**5. Reduction offriction between thermoplastic elastomers and plastics with photochemical fluorination**

In order to treat DNA chip substrate easily, it is necessary that hydrophilicity of substrate is keep for a long time in air. Figure 14 shows relationship between contact angle and time under air after several times irradiation of O2 ion. Hydrophilicity of substrate was kept for about 200 hours at 1 time irradiation of O2 ion, but for 1440 hours at 2 times irradiation. Ikada et al. reported that hydrophilic groups of surface of polymer modified by plasma turn around (hide under) as time passes, therefore hydrophilicity descend [10, 11]. In this study, similar phe‐ nomenon occurred, and it is seemed that hydrophilic groups became difficult to turn around

Micro-Nano Mechatronics — New Trends in Material, Measurement, Control, Manufacturing and Their Applications in

Figure 15 shows relationship between adhesion force of DNA probe to the surface of specimen and several times irradiation of ions. Adhesion force of DNA was about 0.09 nN at untreated, and then increased by repeated irradiation of N2 ion from about 0.13 nN at 1 time irradiation to about 0.62 nN, about 7 times as large as at untreated, at 4 times irradiation. In contrast, adhesion force did not increase at irradiation of O2 ion. From analysis by XPS, it is seemed that electrostatic bond between amino group on surface of specimen formed by ion irradiation and

In conclusion, in order to development of DNA chip made from plastic, ion beam was irradiated to PC include TiO2 and contact angle of specimen was measured. The results clearly

Hydrophilicity of surface of specimen formed by ion irradiation could be kept for a long time

In order to know influence of ion irradiation on adhesion force of DNA, it was measured by force curve measurement using AFM in water. Adhesion force of DNA increased by repeated

Specimens

Untreated N2 × 1 N2 × 2 N2 × 3 N2 × 4 O2 × 1 O2 × 2

**Figure 15.** Relationship between adhesion force of DNA probe to the surface of specimen and several times irradia‐

phosphoric acid in DNA lead to increase of adhesion force of DNA.

showed that contact angle decreased with increasing ion dose.

ion irradiation of N2, but did not by ion irradiation of O2 ion.

Specimen: PC induced TiO2 Ion species: N2, O2 Acceleration voltage: 600 eV Microwave power: 60 W Number of irradiation: 1~4 times Mean±SD, n=5‐7 DNA solution: 0.05 M

Adhesion force of substrate Adhesion force of DNA

by repeated irradiation.

Biomedical Engineering

232

by repeated irradiation.

0

tion of ions.

1

2

Adhesion force, nN

3

In medical field, plastic and glass syringes are widely used to insert medicines into human bodies directly. From a hygiene standpoint, they are disposed after single use. Generally, glass syringes are inferior in the accuracy of dimension and the produce cost and they also require great care at the time of disposal. Thus, replacing glass syringes with plastic ones is desired. Plastic syringes are generally used with silicone oil lubricating the sliding area between barrels and gaskets, where the barrels are typically made of plastics such as PP (Polypropylene) and the gaskets are usually made of either vulcanized rubber or TPE (Thermoplastic elastomer) as shown in Figure 16. Silicone oil is biologically and chemically inert but considered to have some demerits: possibility of accumulation in human bodies and decrease of efficacy because of adsorption of medicine's constituent [12]. These demerits are especially pronounced in prefilled‐type syringes. Therefore, the development of unlubricated plastic syringes is desired for medical use.In this study, in orderto decrease the friction force between barrels and gaskets under unlubricated condition, we tried to fluorinate the surfaces of PP and TPE specimens by using PFPE (Perfluoropolyether) and VUV (vacuum ultraviolet) irradiation with excimer lamp. This method has been already tried to PP [13].

First, we dropped PFPE on a specimen and put a fused silica glass on it to make thin and flat PFPE layer. Then we irradiated them with VUV to make specimen's surfaces react photo‐ chemically with PFPE as shown in Figure 17. After the irradiation, we cleaned the specimen with HFE (Hydrofluoroether) by using ultrasonic cleaner to remove residual PFPE. The effect of the photochemical treatment was evaluated by friction test, measurement of surface free energies, and FTIR (Fourier transform infrared) analysis where ATR (Attenuated total reflection) method was adopted. In the friction measurements, treated PP was slid against non‐ treated TPE. And treated TPE was slid against non‐treated PP. Surface free energies of a specimen were calculated from the measured contact angles of water and CH2I2 droplets on the specimen.

