Evaluation of Methods of

Characterizing the Porosity of

Porous Polymeric Implant

Materials: A Review of the

Current Status of Porosity

Measurements

R. E. Dehl, W. H. Grant and J. M. Cassel

Polymer Science and Standards Division

Dental and Medical Materials

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

February 1981

Annual Report for Period May 1980 - Seotember 1980

•QC

100

III) 56

81-2212

1981

spared tor: jreau of Medical Devices

>od and Drug Administration

Iver Spring, Maryland 20910

NBSIR 81-2212

National Bureau of Standards

Library, E-01 Admin. Bldg.

MAR i 3 1981

riot olc c - - - EVALUATION OF METHODS OF

CHARACTERIZING THE POROSITY OF

POROUS POLYMERIC IMPLANT

MATERIALS: A REVIEW OF THE

CURRENT STATUS OF POROSITY

MEASUREMENTS

R. E. Dehl, W. H. Grant and J. M. Cassel

Polymer Science and Standards Division

Dental and Medical Materials

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

February 1981

Annual Report for Period May 1980 - September 1980

Prepared for: Bureau of Medical Devices

Food and Drug Administration

Silver Spring, Maryland 20910

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

TABLE OF CONTENTS

Page

ABSTRACT v

BACKGROUND 1

POROSITY INFORMATION SUPPLIED BY MANUFACTURERS 3

PTFE - Carbon Composite 3

References Supplied by Manufacturer 8

Porous High Density Polyethylene 9

References Supplied by Manufacturer 12

QUANTITATIVE METHODS FOR POROSITY CHARACTERIZATION 15

ASTM Standard Specifications for Porous 15

Surgical Implants

Standard Specifications for Porous Polyethylene . 15

for Use in Surgical Implants

Standard Specifications for Porous Composites of 17

Polytetrafl uorethyl ene and Carbon for Surgical

Implant Use

Comments on ASTM Standard Specifications 18

Porosity Measurements Described in Published Literature 19

Current Research in Porosity Measurement 20

Published Reference to Porosity Characterization 20

CLINICAL STUDIES OF OSSICULAR REPLACEMENT PROSTHESES 22

PTFE - Carbon Composite 22

Porous High Density Polyethylene 23

SUMMARY 24

i.

REFERENCES 26
FIGURES

Figure 1: Light micrograph and scanning electron

micrographs of PTFE - Carbon composite

implant material

Figure 2: Pore size measurements and SEM photograph

of porous high density polyethylene

implant material
APPENDICES

Appendix I. Letter from Dr. C. A. Homsy to Dr. J. M.

Cassel Concerning Mercury Intrusion

Porosimetry

Appendix II. Catalog and Price List of PTFE - Carbon

Composite Implant Materials from Dow

Corning Wright Corp.

Appendix III. Letter from Dr. R. E. Dehl to Dr. C. A. Homsy Soliciting Opinions About Critical

Porosity Parameters

Appendix IV. Response of Dr. Homsy to Letter from Dr.

Dehl

Appendix V. Letter from Dr. Homsy to Dr. Cassel

Concerning Pore Size and Pore Volume'

Measurements

ABSTRACT

A search of the published literature pertaining to porous polymeric

implant materials has been made. The two porous materials currently

dominant in implant surgery, namely, porous high density polyethylene

and a porous composite of polytetrafluoroethylene and carbon, have

been reviewed with respect to the following criteria pertinent to

their medical applications: (1) information supplied by the manufacturers about their methods of characterizing the porosity of their

materials, (2) recommendations of the ASTM for quantitative porosity

characterization of these materials, and (3) clinical studies of

the materials as replacement prostheses in middle ear surgery.

A computer search for new quantitative methods of measuring

pore size revealed nothing appropriate to these materials. However,

disputes in the current literature suggest that current protocols

for porosity characterization are inadequate for proper interlaboratory comparison of experimental data.

v

NOTICE

Certain commercial materials are identified in this

report in order to adequately specify experimental

procedures.. In no case does such identification

imply recommendation or endorsement by the National

Bureau of Standards nor does it imply that the

identified materials are the best available.

BACKGROUND

The history of polymeric implant materials for bone ingrowth

begins around 1 955, according to Klawitter and Hulbert"

1 . In the

2 early experiments, polyvinyl sponges were implanted in dogs , where

they were found to be well tolerated. After about 4 weeks, vascular

connective tissue and incipient bone ingrowth were observed in the

pores of the sponges. Unfortunately, no description of the pore size

or void volume of these materials was reported. These early studies

were mostly concerned with load bearing skeletal replacement, and the

porous polymers, lacking structural strength, were soon abandoned in

favor of porous ceramic and metal implant materials.

Early work on the ingrowth of various types of tissues into porous

1 ceramic implants led to the following conclusions: •

•

"(1) Mineralized bone growth into porous calcium aluminate

skeletal implants required a minimum interconnection pore

size of 100 ym.

(2) The minimum interconnection pore size showing the potential

for mineralized bone ingrowths, as indicated by the ingrowth

of osteoid tissue, was found to lie between 40 and 100 urn.

(3) The minimum interconnection pore size necessary for fibrous

tissue ingrowth was found to lie between 5 and 15 um."

This appears to be the first systematic study to determine a correlation between pore size and the type of ingrown tissue. More recent

3 work has suggested that 40 - 50 ym is required for organized fibrous

tissue ingrowth, and at less than 40 ym infiltration consists predominately of fibro-histiocytic elements. However, it is clear from studies

- 1 -
such as those discussed below that the rate and perhaps even the type

of tissue ingrowth depend not only on pore size but also upon the

physico-chemical properties of the porous material. Thus, one must be

cautious about referring to an "optimum" pore size except in connection

with a specific material.

During the past decade, porous polymeric implant materials have

been developed for various implant applications. One of these, a

porous composite of polytetrafl uoroethylene and carbon fibers, has been

4

patented , and is currently available from at least one commercial

5 supplier . Another porous polymer which, like the composite, has

undergone rather extensiye clinical trials and experimentation is

porous high density polyethylene. There are at least two commercial

suppliers of this material who have developed proprietary processes for

producing porous polyethylene of specified pore sizes

and pore volumes^. Other polymers currently under investigation

as candidate porous implant materials include porous polysul fone°’ ,

medical grade Bioelectric Polyurethane

10

, and Silicone Rubber

11

. According

12

to White et al_. , the latter two " have shown independent^ effects

1 3 of pore size and biomaterial on incorporation of prosthetic segments ."

Unfortunately, it is difficult to compare the results of different

workers in their clinical studies of porous implant materials, due to

the lack of a commonly accepted system of porosity characterization.

Where standard methods such as ASTM Standard Recommended Practices are

available, they are often avoided in favor of other

- 2 -
methods which are believed to be more appropriate for a particular

material. Clearly, two objectives should be sought in attempting to

devise a rational scheme for characterizing the porosity of implant

materials. First, insofar as possible, methods should be selected

which are applicable to all porous polymeric materials, since this procedure greatly facilitates inter-laboratory comparison of experimental

data. Second, in cases where it is absolutely necessary to use

different methods for different materials to measure the same parameter,

the relationship between the methods (accuracy, reproduci bil ity

,

systematic errors, etc.) should be well understood. Whenever possible,

t.wo or more methods of measuring the same parameter should be used,

because there will inevitably be uncertainties associated with each

method. It is the purpose of this project to provide a critical

evaluation of current methods of porosity characterization and, where

necessary, to suggest additional methods to improve the accuracy and

reliability of porosity measurements.

POROSITY INFORMATION SUPPLIED BY MANUFACTURERS

PTFE - Carbon Composite

The PTFE - Carbon Composite porous implant material is an invention

4

of Dr. C. A. Homsy . It is manufactured in thin sheets (>1 mm).by heat

and pressure treatment of a 4-component system containing PTFE fibers

and pellets, carbon fibers, and NaCl pellets. The salt is extracted

from the fused sheet, leaving a porous material which physically resembles

gray felt. Homsy 's own "characterization" of the porosity of his

material relies heavily on indirect evidence. For example, in a recent

1 4 publication , he states that

- 3 -
" three parameters have been routinely used to assay the

nature of the porosity of the material : (a) the volume and

weight percentages of the four initial ingredients, PTFE resin,

PTFE fiber, graphite fiber, and sodium chloride (NaCl) crystal ;

(b) the grain size distribution of the NaCl crystal; and (c) the

apparent density of the final product."

For quantitative data, he has relied on an independent testing

laboratory (address given) which confirmed

"a pore volume of 80 ± 5 volume percent and a pore size range

as indicated on the product label. Direct optical measurement

of pore size using the SEM indicates a maximum of approximately

400 mi era and a percentage porosity by line intercept techniques

to be approximately 57%.

Homsy then states that "the independent laboratory ... .noted that

their values were low because of limitations intrinsic to the technique,"

There follows a discussion of mercury intrusion porosimetry, in which

the well-known limitations of the Washburn equation are quoted, together

with an opinion by Professor G. D. Armeniades of the Department of

Chemical Engineering, Rice University, Houston, TX, that "the deformability of the matrix of the material leads to substantial distortion

of pore structure. . .which, of course, confounds the results." Nevertheless, the pore volume was estimated using the mercury technique by

another independent laboratory (address given) for Dr. Homsy. They found

- 4-
a pore volume of 65% which, according to Homsy, is a "good confirmation

of the product literature value range of 70 - 90%, considering the bulk

compression during the test." Further comments on the mercury porosimetry

technique appear in a letter from Dr. Homsy to Dr. Cassel (Appendix I ).

