Note: Descriptions are shown in the official language in which they were submitted.
1 3
rentlon relat~ ~n general ~o proathe~ic devlc:e~
havlng co~lng6 of ~,ole~ ted poro~ hermopl~tlcs, ~h~ch
provide ~n opei~ blomechanicfll cr~v:lrcn~ent for fi~tion of
devlce~ by ~ bone in~ro~ch ~ech~nl~m. In one aBpect~ this
~nvention rel~te~ ~o the ~lse of cert~in l~termedlat~ ~odul~ls
the~opl~6elc~ ~nd fiber reinf~rced thermopl~tic6 ~
porous co~t~ng~ foa: region~ of pro~thee~ c device~ where
los~g-term ~one fixation 16 de~ired by t~ue ingrowth. In
a fureher ~pec:t, hi6 invention 1~ directed to ~ proces6
10 for co~ting pro6thetic devices with ~elected pOrou bio~
engine ering the r~nop l ~ 6 ti c ma ~ e rl~ 16 .
~ rior to ~he pre~en~ i nventisn v~rious method~ h~ve
b~n di6closed in the liter~turc for the att~chment of
pro~hetic devices ts sehe musculo~keletal By~tem, The~e
methods can be catcgorized as lnvolvlng: 1) impaction;
2) nails snd 6crews; 3) cemene; ~nd 4j porou~ ~urf~ce
~naterials. The u~e of porous ~urface lmpl~nes for flxatlon
has been recognized ~s po~entially providlng 6igrlifican~
advantage~, however; thi~ technlque ha~ no~ been accepted
~0 by ~he ~rgic~l co~uni~cy ~ec~u~e of problems of early
f~ation and long l:erm stabill~y ~6socis~ed wlth prior ~rt
device~a Prl~r art lnventlons ~nclude lJ. S~ :Patent 2~o~
39986,212 which ~sued October 19, 1976 to B. W, S~uer
de~cr~bing '~mpro~ed"compo~lc~ prosthetic devices con~$n-
~ng ~ porou6 polymeric coatlng for bone f~xaeion by ~ ue
~ngrowth, The porous polyme-lc maeerl.qls which ~re lndieated
to be useful are ~:ho6e having ~ ~peeifie& den6icy and lsleer-
connec~ced pore~ o4 ~I Bpel:if:LC sverage pore dl~meeer. Among
ehe poly~neric maeerial~ di6closed are hlgh den~ley pcly
30 eEhylene ~nd polypropylene o- ~ix~ure~ ~hereof hav~ng
ce2 'C~iD cr:l~ica'l par~eter~ . It 1~ al~o ind~ c~ed t~
1~ ,313
the c~.qting~ c~n be ~ech~nlo~lly ineerlocl~ed or che~n:Lcally
}~n~d ~ ~h~ ~c~. .
U. 5~ P~tent 3~571,134 whlch i~suPd July ~7, 1976 eO
J. Cu ESokro~ rel~ee~ to a deneal pro~,the61~ or pe~nene
or pro~onged lmpl~rleation lr~ ~ J ~w~)one of a llving body .
Ihe l~plant c~n be co~ted with ~,uch ~Laeesl~l~ lil6 vlnyl poly-
~er~ " ~c~l~c poly~ers, polyethylesle ~nd c~rbon fiber
fillet3 Teflon.
J. G~l~nte, et ~1, in J. l~one ancl Joine Surgery, 53A,
No. 1,101 ~lg71) de~crlbe6 ~intered flber meeal compo6ite6
B5 a ba~i~, f3r ~ttarhr~ nt of impl ar t8 to bone and U, S .
Paeent 39808,6~ whieh i~ued on M~y 7~ 1974 to R~ymond G.
Tronæo de6crlbe~ ~t~inle~s ~teel ~nd cobalt~chror~um-mslybde-
nu~ ~lloy pros~che5i6 po~sesslng porou~ ~urface~ or fixstion
by ~ ue lngrow~h.
Al~o, o general intere~ are 1~. S. P tent~ 3,992,725
'Implane~ble Material ~nd Applian e~ ~nd Method of Stabillz-
~ng Body Implan~s", wh~ch 1~6ued on ~ovember 23, 1976 to
C, A. l~omsy~ U. 5, 3,909~852 "ImFlant~ble Sub6til:ute Structure
~0 for ~e IR~S~ Part of ehe Middle Ear Bony Ch~ " which issued
October 7, 1975 to C. A. Hom~y, asld UO S~ 3,971,670 "Im-
plsn~ble Str~aceure ~n~ MP~hod Bf aSaklng SELme" w~ ch l~ued
3uly 27 9 lg76 ~o C . A. ~om~y.
In addi~ion to p~tent~ 3 v~riou~ artloles h~ve appeared
in ~he 3 iterature relatin~ l:o bone ingrowth into porous
msterial~, Typlcal ~r~:icle~ ~nclude, ~n~ong oeher~, S. F.
~3u~bert, "Att~chment of Pros~he~e~ ~o ~he 2~usoulo6kele~al
Sy~ce~D by T1l56Ue Ingrowth and Mech~nic~l In~erlockirlg"~
J. Biomed. Plate2.~ }~e50 S~lpo6i~, 4, 1 (1973~ p~ctor,
30 et ~1, "BQne Gro~th ln~o ~orou~ High-~n6ity Polyethylenel',
30 Blomed~ M6ter. Re~. Sympo~i~, 7, 595 ~1976); C~ omsy
l-L,313
~ t~ ~ ~
"1mplant Stabilization - Chemical and Biochernical Considera-
tions", Orthopedic Clinics of North Americ~, 4, No. 2,295
(1973) and J. ~. ICent, e-t al, "Proplast in Dental Facial
Reconstruction", ()ral Surgery, Oral ~edicine~ Oral Pa~hology,
39, No. 3, 347 (1975).
However, the porous materials disclosed ln t~e 1itera-
ture as being useful for prosthetic clevices provide inappro-
priate biomechanical environments leading to elther of two
wndesirable situations. Yirst, low modu]us-high creep porous
coatings such as porous *Teflon/graphite composites, exhibit
metastable fibrous -tissues in the pores after extended periods.
This tissue is not suited -to support load bearing joint pros-
theses. The fibrous tissue is a metastable precursor to bone
and under normal physiological conditions (including physio-
logical loading conditions) would remodel to bone. The high
loads transmitted through low modulus materials and the excess
creep result in fibrous tissue which fail to remodel to bone.
Other low modulus-high creep ma-terials employed for prosthetic
devices include polyethylenes and polypropylene.
Secondly, high modulus materials such as ceramics (16 x
106 psi) and metals like titanium (17 x 106 psl) and cobalt-
chromium~molybdenum alloy ~34 x 106psi), do not spread suffi-
cient load to the ingrown or surrounding bone to prevent
resorption. In porous metal and ceramic coated femoral and
humeral stems, load is concentrated at the apex of these
prosthetic components causing stress concentrations in the
surrounding bone and subse~uent resorption. In addition,
the bone spicules in the pores of these porous ceramic and
metallic implants do not experience loads, thereby resorbing.
*Trademark
--3--
~ li,3l3
The loss o~: borle ~ro[n the pores in areas of por()us imylantc;
which experience no load has been demonstrated histologicall.y.
This type of bone loss leads to a decrease in composlte
strength (e.g. interfacial shear strength~ and a subsequent
decrease in "in ~Ise'' performance in these high modul~s
porous materials.
The above-cited patents and literature describe t'he
use of porous coatings on pros-theses and describe acceptab'Le
pore size range requi.rements. However, it has been found
that metals, ceramics and polymers sllch as the vinyl polymers,
polyethylene, polypropylene, carbon filled *Teflon and others
disclosed as being useful. for coating prosthe-tic devices do
not establish the proper biomechanical. enviromnent to achi.eve
appropriate early fixation, long-term sta'billty and strength
at the bone-prosthes:is interface. Previ.ously described poly-
meric materials can also lack the toughness, creep resistance
tensile and impact strength and steam sterilizability -to be
acceptable as the polymer of choice for coating prosthetic
devices. Even select high density polyethylene and polypro-
pylene porous compositions~ sta-ted to possess the right amount
of flexibility and strength i.n ~. S~ Patent 3,986,212 are
deficient as will be.discussed be]ow.
