Biomaterials 21 (2000) 1197}1205 Arti"cial tear adsorption on soft contact lenses: methods to test surfactant e$cacy V. Rebeix, F. Sommer *, B. Marchin, D. Baude, Tran Minh Duc Universite & Claude Bernard, 43 Bd. du 11 novembre 1918, F-69622 Villeurbanne Cedex, France Biophy Research, Village d+Entreprises de St Henri, 6 rue Anne Gacon, F-13016 Marseille, France Essilor, 39 Bd. J.B. Oudry, F-94000 Cre & teil, France Received 30 June 1998; accepted 1 October 1999 Abstract Spoilage is a primary factor in the biocompatibility of soft contact lenses (SCL) within the lacrimal #uid. Tears are a complex mixture of proteins, lipids, natural surfactants and salts. The spoilation process is due to a contribution of all these components and of the nature of SCL materials themselves. The aim of this study was to set up methods to observe and quantify lacrimal deposits and to select e$cient surfactants for preventing protein deposits. The present study was performed on PMMA-NVP SCL. The behaviour of SCL in presence of tears was studied by means of an in vitro arti"cial tear model consisting of the main tears components and quanti"ed by a colorimetric technique (BCA) performed directly on the lenses. The nature of the deposit was observed directly by atomic force microscopy (AFM) in a liquid medium showing the same adsorption trend noticed in the quantitative results and identifying speci"c adsorption sites. The assessment of surfactant adsorption was performed using Maron's method, as a mean to evaluate the a$nity of surfactant to the surface, while the action of selected surfactants on pre-treated SCL was assessed using the BCA method. Promising results were obtained with these two di!erent methods which can be used easily for the pre-selection of surfactants for further cleaning solution formulation studies.  2000 Published by Elsevier Science Ltd. All rights reserved. Keywords: Contact lens; Spoilation; Quanti"cation; AFM; Surfactant 1. Introduction Materials are now extensively used for implants and prostheses within the body and along with progress made in surgery have led to a marked improvement in the quality of life in many patients. Convenience for the patient of these implants, during their lifetime within the body, is of great importance and represents the major research interest in this "eld. In fact the contact of these materials with biological membranes and #uids is always followed by the adsorption of biological molecules (pro- teins, lipids) and cells which can form a bio"lm on the surface of these materials, as the implant is recognised by the immune system as a foreign body [1}3]. Formation of the bio"lm is considered to be mandatory for good implantation of most of these devices and acceptance by the body, but it can also become a source of infection, which may lead to rejection of the implant. * Corresponding author. The spoilation behaviour is similar for the SCL within the tear "lm of eye, and the bio"lm formed can stop the wearer from using SCL as a means of visual correction. However, the implications for the patient's health is less dramatic than that occurring with other prosthestetic devices since SCLs are easily removed from the eye, but can damage the eye and provoke conjunctivitis [4]. Improvement of materials used for SCL is the main focus of research in the SCL "eld, even if a palliative solution can be found by using disposable SCL to avoid the complications associated with long time wearing. The necessity to work with biocompatible materials, which are well tolerated within the body and exhibit a relatively low degree of biological adsorption requires us to investi- gate the development of new combinations of polymers and modi"cation of surfaces. This last point is a parti- cularly important aspect of research as a means of improving materials by the modi"cation of surface prop- erties. Among the possibilities available, one issue is the action of surfactants through pre-treatment of SCL with- in cleaning solutions before insertion of SCL into the eye 0142-9612/00/$ - see front matter  2000 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 6 1 2 ( 9 9 ) 0 0 2 2 1 - 5