Biomedical subjects

J C Shelton

Publications and source records attributed to J C Shelton.

At least 19 recordsLinked to original sources

PubMed2006

'Severe' wear challenge to 'as-cast' and 'double heat-treated' large-diameter metal-on-metal hip bearings.

The wear generation of double-heat-treated and as-cast large-diameter metal-on-metal (MOM) hip bearings was investigated using standard- and 'severe'-gait simulations. The test hypothesis was that double heat treatment would change MOM hip wear compared with the as-cast condition. Two groups of high-carbon MOM bearings of 40 mm diameter were manufactured and subjected to either hot isostatic pressing (HIP) and solution annealing (SA) or no heat treatment (as cast). The results showed no statistical difference between the two groups under both running-in and steady state conditions. Even under the most 'severe'-gait simulation published to date, the mean volumetric wear rates were 2.9 and 3.9 mm3 per 10(6) cycles for the HIP-SA and as-cast bearings respectively, showing a ten-fold increase in wear compared with walking. These differences were not statistically different; therefore our hypothesis was negated. Changes in alloy microstructure do not appear to influence the wear behaviour of high-carbon cast MOM articulations with similar chemical compositions. This is in sharp contrast with the published significance of bearing diameter and radial clearance on the wear of MOM hip bearings.

Biocompatible Materials↗

PubMed2006

Metal-on-metal hip simulator study of increased wear particle surface area due to 'severe' patient activity.

This study investigated changes in metal-on-metal (MOM) hip wear and wear particle characteristics arising from a more aggressive patient activity level compared with normal walking. The test hypothesis was that 'severe'-gait conditions will change wear, wear particle sizes, and morphology owing to a decline in joint lubrication. Four carbon MOM hip bearings 40 mm high were subjected to normal-walking and fast-jogging simulations in an orbital hip joint simulator with 25 per cent alpha-calf serum as a lubricant. Co-Cr-Mo wear particles were extracted using an enzymatic method, and prolate ellipsoid equations were used to estimate particle volume and surface area. Fast-jogging simulations generated a sevenfold increase in volumetric wear, a 33 per cent increase in mean wear particle size, and a threefold increase in the number of larger (needle) particles compared with walking. This resulted in a twentyfold increase in total wear particle surface area per 10(6) cycles compared with walking, thereby confirming our hypothesis. The clinical significance of this result suggests that highly active MOM patients may exhibit greater ion release than less active patients.

Biocompatible Materials↗

PubMed2004

An investigation into the effects of the hierarchical structure of tendon fascicles on micromechanical properties.

During physiological loading, a tendon is subjected to tensile strains in the region of up to 6 per cent. These strains are reportedly transmitted to cells, potentially initiating specific mechanotransduction pathways. The present study examines the local strain fields within tendon fascicles subjected to tensile strain in order to determine the mechanisms responsible for fascicle extension. A hierarchical approach to the analysis was adopted, involving micro and macro examination. Micro examination was carried out using a custom-designed rig, to enable the analysis of local tissue strains in isolated fascicles, using the cell nuclei as strain markers. In macro examination, a video camera was used to record images of the fascicles during mechanical testing, highlighting the point of crimp straightening and macro failure. Results revealed that local tensile strains within a collagen fibre were consistently smaller than the applied strain and showed no further increase once fibres were aligned. By contrast, between-group displacements, a measure of fibre sliding, continued to increase beyond crimp straightening, reaching a mean value of 3.9 per cent of the applied displacement at 8 per cent strain. Macro analysis displayed crimp straightening at a mean load of 1 N and sample failure occurred through the slow unravelling of the collagen fibres. Fibre sliding appears to provide the major mechanism enabling tendon fascicle extension within the rat-tail tendon. This process will necessarily affect local and cellular strains and consequently mechanotransduction pathways.

Adaptation, Physiological↗

PubMed2003

Dermal fibroblasts respond to mechanical conditioning in a strain profile dependent manner.

