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Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study
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Original article
Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study N.K. Sonnahalli a,∗, R. Chowdhary b a
Department of Prosthodontics Crown and Bridge and Implantology, Rajarajeswari Dental College and Hospital, No.14, Ramohalli Cross, Kumbalgodu, Mysore Road, Bangalore 560074, India Department of Prosthodontics, Rajarajeswari Dental College and Hospital, Bangalore, India
b
a r t i c l e
i n f o
Article history: Received 25 September 2019 Revised 6 November 2019 Accepted 3 December 2019 Available online xxx Keywords: Maxillofacial Silicone elastomer Silver nanoparticles Physical properties
a b s t r a c t Purpose: The purpose of this study was to evaluate the impact of silver nanoparticle incorporation into maxillofacial silicone material on its hardness, tear strength and color stability. Methods: A total of 180 silicone specimens were fabricated according to the specification of American society for material and testing (ASTM) No. D142 and No. D624. The control samples were fabricated without silver nanoparticles and test samples were fabricate with 20 ppm concentration of silver nanoparticles. For outdoor weathering specimens were placed in a metal cage, which was suspended from the roof for a period of one month. Digital shore A hardness tests (Yuzuki, DIN 53505, ASTM D2240) was used to measure hardness, for tear strength the specimen was placed in the jaws of the universal testing machine (Lloyd instruments, LR 50 K) and stretched at a rate of 500 ram/rain, for color stability Spectrophotometer had been employed and the data recorded in the CIE L∗ a∗ b∗ system. The independent sample’s “t” test was used to test significant differences. Results: The mean difference for hardness between control and test group was 0.54 and t value was 2.08 and (p < 0.05).tear strength 0.66 and “t” value was 0.93 and (p < 0.05) and for color stability it was -0.02 and t value was -0.92 and (p < 0.05). Conclusion: The present study findings suggest that addition of silver nanoparticles at 20 ppm concentration decreased the hardness of Teksil 25(S25) silicone elastomer, and it did not affect tear strength and color stability. © 2019 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.
1. Introduction Maxillofacial prosthetics replaces the missing facial parts that have been lost due to congenital abnormalities, developmental disturbances, tumors and trauma. The main goal of maxillofacial prosthesis is, life like production of missing parts and there by providing patients a normal appearance, social acceptance and psychological wellbeing [1]. Materials used in fabrication of maxillofacial prosthesis should possess some ideal properties such as, good tear strength, tensile strength, hardness, water sorption, color stability and it should be biocompatible [2]. Prosthesis made with such material should possess physical and mechanical properties that are compatible to that of human skin [3].
∗
Silicone is introduced in 1960, from then it has become most widely used and clinically accepted material for fabrication of facial prosthesis, because of its ease of manipulation, physical and mechanical properties and biocompatibility. Silicone material possess a texture similar to that of human skin, its flexibility provides the patient with both wellbeing and comfort [1,4]. However, the silicone material has some limitations. The main problem with the currently used silicone material is its reduced lifetime because of its color instability and early material deterioration, for example it exhibits modified texture, poorly fitting edges because of reduced tear strength [5]. These changes are directly relate to the patients care while handling and hygiene, use of cleaning agents and the type of exposure that the prosthesis undergoes such as temperature fluctuations, UV radiation, solar radiation, moisture, air pollution, climate changes [5]. Various methods have been tried to overcome this polymer deterioration [4–7]. Addition of nanoparticles has become the new
Corresponding author. E-mail address: [email protected] (N.K. Sonnahalli).
https://doi.org/10.1016/j.jpor.2019.12.001 1883-1958/© 2019 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001
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Fig. 1. ASTM No.D412 specifications for dumbbell shaped specimens.
Fig. 3. Metal die.
Fig. 2. ASTM No. D624 specifications for trouser shped specimens.
trend as nanotechnology has become one of the main growing science. Several nanoparticles have been tested and studies have confirmed the effectiveness of nanoparticles in improving the color stability by blocking the ultraviolet rays and also in improving the physical and mechanical properties of silicone elastomer [4–8]. As the nanoparticles are smaller than the UV light wavelength, their electrons vibrate when they hit by such radiation, thereby dissipating one portion of the light while absorbing another. Thus, the smaller the nanoparticles, the better the shielding against solar radiation [9]. Silver nanoparticles along with its broad-spectrum antimicrobial property, it has distinctive physico-chemical properties, including high thermal and electrical conductivity, surface-enhanced Raman scattering, chemical stability, catalytic activity and nonlinear optical behavior [10]. Silver nanoparticles are also used as antifungal agents in maxillofacial silicone and proved their biocompatibility and antifungal properties [11], but its effect on physical, mechanical properties and color stability of the material has not been tested. The purpose of this study was to evaluate the impact of silver nanoparticle incorporation into maxillofacial silicone material on its hardness tear strength and color stability. 2. Materials and methods In total of 180 silicone specimens were fabricated according to the specification of American society for material and testing (ASTM) No. D142 (Fig. 1) and No. D624 (Fig. 2). which included two designs, one was dumbbell shape and other trouser shape (Figs. 1 and 2). Out of which, 90 specimens were made without incorporating silver nanoparticles, which were considered as control group and the other 90 specimens which were incorporated with silver nanoparticles were considered as study group. The samples are divided into three main groups depending on the test and each group is further sub divided into two groups as control and test group for each test Group 1 – for hardness test, under which it was further divided into Group 1a – 30 DS specimens without silver Nano particles and Group 1b – 30 DS specimens with silver nanoparticles. Group 2 – for tear strength test, under which it was further divided into Group 2a- 30 TS specimens without silver Nano particles and Group 2b- 30 TS specimens with silver Nano particles Group 3 – for color stability test, under which it was further divided into Group 3a – 30 DS specimens without silver Nano particles and Group 3b – 30 DS specimens with silver nanoparticles.
