surrace Analyses of Medical Lens

Implants By X-Ray Photoeiectron

Spectroscopy

3

NBS1R 80-2156 (FDA)

TerrenceJ- Jach

Surface Science Division

Center for Thermodynamics

Molecular Science

National Bureau of Standards

U.S. Department of Commer co Washington, DC 20234

September 1980

edical Devices Laboratory’

Food and Drug Administration

Silver Spring. MC 2091

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Surface Analyses of Medical Lens

Implants by X-Ray Photoelectron Spectroscopy

Terrence Jach

Surface Science Division

National Bureau of Standards

CONTENTS

M

INTRODUCTION 1

METHOD 1

RESULTS . 3

SUMMARY 4

REFERENCES 5

Appendix A: Summary of Lenses Tested 6

Appendix B: Relative Intensities of XPS Peak 7

Amplitudes for Carbon and Oxygen

Notes for All Figures 8

INTRODUCTION

A number of manufacturers presently offer plastic lenses as surgical implants

to replace human eye lenses which are damaged or imperfect. The compatabi 1 i ty

and safety of these lenses with human tissue is dependent, in part, on their

surface composition. It is therefore desirable to examine these lenses by a

method which is sensitive to elements in the outermost few atomic layers of the

surface. It is possible that due to contamination or a manufacturing procedure,

a lens which shows low levels of a toxic element in bulk analysis may have

a high concentration of that element a few atoms thick at the surface.

We have examined, using the surface-sensitive technique of X-Ray Photoemission

Spectroscopy (XPS), individual samples of thirteen different lenses supplied by

manufacturers to the Federal Drug Administration. The purpose of the study was

to look for elements which were not ordinarily expected to be present in the

polymer. The surface of each lens was analyzed twice: first, as it came from

the package, and second, after removing the outermost layer of surface material

by a brief period of ion sputtering. To within the limits of elemental

detectability which will be outlined below, only two samples showed any elements

other than carbon and oxygen.

METHOD

The lenses supplied by the FDA consisted of one each of thirteen different

types produced by eight different manufacturers. A list of the lenses is included

as Appendix A. It was assumed that each lens was precleaned by the manufacturer

to whatever extent was considered adequate before sterilization. Each lens was

removed from its sterile package using cleaned forceps and mounted directly on a

sample carousel in the XPS chamber.

1

The chamber was pumped down to an ultimate pressure of 10-9 torr ( 1 0“ 7 Pa)

before measurement.

Using a Physical Electronics 1 04-151 X-Ray Tube with Mg anode and a model

15-255 Analyzer, photoemission spectra were taken over a binding energy range

of 0-1000 eV. The photoelectron pulses were integrated for 1 sec and the

spectrum advanced at 1 ev/s. Minimum elemental concentrations of 3 % (atomic)

were visible. Due to the low photocurrents involved, charging effects on the

highly-insulating lenses were negligible.

Two XPS spectra were taken of each sample lens. The first was made of each

lens without any surface treatment. The second spectrum was taken after 5

minutes of sputtering the lens with an argon-ion beam from a Physical

Electronics 1 04-161 Sputter Ion Gun.

The ion beam removed the surface constituents of the sample by bombardment.

Although the sputter rate is highly dependent on the nature of the sample, a

O rough estimate of the sputter rate was 10 A/minute (lnm/min). It was assumed

O that removal of 50 A (5nm) of surface was adequate to get beneath water and

organic matter which may have covered the surface after manufacturing. The

depth of the surface layer removed was small enough to insure that any residual

surface contamination from molding dies or the chemical process of lens

manufacture should still be visible.

The spectra of the lenses were calibrated with respect to nickel and

gold targets on the carousel which extablished peak positions to within 0.5eV.

The circular area viewed by the analyzer varied between 1 and 3mm in diameter.

The area sampled was large enough compared to the lens diameter that some

slight features in the background of lens spectra may have been due to elements

on the sample carousel at the periphery of the sampled area. Where this was

a question, repeat spectra were taken with the sample slightly displaced. Only

u those elements which showed up consistently in the repeat spectra are cited

here.

2

Positive identification of each element was made only after direct

correlation of more than one spectral line with lines for that element in

2

published spectra.

RESULTS

In the first set of lens measurements (samples unsputtered) the spectra

all showed large peaks due to carbon and oxygen, as might be expected of

hydrocarbon samples. The ratio of carbon to oxygen signals for each lens is

tabulated in Appendix B. In addition, sample No. 9 (the Intermedics lens)

showed a small trace of chlorine before sputtering.

After 5 minutes of sputtering, the ratio of carbon to oxygen changed.

Generally the oxygen peak decreased to about 30% of its pre-sputtered value, and

the carbon peak increased by about 50%. The ratios of carbon to oxygen signals

for each lens is tabulated in Appendix B. Sample No. 12(Iolab lens) showed

a slight trace of nitrogen on the surface after sputtering.

