| Facial disfigurement, which result from congenital abnormalities, cancer resection, or trauma, are restored aesthetically and functionally into artificial prostheses of the missing parts. The properties of the prosthetic materials are the most important factor to affect the final restoration. Silicone elastomer is commonly used as a prosthetic material, but the properties of it still exist many defects. Therefore, the modification of maxillofacial prosthetic silicone elastomer has already become a hot spot of recent researches. At present, the mainly used modified methods are the blending modification and filler modification. The blending modification is blending variety of components to supplement single component, and the filler modification is improving the properties of the silicone elastomer by mixing with different fillers. Filler modification is more simple and flexible. With the rapid development of materials science and medicine, the traditional maxillofacial prosthetic silicone elastomer cannot meet the requirement of clinical use. the weak mechanical and anti-aging properties of the silicone elastomer have severely shorten the service life of the prostheses. Therefore, a new type of maxillofacial prosthetic material with superior and stable mechanical properties and safety biological properties which can also carry out the personalized repairment according to different defects is needed urgently.Nano-TiO2particle is a kind of stable photocatalyst, which has been widely used in the toughening modification of dental materials such as composite resin, glass ionomer cements etc. It has good optical stability and biological safety as an inorganic additive. However, few studies have confirmed that nano-TiO2particles can affect the anti-aging properties of silicone elastomer.The purpose of the study is to modified the maxillofacial prosthetic silicone elastomer by filling nano-TiO2in order to obtain a new type of prosthetic material which possess good mechanical property, good anti-aging properties, and good biocompatibility at the same time. The study examines in depth the impact of aging on the mechanical property and in vitro cytotoxicity of maxillofacial prosthetic silicone elastomer.Materials and methodsPart ⅠIn this study, the maxillofacial prosthetic silicone elastomer (MDX4-4210) was modified by filling the fumed nano-TiO2P25for preparing different concentrations of nano-TiO2modified maxillofacial prosthetic silicone elastomer.Firstly, the silicone elastomer matrix and the diluent were stirred and mixed (1:0.5), and then the different concentration of fumed nano-TiO2particles P25were weighed and added into the uniform silicone elastomer matrix. Then the mixture were stirred for2h until the powder is completely dispersed uniformly into the silicone elastomer matrix by visually observing. According to the introduction, a fixed proportion of the curing agent (10:1) was added, stirring uniformly (10min,1000rpm). The mixture was poured into polytetrafluoroethylene mold and vacuumed in a vacuum oven (15min,1MPa), and then being placed on a flat desktop for4h. Finally, the mixture was slowly cured in a high temperature oven at60℃for4h and another24h curing in room temperature was performed before test.The tensile strength and the elongation at break was measured according to ISO37:2005standard by TH-8201S computer servo control tensile testing machine in four groups (n=9).The tear tear strength was carried out according to ISO34-1:2004standard by TH-8201S computer servo control tensile testing machine in four groups (n=9). The Shore A hardness test was measured according to ISO7619-1:2004standard by LX-A shore A hardness tester in four groups (n=9), each sample was tested five points.The blank silicone elastomer and nano-TiO2silicone elastomer was observed and analyzed by JSM-6700F scanning electron microscopy.Part ⅡThe silicone elastomer containing0%(w/w) and6%(w/w) TiO2nanoparticles were chose to through the four different aging tests.Hot air aging test was performed according to the standard ISO188:2007with the YLCD-8000P high-temperature oven at50℃,100℃,150℃,200℃for72h, and the tensile strength of the silicone elastomer samples