Visible light cured orthopedic polymer casts

An orthopedic cast material is disclosed, which, when wrapped about a body member and cured by exposure to visible light, forms a rigid, high strength immobilizing structure and which comprises an air, light and X-ray permeable fabric impregnated with a formulation comprising (a) acrylate terminated polyurethane oligomers or ethylenically unsaturated polyesters or polyethers, (b) functional acrylate monomers as optional diluents and (c) a photoinitiator which is activated by visible light to initiate the polymerization reaction, whereby the casts produced therefrom show no tendency towards discoloration in ambient light or sunlight, are aesthetic in appearance, are dry to the touch and possess good whiteness.

BACKGROUND OF THE INVENTION 
This invention relates to an orthopedic cast material which, when wrapped 
about a body member and cured by exposure to visible light, forms a rigid, 
high strength immobilizing structure and which comprises an air, light and 
X-ray permeable fabric impregnated with a formulation comprising: (a) 
acrylate terminated polyurethane oligomers, (b) functional acrylate 
diluent monomers as optional ingredients and (c) a photoinitiator which is 
activated by visible light to initiate the polymerization reaction, 
whereby the casts produced therefrom show no tendency towards 
discoloration in ambient light or sunlight. This invention also relates to 
the formulation used for preparing the cast material, and the method of 
forming the cast as well as the cast itself. 
Previously, a leg, arm or finger was immobilized by applying a 
Plaster-of-Paris bandage which subsequently dried to form an immobilizing 
orthopedic cast. Such bandages suffer from the disadvantage that the 
resultant casts are heavy, uncomfortable to wear, insufficiently permeable 
to air and, once set, they rapidly lose their strength when brought into 
contact with water. Furthermore, such casts are generally impermeable to 
X-rays so that if the body member is to be examined by X-rays the cast 
must first be removed from the body member. In such cases, when the cast 
has been removed it may be found that the body member has not healed 
sufficiently and it may then be necessary to reapply a bandage to the body 
member and reform a cast. This is obviously inconvenient. 
Many attempts have been made to provide bandaging materials which are free 
from the above disadvantages. It has, for example, been attempted to 
impregnate bandaging material with polymer solutions which harden under 
exposure to ultraviolet light. The ultraviolet lamps required for this 
purpose are difficult to handle and, moreover, the ultraviolet light only 
reaches the upper layers of the bandage so that the deeper layers harden 
only after a considerable time, if at all. The use of ultraviolet 
radiation suffers from the further disadvantage that it is known to be 
harmful to the human eye and skin (e.g. burns) and when using ultraviolet 
radiation it may be necessary to take considerable care to shield the 
patient and the operator from the radiation during formation of the cast. 
In order to overcome the above-mentioned disadvantages, it has been 
proposed to use orthopedic casting bandages produced from polyurethane 
prepolymers and which are hardened, or cured, by exposure to visible light 
radiation. To circumvent the need for ultraviolet light curing, a number 
of moisture-cured polymer cast systems based on isocyanate-terminated 
urethane prepolymer compositions have been marketed. The polyurethane 
casting bandages suffer from some of the same disadvantages as the 
Plaster-of-Paris bandages. The curing of these cast bandages is initiated 
by immersion into water and afford lightweight, X-ray transparent, porous 
(breathable) polymer casts which cure sufficiently within fifteen to 
thirty minutes to a weight-bearing strength. While superior to 
Plaster-of-Paris in ease of application to body members, rapid setting 
characteristics, and permeability to X-rays, the polyurethane based 
bandages suffer from some disadvantages. For example, the polymerizable 
polyurethane prepolymer formulation contains a polymerization catalyst 
which is, in part, responsible for the reduced thermal stability of the 
casting bandages during prolonged storage, where the bandage may undergo 
premature polymerization and hardening prior to removal from the package. 
Premature polymerization of the isocyanate-terminated urethane prepolymer 
can occur also if traces of moisture enter the package during storage. 
Accordingly, it is absolutely necessary that such prepolymer be prepared, 
coated onto bandage strips, and packaged in sealed containers under 
strictly anhydrous, or nearly so, conditions if one is to preclude 
hardening of the casting tape during storage and prior to actual use. 
Furthermore, it has been found that the cured urethane prepolymer based 
orthopedic casts are sensitive to discoloration (yellowing) on exposure to 
ambient visible light and, in particular, to ultraviolet radiation 
(sunlight). 
By using visible light to effect the cure of the organic material to 
produce the immobilizing cast, it is unnecessary to protect the patient 
and operator from the source of light as would be the case wherein the 
organic material is cured by exposure to ultraviolet radiation. 
Consequently, the use of visible light is more convenient, particularly 
for the operator. Furthermore, the orthopedic cast produced from the 
impregnated fabric of the invention is lightweight and thus is convenient 
to wear and is permeable to X-rays. Visible light sources are, of course, 
relatively cheap and are readily available as contrasted with ultraviolet 
radiation sources. 