The bone ingrowth in porous orthopedic implants can
be considered as a two stage phenomenon. Each s-tage is
i.nfluenced by the pore characteristics and biomechanical
characteristics of the implant. In the first stage and
immediately after implan-ta-tion the porous component fills
with a blood clot which subsequently becomes ~'organized".
Fibroblasts appear in the clot region and fibrogenesis
occurs. The clot is replaced by loose connec-tive tissue
~Trademark
--4--
~ a 11,31~
ancl capillaries. At this point preosteob:lasts begin to
appear in the peripheral pores of implant. These cells can
become osteoblasts or chondroblasts depending upon the
environment. If the original pore size of the implant is
too small or if the pore structure 'has been distorted by
the initial applied loads as will occur with *Teflon, high
density polyet'hylene and polypropylene porous materia'ls,
one or rnore of the above sequence of events car- be in-
terrupted. For example, it is generally believed that
a smaller pore size (~90~) 1eads to the ultimate for~lation
of fibrous tissue, not bone, in the implant. If the
modulus of the materia'L is too low, micromotion occurs
with loading. This would lead to an environment tha-t is
conducive to fibrous or cartilage tissue, not bone, formation.
For example, excessive motion can lead -to disruption of
vascularity and a decrease in oxygen, a condition which
favors cartilage formation.
After bone has filled the pores of the implant, in the
second stage it undergoes remodeling which is influenced
prim~rily by its biomechanical environment~ Spicules in the
implant which experience uniform stress will thicken while
those spicules which experience no stress or excessive stress
(stress concentration) are resorbed. The modulus of metals
and ceramics is so high that the implants do not deform under
the applied loads. The bone spicules in these porous im-
plants thus do not experience sufficient load to thicken.
Bone trabeculae in these higher modulus porous materials
tend to resorb, becoming thinner than the spicules in the
porous implants which are the subJect of this invention.
The above discussion indicates that the biomechanical
environmen-t established by the implant material and the
geometry of the porous substrate have a profound effect on
the biological fate of implants. I-t has now been found
~Trademark -5
~1, 313
~hae cereain ther~Doplastics, here~ter described AS a class
as bioengineering ther~Doplast:Lc~, provide the delicate balance
whlch rnu6t be schieved between para.r~eters affec~ing lo~d trans~
miss~on, ~n:Lcro mo~ion, dimention~l ~tability, Bnd ~trengthO
Bioengineer~ng thermoplastics, us~ally prepared by conder)sat:icn
poly~slerizations ~ ~lso show low metal contamlnation levels
(io e., I,ow tr~nsl~ior- snetal catalysts levels)
and exllibit e~cellent ch~r~cterlstics in biotoxlci~y 6tudies
~uch a6 ~he U0 S, Ph~rmacopi~ ClaBS VI St~nd~rd6. ~ey
10 represent an up~i~ ma~eriAl~ c~tegory for or~hopedic,
dental and ma~illof~cial ~pplications. The tran~ sion
of ~tre~s to b~one in the pore~ of bloengineerin~ thermo-
~l~s6~ic~ mimic~ ~he phy~iologic~1 b~omecharlical emriron-
men~ ~ evi deneed by ~he replication of th~ norm~ one
repair proce~e~. Bone 1~ porous bioengineerlng thermo-
pla~tlc ~mplant remL)delled ~fter a cl~nically appropriace
per~ od to r2'fl ect the rn~gn1tude ~s~d direction of the pre-
~alling ~tres~e~ the ~ tt)mlcal ~l~e. Thi~ occurrence
per~it~ ~e lngrown ~one 'co be a ~tructur~lly eficlent
20 ~ember for ghe lo,sd envlronmen~ ts:) whlch a pro~the~
~ub~ ec ~ d,
It t~, therefore, an ob,~ec~ of the inventlon to pro-
~ide ~fficaciou~ prosthetic device~ cc>mpri3ed of sn inner
lo~d bearin~ functlonal componen~ and ~ outer foa~e~ or
~ tPred porou~ co~e~ng over at leA~ 8 p~r~lon ~hereof,
of seleel~ed ~ic~engineertng ~hermopla6eic~, ~no~her ob~ ec~
0 f ~rli6 invent~os~ o proYide co~ted pro6~heeic devices
which sf~r ~plan~ion achieve & long~term bone fixa~lon
by ~nE;ro~th of ~ 9 into and through ~ ~lee~ porous
30 bioen~:LDeer~ng ~her~pl ~tlc coating ~h ~ubsequen~
. 6
7t~ , 313
rams:idell~ng to ~ozle . A further ob~ ec t ~.~ to provide
proae}l~tle deY~ce h~ving ~ coating of a apeciied poro~ity
~hich provide~ the opti~ ub~t:raee for ~ Bue ingrow~h,
Aslother ob~ec~ o provide pro~the~ic de~rice~ reln ~he
c~e~ng ~xhlbie8 ~u~flclene tor ~ile and 1mPACt ~tren~th
during ~nd ~~:er bone form~tion to ~ccoc~od~ee ~pplied loeds
durlng ln~ertion ~nd ~Isfter ~urgery. ~ f~rther ob~ect i~ to
prov.Lde co~ted pro6thetic device~ whlch can und~rgo &tC~2
at~rlliz~tion wlthout a~er~e ~fecta on ~he co~ing. A
' 10 ~111 f u -ther ob.~ect of thl~ lnvent~on 1~ to pro~de An~o~-
ically ~haped porou~ ~tructures of select bioenglneering
chermopls6l:lcs which are u~eful for reconatruct:ive procedure6.
Asloeher ob~ec~ of 'chl~ invent~on 16 ~:o pravlde porou~ bio-
engineerlng thermopla~tic coating~ ~r senlct:ures coneaisling
~d~ es fc~r enhancemen~ of ~chelr biological arld/or mech-
~nical propertie~. A fur~her ob~ ec~ of ~:hl6 lnventl~n 16
~o pro~ide porou~ bioengineering ~her~Dopl~eic coa~lngs
or ~tnuc~ures containing ~ddi~ive~ for lncreasing wear and
~bra~ion resistance. ~no~her ob~ect i6 to pro~de one or
~ore proces~es for preparing coated prosthe~lc tevices or
~natom~cally ~haped ~tructures eompo~ed of bioengineerln~
then~opls~tlc6~ The importa~ce of the~e ~nd other ob~ec~
will readily become Qpparent to eho6e &killed ~n ;he art ln
~he ligh~ of ~he ~eachlng~ herein ~e~ fortn.
