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Development of an arthroscopic AFM

As illustrated in Fig. 3, for performing IT AFM within the knee joint the scan head of the AFM is inserted under arthroscopic control into the knee and stabilized by two sets of liquid-inflatable balloons (Fig. 3, inset), similar to those used for heart angioplasty. By filling the balloon with saline solution the head is stabilized against the surfaces within the knee joint. For recording the biomechanical properties (elastic modulus) of the cartilage sample a sharp nm-size tip or a micrometer-size spherical tip is mounted in a holder that is attached at the distal end of a piezoelectric actuator tube (piezo). Next, the coarse approach is achieved by changing the volume of opposite balloon pairs. For recording the force-displacement curves the AFM tip is driven by the piezo into and out of the cartilage surface. After each loading/unloading cycle the AFM tip then is moved to its next position. Because of limited space, the optical readout with a laser system is replaced by a piezo-resistive readout that measures the changes of voltage while deflecting the cantilever.



Fig. 3 Illustration of a prototype arthroscopic AFM. The instrument is inserted into the knee cavity under arthroscopic control.