Wettability, water sorption and water solubility of seven silicone elastomers used for maxillofacial prostheses

Effect of artificial aging on color change and mechanical properties of high consistency maxillofacial silicone elastomers

STATEMENT OF PROBLEM

Discoloration and the deterioration of mechanical properties lead to the replacement of maxillofacial prostheses. However, studies on the change in color and mechanical properties of high viscosity elastomers are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of artificial aging on the mechanical and optical properties of high-consistency silicone elastomer (HCR) and compare these properties with a widely used liquid silicone rubber (LSR).

MATERIAL AND METHODS

The specimens were fabricated from HCR (Derma-sil; Spectromatch Ltd.) and LSR (M511; Technovent Ltd.) silicone materials according to the manufacturers' instructions. A total of 325 specimens were used (50 for the tear test, 50 for the tensile and elongation test, 25 for the hardness test, 50 for absorption and solubility, and 50 for color and surface roughness measurements). Four subgroups of HCR with different Shore A hardness values (5, 20, 55, 70) were used. The specimens were subjected to tear (ASTM D624), tensile and elongation (ASTM D41215), hardness (ASTM D2240), absorption and solubility (ADA 12), surface roughness, and color change tests before and after the artificial aging process. Both water bath and ultraviolet (UV) chamber aging methods were used for the absorption and solubility tests. Contrast ratio and relative translucency parameters were also examined in addition to color change. Accelerated aging including UV light, humidity, and heat was carried out for 168 hours. The analyses were performed using 2-way factorial ANOVA and mixed ANOVA designs. Bonferroni multiple comparison test was used for significant results (α=.05).

RESULTS

The hardness values of all groups increased after aging except for the HCR subgroup with Shore A hardness 20 (P<.001). No significant change was found in surface roughness (P=.118), tear strength (P=.374), or elongation percentage (P=.053) after aging for all silicone groups. The only group with a significant change in tensile strength was HCR70 (P=.01). According to the water absorption results, absorption rates were significantly higher after artificial aging compared with bath aging in all silicone groups (P<.001) except LSR (P>.05). The aging method had significant effect on the water solubility of all groups (P<.001). Color change was significantly different among the silicone groups (P<.001).

CONCLUSIONS

The HCR silicone elastomer tested in the study showed optical and mechanical properties compatible with those of a commonly used LSR silicone.

Effect of Extrinsic Pigmentation on Dimensional Stability, Hardness, Detail Reproduction, and Color of a Silicone

OBJECTIVE

 The aim of the study is to evaluate the effect of extrinsic pigmentation on the dimensional stability, hardness, detail reproduction, and color of a silicone after thermocycling.

MATERIALS AND METHODS

 Sixty samples of MDX4-4210 silicone (Dow Corning Corporation Medical Products) with intrinsic pink pigment (H-109-P, Factor II) and intrinsic opacifier (TiO) were fabricated. Two groups were created: Group 1-only intrinsic pigmentation (H-109P, Factor II + TiO) (Control); and Group 2-intrinsic (H-109P, Factor II + TiO) and extrinsic (Tan FE - 215, Factor II) pigmentation. The following tests were performed for each group: dimensional stability, Shore A hardness, detail reproduction, and color. Readings for the tests were taken before and after thermocycling (2,000 cycles). For dimensional stability and hardness, two-way analysis of variance (ANOVA) was used. One-way ANOVA was used for the color test. In case of significant statistical difference, the Tukey test was applied (p <0.05). All samples achieved the same detail reproduction score, therefore, no statistical evaluation was performed.

RESULTS

 For the dimensional stability test, comparing the initial time with the final time, there was a significant contraction in both groups after thermocycling. For the hardness test, comparing the time points, only group 1 showed a significant reduction in hardness after thermocycling. Groups 1 and 2 scored 2 for the detail reproduction test, before and after thermocycling. Comparing group 1 with group 2, there was no significant difference for color change.

CONCLUSION

 Based on the tests performed, extrinsic pigmentation did not show a negative effect on silicone, and therefore it can be indicated. The results of the dimensional, hardness, detail reproduction and color evaluations of the MDX4-4210 silicone were clinically acceptable in all cases in the groups with and without extrinsic pigmentation.

