Bio-Medical Materials and Engineering - Volume 10, issue 1

Authors: Lewis, Gladius

Article Type: Research Article

Abstract: The composition and viscosity of an acrylic bone cement have both been identified in the literature as being parameters that affect the mechanical properties of the material and, by extension, the in vivo longevity of cemented arthroplasties. The objective of the present study was to determine the relative influence of these parameters on a key cement mechanical property; namely, its fracture toughness. Two sets of cements were selected purposefully to allow the study objective to be achieved. Thus, one set comprised two cements with very similar compositions but very different viscosities (Cemex^{\mathrm{TM}} RX, a medium‐viscosity brand, and Cemex …Isoplastic, a high‐viscosity brand) while the other set comprised two cements with similar viscosities but with many differences in composition (Cemex Isoplastic and CMW® 1). Values of the fracture toughness (as determined using chevron‐notched short rod specimens) [K_{\mathrm{ISR}} ] obtained for Cemex RX and Cemex Isoplastic were 1.83 ± 0.12 and 1.85 ± 0.12 MPa\surd m, respectively, with the difference not being statistically significant. The K_{\mathrm{ISR}} values obtained for Cemex Isoplastic and CMW^{\mathrm{TM}} 1 were 1.85 ± 0.12 and 1.64 ± 0.18 MPa\surd m, respectively, with the difference being statistically significant. Thus, the influence of cement composition on its K_{\mathrm{ISR}} is more marked relative to the influence of cement viscosity. Explanations of this finding are offered, together with comments on the implications of the results for the in vivo longevity of cemented arthroplasties. Show more

Keywords: Acrylic bone cement, fracture toughness, cement composition, cement viscosity

Citation: Bio-Medical Materials and Engineering, vol. 10, no. 1, pp. 1-11, 2000

Authors: Konvickova, S. | Cerny, F. | Gurovic, J. | Kvasnicka, I. | Suchanek, J. | Hnatowicz, V.

Article Type: Research Article

Abstract: Coatings of CN_{x} have been prepared on the substrates of material Ti6Al4V, of which the human joint replacements are made. The deposition of the CN_{x} coating was carried out by PACVD method in apparatus with standard arrangement. The methane and nitrogen have been used as precursors for CN_{x} compound. The infrared absorption spectroscopy and Rutherford backscattering spectroscopy were applied on diagnostics of prepared CN_{x} layer. Beside carbon and nitrogen the hydrogen and oxygen were found in the coatings. The sliding tests were carried out with the samples. The counter parts were the …cylinders made of the polyethylene of the same type as for big joint prostheses is used. The tests were carried out in the medium of physiological solution. The CN_{x} coatings perform well under the lower load of 25 and 50 N. When the load is increased to 100 N, the friction coefficient slowly increases, but measured values of μ are typical for boundary lubrication. Show more

Keywords: CN_{x} coating, PACVD method, sliding properties, bioimplants, friction coefficient

Citation: Bio-Medical Materials and Engineering, vol. 10, no. 1, pp. 13-17, 2000

Authors: Hasirci, V. | Lewandrowski, K.U. | Bondre, S.P. | Gresser, J.D. | Trantolo, D.J. | Wise, D.L.

Article Type: Research Article

Abstract: Biodegradable bone plates were prepared as semi‐interpenetrating networks (SIPN) of crosslinked polypropylene fumarate (PPF) within a host matrix of either poly(lactide‐co‐glycolide) – 85 : 15 (PLGA) or poly(l‐lactide‐co‐d,l‐lactide) – 70 : 30 (PLA) using N‐vinylpyrrolidone (NVP), ethylene glycol dimethacrylate (EGDMA), 2‐hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA) as crosslinking agents. Hydroxyapatite (HAP), an inorganic filler material, was used to further augment mechanical strength. The control crosslinking agent (NVP) was replaced partially and totally with other crosslinking agents. The amount of crosslinking agent lost, the characterization change in the mechanical properties and the dimensional stability of the bone plates after in …vitro treatment was calculated. The optimum crosslinking agent was selected on the basis of low in vitro release of NVP from SIPN matrix. Bone plates were then prepared using this crosslinking agent at 5 MPa pressure and at temperatures between 100–140°C to determine if there was any augmentation of mechanical properties in the presence of the crosslinked network. In vitro analysis showed that 90% of the crosslinking agent was lost on plates using NVP as a crosslinking agent. This loss was reduced to 50% when NVP was partially replaced with EGDMA or MMA. EGDMA was determined to be superior because (1) its low release as a crosslinking agent, (2) flexural plate strength of 50–67 MPa, (3) flexural modulus of 7–13 GPa, and (4) manufacturability stiffness of 300–600 N/m. HAP‐loading resulted in an additional increase in values of mechanical parameters. Substituting PLGA with PLA in the PPF‐SIPN did not show any additional improvement of mechanical properties. Show more

Keywords: Semi‐interpenetrating network, bioresorbable, bone plates, poly(lactide‐co‐glycolide), polypropylene fumarate

Citation: Bio-Medical Materials and Engineering, vol. 10, no. 1, pp. 19-29, 2000

Authors: Ceschinski, Harald | Henkes, Hans | Weinert, Hans‐Christian | Weber, Werner | Kühne, Dietmar | Monstadt, Hermann

Article Type: Research Article

Abstract: Guidewires for microcatheters used for the subselective catheterization of small vessels must meet high quality requirements in regard to handling, steerability, radiopacity and physical properties. The aim of this paper is to classify one of the factors that determine the physical and mechanical parameters of a number of existing microcatheter guidewires. A torsion‐testing equipment for guidewires was devised. Nitinol wires were tested and compared with the austenitic stainless steel variants. 13 different commercial wires were tested. Tensile strength, shear modulus and wire diameter are the determining factors of the torsional rigidity of guidewires. By interpreting the measured torsional momentums various …statements concerning the torsional rigidity of different wires can be made. The properties of guidewires are characteristic features of a system and friction and flexible strength examinations have to be carried out to design new variants of wires to meet the requirements of interventional physicians. Show more

Keywords: Torquability, guidewires, torsional momentum, mechanical properties, testing device

Citation: Bio-Medical Materials and Engineering, vol. 10, no. 1, pp. 31-42, 2000

Authors: Pidaparti, R.M. | Akyuz, U. | Naick, P.A. | Burr, D.B.

Article Type: Research Article

Abstract: When bone is subjected to fatigue loading, micro‐cracks initiate and grow. This reduces the mechanical properties and quantitative relationships between stiffness loss and loading cycles may be derived. We developed the relationships between stiffness loss and loading cycles for whole canine femurs subjected to cyclic fatigue in four‐point bending. The fatigue data from experiments followed Weibull statistics. When the stiffness loss is less than 15%, a linear relationship is best‐fitted (R^{2}=0.96 , p<0.0001 ) between the stiffness loss and loading cycles. However, when the stiffness loss is greater than 30%, a power law relationship is best‐fitted (R^{2}=0.97 …, p<0.0001 ) between the stiffness loss and loading cycles. Thus, we conclude that the derived relationships between stiffness loss and loading cycles might be useful for the prediction of bone failure under cyclic bending subjected to an initial strain of 2700 microstrain. Show more

Keywords: Fatigue damage, cortical bone, Weibull statistics, stiffness loss, fatigue

Citation: Bio-Medical Materials and Engineering, vol. 10, no. 1, pp. 43-50, 2000