Laura J. Leslie

The effect of the environment on the mechanical properties of medical grade silicones.

Silicone spacers have been in use as replacement joints in the human hand for over 30 years. Since they were first used there has been a number of designs all of which have had problems with fracture. This may be due to a defect in the material caused during implantation, or by bony intrusions within the arthritic hand after implantation. The aim of this research was to investigate the effect of the environment on the mechanical properties of medical grade silicones used for human implantation. The materials were subjected to static tensile testing after various forms of ageing. The environmental conditions included temperatures of 37 and 80 degrees C and the environments of Ringers solution, distilled water, and air. The environmental conditions employed resulted in reduced mechanical strength with ageing time of the silicones. This research supports the view that failure of silicone implants in the hand could be partly attributed to the effects of environmental ageing of the material.

A comparative study of electronic cigarette vapor extracts on airway-related cell lines in vitro

Abstract The use of electronic cigarettes (ECs) is rapidly increasing worldwide; however, scientific evidence regarding EC cytotoxicity is limited. The aim of this study was to evaluate the acute cytotoxicity of EC vapor extract (ECE) on airway-related cells in vitro. Cigarette smoke extract (CSE), vapor extract of fifteen brands/flavors of ECs and the extract from the E-vehicle (propylene glycol and glycerin) was collected. Extracts, in concentrations of 100–12.5%, were added to human bronchial epithelial (BEAS-2B, IB3-1 and C38), fibroblast (Wi-38) and macrophage (J774 and THP-1) cell lines. Viability was assessed after 24 h using a standard XTT assay. Viability of <70% of control (no extract) was considered cytotoxic according to UNI EN ISO 10993-5 standards. CSE displayed a concentration-dependent influence on cell viability across all four cell lines with 100% producing the most toxic effect, therefore validating the model and indicating higher cytotoxicity than in ECEs. ECEs did reduce viability although this was not correlated with nicotine content or the E-vehicle. However, several flavors proved cytotoxic, with variation between different brands and cell lines. These data indicate that not all ECs are the same and that use of a particular flavor or brand may have differing effects. The cell line used is also an important factor. More research is crucial to ascertain the health effects of different ECs before they can be accepted as a safe alternative to tobacco cigarettes.

Crack-growth of medical-grade silicone using pure shear tests

Abstract Silicone elastomers are commonly used in the manufacture of single-piece joint replacement implants for the finger joints. However, the survivorship of these implants can be poor, with failure typically occurring from fracture of the stems. The aim of this paper was to investigate the crack growth of medical-grade silicone using pure shear tests. Two medical-grade silicones (C6-180 and Med82-5010-80) were tested. Each sample had a 20 mm crack introduced and was subjected to a sinusoidally varying tensile strain, with a minimum of 0 per cent and a maximum in the range 10 to 77 per cent. Testing was undertaken at a frequency of 10 Hz. At various times during testing, the testing machine was stopped, the number of cycles completed was noted, and the crack length measured. Graphs of crack length against number of cycles were plotted, as well as the crack growth rate against tearing energy. The results show that Med82-5010-80 is more crack resistant than C6-180. Graphs of crack growth rate against tearing energy can be used to predict the failure of these medical-grade elastomers.

Cell exclusion in couette flow:evaluation through flow visualisation and mechanical forces

Cell exclusion is the phenomenon whereby the hematocrit and viscosity of blood decrease in areas of high stress. While this is well known in naturally occurring Poiseuille flow in the human body, it has never previously been shown in Couette flow, which occurs in implantable devices including blood pumps. The high-shear stresses that occur in the gap between the boundaries in Couette flow are known to cause hemolysis in erythrocytes. We propose to mitigate this damage by initiating cell exclusion through the use of a spiral-groove bearing (SGB) that will provide escape routes by which the cells may separate themselves from the plasma and the high stresses in the gap. The force between two bearings (one being the SGB) in Couette flow was measured. Stained erythrocytes, along with silver spheres of similar diameter to erythrocytes, were visualized across a transparent SGB at various gap heights. A reduction in the force across the bearing for human blood, compared with fluids of comparable viscosity, was found. This indicates a reduction in the viscosity of the fluid across the bearing due to a lowered hematocrit because of cell exclusion. The corresponding images clearly show both cells and spheres being excluded from the gap by entering the grooves. This is the first time the phenomenon of cell exclusion has been shown in Couette flow. It not only furthers our understanding of how blood responds to different flows but could also lead to improvements in the future design of medical devices.