Interphase Surface Stability in Liquid-Liquid Membrane Contactors Based on Track-Etched Membranes

A promising solution for the implementation of extraction processes is liquid–liquid membrane contactors. The transfer of the target component from one immiscible liquid to another is carried out inside membrane pores. For the first time, highly asymmetric track-etched membranes made of polyethylene terephthalate (PET) of the same thickness but with different pore diameters (12.5–19 nm on one side and hundreds of nanometers on the other side) were studied in the liquid–liquid membrane contactor. For analysis of the liquid–liquid interface stability, two systems widely diverging in the interfacial tension value were used: water–pentanol and water–hexadecane. The interface stability was investigated depending on the following process parameters: the porous structure, the location of the asymmetric membrane in the contactor, the velocities of liquids, and the pressure drop between them. It was shown that the stability of the interface increases with decreasing pore size. Furthermore, it is preferable to supply the aqueous phase from the side of the asymmetric membrane with the larger pore size. The asymmetry of the porous structure of the membrane makes it possible to increase the range of pressure drop values between the phases by at least two times (from 5 to 10 kPa), which does not lead to mutual dispersion of the liquids. The liquid–liquid contactor based on the asymmetric track-etched membranes allows for the extraction of impurities from the organic phase into the aqueous phase by using a 1% solution of acetone in hexadecane as an example.

Effect of Accelerated Aging on the Sorption and Solubility Percentages of Silicone Facial Prostheses

Objective  This study aimed to evaluate the effect of accelerated aging on the sorption and solubility percentages of the MDX4-4210 and A-2186 silicones.

Materials and Methods  Two silicones (A-2186 and MDX4-4210) and three intrinsic pigments (bronze, black, and pink) were used in this study. Thus, six groups were created ( n = 10): Group 1 = bronze MDX4-4210; Group 2 = black MDX4-4210; Group 3 = pink MDX4-4210; Group 4 = bronze A-2186; Group 5 = black A-2186; and Group 6 = pink A-2186. The dimensions of all samples were the same (45-mm diameter (ø) × 1-mm thickness). The samples were aged for a total of 1,008 hours. In this period of 1,008 hours of accelerated aging, the sorption and solubility percentages of each sample were calculated at three time points (252, 504, and 1,008 hours).

Statistical Analysis  Three-way analysis of variance (ANOVA) and the Tukey test were performed (α = 0.05).

Result  Accelerated aging can significantly increase the sorption and solubility percentages of the MDX4-4210 and A-2186 silicones.

Effect of ultraviolet protective agents on maxillofacial silicone elastomer, part 2: Mechanical properties after artificial aging

STATEMENT OF PROBLEM

The addition of ultraviolet (UV) protectives may affect the materials' mechanical properties, which can limit the service life of facial prostheses.

PURPOSE

The purpose of this in vitro study was to investigate the effect of UV protectives on the mechanical properties of maxillofacial silicones after artificial aging.

MATERIAL AND METHODS

Six color groups (unpigmented, white, yellow, red, blue, and mixed) of addition-type maxillofacial silicone were prepared. Four UV protectives, benzophenone-3 (UV-BP), ethylhexyl methoxycinnamate (UV-EM), titanium dioxide (UV-TD), and ethylhexyl salicylate (UV-ES), at 0.5% and 1% concentrations by weight were incorporated into the silicone before polymerization. The specimens were subjected to accelerated aging in a weathering chamber for 300 and 600 hours and to thermocycling. The tensile strength and percentage elongation, tear strength, and hardness of maxillofacial silicones were evaluated. Data were analyzed by using 4-way ANOVA. The differences were compared by the Tukey honestly significant difference test (α=.05).

RESULTS

Tensile strength decreased after 300 and 600 hours of UV aging in 0.5% and 1% UV-BP protective-added groups and increased in thermocycled groups (P<.05). Aging conditions generally showed no effect on the tensile strength of UV-EM, UV-TD, and UV-ES added groups (P>.05). Aging generated a decrease in percentage elongation values compared with nonaged specimens of groups (P<.05). The addition of UV protectives generally did not significantly affect the tear strength of specimens compared with control in the aged groups (P>.05). The hardness of UV protective-added groups increased when compared with that of nonaged groups after 300 and 600 hours of UV aging (P<.05). Also, thermally aged groups showed increased hardness than nonaged groups (P<.05).

CONCLUSIONS

The protective UV-BP addition caused decreased tensile strength, percentage elongation, and tear strength in both concentrations. The UV-EM and UV-ES provided increases in tensile strength and percentage elongation of the silicone in the 0.5% concentration. The addition of UV-BP, UV-EM, and UV-ES did not make significant differences; however, UV-TD significantly decreased the hardness values of the silicone.

