Manufacturing and characterization of friction, surface charge and stiffness of PVA hydrogels for cartilage replacement
The improvements in the healthcare in many countries lead to a higher life expectancy but also to ageing of the population. As an indirect consequence, there is a higher number of people suffering from orthopedic diseases that require joint replacements. The search for high quality implants initiated the research on cartilage replacement by hydrogels, which should assume the role of contact and friction in the joint implants. Here we show the contribution of tribology, surface charge, and nanoindentation for characterization of polyvinyl alcohol hydrogel and porcine articular joint cartilage.
When replacing knee or hip joints, the whole joint is replaced by an artificial implant. Choosing the right material is a challenge since two or more parts are in relative motion in the daily life and, hence, may experience different frictional behavior and even wear[1,2]. In order to recover the full functionality of the joint and to relieve the patient’s pain, the joint implants should fulfill the same function as the original body parts. This is only possible if the frictional properties of the joint implant are very similar to those of a healthy joint. Hence, understanding the frictional properties of joint implants is very important for development of new implant materials.
Hydrogels are considered as potential candidates for cartilage replacement because they are biocompatible and have mechanical properties similar to the joint cartilage. Promising hydrogels are hyaluronic acid, alginate or agarose as well as synthetic hydrogels based on Polyethylene glycol, Polyvinyl alcohol (PVA) or Polyacrylate. The frictional properties of soft hydrogels in combination with the lubrication fluid can be measured using a rheometer with a tribological cell. In this cell the upper specimen is pressed with a predefined normal force on the lower specimen whereas the lubrication fluid is immersed between them. The friction factor (µ, also known as coefficient of friction) is derived by rotating the upper specimen and measuring the rotational torque.
Such setup allows for characterization of cartilage replacement materials with lubrication fluids, comparing artificial with human joint cartilage, and to study the fundamentals of the lubrication mechanisms of cartilage.
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