Collaborative design of assessment criteria to improve undergraduate student engagement and performance

ABSTRACT Student engagement is vital in enhancing the student experience and encouraging deeper learning. Involving students in the design of assessment criteria is one way in which to increase student engagement. In 2011, a marking matrix was used at Aston University (UK) for logbook assessment (Group One) in a project-based learning module. The next cohort of students in 2012 (Group Two) were asked to collaboratively redesign the matrix and were given a questionnaire about the exercise. Group Two initially scored a lower average logbook mark than Group One. However, Group Two showed the greatest improvement between assessments, and the quality of, and commitment to, logbooks was noticeably improved. Student input resulted in a more defined, tougher mark scheme. However, this provided an improved feedback system that gave more scope for self-improvement. The majority of students found the exercise incorporated their ideas, enhanced their understanding, and was useful in itself.

Using three-dimensional rapid prototyping in the design and development of orthopaedic screws in standardised pull-out tests

The majority of orthopaedic screws are designed, tested and manufactured by existing orthopaedics companies and are predominantly developed with healthy bone in mind. The timescales and costs involved in the development of a new screw design, for example, for osteoporotic bone, are high. In this study, standard wood screws were used to analyse the concept of using three-dimensional printing, or rapid prototyping, as a viable stage of development in the design of a new bone screw. Six wood screws were reverse engineered and printed in polymeric material using stereolithography. Three of the designs were also printed in Ti6Al4V using direct metal laser sintering; however, these were not of sufficient quality to test further. Both the original metal screws (metal) and polymeric rapid prototyping screws were then tested using standard pull-out tests from low-density polyurethane blocks (Sawbones). Results showed the highest pull-out strengths for screws with the longest thread length and the smallest inner diameter. Of the six screw designs tested, five showed no more than a 17% variance between the metal and rapid prototyping results. A similar pattern of results was shown between the screw designs for both the metal and rapid prototyping screws in five of the six cases. While not producing fully comparable pull-out results to orthopaedic screws, the results from this study do provide evidence of the potential usefulness and cost-effectiveness of rapid prototyping in the early stages of design and testing of orthopaedic screws.

In vitro investigation into the forces involved during lipofilling

Breast augmentation using implants is the most common aesthetic and reconstructive breast surgical procedure. Complications such as implant rupture maybe related to surgical technique and damage to the implant. Autologous fat transfer (lipofilling) using metallic cannulae has become a standard adjunctive, yet there is little evidence on lipofilling safety in the presence of implants. The aims of this study are to verify the effects of different cannulae and to quantify the forces applied by surgeons during lipofilling. Silicone gel-filled textured implants (200 mL), mounted on a specially constructed mould were ruptured with two different cannulae: type A (hole at tip: sharp) and type B (hole away from tip: blunt), driven at three speeds (10, 100 and 1000 mm/min), and the force at rupture was recorded. In addition, the maximum 10 forces over a 30-s period applied by 11 plastic surgeons against a breast implant in an in vitro environment were recorded using a load cell attached to a type-A cannula. Statistical analysis of comparative results was performed using t-tests, with p < 0.05 considered significant. Results showed that the implant ruptured at forces up to 25% lower when cannula A was used compared to cannula B. This supports current technique in lipofilling in the use of a blunt tipped cannula. There was a significant difference between some displacement rates only, due to the viscoelastic nature of the material. The tactile force that surgeons use during lipofilling was modelled in vitro and showed a range of maximum forces between 0.23 and 16.8 N, with a mean maximum value of 6.9 N. Limitation of this study is that it may not reflect in vivo behaviour of breast implants. More studies are needed to confirm the safety of breast lipofilling in the presence of implants using these data as a starting point.

An investigation into the effects of E-cigarette aerosols using a physiologically relevant in-vitro model

Human bronchial epithelial cells (CALU3) and pulmonary fibroblasts (MRC5) were co-cultured on permeable membranes for 11–14 days at air–liquid interface. A bespoke smoking machine was used to deliver air, whole cigarette smoke (WCS) or EC vapour (ECV) to the airways model under standard ISO:3308 conditions for 7 m. Considering the prolonged vaping habits of EC users compared to cigarette smoking, ECV exposure was additionally investigated at 1 h, 2 h, 3 h, 4.5 h and 6 h time points.