Using UV Laser Surface Treatment to Modify the Wettability Characteristics of Polyamide 6,6 and its Effects on Osteoblast Cell Activity

By: David G. Waugh and Jonathan Lawrence

Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, UK
Lincoln School of Engineering, University of Lincoln, UK

The need for biological implants grows year upon year and it has been realized that there is a drive within the biomedical industry for cheaper and easier to manufacture products. This could be met by the use of polymeric materials; however, it has been seen that polymeric materials can often fail clinically and be rejected by body due to the fact that the surface properties do not give rise to adequate cell growth. One way to counteract this is to treat the polymeric surfaces prior to the implantation such that they then have properties which enhance the cell response and ultimately reduce the failure/rejection rate. Many techniques have been developed for the surface treatment of polymeric materials; however, many only have the ability to modify one surface parameter at any one time and can have detrimental effects on the bulk properties. One promising and interesting method to carry out these surface treatments is that of the use of laser technology which can be applied to a number of different materials ranging from ceramics, to metals, to polymers. Lasers have the ability to change both the surface dimensions (roughness and surface pattern) and the surface chemistry simultaneously which can then lead to a change in the wettability characteristics. Wettability characteristics are those surface parameters which are directly linked to the wetting nature of materials; for instance, the contact angle is the angle the liquid droplet makes with the solid surface and the surface free energy is the energy associated with the solid surface giving rise to the contact angle observed. The wettability characteristics of a material have already been shown that they can be implemented to predict the adhesive nature of materials. As a result of this, many believe that wettability can be implemented as a tool to estimate the bioactive nature of materials. This would give a massive opportunity to the biological industry as it would allow those within the bio-implant field to have the ability to predict whether an implant will fail.

Cytotoxicity (cell death) is usually evaluated by the quantification of plasma membrane damage due to the fact that upon damage of the plasma membrane, lactate dehydrogenase (LDH) is rapidly released into the cell culture medium. As a result of this, LDH is the most common and widely used marker in cytotoxicity studies. In addition to this, Alkaline leukocyte phosphatase (ALP) activity is involved in bone formation and has been shown that ALP is significant in the development of skeletal calcification as it acts at the focal site of bone creation by eradicating inorganic pyrophosphate which is known to potentially inhibit calcification.

On account of lasers offering a convenient means of surface treatment this paper details unique experimentation into using UV lasers for patterning and whole area irradiative processing of nylon 6,6 and the effects this had on the wettability characteristics, cytotoxicity and ALP activity. What is more, the possible effect of wettability characteristics on osteoblast cell response is discussed in terms of resulting cytotoxicity and ALP levels.