Silicone Samples Research Articles

Mechanical behaviour of tissue mimicking breast phantom materials

The mechanical properties of soft tissue have long been of interest in biomedical research and applications, and increasingly for breast cancer imaging. In this paper, the mechanical properties of three different materials used to emulate the mechanical behaviour of real breast tissue are measured: agar, gelatine, and silicone, to assess their suitability for use in phantoms in systems assessing tissue mechanics for diagnostics. Two widely recognised measurement procedures are used. Quasi-static uniaxial compression was performed under a strain rate of 0.5 mm min−1 up to 15% strain with preloads of 0.05, 0.1, and 0.2 N, was used to measure the elastic moduli. Dynamic testing over a frequency range of 0.1–50 Hz for agar and 0.1–100 Hz for gelatine and silicone with the same preload was used to measure the storage moduli. Elastic and storage moduli were (5–81 kPa, 17–85 kPa, 5–112 kPa) and (3–128 kPa, 10–109 kPa, 5–73 kPa) for agar, gelatine, and silicone, respectively at the three preloads. All materials can be cast into arbitrary shapes and are suitable for tissue-mimicking phantoms. Silicone was the most consistent across the different preloads and frequencies, and can provide a range of stiffness ratios of adipose to tumour tissue that match experimentally reported values. More specifically, silicone samples for skin, adipose and tumour tissues show nonlinear stress–strain characteristics at 3 preloads characterised using hyperelastic parameters by fitting Neo-Hookean, Mooney Rivlin and Ogden models. Silicone also does not contain water, so environmental influences do not affect its mechanical properties as much as the other materials, and is thus more durable for consistent re-use. Finally, breast shaped mimicking silicone phantoms were fabricated for in vitro trials of a digital image elasto tomography breast cancer screening system assessing changes in mechanical properties.

A polydopamine peptide coating enables adipose-derived stem cell growth on the silicone surface of cochlear implant electrode arrays.

The simultaneous application of neurotrophic factors with cochlear implantation is proposed to enhance the bioelectrical interface between electrodes and auditory neurons, and thus improve speech intelligibility in patients with cochlear implants (CIs). In cell-based approaches, the goal is to colonize CIs with cells producing neurotrophic factors. This study aims to evaluate whether a polydopamine (PD) functionalization of the hydrophobic silicone surface of the electrode carrier enables colonization of adipose-derived stem cells known to deliver neurotrophic factors. Surface characteristics of PD-coated silicone samples and electrode carriers were determined, and the proliferation and viability of adipose-derived stem cells (ASCs) on these surfaces were subsequently analyzed. A homogenous PD coating and cell growth with regular morphology was observed on coated silicone samples and electrode arrays. Hydrophilicity and cell viability was significantly enhanced by PD surface modification. Insertion forces of coated electrode arrays did not increase compared with untreated CIs. Hence, PD coating of the silicone surface of CIs might allow for sufficient colonization with ASCs as a continuous source of neurotrophic factors. © 2017 Wiley Periodicals, Inc. J Biomater Res Part A: 106B: 1431-1438, 2018.

Characterization of a Laser Extensometer for Split Hopkinson Pressure bar Experiments

This paper examines a laser extensometer to calculate the strain in a sample during split Hopkinson pressure bar (SHPB) experiments. This method offers a non-contact, direct method for measuring sample strain which does not rely on one-dimensional wave propagation assumptions. First a single bar experiment is used to compare the extensometer’s accuracy and frequency response against a laser vibrometer and an accelerometer. The extensometer showed a close match with the vibrometer up to a bandwidth of 10 kHz. With the performance validated, the extensometer is applied to a SHPB experiment with silicone samples. For low strains, the extensometer shows a good match to the strain determined by strain gauges on the bars. At higher strains, the radial expansion of the sample can interfere with the measurement beam from the extensometer and produce inaccurate results.