The "product literature values" of porosity referred to by Homsy

appear identically in four different package inserts which we have seen,

for the PTFE-carbon composite. The four inserts apply to the implant

material in the form of 1 ) Sheeting, 2) Block, 3) Total Ridge and

Posterior Ridge, and 4) Temporomandibular Joint Condylar Prosthesis.

In each case, it is stated that

"The pore size distribution for standard Proplast is 100 to

500 urn with dendritic pore interconnections greater than 200 urn.

The pore volume of Proplast comprises 70 to 90% of the total

material volume."

In some cases, it is also noted that the pore size can be varied

to meet special requirements.

While this is the only quantitative information provided specifically

about the porosity of the material, there is a rather detailed description

given in the product literature about the procedures and precautions to

be observed by the surgeon when handling, shaping, and cutting the

material. Indications and contraindications for surgical use of the

material are given, together with a caveat about potential long-term

hazards of implantation, because ofthe relatively short time that the

material has been in use. A catalog of implant products was obtained from

the marketing company for the PTFE - carbon composite, and the appropriate

pages are reproduced in Appendix II.

- 5 -
In a letter to Dr. Homsy from Dr, Dehl (Appendix III), opinions

were solicited about the critical parameters of porosity. Dr. Homsy's

reply (Appendix IV)., and in particular the concluding paragraphs,

provide an interesting if at times controversial discussion of the

relationship of porosity and other physical properties of the material,

to successful implantation. In another letter to Dr. Cassel [Appendix

V), Dr. Homsy states his beliefs about the best methods by which the

user can verify the porosity of his material. As stated above, he

relies upon indirect methods (i.e., apparent density and tensile

strength measurement), rather than direct observation of porosity to

determine whether his product "is conforming to manufacturing specifications with respect to pore characteristics".

Figure 1 illustrates the morphology of the PTFE-carbon composite.

The top photograph is reproduced from Ref. 15. It is a light photomicrograph which clearly shows the 3 phases present, as well as the

elongation of the pores, due to the rolling of the compact sheet during

manufacture. The middle photograph is an SEM reproduced from literature

provided by the manufacturer, which shows a lacy network of fibers with

a wide range of pore sizes. The bottom photographs, taken from ref, 16,

are similar to the SEM above and are said to illustrate the effect of

trimming off the top surface, leaving a more open network.

- 6 -
Figure 1. Light micrograph and scanning electron micrographs

of PTFE - carbon composite implant material

Incident beam light micrograph of a polished section of plastic embedded

Proplast. G: graphite fiber; T: polytetrafluoroethylene; P: pore.

Si.'iiiinliiit nlm lmii iiHi:niui‘n|iji iliHlo .hows Hit' lnt-iiiv |n>rnii>, NlriHiliirii of I’mpliiHl Tills apim p..rc i iMifiiiiiraliiMi .,11, .w>. Ii.c llipmonli

tissue murowlli

Scanning electron micrographs of (left) (tie rolled closed" suitacr ami mgim a razor-cut open surface ot the sponge. Note die llatiemng and die coinpiession of ihe porosity in die part subjected to die lamination process. cOOi
References Supplied by Manufacturer

(Note: Some of these references duplicate those referred to in

the text.

)

1 . Arem. A.J. and Madden. J.W. Soft Tissue Response 10 Blood Impregnated

PROPLAST* Submitted to Plastic and Reconstructive Surgery. 58:500-586 December. 1979.

2. Bed. W.H.: Augmentation of the Nasomaxillary and Nasolabial Regions O

Surgery. O. Medicine. O. Pathology. 41-691 697 1976

3. Epstein. L.I.: Cdnicai Experience with Proplasl as an Implant Plas. Reconstr. Surg.. 63:219. 1979.

4. Farrell. C.D. and Kent. J.N.: Clinical Applications of PROPLAST m oral and

Maxillofacial Surgery. Alpha Omegan. December, pp. 21-26. 1975

5. Freeman. B.S.: PROPLAST. A Porous Implant lor Contour Restoration

British Journal of Plastic Surgery. 29:158-164. 1976.

6. Hinds. E.C. Homsy. C.A. and Kent, J.N. Use ol a Biocompalible Interlace

for Combining Tissue and Prosthesis in Oral Surgery. Oral Surgery. Oral Medicine. Oral Pathology. 38:512-519. 1974

7. Hinds, E.C. and Kent. J.N.: Genioplasty The Versatility ol Horizontal Osteotomy. J. Oral Surg.. 77:690. 1969.

8. Hinds, E.C. and Kent. J.N.: Surgical Treatment ol Developmental Jaw

Deformities. Chapter 8. The Chin. C.V Mosby. Co St Louis. 1972.

9. Homsy, C.A.: Biocompalibility in Selection ol Materials lor Implantation. J. Biomed. Mater. Res. 4:341-356. 1970.

10. Homsy. C.A.: Cain, T.E.. Anderson. M S and King, J.W Dynamic

Stabilization of Implanted Prosthesis. Proc. Orthop. Res. Soc.. dan. 16. 1970.

J. Bone & Joint Surg. 52A:604. 1970.

11. Homsy. C.A.. Kent. J.fi. and Hinds. E.C.. Materials lor Ora Implantology

Biological and Functional Criteria. ' Journal of the American Dental Association. 86:817-832. 1973.

12. Janeke. J.B.. Komorn. R M.. and Cohn, A.M Proplasl® in Cavity

Obliteration and Tissue Augmentation.'' Archives of Otolaryngology.

100:24-27, 1974.

13. Janeke. J.B.. and Shea. J.J.. PROPLAST* Implants used in Otology and

in Facial Reconstructive Surgery. South African Medical Journal. 50:781-783.

1976.

14. Kent. J.N and Homsy C.A : Pioplasl Implant Mateiie! Presentations beloie FDA Oral Surgery. ENT. and Plastic Surgery Device Classification Panels. Dec. 5. 1977 & Jan. 27. 1978 and March 24. 1978.

15. Kent. J.N.. Homsy. C.A.. Gross. B.D., and Hinds. E.C.. Pilot Studies ol a Porous Implant in Dentistry and Oral Surgery. " The Journal of Oral Surgery. 30:608-616. 1972.

16. Kent. J.N.. Homsy. C.A.. Hinds. E.C.: "Proplast* in Dental Facial Reconstruction.' 5th International Conference on Oral Surgery. Madrid.

Spain. April 1974. Oral Surgery. Oral Medicine. Oral Pathology. 39:347-355. 1975

17. Kent. J.N . LaVelle. W.E.. and Dolan K.D.: Condylar Reconstruction: Treatment Planning Oral Surgery. Oral Medicine. Oral Pathology. 37:489-497. April 1974

18. Kent. J.N. and Westfall. R.L. Presurgical Infusion of Proplast: Primate

Facial Augmentation. J Oral Surg.. (In Press).

19. Kent. J.N.. Zide. M.F . and Homsy, C.A.: Chin and Facial Augmentation

with Prolast: Surgical Management and Long Term Evaluation. Submitted to the J. Oral Surg., July 1979.

20. Merrm. M L.. Parkes. M.L.. and Kamer. F.M.: PROPLAST" Chin Augmentation. ' Presented at the 2nd International Symposium on Plastic and

Reconstructive Surgery of the Head and Neck. June 8-13. 1975. Chicago. Il- linois. 21. Schenek. N.L., Tomilson. M.J.. and Ridgley, C.D.: Experimental Evaluation of a New Implant Material in Frontal Sinus Obliteration. Arch Otol.. 102:524-528. 1976.

22. Whitehead. F. Atrophic rhinitis: PROPLAST* as an Implant Material in Surgical Treatment. Canadian J. Otolaryngology. 4:3. 1975.

- 8-
Porous High Density Polyethylene (PHDPE)

We have identified 2 suppliers of porous polyethylene which

claim to have material for implant usage. Samples of porous polyg ethylene were obtained from Glasrock Corporation in a variety of

shapes, some labeled "large pore size", and others "small pore size".

The physical appearance and other properties of this material are

clearly very different from the composite. The literature accompanying the samples refers to the "proprietary technology" used to

prepare them. It is stated that the " permeable material has

omnidirectional, interconnecting pores, the size of which can be

accurately controlled between 10 and 500 urn, depending on the polymer

used". (The company also prepared porous polymers other than PHDPE.)

From the appearance of the samples, given to fis , the material appears

to be sintered from rather uniform pellets of the polymer resin. In

comparison with the soft, felt- like composite, this material is

relatively hard and inflexible. It is not clear to us whether the

Glasrock material is actually being marketed for surgical implant use.

The literature states a number of uses for their materials, including

^'biomedical filters, blood serum filters, catheter vents, and prostheti

devi ces "

. (Emphasis ours.)

Quantitative information about pore sizes in this material has also

been hard to find, and we have found only two references to experimental

work in which it is clear that the Glasrock material is being used.

15

Spector et aj_. in their animal implant studies of porous polyethylene

state that they obtained the material from Glasrock and that the pore

size was "about 400 urn". Another group^ studying the strength of the
bone-porous polyethylene interface in implant studies of dogs, reported

that their material was from Glasrock and had an average pore size of

"about 250 microns with a highly interconnected porous structure".

3 They also reported a bulk density of 0.32 to 0.36 g/cm and about

65% (open) porosity. They do not report how these numbers were

obtained .