The use of a visible light source to effect photocuring of ethylenically 
unsaturated resin compositions is disclosed in U.S. Pat. Nos. 3,874,376; 
4,071,424 and 4,235,686. U.S. Pat. No. 3,874,376 relates to visible light 
photocurable resin impregnated fabrics for use in preparing orthopedic 
immobilization devices. A method is disclosed for producing rigid 
orthopedic casts by means of exposure to visible light (400-750 nm 
wavelength range) of fabrics of various types which are impregnated with 
compositions consisting of ethylenically-unsaturated resins and monomers, 
a photosensitizer activatable by visible light and certain 
photopolymerization accelerators. Although this patent broadly discloses 
photopolymerizable formulations and refers to a composition containing at 
least one photosensitizer activatable by visible light in the 400-750 nm 
wavelength range, actual photosensitizers disclosed are the diketone type, 
in particular, benzil, camphorquinone, .alpha.-naphthil and p-tolil. Other 
specific photosensitizers disclosed are fluorenone, uranyl salts of 
various types, combinations of manganese carbonyl and organic halides and 
a number of photosensitive dyes which absorb actinic radiation in the 
visible light wavelength range. The preferred photosensitizers of U.S. 
Pat. No. 3,874,376 are fluorenone or the .alpha.-diketones. However, the 
benzil, camphorquinone and fluorenone photoinitiators tend to impart an 
unaesthetic yellow coloration to the cast when used at concentrations 
required to give rapid visible light cures. U.S. Pat. Nos. 4,071,424 and 
4,235,686 merely relate to different aspects of the invention disclosed in 
U.S. Pat. No. 3,874,376. 
U.S. Pat. No. 3,613,675 discloses ultraviolet light photocurable resin 
impregnated bandages for orthopedic cast applications. The resins used are 
blends of ethylenically or acetylenically-unsaturated monomers and 
polymers with various polythiols, catalyzed with photoinitiators such as 
the benzophenones, acetophenone and methyl ethyl ketone. Curing is 
effected by means of exposure to sunlamps, sunlight or radiation from 
xenon lamps, thereby requiring protection of the skin of the patient from 
burn damage. Furthermore, the use of the photoinitiators of U.S. Pat. No. 
3,613,675 tends to result in nonaesthetic, discolored polymer casts. 
Ultraviolet curable orthopedic cast materials, impregnated with a 
photosensitizer and photocurable (meth)acrylate terminated urethane 
prepolymers containing at least two reactive carbon-carbon double bonds, 
are also disclosed in British Pat. No. 1,512,553. The compositions of the 
latter patent are cured rapidly by photoinitiated polymerization and 
crosslinking of the two or more (meth)acrylate groups and do not require 
use of volatile and odoriferous crosslinking comonomers, such as disclosed 
in U.S. Pat. No. 3,421,501 and 3,881,473. However, the major disadvantage 
of this polymer cast system is the use of ultraviolet light and the 
hazards associated therewith. 
In view of the fact that the catalysts used in accordance with the prior 
art (such as those disclosed in U.S. Pat. No. 3,874,376) result in 
non-aesthetic polymer casts, it is indeed surprising that the catalysts 
utilized in accordance with the present invention bring about a cast which 
is essentially white in color and which does not yellow when exposed to 
ambient light or to sunlight. Furthermore, the method of the closest prior 
art (as exemplified by U.S. Pat. No. 3,874,376) requires the use of a 
reducing agent which is normally an amine, as well as a photosensitive 
catalyst. In accordance with the present invention, on the other hand, 
such reducing agent is not essential. In fact, Applicant has found that 
when amines are added, the depth of cure of the cast may not be as good 
and the surface of the cast may tend to be somewhat tacky. In accordance 
with one aspect of the present invention, Applicant has found that the 
addition of certain polyfunctional mercaptans, which participate in the 
reaction, result in dry surface cures. 
SUMMARY OF THE INVENTION 
The present invention relates to an orthopedic cast material which, when 
wrapped about a body member and cured by exposure to visible light, forms 
a rigid, high strength immobilizing structure and which comprises an air, 
light and X-ray permeable fabric impregnated with a formulation comprising 
(a) one or more acrylate terminated polyurethane oligomers or 
ethylenically-unsaturated polyesters or polyethers, 
(b) optionally, one or more functional acrylate or methacrylate monomers as 
reactive diluents and 
(c) a photoinitiator which is activated by visible light in the wavelength 
range 400 nm to 750 nm to generate free radicals to initiate the 
photopolymerization reaction, said photoinitiator being selected from the 
group consisting of 
(A) 1-hydroxy-1-cyclohexyl phenyl ketone of the formula 
##STR1## 
(B) (ring substituted or unsubstituted) 2-hydroxy 2,2-dimethyl acetophenone 
of the formula 
##STR2## 
wherein the substituents R are selected from the group consisting of 
hydrogen, methyl, dimethyl, isopropyl, tertbutyl, chloro, bromo and 
fluoro, or 
(C) blends of (A) or (B) with azobis (isobutyronitrile) of the formula 
##STR3## 
whereby the casts produced therefrom show no tendency towards 
discoloration in ambient light or sunlight. 