Analysis of physical properties of facial silicones with different pigmentations submitted to nonthermal plasma treatment and accelerated aging

STATEMENT OF PROBLEM

Exposure of silicone prostheses to environmental factors can alter their properties, affecting longevity. However, whether nonthermal plasma (NTP) can prevent these alterations is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the surface roughness (Ra), sorption, solubility, and color stability (ΔE₀₀) of the MDX4-4210 and A-120 silicones, with and without NTP treatment in accordance with an independent analysis of the use of 2 pigmentations.

MATERIAL AND METHODS

One hundred sixty specimens were fabricated and distributed into 16 groups (n=10) as per the silicone, pigmentation, and NTP coating. The NTP was applied, and the Ra, sorption, solubility, and ΔE₀₀ were evaluated before and after accelerated aging. ANOVA was used, and the HSD Tukey test was applied (α=.05).

RESULTS

NTP generated an increase in roughness after aging, regardless of pigmentation or silicone. A-120 silicone without NTP showed a reduction in roughness after aging, regardless of pigmentation. For sorption and solubility, the bronze pigmentation (for A-120 and MDX4-4210) presented the smallest results after NTP treatment. For MDX4-4210 with pink pigmentation and NTP, sorption decreased and solubility increased. For A-120 with pink pigmentation and NTP, sorption and solubility increased. Sorption was reduced in all situations, except for A-120 with pink pigmentation, which increased. Regardless of the silicone used, solubility was reduced after NTP for bronze pigmentation. For A-120 and MDX4-4210 with pink pigmentation and NTP, the solubility increased. For both pigmentations, the NTP treatment promoted lower color alteration only for the A-120 silicone after accelerated aging (within the acceptability threshold).

CONCLUSIONS

The NTP protocol of this study, which was applied to facial silicones, generated inconsistent results between the evaluated properties. Therefore, the NTP protocol used does not seem to be ideal for the treatment of silicone surfaces after aging.

Influence of Different Pigment Incorporation Methods on the Sorption and Solubility of Medical Silicones

Objective  The aim of this study is to verify the influence of three pigment incorporation methods (conventional, mechanical, and industrial) on the sorption and solubility of the MDX4-4210 and A-2186 silicones.

Materials and Methods  The groups formed were based on the silicones used (A-2186 and MDX4-4210), intrinsic pigments (pink, bronze, and black), and pigment incorporation methods (conventional, mechanical, and industrial). The dimensions of all samples were 45-mm diameter (ø) × 1-mm thickness. Readings were taken initially and after 1,008 hours of aging.

Statistical Analysis  Three-way analysis of variance and the Tukey's test were performed (α = 0.05).

Results  For sorption and solubility, there was no difference between the incorporation methods for the A-2186 silicone, regardless of the pigment used ( p  > 0.05). For pink MDX4-4210, the industrial and mechanical methods showed higher values of sorption compared with the conventional method ( p  < 0.05). For bronze MDX4-4210, the industrial method showed a higher sorption value compared with the conventional and mechanical methods ( p  < 0.05). For black MDX4-4210, there was no difference between incorporation methods based on sorption ( p  > 0.05). For pink MDX4-4210, the mechanical method showed a higher solubility value compared with the industrial and conventional methods ( p  < 0.05). For black MDX4-4210 and bronze MDX4-4210, there was no statistically significant difference between incorporation methods based on solubility (p > 0.05).

Conclusion  Based on sorption and solubility, for the A-2186 silicone, the conventional, mechanical, and industrial methods of pigment incorporation were equivalent. For the MDX4-4210 silicone, its results of sorption and solubility were varied, and further studies are recommended.

Advancements in Soft-Tissue Prosthetics Part B: The Chemistry of Imitating Life

Each year, congenital defects, trauma or cancer often results in considerable physical disfigurement for many people worldwide. This adversely impacts their psychological, social and economic outlook, leading to poor life experiences and negative health outcomes. In many cases of soft tissue disfigurement, highly personalized prostheses are available to restore both aesthetics and function. As discussed in part A of this review, key to the success of any soft tissue prosthetic is the fundamental properties of the materials. This determines the maximum attainable level of aesthetics, attachment mechanisms, fabrication complexity, cost, and robustness. Since the early-mid 20th century, polymers have completely replaced natural materials in prosthetics, with advances in both material properties and fabrication techniques leading to significantly improved capabilities. In part A, we discussed the history of polymers in prosthetics, their ideal properties, and the application of polymers in prostheses for the ear, nose, eye, breast and finger. We also reviewed the latest developments in advanced manufacturing and 3D printing, including different fabrication technologies and new and upcoming materials. In this review, Part B, we detail the chemistry of the most commonly used synthetic polymers in soft tissue prosthetics; silicone, acrylic resin, vinyl polymer, and polyurethane elastomer. For each polymer, we briefly discuss their history before detailing their chemistry and fabrication processes. We also discuss degradation of the polymer in the context of their application in prosthetics, including time and weathering, the impact of skin secretions, microbial growth and cleaning and disinfecting. Although advanced manufacturing promises new fabrication capabilities using exotic synthetic polymers with programmable material properties, silicones and acrylics remain the most commonly used materials in prosthetics today. As research in this field progresses, development of new variations and fabrication techniques based on these synthetic polymers will lead to even better and more robust soft tissue prosthetics, with improved life-like aesthetics and lower cost manufacturing.