1~ it~ br~ad ~pece ehe pre~ent in~en~ion is direc~ed
to pro~hetic dev~ce6 compri~ed o or coated wieh porous
bioengineerlng thermopla~tic materi~ lch en~bles ~uch
de~ice~ ~o becom~ firmly ~nd perm2ne~ly ~nehored into ~he
mu~culoskel~tal ~y~tem by ti66ue ~ngrcw~h iD~o ~he coaeed
~terl~l.. In one embodiment ehe pro~thetic ~ev~ce~ are
c~prl~ed o ~ loat be~rlng funct~on~l com~onent ~nd o~er
~ 7 -
ï1,313
~e l~a~e ~ por~ion eh~reof, ~ porolu~ oo~ting of fro~ about
0,5 i:o ~bout 10 ~llll~eters ln ehicl~ne~ vf a blo~nglneer~
~ng ehermop~ t~Lc ~ter~al whlch i~ comp~tlbl~ h, ~nd
conduclve :for, the ~ngrowth of c~nceïlou6 and cortlcsl bone
~picule~, ~he coat~rlg h~ring ~he iFollo~ng propere~e~:
n ~verage pore dl~meter oiE iErom about 90 eo
~bou~ 600 ~icron~;
(b~ pore ln~:erconnection6 hsving average dla~zeer6
of gre~er ~h~n ~boS?t 50 ~aicrons;
~c~ Ea modulus of ela~t~c~ey from sboue 250,000 ~co
~bout 3,000,000 pounds per ~quare lnch for the
neat thermoplastic material or ~hf~ ~ein Eorred
thermoplastic snaterial;
(d) ~ porosity of Breater than aboue 50 per cent; and9
(c) ~ ~ot~l creep strain ~f less eh2n one percent at
constar~t litress of 1, 000 pounds per 6quare inch at
ambient temperat~lre ~
~11 of the propereie6 belng ~ufficlent to enable ~tre~ses
applied on ~he muscul~kele~al ~yst~ to be tran~ferred to
bone ~picule~ wiehln the pore~ and malneain ~ufflcient
load as-d pore ~t2bility t~ promote lrreverslble 06~;~ ficatlon~
~/ Hence, it hs~ been ob~erved that he ~n~eerial~ used
,, i~ co~eing ehe load bear~ng ~nct~onal co~ponen~: o pro6ehet-
ic de ~ri c e 8 ~u~ t pO 6 6e 815 l~p~C 1 f iC prope r ~i e ~ ~ f long - eerm
Ibone fi~aeion ~ ~G be ~chieved. Prosthe~lc devices pre-
pared in ~ceordance wi~h the teachi~g o ehi~ ~nvention
h~ve been fGuDd ~o prov~de ~he b~omechanic~l envlroF~ent
nece~6~ry to u:elifos~ly tg~an~}~lt the proper magnitu~e of
applied lo~d~ proE~t~ng the ~esired rem~delllng of bon2
tsabecul~e .
i5
~1 ,313
~ p:cev:lou~ly indioated, ~he ~ter:lal3 ~ployed i21 ~he
pr~p~rEItion o~ the pro~chetlc de~ce~ o:~ thl~ :Invent~on ~re
c1~6~ fled ~ a '9bloen&ineerislg ehermopl~t lc~o One impor~ne
feature of these ~naterial~ 1~ thst theis perfor;~ance ean be
pred~c~ed ~y the u~e of ~aeeal de~ign englneering equ~tion~
for boeh long and hort-term, mc~e ~ngineering de~ign
~qu~elor~6 only ~pply up eo t~e llnear vi.Dcoel~tic limit of
~he materi~l, Algh desl~ity polyethylerae h~6 ~ llnear ~is-
cc)elastie llmit of lc~6 than 0.1 percent ~nd wlth thl~ limit
10 on ~he amo~t of ~er~L n,the ~llowable str~R~ 1B mln:l~l, In
con~ra~c, the linear Yi~coela~eic llmi~ o~ ~loengin~er~Tlg
therpl~tic~ hin the definition of thi~ dl~clo~ure, i8
Bt le8@,t 1 percen~ ~rair10 For e~ample, one o the preferred
englneerirlg ~hermopla~tic maeerl~l~ found to be suieable for
the coating~ of thi~ invention i6 a poly~ulfone whlch hs~ a
2 pcrGent atr~lrl limi~. Henoe, the me~al engineerin~ de61~1
eq.lat;ons or both long ~t 6hort ~::erm can apply up ~co ~his
li~it O
Th~ unique ch~raeterl~tlo~ of the bioengineer~xlg ther~-
pla6tie materi~l~ are s~re cle~rly e~ider~c ~en ~heir per-
fonnaalce ~6 compared to polymeric ~teri~l~ prev~ou~ly di6-
clo~ed as be~ng u~eful or porous fixation device~ If
~he creep ~dulu6 ~xtensively varies ~ith tlme, e~2fles~ion
~ncrea~es ~rkedly, c~u~lng micro di~lacemerlt of a pros~hesis
~der lo~B snd pore di~tort~o~. Cseep 'ce~ h~ve already
beeTl reported ~n ~:he litcral:ure o~ porou~ hl~h den~ y poly-
ethylent? and a polytetrafluorbethylene-graphlt2 ~mpo~te,
bo~h of ~hich have been lnd~o ted ln the pre~ou~ly ei~ed
~atent~ beerl ~b~erveà th~t d gniflc~nt change~ ln
pore structure oceurred upon ccmpress~ve ~resses ~s low as
80 p~i fos the por~w polytetraflllor~e~hylene~graphl~e com-
po~ite~ ~d ~t 300 p~l fo~ t~ ~rou~ h den~ poly~
~et~l5Sle, ~p~ 0 fa~lure ~ 1U8 19~re!~g~1!; for ~h~ ~wo
_ 9 _
ll 9313
reported high d~n~lty polyethylene ~brlc~t~on~ were u:nder
flvc ~ ee~ when ~tre3~ level~ gre~ter than 300 pcl were
~pplied. Ie ~ahould be noeed th~t this repre~er~ta the ~re~
le~els th~t ~ill be experiencPd in ~me orthopedlc ~olr~t ~nd
de~.rlce ~ppllcuelo~ ne ~pore~nc e o ~ir~t~inlng pore
geometrle~ und~r lo~ding envlroTu;pents W~8 indic~ted e~rLier
where it wa~ obse~ed ~h~t fibrou6 t~ s~ue i~ created in ~mall
pore~. Thl6 11~ par~lcul~rly cr:L~lcal ln e~rly po~t-operative
period~ prior to the ingrowth of bone ~en ~he porou~ poly-
lQ ~neric coat~ng on ~oint pros~he~e~ m-uBt h~ve ~ufficient
~tren~ch ~nd rigidity to i2ldependently ~uppor~ ~pplied load
wichout ~si6tance from ingrown bon~. ~he ~trength of prior
polymeric matcrl~ls con:e~ from the ingro~rn bone. Bioeng~ neer-
lng the~opla~tlc porou~ coatlng h~e ~trength llke bone,
Xllu~trstive prosthetic dev1ce~ which are wi~hln the
~oope of ~che ~eachlng& o ~i6 ir~ventlon arc readily apparen~
from the followirlg descr~p~c~ on and from the ~coompanying
drawings ~?herein:
F~E~,ure 1 1B ~a plan vie~ Gf the ~tem and ball porticn
20 of ~ ~o~al hlp pro~he~i6 havlng a co~cing of 8 porou~ blo-
engineerlT~g ~hepla ~tic materia~
F~gure 2 iB a pî~n vlew o an endo6teal blsd~o implas
hsving .q co~ing of ~ porou6 bioeng~neering the~oplas~ic
m~teri~l on ~he blade portlo~s therecr.
Flgure 3 i~ ide plan view of ~noeher endo~eal
plfin~ hsvirl~ the bl~de portion coated ~th ~he porou~ bio
engineering, the:rmopl&~tio rn~terialO
Figure 4 i;s a ~ide plan ~ew of a ~elf~broachlng ~nera-
~ medullary nail hsving a coatlDg over :1~ en~:ire len~'sh of
30 the porou6 bioengiTleer~slg thermoplastic material.
1,313
~ igurc 5 ~ ~ p7 an vlew of ~ pro~ the~lc clevlc2 c~mpri~ed
~entlrely of a porotl6 bioengin~er-ing ther~nopl~t~c m~eeri~l.
F~gure 6 la ~ ~raph deplct~ng the rel~tion6h~p of ln~er-
faciAl she~s strenB~h VerBu6 i~pl~nt~tion t~e of severAl
porous ~ma~erl~
Reerr~ng now to Flgure 1 o the! ~ccomp~nying dr~wing~,
the toeal h~ p prosthe~ls 10 1~ c~mprl~ed of b~ll and ~tem
~ber 12 ~nd cup member 14. ~he ~tem portioal of the b~ll
~nd ~S~em ~emb~ r 12 iB soated over ~ entire surface wlth
porou~ bioeng~neering the~pla2~tlc co~ting 16 of thi6
lTrv~ntion, ~lehough the ~em por~on 1~ depic ted ~n Figure
1 a~ æ a3olld ~tem ~eh ~ groo~e 18 long Bt lea6~ por~lon
of lt~ length, lt can have openlng~, rldge~ or o~her con-
flgura~lon~ ~o provide coaeed ~lte~ for tl~ue growth ~o
flrrrlly ~nchor ~e ~o ~he ~lceletal ~y~eeDl. Cup ~Lember 14 1
likewi~e ~oated on its exterlor ~urace ~ieh the porous
engineering eher~pla~tic 16 . The ~eck 20 9 ball 22 ~nd
lnner ~ur~ce of the cup 24 do rlot3 of courj, contais any
coaei~g O
F$gurec 2 and 3 o the drawlngs depict c~mmerclally ~vailable
implan~ 26 as~d 28 w~ich can be f~bricsted ~n ~ varlety of
20 ~hape~ and ~re de~igned for ~upporelng grc~up6 o ~r~:Lficg~al teeth
The6e d~vices are u~ually ~ ri~ed of cob~lt or tltanl~n ~lloys
and ase ~Ln6ereed irlto ~loe~ cu~ ~D~O ~he alveolar sidge.
