Biomedical subjects

F van Keulen

Publications and source records attributed to F van Keulen.

8 recordsLinked to original sources

PubMed2005

Bone ingrowth simulation for a concept glenoid component design.

Glenoid component loosening is the major problem of total shoulder arthroplasty. It is possible that uncemented component may be able to achieve superior fixation relative to cemented component. One option for uncemented glenoid is to use porous tantalum backing. Bone ingrowth into the porous backing requires a degree of stability to be achieved directly post-operatively. This paper investigates the feasibility of bone ingrowth with respect to the influence of primary fixation, elastic properties of the backing and friction at the bone prosthesis interface. Finite element models of three glenoid components with different primary fixation configurations are created. Bone ingrowth into the porous backing is modelled based on the magnitude of the relative interface micromotions and mechanoregulation of the mesenchymal stem cells that migrated via the bonded part of the interface. Primary fixation had the most influence on bone ingrowth. The simulation showed that its major role was not to firmly interlock the prosthesis, but rather provide such a distribution of load, that would result in reduction of the peak interface micromotions. Should primary fixation be provided, friction has a secondary importance with respect to bone ingrowth while the influence of stiffness was counter intuitive: a less stiff backing material inhibits bone ingrowth by higher interface micromotions and stimulation of fibrous tissue formation within the backing.

Cell Differentiation↗

PubMed2004

The possibilities of uncemented glenoid component--a finite element study.

OBJECTIVE: (1) Determine the initial stress distributions within an uncemented implanted glenoid during elevation of the arm and to investigate whether failure is caused by stresses generated within this implant-bone structure. (2) Compare stress patterns between the uncemented design and two basic models of cemented prostheses. DESIGN: The uncemented component consists of a polyethylene cup with a metal-backing. All material interfaces were assumed to be fully bonded. BACKGROUND: Cemented glenoid components have been frequently vulnerable to failure within itself and at the cement-bone interface. A 3-D finite element analysis of an uncemented design is required to investigate whether clinical observations on failure can be better explained with a stress analysis. METHODS: A 3-D finite element submodel an uncemented prosthesis was generated using CT-scan data and realistic loading conditions (humeral abduction, 30-180 degrees ). The submodelling approach was based on an overall solution of a complete scapula acted upon by all muscles, ligaments and joint reaction forces. RESULTS: High Von Mises stresses (20-70 MPa) were generated in the metal-backing during abduction. Stresses were reduced in the polyethylene cup by 17-20% as compared to the cemented designs. Stresses in the underlying bone were substantially lower than to the natural glenoid. Stress-shielding can be observed in the trabecular bone underlying the prosthesis. The implant-bone interface is secure against interface failure at moderate loads, although the implant-bone (metal-bone) interface around the superior edge of the prosthesis is subject to high stresses (normal: 11.85 MPa, shear: 6.67 MPa) as compared to the cemented prosthesis. Whereas, the cement-bone interface, appears more likely to fail either at locations adjacent to the keel or at locations around the superior edge of the cemented design. The uncemented design therefore appeared to be a reasonable alternative to fixation with cement. RELEVANCE: Results of this study strongly agree with clinical and radiographic findings. Although indications of stress-shielding and separation of modular parts of the prosthesis were apparent, the implant-bone interface seems less likely to fail as compared to cemented designs. Once initial fixation of the implant is achieved, the uncemented design appears to have better prospects than cemented ones.

Equipment Failure Analysis↗

PubMed2004

Numerical simulation of tissue differentiation around loaded titanium implants in a bone chamber.

The application of a bone chamber provides a controlled environment for the study of tissue differentiation and bone adaptation. The influence of different mechanical and biological factors on the processes can be measured experimentally. The goal of the present work is to numerically model the process of peri-implant tissue differentiation inside a bone chamber, placed in a rabbit tibia. 2D and 3D models were created of the tissue inside the chamber. A number of loading conditions, corresponding to those applied in the rabbit experiments, were simulated. Fluid velocity and maximal distortional strain were considered as the stimuli that guide the differentiation process of mesenchymal cells into fibroblasts, chondrocytes and osteoblasts. Mesenchymal cells migrate through the chamber from the perforations in the chamber wall. This process is modelled by the diffusion equation. The predicted tissue phenotypes as well as the process of tissue ingrowth into the chamber show a qualitative agreement with the results of the rabbit experiments. Due to the limited number of animal experiments (four) and the observed inter-animal differences, no quantitative comparison could be made. These results however are a strong indication of the feasibility of the implemented theory to predict the mechano-regulation of the differentiation process inside the bone chamber.

Animals↗

PubMed2004

Stress analysis of cemented glenoid prostheses in total shoulder arthroplasty.

Glenoid component loosening is the most-frequently encountered problem in the total shoulder arthroplasty. The purpose of the study was to investigate whether failure of the glenoid component is caused by stresses generated within the cement mantle, implant materials and at the various interfaces during humeral abduction, using 3-D FE analyses of implanted glenoid structures. FE models, one total polyethylene and the other, metal backed polyethylene, were developed using CT-scan data and submodelling technique, which was based on an overall solution of a natural scapula model acted upon by all the muscles, ligaments and joint reaction forces. Material interfaces were assumed to be fully bonded. Based on the FE stress analysis, the following observations were made. (1) The submodelling technique, which required a large-size submodel and the use of prescribed displacements at cut-boundaries located far away from the glenoid, was crucial for evaluations on glenoid component. (2) Total polyethylene results in lower-peak stresses (tensile: 10 MPa, Von-Mises: 8.31 MPa) in the cement as compared to a metal-backed design (tensile: 11.5 MPa, Von-Mises: 9.81 MPa). The maximum principal (tensile) stresses generated in the cement mantle for both the designs were below its failure strength, but might evoke crack initiation. (3) The cement-bone interface adjacent to the tip of the keel seemed very likely to fail for both the designs. In case of metal-backed design, this interface adjacent to the tip of the keel appears even more likely to fail. (4) High metal-cement interface stresses for a moderate load might indicate failure at higher load. (5) It appears that both the designs were vulnerable to failure in some ways or the other. A part of the subchondral bone along the longitudinal axis of the glenoid cavity should be preserved to strengthen the glenoid structure and to reduce the use of cement.