These net changes indicate that the oxygen present on the original surface

was probably a contamination (e.g., H^O) or oxidation of the plastic.

3

Summary

We have X-Ray Photoemission Spectra on the surfaces of 13 different implantable

plastic eye lenses to study elemental constituents which occur on the surfaces

as a result of manufacturing or handling. The spectra were taken on the surfaces

as removed from their packaging and then again after sputtering to remove about

O 50 A (5nm) of surface material. All lenses showed strong carbon and oxygen

peaks both before and after sputtering, which would be considered normal for a

plastic surface.

No foreign elements were detected with concentrations greater than 3 % before

sputtering except for one lens which showed detectable amounts of chlorine. This

peak disappeared after sputtering. On one lens a detectable amount of nitrogen

appeared after sputtering.

4

References

:

1. Commercial equipment is identified to specify the measurement conditions

and is not intended as an endorsement of this manufacturer by the

National Bureau of Standards.

2. C. D. Wagner, W. M. Riggs, L. E. Davis, J. F. Moulder, and G. E. Muilenberg,

Handbook of X-Ray Photoelectron Spectroscopy ( Perki n-Elmer , Physical

Electronics Div., Eden Prairie, Minn., 1979)

5

Appendix A: Summary of Lenses Tested

Sample No. (Also Figure No.) FDA Assigned No.

1. Precision-Cosmet Co. Inc. 80-59

(Kelmann II) KL-5722-X-B Lot 922

2. Precision-Cosmet Co. Inc. 80-60

(Azar II) AR-21 56-X-A Lot 867

3. Precision-Cosmet Co. Inc. 80-61

(Tennant) AC-43298-X-A

4. Coburn Optical, Professional Products Div. 80-65

MK VIII (Choyce) Control No. 171905

5. Coburn Optical, Professional Products Div. 80-64

MK IX (Choyce) Control No. 216101

6. Heyer Schulte Medical Optics Ctr. 80-56

Model AC-10 Cat. No. 013-1160-115 Lens No. 10791991

7. Heyer Schulte Medical Optics Ctr. 80-62

Model AC-20 Cat. No. 013-2175-120 Lens No. 11791173

8. California Intraocular Lens Co. 80-63

Cilco AC4 Serial 504295 Lot A1492

9. Intermedics Intraocular Inc. 80-53

Model 018 Serial No. 08472

10. Surgidev Corp. 80-54

In-Troc Style 10 Cat. No. S7 610195 Ser. No. 103481

11. McGhan Medical Corp. 80-55

Implens 60 Cat. No. 65-66205 Serial No. SOI -073583

12. Iolab Corp. 80-57

Model 91 Control No. 062879 91 -U 687

13. Iolab Corp. 80-58

Model 91 Control No. 081479 91-50 260

6

1

2

3

4

5

6

7

8

9

10

11

12

13

Ratios of XPS peak Amplitudes,

q ( 15

)

FDA No. Before sputtering After sputtering

80-59 1.1 2.2

80-60 0.90 1.8

80-61 0.86 2.1

80-65 0.90 3.8

80-64 0.82 3.1

80-56 0.80 2.5

80-62 0.81 4.8

80-63 0.96 3.1

80-53 0.79 3.9

80-54 1.1 4.4

80-55 0.81 5.3

80-57 0.82 5.0

80-58 0.90 4.1

7

Note for all Figures

The following elemental lines appear in each x-ray photoelectron spectrum

and are not individually labelled:

Element (line)

C (Is)

0 (Is)

0 (KVV Auger)

C (KLL Auger)

Energy Position (on Binding Energy Scale.)

283 eV

531 eV

745, 767 eV

990 eV

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NBS-114A (REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR-30- 2156

2. Gov't. Accession No. 3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Surface Analyses of Medical Lens Implants by

X-Ray Photoelectron Spectroscopy

5. Publication Date October 1980

6. Performing Organization Code

7. AUTHOR(S)

Terrence Jach

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project/Task/Work Unit No. 541-1457

11. Contract/Grant No. Task 80-07, NBS-BMD

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Sireei, City, state, ZIP)

Mechanics and Materials Branch

Medical Devices Laboratory

Food and Drug Administration

Silver Spring, MD 28110

^y tr f tL y~"nyT irLnjcnL

13. Type oT Report & reriod Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or less factual summary of most s i ghi ficant information. If document includes a s i gni ficant bibliography or

literature survey, mention it here.) Thirteen types of intraocular lens manufactured for human implantation were

examined by X-Ray Photoemission Spectroscopy (XPS). The elements present on the surface of each lens were detected before and after cleaning by ion

bombardment. All lenses showed strong surface coverage of the elements carbon and

oxygen . Trace amounts of chlorine on one lens and nitrogen on another lens were

observed

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Intraocular lenses; surface analysis; X-ray photoelectron

spectroscopy.

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