Circular tubings are used extensively in biomedical implants and devices. It is desirable to determine contact angles on the inner or outer surfaces of such tubing in its final fabricated form. In this study, a technique for the measurement of contact angles on tubing surfaces in an aqueous environment is reported. This has particular applications to biomaterials research, where polymer tubings contact the biologic environment. In this technique, air or octane captive bubble dimensions can be measured, and an underwater contact angle calculated from these dimensions. The validity of the technique was experimentally confirmed using Solution Grade Biomer and NIH standard polyethylene surfaces.
Circular tubings are used in biomedical implants and devices. They are used in shunts, catheters, vascular prostheses, pacemaker wire insulation, needles, connecting tubing for dialysis, intravenous applications, fluid drainage, etc. In the development of new biomaterials for these and other applications, it is useful to measure contact angles on the tubing surface to obtain estimates of surface free energies. Most currently available contact angle measurement techniques are applicable to flat surfaces. When such measurements are made on surfaces that are not flat, it is necessary to maintain a sufficiently small drop or bubble size so that all effects of curvature can be neglected. While it is possible to make such measurements on even highly convoluted surfaces, the case of circular tubing provides an instance where the effect of curvature on drop or bubble dimensions may be calculated.
With such a technique, contact angle measurements can be made on the fabricated material. The method of fabrication of a device has been shown to affect its material surface properties.' A number of investigators may have incorrectly characterized a device fabricated in one way, such as by extrusion, by measuring surface properties on a sample fabricated by another technique such as compression molding or solvent casting on a flat surface. The development of a technique for the measurement of contact angles on the surface of a material in its final form overcomes this problem.
The measurement protocol described here is equally applicable to the determination of contact angles of drops in air and to the evaluation of bubbles using the underwater captive bubble technique first reported by