Advancements in Soft-Tissue Prosthetics Part A: The Art of Imitating Life

Physical disfigurement due to congenital defects, trauma, or cancer causes considerable distress and physical impairment for millions of people worldwide; impacting their economic, psychological and social wellbeing. Since 3000 B.C., prosthetic devices have been used to address these issues by restoring both aesthetics and utility to those with disfigurement. Internationally, academic and industry researchers are constantly developing new materials and manufacturing techniques to provide higher quality and lower cost prostheses to those people who need them. New advanced technologies including 3D imaging, modeling, and printing are revolutionizing the way prostheses are now made. These new approaches are disrupting the traditional and manual art form of prosthetic production which are laborious and costly and are being replaced by more precise and quantitative processes which enable the rapid, low cost production of patient-specific prostheses. In this two part review, we provide a comprehensive report of past, present and emerging soft-tissue prosthetic materials and manufacturing techniques. In this review, part A, we examine, historically, the ideal properts of a polymeric material when applied in soft-tissue prosthetics. We also detail new research approaches to target specific tissues which commonly require aesthetic restoration (e.g. ear, nose and eyes) and discuss both traditional and advanced fabrication methods, from hand-crafted impression based approaches to advanced manufactured prosthetics. We discuss the chemistry and related details of most significant synthetic polymers used in soft-tissue prosthetics in Part B. As advanced manufacturing transitions from research into practice, the five millennia history of prosthetics enters a new age of economic, personalized, advanced soft tissue prosthetics and with this comes significantly improved quality of life for the people affected by tissue loss.

Effect of intrinsic pigmentation on the tear strength and water sorption of two commercially available silicone elastomers

The purpose of this study was to evaluate the water sorption and tear strength of two commercially available silicone elastomers. Silicone test specimens with the dimension of 150 mm × 150 mm × 3 mm were prepared for cosmesil M511 silicone (Cosmedica Ltd, Cardiff, UK) and biomed silicone (MP Sai Enterprises, Mumbai, India). Sixty test specimens were divided equally into two groups-I and II. Group I and II were further subdivided into A, B, and C with 10 specimens each. Subgroup A represented the control group (without colorant), test specimens in subgroup B (incorporated with intrinsic pigments) were evaluated for tear strength, and subgroup C specimens, incorporated with intrinsic pigments were evaluated for water sorption. Students's t test was performed. Among the control group, cosmesil M511 silicone showed more tear strength with the mean of 11.42 ± 0.73 compared to biomed silicone which showed 6.64 ± 0.70. The tear strength values increased for both silicones after intrinsic pigmentation. Cosmesil M511 silicone showed more water sorption compared to biomed silicone. Medical grade cosmesil M511 silicone had better tear strength values compared to biomed silicone.

Effectiveness of antibacterial copper additives in silicone implants

Staphylococcus epidermidis plays a major role in capsular contractures of silicone breast implants. This in vitro study evaluates the antibacterial effect of copper on S. epidermidis in silicone implants. Specimens of a silicone material used for breast augmentation (Cu0) and specimens coated with different copper concentrations (Cu1, Cu2) were artificially aged. Surface roughness and surface free energy were assessed. The specimens were incubated in an S. epidermidis suspension. We assessed the quantification and the viability of adhering bacteria by live/dead cell labeling with fluorescence microscopy. Additionally, inhibition of bacterial growth was evaluated by agar diffusion, broth culture, and quantitative culture of surface bacteria. No significant differences in surface roughness and surface free energy were found between Cu0, Cu1 and Cu2. Aging did not change surface characteristics and the extent of bacterial adhesion. Fluorescence microscopy showed that the quantity of bacteria on Cu0 was significantly higher than that on Cu1 and Cu2. The ratio of dead to total adhering bacteria was significantly lower on Cu0 than on Cu1 and Cu2, and tended to be higher for Cu2 than for Cu1. Quantitative culture showed equal trends. Copper additives seem to have anti-adherence and bactericidal effects on S. epidermidis in vitro.