Pursing of planar elastic pockets

The pursing of a simply- or doubly-connected planar elastic pocket by an applied pressure is analysed from the bending to the stretching regimes. The response is evaluated in terms of maximum deflection and profiles across a range of simply- and doubly-connected circular and square shapes. The study is conducted using experimental and numerical methods and supported by previous analytical results. The experimental method is based on an original 2D optical method that gives access to the pursing direction perpendicular to each image across the field of view. The equations for maximum pursing deflections are developed and compared for a range of thicknesses of silicone samples and shapes from the bending to the stretching regimes. In the case of doubly-connected shapes, dependence of maximum pursing deflection on clamped central circular and square areas or holes is quantified for both regimes. Good agreement is established between the three methods and the study also shows that the optical method may as well be successfully applied to problems of pursing of rubber pockets.

Effect of denture cleansers and accelerated aging on the color stability of maxillofacial silicone: An in vitro study

Aim: Evaluate the effect of denture cleansers and accelerated aging on the color stability of a commercially available maxillofacial silicone. Materials and Methods: A commercially available maxillofacial silicone cosmesil M511 was mixed according to manufacturer's instruction with the incorporation of three pigments, namely, Burnt sienna, Hansa Yellow, and Alizarin red and packed into the stone molds prepared using metal dies according to ASTM standards. After processing, initial color measurement was carried out 72 h following processing using a spectrophotometer. The samples were later subjected to disinfection and accelerated aging for 504 h and 1008 h following which color measurement was carried out. The results were analyzed using one-way ANOVA and Tukey's multiple comparison test (P Results: There was a statistically significant difference in the color stability of the silicone samples pigmented with Hansa Yellow than with Burnt Sienna and Alizarin Red after disinfection and 504 h of accelerated aging. Silicone samples disinfected with Fittydent denture cleanser showed better color stability than samples disinfected with neutral soap. There was a statistically significant difference in the color stability of the samples after 1008 h of accelerated aging irrespective of pigmentation and disinfection method. Conclusions: Silicone samples pigmented with Hansa Yellow had greater color stability than the samples pigmented with other two pigments after disinfection and 504 h of accelerated aging. After 1008 h of aging, all samples showed poor color stability irrespective of pigmentation and disinfection method.

Effect of calcium carbonate nanoparticles on the bonding strength of maxillofacial silicone to acrylic substrate

The clinical life of a maxillofacial prosthesis averages about six months before it needs to be re-fabricated. Most of maxillofacial prosthesis attached to the acrylic resin via adhesive primers detached and have to be re-attached every few months. This in vitro study established to evaluate the effect of adding calcium carbonate nanoparticles at different concentrations on the bonding strength of maxillofacial silicone elastomer to the acrylic resin, before and after accelerated aging. Seventy samples were prepared, ten samples per each group. Each silicone sample sandwiched between two strips of acrylic resin via A-330-G adhesive primer. From each group five samples were undergoing accelerated aging. All samples were tested for shear bond strength by using Instron testing machine. Calcium carbonate nanoparticles have a significant effect on the shear bond strength of maxillofacial silicone to the acrylic resin and the groups that contain the lowest concentrations of calcium carbonate nanoparticles showed the most significant changes. It CaCO3 nanoparticles in trace amount can improve the shear bond strength of maxillofacial silicone elastomer to the acrylic resin after subjecting to accelerated aging.

Polysiloxane-Based Autonomic Self-Healing Elastomers Obtained through Dynamic Boronic Ester Bonds Prepared by Thiol-Ene "Click" Chemistry.

Cross-linked silicone elastomers constructed with dynamic-covalent boronic esters are first synthesized by photoinitiated radical thiol-ene "click" chemistry. The resultant samples can be cut with a sharp knife into two pieces and then healed via the reversibility of the boronic ester cross-linkages to restore the original silicone sample within 30 min. Regulation of luminescent properties is achieved by incorporating organic dye into the elastomers through a "one-pot" thiol-ene reaction. The proposed synthesis procedure demonstrates a new strategy to produce boronic acid silicone materials capable of self-healing without external forces.