Fig. 4. Control Samples.
To make the samples priory a metal die was fabricated in accordance to the specifications given by American society for material and testing (ASTM) No. D142 and No. D624 (Fig. 3), which had a provision for making 10 each of DS and TS specimens at a time. This metal die was fabricated in Brass metal, with the help of CAD and CAM designing, in order to maintain the uniformity of the specimens. 2.1. Making of specimens To make the control specimens using silicone elastomer (M511, Technovent Ltd., South Wales, United Kingdom) Part A, the catalyst and part B, the base were added in the ratio of 9:1(Measurement was carried out using digital weighing machine) (Fig. 4). Part A and part B were mixed with metal spatula on a wider glass slab to minimize the incorporation of air bubbles, this mix was kept in a vacuum chamber later to remove the air bubbles incorporated during mixing. To make the test specimens using silver Nano particle and silicone elastomer, the Silver Nano particles (Nano powder, Ag, Purity 99.9%, 10–20 nm, metal basis) were added to elastomer primer (part B), Nano powder was added with a concentration of 20 ppm and mixed in a glass beaker and kept in the ultrasonic vibrator for proper distribution of the nanoparticles. Thus, mixed Part B was later mixed with Part A of the elastomer material as explained previously (Fig. 5). Thus, mixed elastomer was then placed in the dumbbell and trouser shaped die. The mold was then closed with the metal lid
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001
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3
Table 1 Mean distribution of hardnes test (without nanoparticles and with nanoparticles). Groups Hardness test
Without nanoparticles (Group 1a) With nanoparticles (Group 1b)
Minimum
Maximum
Mean
Std. Deviation
26.0 25.4
30.2 30.6
28.307 27.760
0.8816 1.1379
The specimen was placed in the jaws of the universal testing machine (Lloyd instruments, LR 50 K) and stretched at a rate of 500 ram/rain. From these measurements, the tear strength of that specimen was calculated. 2.4. Color stability test Spectrophotometer had been employed and the data recorded in the CIE L∗ a∗ b∗ system. The color changes (E) are calculated from the L∗ , a∗ , and b∗ values for each specimen, according to the following formula, which determines the three-dimensional color space: Elab∗ = [(L∗ )2 + (a∗ )2 + (b∗ )2]1/2, while luminosity values (L∗ ) were reached using L∗ = L∗ (tx)–L∗ (t0), where (tx) represents immersion time and (t0) the baseline. Before each measurement session, the instrument was calibrated according to manufacturer instruction by using the supplied white calibration standard. CIE Lab color scale was then used to measure the color. A tungsten lamp of D50 standard illuminate was used with a viewing angle of 2° UV filter is positioned to 100% UV. For each specimen the color measurements were made on three randomly selected areas and average of three reading is recorded. 3. Results
Fig. 5. Test samples.
and allowed to polymerize. After polymerization, the specimens were carefully removed and the excess flash was trimmed. Both the control and test group specimens were placed in a metal cage, which was suspended from the roof for a period of one month for natural outdoor weathering. At the end of the allotted exposure time, specimens were removed and washed with detergent. They were later wiped dry and then were evaluated for different properties. 2.2. Shore a hardness test ASTM D2240 standard test method for rubber property durometer hardness type A [12]. A durometer is generally used for soft vulcanized rubber and thermoplastic elastomers. The specimen were 3 mm in thickness. Three specimens were stacked on one another on a hard-horizontal surface for a total of 9 mm to obtain minimum of 6 mm thickness required of the ASTM specification No. D2240. Digital shore A hardness tests (Yuzuki, DIN 53505, ASTM D2240) was used to measure hardness. Five sites were measured for each specimen with 12 mm distance between of each site and a 6 mm distance from the edge of the specimen. The specimen at the bottom of the stack was removed and a new specimen placed on the top and the procedure was repeated to obtain readings for that specimen. 2.3. Tear strength test Tear strength is defined as the maximum force (Newtons) required to break the TS specimen, divided by the thickness of the specimen. The thickness of the specimen (at 3 mm, depending on the degree of mold closure) was measured at the intersection of the trouser leg with a Vernier caliper with digital readout.
Effect of adding silver nanoparticles on hardness, tear strength, and color stability of teksil 25 (S-25) maxillofacial silicone elastomer were evaluated. The mean difference and standard deviation for hardness, tear strength, and color stability of silicone without Nano particles in comparison to silicone with nanoparticles were calculated. The independent sample’s “t” test was used to test significant differences in the physical properties along with the color stability. The maximum hardness values of 30.2 and 30.6 Shore A hardness, for group 1a and group 1b respectively was recorded. The group 1a had a mean hardness of 28.307 with a standard deviation of 0.8816. The group 1b had a mean hardness of 27.706 with a standard deviation of 1.1379 (Table 1). The maximum tear strength values of 20 N/mm and 10 N/mm was for group 2a and group 2b respectively. The group 2a had a mean tear strength of 14.10 with a standard deviation of 3.013. The group 2b had a mean tear strength of 13.43 with a standard deviation of 2.487 (Table 2). The maximum E∗ values of 0.9 and 0.83 for group 3a and group 3b respectively. The group 3a had a mean E∗ of 0.67 with a standard deviation of 0.10. The group 3b had a mean E∗ of 0.69 with a standard deviation of 0.095(Table 3). The independent sample’s “t” test comparing control and test groups with respect to hardness showed mean difference of 0.54 and t value was 2.08 and p value 0.04 (Table 4). As seen in results p value is less (p<0.05). So it can be concluded that statistically there was significant difference between the control and test group with respect to the hardness. The mean difference for tear strength between control and test group was 0.66 and “t” value was 0.93 and p value 0.35. As seen in results p value is more (p<0.05) and for color stability it was −0.02 and t value was −0.92 and p value 0.36 As seen in results p value is more (p<0.05). So it can be concluded that statistically there was no significant difference between the control and test group with respect to the tear strength and color stability.