~e pvst~ 30 and 32 proerude ineQ ehe OTal e~ y and are
u~ed for anchc)rlng ~he art~flcal teeth. A~ ~ho~ :in ~he
drawlng, the ~tem p~or~l ons 34 snd 36 ~n be coaeed wlth the
porGus biQengineering eh2~pla~tic maeerial and ps~de for
~one ~ row~h ~ flrmly aff~x the pro~ehesi ln ~he ~l~eolar
r~dge O
~n ~tr~dullarg 2~il 38 1~ ~llustr~ted lr. Figure 4
30 ~d h~ ~ coating 40 of ~he pOrOUJ ~ioer~ineering ~her~-
11,3'L''
plastic material over its entire length. 'rhese nails areplaced in the medullary canal of long bones, such as
femurs, and are usually limited to the ~iddle one-third
section o-f such bones. These nails are wed,~ed lengthwise
into the medullary canal and press a~ainst the interior of
the cortex. Finally, Fi~,ure 5 provides a pl,an view of a
porous implant 42 which can be used for alveolar ridge re-
construction. Thus, ridge reconstnlctions can be rnade by
using a poro~ls or solid interior bioen~ineering therrnoplastic
implant~ without a load-bearing functional cornponent, carbed
or molded to the desired anatomica'L shape.
Figure 6 is a ~raph depicting the relationship of inter-
facial shear stren,~th in pounds per square inch versus time
in weeks for trochanteric implanted intramedullary rods of
porous polysulfone, porous titanium and porous polyethylene.
The porous polysulfone was prepared in accordance with the
teachings of this invention and exhibited the physical charac-
teristics previously described for bioen~ineering thermo-
plastics. The data for the porous titanlum and polyethylene
implants was reported by other investigators. In each case,
the rods were implanted in do~s in accordance with accepted
surgical techniques.
While each of the tests was performed in a sirnilar
Eashion in dogs, there is the possibility that the results
could vary somewhat because of differences in implantation
and mechanical testing procedures used by the different in-
vestigators. However, these variations are not great enou~h
to prevent comparison. Of particular interest is the fact
that ~he interfacial sheer strength of porous polysulfone
is hi~h enou~h after only two weeks (~150 psi)
,12-
~ ~ ~7~ 3
11,313
to support the static load and most dynamic loads that might
be placed upon a hip prosthesis by a pa~ient immediately
after surgery. This type of data thus evidences the possi-
bility of eaxly weight-bearing postoperatively for polysul-
fone, whereas the porous high density polyethylene exhibits
an inter~acial shear strength value only one-third that of
polysulfone. Indeed, only after extended implant periods,
did the high density polyethylene come up to the two week
value ~or polysulfone, and it fell short of the ultimate
shear s~renR~h value for polysulfone.
As hereinbefore indicated, the materials which are
employed in the present invention are designated as bio-
engineering thermoplastics. These materials are unique
in that they combine melt processability with structural
strength, rigidity, creep resistance, toughness, and steam
sterilizibility. In corporation of glass, carbon or organic
based fibers into the bioengineering thermoplastics extends
the load-bearing and structural characteristics. Bioen-
gineering thermoplastics exhibit bulk tensile or flexural
modulus values in the range of 250,000-500,000 psi. Fiber
relnforced products exhibit modu'lus values up to 3.0 million
depending on the fiber type and loading. These values of
modulus provide the intermediate range required for initial
post-operative support and long-term s~abili~y of implanted
prostheses in high load areas anchored by bone ingrowth.
-13-
1.1,313
Each of these materials when prepared in accordance
with the teachings of this invention provides coatings or
free standing articles having the physical properties herein-
before enumerated. Illustrative of these materials are the
polysulfones, such as, polyphenylsulfone, polyethersulfone,
polyarylsulfones, and the like; polyphenylenesulfide, poly-
acetal, thermoplastic polyes~ers such as the aromatic poly-
esters polycarbonates; aromatic polyamides, aromati.c poly
amideimides, thermoplastic polyimides and the polyaryletherke
tones, polyarylethernitriles, aromatic polyhydroxyethers, and
the like. The most preferred materials for use in the in-
vention are the aromatic polysulfones. These polysulfones
contain repeatin~ units havin~ the formula:
~Ar-S02]
wherein Ar is a divalent aromatic radical containing at
least one unit having the structure:
~-Y-~
-14 -
> 3
~h ~`
~ 11,313-C~l
in which Y is oxygen, sulrur or the rad;ical residuum
of an aromatie diol, such a~ 4,4'-bis(p hydroxyphenyl)-
alkane. Particularly preferred polyary:Lene polyether
polysulfone thermoplastic resins are those composed of
repeating units having the structure shown below:
_ ~_
CH3
_~SO~O ~C ._<~0 __
CH3
-
wherein n equals 10 to about 500. These are commercially
available from Union Carbide Corporation as UDEL*
Polysulfones P~1700 and P-3703. These materials differ
in that P-3703 has a lower molecular weight. Also
useful are Astrel*360 a polysulfone sold by 3M Corporation
and Polysulfone 200 P sold by ICI and Radel polyphenyl-
sulfone sold by Union Carbide Corporation. Certain
crystalline bioengineering thermoplasties like Stilan
from Raychem Corporation, Polyarylene and Phenoxy A
from Union Carbid~ Corporation, are also useful.
*Trademarks.
.. ...
11,313
In practice, the prosthetic devices of- ~his invencion
having an inner load-bearing functional component or those
existing as free standing anatomically shaped devices are
conveniently prepared by one or more methods. In one method
the coating or article can be formed by a sintering technique
whereby particles of the bioengineering thermoplastic material
are heated for a period of time ancl at a temperature suffi-
cient to cause sintering that is, the particles fuse together
at one or more contact points to provide a porous continuous
composite material of the bioengineering thermoplastic. In
a second method, the coating or article can be formed by a
process which involves the formation of a low density foam
of the normally solid thermoplastic material. This second
method which can be described as the dough foam technique is
particularly useful for the preparation of the porous
materials. However, its use is limited to the aforementioned
polysulfones and phenoxy A aromatic polyhydroxyethers.
Porous bioen~ineering thermoplastic coatinv,s and blocks
prepared by these methods exhibit intermediate modulus values,
high strength and high creep resistance. They can uniquely
be fabricated with high total porosities and pore sizes,
while still meeting the strength and biomechanical criteria
observed to be necessary for bone repair and prosthesis fixa-
tion/stabilization. For example, sintered polysulfone having
an average pore size of 200 and a 53 per cent porosity, had
a flexual strength of 2000 psi and flexural modulus of
60,000 psi.
Foamed specimens with a 70 percent porosity had a
flexural modulus of about 105 psi. This value increased to
8 x 105 psi with the introduction o~ 30 weight percent carbon
fibers.
