Bruce Banks, Sharon Miller, and Kim de Groh

Glenn Research Center, Cleveland, Ohio

Amy Chan

Ohio Aerospace Institute, Brook Park, Ohio

Mandeep Sahota

Cleveland State University, Cleveland, Ohio

The Development of Surface Roughness

and Implications for Cellular Attachment

in Biomedical Applications

NASA/TM—2001-211288

November 2001
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NASA/TM—2001-211288

November 2001

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

2001 Fall Meeting

sponsored by the Materials Research Society

Boston, Massachusetts, November 26–30, 2001

Bruce Banks, Sharon Miller, and Kim de Groh

Glenn Research Center, Cleveland, Ohio

Amy Chan

Ohio Aerospace Institute, Brook Park, Ohio

Mandeep Sahota

Cleveland State University, Cleveland, Ohio

The Development of Surface Roughness

and Implications for Cellular Attachment

in Biomedical Applications
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NASA/TM—2001-211288 1 

The Development of Surface Roughness and 

Implications for Cellular Attachment in Biomedical Applications 

Bruce Banks, Sharon Miller, and Kim de Groh 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Amy Chan 

Ohio Aerospace Institute 

Brook Park, Ohio 44142 

Mandeep Sahota 

Cleveland State University 

Cleveland, Ohio 44115 

ABSTRACT 

The application of a microscopic surface texture produced by ion beam sputter texturing 

to the surfaces of polymer implants has been shown to result in significant increases in cellular 

attachment compared to smooth surface implants in animal studies. A collaborative program 

between NASA Glenn Research Center and the Cleveland Clinic Foundation has been 

established to evaluate the potential for improving osteoblast attachment to surfaces that have 

been microscopically roughened by atomic oxygen texturing. The range of surface textures that 

are feasible depends upon both the texturing process and the duration of treatment. To determine 

whether surface texture saturates or continues to increase with treatment duration, an effort was 

conducted to examine the development of surface textures produced by various physical and 

chemical erosion processes. Both experimental tests and computational modeling were 

performed to explore the growth of surface texture with treatment time. Surface texturing by 

means of abrasive grit blasting of glass, stainless steel and polymethylmethacrylate surfaces was 

examined to measure the growth in roughness with grit blasting duration by surface profilometry 

measurements. Laboratory tests and computational modeling was also conducted to examine 

the development of texture on Aclar (chlorotrifluoroethylene) and Kapton polyimide, 

respectively. For the atomic oxygen texturing tests of Aclar, atomic force microscopy was 

used to measure the development of texture with atomic oxygen fluence. The results of all the 

testing and computational modeling support the premise that development of surface roughness 

obeys Poisson statistics. The results indicate that surface roughness does not saturate but 

increases as the square root of the treatment time. 

INTRODUCTION 

 The degree of cellular attachment to polymer surfaces has been shown to significantly 

increase by providing a textured surface as opposed to a smooth surface for peritoneal implants 

in rats [1-2]. Such tests were performed by comparing argon ion beam sputter textured and 

sputter polished polytetrafluoroethylene (PTFE Teflon) implant surfaces. The surface 

texturing produced submicron to multimicron sized cones on what would otherwise be rather 
NASA/TM—2001-211288 2 

smooth surfaces. The number of cells attached per 4x104 cm2 was only ~12 for ion sputter 

polished PTFE, but was 270 for ion beam sputter textured PTFE after 2 days of implantation 

[1-2]. The principal cells attached were macrophages, lymphocytes and to a lesser degree mast 

cells. 

 Atomic oxygen has been shown to produce surface textures in almost all hydrocarbon or 

halocarbon polymers. The resulting textures are quite similar to sputter textured surfaces, 

but much easier to produce. Figures 1 and 2 compare the surface texture of ion beam sputter 

textured PTFE Teflon [3-4] with atomic oxygen textured chlorotrifluoroethylene [5]. 

a. b. 

Figure 1. Comparison of the surface texture of fluoropolymers produced through ion beam 

sputtering and atomic oxygen texturing, a). argon ion beam sputter textured PTFE Teflon, and 

b). low Earth orbital atomic oxygen textured chlorotrifluoroethylene retrieved from the Long 

Duration Exposure Facility. 