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001
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N.K. Sonnahalli and R. Chowdhary / Journal of Prosthodontic Research xxx (xxxx) xxx Table 2 Mean distribution of tear strength (without nanoparticles and with nanoparticles). Groups Tear strength
Without nanoparticles (Group 2a) With nanoparticles (Group 2b)
Minimum
Maximum
Mean
Std. Deviation
9 9
20 19
14.10 13.43
3.010 2.487
Table 3 Mean distribution of color stability (δ e ∗ ) (without nanoparticles and with nanoparticles). groups color stability (δ e ∗ )
without nanoparticles (group 3a) With nanoparticles (Group 3b)
Table 4 Comparison of the groups using independent sample t-test.
HARDNESS TEST TEAR STRENGTH COLOR STABILITY ∗
MEAN DIFFERENCE
T VALUE
p VALUE
0.54 0.66 −0.02
2.08 0.93 0.92
0.04∗ 0.35 0.36
significant.
4. Discussion Silicone is the most accepted and frequently used material in fabrication of maxillofacial prostheses because of its texture and strength which mimic the human tissue, durability, ease in manipulation and coloring, and patient comfort [4]. However, silicone has a short shelf life because of rapid degradation of physical properties and color instability and is difficult to repair, limiting its use in maxillofacial prostheses [4]. Nano-sized particles differ in their physical, chemical and biological properties compared to their macro sized counterparts due to their high surface to volume ratio. Properties of nanoparticles depends on their size and concentration [8]. Nano-sized ZnO, TiO2 , CeO2 have mainly been used as UV shields as they have a high ultraviolet (UV) absorbing and scattering effect [14]. Nano sized SiO2 , TiO2 , and ZnO are characterized by their small size, large specific area, active function, and strong interfacial interaction with the organic polymer. Therefore, they can improve the physical properties and optical properties of the organic polymer, as well as provide resistance to environmental stress-caused aging [10]. The texture of silicone should match with that of the skin of the anatomic area to be restored and hardness of the material influences the texture the material [10–14]. The skin covering the orbital, nasal and ear areas of the maxilla are thin and very close to the bone and cartilage [10,14]. Thus, the silicone should have a hardness values of between 25 and 35 Shore A in order to match the texture of the above mentioned sites. To achieve a best combination of antifungal activity and physical and mechanical properties the concentration of silver nano-particles should be between 10–40 ppm [15]. In the present study addition 20 ppm of silver nanoparticles (AgNP’s) concentration was chosen. Addition of 20 ppm silver nano-particles to the silicone elastomer significantly decreased the hardness of the elastomer (p = 0.04), Even though hardness values were decreased for silicone with silver nanoparticles, the values very much remained within the 25–35 shore-A (mean hardness 27.706). AgNP’s had influence on decreasing the hardness, this reduction in hardness could be because of nature of the nanoparticles [14]. The shape, size and surface charge of AgNP’s can dramatically affect the physical properties [16]. Though, the particle size was small which helps to penetrate between the polymer molecule, the problem with the most of the nanoparticles is that of agglomeration [14,16]. The rate of dissolution depends on the chemical and surface properties of the particle as well as
minimum
maximum
mean
std. deviation
0.50 0.52
0.90 0.83
0.67 0.69
0.10 0.095
its size, and is further affected by the surrounding media [16]. The agglomeration of nanoparticles can be larger than the actual polymer particle size, this may cause voids around these agglomerations, which may have adverse effects on mechanical properties of the material. Therefore, the nanoparticle may require surface treatments to reduce its conglomeration and improve its dispersion into the silicone matrix, which needs to be evaluated further [14]. Findings of the present study are supported by that of Nobrega et al., wherein, addition of TiO2 at concentration of 1% and 2% decreased the hardness values, as the TiO2 particles are smaller in size they had a difficulty in uniform dispersion and tend to agglomerate [14]. They also mentioned that, incorporation of Nano size oxides of Ti, Zn, or Ce at concentrations of 2.0 to 2.5% by weight into a siliconebased elastomer, improves hardness, but when the concentration was 3.0%, the hardness decreased. In other study which revealed that there was a small but significant increase in the hardness as the concentration of the SiO2 Nano filler in the A- 2186 was increased from 0% to 3% [4]. The tear strength of silicone elastomer is clinically very important as the margins surrounding the facial prosthesis are thin and are usually glued with the medical adhesives, and highly susceptibility to tear [2]. Agglomeration of nanoparticles depends on their surface energy and its chemical reactivity, it is important to maintain the proper concentration of the fillers. Otherwise the Nano sized oxide particles may agglomerate. The agglomerated particles acts as an areas of stress concentrations under the external forces thereby decreasing the mechanical strength of the material [7]. But, in the present study, there was no statistically significant changes in tear strength, however, the maximum value obtained for tear strength for silicone with nanoparticles was less than that of the silicone elastomer without nanoparticles. In a study conducted by Han et al., which indicates that, incorporation of Ti, Zn, or Ce based nanoparticles at concentration of 2.0–2.5% by weight into an A-2186 silicone elastomer improved tear strength, but, when the concentration was 3.0%, the tear strength decreased [7]. Nguyen et al., in 2013 stated that addition of nanoparticles(TiO2 , ZnO) did not improve the mechanical properties of the silicone elastomer subjected to accelerated aging [17]. Addition of nano TiO2 decreases the tear strength and nano ZnO will not have any negative effect on the tear strength, But addition of BaSO4 nanoparticles will result in increased tear strength values, which is due to strong association of nanoparticles with silicone chains [13]. The findings of present study is supported by above mentioned studies as addition of AgNP’s in 20 ppm concentration did not affect the tear strength of the material negatively. Addition of surface treated SiO2 nanoparticles at 3% concentration increases the tear strength of silicone elastomer, this probably because surface treated silica fillers have better dispersion in the silicone elastomer [4]. Under deformation, this surface treated silica allows the polymer chains uncoil and slide past neighboring filler particles increasing the crystallization between neighboring PDMS chains. And also, higher surface energy and chemical reactivity of
