| Speaker : |
Prof. Urs Staufer (Institute of Microtechnology-IMT-, University of Neuchatel) |
| Subject : |
Subject : Scanning Force Endoscope |
| Date : |
June 21, 2004 (Conference room 1, Institute of Industrial Science, Komaba campus) |
| Abstract : |
The cartilage in the knee joint is often affected in a knee injury. Depending on
the age of the patient and the severity of the damage, the knee is either replaced by
a prosthesis, or the surgeon tries to repair the cartilage by engineered tissue or by
transplantation. In these latter cases, it would be highly desirable to have a minimally
invasive instrument that allows post-operative monitoring of the affected area.
In a recent study, some of us found that the scanning force microscope (AFM)
is very sensitive in detecting degradation of cartilage, when used as indenter 1 .
Together with the imaging capabilities in the sub-micrometer range, this renders the
AFM and ideal candidate for such an minimally invasive tool. The aspired lateral
resolution of this new instrument, which we call scanning force endoscope (SFE) is
50 nm or better. Its prime application, however, is most likely not imaging but rather
the local measurement of the elasticity, a key bio-mechanical parameter of the
cartilage.
Traditional minimal invasive tools have a diameter of roughly 3 - 5 mm. The
SFE should, hence, fit in a comparable tube-like space. The key issue, however, is
the stabilization of the SFE inside the knee-cavity relative to the surface of the
cartilage. We have developed a pneumatic stage for that purpose. A set of balloons,
similar to those used in angioplasty, wedges the shaft of the instrument between the
bones, ligaments and the fat pad (Fig.1). The scanner is made of an ordinary,
segmented piezo-tube, and the cantilever deflection is measured by means of
integrated piezo-resistors. The tip can be either a regular, pyramidal AFM tip or a
special hemispheric tip, developed for indentation measurements.
The instrument is inserted under arthroscopic control. During that phase, the fragile tip needs a special mechanical protection, which will be removed once the instrument is positioned.
The stability of the pneumatic stage was checked in a series of tests, for which the knee cavity was replaced by a rubber tube. Forcedisplacement curves could be recorded, using a fully operational instrument but again operated in a special test stand. |
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