Another manufacturing company^ advertises ossicular prostheses made

of porous polyethylene, but it is not clear who the manufacturer of the

porous polymer is. We recently received 5 technical publications and

catalogs from this company “. There are 16 varieties of ossicular

replacement prostheses listed and illustrated in their catalogs which

are made wholly or partiy of PHDPE. Fig. 2 is a collection of pertinent

data selected from this literature. The 300.X SEM photograph of PHDPE

clearly shows a very different morphology from the composite. One can

easily see the smooth sintered particles, separated by open channels.

An SEM picture of one of the total ossicular replacement prostheses

("TORP") is also shown.

The method used by this manufacturer to characterize the pore size

distribution is mercury intrusion porosimetry, and a typical plot of

1

pore size vs. volume is shown in Fig. 2. As noted by the authors,

" the majority of pores are between 18 and 35 microns". In the

same publication, the authors state that the porosity (pore volume)

of this material is "approximately 35%"

- 10 -
Figure 2. Pore size measurements and SEM photographs

of porous high density polyethylene implant

material

POROUS POLYETHYLENE

Method of Manufacture

Polyethylene particles are bonded by a special process which controls the temperature, pressure, atmosphere,

and time. Final machining and finishing operations do

not add any detectable amounts of foreign material to the starting material. Porous polyethylene devices can be

produced in a variety, of shapes. Molds can be used to produce parts that require little or no finishing. Rods

and sheets can also be machined to produce devices.

Percent Porosity and Average Pore Size

The percent porosity is the ratio of the volume of pores • to the volume of the material. This factor, along with

the average pore size (the diameter of the pores most

abundant in the material), can be qualified by a mercury

intrusion porosimeter, which is a laboratory instrument.

Figure 6 was'plotted from data obtained when a sample » of porous polyethylene was analyzed. Quantitative optical microscopy can also be used to characterize the material.

JLL

Fiyure 6. Plot obtained from analysis of a sample of porous

polyethylene using a mercury intrusion porosi- meter. Note that the majority of pores are between

18 micron and 35 micron.

PI asti Pore 10 Porous Polyethylene 300X

Tilt- TopTM TO RP® Prosthesis. All Plasti- Pore® Material, 14X

11
References Suppl'ied by the Manufacturer (Note:

may duplicate those referred to in the text.)

1. Alitalo, I.: “Ventral Interbody Implantation tor Fusion of tne Lumbar Spine Using PTFE." Acta Vet Scand (Suppl)

71:1-49, 1979.

2. Altenau, M.M.; and Sheehy, J.L.: "Tympanoplasty: Cartilage °rostneses — A Report of 564 Cases." Laryngoscope

88(6): 895-904, June 1978.

3. Anand, S.C.; St. John, K.R.; Moyle, D.D.; and Williams,

D.F.: "Finite Element Analysis of Medullary Shaft Im- plant." Presented at the 29th Annual Conference on Engineering in Medicine and Biology, Boston, Mass., November

6-10, 1976, and the 8th Annual International Biomaterials Symposium, Philadelphia, Pa., April 9-13, 1976.

4. Anand, S.C.; St. John, K.R.; Moyle, D.D.; and Williams, O.F.: "Stress Distribution in Porous Surfaced Medullary

Implarrts." Ann. Biomed. Eng. 5(41:410-20, December

1977.

5. Austin, D.F.: "The Off-Centered TORP." The American

Journal of Otology, 1(11:19-21, July 1979.

6. Bagwell, J.G.: "An Evaluation of Bone Growth Into Porous High Density Polyethylene." Clemson University, M.S. Thesis, 1974.

7. Bagwell, J.G.; Klawitter, J.J.; Sauer, B.W.; and Weinstein, A.M.: "An Evaluation of Bone Growth Into Porous

Polyethylene." Presented at the 6th Annual Biotnaterials Symposium, Clemson, S.C., April 20-24, 1974.

8. Besser, W.; Insall, J.; Walker, P.S.; Dueland, T.; and Pillar, R.: "Porous Ingrowth Material." Presented at the 23rd Annual Orthopaedic Research Society, Las Vegas, Nev., February 1-3, 1977.

9. Brackmann, D.E.; and Sheehy, J.J_.: "Tympanoplasty:

TORPs and PORPs.” Presented at the Western Section of the Triological Society, San Francisco, Cal.. January 28, 1978, and Laryngoscope 89(1 ): 108-1 14, January 1979.

10. Brown, B.L.; Neel, H., Ill; and Kern, E.B.: "Implants

of Supramid, Proplast, Plasti-Pore, and Silastic." Arch.

Otolaryngol., 105:605-609, October 1979.

11. Cestero, H.J., Jr.; Salyer, K.E., and Toranto, I.R.: "Bone Growth in Porous Carbon, Polyethylene, and Polypropylene Prostheses." J. Biomed. Mater. Res. Symp. 6:1-7, 1975.

12. Chuden, H.G.: "First Results Using the Shea-TORP in Middle Ear Surgery." HNO 26:57-59, 1978.

13. Emmett, J.R.; and Shea, J.J. : "Surgical Treatment of Tympanosclerosis." The Laryngoscope, 88(2):1642-1648, October 1978.

20 .

21 .

22 .

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

14. Ferguson, T.H.; and Greer, R.T.: "Mechanical Properties

of Porous Polyethylene Implant— Bone Composites." 33. Presented at the 9th Annual International Biomaierials Symposium, New Orleans, La., April 15-19, 1977.

15. Fisch, U.: "Reconstruction of the Ossicular Chain." HNO, 34, 26:53-56, 1978.

16. Fisch, U.: Tympanoplasty and Stapedectomy, A Manual

of Techniques. Georg Thieme Verlag, New York, N.Y., 1980, pp. 24, 31-34.

35.

17. Flemming, W.R.: "An Investigation of Bone Ingrowth

Mechanisms in Porous High Oensity Polyethylene Implants." Clemson University, M.S. Thesis, 1975.

36.

18. Glazener, W.E.: "A Study of the Feasibility of Using Porous Polyethylene as a Seal for Transcutaneous Implants." Clemson University, M.S. Thesis, 1975.

37.

19. Glazener, W.E.. and Sauer, 8.W.: "The Use cf Porous

High Density Polyethylene as a Percutaneous Seal." Pre- sented at the 8th Annual International Biomaterials Symposium, Philadelphia, Pa., April 9-13, 1976.

Some of these references

Glazener, W.E., in Park, J.B.: Biomaterials. An Introduction. Plenum Press, New York, N.Y., 155, 1979.

Handrock, M., Mulch, G.; and Hancrock, Chr.: "The Applicabihty of Porous Polyethylene for Tympanoplasty, An

Animal Experimental Study." Arch. Otorhinolaryngol

224:193-206, 1979.

Harner. S.G.; Facer, G.W.; and McDonald, T.J.: "Experience

with a Polyethylene Ossicular Replacement Prosthesis." Arch. Otolaryngol, 105(31:137-9, March 1979.

Hicks, G.W.. Wright, J.W., Jr.; and Wright, J.W., III: "Use of Plasti-Pore for Ossicular Chain Reconstruction: An Evaluation." Laryngoscope, 88(61:1024-33, June 1978.

Hicks, G.W.: '-'Use of Plasti-Pore for Chain Reconstruction."

(Letter) Laryngoscope, 88(10): 1 703, October 1978.

Hornsey, C.A.: "Use of Plasti-Pore for Chain Reconstruction." (Letter) Laryngoscope, 88(101:1703, October 1978.

Hulbert, S.F.; and Bowman, L.S.: "Porous Polymeric

Orthopedic Implants." In: Kronenthal, R.L., et al., ed., Polymers in Medicine and Surgery. Plenum Press, New York, N.Y. 161-166, 1975.

Kinney, S.E.. "Middle Ear Reconstruction Using Cartilage and TORP and PORP." The Laryngoscope, 89(121:2004-7,

December, 1979.

Klawitter, J.; Bhatti, N.; and Bliven, F.: "Attachment ol Prostheses by Bone Growth into Porous Materials — Tech- nique for Microstructural Evaluation." A scientific exhibit presented at the 1973 Annual Meeting of the American

Academy of Orthopaedic Surgeons, Las Vegas, Nev., February 1-6, 1973.

Klawitter, J.J.; Sauer, 8.W., 8agwell, J.G., Weinstein, A. M.; Greer, K.G.; and Hulbert, S.F.: "Characterization of Tissue Growth into Porous Biomaterials." Technical Report No. 6, Office of Naval Research, Department of Navy, June 29, 1974.

Klawitter, J.J.; Sauer, 8.W.; Cooke, F.W.; Hulbert, S.F. "Characterization of Tissue Growth into Porous Biomaterials." Final Report, Office of Naval Research. September

19, 1974.

Klawitter, J.J.; Bagwell, J.G., Weinstein, A. M.; Sauer. B.W.; and Pruitt, J.R.: "An Evaluation of Bone Growth into Porous High Density Polyethylene." J. Biomed. Mater. Res., 10:311-23, 1976.

Lemons, J.E., Weiss, A.B.; and Niemann, K.M.W.: "Prelim- inary Studies on a Composite Tendon Prosthesis Design." Presented at the 21st Annual Orthopedic Research Society, San Francisco, Cal., February 27-March 1, 1975.

Linder, J.L.. "Asymmetric Stress Analysis of an Axisymmetric, Porous Coated, Femoral Head Prosthesis System."

Clemson University, M.S. Thesis, 1978.

Luncelord, E.M.; Weinstein, A.M.; and Sauer, B.W.: "Pros- thetic Replacement of Giant Cell Tumor of the Distal Fejmur Using Porous High Density Polyethylene for Attach- ment to Bone." Film shown at the 43rd Annual Meeting ol the AAOS, New Orleans, La., January 30-February 4, 1976.