Pre-strain Effect on Frequency-Based Impact Energy Dissipation through a Silicone Foam Pad for Shock Mitigation

Silicone foams have been used in a variety of applications from gaskets to cushioning pads over a wide range of environments. Particularly, silicone foams are used as a shock mitigation material for shock and vibration applications. Understanding the shock mitigation response, particularly in the frequency domain, is critical for optimal designs to protect internal devices and components more effectively and efficiently. The silicone foams may be subjected to pre-strains during the assembly process which may consequently influence the frequency response with respect to shock mitigation performance. A Kolsky compression bar was modified with pre-compression capabilities to characterize the shock mitigation response of silicone foam in the frequency domain to determine the effect of pre-strain. A silicone sample was also intentionally subjected to repeated pre-strain and dynamic loadings to explore the effect of repeated loading on the frequency response of shock mitigation.

Potent Antibacterial Activity of Copper Embedded into Silicone and Polyurethane.

A simple, easily up-scalable swell-encapsulation-shrink technique was used to incorporate small 2.5 nm copper nanoparticles (CuNPs) into two widely used medical grade polymers, polyurethane, and silicone, with no significant impact on polymer coloration. Both medical grade polymers with incorporated CuNPs demonstrated potent antimicrobial activity against the clinically relevant bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli. CuNP-incorporated silicone samples displayed potent antibacterial activity against both bacteria within 6 h. CuNP-incorporated polyurethane exhibited more efficacious antimicrobial activity, resulting in a 99.9% reduction in the numbers of both bacteria within just 2 h. With the high prevalence of hospital-acquired infections, the use of antimicrobial materials such as these CuNP-incorporated polymers could contribute to reducing microbial contamination associated with frequently touched surfaces in and around hospital wards (e.g., bed rails, overbed tables, push plates, etc.).

In vivo contaminant partitioning to silicone implants: Implications for use in biomonitoring and body burden

Silicone polymers are used for a wide array of applications from passive samplers in environmental studies, to implants used in human augmentation and reconstruction. If silicone sequesters toxicants throughout implantation, it may represent a history of exposure and potentially reduce the body burden of toxicants influencing the risk of adverse health outcomes such as breast cancer. Objectives of this research included identifying a wide variety of toxicants in human silicone implants, and measuring the in vivo absorption of contaminants into silicone and surrounding tissue in an animal model. In the first study, eight human breast implants were analyzed for over 1400 organic contaminants including consumer products, chemicals in commerce, and pesticides. A total of 14 compounds including pesticides such as trans-nonachlor (1.2–5.9ng/g) and p,p′-DDE (1.2–34ng/g) were identified in human implants, 13 of which have not been previously reported in silicone prostheses. In the second project, female ICR mice were implanted with silicone and dosed with p,p′-DDE and PCB118 by intraperitoneal injection. After nine days, silicone and adipose samples were collected, and all implants in dosed mice had p,p′-DDE and PCB118 present. Distribution ratios from silicone and surrounding tissue in mice compare well with similar studies, and were used to predict adipose concentrations in human tissue. Similarities between predicted and measured chemical concentrations in mice and humans suggest that silicone may be a reliable surrogate measure of persistent toxicants. More research is needed to identify the potential of silicone implants to refine the predictive quality of chemicals found in silicone implants.

The biostability of cardiac lead insulation materials as assessed from long-term human implants.

Accelerated in vitro biostability studies are useful for making relativistic comparisons between materials. However, no in vitro study can completely replicate the complex biochemical and biomechanical environment that a material experiences in the human body. To overcome this limitation, three insulation materials [Optim™ insulation (OPT), Pellethane® 55D (P55D), and silicone elastomer] from cardiac leads that were clinically implanted for up to five years were characterized using visual inspection, SEM, ATR-FTIR, GPC, and tensile testing. Surface cracking was not observed in OPT or silicone samples. Shallow cracking was observed in 17/41 (41%) explanted P55D samples. ATR-FTIR indicated minor surface oxidation in some OPT and P55D samples. OPT molecular weight decreased modestly (∼20%) at 2-3 years before stabilizing at 4-5 years. OPT tensile strength decreased modestly (∼25%) at 2-3 years before stabilizing at 4-5 years. OPT elongation at 4-5 years was unchanged from controls. P55D had no significant changes in molecular weight or tensile properties. Overall, results for OPT and P55D were consistent with and limited to cosmetic surface oxidation. Silicone demonstrated excellent biostability with no identifiable degradation. This study of explanted cardiac leads revealed that OPT, P55D, and silicone elastomer demonstrate similar and excellent biostability through five years of implantation in human patients.

