient (0.11). The evaluation of in vitro platelet adhesion test indicates that the numbers of adhered and activated platelet on the DLC film deposited under the condition of 0V and 9min were remarkably decreased compared with that of the untreated POM.

Abstract: Percutaneous transluminal coronary angioplasty(PTCA) has become increasingly important in the therapy of coronary artery disease. However, the high restenosis occurrence of 20%～30% in patients limits the applications of this method, but the pathogenesis of restenosis has not yet been fully understood.In this paper, static organ culture system was set up to study the process of restenosis formation after PTCA. The common carotid arteries of atherosclerotic rabbits after PTCA were cultured in the artery organ-culture system and maintained in culture for 7 days. After 1d, 2d, 3d, 4d, 5d, 6d and 7d, MTT-test showed that the activity of vessels in the organ culture system unchanged. Pathology and histological technic were applied to check the intimal morphology especially the endothelial denudation and intimal hyperplasia. The concentration of chemical cytokines NO releasing in the process of restenosis were measured .The results showed the method of static organ culture could be successfully applied to keep the activity of culture arteries and study the process of restenosis formation after PTCA. The endothelial denudation and inflammatory cytokines releasing had intimately relationship with the restenosis after PTCA.