 Both directed atomic oxygen beams and isotropic atomic oxygen produces textured surfaces 

in hydrocarbon as well as halocarbon polymers. However, the aspect ratio of the texture is 

greater for the directed atomic oxygen exposures. Because the degree of surface texture appears 

to play such an important role in cellular attachment, it is desirable to explore the range of 

surface roughness that may be possible for various materials and texturing processes. For some 

roughening processes such as abrasive sanding using sandpaper, one would expect that the 

surface roughness would increase to a limiting value because the height of the peaks and the 

depth of the valleys are somewhat dependent on each other and the grit size of the sandpaper. 

However, random microscopic erosive processes where height of the peaks and the depth of the 

valleys are independent of each other should allow surface texture to gradually increase with 

surface treatment. One might expect that such surface texturing processes include abrasive grit 

blasting, atomic oxygen texturing and ion beam sputter texturing. If the development of surface 

roughness occurs by spatially independent erosion processes, then the growth of the roughness 

should obey Poisson statistics. In such surface treatment processes it is postulated that surface 

roughness increases as the square root of the treatment time. Monte Carlo computational 

modeling of atomic oxygen exposed Kapton polyimide has shown that surface roughness 

should increase at a less than proportional rate with atomic oxygen fluence for directed atomic 

oxygen exposure [6]. 

 

10 micron 10 micron 
NASA/TM—2001-211288 3 

 The objective of this investigation was to explore the growth of surface roughness with 

treatment duration for various surface-roughening techniques and for various substrates. The 

premise is that spatially independent erosion processes obey Poisson statistics and thus RootMean-Squared (RMS) roughness should increase proportionally to the square root of the 

treatment duration. The resulting knowledge may allow one to know if there is a limit to the 

surface roughness that is possible for various roughening techniques and on various types of 

materials such as polymers, metals and glass. The information will also be useful for an existing 

collaborative research program between NASA Glenn Research Center and the Cleveland Clinic 

Foundation concerning the adhesion and spreading of osteosarcoma cells on textured Aclar

chlorotrifluoroethylene. 

APPARATUS AND PROCEDURE 

 Surface texturing was performed by two different processes: abrasive grit blasting and 

isotropic atomic oxygen attack in an RF plasma asher. Materials that were textured by abrasive 

grit blasting included glass microscope slides, 300 series stainless steel and 

polymethylmethacrylate. Isotropic atomic oxygen was used to surface texture Aclar

clorotrifluoroethylene. 

Abrasive grit blasting

 

 Aluminum oxide abrasive grit was used in a conventional abrasive grit-blasting system to 

explore RMS roughness growth with grit blasting time. The diameters of these particles ranged 

from 157 to 3150 μm with an average maximum diameter of 795μm. The three materials that 

were textured were placed in an abrasive grit blasting system in which the nozzle was placed in a 

rigid structure such that it was located 38.1 cm from the sample surfaces with the abrasive grit 

flowing in a horizontal direction. The test sample surfaces were perpendicular to the grit flow 

direction and exposed to various durations of abrasive grit blasting with the samples being taped 

to a holder using vinyl electrical tape to prevent the samples from being blown away or moving 

as a result of the air flow. The grit blasting gun air pressure was set at 2.07 x 105

 Pa (30 psi) 

for the glass slides, at 3.45 x 105 Pa (50 psi) for the stainless steel samples, and at 2.76 x 105 Pa 

(40 psi) for the polymethylmethacrylate samples. The microscope slides were 1 mm thick x 

2.54 cm wide x 7.5 cm long. The 300 series stainless steel samples were 3 mm thick x 3.2 cm 

wide x 7.5 cm long. Lastly, the size of the polymethylmethacrylate samples was 4.8 mm thick x 

3.2 cm wide x 8.3 cm long. 

Isotropic atomic oxygen exposure in an RF plasma asher

 

 A 100-watt SPI Plasma Prep II RF (13.56 MHz) plasma asher operated on air at 16.6 Pa 

(125 millitorr), the typical operating pressure, was used to atomic oxygen texture 2.54 cm 

(1 inch) diameter x 0.127 cm (0.005 inch) thick Acylar clorotrifluoroethylene samples. 