Fibroblasts within tissues are exposed to a dynamic mechanical environment, which influences the structural integrity of both healthy and healing soft tissues. Various systems have been proposed to subject such cells to mechanical stimulation in culture. However the diverse nature of the studies, in terms of the strain profiles and the cell types, makes direct comparisons almost impossible. The present study addresses this issue by examining the metabolic response of two cell types subjected to three well defined strain profiles.A young fibroblast cell population, represented by HuFFs, showed both greater cell proliferation and collagen production than adult dermal fibroblasts under unstrained conditions. The three strain profiles produced differing effects on both cell types. Uniaxial strains enhanced [(3)H]-thymidine incorporation for both cell types, whilst biaxial strains either inhibited or had no effect on its incorporation. In contrast, [(3)H]-proline incorporation was inhibited under biaxial and uniaxial strains for the adult fibroblasts, whilst the HuFF cells showed a small increase in proline incorporation under non-uniform and uniaxial strains.

Adult↗

PubMed2003

Development of a technique to determine strains in tendons using the cell nuclei.

Tenocytes detect mechanical stimuli in vivo, and respond through mechanotransduction pathways to initiate matrix remodelling in tendons. Due to the crimped nature of tendon fascicles, the strain field throughout is non-homogeneous. The present study has developed a means to quantify the local strain fields within a fascicle by monitoring the relative movement and deformation of fluorescently labelled tenocyte nuclei. A stage mounted test rig was designed to apply tensile strain to fascicles. Rat tail and bovine extensor tendons were harvested for analysis, and the cell nuclei stained and visualised using an inverted confocal microscope. As the fascicles were subjected to gross strains of up to 5%, the movement of selected tenocyte nuclei were recorded. Results from a series of cell nuclei from both tendon sources revealed that local strains were significantly less than the applied strain. The nuclei length to width ratio, an indicator of cell deformation, also increased with applied strain, most significantly between 2 and 3% applied strain.

Animals↗

PubMed2002

Cancellous bone repair using bovine trabecular bone matrix particulates.

At 5 and 15 weeks post-surgery, biomechanical and histological analyses of cancellous bone defects filled with the bovine trabecular bone matrix (BBM) and hydroxyapatite (Hap) particulates of dimensions 106-150 microm were investigated. It was observed that at 5 weeks post-surgery the stiffness properties of the BBM filled defects were significantly higher than those observed in the Hap filled defects (p < 0.01) but comparable to those recorded in intact cancellous bone from the same anatomical position. Histologically, no significant differences were observed in the percentage of new bone contact with the particles. The biomechanical properties of the Hap filled defects mirrored those in intact cancellous bone only at 15 weeks post-surgery. BBM particles thus appeared to accelerate the early healing of osteotomies. It is therefore suggested that particles of this bioceramic be the subject of intense research for more usage in both periodontal osseous defects and orthopaedic fractures.

Animals↗

PubMed2002

The effects of bovine trabecular bone matrix particulates on cortical bone repair.

This paper reports the effects of a synthetic bone substitute and bone allograft on cortical bone repair in an experimental model. To test the hypothesis that bovine trabecular bone matrix, BBM, can enhance the repair rate of cortical bone, osteotomies were created in the rabbit fibula and filled with either allograft or BBM particulates or left empty as controls. At five weeks post-surgery, mechanical tests and histological evaluations were performed. No significant differences were observed in the mechanical properties of the healing bone in the three animal groups (n=6). Histologically, the medullary cavity was obstructed and the cross-sectional area ratio of the osteotomies to intact bone was approximately 3 : 1. Highly significant area differences were observed between the intact bone group and both the BBM and the allograft groups (p< 0.001). At the junction between the original bone and the newly formed bone, both woven and lamellar bone microstructures were prevalent. However, in the BBM filled defects, the woven bone microstructure was not ostentatious. It is concluded that failure to demonstrate significantly differences between the treatments were due to the small sample sizes and or the efficacy of the tensile analysis.

Journal Article↗

PubMed2001

Influence of training on reliability of surgical knots.