~-16-
11, 313
Wieh r~pect ~o the flrst ~ethod, lt h~ ~eerl
ob62rved tha~ through eareful contxol of t~nper~ture, tlme and
pre~ure, ~11 b~engineerlng thermopl~6tics c~n be ~lntered
~or ~xa~ple, UI~EL~P~1700 poly~ulfor)e can be ~atisf~ctor$1y
sineered glt ~ppr~xl~ely 24S~C and R~del poly~ulfone i~
gener~lly ~ln~red ~t approximately 285C. At 8ppropr~ate
temperatur~s, t~oes ~nd pre6~ure~ ~clle other thermoplastic m~eri~ls
c~n al50 be ~in~ered ~co provide a porous pr~duct ~ultable
for the irleended u~e. It has been obsP2ved, however, and
particul~rly for u~e in pseparlng the c~atings and ~rticles
of Phis islv~ntlon, ~3aat optim~ proper~ies can be obtsined
i~ a unique and facile manner by proper choice of both
(s)particle sixe ~nt (b) molecular weight distr$but~
~ s indic3ted previously, ~he des~sed propert~es are
exh~bi~ed ~y ~he prosthe~ic device when the bi3engineering
~hermoplastic ~a~erial has a porosl.ty of a~u~ 50
per cerlt ~d more preferably frolD about 4Q eo sbout 70
per CeRt. Po20sl~y i~ ~nfluenced by the p~rticle ~ize
~nployed ~ri the ~interlng operationO Particle ~lze ~lso
~nflueslce~ the ~trength of the porous 6irltered maeerials.
Large particles result in large pore 6izes 5 while mall
pareicles lmprove ~;erengeh by ~ncreasing ~he fusion area o
~he part$cles.
It has ~een observed th~e the modulus ~f ~ porous
materl~1 can be pr~dle~ted l:hrough the ~e~nes equ~tion ~r ~hrough
a mod~fied Ralpin-T6si equatlo~ ~e~ce3 ~n order ~o ~chieve
~ aterial ~th a poro~lty, fL~r ~xample, of 55 per cen~, and an
elastic ~dulu~ gseaeer ~han 40,000 p~i,the ~30dulus o~ che
11~313
~eart~8 polymer s~st ~xceed 200,000 p81. Thu~;, ~0. t
polyprGpylene, ~nd ~ll high den6~ty polyethylenes are ~nc~pable
o be~ng fab2~c~ed in ~ m~eri~l of 55 pe:r cent porosity with
~ IDodul~s of 40,000 psi. I:n ~h~ o~eher hsnd 3~nce the modulus
of ~ol~d poly~ulfone exceeds 34~;000 p6i,1~ snat~rial of 55
per c2nt poro~ty who~e ~odulus axt:eeds 70,000 p~i can be
cbe~ined .
Even though lt was po~sible to predlct ~he ~nodulus of ~
therrsopl~stle h~ving ~ deslred poro61ty there ~s no ~imple
~nethod available to abrie~e a materiAl ~ppro~hing these
predictions which would ~e u eful for the device~ of thls
inverl~ion. It was unexpeetedly ~ound, howe~er, thAt the
desired degree of poro~icy could ~e obtained wi~hout
~aeri~icing meohanioal proper~cies b; the proper choice of
particle ~ize, ~oleeular ~e~gh~c distr~bu~ion nd ~int~ring
condit~ons. ~11 thr2e are lnter~related and neccssary to
aeh~ eve ~ coating or srtiele haY~ng the neoes~ary oharacter-
istic~ . ~or example ~ the ~!;intering time and tempers~ure
which resul~cs ln ~ des~sed pore ~ize distri~u~on
~ay ~ot produce the desired modulus o elas~:ieity and/or
tensile 6trengthO S~arting partiele ~ize dis~cribu~clon,
6intering, time and temperature muse ~e ~d~u&ted co aehieve
the de~ired ~alance of pore ~ize, porosi~y, snd mechanieal
properti~s .
With respe~t to p~rtlcle ~ize di~eribueion~ ~ ~lend of
~wo or ~ore differen~ ~izes ~f i:he bi~engineering ~hermo-
plastic lDsterisl ~Ira~ found tv pro~ride ~ 6~ntered material ~hich
be6t ~ec the poro~ity ~d Dechanical requlr2menes needed for a
~ucces~ful prosthet~c device., l ~
lL,313
In practice, a mixture oE particle sizes wherein the
ratio o particle diameters ranges from about 7:1 to about
5:1 has been found to be acceptable. Particle sizes of from
abou~ 300 microns to about 50 microns are particularly
preferred. For example, a mixture of particles which are
retained on a 50 mesh screen (~.S. Standard Sieve) and
pass through a 270 mesh screen have provided coatings and
articles having the desired porosit:y and biomechanical
features. I~ has also been observed that optimun results
are achieved when the particle size distribution ranges
from abou~ 40 to about 60 weight per cent.
As indicated, the sintering conditions are also im
portant to achieve the desired properties. Sintering has
been accomplished by charging a metal mold with powder and
heating the mold to a prescribed sintering temperature, Ts,
greater than the glass transition temperature, Tg, and less
than the melting or melt processin~ temperature, Tm, (i.e.
T~ cTS cTm). The sintering temperature is held constant
for a given time, t. Essentially, no pressure, other than
that induced by differential thermal expansion, is applied.
The application o~ pressure at Ts leads to fluxing of the
mat.rial. This indicates that if pressure is applied, lower
temperatures and shorter time cycles must be employed to
retain porosity in the sintered parts. Experiments were run
and set forth in the examples to delineate the effects of the
sintering conditions on the pore size, porosity, and tensile
properties of the porous sintered plastic for various powder
size and molecular weight distributions.
-19-
~ 3
11, ~13
Xn ~ 0ec~:l ~Dethod lt h~ been fo~d that ~lnce ~ome
~bioen~lneering thenDopl~tlc~ slre ~oluble in low-boillng
organ~c ~olvent3 ~ llolven~ fo~ming t~c~lque ean be utllized
~or ~olding open cell porou~ fo~m co~t~ngs orlto protheses or
for the preparation of foa~ed articles. Porous fo~ed
coatings ~d ar~lcles o~er advant~ge6 over sintered porous
coatings ~nd articles in that higher porosltle~ can be
l~chieved at hi&,her ~creng~hs, due eo the thin conti~uous
pore walli obe~lned in the ft~ing pr.ocesses. FurthPr, low
f~brica~ion eemperaeures are experienced due to the plAsti-
c~zing effect~ of the ~olvent on the ~hermvpla~tic. This tecl.nique is not ~men~ble to Teflon, polyethylene or polypropylene
being desoribed as preferred materials ~n prior art paten s.
This solvent foaming technlque for fabr~ca~ng low
density~ oEmed artisles c~prises the ~eeps o:
(a) ~lend~ng at least ~ne nor~ally ~olid bioe~gineering
thenmoplastic with about 25 to about 80 parts, per 100 par~s
by weight~ of ~ normally liquid orRanic ~ol~ene having a
601ubili~y parameter~S ~ withln (1.3 calories per co) of
that of ~he thermoplastio~ or a ~ixeure of normally liquid
~rga~ic solvents havln~ the ~ame Rolu~ility psrameter;
(b) ~lending the ~ixture obtalned ~n ~tep (a) with at
les~t about 1 par~ by weighe 7 per hundred par~s of then~o-
plas~ic, of wa~er whereby a non-tacky hydrogel dough is
ob~ned;
(c) ~h~p~ng ~he hydrogel do~gh obtained in step ~b);
(d) vsporizing the ~ol~ent and water a~d
(e~ ~eco~ering a f~Emed re~n article,
It ha~ ~e n foun~ tb~t foam preparet i~ ~his ~anner posseses
~he de~ired degree~ of ~oth poro~i~y ~d b~amechan~oal proper-
eie~ .
en observed, however, ~ha~ the ~alues of ~he
-20~
11,313
~olubility p~r~meeer~ of the ~or~lly llquld organlc
~olven~ u~od ~r~ ~alrly cr1~1c~1 ~6 ~ enced by the fact
~hat wieh ~ preerred ther~opl~st~c ~2sin ~uch ~8 the
polysulfone depicted ~bove there is a tlstinct
diference ~etween struct~rally ~$mil,~r ~o~v~nt isomers.
