The Biocompatibility Research For Titanium Alloy Via Electrochemical Corrosion

Object: Titanium and titanium alloy which have great biocompatibility and mechanical function, were extensive used in medical area, especially for the base materials of dental implant in recently several decades.There are numerous reports demonstrate that the surface roughness of dental implants affects the rate of osseointegration and bio-mechanical fixation. The rate and quality of osseointegration in dental implants are related to their surface properties. Surface composition, hydrophilicity and roughness are parameters that may play a role in implant–tissue interaction and osseointegration. Surface roughness can be divided into three levels depending on the scale of the features: macro-, micro- and nano-sized topologies. The high roughness resulted in mechanical interlocking between the implant surface and bone growth, improving the osseointegration and clinical result. Surface profiles in the nanometer range play an important role in the adsorption of proteins, adhesion of osteoblastic cells and thus the rate of osseointegration, now many researcher are trying to develop a nanometer range surface of dental implant. There are many technical skills to treat surface topography of dental implant, such as titanium plasma-spraying, grit-blasting, acid- etching, anodization, et al. A micron-nano scale roughness surface for titanium alloy materials were got in electrochemical corrosion skills, which had better bioactivity. Electrochemical corrosion refers to the damage between metal and electrolyte via electrochemical reaction, the electron flow of metal inside and electrolyte ion made loop between platinum electrode and titanium alloy, the surface of titanium alloy specimen lose titanium atoms electron into titanium ions , the hydrogen ions in solution change into hydrogen which spill over from cathode. This allows the speed of electrochemical corrosion far greater than chemical corrosion, which can get slightly roughness surface in a very short period of time. There are many factors affected the rough surface of titanium alloy application the electrochemical corrosion approach, such as temperature, current density, electrolyte composition, electrolyte concen- tration, electrolysis time, the distance between cathode and positive pole, et al. This study made hemolysis test and bone implant test for the biocompatibility detection of titanium alloy via electrochemical corrosion according to the ISO 7405:1997 and YY/T 0127.4--1998.Methods: Hemolysis test: cut down the electrochemical corrosion sur- face of titanium alloy, and put them into three test tubes which containing 10ml saline as experimental group after anhydrous alcohol, acetone, dis- tilled water ultrasonic cleaning. Then 0.2 ml diluted blood was added to this standard tube and the mixtures were incubated for 60 min at 37℃. Similarly, normal saline solution was used as a negative control and deionized water as a positive control.After this period, all the tubes were centrifuged for 5 min at 3000 rpm and the supernatant was carefully removed and transferred to the cuvette for spectroscopic analysis at 545 nm. The hemolysis was calculated based on the average of three replicates.Bone implant test: cut down the electrochemical corrosion surface of titanium alloy, 4mm diameter, 1mm thickness, disc-shaped, with SLA surface and its mechanical cutting surface as the control group. All the specimens were autoclave sterilization after cleaning. Two implantation fossa were prepared in the left leg of rabbit tibia proximal. Then put the experimental group implanted into the proximal and the control group implanted into the distal, the distance between two implanted specimens was 1cm. After the operation, those animals were sacrifice in three time points of 4 weeks, 8 weeks, 12weeks. Then HE staining was taken.Results: the hemolysis of titanium alloy via electrochemical corrosion was 0.478%, less 5% safety rate. In generally observed, the areas of experimental animal surgery have a slight redness, swelling, and no incision crack after three days. Incision healed after five days, animals without infection and death during the experiment time. In 4 weeks, specimens-bone closely linked together, but new organization around the specimen was deeper color, it was not as hard as surrounding normal bone .In 8 weeks, the new bone around the specimen was slightly shallow color than 4-week groups, and close to the specimen, some part of the specimen was covered by normal bone tissue. In 12 weeks, new bone completely covered the specimen, and there was no difference between the normal bone tissue and new bone color.Conclusion: Titanium Alloy which treated in mixed acid electrolyte by electrochemical corrosion was safety, but further studies need to be done before applied in pre-clinical. In the HE staining, the new bone tissue was relatively small in 4 weeks machine groups, and the surface of new bone was not continuous, porous, irregular shape; The continuity of new bone is better and less porous in the interface of SLA groups; the new bone was more mature and showing lamellar-like arrangement near the interface in experimental groups, and more osteoblasts can be seen in the interface between specimens and new bone. In 8 weeks, the new bone tissue was continuously and without interrupt, but the structure of collagen fiber was more disordered, and there was not obvious lamellar structure in mechanical groups; the structure of new bone showed like–lamellar and continuous in SLA groups; There was more mature bone tissue and haversian canal in experimental group; In 12 weeks, the new bone was thin in machinery groups; the new bone was dense and continuous, and there was not the clear boundary with the old bone in SLA group and experimental group. There were no fibrous package and inflammatory cells in all groups.