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the nanoparticles allowed them to interact with the silicone elastomer matrix and improved the chemical bonding because of surface treatment [4]. Color degradation of silicone elastomer limits life time of the prosthesis, and often requires fabrication of new prosthesis within 6 months to 1 years [1]. The reason for this early color deterioration can be attributed to certain environmental factors such as solar radiation, temperature and water. Solar radiation reaching earth consist mostly of Ultraviolet, visible and infrared radiation. The UV radiation has a large impact on color stability [18]. Many inorganic nanoparticle such as nano-TiO2 , nano-ZnO, nano-CeO2 and nanoBaSO4 are widely used as UV absorbers [9]. UV radiation is an electromagnetic wave, when UV light acts on nano-particles in the media, As the nanoparticles are smaller than the UV light wavelength, their electrons vibrate when they are hit by such radiation, thereby dissipating one portion of the light while absorbing another. Thus, the smaller the nanoparticles, the better the shielding against solar radiation [9]. Many studies reported when inorganic nanoparticles such as nano-TiO2 at concentration of 2–2.5% and nano-CeO2 at 1% by weight used has a oacifiers for silicone A-2186 exhibited the least color changes [9,10]. Incorporation of nano-oxides such as TiO2 and ZnO improved the color stability of Cosmosil M511. But comparatively, nano-ZnO showed the most color stability after being subjected to outdoor weathering [10]. In the present study, the addition of 20 ppm AgNP’s did not affect the color stability, the mean E∗ values obtained were 0.69 with a standard deviation of 0.095. But the values obtained were well below the acceptability threshold (E∗ ==3.1). The silver nanostructures have exceptional optical properties because of their distinctive interaction with light, which causes the collective coherent oscillation of their free electrons. These oscillation of the free electrons result in either radiative decay with a strong visible scattering of light, or nonradiative decay by converting photon energy into thermal energy [15]. This properties of AgNP’s depend on its particle size, shape and the concentration, mostly at different concentration and particle size it can improve the color stability of the elastomer and can be used as opacifier. Since addition of silver nano-particles did not negatively affect the properties it can be used as an antifungal agent in the maxillofacial silicone elastomer to improve the longevity of the prosthesis. One of the limitations of this present study was to evaluate the effects of various concentrations of silver nanoparticles on properties of silicone elastomer. So further research is required. 5. Conclusion
5
Declaration of Competing Interest We have no conflict of interest. References [1] Haug SP, Andres CJ, Moore BK. Color stability and colorant effect on maxillofacial elastomers. Part I: colorant effect on physical properties. J Prosthet Dent 1999;81:418–22. [2] Aziz T, Waters M, Jagger R. Analysis of the properties of silicone rubber maxillofacial prosthetic materials. J Dent 2003;31:67–74. [3] Kantola R, Lassila LVJ, Tolvanen M, Valittu PK. Color stability of thermochromic pigment in maxillofacial silicone. J Adv Prosthodont 2013;5:75–83. [4] Zayed SM, Alshimy AM, Fahmy AE. Effect of surface treated silicon dioxide nanoparticles on some mechanical properties of maxillofacial silicone elastomer. Int J Biomater 2014;2014:750398 Epub 2014 Dec 9. [5] Kiat-Amnuay S, Mekkayarajjananonth T, Powers JM, Chambers MS, Lemon JC. Interaction of pigments and opacifiers on color stability of MDX4-4210/type a maxillofacial elastomers on artificial ageing. J Prosthet Dent 2006;95:249–57. [6] Mouzakis DE, Papadopoulos TD, Polyzois GL, Griniari PG. Dynamic mechanical properties of a maxillofacial silicone elastomer incorporating a zno additive: the effect of artificial aging. J Craniofac Surg 2010;21:1867–71. [7] Han Y, Kiat-amnuay S, Powers JM, Zhao Y. Effect of nano-oxide concentration on the mechanical properties of a maxillofacial silicone elastomer. J Prosthet Dent 20 08;10 0:465–73. [8] El-Nour KM, Eftaiha AA, Al-Warthan A, Ammar RA. Synthesis and applications of silver nanoparticles. Arab J Chem 2010;3:135–40. [9] Han Y, Zhao Y, Xie C, Powers JM, Kiat-amnuay S. Color stability of pigmented maxillofacial silicone elastomer: effects of nano-oxides as opacifiers. J Dent 2010;38:e100–5. [10] Wang L, Liu Q, Jing D, Zhou S, Shao L. Biomechanical properties of nano- TiO addition to a medical silicone elastomer: the effect of artificial ageing. J Dent 2014;42:475–83. [11] Meran Z, Besinis A, De Peralta T, Handy RD. Antifungal properties and biocompatibility of silver nanoparticle coatings on silicone maxillofacial prostheses in vitro. J Biomed Mater Res Part B Appl Biomater 2018;106:1038–51. [12] ASTM Standard D2240. Standard test method for rubber property—durometer hardness. West Conshohocken: American Society for Testing and Materials; 2005. [13] Goiato MC, Haddad MF, Santos DM, Pesqueira AA, Moreno A. Hardness evaluation of prosthetic silicones containing opacifiers following chemical disinfection and accelerated aging. Braz Oral Res 2010;24:303–8. [14] Nobrega AS, Andreotti AM, Moreno A, Sinhoreti MA, dos Santos DM, Goiato MC. Influence of adding nanoparticles on the hardness, tear strength, and permanent deformation of facial silicone subjected to accelerated aging. J Prosthet Dent 2016;116:623–9. [15] Akash RN, Guttal SS. Effect of incorporation of nano-oxides on color stability of maxillofacial silicone elastomer subjected to outdoor weathering. J Prosthodont 2015;24:569–75. [16] Wei L, Lu J, Xu H, Patel A, Chen ZS, Chen G. Silver nanoparticles: synthesis, properties, and therapeutic applications. Drug Discov Today 2015;20:595–601. [17] Nguyen CT, Chambers MS, Powers JM, Kiat-Amnuay S. Effect of opacifiers and UV absorbers on pigmented maxillofacial silicone elastomer, part 2: mechanical properties after artificial aging. J Prosthet Dent 2013;109:402–10. [18] Siddiquey IA, Ukaji E, Furusawa T, Sato M, Suzuki N. The effects of organic surface treatment by methacryloxypropyltrimethoxysilane on the photostability of TiO2 . Mater Chem Phys 2007;105:162–8.