Atomic oxygen fluence measurements were made using 0.127 mm thick polyimide Kapton H 

fluence witness samples. The samples were vacuum dehydrated to accurately determine 

mass loss as a function of time for various texturing durations. The asher was operated at a 

fixed condition such that the Kapton effective flux for all the exposures was 7.21 x 1015

atoms/(cm2s). The atomic oxygen fluence for each exposure was measured using ASTM E 

2089-00 Standard Practices. 
NASA/TM—2001-211288 4 

Surface roughness characterization

 The RMS surface roughness of samples exposed to grit blasting was measured using a 

Dektak IIA profilometer using a scan length of 1 mm. Samples exposed to isotropic atomic 

oxygen in the RF plasma asher were characterized for surface roughness using a Park Scientific 

Auto Probe LS atomic force microscope (AFM) operated in the contact mode. The AFM was 

used for characterizing the surface roughness of clorotrifluoroethylene to prevent surface damage 

from occurring in this low elastic modulus material. Tests were also conducted to identify a scan 

length for the profilometer, as well as the AFM, that produced RMS values that were 

characteristic of the true surface roughness as opposed to the pristine surface waviness. 

RESULTS AND DISCUSSION 

 The RMS roughness for the grit blast textured surfaces was found to be dependent upon the 

scan length used during profilometry for scan lengths greater than 100 μm. This was thought 

to be caused by the gradual waviness of the surface as opposed to true microscopic roughness. 

Thus a scan length of 100 μm was used for RMS roughness characterization of these surfaces. 

Figures 2, 3, and 4 show the resulting RMS roughness obtained for grit blasting of glass 

microscope slides, 300 series stainless steel and polymethylmethacrylate, respectively. 

0

10000

20000

30000

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42

Time (s)

RMS rougness 

(Angstroms)

Experimental Data

Theoretical Data

Figure 2. RMS roughness of grit blasted glass microscope slide surfaces as a function of grit 

blasting duration and Poisson theory fit to data. 
NASA/TM—2001-211288 5 

0

5000

10000

15000

0 5 10 15 20 25 30 35 40

Time (s)

RMS roughness 

(Angstroms)

Experimental Data

Theoretical Data

Figure 3. RMS roughness of grit blasted stainless steel as a function grit blasting duration and 

Poisson theory fit to data. 

0

5000

10000

15000

0 5 10 15 20 25 30 35 40

Time (s)

RMS roughness 

(Angstroms)

Experimental Data

Theoretical Data

Figure 4. RMS roughness of grit blasted polymethylmethacrylate as a function grit blasting 

duration and Poisson theory fit to data. 
NASA/TM—2001-211288 6 

Figure 5 shows the resulting RMS roughness obtained for isotropic atomic oxygen exposure 

of Aclar chlorotrifluoroethylene. 

0

100

200

300

400

500

600

700

0 2E+20 4E+20 6E+20 8E+20 1E+21

Atomic Oxygen Fluence (atoms/cm2)

RMS Roughness (nm)

Experimental Data

Theoretical Data

Figure 5. RMS roughness of Aclar chlorotrifluoroethylene as a function of isotropic atomic 

oxygen fluence and Poisson theory fit to data. 

 As can be seen from all four materials, there appears to be reasonable agreement with a 

square-root-of-treatment Poisson theory fit to the experimental data for development of surface 

roughness with treatment duration. Although the rate of development of surface roughness 

is dependent upon the texturing particles (abrasive grit or oxygen atoms), impact conditions 

(pressure or energy) and substrate material, the RMS roughness simply can be predicted by a 

different constant of proportionality that is multiplied by the square root of the treatment duration 

to obtain a reasonable fit to the experimental data. Thus, for such spatially independent erosion 

processes, the surface roughness does not reach a limit with treatment duration but rather 

any degree of surface roughness should be achievable with sufficient duration of treatment. 

 Preliminary results of isotropic atomic oxygen treated Aclar to a Kapton H effective 

fluence of up to 7.4 x 10-20 atoms/cm2

 have shown significant increases in adhesion of 

osteosarcoma cells over untreated smooth surface Aclar samples [7-8]. 
NASA/TM—2001-211288 7 

SUMMARY 

 The dependence of surface roughness upon treatment duration was explored using abrasive 

grit blasting of glass microscope slides, 300 series stainless steel and polymethyl methacrylate 

and isotropic atomic oxygen exposure of Aclar chlorotrifluoroethylene. There appears to be 

reasonable surface roughness agreement with a square-root-of-treatment Poisson theory fit to the 

experimental data thus indicating that using such surface roughening processes, where spatial 

independence occurs, allows one to obtain any degree of surface roughness by simply adjusting 

the treatment duration. Preliminary results of atomic oxygen treated Aclar samples indicate 

significant increases in osteosarcoma cell adhesion in comparison to untreated smooth surfaces. 