Centrifugal deposition of iron oxide magnetic nanorods for hyperthermia application

Centrifugal deposition of iron oxide was performed to manufacture magnetic nanorods in an aqueous solution. The nanorods were examined by electron microscopy. The diameter of the nanorods ranges from 10 to 20 nm. The length is about 150 nm. The nanorods were incorporated into a silicone polymer to simulate body tissues injected with magnetic nanomaterials. Then the magnetic nanorod-containing silicone samples were put into a microwave to examine the external electromagnetic field induced heating behavior. Dramatic increase in temperature was observed when the nanorods were exposed to the external electromagnetic field for 2 seconds. It is concluded that the nanorods generate intensive heating effect and they have the potential for hyperthermia application.

Graphene nanoplatelet-reinforced silicone for the valvular prosthesis application.

Newly developed elastomer heart valves have been shown to better re-create the flow physics of native heart valves, resulting in preferable hemodynamic responses. This emergence has been motivated in part by the recent introduction of percutaneous valve approaches in the clinic. Unfortunately, elastomers such as silicone are prone to structural failure, which drastically limits their applicability the development of a valve prosthesis. To produce a mechanically more robust silicone substrate, we reinforced it with graphene nanoplatelets (GNPs). The nanoplatelets were introduced into a two-part silicone mixture and allowed to cure. Cytotoxicity and hemocompatibility tests revealed that the incorporation of GNPs did not adversely affect cell proliferation or augment adhesion of platelets on the surface of the composite materials. Static mechanical characterization by loading in the tensile direction subsequently showed no observable effect when graphene was utilized. However, cyclic tensile testing (0.05 Hz) demonstrated that silicone samples containing 250 mg graphene/L of uncured silicone significantly improved (p<0.05) material fatigue properties compared with silicone-only controls. This finding suggests that for the silicone-graphene composite, static loads were principally transferred onto the matrix. On the other hand, in cyclic loading conditions, the GNPs were recruited effectively to delay failure of the bulk material. We conclude that application of GNPs to extend silicone durability is useful and warrants further evaluation at the trileaflet valve configuration.

Change in color of a maxillofacial prosthetic silicone elastomer, following investment in molds of different materials.

Purpose:In the authors’ experience, the color of silicone elastomer following polymerization in molds made of gypsum products is slightly different from the color that was matched in the presence of the patient, before the silicone is packed. It is hypothesized that the investing materials and separating media have an effect on the color during the polymerization process of the silicone.Materials and Methods:This study compares and evaluates the change in color of silicone elastomer packed in three commonly used investing materials - Dental stone (white color), dental stone (green color), and die stone (orange color); coated with three different separating media – Alginate-based medium, soap solution and a resin-based die hardening material. Pigmented silicone samples of dimensions 1.5 cm × 2 cm × 0.5 cm were made from the elastomer in the above-mentioned mold materials using combinations of the mentioned separating media. These served as test group samples. Control group samples were made by packing a mix of the same pigmented elastomer in stainless steel molds. The L*, a*, b* values of the test and control group samples were determined using a spectrophotometer. The change in color (Delta E) was calculated between the control and test groups.Results:The mean L, a, b values for the control group were, 31.8, 26.2, and 36.3, respectively. Average values of change in color (Delta E) for samples packed utilizing alginate-based medium, die hardener, and soap solution, respectively in white dental stone (2.70, 2.74, and 2.88), green dental stone (2.19, 2.23, 2.42), and orange die stone (3.19, 2.72, 2.80) were tabulated.Conclusion:Among the investing materials studied, die stone showed the most color change (3.19), which was statistically significant. Among the separating media, die hardener showed the least color change (2.23). The best combination of an investing material and separating media as per this investigation is a dental stone (green) and alginate-based separating medium.

