Key Engineering Materials Vols. 330-332

Abstract: In this study, an ACP-DCPD based Calcium phosphate cement (CPC) scaffold with a porosity of 88% was prepared by using Na3PO4 as a poregen and then modified by collagen and chitosan. The results showed that collagen and chitosan obviously increased the compressive strength. Cell culture showed that the cell can migrate, attach, proliferate and differentiate on the surface of the materials and the pores walls. This CPC scaffold modified with collagen or chitosan was a promising material to be used in bone tissue engineering.

Abstract: We have developed a porous titanium implant sintered with spacer particles (porosity = 50 %, average pore size ± standard deviation = 303 ± 152 !m, yield compression strength = 100MPa). This porous titanium was successfully treated with chemical and thermal treatment that gives a bioactive micro-porous titania layer on the titanium surface, and it is expected as effective biomaterial for biological fixation on load bearing condition. In this study, ten adult female beagle dogs underwent anterior lumbar interbody fusion at L6-7 using either BT-implant or non-treated implant (NT-implant), then followed by posterior interspinous wiring and facet screw fixation. The radiographic evaluations were performed 1, 2 and 3 months postoperatively using X-ray fluoroscopy. Animals were sacrificed after 3 months postoperatively, and fusion status was evaluated by manual palpation. Histological evaluation was also performed. Both histological and radiological evaluation revealed that interbody fusion was achieved in 5 of 5 dogs (100%) in BT-group and 3 of 5 dogs (60%) in NT-group. In BT implants, we could observe a large amount of new bone formation from periphery to the center of the implant, whereas in NT implants, fibrous tissue formation was still observed even in the implants with successful fusion. The results of this study indicate that porous bioactive titanium implant will represent a new osteoconductive biomaterial with improved fusion characteristics.

Abstract: Chemical treatment of polycaprolactone was carried out to bioactivite the biodegradable polymer for bone tissue engineering application. The results show that surface modifications are necessary to introduce functional groups such as carboxylic groups for the effective induction of apatite nucleation, prior to SBF treatment. The functional groups, acting as anchors between the polymer and the apatite nuclei, dictate the duration of the induction period need for apatite nucleation. After the surface treatment with sodium hydroxide solution, the apatite nuclei will form and grow spontaneously into a dense and uniform layer of apatite, by taking up Ca2+ and PO4 2- ions that are present in the SBF, as SBF is supersaturated with respect to apatite. Similar surface treatment was applied to electrospun PCL nanofibres. Biomimetic apatite/PCL nanofibres were formed which can potentially be used as bone tissue engineering scaffolds.

Abstract: Antibacterial Ag-doped TiO2 porous monolithics were firstly prepared by hybridization of polyethylene glycol, Ti(OC4H9)4 and AgNO3 via sol-gel method following by heat-treatment to remove the organic components. Thermogravimeter−differential thermal analysis, pore structure, infrared spectra, ultraviolet−visible spectra, release speed of silver ions into 30°C water and antibacterial properties of Ag-doped TiO2 samples made at different temperature were studied. The results showed that anatase phase and uniform pore structure can be formed after heated at 500°C. Ag+ ions from the samples heated at 500°C were stably released into water at 30°C up to 14 days. The material treated at 500°C has the best antibacterial property and can restrain Escherichia coli effectively.

Abstract: The present investigation gives a comparison of the structure and properties of porous Ti6Al4V made by sponge replication (Sponge Ti) and directly 3D fiber deposition (D3DF Ti) and cancellous bone. Although the macrostructure of these two materials differs, their microstructure seems to be similar. Both scaffolds reveal an open pore structure, while D3DF Ti shows a fairly regular open pore structure, sponge Ti6Al4V exhibit an irregular open pore structure similar to that of cancellous bone. The mechanisms resulting in mechanical properties like stiffness or strength are, accordingly, different. The compressive strength and E’ modulus of Ti6Al4V scaffold are higher than that of cancellous bone,. The permeability results show both Ti6Al4V scaffolds are quite comparable with cancellous bone.