Arthroplasty, Replacement↗

PubMed2004

Factors enhancing lycopene production by a new Mycobacterium aurum mutant.

A mutant strain of Mycobacterium aurum was isolated that produced mainly lycopene (>80%) with a total carotenoid content of 1.2 mg g(-1) dry biomass when grown on yeast extract and glucose. Lycopene content of the cells could be significantly increased, up to 7.4 mg g(-1) biomass, by growing the cells at suboptimal initial culture pH (pH 6-6.4) or by using high salt concentration (85 mM NaCl) in the culture medium, although a 25-40% decrease in biomass production occurred in both cases. Highestproductivity (4 mg lycopene l(-1) d(-1)) was obtained by cultivating the cells at pH 6.

Biomass↗

PubMed2004

Isolation of a beta-carotene over-producing soil bacterium, Sphingomonas sp.

A carotenoid-accumulating bacterium isolated from soil, identified as a Sphingomonas sp., grew at 0.18 h(-1) and produced 1.7 mg carotenoids g(-1) dry cell, among which beta-carotene (29% of total carotenoids) and nostoxanthin (36%). A mutant strain, obtained by treatment with ethyl methanesulfonate, accumulated up to 3.5 mg carotenoids g(-1) dry cell. Accumulation of beta-carotene by this strain depended on the oxygenation of the growth medium, with maximal accumulation (89%) occurring under limiting conditions. Beta-carotene accumulation could be further enhanced by incubating the cells in the presence of glycerol (either not or only slowly assimilated) and yeast extract resulting in an accumulation of 5.7 mg beta-carotene g(-1) dry cell wt. The strain used lactose as carbon source with similar biomass and carotenoid production, providing a viable alternative use for cheese whey ultra-filtrate.

Genetic Engineering↗

PubMed2004

Development and experimental validation of a three-dimensional finite element model of the human scapula.

A new modelling approach, using a combination of shell and solid elements, has been adopted to develop a realistic three-dimensional finite element (FE) model of the human scapula. Shell elements were used to represent a part of the compact bone layer (i.e. the outer cortical layer) and the very thin and rather flat part of the scapula--infraspinous fossa and supraspinous fossa respectively. Solid elements were used to model the remaining part of the compact bone and the trabecular bone. The FE model results in proper element shapes without distortion. The geometry, material properties and thickness were taken from quantitative computed tomography (CT) data. A thorough experimental set-up for strain gauge measurement on a fresh bone serves as a reference to assess the accuracy of FE predictions. A fresh cadaveric scapula with 18 strain gauges fixed at various locations and orientations was loaded in a mechanical testing machine and supported at three locations by linkage mechanisms interconnected by ball joints. This new experimental set-up was developed to impose bending and deflection of the scapula in all directions unambiguously, in response to applied loads at various locations. The measured strains (experimental) were compared to numerical (FE) strains, corresponding to several load cases, to validate the proposed FE modelling approach. Linear regression analysis was used to assess the accuracy of the results. The percentage error in the regression slope varies between 9 and 23 per cent. It appears, as a whole, that the two variables (measured and calculated strains) strongly depend on each other with a confidence level of more than 95 per cent. Considering the complicated testing procedure on a fresh sample of scapula, the high correlation coefficients (0.89-0.97), the low standard errors (29-105 micro epsilon) and percentage errors in the regression slope, as compared to other studies, strongly suggest that the strains calculated by the FE model can be used as a valid predictor of the actual measured strain. The model is therefore an alternative to a rigorous three-dimensional model based on solid elements only, which might often be too expensive in terms of computing time.

Aged↗

PubMed2003

Towards a cost effective strategy for cutinase production by a recombinant Saccharomyces cerevisiae: strain physiological aspects.

Although the physiology and metabolism of the growth of yeast strains has been extensively studied, many questions remain unanswered where the induced production of a recombinant protein is concerned. This work addresses the production of a Fusarium solani pisi cutinase by a recombinant Saccharomyces cerevisiae strain induced through the use of a galactose promoter. The strain is able to metabolise the inducer, galactose, which is a much more expensive carbon source than glucose. Both the transport of galactose into the cell-required for the induction of cutinase production-and galactose metabolism are highly repressed by glucose. Different fermentation strategies were tested and the culture behaviour was interpreted in view of the strain metabolism and physiology. A fed-batch fermentation with a mixed feed of glucose and galactose was carried out, during which simultaneous consumption of both hexoses was achieved, as long as the glucose concentration in the medium did not exceed 0.20 g/l. The costs, in terms of hexoses, incurred with this fermentation strategy were reduced to 23% of those resulting from a fermentation carried out using a more conventional strategy, namely a fed-batch fermentation with a feed of galactose.

Biomass↗