It is preferred that the formulation also include a surface cure modifier 
so that after curing the resultant cast is non-tacky. The surface cure 
modifiers utilized in accordance with the invention are preferably esters 
of 3-mercapto propionic acid, such as trimethylolpropane 
tris(3-mercaptopropionate), pentaerythritol tetrakis 
(3-mercaptopropionate) and polyethylene glycol di(3-mercaptopropionate). 
It is desirable that the formulation should include fillers or other 
opacifying agents to improve cast whiteness and optionally other additives 
to modify the flow characteristics of the formulation and improve the dark 
storage stability. 
The preferred fabric consists of a fiberglass web, the formulation 
comprising between 40% and 60% by weight of the total weight of the 
impregnated material. 
In the formulation of the invention, it is preferred that the 
photoinitiators or blends of two or more photoinitiators comprise from 
about 0.5% to about 20% by weight (and more preferably from about 5% to 
15% by weight) based on the total weight of the (meth) acrylate monomer 
components. 
In the formulation of the invention, it is preferred that the weight ratio 
of the oligomers (a) to the reactive diluent monomers (b) should vary 
between 40/60 and 100/0. The weight ratio of (a) to (b) may also desirably 
vary between 60/40 and 80/20. 
A preferred formulation of the invention comprises about 70 parts of 
oligomer (a), about 30 parts of reactive diluent monomer (b), about 10 
parts of a photoinitiator (c), about ten parts of a surface cure modifier, 
and between 0 and 5 parts of an opacifying agent. 
In the material of the invention the following components are preferred: 
(a) is an aliphatic type diacrylate-terminated polyurethane oligomer; 
(b) is trimethylolpropane triacrylate or pentaerythritol triacrylate; 
(c) is a photoinitiator of structure (A) or (B) and 
the surface cure modifier is trimethylolpropane tris(3-mercaptopropionate) 
and the opacifying agent is zinc diacrylate, and the fabric comprising a 
fiberglass web. 
In a further desirable embodiment of the invention, the components of the 
formulation are present in the following weight ratios: 
About 100 parts of oligomer (a), 0 parts of monomer (b), 10 parts of the 
photoinitiator (c), 0 to 10 parts of trimethylolpropane 
tris(3-mercaptopropionate) as a surface cure modifier (d), and 0 to 5 
parts of zinc diacrylate as an opacifying agent (e). 
In one desirable formulation of the invention, the oligomeric monomer 
component (a) is prepared from isocyanate terminated prepolymers, wherein 
the isocyanate moiety and the prepolymer is either aliphatic or aromatic 
and the reactive diluent monomer (b) is a polyfunctional acrylate or 
methacrylate ester. A preferred filler in connection with said formulation 
is zinc diacrylate. 
The present invention includes the package which is adapted to contain the 
impregnated fabric of the invention, which package comprises a light-proof 
aluminum foil sealed bag. 
The present invention also includes the rigid, high strength immobilizing 
cast, which is porous, breathable and translucent, comprising the 
impregnated fabric which has been cured by exposure to light. 
The invention also includes the formulation utilized for impregnating the 
fabric. 
In addition, this invention includes the method of forming an orthopedic 
cast which comprises wrapping a body member with the material of the 
invention and curing and hardening the latter by exposing same to visible 
light in the wavelength range of 400 nm to 750 nm for at least two minutes 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the present invention there is provided an orthopedic 
cast bandage suitable for application to a leg, arm, finger or other body 
member and from which an immobilizing orthopedic cast permeable to X-rays 
is obtained in which disadvantages of prior art orthopedic casts are 
substantially overcome. The present orthopedic cast bandage is stable and 
it avoids the use of heat, ultraviolet radiation or water activation to 
effect curing or hardening of the immobilizing orthopedic cast. 
The present orthopedic cast bandage consists of a fiberglass fabric or 
other fabric material sufficiently transparent to visible light radiation, 
which is impregnated with a photopolymerizable monomer composition 
containing a photoinitiator activated by visible light. Upon exposure to 
visible light, photocuring is rapid and complete within about 10 minutes 
exposure to provide high strength, lightweight, non-tacky casts exhibiting 
the desired degree of whitness and resistance to discoloration (yellowing) 
in ambient light or sunlight. 
The photochemically sensitive binder coating on the casting bandages 
consists of an acrylate-terminated polyurethane oligomer, one or more 
polyfunctional acrylate or methacrylate monomers, a photoinitiator system, 
a surface cure modifier, and an opacifying agent (filler) to improve cast 
whiteness. Other additives such as antioxidants, light stabilizers and 
polymerization inhibitors (hindered phenols) may also be added to the 
formulation to improve the shelf-life stability of the impregnated bandage 
tape and minimize discoloration of the cast upon exposure to sunlight or 
ambient light. 
Oxygen inhibition of polymerization is a common and undesirable side 
reaction which occurs during free radical polymerization of 
ethylenically-unsaturated monomers and can result in partially cured 
polymeric compositions having tacky surface properties. The specific 
photopolymerization monomer formulations used in the present invention are 
not as sensitive to oxygen-inhibition of polymerization, thereby providing 
aesthetic, hard, tack-free casts. 