OBJECTIVES: To determine whether trainees in obstetrics and gynaecology tie adequate surgical knots and to assess whether formal training improves knot tying skills. DESIGN: A comparative study assessing surgical knots before and after tuition. POPULATION: Fourteen trainees in a single obstetrics and gynaecology department. SETTING: A basic surgical skills workshop based in a London teaching hospital. METHODS: Trainees tied surgical knots around a 120mm jig using 2/0 glycan polymer. Each trainee tied 11 knots before and after a two and a half hour teaching session. Knots were tested using a mechanical testing machine. OUTCOME MEASURES: Knot strength (N); proportion of knots that were 'secure' (defined as those that eventually failed on the testing device by breakage rather than slippage); proportion of knots that were 'dangerous' (defined as those with a tensile strength of < 5 N). RESULTS: After tuition, the median knot strength of the whole group was 5.7 N stronger than before instruction (95% CI 4.6-12.3 N). Prior to tuition 13.5% (20/148) knots tied had a tensile strength of < 5 N. This was compared with 3.4% (5/148) after tuition (OR = 0.2, 95% CI 0.1-0.6). Before instruction 55.4% (82/148) of the knots were secure compared with 66.9% (99/148) after tuition (OR = 1.6, 95% CI 1.0-2.7). CONCLUSION: Knot tying workshops can improve the ability of trainees in obstetrics and gynaecology to tie reef knots.

Clinical Competence↗

PubMed2000

A system for monitoring the response of uniaxial strain on cell seeded collagen gels.

The success of cell seeded constructs for the repair of collagenous tissues may be improved by the use of mechanical stimulation in vitro. A mechanical loading apparatus, termed the cell straining system, was developed according to a set of design criteria, to enable cell seeded constructs to be cyclically loaded in tension. A suitable cell seeded collagen gel model system was used to characterise the apparatus. These gels were subjected to a cyclic strain of 10% superimposed on two separate tare loads of 2 and 10 mN, while being maintained in cell culture conditions. The computer controlled apparatus was shown to be capable of monitoring the individual loads on six specimens simultaneously, to an accuracy of 0.02 mN. Results indicated a wide variability between individual specimens. Following cyclic loading, the cell seeded collagen gels exhibited an increase in structural stiffness compared with the unloaded controls. This novel and versatile apparatus will provide a means of enhancing structural and mechanical integrity of tissue engineered repair systems.

Biomechanical Phenomena↗

PubMed2000

Investigation and quantification of the blood trauma caused by the combined dynamic forces experienced during cardiopulmonary bypass.

Blood is exposed to various dynamic forces during cardiopulmonary bypass (CPB). Understanding the damaging nature of these forces is paramount for research and development of the CPB circuit. The object of this study was to identify the most damaging dynamic non-physiological forces and then quantify this damage. A series of in vitro experiments simulated the different combinations of dynamic forces experienced during CPB while damage to the blood was closely monitored. A combination of air interface (a) and negative pressure (P) caused the greatest rate of change in plasma Hb (deltap Hb) (4.94 x 10(-3) mg/dl/s) followed by negative pressure and then an air interface. Shear stresses, positive pressures, wall impact forces and a blood-nonendothelial surface caused the least damage (0.26 x 10(-3) mg/dl/s). An air interface showed no threshold value for blood damage, with the relationship between the size of the interface and the blood damage modelled by a second-order polynomial. However, negative pressure did exhibit a threshold value at -120 mm Hg, beyond which point there was a linear relationship. Investigating the reasons for the increased blood trauma caused by the low-pressure suction (LPS) system makes it clear how research into minimizing or completely avoiding certain forces must be the next step to advancing extracorporeal technology.

Cardiopulmonary Bypass↗

PubMed2000

Fixation of the acetabular cup in cemented total hip replacement: improving the anchorage hole profile using finite element method.