Within the limitations of the study addition of silver nanoparticles at 20 ppm concentration, decreased the hardness of Teksil 25(S25) silicone elastomer, and it did not affect tear strength and color stability.
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001
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Journal of Prosthodontic Research xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Prosthodontic Research journal homepage: www.elsevier.com/locate/jpor
Original article
Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study N.K. Sonnahalli a,∗, R. Chowdhary b a
Department of Prosthodontics Crown and Bridge and Implantology, Rajarajeswari Dental College and Hospital, No.14, Ramohalli Cross, Kumbalgodu, Mysore Road, Bangalore 560074, India Department of Prosthodontics, Rajarajeswari Dental College and Hospital, Bangalore, India
b
a r t i c l e
i n f o
Article history: Received 25 September 2019 Revised 6 November 2019 Accepted 3 December 2019 Available online xxx Keywords: Maxillofacial Silicone elastomer Silver nanoparticles Physical properties
a b s t r a c t Purpose: The purpose of this study was to evaluate the impact of silver nanoparticle incorporation into maxillofacial silicone material on its hardness, tear strength and color stability. Methods: A total of 180 silicone specimens were fabricated according to the specification of American society for material and testing (ASTM) No. D142 and No. D624. The control samples were fabricated without silver nanoparticles and test samples were fabricate with 20 ppm concentration of silver nanoparticles. For outdoor weathering specimens were placed in a metal cage, which was suspended from the roof for a period of one month. Digital shore A hardness tests (Yuzuki, DIN 53505, ASTM D2240) was used to measure hardness, for tear strength the specimen was placed in the jaws of the universal testing machine (Lloyd instruments, LR 50 K) and stretched at a rate of 500 ram/rain, for color stability Spectrophotometer had been employed and the data recorded in the CIE L∗ a∗ b∗ system. The independent sample’s “t” test was used to test significant differences. Results: The mean difference for hardness between control and test group was 0.54 and t value was 2.08 and (p < 0.05).tear strength 0.66 and “t” value was 0.93 and (p < 0.05) and for color stability it was -0.02 and t value was -0.92 and (p < 0.05). Conclusion: The present study findings suggest that addition of silver nanoparticles at 20 ppm concentration decreased the hardness of Teksil 25(S25) silicone elastomer, and it did not affect tear strength and color stability. © 2019 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.
1. Introduction Maxillofacial prosthetics replaces the missing facial parts that have been lost due to congenital abnormalities, developmental disturbances, tumors and trauma. The main goal of maxillofacial prosthesis is, life like production of missing parts and there by providing patients a normal appearance, social acceptance and psychological wellbeing [1]. Materials used in fabrication of maxillofacial prosthesis should possess some ideal properties such as, good tear strength, tensile strength, hardness, water sorption, color stability and it should be biocompatible [2]. Prosthesis made with such material should possess physical and mechanical properties that are compatible to that of human skin [3].
∗
Silicone is introduced in 1960, from then it has become most widely used and clinically accepted material for fabrication of facial prosthesis, because of its ease of manipulation, physical and mechanical properties and biocompatibility. Silicone material possess a texture similar to that of human skin, its flexibility provides the patient with both wellbeing and comfort [1,4]. However, the silicone material has some limitations. The main problem with the currently used silicone material is its reduced lifetime because of its color instability and early material deterioration, for example it exhibits modified texture, poorly fitting edges because of reduced tear strength [5]. These changes are directly relate to the patients care while handling and hygiene, use of cleaning agents and the type of exposure that the prosthesis undergoes such as temperature fluctuations, UV radiation, solar radiation, moisture, air pollution, climate changes [5]. Various methods have been tried to overcome this polymer deterioration [4–7]. Addition of nanoparticles has become the new
Corresponding author. E-mail address: [email protected] (N.K. Sonnahalli).
https://doi.org/10.1016/j.jpor.2019.12.001 1883-1958/© 2019 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001
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Fig. 1. ASTM No.D412 specifications for dumbbell shaped specimens.
Fig. 3. Metal die.