The sources of visible light used in this invention include those provided 
by incandescent spotlights of 150 watt capacity, tungsten-halogen lamps 
(Kodak Slide Projector), plant lights, daylight fluorescent tubes and 
other sources providing energy in the 400-750 nm wavelength range and 
essentially free of significant actinic radiation in the ultraviolet range 
(about 200 to 400 nm). In the practice of this invention for 
immobilization of cast-wrapped body members, a bank of such suitable light 
sources would be utilized to assure complete photocuring of the cast 
within a short time. 
The rate of curing of the cast is dependent on the intensity of the visible 
light source. With the preferred tungsten/halogen and 150 watt spotlight 
sources, exposures at distances ranging from about 3 to 20 inches effected 
rapid photocuring of a 5-ply fiberglass casting bandage within ten 
minutes. The outermost surface layers of the cast generally cured to hard 
composites within about 1 to 2 minutes, with the balance of the ten-minute 
exposure period required to cure the deeper layers of the cast in contact 
with the body member. 
As a result of the photosensitivity of the formulations to visible light, 
the fabrics are coated in subdued or diffuse lighting. To prevent 
premature photopolymerization and maintain good shelf storage stability, 
the impregnated fabrics are packed in light-proof aluminum foil sealed 
bags. Evaporation losses are insignificant because of the low volatility 
of the components of the photocurable formulations used in this invention. 
The shelf life of the casting tapes can be further improved by addition of 
certain free radical inhibitors (hydroquinone, p-methoxyphenol, 
2,6-di-t-butyl-p-cresol, other hindered phenols) and ultraviolet absorbers 
to the monomer formulation, the concentrations being suitably adjusted so 
as to maintain a fast rate of photopolymerization when utilized as 
orthopedic immobilization casts or splints. 
The methods for coating or impregnating the fiberglass casting bandages 
with the photopolymerizable monomer formulations can be varied. In one 
method, the fabric is dipped into the formulation and the impregnated 
bandages run through squeeze rolls to remove excess monomer. Higher 
viscosity formulations can be pre-warmed, if necessary, to improve their 
flow rate and facilitate even coating of the fabric bandages. Although 
less desirable from an environmental polution standpoint, the resin can be 
diluted to the desired applications viscosity with a volatile solvent, 
such as methylene chloride, toluene, and the like, and the bandage air 
dried in subdued lighting to obtain a substantially solvent-free resin 
impregnated casting bandage. 
The primary monomer components of the photopolymerizable formulations are 
ethylenically-unsaturated polyesters, polyethers, and polyurethanes 
containing at least two acrylate or methacrylate groups capable of 
undergoing photoinitiated polymerization and crosslinking. The preferred 
monomers are the acrylate-terminated polyurethane oligomers of relatively 
high viscosity and available from several commercial sources. Examples are 
Uvithane 782, 783, 788, and 893M polyurethane oligomers sold by Thiokol 
Corporation; Uvimer 530 and 775 available from Polychrome Corp.; and 
Photomer 6008 from Diamond Shamrock Co. 
The aliphatic type polyurethane oligomers (Uvithane 788 and 893, Uvimer 
530, and Photomer 6008) are preferred over the corresponding aromatic 
types (Uvithane 782 and 783) due to greater resistance towards 
discoloration in sunlight or other ultraviolet light sources of the 
polymeric casts prepared therefrom. 
Oligomeric acrylate and methacrylate terminated monomers, also suitable for 
visible light initiated photopolymerization, are those which can be 
readily prepared by esterification of polyol ethers, such as polyethylene 
glycol and poly(tetramethylene ether)glycol and hydroxyl-terminated 
polyesters, with (meth)acrylic acid. Direct esterification of carboxylic 
terminated polyesters with the hydroxyethyl and hydroxypropyl esters of 
(meth)acrylic acid provide reactive polymers as well. A specific example 
is the acrylate-epoxy resin, Epocryl 370, sold by Shell Chemical Co., and 
which has the following idealized structure: 
##STR4## 
The (meth)acrylate oligomers mentioned above are generally high viscosity 
resins which can be somewhat difficult to formulate and apply to fabric 
bandages because of their viscosity. In order to overcome this problem, it 
is common practice to blend oligomeric monomers with lower viscosity 
polyfunctional acrylate and methacrylate monomers to achieve a more 
desirable applications viscosity. These polyfunctional monomers 
copolymerize with the oligomeric monomer components in the formulation and 
can often impart improved mechanical properties to the resultant 
photocured polymer. Typical polyfunctional monomers useful as reactive 
diluents are N-vinylpyrrolidone and the acrylate and methacrylate esters 
of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene 
glycol, 1,3-butylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl 
glycol, trimethylolpropane, pentaerythritol, tripropylene glycol; 
tetrahydrofurfuryl alcohol, and ethylene glycol monomethyl ether. In 
accordance with the present invention the most preferred reactive diluents 
for the oligomeric (meth)acrylate monomers are 1,4-butanediol diacrylate, 
trimethylolpropane triacrylate, pentaerythritol triacrylate and 
tetraethylene glycol dimethacrylate. In general, the acrylate esters are 
preferred over the corresponding methacrylate esters because of their more 
rapid rate of photopolymerization and somewhat lesser sensitivity to 
oxygen-inhibition of polymerization at the polymer bandage/air interface. 