Thus, ~or ~xample, the ~bove-de~cribe~d polyaulfone,
which has ~ solubility parameter calculated to be
10.55, i~ ~olu~le ln 1,1,2-trichloroethane h~ving a solubility
parameter of 10.1~ but lnsoluble in l,l,l-trichloroethane ha~ing
a solubility p~rameter of B.S7. ~owever, a mix~ure of organic
~olvents which indi~idu~lly i~ unsAti~factory can be used as
lo~g as the average solubillty par2meter of the mixtur~ is
w~hin ~1.3 calories per cc) / of the re6in being blown.
In addi~icn, i ehe Tg of ~he poly~er ~hat i~ ~o be p~astici~ed
is exoeptionally high ~n value, plasticity of the gel can be
prolanged during the ~oaming 6tep by fosming ~ ~ixture of
~olven~s, one of wh~ hould h~ve a much higher boiling point
value. Thus for example while ~thanolor l,l,l~trichloroethane
ca~not ~e used ~ndividually wlth the polysulfone
depic~ed ~bove a ~ixture compri~ng equal parts by volume of
ethanol ~nd l,l,l-trich~Droethane c~ be u~ed. Other c~mb~n-
ations ~h~ch funct:lon a6 organic ~olvents for poly~ulfone
are:
95Z chloroform ~nd 5Z water,
R5% methylene chloride, cthanol 2~% ~nd w~er 5%,
'3S7. tetrahytrofursn ~d wat2r 5~,
~ 5Z ~e~hylene chlor~de, 10% ~oetone, 10% ethanol,
An~ 5Z w~ter, ~nd
8QZ cyclohexanone, ~hanol 15~ ~nd ~ter 5~.
11,3~3
The ~mo~t of water ~Ddted ~ mot crlt:Lc~l ~ut
gener~lly 8~ lesst 1 p~rt ia r~quired per 100 p~rt6
by weight of resill. There $~ no ~axim~D ~mount becau~e
excess lda~r ~ep~rates frc7m ~he dough-llke ~8~ ~S ~1
~eparaee ph~s2~ ~3ecau~e of ehe ptia'se ~eparat$on, where
the ~olvent esnployed ls for the mos~ p~rt not ~iscible wi~h
the waePr phase, the exces~ w~ter ~ct~ ~s ~ proteetive
~lanke~ whlch prevents rapld ~olvent 10~i6 rom the pla~
~ized polymer. Thi6 e~ture ~llows the plastir~2ed poly-
eric gel to be exposed ~ sn open ve~sel dur$ng handl~g
and trans~er wLthout ~ealed eontainment. In this :Eorm the
poly~ae~ blend can be easily transfeEred frclm one ve6sel ~r
container 1:0 another asld can be ~haped ~nd ~olded or other-
~se worked without the necessity ~or using coneamina~lng
release agents. Simple mixing equipment known to those
~killed in 'che art ~ ~11 that is required to blend the wa~er
~ c ehe ~nixture of ther;aoplastic res~n a:nd liquid organic
601vesll:. The resultant hydrogels can ~e u~ed immedistely or
~f desired s~Q2ed indefinitely under water End then recoYeret
and u~ed without urthe~ tre~tment.
l~e c~rganic solvent orlce ~t diffuses lnto polymer resisl,
6erves two purpo~es, namely, ehe formatio~ of ~ gel retain~g
R finite ~olven~ concentration 1~ ~ plasticized fOD and
secondly ~he ~ol~ en~ ~erve~ a6 ~ ~lowing or fo~ming agent at
~ much lower eempera~ure ~nd vl~coslty thasl tha~ which would
be required ~o foam the orlginal r~on-pl~stlc$2ed polym~r resin
~th 8 convcn~:iono~ ;a51!0U6 type l~lowing or fo~ing ~gent,
~t ~low~g ~emper~ures ~f ~rc~ 165-200C. nece~sary for
~2 ~
,313
polysulfone~, ~nost of the co~nonly u~ed organic
~olverlts difuse out of the polymer blend oo quickly
to provide sdequate ~lowing of the resin. Durlrlg the
blowlng operatlon the waeer in the Ihydrogel ls also
r~ ved wieh ~lle normslly liquid F:~rganic ~ol~nt, ~hus
~h~le the ~econt order er~n~it~or~ t~perature (Tg) o ~he
polymer ~esin ~eing ~reated in this ~anner i~ 10WeÆeà~
enh~ncing the pr~ce~sing of the poly~er ~t lower ~emperature,
the llquid or~n~e solvent and the water being fugitive in
na~ure ~ w~en removed fr~ ~he polymer resin leave ~he foa:med
~r~lcle with ~he physic~l pr~perties of the or~ginal resln
prior eo processing. Th~6 i~ extremely i~portant ln the case
of pol~ers which are difficult to process ~ecau~e of thelr
~i5eoelastic snd rheolog~cal propereies or hea~ ~nstability,
T~e wlde latltude o~ condltlons under ~hioh the
foaming operation c~n ~e carriet o~lt in th$s process was
al~o ~uite surpri~ing. Thus for example, while ~ c~n
prac_ice ~he foaming ~ep at higher temperatures, one can
~l~o oper~te at: ~h~ other end oiF the ~pect~, that is, ag
room te$pera~ure or ~y placing the hydroge~ in ~ Yacuum de~iee,
6u~h a~, ~ vacuu;~ o~ven ~nd ~ith organie ~olvents o low vol~
~tility9 ~uch s/ me~hylene ~hlor~de, re~d~ly remoYe ~he
~olvent ~nd water in a relatlvely ~horl: time.
-23-
~ 11,313
As previously indicated, another embodiment of this
inventiorl is directed to prosthe~ic devices which do not
contain a separate inner load-bearing functional component
but rely on the s~ructural integrity of the bioengineering
thermoplastic material itself. For example, a porous block
can be carved to an anatomically appropriate shape, and used
to augment atrophic mandibular alveolar ridges and deficient
facial contours in the mental, mandibular border, and
zygomatic areas. Other devices, can include bone gap bridges
and bone caps ~used to control bone overgrowth in amputees)
which are either totally porous bioengineerino therm~plastics,
or bioengineering thermoplastic coated metals or bulk polymers
(relnforced and unreinforced). The alveolar ridge recon-
struction au~,mentation device shown in Fi,gure 5 is prepared
fr,om a porous bioengîneerin~ thermoplastic composite by
moldino and/or carving a block of the composite to the de-
sired shape.
The porous bioengineering thermoplastics can also be
carved to anatomical shapes without destruction or collapse
of ~he surface porosity. Bone gap bridges, bone caps and
other pre-sized implants can be machined without destroyin~
the porosity and surface of the porous engineering thermo-
plastics. Porous high density polyethylene, polypropylene,
and the polytetrafluoroethylene creep and "feather" durin~
carving and machining operations.
The ~igh stren~th-low creep o the bioen~ineerin,o,
thermoplastics and reinforced bioen,~ineering the,rmoplastics
also translate to the load-bearing components of prosthetic
devices and implants. For this reason, prostheses can be
-24-
3 313
~eveloped ~cQrpora~lng ~ co~Dpo~te ~yst~m of bloengine~rlng
eher~opla~eic load-be~rin~ c~mponents ~nd srtl~ul~tlng ~urfaoes,
~ith porou~ 'bloeng:Lneering, thermopls6tlc coatings ln areQs ~here
~laetachm2nt to ehe ~ 60ulo6kelet~1 ~yBtem iL6 tesired. Ttle blo-
engineering thermoplastlos remaln tough af~er be~rlg filled
with reinforcillg fillers, where polyolef~s auch A8 high
density polyethylene become brittle ~t hlgh fiber loadir:~gs.
Bone gap bridges and joint prostheses demons~rate this prlnciple,
Such impl~ntable~ ~e rendered more useful beoau~e
~f the ability to achieve high ~neerfacial ~trengeh~ between
the ~ulk lo~d-bearing component and the porous coat~ng when
the iden~clcal ~aterials ~re co~n~iDed ~ thc oonstruc~cion.
