Browsing by Author "Saikko, Vesa"

Filter results by typing the first few letters
Now showing 1 - 20 of 42
  • A12-station anatomic hip joint simulator
    (2005) Saikko, Vesa
     School of Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Adverse condition testing with hip simulators
    (2015) Saikko, Vesa
     School of Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Analysis of UHMWPE wear particles produced in the simulation of hip and knee wear mechanisms with the RandomPOD system
    (2015) Saikko, Vesa; Vuorinen, Vesa; Revitzer, Hannu
     School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Analysis of wear produced by a 100-station wear test device for UHMWPE with different contact pressures
    (2022-07) Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In orthopaedic tribology, a useful wear test device must produce clinically relevant wear with low variation and have a large capacity for adequate sample sizes and simultaneous testing of several samples. The present study emphasized statistical considerations that are often overlooked. The 100-station SuperCTPOD device was used to study the effect of contact pressure, 0.5–3.0 MPa, on UHMWPE wear with a sample size of 10. The mean wear rate varied from 2.00 to 5.06 mg/106 cycles and the SDs from 0.18 to 0.54 mg/106 cycles. The lowest difference between means was 0.56 mg/106 cycles with ≥ 80% power. The study provided corroborative evidence for the usefulness of the present large capacity wear test system.
  • Behavior of marine thruster lip seals under typical operating conditions
    (2025-01) Morad, Omar; Viitala, Raine; Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Marine thruster lip seals pose a condition monitoring challenge, yet they are seldom studied tribologically. The present work studies the behavior of a 300 mm diameter NBR marine thruster lip seal (n = 3) under typical operating conditions. Frictional torque and subsurface temperature were measured under 27 combinations of oil temperature, oil pressure, and rotational speed. The frictional torque increased with increasing oil pressure and decreased with increasing oil temperature. The subsurface temperature increased with increasing oil temperature, oil pressure, and rotational speed. There was no clear relation between the frictional torque and subsurface temperature. The frictional torque ranged 9.6–14.4 Nm, and subsurface temperature 57–94 °C. Preliminary wear measurements showed a wear track width of 0.2–0.3 mm and a wear rate of 0.031 ± 0.001 mm3/hour.
  • The effect of acetabular cup position on wear of a large-diameter metal-on-metal prosthesis studied with a hip joint simulator
    (2013) Saikko, Vesa; Ahlroos, Tiina; Revitzer, Hannu; Ryti, Oskari; Kuosmanen, Petri
     School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of CoCr Counterface Roughness on the Wear of UHMWPE in the Noncyclic RandomPOD Simulation
    (2017) Saikko, Vesa; Vuorinen, Vesa; Revitzer, Hannu
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of CoCr Counterface Roughness on the Wear of UHMWPE in the Noncyclic RandomPOD Simulation
    (2017) Saikko, Vesa; Vuorinen, Vesa; Revitzer, Hannu
     School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of Component Position and Inward–Outward Rotation on the Wear of Different Ultra-High Molecular Weight Polyethylenes in an Orbital Bearing Type Hip Joint Simulator
    (2023) Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The orbital bearing machine is the world’s most widely used hip joint simulator design for wear testing of prosthetic hips. It has been used with inverted and anatomic component position and with and without inward–outward rotation. Still the effect of component position on the wear of the most widely used bearing material, ultrahigh molecular weight polyethylene (UHMWPE), has not been studied directly. With a modified orbital bearing machine, the effects of the component position, anatomic versus inverted, and of the inward–outward rotation, present versus absent, on polyethylene wear were studied for the first time. Acetabular liners made from different ultra-high molecular weight polyethylenes articulated against alumina femoral heads in alpha calf serum. The inverted position resulted in the most realistic, burnished appearance of the polyethylene bearing surfaces. In the inverted position, the wear rate decreased with increasing gamma dose that is known to improve wear resistance by cross-linking. In the anatomic position, the bearing surface was not always entirely burnished. The wear was similar with and without inward–outward rotation. The mean wear rate of vitamin E stabilized highly cross-linked ultra-high molecular weight polyethylene was close to clinical observations. Clinically relevant wear could be produced with the orbital bearing machine for both established and advanced bearing materials. The inverted position appeared preferable in the orbital bearing machine. Inward–outward rotation did not appear important.