The concentration of the oligomeric (meth)acrylate-terminated urethane and 
reactive diluent monomers can be varied so as to achieve a suitable 
applications viscosity, photopolymerization cure rate, and desirable 
strength properties of the cured polymer cast. The oligomeric monomer may 
be the sole monomer component in the photopolymerization formulation or it 
may be blended with the multifunctional (meth)acrylate monomers in 
different proportions. In the preferred composition of this invention, the 
monomer components may consist of about 40 to 100 parts by weight of one 
or more of the acrylate-terminated urethane oligomers and about 0 to 60 
parts by weight of one or more of the reactive diluent monomers. 
The photoinitiators are key ingredients in the photochemical formulation, 
since they function as the source of free radicals required for 
polymerization of the vinyl monomer components in the formulation. For the 
practice of this invention, only certain specific photoinitiators were 
found useful in providing aesthetic polymer casts which were not 
discolored after photocuring with visible light or following extended 
exposure of the polymer cast to ambient light or sunlight. Many of the 
photoinitiators commonly used in ultraviolet cured systems impart an 
undesirable yellow or other discoloration when utilized in the visible 
light cured formulations (such as those of the present invention), 
examples being photoinitiators such as benzil, camphorquinone, 
9-fluorenone, 2-methylanthraquinone, diacetyl, benzanthrone, 
thioxanthen-9-one, and benzoin isobutyl ether. A number of these 
photoinitiators are also unsatisfactory because of the tendency to afford 
polymer casts having an undesirable degree of surface tack or greasiness, 
this effect generally being known to be due to oxygen inhibition of 
polymerization at the air/cast surface interface. The initiators useful in 
accordance with the present invention are (A) 1-hydroxy-1-cyclohexyl 
phenyl ketone (Irgacure 184, Ciba-Geigy), (B) 
2-hydroxy-2,2-dimethyl-acetophenone (Darocure 1173, E. Merck), and a 
series of aryl ring-substituted derivatives of Darocure 1173 known as 
Darocure 1116, 1398, 1174, and 1020 [(See Curing by U.V. Radiation (Part 
2) J. Ohngemach, et al, Kontakte 3, 15(1980)], and (C) blends of (A) or 
(B) with azobis (isobutyronitrile). 
The formulae of the above mentioned compounds are as follows: 
##STR5## 
The concentration of the preferred photoinitiators, or blends of two or 
more photoinitiators, in the formulation can range from about 0.5% to 
about 20% by weight (preferably 5%-15% by weight) based on the total 
weight of the (meth)acrylate monomer components. The preferred 
concentration is dependent on the reactivity of the monomer components, 
light absorption characteristics of the photoinitators, and the presence 
of any other additives in the formulation, such as antioxidants, fillers, 
and ultraviolet absorbers, which may have an effect on the overall rate of 
the photochemical reaction. For each monomer formulation, there is 
generally an optimum photoinitiator concentration range, this being about 
5%-10% by weight of the monomers. It has been found that the addition of 
larger than optimum concentrations can either have no additional 
beneficial effects or, in many instances, may retard the 
photopolymerization kinetics and give rise to polymer casts having an 
undesirable degree of surface tackiness. The optimum concentration is 
preferably determined experimentally for each monomer/photoinitiator 
formulation. 
Azo catalysts, such as azobis (isobutyronitrile), are also commonly used as 
photoinitiators. However, when 1%-5% by weight concentrations of the 
latter were used as the sole photoinitiator, photocuring of the unfilled 
monomer formulations gave only soft polymer gels. When a blend of 5% of 
azobis (isobutyronitrile) and about 2% Irgacure 184 or Darocure 1173 was 
used, the formulation polymerized to a hard, dry, opaque white polymer 
within one minute exposure to visible light, indicating also a synergistic 
photoinitiator effect. 
Although tertiary organic amines have been commonly used in the past to 
accelerate the photopolymerization reaction, their use is undesirable in 
the present invention since they often tend to impart a yellow coloration 
to the resultant cast. 
Surface cure modifiers, such as certain esters of 3-mercaptopropionic acid, 
constitute a preferred ingredient of the photopolymerizable formulation of 
the present invention. As disclosed in the Journal of Radiation Curing, 
April, 1980, pp 10-13, the addition of increasing concentrations of 
trimethylolpropane tris(3-mercaptopropionate) (TMPTMP) results in a 
gradual improvement in the surface cure during ultraviolet light-initiated 
photocuring of certain acrylate urethane oligomer formulations. Dry 
surface cures result on addition of 5 to 20 (and preferably 5 to 10) parts 
TMPTMP per 100 parts of ethylenically unsaturated monomer blends. When 
extended to the visible light cured polymer casts of this invention, 
excellent surface cures (non-tacky) result from addition of 5 to 10 parts 
TMPTMP to the formulation. Higher concentrations of TMPTMP are not always 
beneficial and sometimes result in poorer surface cures. The preferred 
surface cure modifiers for the compositions of this invention are TMPTMP, 
pentaerythritol tetrakis(3-mercaptopropionate), and polyethylene glycol 
di(3-mercaptopropionate) of molecular weight 326-776, the TMPTMP being 
much preferred. 
