Papers by Author: Hua Liu

Abstract: Nanometer titanium dioxide powders were prepared by hydrolysis of titanium-tetrabut- oxide with ethanol. Using the process that titanium alloys were embedded by the nanometer TiO₂ powders and sintered in the high temperature furnace, the nano-TiO2 / titanium alloy biomaterials was fabricated out. The particle size of TiO₂ particles on the surface of Ti alloy was mainly 50-70 nm. The experimental results indicated that the films of nanocrystalline titanium oxide powders on the surface of Ti alloy were with an excellent biocompatibility. By cultivation in the simulated body fluid for 7 days, the Ca phosphates were deposited on the specimen surface, and n (Ca) / n (P) atom ratio is about 1.61:1, which is similar to that of HA and human bone. The nano-TiO₂ / titanium alloy possessed favorable cell compatibility testified by the cell cultivation experiment.

Abstract: Calcium phosphate cement (CPC) sets in situ to form hydroxyapatite and is highly promising for a wide range of clinical applications. However, its low strength limits its use to only non-stress applications, and its lack of macroporosity hinders cell infiltration, bone ingrowth and implant fixation. The aim of this study was to develop strong and macroporous CPC scaffolds by incorporating chitosan and water-soluble mannitol. The incorporation of chitosan could improve the handling properties of CPC. Mannitol provided the needed early strength of CPC and then dissolved to create macropores for tissue ingrowth. This study investigated the effects of mannitol volume fraction (0-70%) on CPC composite mechanical properties and macroporosity of the scaffold after mannitol dissolution.

Abstract: We developed a calcium phosphate cement that could be molded into any desired shape due to its chewing-gum-like consistency after mixing. The powder component of the cement consists of tricalcium phosphate (TCP). The liquid component consists of chitosan, citric acid and glucose solution. In this study, we used four groups of cement to investigate the mechanical properties and biocompatibility of the new biomaterial in vivo. The setting times of the cements were 5-30 min. X-ray diffraction analysis showed that the products were hydroxyapatite (HA) and dicalcium phosphate anhydrous. When the concentration of citric acid was increased, the compressive strength of specimen increased. The animal experiments showed that the material was nontoxic and osteoinductivity.

Abstract: Nanometer titanium dioxide powders were prepared by hydrolysis of titanium-tetrabutoxide with ethanol. The powder particle size of TiO₂ in the structure of anatase-type is mainly between 5 and 10 nm. Using the process that titanium alloys were embedded by the nanometer TiO₂ powders and sintered in the high temperature furnace, the nano-TiO₂/titanium alloy biomaterials was fabricated out. The particle size of TiO₂ particles on the surface of Ti alloy was mainly 50-70 nm. The method is a simple and adaptable technique for surface modification of the titanium alloys.

Abstract: The aim of this study was to develop a novel injectable hydroxyapatite for bone repair materials. This study was based on the in situ setting properties of calcium phosphate cement (CPC), which properties were improved. The solid phase consisted of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA). The liquid phase was the weak acidic solution of chitosan. The CPC powder was mixed with the chitosan solution to form a paste that could conform to the bone cavity even for irregularly shaped cavities. All the by-production disappeared by neutralization reaction. The CPC paste could then set in situ to form hydroxyapatite (HA) as the final product. The chemical process of CPC hydration was studied. The process was controlled by dissolution and precipitation chemical reaction. The kinetic model of hydration reaction was established. The effects of preparing conditions, such as powder to liquid ratio and particle size, on setting time and compressive strength were investigated systematically. The optimal condition was that the liquid phase contained 3% chitosan, 5% citric acid and 15% glucose (wt%), powder to liquid ratio was 0.8 g/ml, and powders were respectively ground for 40 hours.

Abstract: Calcium phosphate cement (CPC) sets in situ to form solid hydroxyapatite, can conform to complex cavity shapes without machining, has excellent osteoinductivity, and is able to be resorbed and replaced by new bone. Therefore, CPC is promising for craniofacial and orthopaedic repairs. However, its low strength and lack of macroporosity limit its use. This study investigated CPC reinforcement with absorbable fibers, the effects of fiber volume fraction on mechanical properties and macroporosity, and the biocompatibility of CPC-fiber composite. The liquid phase of CPC in this study was the weak acidic solution of chitosan. Chitosan has favourable biocompatibility, which has high viscosity in solution. The incorporation of chitosan could improve the handling properties of CPC. The liquid phase contained citric acid could strongly improve the hydration rate of CPC, which shortened the setting time and increased the compressive strength of CPC. In addition, the weak acidic environment around the biomaterials could accelerate the degradation of CPC, which was important to bone tissue engineering. The rationale was that large-diameter absorbable fibers would initially strengthen the CPC graft, then dissolve to form long cylindrical macropores for colonization by osteoblasts. Compressive strength was measured vs. fiber volume fraction from 0% (CPC Control without fibers) to 70%. Animal experiment showed that the material had osteoinductivity and biodegradability when the material was implanted into the muscle pouches in the thigh of rabbits. Compressive strength (mean ± SD; n=3) of CPC with 70% fibers was 0.8± 0.1 MPa. Long cylindrical macropores 100~300 μm in diameter were created in CPC after fiber dissolution, and the CPC-fiber scaffold reached a total porosity of 75.1±1.2% with 70% fibers. The new CPC-fiber formulation had good potentiality of ectopic bone induction. The method of using large-diameter absorbable fibers in bone graft for mechanical properties and formation of long cylindrical macropores for bone ingrowth may be applicable to other tissue engineering materials.