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Radiation Enhanced Porosity and Roughness of Biomaterials
A. L. Evelyn', M. G. Rodrigues2, D. Ila', R. L. Zimmerman', D. B. Poker3, D. K. Hensley3
'Center For Irradiation of Materials, Alabama A&M University, Normal, AL 35762, USA
2University of Sao Paulo, DFM-FFCLRP, Ribeirdo Preto, SP 14040-901, Brazil
3Oak Ridge National Laboratory, SMAC, Oak Ridge, TN 37831, USA
Glassy Polymeric Carbon (GPC), made from cured phenolic resins, is sufficiently chemically inert
and biocompatible that it is suitable for medical applications, such as heart valves and other
prosthetic devices. We have used energetic ion bombardment of the partially and fully cured
precursor phenolic resins to enhance biological cell/tissue growth on, and to increase tissue
adhesion to, prosthetic devices made from GPC. GPC samples were bombarded with energetic ions
to 10 MeV. The surface topography and increased surface roughness was observed using optical
microscopy and atomic force microscopy (AFM). The increased porosity was measured by
introducing lithium from a molten LiCI salt into the GPC and using (p, a) nuclear reaction analysis
(NRA) to measure the concentration of Li retention in the modified GPC. The NRA measurements
of increased pore availability were correlated with the observations of increased surface roughness.
Glassy Polymeric Carbon (GPC) is made from cured phenolic resins (resol), Fig. L.a, in an inert
environment. After curing at 60*C, Fig. .b, the resin is pyrolyzed at low temperature rates to avoid
changing shape or disruption due to volatile decomposition products (1). Heat treatment to 550 C
produces a conducting material due to hydrogen release and conjugation of the aromatic rings
forming graphene planes in random arrangement (2). For heat treatment at 6500 C, the material still
presents open porosity due to space between the ribbons. Further heat treatment to 1000*C the GPC
pores remain but progressively close, reducing permeability as the graphitic planes aggregate
themselves to form the final structure of the GPC, Fig. l.c, (3). The final GPC structure is as
random graphene planes shown in Fig. 2 and the material appears dark, hard and vitreous. Its
density (1.45) is significantly lower than that of graphite from which one may deduce a relative pore
volume of about 35%.
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Fig. 1: Structures of a) resol, b) the polymer which forms at 130*C and c) a graphene plane as
heat treatment is increased beyond 700*C.
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Evelyn, A.L.; Rodrigues, M.G.; Ila, D.; Zimmerman, R.L.; Poker, D.B. & Hensley, D.K. Radiation Enhanced Porosity and Roughness of Materials, article, April 24, 2000; Tennessee. (digital.library.unt.edu/ark:/67531/metadc724918/m1/2/: accessed December 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.