These comblnatiorls are not achievable with polyol2fins due ~co
the poor 6tructural char~c~erl6t~c~ vf these m~teril~s, nor
~ith cer~ics o!r ~netals because of the ~iomech~ cal unsuit~biliey
of the respective porous co~:ingsO
In ~o~t pro~heses where the bioengineering thermo-
pla~tic ~st also form the ~ri:iculating ~urface, ~ is of cen
de~ able ~o ~nc~rporate adti~ives ~lch increase ~he ~dear ~Lnd
~rasi~ re5i~;t~1rlCe of ~he composite. C~rbon fib~r, graphite
f~ber~ tefl~l molybdenum disulfide are useul ~ddiei~res which
~fford wear re6ilstance engineer~ng thermopla~l:ic~ ~qual or
3uper~0r l:o ~elf~lubricated materials typ~e~lly u ed ln
co~erci~lly ava:~lable ~D~n~ pros~che~s.
In ~ou~nal ~earin~, wear 'cests*, the fci~Low~r~g comparative
re~ults were ob~ed:
*C~ndi~lon6 ~T?I-D1242 - 1400 hours, 110 ppm, 5 lbs. ~n level a~
- 2 5 -
ll, 313
~ ~e~b~ L~
C~n~crol Hl)E'E 0 . 0806
C~trol polypropylene û. 0404
UDEL poly~ulone 0 ~ 2 794
UDEL br~th 20% c~ n fiber û.~362
WEL wi~h 20% graphite ~ . 0324
C:csmpos~eions with esrbon fiber ~re pref~rred for the
~ n~ec~ion s~olding ~r ~achin~ng of articul~tirlg pr~thes~ ~uch
as acetsbulsr cup~, t~bi~, snd gleno~d co~npe~ents of ~o~al
kn~e and ~houlder repl~cements,
In ~other embo~meTIt of this invention ~ilyl re~ctlve
polymers like ~llyl reaetion poly6ulfone ~re utilized for
bond~ng porous polymerlc c~atings to ~etal ~ubstrates.
Silyl re~ctlve polysulfone (PSFSR) resins possess
th~e~ ~portaT~c features. First, the presence of hydr~lyzable
s~l~ne end grsups provld~s an inherent coupling abiligy ~o
metaLlic ~urfaces. Secorld, the PSF-SR resins have a low r~el~
(or ~olution) vi cosity whlch ~reatly ~acilitates ~Iwetting~
turirlg t'ne fonnatiorl of ~dhesive ~onds. Third, they are
polymer~c adhesiv~ which exhibit no ~olubility ~n physlological
fluids ant hence have no biologic~ oxicolog~ cal effects when
~nplanted .
The lo~d he~rlng $us~ctlon~1 c~ponent o 'che pr~thetlc
d~vicc~ of thi~ ~nvention can l~e c~prised of a variety of
etals ~snd ~allDy~ knOwn 1S~ ~he ~rt. Whlle Eltsnium and
tantslu~ ~re, l~or the 2no~t part, the only p~re meeal6 con-
~idered as ~a~e ~or ~neernsl use, ~ v~rleey o alloy6 h~ve
fo~d general ~cceptance. 5tainles6 ~teel~ ~ cobal~ base
~lloys ~nd titanlum baseJ~lloy~ all ~re tolerated by
the body 85 well as be~ng corro~ion re~istant ~nd
~abriea~ed ~to de61sed ~hape.
-27-
~ 11,313
EXA~LE I
ErFEcr l~r sln~~ c cD~~ ON PORE SIZE
For this ~xper~ment ~imple molds were abr~c~ted from
3/8 inch outer t~ameter s~eel tubin~z. The tublng w~s cut to
a 6 ~nch lengeh ~nd fi~ted wlth t~rleaded end plugs. Wall
thickness of the tubing was ~pproximaeely 0 038 ~nch. The
lesulting ~ln~ered pl~s~ic part had ~ dismeter of 0.300 inch
and w~s 6 inches long. Thi~ proved to be a cont~enient s~mple
size for tensile proper~y characterization.
PSF-3703 powder with the part~cle ~ize distributio~
~hown in T~ble I below was u~ed This material was sintered
according ~o ~he following ~ehedule: pack powder in ~ molt;
immerso ~old ~n an oll bath at 220C or various t~mes ranging
fr~m 10 to 30 ~in. The resul~ing rod of 0.300 inch diameter
was then cu~ ~o ~ample lengehs of 2.5 inches.
Interconnecti~g pore ~i~e distribution was then tetermined
through mercury ~ntrusion poroslmetFy. Daea are repor~ed in
Table I ~ Characeerist~c pore siæe is 6hown as t~e percen~sge
of pores larger than or equal to 132f~. ~s the time a~ temper-
~ture ~s increased fr~m 10 to 30 min~tes, the number of pores
132~ in diameter lnereasesO However, i he ~ateria~ is held
at 220C for times greater than 30 m~nutes~ ~he resulting sample
would no longer be porous. On ~he ~ther hand, if ~he ~aterial
were expo~ed ~o ~:emperaeure for le~s than 10 minute , litele
or no s~tering would have occurred. Thus, ~here i an opeimum
time st temperature~nd t~mperature for a ~l~e~ part~cle ~ize
~nd ~olecular welght fii~tsl~ueion to aehie~e a desired pore
~ize.
-28-
6'~
11, 313
_AE~LE I
U S SCREEN DISTRIBUTION
~, on 35 ~~
Oil 40Trace
on 50 __
on 6014.0
on 8050,0
on 10018 . 0
th~u 10 0 ~~
on 14010.0
on 2 30 4 . 0
thr~ 230 4.0
Sinterin~ Time% Pore Volume
1~ 49.~
12 52.6
14 56. 5
16 58.1
18 ~1.8
69.5
?5.4
-2~
ll,313
EXAMPLE II
EFFECT OF MOLECULAR WEIGHT ON SINTERING
_ _ _
The following experiment was conducted to demon-
strate the efect of a low molecular weight tail upon
sintering conditions and resultin~ mechanical properties.
PSF-3703 was "plasticized" via the addition of 0.5 and 1.0
weight percent of diphenysulfone. Blendin~ was accomplished
in an E~an 1 inch labora~ory extruder. The "plasticized"
PSF was then ground into powder on a laboratory WEDCO
grinder. The resulting powder was sintered into porous rods
0.300 inch diameter and 6 inches long, Tensile properties of
the rods were measured.
Table II presents the mechanical properties or the
porous materials after sintering for 20 minutes at various
tempera~ures. The material containing 1 wt. % diphenylsul
fone was weakly sintered at 200C while the o~her materials
did not sinter at this temperature. In all cases, as the
sintering temperature is increased, the "plasticized"
material possesses superior mechanical properties in the
porous sintered form. It is evident ~hat addition of
dipl~enylsulfone, (or similar low molecular weight species)
pro~ide a method to control sinterin,~ conditions. Speci-
fically, shorter sinterin~ time cycles at a given tempera-
ture or lower temperatures at a given time may be possible.
-30-
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11 ,313
EXAMPLE I I I
_e~ t ic Co~ed _Prosthes is
The ~ter~ ~ectlon of ~ Ric~rds MQnufacturlng c~snine
f~moral c~mponene was dlp co~ted ~n a lO percent ~olu~lon
~f PSF-SR./n~ethylene chlor~de, air dried ~nd baked at 110C
for 1 hour. The ~tesn ~3ection of the prosthesls was ~hen
dip coatet wlth ~ 15 percent ~olution of P-3703/te~ra-
hyàro~r~n ~nd while tac3cy, dusted with powdered ~-3703.
The prlmed prosthes~s w~s pl~ced ln 9 eapered sluminum
~old whose c~vi~y repl~cated ~che ~tem section of the
emoral cosnporlent, ~th a tolerance of lO0 mil. The cavity
was loo~ely plicked with powdered P-3?03, ~ealed st ~he
bot~om and pl~ced ~n ~n oil ba h at 215C for ~4 minutes.
After cooling, ehe prosthesis was removed. The ~tem sec-
tion h~d a tigh~ly ~dherarl~ coatis~ of porous polysulfone.
~32-
6 1 11,313
EXAMPLE IV
__._ _
~3~
~T~_3:#LJUo~5L~5:~Cl~
.
