doc. Ing. David Nečas, Ph.D.
E-mail:   necas@fme.vutbr.cz  Dept.:   Institute of Machine and Industrial Design Dept. of Tribology Position:   Associate Professor Room:   A3/608

Publications:

• NEČAS, D.; VRBKA, M.; GALANDÁKOVÁ, A.; KŘUPKA, I.; HARTL, M.:
  On the observation of lubrication mechanisms within hip joint replacements. Part I: Hard-on-soft bearing pairs, Elsevier
  journal article in Web of Science
• NEČAS, D.; VRBKA, M.; GALLO, J.; KŘUPKA, I.; HARTL, M.:
  On the observation of lubrication mechanisms within hip joint replacements. Part II: Hard-on-hard bearing pairs, Elsevier
  journal article in Web of Science
• NEČAS, D.; JAROŠ, T.; DOČKAL, K.; ŠPERKA, P.; VRBKA, M.; KŘUPKA, I.; HARTL, M.:
  The effect of kinematic conditions on film thickness in compliant lubricated contact, The American Society of Mechanical Engineers
  journal article in Web of Science
• NEČAS, D.; VRBKA, M.; KŘUPKA, I.; HARTL, M.:
  The Effect of Kinematic Conditions and Synovial Fluid Composition on the Frictional Behaviour of Materials for Artificial Joints, MDPI
  journal article in Web of Science
• NEČAS, D.; VRBKA, M.; REBENDA, D.; GALLO, J.; GALANDÁKOVÁ, A.; WOLFOVÁ, L.; KŘUPKA, I.; HARTL, M.:
  In Situ Observation of Lubricant Film Formation in THR Considering Real Conformity: The Effect of Model Synovial Fluid Composition , Elsevier Ltd.
  journal article in Web of Science
• NEČAS, D.; SAWAE, Y.; FUJISAWA, T.; NAKASHIMA, K.; MORITA, T.; YAMAGUCHI, T.; VRBKA, M.; KŘUPKA, I.; HARTL, M.:
  The Influence of Proteins and Speed on Friction and Adsorption of Metal/UHMWPE Contact Pair, Elsevier
  journal article in Scopus
• NEČAS, D.; VRBKA, M.; URBAN, F.; GALLO, J.; KŘUPKA, I.; HARTL, M.:
  In situ observation of lubricant film formation in THR considering real conformity: The effect of diameter, clearance and material, Elsevier Ltd.
  journal article in Web of Science
• NEČAS, D.; VRBKA, M.; KŘUPKA, I.; HARTL, M.; GALANDÁKOVÁ, A.:
  Lubrication within hip replacements – Implication for ceramic-on-hard bearing couples, Elsevier Ltd.
  journal article in Web of Science
• NEČAS, D.; VRBKA, M.; URBAN, F.; KŘUPKA, I.; HARTL, M.:
  The effect of lubricant constituents on lubrication mechanisms in hip joint replacements, Elsevier Ltd.
  journal article in Web of Science
• VRBKA, M.; NEČAS, D.; BARTOŠÍK, J.; HARTL, M.; KŘUPKA, I.; GALANDÁKOVÁ, A.; GALLO, J.:
  Stanovení součinitele tření hlavic a jamek TEP kyčle,
  Acta Chirurgie Orthopaedicae et Traumatologie Čechoslovaca, Vol.82, (2015), No.5, pp.341-347, ISSN 0001-5415, Česká společnost pro ortopedii a traumatologii, Galén, spol. s r.o.
  journal article - other
• KOŠŤÁL, D.; NEČAS, D.; ŠPERKA, P.; SVOBODA, P.; KŘUPKA, I.; HARTL, M.:
  Lubricant Rupture Ratio at Elastohydrodynamically Lubricated Contact Outlet, Springer
  journal article in Web of Science
• VRBKA, M.; NEČAS, D.; HARTL, M.; KŘUPKA, I.; URBAN, F.; GALLO, J.:
  Visualization of lubricating films between artificial head and cup with respect to real geometry, Elsevier
  journal article in Scopus

List of publications at Portal BUT

Abstracts of most important papers:

