Key Engineering Materials Vols. 330-332

Abstract: Improved cement technique by interposing less than two layers of hydroxyapatite (HA) granules between bone and bone cement at the cementing (Interface Bioactive Bone Cement : IBBC) have been performed in total knee arthroplasty (TKA). 140 knees (120 patients) could be followed up clinically and radiologically. As a control, clinical results of TKA with conventional cementing (Non-IBBC) were used. In IBBC cases, the appearance rate of the radiolucent lines on the tibial components and the periprosthetic osteolysis of the tibial components were significantly low. In IBBC, bone cement bound to HA mechanically immediately after surgery and HA granules bound to the bone physicochemically after bone ingrowth into the spaces around the HA granules. Thus, we believe that IBBC is a method combining the advantage of cementless HA coating and bone cement.

Abstract: In this paper, the hydration product of calcium phosphate cement with bioactive glass containing Si was used to investigate the effect of chemical composition on its bioactivity. The variation of concentrations of Ca2+, P and Si in TE solution complemented with electrolytes typical for plasma (TEE) and the formation of amorphous calcium phosphate layer on the surface of the materials were investigated by immersing the designed materials in TEE solution in vitro. The results showed that the composition of the bioactive composite CPC greatly affected its behavior in the solution and the formation of bioactive apatite. After immersed in TEE solution, the Ca ions were uptaken for all the samples, showing the decreases of Ca concentration during the entire duration, but the concentration of P ions increased sharply at the initial stage, and then decreased due to the formation of amorphous calcium phosphate layer on the surface of the materials. FTIR revealed that the layer was poorly crystallized Ca-deficient carbonate apatite. The thickness of the layer was more than 12 um, which layer was composed of rod-like apatite with directional arrangement. All the data obtained would be useful for the design and optimization of the orthopedic degradable implant inorganic materials.

Abstract: A composite bone cement designated G2B1 that contains β tricalcium phosphate particles was developed as a bone substitute for percutaneous transpedicular vertebroplasty. In this study, both G2B1 and commercial PMMA bone cement (CMW1) were implanted into proximal tibiae of rabbits with a metal frame fixed on it, and their bone-bonding strengths were evaluated at 4, 8, 12 and 16 weeks after implantation using a detaching test. Some of the specimens were evaluated histologically using Giemsa surface staining and scanning electron microscopy (SEM). It was found that the bone-bonding strength of G2B1 was significantly higher than that of CMW1 at each time point, and significantly increased from 4 weeks to 8 and 12 weeks, while it decreased significantly from 12 weeks to 16 weeks. Giemsa surface staining and SEM showed that G2B1 contacted bone directly without intervening soft tissue in the specimens at each time point, while there was always a soft tissue layer between CMW1 and bone. The results indicate that G2B1 has excellent bioactivity.

Abstract: In this study, the antibacterial effects of glass ionomer cement containing silver-zeolite were evaluated. New antibacterial glass ionomer cements with silver-zeolite were prepared as follows. Silver-zeolite (1, 3, and 5 wt%) was incorporated into the glass ionomer cement powder and then mixed with the polyacidic liquid at the ratio recommended by the manufacturer. Agar diffusion test was used to evaluation of antibacterial effect. Setting time, film thickness and compressive strength were also determined. Paired samples t-tests and ANOVA were used, and P<0.05 was considered significant. Film thickness and setting time were increased dependent on the amount of silver-zeolite. Glass ionomer cement with 1 wt% of silver-zeolite seemed to increase the compressive strength. However, increasing ratio of compressive strength was diminished beyond 3 wt%. Glass ionomer cements containing silver-zeolite have been successfully demonstrated to have antimicrobial effects on S. mutants in vitro. These results indicate that glass ionomer cement containing silver-zeolite have the potential to enhance antibacterial of dental cement in oral cavity.

Abstract: Low crystalline apatite (LCA) and calcium phosphate cements (CPC) based on amorphous calcium phosphate and dicalcium phosphate dihydrate (1 to 1 ratio) were combined with bioresorbable PLGA copolymer (0 to 20 wt.%) for preparation of solid-formed devices. A pilot manufacturing based on powder processing techniques using isostatic pressure (44,000 psig) was conducted. Processing parameters such as isostatic pressure, temperature, times and device dimension were varied to achieve appropriate mechanical properties comparable to that of allograft bone dowel used as a gold standard in clinical application. The solid-form devices were characterized for physico-chemical and mechanical performance, as well as subjected to an in-vitro wet environment incubation at body temperature (37°C). Fluid diffusion was investigated to evaluate the fluid absorption (through microporosity) and the compressive strength of wet devices vs. incubation time (up to 30 days) was also studied. The shear strength and compressive strength of pure LCA dowels was respectively 26 and 122 MPa, which corresponds to a process densification of about 30%. The compressive strength was dramatically improved with addition of various amounts of copolymer. The maximum compressive strength of 180 MPa was obtained for dowels containing 10 wt.% copolymer. Calcium phosphate composite also increased the shear strength to about 42 MPa. These mechanical performances were significantly higher than that of allograft bone dowel (MD-II™), reported about 10 MPa. A pilot sheep interbody fusion of lumbar spine (L3/L4 and L4/L5) demonstrates mechanical integrity and intervertebral fusion at 6 months. LCA was found to be the most suitable CaP material because of its biocompatibility, chemical composition, nano-structure and high specific surface area that exhibits in-vivo biointegrity and cell mediated process.

