The semi-permeability of silicone: a saline-filled breast implant with intraluminal and pericapsular Aspergillus flavus

Fungal infection of breast implants is a rare complication. Growth of fungi within the lumen of saline-filled implants has previously been demonstrated in laboratory studies, however, clinical infections are rare. We report a case of Aspergillus flavus growth within and around a saline-filled breast implant that was inserted 18 months previously. This was successfully treated with implant removal and wound irrigation. Possible routes of microbial contamination as well as survival mechanisms of organisms within saline-filled implants are discussed. This case re-iterates that the silicone envelope of a saline-filled implant is selectively permeable and we believe this is instrumental in facilitating intraluminal microbial growth. This also emphasises the importance of stringent asepsis when dealing with saline-filled breast implants including avoiding contamination of the saline filling fluid.

Colonic adenocarcinoma presenting as a cutaneous metastasis in an old operative scar

Cutaneous metastasis from colon cancer is an uncommon event that usually occurs after identification of the primary tumour and generally indicates diffuse disease. Incisional metastasis occasionally occurs following laparoscopic or open colon cancer resection. However, to the authors' knowledge only one previous case of colon cancer presenting as a cutaneous metastasis in an old operative scar has been reported. We describe a case of colon cancer presenting as a cutaneous metastasis in an old cholecystectomy scar and discuss possible pathophysiological mechanisms.

Nitric oxide is a mediator of apoptosis in the rheumatoid joint

OBJECTIVE

To study the role of nitric oxide (NO) derived from the inducible nitric oxide synthase (iNOS) pathway in the induction of apoptosis in the rheumatoid joint.

METHODS

Joint tissue was obtained from four rheumatoid arthritis (RA) patients, three osteoarthritis patients and two patients with a fractured neck of the femur (NOF#), and apoptotic cells were identified in cryosections using the TUNEL (terminal dUTP nick end labelling) assay. Expression of iNOS was determined using immunohistochemistry. NO synthesis and the effect of NOS inhibitors on apoptosis levels were studied in explant cultures of RA cartilage and synovium.

RESULTS

Numbers of apoptotic cells were greatly increased in rheumatoid synovium and articular cartilage compared with NOF# and osteoarthritic synovium. Immunohistochemistry showed co-localization of iNOS staining and apoptosis in the synovial lining layer and articular cartilage. The NOS inhibitor L-NMMA (L-N(G)-monomethylarginine) strongly inhibited apoptosis in explant cultures of synovium and cartilage, and this was reversed by the NO donor S-nitroso-acetyl-penicillamine.

CONCLUSION

This study indicates that NO acts as a mediator of apoptosis in RA and suggests that NOS inhibitors reverse this process.

Auditing outcomes after treatment of Scottish patients with uveal melanoma in Liverpool

Uveal melanoma is the most common primary intraocular malignant tumour, although it is a rare condition. Between January 1993 and December 1997 a total of 120 patients were referred from Scotland to the Ocular Oncology Service at St. Paul's Eye Unit in Liverpool. Of these, 98 had uveal melanoma, which was treated with primary enucleation (24), or by conservative methods, consisting of plaque radiotherapy (30), proton beam radiotherapy (19), trans-scleral local resection (19), or endoresection (6). After conservative treatment, 92% of eyes were retained, with 65% of eyes maintaining the same level of vision as at presentation or better. The main complications were retinal detachment (8), death from metastatic disease (7) and local tumour recurrence (4). This study gives an overview of the treatment of uveal melanoma and demonstrates that most patients with uveal melanoma can be treated conservatively, with the large majority retaining the eye and good vision.

Immunolocalization of inducible nitric oxide synthase in synovium and cartilage in rheumatoid arthritis and osteoarthritis

Nitric oxide has been implicated as a mediator of inflammatory arthritis, and recent work has shown that pro-inflammatory cytokines stimulate NO production in vitro by activation of the inducible nitric oxide synthase (iNOS) pathway. In order to identify the cellular sources of NO production within the joint, we have used immunohistochemical techniques to study the distribution of iNOS in synovium and cartilage from normal and diseased joints. iNOS was most strongly expressed in the synovial lining layer, subsynovium, vascular smooth muscle and chondrocytes from patients with rheumatoid arthritis (RA). Analysis of serial sections, coupled with double immunofluorescent staining, showed that the CD68+ macrophages in the synovial lining layer and, to a lesser extent, fibroblasts were the predominant source of iNOS within synovium, whereas T cells, B cells and neutrophils were negative. A similar pattern of iNOS staining was seen in osteoarthritis, but fewer cells were iNOS positive and the intensity of staining, particularly in cartilage, was much weaker than in RA. In contrast, no evidence of iNOS was detected in non-inflammatory synovium or in cartilage derived from normal joints (fractured neck of femur). In conclusion, these data support the hypothesis that synovium and cartilage are important sources of increased NO production in patients with inflammatory arthritis. Localization of iNOS at these sites within the inflamed joint raises the possibility that increased local production of NO may contribute to the pathogenesis of inflammatory arthritis by increasing synovial blood flow and by modulating cellular function within synovium and articular cartilage.

Computer-assisted Prediction of Drill-failure Using In-process Measurements of Thrust Force

A real time control system has been developed in the laboratory to monitor the performance of twist drills. Emphasis has been placed on the prediction of the incipient failure of the drill and retraction before significant damage has occurred. It has been found that the gradient of the drilling thrust force, calculated using a digital filter with the necessary frequency specifications, exhibits a sharp increase several seconds before any serious failure. Details of the filtering technique and results for several cutting conditions are presented.