• NEČAS, D.; VRBKA, M.; GALANDÁKOVÁ, A.; KŘUPKA, I.; HARTL, M.:
  On the observation of lubrication mechanisms within hip joint replacements. Part I: Hard-on-soft bearing pairs, Elsevier
  journal article in Web of Science
  The present study describes the lubrication mechanisms within artificial hip joints considering real conformity of rubbing surfaces. Part I is focused on hard-on-soft material combination, introducing the fundamentals of lubrication performance. These pairs have not been explored in terms of in situ observation before. The contact of metal femoral component articulating with transparent polymer acetabular cup was studied using a hip joint simulator. The film formation was evaluated by fluorescent microscopy method. Various model synovial fluids were employed while the key constituents, i.e. albumin, γ-globulin, and hyaluronic acid were fluorescently stained to determine its role in film formation process. Two types of the tests were performed. The first dynamic test aimed on the development of film thickness under constant load during motor driven swinging motion mimicking flexion-extension. Subsequently, a combined test was designed consisting of the three phases; static part with loading/unloading phase (1), pendulum swinging till spontaneous damping of the motion due to friction (2), and static observation under the constant load (3). The results clearly confirmed that the interaction of constituents of synovial fluid plays a dominant role and substantially influences the lubrication conditions. In particular, the main finding coming from the present study is that γ-globulin together with hyaluronic acid form relatively thin stable boundary layer enabling the enhanced adsorption of albumin, thus increasing the lubricant film. Part II of the present study is focused on hard-on-hard pairs while the main differences in film formation process are highlighted among others.
• NEČAS, D.; VRBKA, M.; GALLO, J.; KŘUPKA, I.; HARTL, M.:
  On the observation of lubrication mechanisms within hip joint replacements. Part II: Hard-on-hard bearing pairs, Elsevier
  journal article in Web of Science
  The present paper represents Part II of the extensive study focused on the lubrication of hip joint replacements. The main goal is to assess the fundamentals of lubrication considering both hard-on-soft (Part I) and hard-on-hard (Part II) bearing pairs. In addition, the effect of individual constituents contained in the model fluid is clarified. For this purpose, multiple model fluids of various composition were employed. In this part of the study, metal-on-glass contact representing hard bearing pairs was observed in situ using pendulum hip joint simulator in combination with thin film colorimetric interferometry method. The designed test consists of initial static loading/unloading phase for the determination of adsorption of molecules on rubbing surfaces. This period is followed by swinging of the pendulum and latest static part under constant load. Three groups of measurements were carried out while fourteen different lubricants were tested. Initially, the experiments were performed with albumin-based model fluid. In that case a substantial positive effect of hyaluronic acid was identified. In contrast, the fluids with γ-globulin as a base constituent showed improved lubrication conditions when phospholipids were added to the solution. Finally, considering the complex fluid, a combined effect of hyaluronic acid and phospholipids caused a better endurance of the lubricant film. The latest part of the paper aims on the comparison of film formation considering hard and soft pairs, highlighting some clear differences. In general, hard pairs exhibit clear decreasing tendency of the film during swinging motion while opposite behaviour was observed for soft pairs.
• NEČAS, D.; VRBKA, M.; REBENDA, D.; GALLO, J.; GALANDÁKOVÁ, A.; WOLFOVÁ, L.; KŘUPKA, I.; HARTL, M.:
  In Situ Observation of Lubricant Film Formation in THR Considering Real Conformity: The Effect of Model Synovial Fluid Composition , Elsevier Ltd.
  journal article in Web of Science
  The present paper explores the effect of synovial fluid composition on lubricant film formation in hip replacements. The measurements were realized utilizing pendulum hip joint simulator, while the film thickness was evaluated using optical interferometry. Contact couples consisted of metal and ceramic femoral heads articulating with glass acetabular cups. As the test lubricants, various model fluids were employed. Initially, static tests, aimed on the effect of material and load on adsorption, were conducted. It was found that adsorbed film thickness increases independently of the head material. Consequently, swinging flexion-extension experiments were realized, revealing that the film formation is substantially affected by composition of model fluid. The thickest film was observed when higher concentration of hyaluronic acid and phospholipids was applied.
• NEČAS, D.; VRBKA, M.; URBAN, F.; GALLO, J.; KŘUPKA, I.; HARTL, M.:
  In situ observation of lubricant film formation in THR considering real conformity: The effect of diameter, clearance and material, Elsevier Ltd.
  journal article in Web of Science
  The aim of the present study is to provide an analysis of protein film formation in hip joint replacements considering real conformity based on in situ observation of the contact zone. The main attention is focused on the effect of implant nominal diameter, diametric clearance and material. For this purpose, a pendulum hip joint simulator equipped with electromagnetic motors enabling to apply continuous swinging flexion–extension motion was employed. The experimental configuration consists of femoral component (CoCrMo, BIOLOX®forte, BIOLOX®delta) and acetabular cup from optical glass fabricated according to the dimensions of real cups. Two nominal diameters were studied, 28 and 36 mm, respectively, while different diametric clearances were considered. Initially, a static test focused on the protein adsorption onto rubbing surfaces was performed with 36 mm implants. It was found that the development of adsorbed layer is much more stable in the case of metal head, indicating that the adsorption forces are stronger compared to ceramic. A consequential swinging test revealed that the fundamental parameter influencing the protein film formation is diametric clearance. Independently of implant diameter, film was much thicker when a smaller clearance was considered. An increase of implant size from 28 mm to 36 mm did not cause a substantial difference in film formation; however, the total film thickness was higher for smaller implant. In terms of material, metal heads formed a thicker film, while this fact can be, among others, also attributed to clearance, which is more than two times higher in the case of ceramic implant.
• VRBKA, M.; NEČAS, D.; HARTL, M.; KŘUPKA, I.; URBAN, F.; GALLO, J.:
  Visualization of lubricating films between artificial head and cup with respect to real geometry, Elsevier
  journal article in Scopus
  The aim of this study is to propose a novel experimental approach enabling in-situ observation of film formation within hip joint replacements with respect to real geometry (including radial clearance) of rubbing surfaces. A pendulum hip joint simulator in combination with thin film colorimetric interferometry was employed for film thickness evaluation between metal femoral head and glass acetabular cup lubricated by bovine serum solution. Glass acetabulum was developed according to dimensions of artificial cup so the real radial clearance between components was considered. The pendulum, deflected at an initial position, was released and allowed to oscillate freely in the flexion-extension plane; therefore the transient character of motion was considered. Maximum central film thickness of 232 nm was measured at the beginning of the experiment. After a short time it decreased and became quite stable (around 90 nm) until the end of the measurement. The preliminary results shown that novel experimental approach seems to be a very powerful tool for studying lubrication processes within artificial hip joints while considering different loading and kinematic conditions, influence of geometry, clearance and material combination of contact pairs.