  • Effect of contact area on the wear of ultrahigh molecular weight polyethylene in noncyclic pin-on-disk tests
    (2017) Saikko, Vesa
     School of Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of contact area on the wear of ultrahigh molecular weight polyethylene in noncyclic pin-on-disk tests
    (2017-10-01) Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The 16-station RandomPOD pin-on-disk device with non-cyclic biaxial motion and load was used to study the effect of contact area on the wear of ultrahigh molecular weight polyethylene as used in total hip prostheses. The counterface was polished CoCr and the lubricant was diluted serum. The wear factor increased strongly and linearly with increasing contact area, which was in agreement with clinical findings for total hip prostheses. The coefficient of friction also increased strongly with increasing contact area. With small contact area the lumpy topography of the worn surface differed from the burnished appearance typical of retrieved acetabular cups. The nominal contact pressure should be kept below 2 MPa in pin-on-disk tests intended to simulate clinical wear mechanisms.
  • Effect of contact pressure on wear and friction of ultra-high molecular weight polyethylene in multidirectional sliding
    (2006) Saikko, Vesa
     School of Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of increased load on the wear of a large diameter metal-on-metal modular hip prosthesis with a high inclination angle of the acetabular cup
    (2016) Saikko, Vesa
     School of Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of increased load on the wear of a large diameter metal-on-metal modular hip prosthesis with a high inclination angle of the acetabular cup
    (2016-04-01) Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In some earlier hip simulator studies of large-diameter metal-on-metal (MoM) hip prostheses high, unexplained variation in wear has been observed. In the present study it was found that high variation occurs when the tribological endurance limit of the MoM device in question is being approached. When the limit is exceeded, high wear takes place uniformly, and the variation is low. Below the limit, both the wear and its variation are low. The endurance limit was exceeded by increasing the peak load from 2 kN to 3 kN, to simulate obesity. The acetabular cup inclination angle was high, 70°. Potential clinical wear problems can be predicted by hip simulator studies provided that relevant adverse test conditions are included.
  • Effect of inward-outward rotation on hip wear simulation
    (2020-03-05) Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The ISO 14242-1 standard specifies a three-axis motion for the wear testing of prosthetic hips. Multidirectionality of the relative motion and serum-based lubrication are known to be necessary for the reproduction of clinical wear mechanisms. For multidirectionality however, biaxial motion has been shown to be sufficient. To a biaxial hip joint simulator that incorporated flexion-extension (FE, range 46°) and abduction-adduction (AA, range 12°), a third motion component, inward-outward rotation (IOR, range 12°) was added according to the ISO 14242-1 standard. Due to the addition of the IOR, the wear rate of vitamin E stabilized, extensively cross-linked polyethylene (VEXLPE) liners decreased by 50 per cent. This was probably attributable to the increased linearity of the relative motion in the stance phase, caused by the simplified motion waveforms and their relative phases specified in the standard. In order not to underestimate the wear rate, the established biaxial motion is preferred.
