Tear Strength Analysis of MDX4-4210 and A-2186 Silicones with Different Intrinsic Pigments Incorporated by Mechanical and Industrial Methods

Facile Modification of Medical-Grade Silicone for Antimicrobial Effectiveness and Biocompatibility: A Potential Therapeutic Strategy against Bacterial Biofilms

A one-step modification of biomedical silicone tubing with N,N-dimethyltetradecylamine, C14, results in a composition designated WinGard-1 (WG-1, 1.1 wt % C14). A surface-active silicon-amine phase (SAP) is proposed to account for increased wettability and increased surface charge. To understand the mechanism of antimicrobial effectiveness, several procedures were employed to detect whether C14 leaching occurred. An immersion-growth (IG) test was developed that required knowing the bacterial Minimum Inhibitory Concentrations (MICs) and Minimum Biocidal Concentrations (MBCs). The C14 MIC and MBC for Gm- uropathogenic E. coli (UPEC), commonly associated with catheter-associated urinary tract infections (CAUTI), were 10 and 20 μg/mL, respectively. After prior immersion of WG-1 silicone segments in a growth medium from 1 to 28 d, the IG test for the medium showed normal growth for UPEC over 24 h, indicating that the concentration of C14 must be less than the MIC, 10 μg/mL. GC-MS and studies of the medium inside and outside a dialysis bag containing WG-1 silicone segments supported de minimis leaching. Consequently, a 5 log UPEC reduction (99.999% kill) in 24 h using the shake flask test (ASTM E2149) cannot be due to leaching and is ascribed to contact kill. Interestingly, although the MBC was greater than 100 μg/mL for Pseudomonas aeruginosa, WG-1 silicone affected an 80% reduction via a 24 h shake flask test. For other bacteria and Candida albicans, greater than 99.9% shake flask kill may be understood by proposing increased wettability and concentration of charge illustrated in the TOC. De minimis leaching places WG-1 silicone at an advantage over conventional anti-infectives that rely on leaching of an antibiotic or heavy metals such as silver. The facile process for preparation of WG-1 silicone combined with biocidal effectiveness comprises progress toward the goals of device designation from the FDA for WG-1 and clearance.

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.

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.

Analysis of Color and Hardness of a Medical Silicone with Extrinsic Pigmentation after Accelerated Aging

Objective  The aim of this study is to evaluate the color alteration and shore A hardness of a medical silicone with extrinsic pigmentation, before and after accelerated aging.

Materials and Methods  Twenty samples (Silastic Q7–4735) were made with an intrinsic pigmentation. This intrinsic pigmentation was composed of a pink pigment (H-109-P, Factor II) and an opacifier (ZnO). All samples had standardized dimensions (45-mm diameter and 2-mm thickness). Half of the 20 samples manufactured subsequently received an extrinsic pigment (Tan FE–215, Factor II). Therefore, two groups were created ( n = 10): Group 1, group with intrinsic pigmentation and without extrinsic pigmentation (control) and Group 2, group with intrinsic and extrinsic pigmentation. Samples were submitted to color and Shore A hardness tests, before and after 1,008 hours of aging.

Statistical Analysis  Color alteration data were submitted to Student’s t -test ( α = 0.05). Shore A hardness data were submitted to two-way analysis of variance and Tukey test ( α = 0.05).

Results  The incorporation of the extrinsic pigment on the silicone did not affect its color (ΔE) when the two groups were compared ( p = 0.232). Regarding the hardness test, the interaction between group and period did not interfere with the hardness results( p =0.599). However, the period factor showed that there was a reduction in the hardness of the silicone after aging ( p < 0.05).

Conclusion  In this study, all the hardness and color results of the silicone used were clinically acceptable, regardless of the presence of extrinsic pigmentation.

The Effect of Nano Zinc Oxide Particles on Color Stability of MDX4-4210 Silicone Prostheses

Objective  This article aimed to study the effect of different concentrations of nano zinc oxide particles on the color change of MDX4–4210 facial silicone elastomer after artificial aging.

Materials and Methods  Silicone specimens ( N = 150) were fabricated by incorporating intrinsic pigments and divided into three groups—white, yellow, and red, each group consisting of 50 specimens ( n = 50). In each color, specimens were subdivided into five subgroups according to the quantity of zinc oxide nanoparticles (0, 0.5, 1.0, 1.5, and 2.0% weight), where the 0% weight served as the control in each group. All specimens were then subjected to artificial aging using an accelerated aging machine chamber for 12, 24, 48, and 72 hours. L*a*b* values of specimens were noted after a different aging period by a spectrophotometer and ∆ E * was calculated.

Statistical Analysis  Two-way repeated analysis of variance (ANOVA) was done to examine the effects under test conditions (concentration and aging time) of each color group. Then color, concentration, and the aging period were subjected to three-way repeated ANOVA to investigate the effects of different colors and concentrations on ∆ E *. Bonferroni’s test was performed to identify differences between groups. The significant level was at p = 0.05.

Results  The control group showed significantly higher ∆ E * values than the test groups. The 1.5% test group showed significantly lower ∆ E * compared with the others. The 0.5 to 2.0% of nano zinc oxide significantly decreased the color change of the silicone elastomer ( p < 0.05), but there were no significant differences among groups.

Conclusions  Incorporation of 1.5% of nano zinc oxide can improve the color stability of silicone prosthesis (MDX4–4210).

Influence of Different Pigmentations and Accelerated Aging on the Hardness and Tear Strength of the A-2186 and MDX4-4210 Silicones

Objective

To evaluate the influence of different pigmentations and accelerated aging on the hardness and tear strength of the A-2186 and MDX4-4210 silicones.

Materials and Methods

The samples A-2186 and MDX4-4210 were manufactured without and with pigmentations (black, bronze, and pink). For the Shore A hardness test, 80 samples of each silicone were fabricated, and for the tear strength test, 320 samples of each silicone were fabricated. Eight groups were created for each test (n = 10). These tests were performed before and after 252, 504, and 1008 hours of aging. Three-way repeated-measures analysis of variance and the Tukey test were performed (α = 0.05).

Results

The A-2186 silicone showed higher hardness and tear strength when compared with the MDX4-4210 silicone (p < 0.05), except in the hardness of the A-2186 and MDX4-4210 groups without pigmentation after 1008 hours (p > 0.05). All hardness values were between 25 and 35 units, regardless of the silicone type, period, and pigmentation (or no pigmentation). In most situations, the hardness of silicones used increased after 252 hours (p < 0.05). The nonpigmented MDX4-4210 group and all A-2186 groups showed an increase in tear strength after 252 hours (p < 0.05). For the nonpigmented MDX4-4210 group, from 252 to 1008 hours, there was no change in tear strength (p > 0.05). All pigmented MDX4-4210 groups showed no change in tear strength from 0 (initial) to 1008 hours of aging (p > 0.05). In all A-2186 groups, from 252 to 504 hours, there was a reduction in tear strength (p < 0.05), and from 504 to 1008 hours, there was an increase in tear strength (p < 0.05), except in the bronze A-2186 group (p > 0.05).

Conclusion

In most situations, the A-2186 silicone showed significantly higher values of hardness and tear strength than the MDX4-4210 silicone. All hardness values were considered clinically acceptable. Accelerated aging could increase, decrease, or not significantly change the hardness and tear strength of the silicones used. The results of hardness and tear strength suggest that MDX4-4210 was more influenced by the presence of pigmentation after aging.