Long-term studies have shown that failure of the acetabular component in total hip replacement increases exponentially ten years following surgery and occurs mostly at the bone-cement interface. During the cemented fixation of the acetabular cup, straight anchorage holes, 3-15 mm diameter and 3-20 mm deep, are drilled in the acetabulum in order to increase torsional resistance at the bone-cement interface. The aim of this paper is to provide guidelines for improving the profile of anchorage holes. Results from our finite element models show that the efficiency of anchorage holes may be improved if they are drilled perpendicularly to the acetabulum floor and if they have chamfered necks. A 10 degree inclination of the anchorage hole increases Von Mises stress in the cement mantle by 6% while creating chamfered anchorage holes, instead of straight holes, decreases it by 14%. Increasing depth of anchorage holes does not improve efficiency.

Acetabulum↗

PubMed1998

Quantification of holographic fringe data: comparison of intact and implanted femurs.

The strains developed on the surface of a femur with and without an implanted femoral hip replacement were investigated using holographic interferometry (HI). Interferometric fringe data from the four aspects of the loaded femur were quantified and the resulting curvature calculated. Curvature was related to the strain along the long axis of the femur and the results for the intact and implanted femur compared. Changes were found in femoral strain patterns resulting from the implantation of both a cemented and an uncemented Norwich femoral component. All four aspects of the proximal 120 mm of the femur showed reduced strain as a result of prosthesis implantation irrespective of the method of prosthesis fixation. The distal half of the femur showed no such changes. No statistical difference was found between the loading patterns in the proximal femur of the uncemented and the cemented prosthesis.

Arthroplasty, Replacement, Hip↗

PubMed1998

Laser speckle photography to measure surface displacements on cortical bone--verification of an automated analysis system.

A non-contact strain measurement method that could be used in a physiological environment was adapted to determine accurately the mechanical properties of bone. The technique of laser speckle photography was applied to record in-plane surface displacements. An automated image analysis system, based on a Fast Fourier Transform algorithm, was developed for data acquisition and its accuracy and precision verified. It was established that the technique could be used at magnifications of up to 60x , providing an ultimate resolution of approximately 1 microm. Displacement measurements on cortical bone submerged in water were demonstrated, which is of great value in determining the true physiological properties of bone.

Biomechanical Phenomena↗

PubMed1998

Influence of aging heat treatment on mechanical properties of biomedical Ti-Zr based ternary alloys containing niobium.

Titanium-zirconium based alloys containing a small amount of niobium were investigated in order to evaluate their possible use as biomedical materials. Zirconium, which belongs to the IVa group, is known to have good corrosion resistance and biocompatibility similar to titanium. As the titanium-zirconium system shows a complete solid solution, a wide variation of alloy design is available and large quantities of solid-solution hardening must be possible. Niobium, having a beta-phase stabilizing effect, was chosen as a ternary element in order to control desirably the microstructure. There have been no reports which suggest its harm to a living body. The alloys containing 2% or 3% niobium showed the highest hardness value after aging heat treatment at 773 K. In contrast to this, no alteration of hardness was seen in specimens aged at 1073 K. Through conventional X-ray diffractometry and in situ X-ray analysis using a hot stage, beta-phase precipitation in the A matrix was identified. From the above results, it is concluded that alloys containing 2%-3% niobium are hopeful candidates for new kinds of biomedical alloys, when they are heat treated under suitable conditions.

Journal Article↗

PubMed1996

Strengths and weaknesses of laparoscopic and open mesh inguinal hernia repair: a randomized controlled experimental study.

There are no objective data available on the relative strengths of inguinal hernia repairs. The aim of this randomized controlled study was to measure th force required to disrupt laparoscopic and open mesh repairs in a porcine model. Eleven pigs had inguinal hernia repair following randomization to an open mesh group (n = 5) or a transabdominal preperitoneal laparoscopic group (n = 6). Four weeks after operation the pigs were killed and the pelvic girdles were mounted in a test jig on a mechanical testing machine. The applied disruption forces were measured and recorded. Mean(s.d.) force required to disrupt the normal inguinal canal (n = 11) was 68.6(30.1) N with no difference between groups. The open mesh repair required 110.3(41.4) N and the laparoscopic mesh 220.0(95.2) N. Both open and laparoscopic mesh repairs were stronger than the normal side (P < 0.03). The laparoscopic mesh repair was stronger than the open mesh repair (P = 0.04). This model provides a standardized method for mechanically testing inguinal hernia repairs in pigs. It confirms that both open and laparoscopic mesh hernia repairs are stronger than the non-herniated normal side at 4 weeks after operation. Laparoscopic mesh repair is stronger than open mesh repair. The weakest points of the repairs correlate well with those identified in clinical reports.

