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Electron Beam and Ion-Plasma Treatment of Pain-Less Syringe Needle

A.G. Remnev, K. Uemura, K.V. Shalnov, V.R. Kukhta, R. Purwadi, and T. Ochi*

ITAC Ltd., Nagata Seiki Co., Kamisuwa 8-2, Tsubame, 959-0181, Japan Phone: (0256) 91-33-15, Fax: (0256) 98-57-78, E-mail: aleksey_remnev@itac-j.co.jp

*Terumo Corporation, 1727-1, Tsuijiarai, Syowa-cho, 409-3853, Japan

Abstract – The technology for medical needle de-burring and sharpening in mass-scale production was developed. The technology is based on the com-bined application of the high current microsecond electron beam irradiation and the ion sputtering in the low pressure glow discharge plasma with hol-low cathode. As a result of the electron beam irra-diation deburring and surface smoothening occur. Shape modification and sharpening of the needle occur after following ion plasma sputtering. The needle shape modification was examined with scan-ning electron microscope. The injection of the nee-dle into the human body was simulated by penetra-tion into the 55 um plastic film. For the certain types of the needle, the penetration force reduced from 0.4N down to 0.2N. The technology makes cur-rently used electropolishing and silicone oil treat-ment unnecessary.

1. Introduction

Even with the advancement of technology, problems of burr removal are still encountered by manufacturers and researchers. The proper control of burrs in manu-facture and the selection of suitable deburring tech-niques can reduce manufacturing costs.

Now days, in case of syringe needle following fin-ishing processes are used: sand blasting, electropoli- shing, honing, silicone coating. These processes are applied in purpose of the needle surface polishing, de-burring and tips and edges sharpening in mass-scale production. Silicone coating was prohibited on 1975, but, some specify medical silicone oil is still used now, that may create the plugging, allergy, etc.

For means of deburring and polishing high current microsecond electron beam irradiation(HCEB) proc-ess seems to be suitable, which was successfully ap-plied for polishing of die steel, titanium implants, etc. [1–3]. This process decreases surface roughness of needle and remove burrs.

The glowing discharge ion-plasma etching(GDPE) is widely used for the purpose of surface cleaning, activating and to some degree for deburring and edges sharpening [4].

The paper describes new combined process of

HCEB and GDPE dry finishing of medical syringe needle which can increase a penetrating ability of nee-dle and to replace the conventional wet processes. Following issues were demanded for the new process:

– needle’s shape modification; – tip and edges sharpening; – topography modification for the purpose of fric-

tion decrease; – homogenization of the structure and defects

elimination. In addition the method of evaluation of penetrating

ability of the needle was described. The method was applied for comparison of effectiveness of the stan-dard finishing processes (i.e., sandblasting, electro-polishing) with the developed HCEB + GDPE finish-ing process.

Fig. 1. Different types of processed needle: a – 18G/ Ø 1.25 mm; b – 19G/Ø 1.085 mm; c – 27G/Ø 0.34 mm; d – 33G/Ø 0.2 mm

The process was applied to several stainless steel Lancet needle types including the smallest 33G-type needle with the outer diameter of 200 µm. All samples were supplied by TERUMO Corp. (Fig 1).

2. HCEB

Presence of burrs on the edges of the needle and high roughness has negative influence on the penetrating ability of the needle.

Sometimes the GDPE can be used to eliminate

burrs, unfortunately in case of needle we couldn’t at-tain it without damaging the needle itself. For total burrs elimination and cleaning the HCEB process was used. Moreover HCEB provides surface polishing, homogenization and defects removal. This effect oc-curs due to ultrafast heating (109–1011 K/s) and coo- ling down and heavy gradient of temperature (106–108 K/cm).

HCEB treatment was carried out with Corrosion Resistance System® (Nagata Seiki) designed for die steel and Ti finishing treatment. Principle of operation is illustrated in Fig. 3.

The samples were installed in the experimental holder (Fig. 2) and were irradiated with the following

a

bcd

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parameters: N = 20 – pulse number; Uc = 26 kV – accelerating voltage; Um = 1 kV – magnetic coil vol- tage; L = 60–90 mm – distance from the gun to the needle tips; P – working pressure.

a

b

c

Fig. 2. Separated batch positioning of the samples (a), SEM of tip and edges before HCEB treatment (as manufactu- red) (b), tip and edges after HCEB treatment (c)

Fig. 3. Electron gun schematic

Using these parameters we could obtain successful deburring and surface smoothening (Figs. 2, b and c, Fig. 4). However because of heat concentration tips and the edges became rounded, which apparently will increase the penetrating resistance of a needle.

The experiments showed slightly inhomogeneous results, likely due to different orientation of the needle in the holder. Thus for the smallest 33G needle: Rtip = (5.5 ± 0.6) µm – radius of the rounded tip; Redge = (3.25 ± 0.65) µm – radius of the rounded edge.

For the bigger types of needle the deviation is much less.

Fig. 4. Surface profile investigated with laser microscope: a – before HCEB; b – after HCEB

3. GDPE

For the purpose of sharpening the previously rounded tips and edges of the needle, GDP etching of the HCEB treated needle has been carried out. The etching system is the triode system with cold hol-low cathode plasma generator, and negative (some cases sinusoidal) biased sample. The filtration of me-tallic plasma was used [5]. Similar method of sharpen-ing was used in work on field emitters sharpening [6] and named as field directed plasma sputtering.

Processed needle were exposed for anisotropic ion bombardment which under certain conditions led to the shape modification, polishing and sharpening. The schematic is shown in Fig. 5.