To 400 ~ms. of UDEL polysulfone Pol700 re~in ln 8
one g~llon wide mouth ~r WAS added 31~.2 gms. of ~eehy-
lene chlorlde wleh ~gitatlon. The ~ar W8S sealed ~nd
~ wed to ~tand at room temper~ture for 16 hours. A
polysulfone/m~ehylene ~hloride brown gel w~s obt~ined
to which 558 gms of water were added with mixing. The
brown ~el turned white i~ col~r. These proportions
formed a 6tandard dough mix (SDM). A 30 g. port~on of
ehe SDM was shaped t room temperature ~y h~nd compres-
~ion into ~ l/8l' aluminum met~l pl~te 8" x 8" ha~ing a
circular hole ~easuring 4 7/B" in diameter. The result-
~n~ dough preform was then insertet ~t 155C. islto ~ heated
t~lescoping ~ype ~luminum mold eonsisting of an upper 5"
~luminum disc, fastened to the upper pl~ten of a F)ress,
which ~lides ~to a ring ~nd ~eets asloeher 5" ~l~in~
disc within the ring. The ring and bott~3 disc were not
astened to ~he bottom plae~n of the press.
Vpon insertion of the dough preform the press was
closet all~wing both disc mold ~urf~ces ~o campress ~he
preformed dough wi~h a pressure of 50 psi. During the
following 15~25 ~econts 8 pressure build up ~ccurs due
~o the volatillzat~on of ~he solvents. The pressure
~uilds up to ~52 psl at which poine the press was released
clowly ~o main~in 3 pres~ure ~f 125 to 150 ps~. The
rele~se of the pres&ure all~ws movemen~ o the mold sur-
faces sctivatlng 8n exp~n~ion of the ~old with ~ubsequent
~ele~se of ~olvent snd ~ater vapor from the mold ~nd
_33-
11 ,313
poly~aer exp~n~on. D~ring the dwell time ln the ~Dold
continuous ~olvene and w~ter vapor 108E; further reduces
ehe pressure to ~boue 50 p~i or :Le~ feer ~ tot~l of
~our ~in~ee6 ehe ~old was cpened and he fD~med disc
w s removed. The di~c h~d ~mo~eh ~urface6 orl both IYides
~nd had ~ ~erts~ty of 0.19 g. cc. ~che ~urf~ces when
s~achinet ~eve~led ~n open pore nl~twork and the dlsc
eould be cut to desired ~h~pesO
-34-
11,313
., LE Y
S~men ~ 6 o f
P ous Bioen~lnee~ Ther~
St~nle~s steel p~tes 0.0625" x 1" x 4" (type 304)
were ~ip co~ted ln ~ 10 wt. percent of PSF-SR solutlon
uslng methylerle chlorite ~s A ~olvent. The PSF-SR h~d
~n R.V. of 0.45. A~ter a~r drylng for 1 hour ~nd oven
~rying for lû minutes at 110C l:he ~amples were subsequen~-
ly dlp coated a~ain ~n a 15 wt. percen~ ~olution of P-37 03,
a lower ~nol. wt. polysulfone, ln r~eehyiene chloride, air
dri~d 1 hour, oven dried 110C for 15 minutes. The ~amples
were then b~ked in ~ hoe alr oven for 5 minutes at 24S C
- removed ~nd immedia~ly were powder co~ted with 40 mesh
powdered P-3703 polysulone, u~ing a e~pped ~ieve. The
s~mples ~ere ~hen clamped together to form lap-shear tes~
speciDlesls ~nd placed i~ ~ 240 C hot ~ir ~erl or 1/2 hotlr
to fuse. The same procedure was repe~ted only P~1700
powdered (40 mesh) resir~ was ~ifted c~ver the pr~ed, hot
~mple plates. The ~amples were then tested ~n lap
~he~r followirlg ASTM D11:02-72 method. In eable XII below
Che results ob~ ained are set forth:
Table III
___ _
~o3703 1596 ~ohesive
P-37û3 1435 Collesive
P~1700 1407 ~ohesive
P~1700 1340 Cohe5ive
-35-
,313
~LE VI
ah~L~y~t ~ of
h e n ~
Stainlgss ~teel ~trlps (type 304) .0625" x 1" x 4"
were ~shed ~n hexnne f~llowed by i ~oprop~nol ~nd dried .
~he str~ps were the~ dlp co~ted ln a 10~ y wt. polysulfone
SR ~R.V. 0~ 517) methylene chîoride solut~on u~ing a
~echanic~ dlpping motor which provided ~ uni~orru r~te
of withdr~wal from ehe ~;olution of the ~t~inle~s ~trip of
4"/lol/2 o~inutes. The 6trips were air dried ae room
temper~ture ~or 2 hours and ehen hot ~ir oven baked ~t
various temperseures for 1/2 hour. ~fter dryin~, the
spec~mens were ~p~ced 3/16" ~par~ with shlms, clamped
eoge~her ~nd ~ 15% by we. carbon fiber filled polysulfone/
CH2C12~H~0 dough was inserted between the stainless pla~es.
The ~ssembly was pl~ced in a hot ~ir oven ~ 150C for
15 minute~ to oam the "dough" and ho~d it to the me~al
plaees. The ~ampl s were ehen tested ln lap ~hear ollow-
lng th~ ASTM ~1002-72 method. The results obtalned are
8e~ forth ~n ~ble IV below:
Table IV
C :~ c She~r S~ ~e ~f F~ c
R.T. a$r dry 245.2 Adh~sive
190JC 10 min. 428.5 A~heslve 25%
Cohesive 757
240C 10 ~in. 444 Co~esive
~6-
3~ 13
The ~a~ae procedure w~s repeat~d to cO~e lden~ic~l
~ lnl~ss ~teel 3t~ip6 ~IBing ~ lO wt. percerlt 801ution
of P-l~00 polysulfone ~n ~ethylene chloride. ~he
result~ 4bts~ned ~re ~et orth ~n Tsble V below:
Tab le V
Co a t i~ _r e r ~ c S~he 2 r S t ren~ ~ 3 ~l ~ r~
R.T. ~ir dry (coatlng peeled of)
190C lO minO 113~1 ~dhesive
~40~C 10 ~nin. 340 Cohe~ve
320C lO Dlln. 410 Cohesive
-37-
11>313
~LE StII
' ~E~ulu~
D- n T~5!Lc 6
Ir~ order to de~Donseraee the ~lfference~ creep
o~odulu~ ~t ~5~ ~or the ~ioen~ eeslng ther~opl~s~lc6
of ~hi~ ~nv~ntlon ~nd other ~teri~l~, d~ta w~ compil~d
16 ~et forth ~n T~bl2 VI ~e15JW:
T~b le V I
Y4t~ri~ 1t~1 Appl:led C:ree~ (apparene~ dulus
_ss L~ t ous~nd p. ~.1.
1 hr. 100 hr. 1000 hr.
ENGINEERING
PLASTICS
@l 360 * ~00 2~30 1365
~C:I 3~ ~ * 40~ 35~ 320 310
P-1700 * 4000 345 3~0 325
41~111** 3000 345 ~0 310
OIXER
~TERIA~
Dlaken P~G 3.02*** 1450 386 ~69 ~. A.
~,EX 6050~* 3500 30 ~ . 5 N. A.
St~nyl~n 930~**** 1~75 ~70 80 31
~rofuc 6423***** 1500 104 58 37
Propathe~e GWM
201*~*** 72S ~4 ~6 e-l
-
*P o ly~ul f one ****~IDPE
*~Polycarbonat:e ****~Polypropylene
3'l
~ .
~ lthc)ugh the ~nven~ion has beerl ~llustratecl by ehe pre~
cedin~ exs~ples, ~e i6 ~ot to be cons t~led ~6 ~e!~lg limlted ~
the materlal~ e~ployed there~n, ~ut r~her the is~vention relates
. . .
t~ the ,~eneri~ ~re~ a~ here~nbefore di~closet. V~r~0~l6 d:Li-
~atio~s and esDl)QdiDents can ~e mate without departing from the
~pirit ~d ~cop~ thereof.
-39