REFERENCES 

1. Banks, B. A., Chapter 11 in Ion Bombardment Modification of Surfaces in Biomedical 

 Applications, edited by O. Auciello and R. Kelly, Elsevier Publishing Co., 1984. 

2. Picha, G. J., “Tissue Response to Peritoneal Implants”, NASA CR-159817, June 1980. 

3. Banks, B. A., Chapter 17 entitled "Topography: Texturing Effects" in Handbook of Ion Beam 

Processing Technology, edited by Jerome J. Cuomo, Stephen M. Rossnagel, and Harold R. 

Kaufman; Noyes Publications, 1988. 

4. Banks, B. A., "Ion Beam Applications Research - A 1981 Summary of Lewis Research 

Center Programs," NASA TM No. 81721; presented at the 15th IEP Conference cosponsored 

by the AIAA, Japan Society for Aeronautical and Space Sciences, and Deutsche Gesselschaft 

for Luft und Raumfahrt, Las Vegas, Nevada, April 21-23, 1981. 

5. de Groh, K. K., Banks, B. A., and Smith, D. C., “Environmental Durability Issues for Solar 

Power Systems in Low Earth Orbit”, Proceedings of the 1995 International Solar Energy 

Conference, Lahaina, Maui, Hawaii, NASA TM 106775, March 19-24, 1995. 

6. Banks, B. A., Stueber, T.J., Snyder, S. A., Rutledge, S. K., and Norris, M. J., "Atomic 

 Oxygen Erosion Phenomena," presented at the American Institute of Aeronautics & 

 Astronautics, Defense and Space Programs Conference, Huntsville, AL, Sept. 23-25, 1997. 

7. ASTM E 2089-00 Standard Practices for Ground Laboratory Atomic Oxygen Interaction 

Evaluation of Materials for Space Applications, approved May 10, 2000, published June 

2000. 

8. Personal communication with Ron Midura of the Cleveland Clinic Foundation 
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

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NASA TM—2001-211288

E–13092

WU–251–30–07–00

13

The Development of Surface Roughness and Implications for

Cellular Attachment in Biomedical Applications

Bruce Banks, Sharon Miller, Kim de Groh, Amy Chan, and Mandeep Sahota

Surface roughness; Oxygen atoms; Profilometers; Grit

Unclassified -Unlimited

Subject Category: 23 Distribution: Nonstandard

Prepared for the 2001 Fall Meeting sponsored by the Materials Research Society, Boston, Massachusetts,

November 26–30, 2001. Bruce Banks, Sharon Miller, and Kim de Groh, NASA Glenn Research Center; Amy Chan,

Ohio Aerospace Institute, 22800 Cedar Point Road, Brook Park, Ohio 44142; Mandeep Sahota, Cleveland State

University, 1983 E. 24th Street, Cleveland, Ohio 44115–2403. Responsible person, Bruce Banks, organization code 5480,

216–433–2308.

The application of a microscopic surface texture produced by ion beam sputter texturing to the surfaces of polymer implants has been

shown to result in significant increases in cellular attachment compared to smooth surface implants in animal studies. A collaborative

program between NASA Glenn Research Center and the Cleveland Clinic Foundation has been established to evaluate the potential

for improving osteoblast attachment to surfaces that have been microscopically roughened by atomic oxygen texturing. The range of

surface textures that are feasible depends upon both the texturing process and the duration of treatment. To determine whether

surface texture saturates or continues to increase with treatment duration, an effort was conducted to examine the development of

surface textures produced by various physical and chemical erosion processes. Both experimental tests and computational modeling

were performed to explore the growth of surface texture with treatment time. Surface texturing by means of abrasive grit blasting of

glass, stainless steel, and polymethylmethacrylate surfaces was examined to measure the growth in roughness with grit blasting

duration by surface profilometry measurements. Laboratory tests and computational modeling was also conducted to examine the

development of texture on Aclar® (chlorotrifluoroethylene) and Kapton® polyimide, respectively. For the atomic oxygen texturing

tests of Aclar®, atomic force microscopy was used to measure the development of texture with atomic oxygen fluence. The results of

all the testing and computational modeling support the premise that development of surface roughness obeys Poisson statistics. The

results indicate that surface roughness does not saturate but increases as the square root of the treatment time.