before and after aging were tested.UV aging test was performed according to ASTM D4587-01by QUV/Spray UV aging box for24h,48h,72h, and the tensile strength of the silicone elastomer samples before and after aging were tested.Stress fatigue was performed by Electro Force3510high precision biological material testing system for66700,133000,200000,266700times cyclic loading, and the tensile strength of the silicone elastomer samples before and after aging were tested.Samples were soaked by artificial saliva for15d,30d,60d, and the tensile strength of the silicone elastomer samples before and after aging were tested.Part ⅢThe unaging and aging silicone elastomer containing6%(w/w) nano-TiO2particles were chose to through in vitro cytotoxicity test (MTT) in accordance with ISO10993-5:2009.Statistical analysisAll date were analyzed using One-Way analysis of variance (ANOVA) in the part1-2and Two-way classification ANOVA in part3(a=0.05). Levene’s test of homogeneity of variance was used (a=0.1). If a significant difference among means was found student Newman-Keuls multiple comparison tests was performed when equal variance were assumed and Dunnett’s T3post-hoc test was used when equal variance were not assumed to determine differences between any of the groups at a significance level of P<0.05.Results1. Silicone elastomer matrix were mixed with nano-TiO2particles uniformly. After curing, smooth, bubble-free, no crack defect composite materials were obtained.2. The tensile strength represents the overall strength of prosthetic materials and the elongation at break represents flexibility of prosthetic material. The tensile strength significantly increased with increasing concentrations of nano-TiO2particles added into the silicone elastomer compared with the control group (P＜0.05). However, there was no significant different between SE-4%(w/w) and SE-6%(w/w). The tensile strength of silicone elastomer composite materials were respectively2.65±0.09MPa for control group,2.80±0.25MPa for2%group,3.01±0.35MPa for4%group, and3.29±0.40MPa for6%group.3. There was a significant increase in the elongation at break for the SE-2%(w/w) that compared to the control group (P＜0.05), while the mixing of6%(w/w) nano-TiO2particles with the silicone elastomer significantly decreased (P＜0.05). The tensile strength of silicone elastomer composite materials were respectively203.23±31.20%for control group,254.28±20.14%for2%group,192.83±16.46%for4%group, and142.15±14.63%for6%group. With the increase of the concentration of nano-TiO2particles, the elongation at break of nano-TiO2silicone elastomer composite material first increased and then decreased.4. One of the most important mechanical property of the maxillofacial prostheses is the tear strength of silicone elastomer. The incorporation of2%(w/w) nano-TiO2particles into the silicone elastomer increased the tear strength compared with the control group (P＜0.05). There was no significant difference between the control group and SE-2%, SE-4%(w/w) TiO2group (P＞0.05). However, there is a significantly decreased of the SE-6%(w/w) TiO2groups (P＜0.05). The tear strength of silicone elastomer composite materials were respectively10.21±1.19MPa for control group,12.58±1.91MPa for2%group,10.50±0.77MPa for4%group, and6.03±0.53MPa for6%group. With the increase of the concentration of nano-TiO2particles, the tear strength of nano-TiO2silicone elastomer composite material first increased and then decreased.5. Shore A hardness range of the silicone elastomer plays an important role in the personalization repairment of different defect portion. For shore A hardness showed a significant increase for all the different concentration of nano-TiO2silicone elastomers (P＜0.05). The shore A hardness of silicone elastomer composite material was respectively25.07±1.13for control group,28.67±0.84for2%group,30.53±1.13for4%group, and31.97±1.65for6%group. The shore A hardness of all the specimens were in the range of ideal values, which can meet the hardness requirement of repairing the parts such as nose and ears that has cartilage.6. A representative SEM photography of the fractured surface of SE-2%(w/w) and4%(w/w) TiO2group revealed that the