Fig. 2. ASTM No. D624 specifications for trouser shped specimens.
trend as nanotechnology has become one of the main growing science. Several nanoparticles have been tested and studies have confirmed the effectiveness of nanoparticles in improving the color stability by blocking the ultraviolet rays and also in improving the physical and mechanical properties of silicone elastomer [4–8]. As the nanoparticles are smaller than the UV light wavelength, their electrons vibrate when they hit by such radiation, thereby dissipating one portion of the light while absorbing another. Thus, the smaller the nanoparticles, the better the shielding against solar radiation [9]. Silver nanoparticles along with its broad-spectrum antimicrobial property, it has distinctive physico-chemical properties, including high thermal and electrical conductivity, surface-enhanced Raman scattering, chemical stability, catalytic activity and nonlinear optical behavior [10]. Silver nanoparticles are also used as antifungal agents in maxillofacial silicone and proved their biocompatibility and antifungal properties [11], but its effect on physical, mechanical properties and color stability of the material has not been tested. The purpose of this study was to evaluate the impact of silver nanoparticle incorporation into maxillofacial silicone material on its hardness tear strength and color stability. 2. Materials and methods In total of 180 silicone specimens were fabricated according to the specification of American society for material and testing (ASTM) No. D142 (Fig. 1) and No. D624 (Fig. 2). which included two designs, one was dumbbell shape and other trouser shape (Figs. 1 and 2). Out of which, 90 specimens were made without incorporating silver nanoparticles, which were considered as control group and the other 90 specimens which were incorporated with silver nanoparticles were considered as study group. The samples are divided into three main groups depending on the test and each group is further sub divided into two groups as control and test group for each test Group 1 – for hardness test, under which it was further divided into Group 1a – 30 DS specimens without silver Nano particles and Group 1b – 30 DS specimens with silver nanoparticles. Group 2 – for tear strength test, under which it was further divided into Group 2a- 30 TS specimens without silver Nano particles and Group 2b- 30 TS specimens with silver Nano particles Group 3 – for color stability test, under which it was further divided into Group 3a – 30 DS specimens without silver Nano particles and Group 3b – 30 DS specimens with silver nanoparticles.
Fig. 4. Control Samples.
To make the samples priory a metal die was fabricated in accordance to the specifications given by American society for material and testing (ASTM) No. D142 and No. D624 (Fig. 3), which had a provision for making 10 each of DS and TS specimens at a time. This metal die was fabricated in Brass metal, with the help of CAD and CAM designing, in order to maintain the uniformity of the specimens. 2.1. Making of specimens To make the control specimens using silicone elastomer (M511, Technovent Ltd., South Wales, United Kingdom) Part A, the catalyst and part B, the base were added in the ratio of 9:1(Measurement was carried out using digital weighing machine) (Fig. 4). Part A and part B were mixed with metal spatula on a wider glass slab to minimize the incorporation of air bubbles, this mix was kept in a vacuum chamber later to remove the air bubbles incorporated during mixing. To make the test specimens using silver Nano particle and silicone elastomer, the Silver Nano particles (Nano powder, Ag, Purity 99.9%, 10–20 nm, metal basis) were added to elastomer primer (part B), Nano powder was added with a concentration of 20 ppm and mixed in a glass beaker and kept in the ultrasonic vibrator for proper distribution of the nanoparticles. Thus, mixed Part B was later mixed with Part A of the elastomer material as explained previously (Fig. 5). Thus, mixed elastomer was then placed in the dumbbell and trouser shaped die. The mold was then closed with the metal lid
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001
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3
Table 1 Mean distribution of hardnes test (without nanoparticles and with nanoparticles). Groups Hardness test
Without nanoparticles (Group 1a) With nanoparticles (Group 1b)
Minimum
Maximum
Mean
Std. Deviation
26.0 25.4
30.2 30.6
28.307 27.760
0.8816 1.1379
The specimen was placed in the jaws of the universal testing machine (Lloyd instruments, LR 50 K) and stretched at a rate of 500 ram/rain. From these measurements, the tear strength of that specimen was calculated. 2.4. Color stability test Spectrophotometer had been employed and the data recorded in the CIE L∗ a∗ b∗ system. The color changes (E) are calculated from the L∗ , a∗ , and b∗ values for each specimen, according to the following formula, which determines the three-dimensional color space: Elab∗ = [(L∗ )2 + (a∗ )2 + (b∗ )2]1/2, while luminosity values (L∗ ) were reached using L∗ = L∗ (tx)–L∗ (t0), where (tx) represents immersion time and (t0) the baseline. Before each measurement session, the instrument was calibrated according to manufacturer instruction by using the supplied white calibration standard. CIE Lab color scale was then used to measure the color. A tungsten lamp of D50 standard illuminate was used with a viewing angle of 2° UV filter is positioned to 100% UV. For each specimen the color measurements were made on three randomly selected areas and average of three reading is recorded. 3. Results
Fig. 5. Test samples.
and allowed to polymerize. After polymerization, the specimens were carefully removed and the excess flash was trimmed. Both the control and test group specimens were placed in a metal cage, which was suspended from the roof for a period of one month for natural outdoor weathering. At the end of the allotted exposure time, specimens were removed and washed with detergent. They were later wiped dry and then were evaluated for different properties. 2.2. Shore a hardness test ASTM D2240 standard test method for rubber property durometer hardness type A [12]. A durometer is generally used for soft vulcanized rubber and thermoplastic elastomers. The specimen were 3 mm in thickness. Three specimens were stacked on one another on a hard-horizontal surface for a total of 9 mm to obtain minimum of 6 mm thickness required of the ASTM specification No. D2240. Digital shore A hardness tests (Yuzuki, DIN 53505, ASTM D2240) was used to measure hardness. Five sites were measured for each specimen with 12 mm distance between of each site and a 6 mm distance from the edge of the specimen. The specimen at the bottom of the stack was removed and a new specimen placed on the top and the procedure was repeated to obtain readings for that specimen. 2.3. Tear strength test Tear strength is defined as the maximum force (Newtons) required to break the TS specimen, divided by the thickness of the specimen. The thickness of the specimen (at 3 mm, depending on the degree of mold closure) was measured at the intersection of the trouser leg with a Vernier caliper with digital readout.