Animals↗

PubMed1996

A comparison of the strength of knots tied by hand and at laparoscopy.

BACKGROUND: The strength of knots tied at laparoscopy was compared with that of hand-tied knots. STUDY DESIGN: The force needed to undo or break eight types of knots that were tied in fresh postmortem human stomachs was measured. The knotting performance of nylon, polyglactin 910, braided silk, polytetrafluoroethylene, braided polyester fiber, braided polyester suture, polyamide 66, and polydiaxone was also compared. RESULTS: Measurements of knot strength of two to six half hitches (hand tied) showed that four half hitches were necessary to tie a secure nonslipping knot with most monofilament threads (nylon, polytetrafluoroethylene, braided polyester suture, and polyamide 66), while three half hitches were adequate to secure a knot when polyglactin 910, braided polyester fiber, silk, and polydiaxone were used. Additional throws did not increase knot strength once the knot no longer slipped (p = NS). Some commonly tied knots, three half hitches and surgical knots at laparoscopy were weaker than the same hand-tied knots (p < 0.05) but an additional throw increased knot security (p < 0.01). Differences between laparoscopic and hand-tied knot strengths were greater for monofilament than multifilament threads. There was a wider distribution of strengths for laparoscopically tied than hand-tied knots. Four half hitches were the most secure configuration for laparoscopically tied knots and were significantly stronger than three half hitches and surgical knots (p < 0.01). The extracorporeally tied slipknot (Roeder loop) was significantly less secure than four half hitches (p < 0.05). CONCLUSIONS: This study demonstrates that laparoscopically formed knots may be weaker than those tied by hand and shows that improvements in knot strength at laparoscopy can be achieved by choice of optimal knot configuration for different suture materials.

Evaluation Studies as Topic↗

PubMed1995

Mechanical analysis of maxillofacial miniplates.

The effect of compression and tensile forces on different types of maxillofacial miniplates was measured, in both as supplied and after bending states. Tests showed all plates showed values of tensile force at failure in excess of that found in most clinical situations; twisting through 90 degrees about the long axis had little effect. In flatwise bending tests there was a wide scatter of values of bending stiffness and ultimate load, indicating that some plates may be stronger than necessary. Repeatedly bending the plates reduced their bending stiffness, particularly in the continuous holed plates, and increased their ultimate load to failure. Values of bending stiffness and ultimate load were much larger when bending in the edgewise direction, with large differences between manufacturers. The data generated in the current study may assist the surgeon in deciding which type of plate to select for a particular clinical situation.

Bone Plates↗

PubMed1993

Hydrogels as an interface between bone and an implant.

The use of fully hydrated hydrogels in the body has been well established. The forces a hydrogel generates on swelling when it is placed in a constrained space were investigated with a view to providing a mechanism for fixing a prosthesis in the intramedullary cavity. A cross-linked poly(2-hydroxyethyl methacrylate) [p(HEMA)] hydrogel was investigated as a potential material. In vitro mechanical tests were carried out to determine the stresses generated in the p(HEMA) when it was placed in water and not allowed to swell. Pull out loads of up to 375 N indicated that the system could be used successfully in vivo. Consequently, the material was placed intraosseously at two sites in a rabbit animal model, in the mid-shaft (diaphysis) and the lower end (metaphysis) of the femur. Histological examination showed there was no adverse bone response; bone was growing from the endosteal surface up to and into the hydrogel in the diaphyseal implants and surrounded the hydrogel in the metaphysis. As a result of the shape and size variations in the rabbit femur, in vivo mechanical tests were found to give lower values than those obtained in vitro.

Animals↗