The information on the frictional resistance of a self-propelled robotic capsule endoscope moving inside the body is very important for the design and the performance enhancement of such parameters of the capsule endoscope as power consumption, motion control and positioning accuracy. Based on this motivation, the ultimate goal of this research was to develop an analytical model that can predict the frictional resistance of the capsule endoscope moving inside the living body. In this work, experimental investigations of the fundamental frictional characteristics and the viscoelastic behaviors of the small intestine were performed by using custom-built testers and various capsule dummies. The small intestine of a pig was used for the experiments. Experimental results showed that the average frictional force was 10-50 mN and higher moving speed of the capsule dummy resulted in larger frictional resistance of the capsule. In addition, the friction coefficient did not change significantly with respect to the apparent area of contact between the capsule dummy and the intestine, and also the friction coefficients decreased with an increase in the normal load and varied from 0.08 to 0.2. Such frictional behaviors could be explained by the lubrication characteristics of the intestine surface and typical viscoelastic characteristics of the small intestine material. Also, based on the experimental results, a viscoelasticity model for the stress relaxation of the small intestine could be derived.KEY WORDS: biotribology, capsule endoscope, small intestine, stress relaxation, viscoelasticity Nomenclature F Friction force (N) l Friction coefficient N Normal force applied to the capsule (N) r(t) Stress applied to the small intestine (Pa, N/m 2 ) 0Strain applied to the small intestine t Time

Recently, the manipulation of a single cell has been receiving much attention in transgenesis, in-vitro fertilization, individual cell based diagnosis, and pharmaceutical applications. As these techniques require precise injection and manipulation of cells, issues related to penetration force arise. In this work the penetration force of living cell was studied using an atomic force microscope (AFM). L929, HeLa, 4T1, and TA3 HA II cells were used for the experiments. The results showed that the penetration force was in the range of 2~22 nN. It was also found that location of cell penetration and stiffness of the AFM cantilever affected the penetration force significantly. Furthermore, double penetration events could be detected, due to the multi-membrane layers of the cell. The findings of this work are expected to aid in the development of precision micro-medical instruments for cell manipulation and treatment.

The binding force between a liposome and the C2A domain of synaptotagmin I was determined by an atomic force microscopy (AFM). Liposomes were immobilized on the surface of the L1 sensor chip and the C2A domains, which recognize phosphatidylserine, were chemically conjugated onto a gold-coated cantilever tip. The average interaction force between the C2A domain and the liposome was 306 (+/-57) pN while the force between untreated cantilever and the liposome was 58 (+/-16) pN. This work helps understand the physicochemical interactions between proteins and lipid vesicles for the design of high affinity protein probes against the apoptotic cell surface.

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