Abstract: Porous ceramics of hydroxyapatite was fabricated utilizing the crystal growth of thin ice columns parallel to one another in gelatin gel containing hydroxyapatite nanoparticles. The obtained ceramics possessed unidirectional pore channels with a porosity of around 75% and showed compressive strength of up to 13.1 MPa. As control materials, porous hydroxyapatite ceramics with a directionless pore structure were also fabricated by isotropic freezing and compared with the unidirectional samples regarding compressive strength and tissue reaction in vivo. Although the porosity and pore size distribution were similar, the compressive strength and new bone formation ability of the unidirectional samples were significantly greater than those of the random structured porous ceramics.

Abstract: Time-controlled releases of proteins from hydroxyapatite/chondroitin sulfate (HAp/ChS) spherical microparticles were achieved by the addition of zinc cation into the mixture solutions of HAp/ChS and protein as a novel formulation. The initial bursts of proteins, such as cytochrome c and bovine serum albumin, were apparently suppressed by the amount of zinc cation, which could be attributed to the formation of coordinate bonds of zinc cation among proteins and/or ChS moleculars. The increase of molecular lengths of ChS chains decreased the adsorbed amount of proteins, which did not apparently affected to the release of proteins.

Abstract: The advantages of local antibiotic administration - high local levels with low systemic toxicity - are nowadays recognized as an efficient way for anti-infection therapies consecutive to the orthopaedic implant surgery. Aimed at assessing the feasibility of using Hydroxyapatite as drugdelivery carrier in addition to its well-known bone reconstruction bioactivity, a pure HA ceramic with specific internal pore size and porosities was under our investigation. The antibiotic release and antibacterial effect were determined by UV spectrophotometry and disk agar diffusion assays after impregnation with different antibiotics and their release in different solvents. No differences were found after the ATB impregnation under normal pressure or under vacuum conditions. The influences of impregnation time on the duration of the ATB release and on the antibacterial efficiency were more evident for Vancomycin than for Ciprofloxacin and Gentamycin. In all cases, the ATBs penetrated micro-porous and meso-porous HA samples and showed significantly stronger and longer anti-bacterial effects than dense HA samples. The ATBs releases in PBS were relatively slower and the antibacterial effectiveness subsequently prolonged with respect to those in human plasma. All tested HA samples with or without ATB impregnation exhibited very good biocompatibility as shown by cell proliferation tests. It revealed a promising perspective for further improving the antibacterial efficiency by other surface functionalization methods for achieving a controllable drug delivery with antibiotic loaded HA.

Abstract: Calcium sulphate hemihydrate/α-tricalcium phosphate (CSH-TCP) cement are promising bone replacement materials with controllable-degradation rate and setting time and excellent delivery matrix for sustained release. In the present study, setting behaviors of binary bone cement composed of α-TCP and CSH and release of ciprofloxacin from this cement were investigated in vitro. XRD and SEM results demonstrated that the setting products of CSH-TCP cement were calcium sulphate dihydrate with pillar morphology and hydroxyapatite with needle morphology. Only 20% ciprofloxacin was released from CSH-TCP cement in 7 days in vitro. Fibers of hydroxyapatite enhanced strength of binary cement through fiber-reinforce mechanism. At initial stage (less than 100 hours), the release of ciprofloxacin from CSH-TCP cement was diffusion control, and at subsequent stage the release was matrix dissolution & diffusion control.

Abstract: A laminin–DNA–apatite composite layer was successfully formed on the surface of an ethylene–vinyl alcohol copolymer. The immobilized DNA was transferred to the cells adhering onto the laminin–DNA–apatite composite layer more efficiently than those adhering onto a lamininfree DNA–apatite composite layer. It is considered that laminin immobilized in the surface layer enhances cell adhesion and spreading, and DNA locally released from the layer is effectively transferred into the adhering cells, taking advantage of the large contact area. The present gene transferring system, which shows high efficiency and safety, would be useful in gene therapy and tissue engineering.