Mayer, R.D.: "Work-To-Fracture of High Oensity Poly- ethylene Bone Composite." Clemson University, M.S. Thesis. 1977.

Merritt, K.; Shafer, J.W.; and Brown, S.A.: "Implant Site Infection Rates with Porous and Dense Materials." J. Bio- med. Mater. Res., 13:101-108, January 1979.

Meyer, L.C., and Sauer, 8.W.: "The Use of Porous High Density Polyethylene Caps in the Prevention of Apposi- lional BoneGrowth in the Juvenile Amputee: A Preliminary Report." Inter-Clinic Information Bulletin, Volume XIV, Nos. 9 and 10:1-4, 1975. Also presented at the Piedmont Orthopaedic Society, Phoenix, Ariz., May 5-9, 1976.

:

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- 12 -
3fl Movie, 0 D.. Mayer, R.Q.; Sauer, 8 W . and Cooke, F W.

"Fracture Toughness of Bone — Prosthetic Material Composites.'' Presented at the 29th Annual Conference on Engineering m Medicine and Biology , Boston Mass November

6-10. 1976, and the 9th Annual International Buirn.itei ials Symposium, New Orleans, La.. April lb-19, 19/7.

39. Pruisner, P.; Lade, R.: and Zichner. L.: "Comparing In- vestigations c* Mechanical Loading Capacity of the Implant Bed with Test Bodies of Different Materials." Pre- sented at the 10th Annual International Biomateoals

Symposium, San Antonio, Tex., April 22-May 2, 1978.

40. St. John, K.R.: "Stress Analysis of Intramedullary Implants with Porous Coatings by the Finite Element Method." Clemson University, M.S. Thesis, 1977.

41. Salman, N.N.: "Polymeric Metal Coating." Clemson University, M.S. Thesis, 1977.

42. Saraneno, C.A.; Gray, W.C.; Blanchard. C.L.: "Use of Tragal Cartilage with Total Ossicular Replacement Prosthesis.” Arch. Otolaryngol, 104:213, 1978.

43. Sauer, B. W.; Hulbert, S. F.; and Klawitter, J. J.: "Experimental Technique: An Often Neglected Variable in Biomaterials Evaluation." Presented at the 5th Annual Biomaterials Symposium, Clemson, S.C., April 14-18, 1973.

44. Sauer, B. W.; Weinstein, A. M.; Klawitter, J. J. and Bagwell,

J. G.: "Porous Polyethylene: An Interfacial Material for Implanted Prosthesis." Presented at the 20th Annual

Meeting of the Orthopedic Research Society, Dallas, Tex., January 15, 1974.

45. Sauer, B. W.: "Porous Polyethylene: A Tissue-Implant Interfacial Material." Invited Paper presented at the Annual

Congress of the Societe Beige de Chirurgie Orthopedique

et de Traumatologie, Brussels, Belgium, May 24-26, 1974.

46. Sauer, 8. W.: "Methods of Prosthetic Fixation to Bone."

Paper presented at the 6th Annual Meeting of the Hip

Society, Columbia, S.C., August 2-3, 1974.

47. Sauer. 8.W.; Weinstein, A.M.. Klawitter, J.J., Hulbert, S.F.; Leonard, R.B.; Bagwell, J.G.: "The Role of Porous Polymeric Materials in Prosthesis Attachment." J. Biomed.

Mater. Res. Symp., 5, Part 1:145-153, 1974.

48. Sauer, B.W.; Weinstein, A.M.; Meyer, L.C.; and Hopkins,

J.E.: "Clinical Experience with Porous High Density Polyethylene as an Implant-Tissue Interface." Presented at the

, 6th Annual International Biomaterials Symposium, Clemson, S. C.. April 20-24, 1974.

49. Sauer, S.W.: "Clinical Experience with Porous High Density

Polyethylene as a Bone - Implant Interfacial Material." Pre- sented at the 7th Annual Biomaterials Symposium, Clem-

, son, S. C„ April 26-30, 1975.

50. Sauer, B.W.; Spector, M.; and Flemming, W.R.: "Ingrowth

i- Kinetics of 8one in Porous High Density Polyethylene."

Presented at the 28th Annual Conference on Engineering

in Medicine and Biology, New Orleans, La., September

20-24, 1975.

il 51. Sauer, B.W.; Thatcher, J.C., and Cooke, F.W.: "Strength of

i- of Attachment of a Porous High Density Polyethylene Interif facial Material to Metallic Prosthesis Components." Presentj. ed at the 8th Annual International Biomaterials Symposium,

Philadelphia, Pa., April 9-13, 1976.

/

j. 52. Sauer, B.W.: "Correction of Faulty Ear Carriage in the Dog

with Porous Polyethylene Implants. " Veterinary Medicine/

Small Animal Clinician. 1071-1075, August 1976.

le

o- 53. Sauer, B.W.; Moyle, D.D.; and Cooke, F.W.: "Design and

Testing of Prostheses Systems Using Porous High Density

Polyethylene as an Interfacial Material." Presented at the

)h 23rd Annual Orthopaedic Research Society, Las Vegas,

si- New., February 1-3, 1977.

i V

/, 54. Sauer, B.W.; Henke, J.S.; and Kenner, G.W.: "Fixation of

nl Turkey Tarsometatarsal-Phalangeal Joint Using a PHDPE

6. Interfacial Layer." Presented at the 24th Orthopaedic Research Society, Dallas, Tex., February 21-23, 1978.

bb Sauer, B W., LaOC, R B., Henxe. J.S.. and Kenner, G.W

"An Evaluation of Functionally Loaded Prostheses Stabilized by Porous High Density Polyetnylene Coatings " Presented at the 11th International Biomaterials Symposium Clemson, S.C ., April 28 May 1, 1979.

B6. Sauer, H W.. Laue, R.B., a no Mercer, H.A. "Fixation

of Canine Femoral Head Prostheses Using Porous High

Density Polyetnylene Coatings," presented at the 11th Annual International Biomaterials Symoosium, Vienna,

.* Austria, April 8-12, 1980.

57. Sauer, 8.W.; Lade, R.B., and Mercer, H.A.: "Porous Polyethylene-Autogenous Tissue Tracheal Prosthesis." Presented

at the 11th Annual International Biomaterials Symposium,

Vienna, Austria, April 8-12, 1980.

58. Shea, J.J.: "Plasti-Pore Total Ossicular Replacement Prosthesis." The Laryngoscope, 36(2) :239-240, February 1976.

59. Shea, J.J.: "Biocompatible Plastic Implants in Tympanoplasty. " Presented at the Jubilee Meeting of the Royal

Australian College of Surgeons, Melbourne, Australia,

May 1977.

60. Shea, J.J.; Emmett, J.R.. Smyth, G.D.L.: "Biocompatible

Implants in Otology." O. R. L. Digest, 39:9-15, January

1977.

61. Shea, J.J.; and Emmett, J.R.: "8iocompatible Ossicular Implants." Arch. Otolaryngol, 104:191-196, 1978.

62. Shea, J.J.. "Alloplastic Materials for Otologic Reconstruction." Presented at the 10th Annual International Biomaterials Research Symposium, San Antonio, Tex.,

April 29-May 2, 1978.

63. Shea, J.J., and Emmett, J.R.: "Tympanoplasty: Indications for and Technique of Operation." An instructional course reported in Otolaryngol Head Neck Surgery, 87:45,

May-June 1979.

64. Sheehy, J.L., Brackmann, D.E.. and Graham, M.D.: "Chol- esteatoma Surgery: Residual and Recurrent Disease. *A

Review of 1,024 Cases.” Annals of Otology, 86(4-1):

451-462, July-August 1977.

65. Sheehy, J.L.. "TORPs and PORPs in Tympanoplasty."

Clin. Otolaryngol. 3(4): 451-4, November 1978.

66. Skinner, H.B., Shackleford, J.F.; Lin, H.J.; Cutler, A., and

Benson, D.R. "Imerfacial Strength of Porous Polyethylene

Implant- Bone Composites." Presented at the 30th Annual

Conference on Engineering in Medicine and Biology, Los

Angeles, Cal., November 5-9, 1977.

67. Skinner, H.B., Shackelford, J.F., and Lin, H.J.: "Tensile Strength of Bone (Bone/Porous Polyethylene) Interface." Siomater. Med. Devices Artif. Organs, 7 ( 1 ) : 1 33-9 , 1979.

68. Smyth, G.D.; Hassard, T.H.; Kerr, A.G.; and Houlihan, F.P.. "Ossicular Replacement Prosthesis." Arch. Otolaryngol.,

104(61:345-51, June 1978.

69. Spector, M., Flemming, W.R., Jr.; and Sauer, B.W.: "Ultrastructure of Tissue Growing Into Porous Bone Implants:

Tissue Attachment. " Presented at the 21st Annual Meeting

of the Orthopedic Research Society, San Francisco, Cal., February 27-March 1, 1975.

70. Spector, M., Flemming, W.R., Jr., and Sauer, B.W.. "An

Ultra-Structural Study of Tissue Growing Into Porous Bone

Implants." Presented at the 7th Annual International Bio- materials Symposium, Clemson, S.C., April 26-30, 1975.

71. Spector, M.; Flemming, W.R., and Sauer, 8 W.: "Early

Tissue Infiltrate in Porous Polyethylene Implants into Bone: A Scanning Electron Microscope Study." J. Biomed. Mater.

Res. 9151:537-42, September, 1975.