nano-TiO2particles uniformly distributed into the silicone elastomer matrix. While SE-6%(w/w) group appeared the nano-TiO2particles agglomeration in silicone elastomer matrix.7. With the increase of hot air aging temperature, the tensile strength of each group for SE-0%(w/w) nano-TiO2silicone elastomer was:2.76±0.41MPa,2.75±0.25MPa,2.69±0.21MPa,2.22±0.21MPa, and2.02±0.10MPa. The tensile strength decreased significantly compared to the control group when the tensile strength of200℃group declined significantly compared to the other groups (P＜0.05). The tensile strength of each group for SE-6%(w/w) nanoTiO2silicone elastomer was:3.13±0.42MPa,3.26±0.45MPa,2.98±0.28MPa,3.17±0.23MPa, and3.07±0.37MPa. There was no significant difference between the control and hot air aging group (P＞0.05). The results indicated that the anti-hot air aging performance of nano-TiO2silicone elastomer was significantly improved. 8. With the increase of UV aging times, the tensile strength of each group for SE-0%(w/w) nano-TiO2silicone elastomer was:2.76±0.41MPa,2.43±0.23MPa,2.30±0.39MPa, and2.25±0.42MPa, There was no significant difference between the control and hot air aging group (P＞0.05). The tensile strength of each group for SE-6%(w/w) nanoTiO2silicone elastomer was:3.13±0.42MPa,3.24±0.39MPa,2.91±0.59MPa, and3.20±0.44MPa. There was no significant difference between the control and hot air aging group (P>0.05). The results indicated that the anti-UV aging performance of two types of silicone elastomer was excellent.9. With the increase of fatigue loading times, the tensile strength of each group for SE-0%(w/w) nano-TiO2silicone elastomer was:2.76±0.41MPa,2.77±0.26MPa,2.67±0.21MPa,2.91±0.47MPa, and2.49±0.39MPa. There was no significant difference between the control and hot air aging group (P＞0.05). The tensile strength of each group for SE-6%(w/w) nanoTiO2silicone elastomer was:3.13±0.42MPa,3.17±0.20MPa,3.36±0.51MPa,3.27±0.32MPa, and3.27±0.48MPa. There was no significant difference between the control and stress fatigue group (P＞0.05). The results indicated that the anti-stress load capacity of two types of silicone elastomer was excellent.10. Absorbent is an important property of prosthetic materials. After a periods of using, the strength of the prosthesis was affected due to the absorption of saliva, sweat or snivel. The tensile strength of each group for SE-0%(w/w) nanoTiO2silicone elastomer was:2.76±0.42MPa,2.43±0.45MPa,2.42±0.48MPa, and2.19±0.18MPa. The tensile strength of each group for SE-6%(w/w) nano-TiO2silicone elastomer was:3.13±0.42MPa,3.16±0.33MPa,2.78±0.09MPa, and2.77±0.13MPa. There was no significant difference between the control and hot air aging group for SE-0%(w/w) and SE-6%(w/w) nano-TiO2silicone elastomer (P>0.05).11. The cytotoxicity test (MTT assay) showed that cytotoxicity of nano-TiO2silicone elastomer material was grade0. The silicone elastomer filled with nano-TiO2 particles had good biocompatibility. While cytotoxicity of negative control group was grade4. After temperature aging, the saliva soaking and stress fatigue, the specimens still maintain good biocompatibility, and the OD values were no significantly declined. But after UV aging, the cytotoxicity of specimens was significantly increased compared with the control group, and the OD values were significantly decreased.Conclusion1. Nano-TiO2has significant effect on the tensile strength, elongation at break, tear strength and shore A hardness of maxillofacial prosthetic silicone elastomer.2. Nano-TiO2can significantly improve the anti-heat aging property of the silicone elastomer prosthetic materials. The blank silicone elastomer and nano-TiO2silicone elastomer can resist the UV aging, stress fatigue and saliva soaked.3. Nano-TiO2prosthetic silicone elastomer has good biocompatibility for24h.4. Temperature aging, saliva soaking and stress fatigue can affect the cytotoxicity of nano-TiO2silicon elastomer. However, UV aging cannot result in the cytotoxicity of nano-TiO2silicone elastomer. The research showed that after using for a period of time, environmental aging may lead to a certain degree of cytotoxicity of the prostheses. |
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