The Study Of Nickel-titanium Shape Memory Alloy's Biocompatibility And Ototoxicity After Implanting In Guinea Pigs' Acoustic Vesicle

ObjectiveBecause of its excellent shape memory effectsuperela- sticity, perfect biocompatibility and corrosion resistance, nickel- titanium shape memory alloy (NT-SMA) has widely clinical application. It has been used as bone internal fixer, intravascular stent and tracheal stent. Also, some scholars selected NT-SMA as ossicular prosthesis in recent years. As the inner ear is vulnerable to toxic substances especially, the biocompatibility and biological toxicity of the ossicular prosthesis which is implanted in middle ear are very necessary. The purpose of this study was to explore the NT-SMA's biocompatibility and biological toxicity after being implanted in guinea pigs' acoustic vesicle.Methods90 healthy guinea pigs with acute hearing were used in this study. One ear of each guinea pig was selected as the experimental group (NT-SMA implanted group) randomly. Another ear of 90 guinea pigs was selected as control group I (Ti implanted group) and control group II (opened acoustic vesicle without implanting any materials) equally. The auditory function was evaluated by auditory brainstem response(ABR) and distortion otoacoustic emission response(DPOAE) at pre-implantation, and at pre-execute of 7th, 14th, 28th, 56th, 112th day after operation. Then, whether there were granulation hyperplasia around the implanted materials were observed, and the materials were taken out after acoustic vesicles being opened. The surface topography and the elemental composition of the surface were observed and analyzed by the Field Emission Scanning Electron Microscope (FEI Co., USA)and the Energy Dispersive Analysis (EDAX Co., USA). The morphological observation to cochlea was carried by HE-staining of cochlear slice, and the hair cell's organelle were observed by transmission electron microscope. The apoptosis and deletion of hair cells were observed by AO-PI fluorescent staining.ResultsThe biocompatibility of NT-SMA in guinea pig's acoustic vesicle:(1) There were neonatal bone tissue on the surfaces of NT-SMA or Ti material but no inflammatory granulation tissue around them, and no obvious change in the acoustic vesicles without implanting. There is also no corrosion spot and color change on the serface of the NT-SMA and Ti implant after being implanting in the acoustic vesicles. (2) Neonatal bone tissue, which containing C, N, O, Ca, P and very slight of Ni and Ti elements, scattered on the surface of NT-SMA at 7^th day, gradually interweaved into mesh from 14^th to 56^th day and finally emerged to amella at 112^th day after implanting, just as the same as on Ti, were observed by the Scanning Electron Microscopy and Energy Dispersive Analysis. The toxicity of NT-SMA in guinea pig's acoustic vesicle and inner ear: (1) There was no significant difference between the threshlod of auditory brain stem response (ABR) at pre-operation and the threshold of ABR at 7^th, 14^th, 28^th, 56^th, 112^th day after operation, in every group, seperately (p>0.05). Meanwhile, DPOAE through rates at pre-operation and at 7^th, 14^th, 28^th, 56^th, 112^th day after operation were 100% in the 3 group. (2) HE-staining of the cochlear slice showed that there was no obvious change or morphological variation in the cochlear tissues and cells after NT-SMA and Ti implanting in the acoustic vescila. (3) The scanning electron microscopy showed that the shape of the Hair cells' stereocilia were arranged normally, and neither stereocilia deletion, nor disarrangement occurred. (4) No abnormal in the stereocilia and the organella of hair cells observed by transmission electron microscopy. (5) No apoptosis of hair cells and only a cuple of outer hair cells deletion in the outermost line observed by AO-PI fluorescent staining.Conclusion1. No significant inflammatory reaction occurs after NT-SMA being implanted in guinea pigs' acoustic vesicle, and the bone-formation reaction and biocompatibility of NT-SMA in the acoustic vesicle are outstanding.2. There is no significant damage to hearing, no obvious morphological changes in cochlea, neither apoptosis of hair cells induced by NT-SMA implanted in the acoustic vesicle. There is no significant ototox-icity of the NT-SMA implanted in the acoustic vesicle.3. There is no significant difference of biocompatibility and biological toxicity between NT-SMA and Ti in middle ear and inner ear.4. There is a slight releasing of Ni releasing from NT-SMA without surface treatment when it is implanted in the acoustic vesicle of the guinea pigs. The surface treatment of NT-SMA ossicular replacement prosthesis is necessary to preventing Ni releasing.