72. Spector, M.. Draughn, R.A.. Sauer. B.W.. and Young, F.A.. "The Effects of Loading on the Pore Structure of Low

Modulus Porous Implant Materials." Presented at the 54th

General Meeting of the IAOR. Miami, Fla., March 25-28. 1976.
73. Spector, M.; Kreutner, A.; and Sauer, 8.W. "Scanning

Electron Microscopy of the Bone Response to Porous Orthopedic and Dental Imolants." Presented at the 9th Annual Scanning Electron Microscope Symposium, Toronto, Canada, April 6-7, 1976.

74. Spector, M.; Kreutner, A.; and Sauer, B.W.: "Scanning

E'ectron Microscopy of the Healing Response to Porous Orthopedic and Dental Implants." pp. 299-306, in: Johari, 0.; and Becker, R.P., ed.: Scanning Electron Microscopy/

1976/11. Chicago, 111., 1976.

75. Spector, M.; Flemming, W.R.; Kreutner, A.; and Sauer,

B.W.: "Bone Growth Into Porous High Density Polyethylene." J. Biomed. Mater. Res., 7:595-603, 1976.

76. Spector, M.; Sauer, B.W.; and Young, F.A. "Performance

of Porous Titanium and Porous High Density Polyethylene

Tooth Roots." Presented at the 8th Annual International Siomaterials Symposium, Philadelphia, Pa.. April 9-13, 1976.•

77. Spector, M.; Sauer, B.W.: "Histological Factors Controlling Bone Growth Into Porous Biomaterials." Presented at the 8th International Biomaterials Symposium, Philadelphia,

Pa., April 9-13, 1976.

78. Spector, M.; and Kreutner, A.: "The Nature of the Fibrous

Tissue in Porous Bone Implants." Presented at the 23rd Annual Meeting of the Orthopedic Research Society, Las

Vegas, Nev., February 1-3, 1977.

79. Spector, M.; Young, F.A.; Marcinak, C.F.; and Kresch, C.H.:

"Clinical and Histological Evaluation of Porous Titanium

and Porous High Density Polyethylene Tooth Roots.” Pre- sented at the 11th Annual International Biomaterials Symposium, Clemson, S.C.. April 28-May 1, 1979.

80. Spector, M; Harmon, S.L.; and Kreutner, A.. "Characteristics of Tissue Growth Into Proplast and Porous Polyethyl- ene Implants in Bone." J. Biomed. Mater. Res., 13:677-692. September 1979.

81. Soector, M.; Marcinak, C.F.; Young, F.A., Eldridge, J.T., and Harmon, S.L.: "Artificial Tooth Roots with Porous Polymer Coatings," Presented at the 11th Annual Inter- national Biomaterials Symposium, Vienna, Austria, April 8-12, 1980.

82. Thatcher, J.C.: "Strength of Attachment of a Porous High

Density Polyethylene Interfacial Material to Metallic Prosthesis Components," Clemson University, M.S. Thesis, 1976.

83. Trent. P.S.. Besser, W.; Dueland, R.; and Insall, J.. "Total Knee Prosthesis Combining Porous Ingrowth and Initial Stabilization." Presented at the 24th Annual Orthopaedic

Research Society, Dallas, Tex., February 21-23, 1979.

84. Wayoff, M.: "Le piastipore en tympanoplastie." J. Fr. Otorhinolaryngol., 28(51:322-326, May 1979.

85. Weinstein, A.M.; Klawitter, J.J.; Sauer, B.W.; and Bagwell,

J.G.: "Structure-Properties Relationships for Porous High

Density Polyethylene." Presented at the 21st Annual

Meeting of the Orthopedic Research Society, San Francisco, Cal., February 27-March 1, 1975.

86. Zichner, L.; Lade, R.; and Prussner, P.: "Comparing Histological Evaluations of Tissue Around Partly and Totally

Loaded Spacers of Different Materials." Pre-sented at the 10th Annual International Siomaterials Symposium, San

Antonio, Tex., April 29-May 2, 1978.

- 14-
QUANTITATIVE METHODS FOR POROSITY CHARACTERIZATION

ASTM Standard Specifications for Porous Surgical Implants

It is interesting to compare the recommended procedures for

characterization of pore volume and pore size contained in the current

ASTM draft Standard Specifications for the PTFE-carbon compo'site and

for porous polyethylene. The pertinent paragraphs are excerpted below.

(1) Standard Specification for Porous Polyethylene for Use

in Surgical Implants. Draft #10 F-4.20 ,01 .07 (.3/80).

2.3 This specification is applicable to all device standards

in which porous polyethylene is used...... It is expected

that the pore size, pore volume, and the mechanical

properties will be specified in the particular device

standard.

- 15 -
3. Applicable Documents

3.9 ASTM D2873. Standard Method of Test for Interior

Porosity of Poly(vinyl chloride) (PVC) Resins by

Mercury Intrusion Porosimetry.

3.10' ANSI /ASTM E562. Determining Volume Fraction by

Systematic Manual Point Count.

3.11 ASTM F316-70. Pore Size Characterization of Membrane

Filters for Use with Aerospace Fluids.

6. Test Methods

6.3 Average pore diameters shall be established.

6.3.1 Pore size can be measured in accordance with

ASTM F316-70.

6.3.2 Pore size can-be measured by-Mercury Intrusion

Porosimetry. (ASTM D2873 is an acceptable method.).

6.4 Average pore volume shall be estimated by one of the

following methods

:

6.4.1 Pore volume can be measured by Mercury Intrusion

Porosimetry. (ASTM D2873 is an acceptable method.)

6.4.2 Pore volume can be approximated by measurement by

weiqht of a saturant of known specific gravity

and relating its volume t« the matrix volume.

6.4.3 Pore volume can be estimated by Optical Microscopy

as described in ANSI/ASTM E562.

- 16 -
(2) Standard Specifications for Porous Composites of Polytetrafl uoroethylene and Carbon for Surgical Implant Use. Task Force F4. 20. 04. 05.

4.4 Porosity Characterization

4.4.1 Volume Pores, Specimens of composite with apparent

density within the limits indicated under paragraph

4.2.4 will exhibit pore volume between 70 and 85%.

This range of pore volume can be conveniently corroborated by confined pressurization at greater than

1000 Kg/cm^ (9.8-10^N-m"^) and computation of the

ratio of post-pressurization dimension to pre-pressurization dimension measured in the direction of

s pressurization. It has been determined that direct

measurement of pore volume using mercury intrusion

technique is not appropriate for composites which

are subject to this standard specification.

4.4.2 Pore Size Range. Direct optical examination of

scanning electron photomicrographs of the composite surface prepared by sharp (i.e., fresh scalpel) dissection

of a specimen of composite is recommended for determination of pore size range. The intrinsic softness of the

composite requires care in specimen preparation such

that cutting procedure does not distort and occlude some

- 17 -
of the pores. Inspect before cutting to determine

plane of fibrous orientation. Cut in a direction

parallel to this plane. Such determination should

indicate a pore size range between approximately 80

microns and 400 microns and inter-pore connections of

the order of 100 microns.

Comments on ASTM Standard Specifications

It should be emphasized that both of the above documents are presently

in draft form, and there may be changes in them before they become final.

However, certain contrasts between their approaches to porosity characterization are interesting to note. For the porous composite, no mention is

made of any of the ASTM test methods related to porosity characterization,

whereas the porous polyethylene specification relies heavily on existing

ASTM methods. For the porous composites it is stated that the mercury

intrusion technique is "not appropriate". As we have discussed above,

previous statements by Homsy indicated his belief that the composite

material is too soft and compressible for mercury intrusion, even at

the very low pressures required to measure pore sizes of 80 - 400 urn.

No mention is made of ANSI/ASTM E562-76, "Determining Volume Fraction

by Systematic Manual Point Counting". Paragraph 1.5 of that document

states that "In case of dispute involving other manual approaches or

techniques for estimating volume fraction of a second phase or constituent

[e.g., the void volume in a porous solid ] the point counting practice

described herein shall be the reference method". The "confined

pressuri zation" method mentioned above for measuring void volume in

-1G-
the composite is not well defined, but neither is the void volume (70-85i£)

very precisely specified, so that the method is perhaps appropriate to

the desired precision. Similarly, the broad range of pore sizes given

for the composite seems to imply that the authors feel that the pore

sizes are not critical to surgical implant applications. It is very

difficult to understand how these paragraphs for the composite can be

considered part of a Standard Specification because no attempt is made

to relate specified pore size to any particular implant application.

By contrast, for the porous polyethylene the ASTM methods suggested

for characterizing both pore size and pore volume are carefully written

with respect to the recommended procedures, apparatus, and statistical

analysis of error. Also, the authors of the latter document recognize

that the pore size must be specified for each particular device, and

o that simply stating a wide range of "acceptable" pore sizes does not

specify anything.

Porosity Measurements Described in Published Literature

A computer search of existing literature was performed to

determine (1) whether new methods of determining porosity are being

developed which could be applicable to the porous polymer implant

materials, and (2) to what extent the current porous implant

materials are being monitored either by the users or by independent

testing laboratories , with respect to their porosity characteristics

.

- 19 -
(1) Current Research in Porosity Measurement

A computer search of chemical and physical abstracts for the years

1972-present using the key words "Porosity Measurement", evoked 42

references. There were no specific references to implant materials,

and none that seem to offer promise of improving the accuracy of measurements of pore size or pore volume relative to current methods. The

term "porosity" is applied to such industrially important properties as

the integrity of film coatings and the flow properties of packed beds

consisting of metal ores, ion exchange resins, coal, cement, etc. As a

group, these references are concerned with operational definitions of

porosity suitable to industrial processing or quality control, rather

than to quantitative pore size or volume measurements. It is apparent

that for quantitative porosity characterization of the implant materials

. we will have to. rely upon established techniques such as ASTM methods,

or invent new methods which are suitable for each particular material.

