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Skin tribology with compliant materials for medical and healthcare applications

Final Activity Report Summary - TRIBIO (Skin tribology with compliant materials for medical and healthcare applications)

The objective of the TRIBIO project was to facilitate knowledge transfer between Szczecin University of Technology (SUT), Poland, now known as the West Pomeranian University of Technology, and Philips Applied Technologies (Apptech), The Netherlands. SUT, the Institute of Materials Science and Engineering and its associated research groups have an extensive capability regarding the modelling of mechanical behaviour and the characterisation and evaluation of high compliancy polymer and elastomer materials using advanced AFM and nanoindentation techniques and provided knowledge transfer in these areas. Apptech has more than 25 years experience in the field of tribology, including, in connection with electric shaving applications, experience related to human skin and in-vivo skin friction experiments and regarding medical and healthcare products in general. Within TRIBIO, Apptech provided knowledge transfer in tribology, particularly of human skin and tissue in medical and healthcare applications.

The associated research objectives of TRIBIO was to develop prediction methods and design methodologies for controlling the friction behaviour of human skin and tissue against products, particularly those containing high compliancy materials such as silicone rubbers. The intention was to provide enablers for design engineers involved in the development of advanced products with optimum functional performance and comfort. The specific goals of the research project were:
- Through a combination of experiment and application of theory, develop prediction methods (physical/analytical models) for the tribological behaviour of human skin and tissue in contact with product materials.
- Characterise the relevant specific product and biomaterials involved and validate the models experimentally.
- Develop "best practice" design methodology for skin friction control based on the above.

The project resulted in the development of several models that predict the elasto-hydrodynamic friction behaviour of skin and other tissue in contact with product surfaces and that describe the elastic behaviour of soft hydrogel materials during indentation testing. Different test set-ups and experimental protocols were developed to enable the friction behaviour against skin and other tissue to be investigated and to validate the models. The first enabled the simultaneous measurement of skin lateral and vertical deformation and skin friction during rubbing of a probe (simulating a product) over the skin surface. A second test set-up enabled measurement of the skin friction during rubbing of elastomer product surfaces over the skin. A third test set-up was developed to simulate as closely as possible the conditions during contact between an eyelid and the eye during blinking, and to measure the vertical (normal) and horizontal (friction) forces transmitted by the eyelid to the eye surface. In addition, the mechanical properties of hydrogels were investigated by indentation testing.

On the basis of experiments carried out using the experimental set-ups, practical design rules were developed that are relevant to the design of products that contact and rub against skin and other human tissue.

The TRIBIO project has resulted in several publications:
- M. Kwiatkowska, S.E. Franklin, C.P. Hendriks: "Simultaneous measurement of skin deformation and friction", Poster L-204 in Proceedings of Int.Symp. on Friction, Wear and Wear Protection, Aachen, Germany, 09-11 April 2008.
- M. Kwiatkowska, S.E. Franklin, C.P. Hendriks, K. Kwiatkowski: "Friction and deformation behaviour of human skin", Wear 267 (2009) 1264-1273.
- S.E. Franklin, P. Kochmanski: "Friction behaviour of textured silicone rubber against human skin", Proc. World Tribology Congress, Kyoto, Sept. 2009.
- C.P. Hendriks, S.E. Franklin: "Influence of surface roughness, material and climate conditions on the friction of human skin", Tribology Letters, DOI 10.1007/s11249-009-9530-7.