Plasma-Assisted Hydrophilization of Cochlear Implant Electrode Array Surfaces Enables Adhesion of Neurotrophin-Secreting Cells

Objective: To evaluate plasma treatment for enhancing the biocompatibility of cochlear implant (CI) silicone surfaces, thus allowing colonization with human adipose-derived stem cells (hASCs) that are known to provide neurotrophic support. Methods: Silicone samples and CI electrode arrays were treated with 4 low-pressure plasmas of different characteristics. The hydrophilicity of plasma-treated and control surfaces as well as the adherence and morphology of hASCs were assessed. Finally, the insertion forces of electrode arrays were determined and the colonization potential of the electrode arrays with hASCs were tested. Results: The hydrophilicity of the silicone surfaces was significantly enhanced after plasma treatment, as was the adherence of hASCs. The characteristic morphology of hASCs was observed when grown on plasma-treated but not on untreated silicone surfaces. The insertion forces of plasma-treated electrode arrays were similar to those of untreated arrays, and the colonization of plasma-treated electrode arrays with hASCs was feasible. Conclusion: Plasma treatment of CI electrode arrays enhances their biocompatibility and allows for the colonization with hASCs that are known to produce neurotrophic factors. i 2014 S. Karger AG, Basel

A surface with a biomimetic micropattern reduces colonization ofMycobacterium abscessus

Nontuberculous mycobacteria (NTM) are ubiquitous organisms found in soil, water, and biofilms. Engineered surface topography has been proposed as a method to reduce microbial biofilm formation. The Sharklet(®) micropattern silicone surface has been shown to reduce biofilm formation of pyogenic bacteria. We hypothesized that this micropattern surface will also reduce colonization by Mycobacterium abscessus, a human pathogen. Smooth and micropattern silicone samples were incubated with 1 × 10(6) M. abscessus mL(-1) for 2 and 4 days. After processing to optimize recovery of adhered mycobacteria, there was a 75% and 50% reduction in the number of viable M. abscessus recovered from the micropattern surfaces compared to the smooth surfaces at 2 and 4 days after inoculation, respectively. Ziehl-Neelsen staining after measures to remove the adherent microorganisms revealed fewer residual M. abscessus on the micropattern samples as compared to smooth samples, validating the quantitative culture results. Microscopic observation of 2, 4, and 8 day M. abscessus cultures on micropattern samples showed that the organisms preferentially colonized within the channels between the rectangular features. In summary, a micropattern surface reduces the colonization of a pathogenic NTM. It remains to be seen whether this micropattern can reduce infections in humans.

Silicone-Based Tissue-Mimicking Phantom for Needle Insertion Simulation

Silicone-based tissue-mimicking phantom is widely used as a surrogate of tissue for clinical simulators, allowing clinicians to practice medical procedures and researchers to study the performance of medical devices. This study investigates using the mineral oil in room-temperature vulcanizing silicone to create the desired mechanical properties and needle insertion characteristics of a tissue-mimicking phantom. Silicone samples mixed with 0, 20, 30, and 40 wt. % mineral oil were fabricated for indentation and needle insertion tests and compared to four types of porcine tissues (liver, muscle with the fiber perpendicular or parallel to the needle, and fat). The results demonstrated that the elastic modulus and needle insertion force of the phantom both decrease with an increasing concentration of mineral oil. Use of the mineral oil in silicone could effectively tailor the elastic modulus and needle insertion force to mimic the soft tissue. The silicone mixed with 40 wt. % mineral oil was found to be the best tissue-mimicking phantom and can be utilized for needle-based medical procedures.

