1 REVISED 1 Reduced curvilinear velocity of boar sperm on substrates 2 with increased hydrophobicity 3 Matthew Mears, 1,* Thomas M. Kennelly, 1 Jonathan R. Howse, 2 4 Drew S. Tarmey, 3 Mark Geoghegan, 1 and Allan A. Pacey, 4 5 1 Department of Physics and Astronomy, The University of Sheffield, Sheffield, S3 7RH, United Kingdom 6 2 Department of Chemical and Biological Engineering, The University of Sheffield, Sheffield, S1 3JD, United Kingdom 7 3 School of Medicine, University of Nottingham, Royal Derby Hospital, Uttoxeter Road, Derby, DE22 3DT, United Kingdom 8 4 Academic Unit of Reproductive and Developmental Medicine, The University of Sheffield, Level 4, The Jessop Wing, 9 Sheffield, S10 2SF, United Kingdom 10 * corresponding author: m.mears@sheffield.ac.uk 11 12 Abstract 13 The curvilinear velocity (VCL) of boar spermatozoa between standard microscopy glassware decreases when the 14 slides are coated with the hydrophobic polymer polystyrene (PS) compared to the less hydrophobic poly(methyl 15 methacrylate) (PMMA) coating. Sperm from three boars were observed and analyzed using particle tracking 16 software. VCL did not differ significantly between coatings of different thickness, indicating no penetration of the 17 sperm into the coating and that only the surface layer of the polymer film interacts with the sperm and buffer 18 medium. The curvilinear velocity of sperm between PS-coated surfaces was significantly reduced compared to 19 PMMA surfaces (p < .0001), and this was attributed to a stronger hydrophobic effect between PS and water. The 20 size of this effect varied between different boars, perhaps as a consequence of variations in hydrophobicity of 21 sperm from different boars or different ejaculates. The modification of surface properties in this way may improve 22 our understanding of sperm behavior and may provide improvements to assisted conception techniques as animal 23 or human sperm used in assisted conception are frequently manipulated in laboratory plastics as part of diagnostic 24 procedures (e.g. semen analysis) or before injection into an oocyte or during the co-incubation with the oocyte in 25 IVF. Controlling the velocity of sperm using the interaction properties of inert polymer coatings could lead to new 26 sperm selection procedures for clinical use or the development of model systems to better understand sperm- 27 surface interactions. 28 29 30