The TMPTMP surface cure modifier gives improved surface cures for the 
acrylate-urethane oligomer formulations which are catalyzed with Iragacure 
184 and Darocure 1173 photoinitiators. When different photoinitiators are 
used, such as camphorquinone, poor surface cures and yellow discoloration 
resulted (See Example 11). 
Fiberglass polymer casts, prepared from unfilled monomer formulations, 
generally have a translucent or glassy apearance, this being due primarily 
to the transparency or translucency of the glass fabric itself. The 
opacity of the polymer cast is increased on addition of white fillers to 
the formulation, this resulting in casts which are more aesthetic in 
appearance. Suitable fillers are zinc oxide, zinc carbonate, calcium 
oxide, calcium carbonate, calcium silicate, titanium dioxide, magnesium 
oxide, natural and synthetic resins, diatomaceous earth, a variety of 
synthetic silicas, zinc diacrylate, and zinc dimethacrylate. The 
concentration of filler used in the formulation must be carefully balanced 
so as not to reduce the visible light transmittance of the composition or 
rate of photocuring. Concentrations of about 5%-10% by weight of fillers 
such as zinc diacrylate, zinc dimethacrylate, and the synthetic silicas 
are effective opacifying agents and do not affect the photocuring rate. It 
is surmised that the zinc (meth)acrylates may function as reactive fillers 
which copolymerize with the other monomers present to introduce ionomer 
type crosslinks. 
The monomer formulations may contain antioxidants to improve the shelf-life 
(decreased dark reaction) of the casting bandages, ultraviolet stabilizers 
to minimize discoloration in ambient light or sunlight, optical 
brighteners for whiteness improvement, viscosity modifiers or thixotropic 
agents to minimize sagging or loss of the photopolymerizable formulation 
from the cast fabric during storage, and other additives which improve the 
aesthetic characteristics of the polymer casts without having a 
deleterious effect on the photocuring reaction. 
Experimental casts were prepared by wrapping the wet, tacky, 
monomer-impregnated fiberglass fabric strips around a 2.75 inch diameter 
mandril (pre-wrapped with silicone treated release paper) to give a 5-ply 
fiberglass cast. The mandril was rotated continuously while exposing the 
impregnated bandage to visible light for a total of 10 minutes. The cured 
cast was removed and evaluated for surface tack, color, susceptibility to 
discoloration in sunlight, and crush strength (pounds of force required to 
effect a 10 mm diametrial compression of the cast). 
The bandaging material of the present invention possesses the following 
properties: 
1. The material is highly permeable to X-rays so that X-ray photographs can 
be taken through the bandage without any shadow; 
2. the bandages required for producing a given supporting effect are much 
lighter than the known Plaster-of-Paris bandages; 
3. the bandages are resistant to water; 
4. the bandages may attain weight bearing strength after only 10 minutes; 
5. the heat of reaction produced during the hardening of the bandage is 
slight compared with the conventional Plaster-of-Paris bandages; 
6. the cast prepared from the bandages according to the present invention 
have excellent permeability to air and facilitate moisture evaporation 
from body surfaces; 
7. no eye protection is required for the patient or the applicator, as 
would be the case when ultraviolet radiation is used. 
The present bandage can be applied to the patient immediately. It requires 
only that the prepared casting substance be unwrapped and bandaged onto 
the limb. It requires neither a pail of water nor the soaking of prepared 
plaster-gauze material in water. It has the advantage, too, that no new 
equipment is required. It is only necessary to expose the wrapped bandage 
to visible light sources of suitable intensity for a time period of about 
10-15 minutes, at the end of which time the bandage will have hardened 
sufficiently to a weight-bearing strength. 
The following examples serve to illustrate the effects of various 
components of the monomer formulation on the photocure rates, strength 
properties and overall aesthetics, such as color and resistance to 
sunlight discoloration of the polymer casts. 
EXAMPLE 1 
A 2.75 inch diameter mandril was mounted horizontally and connected to a 
stirring motor. The mandril was covered with a single layer sheet of paper 
coated with a silicone release agent. A 45 inch strip of fiberglass fabric 
of 3-inch width was dipped into a photopolymerizable formulation 
consisting of a blend of 70 parts by weight of an acrylate-terminated 
polyurethane oligomer (Uvithane 783), 30 parts trimethylolpropane 
triacrylate (TMPTA), 10 parts trimethylolpropane tris 
(3-mercaptopropionate) (TMPTMP), and 10 parts 2-hydroxy-2, 
2-dimethylacetophenone (Darocure 1173) as photoinitiator. The excess of 
formulation was removed from the fabric strip to give a resin content of 
50% by weight. The impregnated bandage was wound onto the mandril to give 
a 5-ply wrap. While rotating the bandage continuously, it was exposed to 
visible light directed from a 150 watt spotlight (General Electric) 
mounted about 12 inches above the bandage. After a 10 minute exposure to 
light, the cast was removed and evaluated for color, hardness, crush 
strength, overall aesthetics, and degree of tackiness or dryness on the 
outer (air side) and inner (mandril side) surfaces. 