(2) Published References to Porosity Characterization

In the early studies of porous ceramic implants, relating pore

size to the type of tissue ingrowth^, three types of measurements were

used to characterize the porosity. The void volume was measured by

"Archimedes density", which is presumably equivalent to apparent density,

and by the "Point Count" method, which is not further described but

presumably refers to the Optical Point Count method as described, for

example, in ANSI/ASTM E562-76. The pore size distribution was determined by mercury intrusion porosimetry. These methods of characterization are also being used by some workers to measure pore size and

- 20 -
volume in polymeric materials, even though some of the methods which

work well for hard materials may be less than ideal when applied to

relatively soft and flexible polymers.

As previously mentioned, Dr. Homsy is convinced that mercury

porosimetry cannot be used to measure pore size distributions in the

PTFE-carbon composite, because of possible pressure distortion of the

1

4

pores. In a recent published exchange, Homsy is critical of Spector

1 5 et al . for using both mercury porosimetry and optical techniques to

characterize the porosity of the composite material, and he quotes two

23 "authorities 1 ' to prove his case. Spector's reply defends his own

use of "conventional" techniques and also defends his own experimental

results, which disagree with Homsy 1 s "independent laboratory". The

di screpancy. between the interconnecting pore sizes claimed by T:he two

authors is quite large (50 ym vs. a minimum of 200 yi?)and it is difficult

at first to understand how two laboratories using the same techniques

could disagree so much. Yet, examination of Fig. 1 could lead one to

wonder whether the very definition of a "pore" in such a complex matrix

may be subject to debate. This point must be resolved before meaningful

pore size measurements can be made.

We have examined many papers describing clinical trials of porous

polymeric implants, but we have not as yet discovered any other studies

of these materials in which the authors attempt either to measure the

pore size or to correlate pore size with in vivo performance. Most

authors, if they mention porosity at all, simply state the porosity

information provided by the manufacturers. This is perhaps not

surprising, because surgical clinicians who use the materials are not

- 21 -
likely to be expert in the use of physical methods of porosity characterization. It would seem that the clinicians are heavily dependent

on the manufacturers to provide materials suitable for their intended

implant applications.

CLINICAL STUDIES OF OSSICULAR REPLACEMENT PROSTHESES

PTFE - Carbon Composite

The first published reference to the use of the PTFE-carbon compo24 site in middle ear surgery appeared in 1974 . Dr. Shea, a co-author of

this paper, is a surgeon who has also designed and worked with PHDPE

ossicular prostheses, as discussed below. Reference 24 describes the

use of a total ossicular replacement prosthesis in humans and states

that animal studies "are now underway to determine the effect on the

inner ear of a Proplast as an oval window seal". The results of this

25 latter study, which were encouraging, appeared in 1977. Pictures

are shown in reference 24 of the ossicular prosthesis, which consists

of a rod of solid PTFE with a small pad of the composite attached at

each end for tissue ingrowth. As of the date of the publication,

none of the first 23 such prosthesis implanted had been extruded

(rejected) which, according to the authors, "is not true of any other

26 artificial columella prostheses". In a later publication, Janeke

and Shea report that of 33 patients receiving this ossicular replacement none had been extruded over a 24 month period, " by which

time most implants would have been extruded if they had been

- 22 -
Teflon or Silastic....". Clearly, the initial results were encouraging,

but the authors caution that more time for postoperative followup was

needed to properly assess the material.

Despite the encouraging outlook for the composite prostheses, we

have not found many further references to the use of the composite material

in middle ear surgery. Recent references, as described in the following

section, appear to be mostly concerned with the PHDPE prostheses.

Porous High Density Polyethylene

As discussed previously in this report, we have received catalogs

and extensive references to clinical uses of PHDPE ossicular implants.

This bibliography (pp. 12-14) includes manv references which we have not,

as of this writing, had the chance to examine. One which has just been

27 received is a good review article about the use of many kinds of biomaterials in head and neck surgery. We will continue our study of this

literature in hope of obtaining more information about PHDPE prostheses,

and we will be especially watchful for any studies which may specifically relate the porosity of the material to the eventual success or

failure of the implants.

Comments of Dr. Shea excerpted from two of the references provided

by the manufacturer of PHDPE prostheses (refs. 58 and 60, p . 1 3) provide

a brief glimpse at his experiences with this material. In ref 58, he

states that " the Plasti-Pore Total Ossicular Replacement Prosthesis

[is] superior to the total ossicular replacement made of Proplast and

Teflon previously reported and all other natural or synthetic columellas."

- 23 -
In ref. 60 he goes on to state that the PHDPE prosthesis " has

the advantage of being slightly flexible and compressible compared

to the rigid Teflon strut used in combination with Proplast."

Other authors have commented that the PHDPE material, due to

its small pore size (Fig. 2), does not allow as much tissue ingrowth

as might be desirable. Clearly, the problem is complex and involves

a great deal more than consideration of pore size and pore volume

alone. A very important first step in understanding the behavior

of these materials, however, will be to establish a meaningful

system of pore characterization.

t

SUMMARY

Although our search of existing literature is not complete,

we have examined a large number of representative examples of recent

literature pertaining to porous polymeric implant materials. Certain

generalizations may be drawn from this study, which will be helpful

in guiding our future efforts, namely:

(1) The success or failure of a tissue-inviting porous implant is,

as expected, apparently dependent on many factors other than the

"porosity" of the material.

- 24-
(2) Although porosity is certainly an important property of these

materials it is impossible at the present time to relate the successor failure of a porous implant to the dimensions of the pores. This

is because there is no general agreement about how to measure the

pore dimensions. Not only do different methods probably give different

results, but there is no assurance at present that different workers are

getting the same results using the same method.

(3)

. Surgical clinicians do not, as a general rule, bother to check the

porosity or other physical properties of their materials. They are

thus totally dependent on the manufacturer for information about the

materials and their suitability for implant applications.

(4) The morphologies of the porous polymer material s„ in particular

the PTFE - carbon composite, suggest that it will be difficult to devise

a rational working definition of a "pore" which will be necessary for

applying some of the quantitative measurement techniques currently in

use (e.g., optical line intercept).

In conclusion, there is clearly a need to devise a rational protocol for quantitative comparison of the porosity of porous implant

materials

.

- 25 -
REFERENCES

1. Klawitter, J. J. and Hulbert, S. F. , "Application of Porous Ceramics

for the Attachment of Load Bearing Internal Orthopedic Applications".

J. Biomed. Mater. Res. Symposium No. 2 (Part 1), 161-229 (1971).

2. Struthers, A. M. Plastic Reconstr. Surg. _1_5 (1 955).

3. White, R. A., Lawrence, R. S., Hirose, F. M. , Nelson, R. J.,

Transactions of the 5th Annual Meeting, Society for Biomaterials,

Clemson, South Carolina, April 1979.

4. Homsy, C. A., "Implantable Material and Appliances and Method of

Stabilizing Body Implants", U. S. Patent No. 3,992,725, Nov. 23,

1976.

5. Wright Manufacturing Co., P. 0. Box 100, Arlington, TN. 38002.

6. Glasrock Products, Inc., Porex Division, Fairburn, GA. 3021 3.

7. Richard's Manufacturing Co., Inc., Memphis, TN. 38116.

8. Spector, M. , Michno, M. J., Smarook, W. H., and Kwiatkowski, G. T.

J. Biomed. Mater. Res. T2, 665-677 (1978).

9. Ballintyn, *N. J. and Spector, M. , Biomater. Med. Dev., Art. Org. _7(1 ) ? 23-29 (1979).

10. Goodyear Tire and Rubber Co., Akron, OH.

11. MDX-4 4210, Dow Corning Corp., Midland, MI.

12. White, R. A., White, E. W. and Nelson, R. J., Biomater., Med. Dev.

Art. Org. 70), 127-1 32 (1979).

13. Hiratzka, L. F. , Gocken, J. A., White, R. A., Wright, C. B., Arch.

Surg. (in press)

14. Homsy, C. A., J. Biomed. Mater. Res. J_3, 987-990 (.1979).

15. Spector, M. , Harmon, S. L. and Kreutner, A., J. Biomed. Mater. Res.

13, 677-692 (1979).

16. Arem, A. J. and Madden, J. W., Plastic Reconstr. Surg. 5J3, 580-

536 (1976)

17. Skinner, H. B., Shakelford, J. F. , Lin, H.-J., and Cutler, A. D.

,

Biomat., Med. Dev., Art. Org. _7 ( 1 ) , 1 33-1 39 (1979).

- 26 -
18. " PI asti- Pore Material Technical Information", Technical Publication

No. 4240, 1980.

19. "Materials for Otologic and Microsurgical Implants", Technical

Publication No. 4232, 1980.

20. "A Scanning Electron Microscope Study of Otologic Implants",

Technical Publication No. 4216, 1980.

21. Plasti-Pore Implants, Advertising Brochure No. 3187 (Rev. 12/78).

22. Tilt-Top T0RP Prosthesis (All Plasti-Pore Material and Polyethylene

Shaft), Catalog pp. 34.13 and 34.14 (1979).