Effect of adding silver nanoparticles on hardness, tear strength, and color stability of teksil 25 (S-25) maxillofacial silicone elastomer were evaluated. The mean difference and standard deviation for hardness, tear strength, and color stability of silicone without Nano particles in comparison to silicone with nanoparticles were calculated. The independent sample’s “t” test was used to test significant differences in the physical properties along with the color stability. The maximum hardness values of 30.2 and 30.6 Shore A hardness, for group 1a and group 1b respectively was recorded. The group 1a had a mean hardness of 28.307 with a standard deviation of 0.8816. The group 1b had a mean hardness of 27.706 with a standard deviation of 1.1379 (Table 1). The maximum tear strength values of 20 N/mm and 10 N/mm was for group 2a and group 2b respectively. The group 2a had a mean tear strength of 14.10 with a standard deviation of 3.013. The group 2b had a mean tear strength of 13.43 with a standard deviation of 2.487 (Table 2). The maximum E∗ values of 0.9 and 0.83 for group 3a and group 3b respectively. The group 3a had a mean E∗ of 0.67 with a standard deviation of 0.10. The group 3b had a mean E∗ of 0.69 with a standard deviation of 0.095(Table 3). The independent sample’s “t” test comparing control and test groups with respect to hardness showed mean difference of 0.54 and t value was 2.08 and p value 0.04 (Table 4). As seen in results p value is less (p<0.05). So it can be concluded that statistically there was significant difference between the control and test group with respect to the hardness. The mean difference for tear strength between control and test group was 0.66 and “t” value was 0.93 and p value 0.35. As seen in results p value is more (p<0.05) and for color stability it was −0.02 and t value was −0.92 and p value 0.36 As seen in results p value is more (p<0.05). So it can be concluded that statistically there was no significant difference between the control and test group with respect to the tear strength and color stability.
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001
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N.K. Sonnahalli and R. Chowdhary / Journal of Prosthodontic Research xxx (xxxx) xxx Table 2 Mean distribution of tear strength (without nanoparticles and with nanoparticles). Groups Tear strength
Without nanoparticles (Group 2a) With nanoparticles (Group 2b)
Minimum
Maximum
Mean
Std. Deviation
9 9
20 19
14.10 13.43
3.010 2.487
Table 3 Mean distribution of color stability (δ e ∗ ) (without nanoparticles and with nanoparticles). groups color stability (δ e ∗ )
without nanoparticles (group 3a) With nanoparticles (Group 3b)
Table 4 Comparison of the groups using independent sample t-test.
HARDNESS TEST TEAR STRENGTH COLOR STABILITY ∗
MEAN DIFFERENCE
T VALUE
p VALUE
0.54 0.66 −0.02
2.08 0.93 0.92
0.04∗ 0.35 0.36
significant.
4. Discussion Silicone is the most accepted and frequently used material in fabrication of maxillofacial prostheses because of its texture and strength which mimic the human tissue, durability, ease in manipulation and coloring, and patient comfort [4]. However, silicone has a short shelf life because of rapid degradation of physical properties and color instability and is difficult to repair, limiting its use in maxillofacial prostheses [4]. Nano-sized particles differ in their physical, chemical and biological properties compared to their macro sized counterparts due to their high surface to volume ratio. Properties of nanoparticles depends on their size and concentration [8]. Nano-sized ZnO, TiO2 , CeO2 have mainly been used as UV shields as they have a high ultraviolet (UV) absorbing and scattering effect [14]. Nano sized SiO2 , TiO2 , and ZnO are characterized by their small size, large specific area, active function, and strong interfacial interaction with the organic polymer. Therefore, they can improve the physical properties and optical properties of the organic polymer, as well as provide resistance to environmental stress-caused aging [10]. The texture of silicone should match with that of the skin of the anatomic area to be restored and hardness of the material influences the texture the material [10–14]. The skin covering the orbital, nasal and ear areas of the maxilla are thin and very close to the bone and cartilage [10,14]. Thus, the silicone should have a hardness values of between 25 and 35 Shore A in order to match the texture of the above mentioned sites. To achieve a best combination of antifungal activity and physical and mechanical properties the concentration of silver nano-particles should be between 10–40 ppm [15]. In the present study addition 20 ppm of silver nanoparticles (AgNP’s) concentration was chosen. Addition of 20 ppm silver nano-particles to the silicone elastomer significantly decreased the hardness of the elastomer (p = 0.04), Even though hardness values were decreased for silicone with silver nanoparticles, the values very much remained within the 25–35 shore-A (mean hardness 27.706). AgNP’s had influence on decreasing the hardness, this reduction in hardness could be because of nature of the nanoparticles [14]. The shape, size and surface charge of AgNP’s can dramatically affect the physical properties [16]. Though, the particle size was small which helps to penetrate between the polymer molecule, the problem with the most of the nanoparticles is that of agglomeration [14,16]. The rate of dissolution depends on the chemical and surface properties of the particle as well as
minimum
maximum
mean
std. deviation
0.50 0.52
0.90 0.83
0.67 0.69
0.10 0.095