The resultant cast was white in color, dry (no tackiness), hard, and showed 
a crush strength of 45 lbs. The crush strength was the force, in pounds, 
required to effect a 10 mm diametrical compression of the cured cast when 
compressed between two platens at a compression rate of 15 inches per 
minute. The resistance of the cast to discoloration in sunlight was 
excellent. No yellowing resulted after 5 hours exposure. 
EXAMPLE 2 
To simulate the protective wrap ordinarily used to protect body members 
from direct contact with immobilization cast bandages, the apparatus for 
preparation of the experimental cast in Example 1 was modified by covering 
the mandril with an ORTHOPLAST stockinette. A 3-inch wide by 45 inch 
length of fiberglass bandage was impregnated with the formulation of 
Example 1 to a resin content of 52% by weight and the bandage wrapped on 
the mandril and cured in the same manner. The polymer cast produced was 
white, dry to touch on the surface, and showed a crush strength of 32 lbs. 
No discoloration or yellowing of the cast resulted after 5 hours exposure 
to sunlight. 
The lower, but acceptable, crush strength of the polymer cast as compared 
to that of Example 1 was a consequence of partial absorption of the 
incident visible light by the stockinette fabric used as an underwrap. The 
more reflective white-colored silicone release paper used in Example 1 
resulted in a greater degree of internal reflectance of light and higher 
crush strength of 45 lbs. Still higher strength properties can be achieved 
using a more highly reflective underwrap, such as a thin layer of aluminum 
foil. 
EXAMPLE 3 
Using the method of Example 1 and replacing the 10 parts Darocure 1173 in 
the formulation with 10 parts of 1-hydroxy-1-cyclohexyl phenyl ketone 
(Irgacure 184) as photoinitiator, a surface-dry, white, polymer cast 
showing a crush strength of 40 lbs. at a resins content of 51% by weight 
was obtained. Exposure of the cured cast to sunlight for 5 hours did not 
result in any discoloration or yellowing of the cast. 
EXAMPLE 4 
3" wide.times.36" length of fiberglass fabric was impregnated with the 
formulation of Example 3. The impregnated bandage was cut into 6" strips 
and a six layer laminate prepared. The laminate was placed on the curved 
surface of the 2.75 inch diameter mandril to simulate the curvature of an 
orthopedic splint and exposed to visible light from a 150 watt spotlight 
for 10 minutes. The splint cured to a hard, rigid, non-discolored, and 
non-tacky (top and bottom surfaces) laminate having a resin content of 49% 
by weight. No discoloration resulted after a 3 hour exposure of the cured 
splint to sunlight. 
EXAMPLE 5 
The formulation of Example 3 was modified by the addition of 5 parts by 
weight of zinc diacrylate as filler. A fiberglass bandage strip was 
impregnated with the formulation and a photocured polymer cast prepared in 
the manner of Example 1. A hard, white, dry to touch, 5-ply copolymer cast 
showing a crush strength of 46 lbs. at a resins content of 50% by weight 
was obtained. No discoloration or yellowing of the cast resulted on 
exposure to bright sunlight for 3 hours. 
EXAMPLE 6 
The intensity of the visible light source had a significant effect on the 
rate of photocuring and the strength properties of the cured cast. For 
example, when a lower intensity and more diffuse 150 watt floodlight was 
used in place of the 150 watt spotlight of Example 3, 10 minutes 
photocuring gave a flexible, lower strength polymer cast having a crush 
strength of only 18 lbs. The surface of the cast was also slightly tacky. 
When photocured with the more intense 150 watt spotlight for the same time 
period, higher strength polymer casts of greater than 40 lbs. crush 
strengths are obtained. 
EXAMPLE 7 
A glass bandage strip was impregnated with a formulation consisting of 70 
parts of an acrylate terminated polyurethane oligomer of relatively high 
viscosity (Uvithane 893), 30 parts trimethylolpropane triacrylate (TMPTA), 
10 parts trimethylolpropane tris(3-mercaptopropionate) (TMPTMP), and 10 
parts 1-hydroxy-1-cyclohexyl phenyl ketone (Irgacure 184) to a resins 
content of 52%. The wet bandage was wound onto the mandril to give a 5-ply 
cast. The mandril was not rotated. Instead, the wet cast was irradiated 
for a total of 10 minutes using a hand-held 150 watt spotlight. A dry, 
non-discolored polymer cast showing a crush strength of 45 lbs. was 
obtained. No yellowing resulted on exposure of the cured cast to sunlight 
for one hour, but the crush strength was increased from 45 lbs. to 60 lbs. 
as a result of postcuring in sunlight. The experiment indicated that 
greater than 10 minutes exposure to a hand-held 150 watt spotlight was 
necessary to achieve a fully-cured polymer cast. 