Fig. 5. GDPE experimental setup: 1 – holder with samples; 2 – chamber; 3 – bulk plasma; 4 – water cooled hollow cathode

The parameters were varied in the following ranges: PAr = 0.4–0.5 Pa, Udischarge = 10–90 A, Ubias = = –100 – 400 В, Tprocess = 1–6 h.

The needle were installed to the holder in the same batch manner as for HCEB (Fig. 2, a). One of the im-portant tuning parameter was the distance between neighboring needle, pitch – p (Fig. 2, a). The higher p is the larger the emissive surface of the plasma sheath corresponded to every single needle is. Consequently higher p leads to the higher ion current on the needle:

2 ,∝ij p (1)

where ji is the averaged current density for the one needle in the batch.

1 2 3

4

Bias voltagepower supply

Arc discharge power supply

Gas

I(t), A

V(t), kV t

a b

Arc triggerpower supply

Discharge power supply

High voltage power generator

Solenoid power supply

Triger unit

Control and synchronization unit

Electron beam Structure

Cathode plasma Cathode

Anode plasma Anode

Solenoid 3rd pulse

2nd pulse

1st pulse

Solenoid

Cathode

Electron gun Electron beam Workpiece

Vacuum operating chamber

Holder with samples

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The most complicated task was to determine an appropriate set of tuning parameters such as: discharge current Idischarge (i.e., power delivered to the plasma), Ubias and p.

All this parameters of the discharge strongly influ-ence the main determinative parameters of the needle etching process, which are: current density distribu-tion on the surface of every needle j(r), energy of bombarding ions W(r), and the angles of arrival of the ions at the different parts of needle θ(r), where r is the coordinate indicating a curtain position on the nee-dle’s surface. It was founded out that different parts of needle are etched in the different ways, for example on the tip we obtained topography which is different from those on the body of the needle. This phenomena occur due to r dependence of J, W, θ.

Also the actual relation between J, W, θ, and r de-pends on the plasma sheath shape from which the ions are emitted. The plasma sheath distance to the biased object d can be estimated by the following expressions

( )3/42 2 ,3

= λbias e dd U T (2)

( )( )1/220 ,λ = εd e ekT n e (3)

where λd is the Debye radius; Te is the electron tem-perature which is weakly dependent on the Idischarge; ne is the electron density which is strongly dependent on the Idischarge.

With matching appropriate tuning parameters sig-nificant shape modification, polishing and sharpening were achieved without any damage of the needle (Fig. 6).

Fig. 6. Initial sample (a), after EB (b), after EB + GDPE (c)

4. Measurement of penetration force

Suzuki et al. reported that the level of pain for pene-tration of needle in vivo correlates with the force re-quired to penetrate plastic film of certain thickness [7]. Penetration forces required for needle to penetrate 0.05 mm plastic film at 10 mm/min velocity were measured with HEIDON-14DR tribogear tester (Fig. 7). Real-time changes in penetrating force were measured

from initiation of penetration at the tip until some length of body of needle.

Fig. 7. Penetration resistance measurement setup: 1 – dyna- mometer; 2 – lever; 3 – plastic film; 4 – needle

Decrease of this force as the result of HCEB + + GDPE treatment was considered as the main condi-tion for pain removal.

The measurements were conducted for initial samples (no finishing), for needle that were finished with conventional electropolishing process (EP) and for needle finished with discussed process (HCEB + + GDPE). Typical results for 18G needle are pre-sented in Fig. 8.

Fig. 8. 18G needle penetrating force after different finishing process: a – initial; b – electropolished; c – HCEB + GDPE

On the penetration force graphs one can determine three peaks. Peak I is corresponded to the initial frac-ture of the film by the needle’s tip, peak II is corres- ponded to junction of two edges, peak III is corres- ponded to junction of the cutting edge and the body of

a

b

c a b

c

Distance

Pene

tratio

n re

sist

ance

, N

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needle, after this the force becomes constant on the area of the main tube (IV).

Also 33G samples were evaluated at TERUMO corp.

5. Conclusion

New combined method of EB and GDPE for medical needle finishing was developed and carried out for different types of needle. Treated samples were ob-served with SEM and Laser microscope. Their pene-tration resistances were measured.

Described process provides cleaning, significant positive shape modification, surface polishing, de-crease of surface defects, sharpening of edges and tips of the needle.

Dramatic decrease of penetrating force was ob-tained for the treated needle. Mentioned improvements let us to consider HCEB + GDPE treatment as alterna-tive for conventional deburring and finishing processes, such as electrical, chemical, mechanical, thermal fini- shing in mass-scale production. Described process can make silicone anti-frictional coating of needle unne- cessary.

References

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[2] D.I. Proskurovsky, V.P. Rotshtein, G.E. Ozur, Y.F. Ivanov, and A.B. Markov, Surface and Coa- ting Technology 125, 1, 49 (2000).

[3] J. Tokunaga, T. Kojima, S. Kinuta, K. Wakabaya- shi, T. Nakamura, H. Yatani, and T. Sohmura, Den-tal Materials J. 28, 5, 571 (2009).

[4] L.B. Begrambekov, Solid Surface Modification un-der Ion and Plasma Treatment, Moscow, Depart-ment of Education of Russian Federation, 2001, pp. 4–9.

[5] P.M. Shanin, N.N. Koval, Yu.Kh. Akhmadeev, and S.V. Grigoriev, J. Tech. Phys. 74, 5, 24 (2004).

[6] E.D. Lee, Master Degree Thesis, B.S., University of Illinois at Urbana-Champaign, 2007.

[7] Toshiyasu Suzuki, Akira Tanaka, Haruo Fukuya- ma, Junichi Nishiyama, Masahiro Kanazawa, Ma-satoshi Oda, and Miwa Takahashi, Tokai J. Exp. Clin. Med. 29, 4, 175 (2004).