its size, and is further affected by the surrounding media [16]. The agglomeration of nanoparticles can be larger than the actual polymer particle size, this may cause voids around these agglomerations, which may have adverse effects on mechanical properties of the material. Therefore, the nanoparticle may require surface treatments to reduce its conglomeration and improve its dispersion into the silicone matrix, which needs to be evaluated further [14]. Findings of the present study are supported by that of Nobrega et al., wherein, addition of TiO2 at concentration of 1% and 2% decreased the hardness values, as the TiO2 particles are smaller in size they had a difficulty in uniform dispersion and tend to agglomerate [14]. They also mentioned that, incorporation of Nano size oxides of Ti, Zn, or Ce at concentrations of 2.0 to 2.5% by weight into a siliconebased elastomer, improves hardness, but when the concentration was 3.0%, the hardness decreased. In other study which revealed that there was a small but significant increase in the hardness as the concentration of the SiO2 Nano filler in the A- 2186 was increased from 0% to 3% [4]. The tear strength of silicone elastomer is clinically very important as the margins surrounding the facial prosthesis are thin and are usually glued with the medical adhesives, and highly susceptibility to tear [2]. Agglomeration of nanoparticles depends on their surface energy and its chemical reactivity, it is important to maintain the proper concentration of the fillers. Otherwise the Nano sized oxide particles may agglomerate. The agglomerated particles acts as an areas of stress concentrations under the external forces thereby decreasing the mechanical strength of the material [7]. But, in the present study, there was no statistically significant changes in tear strength, however, the maximum value obtained for tear strength for silicone with nanoparticles was less than that of the silicone elastomer without nanoparticles. In a study conducted by Han et al., which indicates that, incorporation of Ti, Zn, or Ce based nanoparticles at concentration of 2.0–2.5% by weight into an A-2186 silicone elastomer improved tear strength, but, when the concentration was 3.0%, the tear strength decreased [7]. Nguyen et al., in 2013 stated that addition of nanoparticles(TiO2 , ZnO) did not improve the mechanical properties of the silicone elastomer subjected to accelerated aging [17]. Addition of nano TiO2 decreases the tear strength and nano ZnO will not have any negative effect on the tear strength, But addition of BaSO4 nanoparticles will result in increased tear strength values, which is due to strong association of nanoparticles with silicone chains [13]. The findings of present study is supported by above mentioned studies as addition of AgNP’s in 20 ppm concentration did not affect the tear strength of the material negatively. Addition of surface treated SiO2 nanoparticles at 3% concentration increases the tear strength of silicone elastomer, this probably because surface treated silica fillers have better dispersion in the silicone elastomer [4]. Under deformation, this surface treated silica allows the polymer chains uncoil and slide past neighboring filler particles increasing the crystallization between neighboring PDMS chains. And also, higher surface energy and chemical reactivity of
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001
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the nanoparticles allowed them to interact with the silicone elastomer matrix and improved the chemical bonding because of surface treatment [4]. Color degradation of silicone elastomer limits life time of the prosthesis, and often requires fabrication of new prosthesis within 6 months to 1 years [1]. The reason for this early color deterioration can be attributed to certain environmental factors such as solar radiation, temperature and water. Solar radiation reaching earth consist mostly of Ultraviolet, visible and infrared radiation. The UV radiation has a large impact on color stability [18]. Many inorganic nanoparticle such as nano-TiO2 , nano-ZnO, nano-CeO2 and nanoBaSO4 are widely used as UV absorbers [9]. UV radiation is an electromagnetic wave, when UV light acts on nano-particles in the media, As the nanoparticles are smaller than the UV light wavelength, their electrons vibrate when they are hit by such radiation, thereby dissipating one portion of the light while absorbing another. Thus, the smaller the nanoparticles, the better the shielding against solar radiation [9]. Many studies reported when inorganic nanoparticles such as nano-TiO2 at concentration of 2–2.5% and nano-CeO2 at 1% by weight used has a oacifiers for silicone A-2186 exhibited the least color changes [9,10]. Incorporation of nano-oxides such as TiO2 and ZnO improved the color stability of Cosmosil M511. But comparatively, nano-ZnO showed the most color stability after being subjected to outdoor weathering [10]. In the present study, the addition of 20 ppm AgNP’s did not affect the color stability, the mean E∗ values obtained were 0.69 with a standard deviation of 0.095. But the values obtained were well below the acceptability threshold (E∗ ==3.1). The silver nanostructures have exceptional optical properties because of their distinctive interaction with light, which causes the collective coherent oscillation of their free electrons. These oscillation of the free electrons result in either radiative decay with a strong visible scattering of light, or nonradiative decay by converting photon energy into thermal energy [15]. This properties of AgNP’s depend on its particle size, shape and the concentration, mostly at different concentration and particle size it can improve the color stability of the elastomer and can be used as opacifier. Since addition of silver nano-particles did not negatively affect the properties it can be used as an antifungal agent in the maxillofacial silicone elastomer to improve the longevity of the prosthesis. One of the limitations of this present study was to evaluate the effects of various concentrations of silver nanoparticles on properties of silicone elastomer. So further research is required. 5. Conclusion
5
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Within the limitations of the study addition of silver nanoparticles at 20 ppm concentration, decreased the hardness of Teksil 25(S25) silicone elastomer, and it did not affect tear strength and color stability.
Please cite this article as: N.K. Sonnahalli and R. Chowdhary, Effect of adding silver nanoparticle on physical and mechanical properties of maxillofacial silicone elastomer material-an in-vitro study, Journal of Prosthodontic Research, https://doi.org/10.1016/j.jpor.2019.12.001