Detection of Stiff Nodules Embedded in Soft Tissue Phantoms, Mimicking Cancer Tumours, Using a Tactile Resonance Sensor

Background: Prostate cancer (PCa) is the most common form of cancer among males in Europe and in the USA and the most common curative treatment is removal of the prostate, i.e. prostatectomy. After the removal, the prostate is histopathologically analysed. One area of interest is to examine the perifery of the prostate, as tumours on and near the surface can indicate that the PCa has spread to other parts of the body. There are no current methods to examine the surface of the prostate at the time of surgery. Tactile resonance sensors can be used for detecting areas of different stiffness in soft tissue. Human prostate tissue affected by cancer is usually stiffer than healthy tissue, and for this purpose, a tactile resonance sensor was developed. The aim of this study was to investigate the depth at which embedded stiffer volumes could be detected, using soft tissue phantoms. Methods: With the tactile resonance sensor used in this study, the shift of the resonance frequency and the force at contact with tissue can be measured, and combined into a tissue stiffness parameter. The detection sensitivity of the sensor at impression depths, 0.4 and 0.8 mm, was measured for detection of inserted nodules of stiff silicone in softer silicone and in chicken muscle tissue, mimicking prostate tissue with cancer tumours. Results: Measurements on the silicone samples detected the hidden stiffer object at a depth of 1 - 4 mm with a difference in the stiffness parameter of 80 - 900 mN/kHz (p < 0.028, n = 48). At the depth 5 - 6 mm the difference was smaller but still significant < 30 mN/kHz (p < 0.05, n = 24). For the measurements on chicken muscle, the detectable depth was 4 mm (p < 0.05, n = 24). Conclusion: This model study suggests that, with only a small impression depth of ≤1 mm, the resonance sensor system described here can detect stiffness variations located at least 4 mm in silicone and chicken muscle, mimicking tumours in prostate tissue.

Epicutaneous patch test—A new diagnostic option to prevent the rejection of silicone-covered cochlear implants in children

ObjectivesCochlear implantation (CI) is a revolutionary method for hearing rehabilitation in patients with severe or profound sensorineural hearing loss. One of the surgical complications may be the necrosis of the skin flap above the receiver-stimulator coil, resulting in device extrusion. Our aim was to find the plausible causes of the silicone covered implant rejection. Patients and methodsAuthors present four cases of cochlear implant rejection, briefly describe their dermato-surgical solutions and analyse their innovative method – the epicutanoeus patch testing with silicone samples. ResultsThey observed positive skin reaction in three of the four cases. ConclusionAuthors analyse the applicability and results of their surgical solutions and the epicutaneous testing in connection with the prevention of skin flap necrosis and rejection of silicone-covered cochlear implants.

On the origins of GEMS grains: A reply

The Comment by Bradley challenges our chemical and isotopic measurements of GEMS grains, arguing that pervasive infiltration of silicone oil and sample heating undermine our comparisons with equally uncertain interstellar grain compositions. However, we have already shown that such effects are negligible and cannot account for the extraordinary chemical variability of GEMS grains. Our data are also in excellent agreement with previous GEMS grain chemical analyses, and with GEMS grains in micrometeorites and within IDPs recently collected without the use of silicone oil. The order of magnitude variations in element abundances displayed by GEMS grains rule out a common origin by the extensive chemical and isotopic homogenization of circumstellar grains, as proposed by Bradley. The vast majority of GEMS grains also do not have radial compositional gradients, crystalline “relict” cores, or rims of condensed materials indicative of radiation exposure. The average element abundances of GEMS grains differ significantly and systematically from solar abundances and from those inferred for interstellar silicates based on element depletion patterns. A few GEMS grains have highly anomalous O isotopic compositions consistent with a condensation origin in evolved O-rich stellar envelopes and supernovae. Yet, on average, GEMS grains have O isotopic compositions very near to terrestrial and meteoritic values. These and other observations discussed in our paper place a strict upper limit on the number of GEMS grains that have preserved presolar origins.