In the experimental results, it was confirmed that the friction coefficient between treated TPE and non‐treated PP was decreased by up to 77% as shown in Figure 18. Moreover, C‐F peak, which indicates fluorination of surfaces of specimens, was detected in FTIR spectra. And surface free energies of them decreased. It is suggested that the surfaces of both PP and TPE were fluorinated and fluorination of TPE was predominantly effective for decreasing the friction coefficient between PP and TPE. We expected that the photochemical fluorination changed only chemical property. Thus,to validate possibility of other changes, we investigated the change in real contact areas between fluorinated TPE specimens and a glass plate (BK7) with contact microscope. Contrary to our expectation, decreases in real contact area of fluorinated TPE were observed with decreasing friction coefficient, indicating the change in surface mechanical properties of the fluorinated TPE specimens. Accordingly, it is indicated that the decreasing of friction coefficient between fluorinated TPE and non‐treated PP is attributed to decreasing of real contact area and adhesion arisen from the reduction of surface free energy.

**6. Reduction of adhesion of CIIR rubber to steel plate with plasma**

Adhesion, or the sticking of different materials at their interface, is of general interest in many branches of technology, including micro‐electronic devices, medical products and manufac‐ turing. Adhesion between rubbers and metals is often the main source of trouble in a machine. Thus, if molded rubber products easily stick to molds, rollers, and pick‐up hands made of metals, the productivity of their manufacturing line becomes low. Therefore, efficient utiliza‐ tion ofrubber sheets demands modifications on some desirable properties ofthe rubber surface without affecting the bulk characteristics. Plasma treatment is one of the most employed methods to attain this goal. One of the most significant benefits of the plasma process is it offers and additional advantage that the surface modification does not affect the desirable bulk

Tribology for Biological and Medical Applications 235

In a previous study, we have demonstrated that the surface wave‐excited plasma treatment reduced the adhesion force between a medical rubber, chloride‐isobutene‐isoprene rubber

We have also shown a decrease in the real contact area with increasing time and micro wave power, and a similar trend in the residual rates of the adhesion force and the real contact area of CIIR rubber. Therefore, it is assumed that the adhesion force is strongly subjected to the real contact area [14]. However, the main reason for the reductions in the real contact area remains unknown.Recent works have shown that plasma treatmentincreases the roughening ofrubber surfaces [15]. The surface roughness may affect the adhesion force, which is largely dependent

The objective of this research, we report on our attempts to clarify the factor to reduce the adhesion force during the surface wave excited plasma treatment process. It is also attempted to figure out the Young's modulus behavior in micro scale to measure without bulk property by using micro slicer and surface roughness changes are measured by 3D laser scanning

Results of adhesion forces between CIIR rubber and stainless‐steel ball as a function of plasma treatmenttime at 200Ware shown in Figure 19.Itis apparentfrom the figures thatthe adhesion force dramatically decreased with oxygen plasma treatment according to treatment time. Similar decreasing trend was also observed with argon plasma treatment. However, at 1 min treatment time, the adhesion force was higher with argon treatment than oxygen plasma treatment of CIIR rubber. After 1 min, argon plasma treatment was more effective than oxygen plasma treatment in decreasing the adhesion force. The adhesion force couldn't be measured after 10 min because it was lowerthan the measurable value of 0.001 N.In summary,the figures showed that plasma treatmenttime is a very importantfactorthat decreases the adhesion force. Load‐penetration depth curves by using the nano‐indenter with 50 μN maximum loads were obtained. The thickness of the prepared CIIR rubber was about 3 mm for the general thickness and about 50 μm for the cutting thickness by using the microwave slicer. Despite the same conditions, the penetration depth obtained from the 3mm thickness CIIR rubber was clearly

(CIIR) and stainless‐steel ball (SUS440C) by using oxygen and argon gases.

on the contact geometry and surface topography [16].

**irradiation**

properties of the rubber.

microscope.

**Figure 16.** Schematic view of plastic syringe

**Figure 17.** Schematic of photochemical treating process with UV and PFPE.in vacuum

**Figure 18.** Relation between irradiation time to TPE and friction coefficient.