Abstract: Crystallized apatite behaved to plaster of Paris was prepared by the chemical method. Apatite powder was mixed with chitosan. In this study, it was also studied the effect of HA seed and sodium hydrogen phosphate as an additive on their mechanical strength, compared with the normal calcium phosphate cements. Setting time of paste cements was determined using Gillmore method. Phases of cement obtained from a crushed cylinder were analyzed using XRD analysis. From the results, chitosan was effective both in increasing mechanical properties and accelerating hardening of the normal bone cements. Nevertheless, the compressive strength of chitosan-crystallized apatite composites was not significantly improved as compared to the controlled one. In addition, it was found that the mechanical strength of the cements decreased when increasing the concentration of HA seed and an additive.

Abstract: In this study modified starch were used as anti-washout promoters of injectable calcium phosphate cement (CPC) and the effects of the modified starch on the injectability, anti-washout performance, setting time, compressive strength, phase evolution and microstructure of this cement were investigated. The injectability of the cement was improved by adding the modified starch (0.5-2.0%). After mixing with modified starch (0.5-2.0%), the cement showed better anti-washout performance than that without modified starch after immersed and shaken in SBF. Especially, when the content of the modified starch was 1.0%, the remaining percentage of the cement was reached to 92.6%, but only 5.9% of the CPC paste remained and set for the sample without modified starch after shaken for 2 hrs. The compressive strength of cements significantly increased from 44 MPa to 54 MPa when 0.5% of modified starch was added. And a slight increase on the mechanical strength can be observed for other concentrations. Powder X-ray diffraction analysis revealed no significant difference for the conversion of the cement to hydroxyapatite for any concentrations of modified starches. The influence of the modified starch on the microstructure of the set cement was also studied. The results showed the modified starch would reduce the acicular crystal size of hydroxyapatite accompanied with little flaky crystals generation and made a compact structure. It is concluded that modified starch, a suitable anti-washout promoter, improved the performance of CPC.

Abstract: An injectable bone substitute (IBS) made of a suspension of calcium phosphate ceramic was used to filled dental root canal after removing of canal pulp. Compared with current filling materials, which are toxic to periapical tissues, calcium phosphate materials, due to their biocompatibility and bioactive properties, may be viewed as possible alternatives. The aim of this study was first to determine if an injectable bone substitute could be used to obtain further healing of apical tissue by the neoformation of a mineralized barrier. In the next step, the paper will focus on rheological measurements as a tool for physical characterisation and on the improvement of the injection technique. Rheology concerns the flow and deformation of the suspension and, in particular, its behaviour in the transient area between solids and fluids. The results showed that injection is possible with a good level of BCP granules at the end of the root dental canal with extracted tooth. Other experiments with other animal models closer to a Human model have to be performed before human trials.

Abstract: The purpose of this study was to evaluate histologically the effect of LiF-maleic acid added calcium aluminate (LM-CA) bone cement and calcium aluminate-polymethylmethacrylate (CA-PMMA) composite bone cement on bone regeneration in rat calvarial defect. After calvarial defects in 8 mm in diameter were created, three groups of 10 animals, a total of 30, each either received LM-CA bone cement, CA-PMMA composite bone cement or a sham-surgery control. Histologic analysis was done at 2 weeks and 8 weeks of healing periods. We concluded that LM-CA bone cement can be used as a bioactive bone graft material due to ability of bonding to the existing bone and CA-PMMA can be used as a graft material for augmentation of bone-volume due to dimensional stability.

Abstract: Control of protein release without the initial burst from zinc containing hydroxyapatite porous microparticles (Zn-HAp) was investigated with a novel formulation method. The formulation method was a coat of polyL(L-lactide; PLA) on the microparticle with nano-thickness, which obviously suppressed the initial burst of protein release compared with the microparticles without the formulation, the coat of PLA. The HAp/PLA microparticle with 1-20μm of the size distribution was available for the drug delivery carrier of proteins without the degradation.