EXAMPLE 8 
A fiberglass bandage was impregnated with a formulation consisting of 70 
parts of an acrylate terminated polyurethane oligomer of relatively high 
viscosity (Uvithane 893), 30 parts pentaerythritol triacrylate (PETA), 10 
parts trimethylolpropane tris(3-mercaptopropionate) (TMPTMP), and 10 parts 
1-hydroxy-1-cyclohexyl phenyl ketone (Irgacure 184) and photocured 
according to the method of Example 1 to give a hard, white, non-tacky 
polymer cast having a crush strength of 50 lbs. On exposure to sunlight 
for 3 hours, an insignificant degree of yellowing resulted. 
EXAMPLE 9 
Using the method of Example 1, visible light curing of a wrapped fiberglass 
cast impregnated with a formulation consisting of 100 parts of an acrylate 
terminated polyurethane oligomer of relatively high viscosity (Uvimer 
530), 5 parts zinc diacrylate, 10 parts 1-hydroxy-1-cyclohexyl phenyl 
ketone (Irgacure 184) (no surface cure modifier was used) gave a white, 
dry-surface polymer cast with a crush strength of 80 lbs. 
EXAMPLE 10 
To determine the optimum concentration of trimethylolpropane 
tris(3-mercaptopropionate) (TMPTMP) required as a surface cure modifier, a 
formulation containing 70 parts of an acrylate terminated polyurethane 
oligomer of relatively high viscosity (Uvithane 783), 30 parts 
trimethylolpropane triacrylate (TMPTA), and 20 parts 
1-hydroxy-1-cyclohexylphenyl ketone (Irgacure 184) are spiked with 0, 5, 
and 10 parts of trimethylolpropane tris(3-mercaptopropionate) (TMPTMP). 
The formulations are transferred to 8 mm deep molds and individually 
exposed to visible light from a 150 watt spotlight. As shown in the table 
below, the photocuring reaction is accelerated by addition of increasing 
amount of TMPTMP, with the optimum surface cures (non-tacky) obtained with 
use of 5 or 10 parts of TMPTMP in the formulation: 
______________________________________ 
TMPTMP, Dry surface cure 
Parts by Wt. Time, Minutes 
______________________________________ 
0 8 
5 4 
10 4 
______________________________________ 
EXAMPLE 11 
An unfilled monomer blend consisting of 40 parts of an acrylate terminated 
polyurethane oligomer of relatively high viscosity (Uvithane 783), 60 
parts (1,4-butanediol diacrylate (BDDA), 10 parts trimethylolpropane 
tris(3-mercaptopropionate) (TMPTMP), and 1 part camphorquinone gave hard, 
tacky, yellow colored polymers on exposure to visible light for 2 minutes. 
This example shows that camphorquinone when used in the formulations of 
this invention results in a yellow colored photopolymer not suitable for 
orthopedic polymer casts. 
EXAMPLE 12 
Using the general method of Example 1, non-tacky, dry polymer casts (55-58% 
by weight resin) showing crush strengths of 26-32 lbs. were obtained from 
a formulation consisting of 60 parts of an acrylate terminated 
polyurethane oligomer of relatively high viscosity (Uvithane 783), 40 
parts tetraethylene glycol diacrylate (TTEGDA), 10 parts 
trimethylolpropane tris(3-mercaptopropionate) (TMPTMP), and 5 parts 
1-hydroxy-1-cyclohexyl phenyl ketone (Irgacure 184). 
Replacement of the diluent monomer in the above formulation with a blend of 
30 parts TTEGDA and 10 parts trimethylolpropane triacrylate (TMPTA) gave a 
polymer cast (54% by weight resin) with a highly improved crush strength 
of 55 lbs. This experiment showed that cast strength properties could be 
increased by addition of trimethylolpropane triacrylate (TMPTA) and 
related monomers, such as pentaerythritol triacrylate (PETA) to the 
formulation. (See Example 8). 
EXAMPLE 13 
An unfilled formulation consisting of 70 parts of an acrylate terminated 
polyurethane oligomer of relatively high viscosity (Uvithane 788), 30 
parts trimethylolpropane triacrylate (TMPTA), 10 parts trimethylolpropane 
tris(3-mercaptopropionate) (TMPTMP), and 10 parts 1-hydroxy-1-cyclohexyl 
phenyl ketone (Irgacure 184) was photocured for 10 minutes with a 150 watt 
spotlight at 8 inches from the 8 mm deep specimen mold. A dry surface cure 
resulted after 4 minutes exposure. The polymer specimen was clear, 
colorless, slightly brittle, and did not yellow to a significant extent on 
exposure to sunlight for one hour. 
Having now described the invention in detail, it should be readily apparent 
to one skilled in the art that there are various modifications and 
alterations which may be made without departing from the spirit and scope 
of the present invention.