23. Spector, M. , J. Biomed. Mater. Res. J_3, 991 (1979).

24. Shea, J. J. and Homsy, C. A., Laryngoscope 84, 1835-1845 (1974).

25. Mischke, R. E. , Hyams, V., Shea, J. J. and Gross, C. W., Arch.

Otolaryngol. 103 , 489-492 (1977).

26. Janeke, J. B. and Shea, J. J., South African Med. J., 50_, 781-783

(1976).

27. Griffiths, M.*V., "Review-Biomaterials in Reconstructuve Head

and Neck Surgery", Clin. Otolaryngol, 4, 363-376 (1979).
APPENDIX I

Letter from Dr. C. A. Homsy to Dr. J. M. Cassel concerning Mercury Intrusion

Porosimetry

.

28
THE METHODIST HOSPITAL texas medical center

6516 BERTNER • HOUSTON, TEXAS 77030 • (713) 790-3311 • CABLE: METHHOSP

7 January 1980

James M. Cassel, Chief

Dental and Medical Materials

Polymer Science and Standards Division

U.S. Department of Commerce

National Bureau of Standards

Washington, D.C. 20234

Dear Mr. Cassel :

Thank you for your letter of December 27th. I am sure that the Dow

Corning Corporation who market Proplast® implant material can provide you

with a block specimen. The 40 mm x 60 mm x 8 mm dimensions which you

mention, is, in fact, a commercially available size. Incidentally, because

of the way in which the materia-1 is manufactured, the 40 mm x 60 mm faces of

such a block, have a somewhat reduced surface porosity. Since the blocks are intended to be carved into finished shapes by the surgeon, this characteristic is not clinically significant but may bear on possible porosity measurement of an uncarved block.

Also, we have, in the past, discussed the potential usefulness of mercury

intrusion porosimetry in studying the porosity of a material such as Proplast

with American Instrument Company. Mr. Samuel Greenberg of that company wrote

to us that the data obtainable using the porosimeter with resilient materials

would be suspect since the applied pressure would distort and compress the

normal structure of the pores.

In addition, we have discussed the use of mercury porosimeter with Hillar

M. Rootare who has written extensively on mercury porosimetry and is now employed

by MicroMeritics Instruments Corporation, 5680 Goshen Springs Road, Norcross,

Georgia 30093. Dr. Rootare also did not encourage the usefulness of the standard mercury porosimeter for characterizing relatively soft materials such as Proplast implant material. Additional information on this subject is contained

in a recent communication to the Journal of Biomedical Materials Research from

us, a copy of which is enclosed. Best wishes for the New Year.

i nr* av»al \/

Charles A. Homsy, Sc.D., Director

Prosthesis Research Laboratory

Fondren Orthopedic Center

CAH/klw

Enclosure
APPENDIX II

Catalog and Price List of PTFE-Carbon Composite Implant Materials from

Dow Corning Wright Corporation.

30
Proplast® Surgical Implants

Supplied Non-Sterile

Description

Sheeting

30mm x 40mm

(2 Pieces)

30mm x 40mm

(2 Pieces)

Thin Sheeting

15mm x 15mm

(10 Ea. Per Box)

15mm x 15mm

(10 Ea. Per Box)

15mm x 15mm

(10 Ea. Per Box)

15mm x 15mm

(10 Ea. Per Box)

Sheeting wlporous Teflon®

30mm x 40mm, White/Black

(2 Pieces)

0 5mm WHITE TEFLON' .

30mm x 40mm, White/Black

(2 Pieces)

30mm x 40mm, White/Black

(2 Pieces)

Sheeting w/non-porous

Teflon®

30mm x 40mm

(2 Pieces)

30mm x 40mm

(2 Pieces)

30mm x 40mm

(2 Pieces)

30mm x 40mm

(3 Pieces)

0 2mm CLEAR TEFLON®

Sheeting w/silicone

elastomer

30mm x 40mm

(2 Pieces)

0 2mm CLEAR SILICONE

Teflon* It t registered trademark of the OuPont Company.

Quantity Size Cat. No Price

1 box 1 0mm P 91 1 90 $36.00

1 box 2.0mm P 911.91 $78.00

1 box 0.35mm P 911.86 $91.50

1 box 0.65mm P 911.87 $91.50

1 box 0.80mm P 911.88 $91.50

i box 1.00mm P 911.89 $91.50

i box 1 5mm P 911.95 *$118.00

1 box 2.5mm P 911 96 $157.00

1 box 4 5mm P 911 97 $234.00

1 box 1 2mm P 911.94 $ 51.00

1 box 2.2mm P 911.92 $ 87.00

1 box 3.2mm P 911.93 $129.00

1 set 1.2mm, 2.2mm,

& 3.2mm P 911.99 $133.00

1 box 1 2mm P 911.98 $51.00

31
Proplast9 Surgical Implants

Supplied Non-Sterile

Description

Diagrams Are NOT Actual Size

Propiast9 Block,

Small Facial

15mm x 40mm

1 5mm x 40mm

15mm x 40mm

Propiast9 Block,

Large Facial

40mm x 60mm

40mm x 60mm

40mm x 60mm

Propiast9 Block, Oval

15mm x 40mm

15mm x 40mm

15mm x 40mm

Propiast9 Ridge, Total “U" Shaped

"U" Shaped

"U"

Propiast

Shaped

9 Ridge,

A

Posterior

10mm x 40mm

(2 Pieces)

10mm x 40mm

(2 Pieces)

10mm x 40mm

(2 Pieces)

Quantity Size Cat. No

Suggested

Price

1 box 6mm* P 911 26 $58.00

1 box 8mm* P 91 1 28 $78.00

1 box 10mm* P 91 1 30 $96.00

1 box 6mm* P 91 1 46 $216.00

1 box 8mm* P 91 1 48 $293.00

1 box 10mm* P 91 1.50 $362.00

i box 6mm* P 911.76 $51.00

1 box 8mm* P 91 1.78 # $67.00

1 box • 10mm* P 911.80 $82.50

1 box 6mm* P 91 1 06 $142.00

1 box 8mm* P 911.08 $180.00

1 box 10mm* P 911.10 $225.50

1 box 6mm* P 911.05 $ 78.00

1 box 8mm* P 911 07 $103.00

1 box 10mm* P 911 09 $129.00

32
Proplast® Surgical Implants

Supplied Non-Sterile

Description

Quantity Size Cat No Price

Proplast® Stabilized TMJ

Prosthesis/TMC

Flat Shank i Prosthesis/TMC Flat Shank ""1r T 1 box 40mm P 912.22 $172.00

Proplast® Stabilized TMJ

Prosthesis/TMCK a

t

1 box 47mm P 912.24 $196.00

Box Shank

Prosthesis/TMCK 8ox Shank '"."'i1

: 1

'

1 box 40mm P 912.23 $172.00

Bone Screws actual size aaj 1 box 47mm P 912.25 $196.00

(4 ea.)

• " lliTTD 1 box *8. 0mm P 912.26 $30.00

Screw Driver - "T a ,

•*> _ .,/

1 box *1 1 0mm P 912.28 $36.00

TMJ Template (Kent Design) *— 1 box P 912.35 $98.00

1 box P 912.40 $86.00

•Length measured medially from lateral cortex of mandible

Proplast® Chin

Kent Design

Dimensions (mm)

-A M A S s 6mm 48 6 ^

8mm 54 8 10mm 60 10

Qty. Description Cat. Suggested

No. Resale Price

1 box 6mm P 91 1 66 $121.00

1 box 8mm P 91 1 68 $130.00

1 box 10mm P 91 1 70 $147.00

i box sizers H P Silicone

set of 3 P 911 65 $ 77.00

Proplast* Malar

Kent Design

Dimensions (mm) h-—A i^ F A B %

6mm 40 6 "

. 10mm 40 10

1 box 6mm P 91 1.62 $108.00

1 box 10mm P 91 1 64 $121.00

33
APPENDIX III

Letter from Dr. R. E. Dehl to Dr. C. A. Homsy soliciting opinions about

Critical Porosity Parameters.

34
November 9, 1979

Dr. Charles Horasy

Methodist Hospital

Fonderan Orthopedic Center

Houston , Texas 77030

Dear Dr. Homsy:

The Bureau of Medical Devices (FDA) has requested our assistance In

developing methods for characterizing and specifying the porosity of

porous Implant materials. Your name was suggested to us by H. R.

Sauberman at the BMD t as one who is quite knowledgeable about the

clinical applications of such materials. We have read about some of

your work in this area (e.g. Shea and Homsy, Laryngoscope, 1974),

and we would very much like to solicit your opinion about the critical

parameters of poroxity which need to be specified.

In particular, we are concerned about the following questions:

(1) Is the total void volume useful as a parameter for intercoiapa risen of porous materials?

(2) Is there a “critical " range of pore diameters and lengths for

optimum tissue ingrowth?

(3) What role do “thrupores 1* play in the tissue ingrowth process and

would it be desirable to measure their contribution to the total void?

(4) Do you think that surgical procedures currently in use affect the

tissue ingrowth process by changing the surface porosity?

(5) Are there any other aspects of porosity characterization which you

feel should be specified?

We would appreciate any reprints or other information which you can

supply us that have a bearing on this problem. Thank you in advance

for any assistance that you can provide.

Sincerely yours.

Ronald E. Dehl

Dental and Medical Materials

Polymer Science and Standards Division

Phone (301) 921-3336

35
APPENDIX IV

Response of Dr. Homsy to letter from Dr. Dehl.