  • Effect of Lubrication Conditions on the Wear of UHMWPE with Noncyclic Motion and Load
    (2019-11-02) Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In orthopaedic tribology, one of the most debated issues is the optimal lubricant. Many different types, concentrations, additives and temperatures of serum-based lubricants are in use. With the multidirectional RandomPOD wear test device, several different lubrication conditions were studied for conventional, gamma-sterilized ultrahigh molecular weight polyethylene (UHMWPE) against polished CoCr. The conditions included dry, deionized water, phosphate buffered saline (PBS) and Alpha calf serum. Only with serum, wear was similar to that known to occur clinically. It was highly linear and of substantial magnitude. Polyethylene surface was burnished and no macroscopic wear debris was produced. The absence of polyethylene transfer, however, was not limited to serum lubrication only. With PBS, no transfer occurred and the same held true occasionally with dry sliding. An increased temperature, 37 °C, as opposed to 20 °C, of 1:1 diluted serum was found to increase the standard deviation of wear factor 2.7 to 4.4-fold, depending on whether an antimicrobial additive, NaN3, was absent or present (0.2%). In the absense of NaN3, the mean wear factor at 20 °C was 2.9-fold higher than at 37 °C. In the presence of NaN3, the corresponding difference was 1.8-fold. A one-day vs. a 6-day serum change interval resulted in wear factors not statistically different from each other. The same held true for the wear factors with undiluted serum vs. serum diluted 1:1. The lubrication conditions appear to have significant effects in wear studies of orthopaedic implant materials and so they need to be carefully chosen.
  • Effect of random variation of input and various daily activities on wear in a hip joint simulator
    (2020-06-09) Viitala, Raine; Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The ISO 14242-1 standard specifies fixed, simplified, sinusoidal motion and double-peak load cycles for wear testing of total hip prostheses. In order to make the wear simulation more realistic, random variation was added for the first time to the motion and load control signals of a hip joint simulator. For this purpose and for the simulation of various daily activities, computer-controlled, servo-electric drives were mounted on a biaxial hip simulator frame and successfully introduced. Random variation did not result in a statistically significant difference in the wear factor of large diameter VEXLPE liners compared with fixed sinusoidal waveforms. However, level walking according to biomechanical literature surprisingly resulted in a 134 per cent higher, and jogging in a 57 per cent lower wear factor compared with the fixed sinusoidal waveforms. These wear phenomena were likely to be caused by a variation in the lubrication conditions and frictional heating. Simplified motion waveforms may result in an underestimation of wear in walking.
  • Effect of serum dilution fluids on the wear of unirradiated and high dose gamma-irradiated, vitamin E stabilized UHMWPE
    (2019-07-15) Saikko, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In orthopaedic tribology, the ISO 14242-1 standard recommends that the serum lubricant is diluted with deionized water (DW). Sometimes, phosphate buffered saline (PBS) is used instead for the dilution. Noncyclic, multidirectional pin-on-disk tests showed that the dilution of alpha calf serum with PBS or phosphate buffer resulted in a 5–40-fold decrease in the wear factor of unirradiated and of vitamin E stabilized, highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) compared with DW dilution. It appears that the phosphates were mainly responsible for this phenomenon. PBS dilution may result in a substantial underestimation of clinical wear. With 1:1 DW dilution, the mean wear factor of highly crosslinked UHMWPE was 5.7-fold lower than that of unirradiated UHMWPE.
  • Effect of shelf versus accelerated aging of UHMWPE on delamination in knee wear simulation
    (2014) Saikko, Vesa
     School of Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of Sliding Velocity on UHMWPE and VEXLPE Friction Against CoCr in Multidirectional, Serum Lubricated Conditions
    (2023-03) Saikko, Vesa; Morad, Omar; Viitala, Raine
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The recently introduced four-station friction RandomPOD device was utilized in multidirectional, circular translation pin-on-disk (CTPOD) tests. The effect of sliding velocity on friction with orthopaedic bearing materials was studied. The tests included UHMWPE and VEXLPE pins against polished CoCr disks in serum lubrication at 37 °C. In the constant velocity tests, the sliding velocities used were from 5 to 50 mm/s at intervals of 5 mm/s. The test length with each velocity was 24 h. In the constant acceleration tests, the velocity steadily increased from 0 to 50 mm/s in 24 h. In all tests, the sample size was 4. No strong effect of velocity on friction was observed. This indicated a boundary lubrication mechanism. With sliding velocities above 10 mm/s, VEXLPE showed significantly lower friction than UHMWPE. The finding was in agreement with earlier dynamic RandomPOD tests. Clinically, the use of VEXLPE may result in lower frictional heating.