On-Line Estimation of Tool/Chip Interface Temperatures for a Turning Operation

This research has been concerned with the measurement of on-line temperature in a turning operation. The goal has been to develop a measurement sensor and algorithms that allow tool-chip interface temperatures to be estimated during machining. The measuring scheme relies on the signal from a standard thermocouple, located at the bottom of the tool insert, the response time of which has been observed to be on the order of one second. The important feature of the prediction scheme is that it can also estimate the interface temperatures for an interrupted cut and for the case when tool wear is present. The estimated interface temperatures have been compared with those obtained with a previously described metallographic technique [1] and a difference of 5–13 percent between these two results has been reported.

Active Control of a Compliant Wrist in Manufacturing Tasks

A robotic wrist unit has been constructed and is functioning on a large industrial robot used to load, assemble, and finish parts in an automated metal working cell. The wrist uses force feedback and remote-center-compliance techniques similar to those that have been developed for assembly robots. The wrist employs four spherical hydraulic actuators that behave as adjustable springs with a stiffness that varies between 5.8 × 103 and 7.9 × 103 N/m. This allows the center of compliance to be projected over a range from 25 to 157 mm out from the upper platform of the wrist. The wrist has 5 1/2 degrees-of-freedom, being compliant in each direction except axial extension. Deflections of ± 4.6 mm in the radial plane and 5.1 mm in compression are possible. The accuracy of the sensors over this working range is within 0.025 mm for translations and within 0.001 rad for rotations.

Further Developments in Applying the Finite Element Method to the Calculation of Temperature Distributions in Machining and Comparisons With Experiment

The finite element program developed in previous work [1] for calculating the temperature distributions in the chip and tool in metal machining has been extended in its range of application. Specifically, the program no longer needs a flow field as input and it can accommodate a wide range of shear angle and contact lengths. An important feature of this paper is that temperature fields from the finite element method have been compared with temperatures obtained with a previously described metallographic method [7]. This is the first time these two techniques have been used for the same machining conditions and the comparisons are very good.

Adaptive Control in Machining—A New Approach Based on the Physical Constraints of Tool Wear Mechanisms

An optimization procedure for adaptive control based on the physical constraints of the machining process is proposed. Three different modes of tool failure have been examined and constraints for each mode of failure identified accordingly. A mapping procedure has then been used to transform these constraints into a control variable space and obtain a “safe working range.” The optimum working conditions are determined in terms of the control variables (cutting speed and feed rate) based on a chosen performance index (metal removal rate, in this case). Also, further consideration of time-varying situations such as tool wear and engage-exit conditions can be included in this formulation. Several numerical examples are presented for the identification of the dominant modes of failure, in particular, experimental cases. The results are in good agreement with the experimental data available.

Application of Plastic Boundary Layer Theory to Metal Machining

In the metal machining operation, material is deformed at high rates in thin plastic zones. This paper explores the possibility that the features of such shear zones can be described by a theory for plastic boundary layers. The analysis draws on Oldroyd’s solution for the two-dimensional plastic flow of a Bingham solid over a flat knife. The way in which such a solution can be adapted to both the secondary and primary deformation zones in machining is described. A theoretical equation is derived that uses material properties to predict the tool-face pressure gradient along the contact length. An analysis for brass gives very good agreement between this approach and the experimental data for the tool-face pressure gradient obtained by Rowe and Wilcox.

Predicting the Shear Plane Angle in Machining From Workmaterial Strain-Hardening Characteristics

An upper-bound type analysis is presented for predicting the “shear plane angle,” φ, in machining, using workmaterial strain-hardening characteristics. The degree of strain-hardening is quantified by referring to standard reference tables for yield strength and ultimate strength. In the model, the first step is to formulate the lowest amount of plastic work needed to cause a shear instability (collapse) in severely strain-hardened material. (In an upper-bound analysis this occurs on a plane at (φ = 45 + α/2.) However, due to work-hardening, this deformation zone geometry is nonunique and the shear plane can “rotate” into the softer material ahead of this initial instability. Using the proposition that the plastic work input remains constant, an equation is then derived which can be used to calculate the degree of shear plane rotation and hence the final position that the shear plane adopts for various workmaterials. In discussion, it is emphasized that this is an introductory analysis which ignores friction at the rake face and the high strain rates and temperatures that arise in practice; however, the agreement between this new, predictive model and experimental data is exceptionally good.

Effect of Rake Face Design on Cutting Tool Temperature Distributions

Turning experiments have been carried out on a low carbon iron using steel tools of different side rake face geometry. Temperature distributions have been determined using a recently developed metallographic method. It has been found that when using tools which have a controlled chip-tool contact length of 0.5 mm. the temperatures are ∼30 per cent lower than when using conventional, 6 deg rake tools and, as a result, tool life is longer. Theoretical equations are described which allow the calculation of the temperature distribution along the chip tool interface and the tribological conditions in this region are also considered in detail. There is good agreement between the calculated and measured temperature distributions.

Correlation of Tempering Effects With Temperature Distribution in Steel Cutting Tools

Experimental methods are described for determining the temperature distribution in steel cutting tools over the range 150 C to 1000 C. The techniques correlate temperature with changes in microstructure and hardness that arise due to the heat conducted into the tool. Results are presented for the machining of low carbon iron and commercially pure copper, and the effectiveness of cutting coolant is evaluated for a range of cutting speeds and for two different methods of application. Simple models for the heat sources in chip formation are derived and used to verify the experimental work by calculating the temperatures on the rake face.