36
THE METHODIST HOSPITAL texas medical center

6516 BERTNER • HOUSTON, TEXAS 77030 • (713) 790-3311 • CABLE: METHHOSP

15 November 1979

Mr. Ronald E. Dehl

Dental and Medical Materials

Polymer Sciences and Standards Division

National Bureau of Standards

Washington, D.C. 20234

Dear Mr. Dehl,

Thank you for your letter of November 9th in which you requested an opinion concerning critical parameters of porosity for porous implant

materials. In response to your questions respectively, I can provide the

following comments:

(1) The total void volume is useful as a parameter for inter-comparison

of porous materials because it is a direct measure of the relationship between

ingrown tissue volume and implant volume. Generally, it is desirable to maximize the ratio of ingrown tissue volume to implant volume since this would

naturally tend to make more normal the three dimensional tissue structure

within the implant material. The usual objective in application of porous

implant material is to develop healthy tissue within the pore volume inherent to the implant material; as, for example, in maxillofacial surgery where

soft tissue profile restoration is the objective. This is not to say, however,

that the useful range of total void volume is narrow. Total void volume greater

than about 50% to 60% will probably be effective in entertaining and maintaining tissue ingrowth; however, other things being equal , the larger the total

void volume, the better.

(2) The literature generally shows that there is a minimum pore size

below which tissue ingrowth is seriously inhibited. This is generally reported

to be in the range of 30 to 50 micra. Naturally, the larger the pores and the

interpore connections, the easier it is for tissue to develop within the porosity.

Practical upper limits to pore diameter and pore volume are usually dictated by

the mechanical requirements to be placed on the porous implant material in a given application. Generally, in the development of the PTFE/graphite porous

material (Proplast®), here in our Laboratory, we were guided by the belief that

the larger the pore volume, pore diameters, and interpore connections, the

better. Also, we have maintained that the mechanical characteristics of a porous implant material should more closely approximate soft tissue than hard

tissue when some relative motion may be expected between surrounding tissue

and the implant. This specification minimizes interfacial stress on ingrowth

tissue and also allows physiological physical forces to be sustained by the

ingrown tissue.

37
Mr. Ronald E. Dehl - 2 - 15 November 1979

(3) I do not understand the meaning of "thru pores." If you mean a pore which passes completely through the implant material, then I think if

these were large enough in diameter ( >100/40, ingrowth rates would be

enhanced. However, the ratio of "thru pores" to micro-porosity within the

matrix of the material could be quite high and yet tissue ingrowth (and effective coupling between the implant and surrounding tissue) coufd be less than

optimal if the matrix does not effectively entertain tissue ingrowth at the

micro level. Therefore, "thru pores" could play a role in the tissue ingrowth

process but must not be the predominant factor in the total void volume.

(4) Porous implant materials currently in surgical use are either supplied

in the finished shape for implantation or, in the case of the soft varieties

such as Proplast implant material, allow carving by the surgeon to facilitate

specific anatomical requirements. There are two possible ways that surgical

procedures could effect the surface porosity for the latter material: (a) by

manual compression of the material or compression during the carving process;

(b) by maladroit carving procedures using dull instruments. In the case of

Proplast implant material the various surgical procedures for which it is used

require attention to appropriate surgical technique, which as described in the

product literature for the material. The clinical reports on this material

are quite positive and indicate that necessary care in manipulation is not

difficult to exercise.

(5) Early in our experimental work which led to development of the •

* PTFE/carbon composite, we conducted extensive animal implantation studies

with a variety of candidate porous implant materials. One particularly illuminating set of experiments was a direct comparison between two porous materials

of the same pore volume and pore size distribution where one was entirely of

PTFE polymer and the other was a composite of PTFE/graphite fiber such that

the graphite fiber is disposed on the PTFE matrix. The latter materials was. the prototype for what ultimately became available as Proplast implant material.

What was interesting about this experiment was the much more rapid tissue

ingrowth with the composite as compared to the porous polymer. The enclosed

paper published in 1972 describes these findings. We believe there may be two

main reasons for the observed difference in ingrowth rate: the one relating

to the higher surface-free energy exhibited by the composite which is engendered

by the carbon fiber ingredient; the second, the higher specific surface area exhibited by the composite. Both factors can be interpreted as allowing for

more effective cellular adhesion to the matrix and movement of the cells within

the matrix. The cells, specifically fibroblasts, elaborate the collagen matrix

of the ingrowing fibrous tissue.

We have enclosed a selection of reprints which may be helpful in your

examination of the matter of porosity in porous implant materials. Please do

not hesitate to write or call should you have further questions. We are pleased

to be of assistance.

Sincerely,

Homsy, Sc. D. director

Prosthesis Research Laboratory

Fondren Orthopedic Center

CAH/klw

Enel osures

38
APPENDIX V

Letter from Dr. Homsy to Dr. Cassel concerning pore size and pore

volume measurements.

39
THE METHODIST HOSPITAL TEXAS MEDICAL CENTER

6516 BERTNER • HOUSTON. TEXAS 77030 • (713) 790-3311 • CABLE: METHHOSP

15 November 1979

James M. Cassel , Chief

Dental and Medical Materials

Polymer Sciences and Standards Division

National Bureau of Standards

Washington, D.C. 20234

Oear Mr. Cassel

,

Thank you for your letter of November 9th in which you commented on the

draft standard on porous composites of polytetrafl uoroethyl ene and carbon

for surgical implant use. I am copying your letter to Professor K. Piekarski

at the University of Waterloo, Ontario, Canada, who is the Task Force Chairman for porous composites. There was considerable discussion concerning

tradename identification of a specific porous composite for which the standard had been drafted. I agree that it would not be appropriate to specify

a tradename and ’will re-present this point of view at the Task Force meeting in Williamsburg later this month.

The matter of performance criteria for pore characteristics has been a vexing one. The Proplast® composite is soft and almost felt-like. Therefore,

we found mercury intrusion porosimetry to. be inefficient for pore characterization. However, the tensile strength and apparent density parameters in the

standard directly reflect pore volume and character. Specific pore size distribution is controlled by the manufacturing process as disclosed in U.S.

Patent No. 3,992,725 and the specific methodology is set out in detail in

the Manufacturing Product Record for the product as called for under the FDA

Good Manufacturing Practice requirements for critical devices.

We have also used direct optical line intercept techniques of SEMs to

determine pore volume and pore size distribution; however, this is a tedious

and inherently imprecise technique which tends to provide values on the low

side. For example, the Teachable filler used during the manufacturing process

for Proplast material is selected to produce a pore size distribution range

of between 60 and 500 micra and a pore volume of 75-85%. TheJine intercept

technique indicates a pore size range of 80 to 400 micra and a pore volume of

57%.

Generally, the larger the average pore size, the larger the pore interconnections and the greater the pore volume, the more rapidly does tissue

ingrow into biocompatible porous matrices. Proplast was designed to have a very high pore volume and the largest pore sizes and pore size interconnections compatible with mechanical requirements for the various implant functions

for which the material is used. I believe that the end user can readily con- firm through apparent density and tensile strength measurement that the product

40

1 was sick. and ye visited me”—Matt. 25:3
Mr. James M. Cassel 15 November 1979

is conforming to manufacturing specifications with respect to pore characteristics. Of course, underlying the standard specification must be the manu- facturing controls which are monitored by FDA for all critical implant devices.

Thank you very much for your interest in this particular standard. As

you can see, we were keen on developing a true performance standard including

biocompatibility assay with the view that ultimately such performance standards will become de facto regulatory standards and meet the needs of FDA and

the public. Any suggestions for improving the standard are welcomed. If you

will be at the Williamsburg meeting, perhaps we can get together and talk

further

.

Charles A. Homsy, Sc.D., Director

Prosthesis Research Laboratory

Fondren Orthopedic Center

Research Associate Professor

Baylor College of Medicine

CAH/klw

cc: Professor K. Piekarski

USCOMM-NBS-DC

41

NBS-U4A REV. 2-80

U.S. DEPT. C F COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 81-2212

2. Performing Organ. Report No. 3. Publication Date

4. TITLE AND SU8TITLE

Evaluation of Methods for Characteri zing the Porosity of Porous

Polymeric Implant Materials : A Review of the Current Status of

Porosity Measurements

5. AUTHOR(S)

R. E. Dehl, W. H. Grant, and J. M. Cassel

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8 . Type of Report & Period Covered

May 22 - Sept. 30/80

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Bureau of Medical Devices

Food and Drug Administration

Silver Spring, Maryland 20910

10. SUPPLEMENTARY NOTES

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

11. ABSTRACT (A 200-word or less factual summary of most significant information,

bi bliography or literature survey, mention it here)

If document includes a significant

A search of the published literature pertaining to porous polymeric implant

materials has been made. The two porous materials currently dominant in implant

surgery, namely, porous high density polyethylene and a porous composite of polytetrafl uoroethyl ene and carbon, have been reviewed with respect to the following

criteria pertinent to their medical applications: (1) Information supplied by the

manufacturers about their methods of characterizing the porosity of their material s. (2) recommendations of the ASTM for quantitative porosity characteri zation of these

materials, and (3) clinical studies of the materials as replacement prostheses in

middle ear surgery. A computer search for new quantitative methods of measuring

pore size revealed nothing appropriate to these materials. However, disputes in

the current literature suggest that current protocols for porosity characterization

are inadequate for proper interlaboratory comparison of experimental data.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Ossicular prosthesis; porosity measurement; porous biomaterials;

porous polyethylene; PTFE-carbon composite: synthetic implants

13. AVAILABILITY

LXJ Uni tmited

j

j For Official Distribution. Do Not Release co NTIS

| | Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Price
1 .