**4. Increasing of bonding strength between probe DNA and polymer substrate for DNA chip with ion beam irradiation**

Mapping of all DNA sequence of human had finished by The International Human Genome Project in 2000. Thus difference of gene of each human can be measured. If distinctive sequence in DNA sequence of human having disease caused by gene can be found, observation of mechanism of such disease and development of new medicine moved ahead well. DNA chip is an apparatus to examine DNA, on which DNA is fixed. Existing DNA chip is "for research and development", and expensive. So, "for clinic", inexpensive, more reliable and sensitive DNA chip is needed as shown in Figure 12.

Therefore DNA chip made from a plastic was suggested [8]. For high reliability and sensitivity, affinity between DNA and plastic must be higher. But plastic is hydrophobic, affinity to DNA

is not well. Therefore, it is necessary to improve affinity between DNA and plastic by modi‐ fying surface of plastic hydrophilicity using surface modification. In this study, in order to achieve DNA chip made from a plastic, it is purpose to develop technology to improve adhesion force of DNA [4]. In particular, influence of ion species and ion dose on wettability and surface roughness of PC (polycarbonate) included TiO2 at ion irradiation is revealed. And in order to keep hydrophilicity after irradiation, influence of atmosphere in storage and irradiation times on keeping time of hydrophilicity is revealed. In addition, influence of ion irradiation on adhesion of DNA is revealed.

At first, PC included TiO2 was set in ECR ion irradiation apparatus, and it was exhausted to 5.0×10‐<sup>3</sup> ∼ 3.0×10‐<sup>4</sup> Pa in vacuum chamber. Then ionized gas in plasma source was accelerated, irradiated on the surface of specimen. In this study, Ar, N2 and O2 ions were irradiated on the surface of specimen controlling ion dose (cm‐<sup>2</sup> ).

Before ion irradiation, 0.25 l distillated water was dropped on the surface of specimen, contact angle α deg was measured by optical microscope. Contact angle was average value of 7 times measurement per a specimen. And the specimen after irradiation was stored in air or water, contact angle was measured every several hours.

0

0

30

60

Contact angle

is ion irradiation times.

, deg

90

120

0 3 6 9 12 15

0 480 960 1440 1920 2400

Time , hour

**Figure 14.** Relationship between contact angle and time under air after several times irradiation of O2 ion, '× Number'

cm -2 **Ar N2 O2**

Tribology for Biological and Medical Applications 231

Ion dose D , x1019

**O2 x 1 O2 x 2 Untreated**

Specimen : PC included TiO2

Acceleration voltage : 600 V Microwave power : 60W Liquid sample : Water Mean±SD,n=7

Ion species : N2

**Figure 13.** Relationship between ion dose and contact angle of water on the PC included TiO2.

Specimen : PC included TiO2 Ion species : Ar, N2, O2 Acceleration voltage : 600 V Microwave power : 60W Mean±SD,n=7

30

Contact angle

, deg

60

90

Then, in order to know influence of ion irradiation on wettability of the surface of plastic substrate, specimens were analyzed by SEM, AFM, and XPS.

In order to know influence of ion irradiation on adhesion force of DNA, it was measured by force curve measurement using AFM in water [9]. 0.05 M DNA solution (SSC buffered) was dropped on the substrate, and DNA was fixed by UV crosslinker after drying. DNA was 400 base length, of which molecular length was 290 nm. After fixing, the substrate held in water, AFM force curve measurement was conducted. AFM cantilever was made from silicon, of which constant of spring was 0.03 nN/m, and peak radius was about 10 nm. And contact force between cantilever and substrate was about 5 nN.

Figure 13 shows relationship between ion dose D and contact angle α of water on the PC included TiO2. the value of α was about 75 deg at untreated, and then rapidly decreased, finally became less than 8 deg at more than 4×1019 cm‐<sup>2</sup> .From analysis by AFM and XPS, it is seemed that increase of TiO2, which is hydrophilicity, on surface of specimen and increase of surface roughness lead to decrease of contact angle.

**Figure 12.** The proposed DNA chip made from plastic substrate

**Figure 13.** Relationship between ion dose and contact angle of water on the PC included TiO2.

is not well. Therefore, it is necessary to improve affinity between DNA and plastic by modi‐ fying surface of plastic hydrophilicity using surface modification. In this study, in order to achieve DNA chip made from a plastic, it is purpose to develop technology to improve adhesion force of DNA [4]. In particular, influence of ion species and ion dose on wettability and surface roughness of PC (polycarbonate) included TiO2 at ion irradiation is revealed. And in order to keep hydrophilicity after irradiation, influence of atmosphere in storage and irradiation times on keeping time of hydrophilicity is revealed. In addition, influence of ion

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

At first, PC included TiO2 was set in ECR ion irradiation apparatus, and it was exhausted to 5.0×10‐<sup>3</sup> ∼ 3.0×10‐<sup>4</sup> Pa in vacuum chamber. Then ionized gas in plasma source was accelerated, irradiated on the surface of specimen. In this study, Ar, N2 and O2 ions were irradiated on the

).

Before ion irradiation, 0.25 l distillated water was dropped on the surface of specimen, contact angle α deg was measured by optical microscope. Contact angle was average value of 7 times measurement per a specimen. And the specimen after irradiation was stored in air or water,

Then, in order to know influence of ion irradiation on wettability of the surface of plastic

In order to know influence of ion irradiation on adhesion force of DNA, it was measured by force curve measurement using AFM in water [9]. 0.05 M DNA solution (SSC buffered) was dropped on the substrate, and DNA was fixed by UV crosslinker after drying. DNA was 400 base length, of which molecular length was 290 nm. After fixing, the substrate held in water, AFM force curve measurement was conducted. AFM cantilever was made from silicon, of which constant of spring was 0.03 nN/m, and peak radius was about 10 nm. And contact force

Figure 13 shows relationship between ion dose D and contact angle α of water on the PC included TiO2. the value of α was about 75 deg at untreated, and then rapidly decreased, finally

that increase of TiO2, which is hydrophilicity, on surface of specimen and increase of surface

**DNA adhesionarea**

.From analysis by AFM and XPS, it is seemed

irradiation on adhesion of DNA is revealed.

Biomedical Engineering

230

surface of specimen controlling ion dose (cm‐<sup>2</sup>

contact angle was measured every several hours.

between cantilever and substrate was about 5 nN.

became less than 8 deg at more than 4×1019 cm‐<sup>2</sup>

**Figure 12.** The proposed DNA chip made from plastic substrate

roughness lead to decrease of contact angle.

substrate, specimens were analyzed by SEM, AFM, and XPS.

**Figure 14.** Relationship between contact angle and time under air after several times irradiation of O2 ion, '× Number' is ion irradiation times.

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 by repeated irradiation.

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

Tribology for Biological and Medical Applications 233

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

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

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

**photochemical fluorination**

lamp. This method has been already tried to PP [13].

the specimen.

free energy.

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

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 showed that contact angle decreased with increasing ion dose.

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

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

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