U dugogodišnjoj kliničkoj primjeni titanija sve se više uočavaju štetni učinci kao što je otpuštanje iona Ti4+ uslijed neprihvatljivog biokorozijskog ponašanja. Magnezij se u posljednje vrijeme često primjenjuje u biointeraktivnim konceptima oseointegracijskih površina kao značajan čimbenik oseointegracije u biodegradacijskom procesu otpuštanja iona Mg2+. Kako se titanij i magnezij ne mogu legirati, metalurgija praha smatra se tehnikom izbora za proizvodnju titanij-magnezijeva kompozitnoga materijala. Svrha ovog rada je istraživanje biokorozijskih svojstava titanij-magnezijeva materijala kroz proučavanje otpuštanja iona Ti4+ i Mg2+ te promatranje promjena nastalih na površini. Pripravljene su tri vrste materijala, s 1, 2 i 5 % magnezija u titanijskoj osnovi. Kao kontrolna skupina upotrijebljen je komercijalno čisti titanij stupnja 4. Za otpuštanje iona Ti4+ i Mg2+ korišten je test uranjanja u četiri vrste otopina: umjetnoj slini, umjetnoj slini s pH 4 i s dodanim fluorom te Hankovoj otopini koje su zatim analizirane metodom masene spektrometrije induktivno spregnutom plazmom. Površine uzoraka karakterizirane su skenirajućom elektronskom
mikroskopijom, energijskom disperzivnom spektroskopijom, rendgenskom difrakcijskom analizom te profilometrijskim određivanjem hrapavosti površine. Rezultati istraživanja pokazali su značajno manje otpuštanje iona Ti4+ u usporedbi s kontrolnom skupinom. Dok su na otpuštanje iona Ti4+ statistički značajan utjecaj imale vrste otopina, otpuštanje iona Mg2+ bilo je pod utjecajem vrste ispitivanog materijala. Na površinama je uočena intenzivnija fizikalno kemijska aktivnost ispitivanog materijala koja sugerira na zaključak o potencijalnoj biointeraktivnosti istog. Istovremeno, magnezijeva korozija se je u nekim uvjetima pokazala neprihvatljivom za primjenu in vivo. Stoga su potrebna daljnja istraživanja strukture i sastava
inovativnog titanij-magnezijeva kompozitnoga materijala proizvedenog tehnikom metalurgije praha.
|Abstract (english)|| |
Introduction: Titanium and its alloys have been widely used as an implantable alloplastic biomaterial in the field of dental medicine for the last half century. Good mechanical properties, favourable corrosion behaviour and excellent biocompatibility are mentioned as the main reasons for such a large clinical application. The important bio-corrosive characteristic of titanium is the formation of dioxide layer of TiO2 which protects the metal of dissolving. However, such a surface layer plays poor protective role in some environmental conditions such are low pH value of the medium and the presence of fluorides. Magnesium enhances osteoinduction, osteoconduction and osseointegration of implantable biomaterial by promoting some osteogenic processes in the alveolar bone during a peri-implant bone formation. However, magnesium, as a pure metal, demonstrates poor bio-corrosive behaviour resulting in the gaseous H2 evolution and the alkalization of surrounding area. The powder metallurgy technique has been shown as the method of choice to unify the positive properties of two metals. In that way produced titanium-magnesium composite material could demonstrate better corrosive behaviour and develop an innovative and biomimetic surface characteristics in order to improve the process of osseointegration of such an implantable material. Aim: The aim of this study is to investigate the bio-corrosive characteristics of titanium-magnesium composite by determining the amount of released titanium and magnesium ions and by observing the surface changes during the corrosion test in simulated body fluids. Materials and methods: Three groups of innovative titanium-magnesium
composite were produced by means of powder metallurgy technique: 1 mass%, 2 mass% and 5 mass% of magnesium in titanium matrix. Commercially pure titanium was used as a control group. The standardized static immersion test was used to carry out the bio-corrosion testing. Artificial saliva, artificial saliva with pH 4, artificial saliva with fluorides added and Hank’s balanced salt solution were prepared. The amount of released titanium and magnesium ions in the solution were determined by means of inductively coupled plasma mass spectrometry. The surface topography was observed by means of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis. To compare the surface roughness before and after the immersion, profilometry method was emloyed. Statistical evaluation was done by Statistica 7.0 software package. Significance level in all tests was set to p<0.05. Results and discussion: The amount of released titanium ions from all of three tested groups was significantly lower in comparison to the control group except in the case when the 5 mass% magnesium in titanium tested group was immersed in Hank’s balanced salt solution. According to the literature data, the amount of released titanium ions from tested material obtained in this study can’t provoke any biologically harmful side effect. Statistical analysis showed the significant influence of the type of solution on titanium ions release. At the same time, the magnesium ions release was more intense and faster than the titanium corrosion and under the influence of type of tested material. According to the literature data, the results of this investigation revealed that only the composite with 1 and 2 mass% of magnesium in titanium matrix performed biologically favourable corrosive behaviour. In the case of 5 mass% magnesium in titanium matrix group, the magnesium corrosion could provoke harmful biological side effects. Surface topography examination showed that localized forms of
corrosion, dominantly pitting, prevailed on the surfaces of tested materials whereas the generalized corrosion was distinctive for the material of the control group. Chemical microanalysis of the surface after immersion revealed the presence of the atoms contained in the solutions and crystallographic examination confirmed the presence of hydroxyapatite and magnesium-oxide crystals formations. This could refer to the potentially biomimetic surface characteristic of the innovative titanium-magnesium composite. Profilometric study of the tested surfaces revealed that the vertical dimension of the roughness increased more than any other. Conclusion: Based on the bio-corrosion tests performed, one can conclude that the innovative titanium-magnesium composite showed better corrosive behaviour in terms of titanium ions release. The surface changes observed suggest the high bio-interactive potential of the tested material. The magnesium to titanium matrix ratio is found as the most significant factor in the development of a biodegradable titanium-magnesium composite concept with an acceptable magnesium corrosion rate. Since the results of the magnesium release revealed, in
certain conditions, poor corrosive behaviour, further research on the development of titaniummagnesium composite are recommended.