Process for taking impressions, particularly of the human body, and corresponding material

An impression of a portion of a human body is made by forming a preform of tandard profile of polymeric material with shape memory that is substantially rigid at ambient temperature and flexible and elastic at a higher working temperature, bringing the preform to that working temperature, and placing the preform on that body portion. After cooling of the preform to below the working temperature, the preform is removed from the body portion and a positive model is cast from the preform. The preform is then returned to the working temperature without physical constraint, whereupon the preform resumes its standard profile and so can be re-used a number of times. The polymeric composition comprises at least one elastomer and one polycaprolactone diluted in a composition of solvents that dissolve the polymers. The elastomer is polyurethane. The composition of solvents comprises dimethyl-formamide to dissolve the polyurethane, toluene to dissolve the polycaprolactone, and methylethylketone as a buffer.

The present invention relates to a process for taking impressions for 
producing products adapted to the shape of a portion of a person's 
anatomy, particularly for the production of orthopaedic shoes. The 
invention also relates to material permitting the practice of this 
process. 
Podo-orthesists, for example, produce shoes permitting persons having 
deformed or withered or mutilated feet, to have walking shoes. 
The first step consists in taking the imprint of the foot of the person. 
This step is at present carried out with plaster strips. These strips are 
wound about the foot after having been moistened to activate the plaster. 
There are drawbacks connected with the emplacement of these strips, both 
from the point of view of handling which requires a certain manual skill, 
as well as the point of view of comfort of the person whose foot and 
clothing must be protected from possible splattering of plaster. 
Even if the time consumed is reduced, it must not be too great because the 
emplacement of the strips requires a certain time and it is not possible 
to slow the setting of the plaster in the course of emplacement, which 
requires the provision of a safety margin which substantially increases 
the time of setting of a plaster cast. 
This cast is a female replica and the male impression is produced for 
producing a first trial of the shoe. 
Once the drying time for the strip has passed, it is cut off to be 
withdrawn from the foot of the person. 
Polyurethane is then cast into the mold to provide a positive model, and 
this rough model is finished by machining and corrected. The corrected 
shape, which thus has an entirely suitable surface, permits the technician 
to produce the shoe. 
This method is costly in material, but the operating time is greater and it 
also leads to the disagreeable results mentioned above. 
It would be interesting to have a process using a material which ensures 
taking a sharp impression and which permits repeating this several times. 
The object would be to be able to adjust optimally the configuration of the 
material to the foot of the person and hence to be able to take again the 
imprint almost instantaneously if that is necessary. 
The object of the present invention is to provide a process for taking 
impressions of a portion of the anatomy of a human being, particularly a 
foot for the provision of orthopaedic shoes, which are characterized in 
that it comprises the following steps: 
making a preform of a standard profile in polymeric material with shape 
memory, substantially rigid at ambient temperature and flexible and 
elastic at its working temperature, in either case the temperature being 
tolerable by the human skin, 
raising the temperature of the preform to the working temperature, 
fitting the preform about the part in question, 
waiting for cooling of the preform to below its working temperature, 
retracting the preform from the portion in question and casting the 
positive shape, and 
returning the preform to its initial standard shape by raising its 
temperature to its working temperature without constraint of the preform, 
so as to be able to reuse the preform for taking another impression. 
More particularly, the preform is brought to the working temperature by 
passage through a hot water bath or through a hot air oven. 
The invention also relates to the making of the preform which comprises the 
following steps: 
immersing in a bath or spray a preform of standard shape with a composition 
of polymers having shape memory diluted in a solvent, 
evaporating the solvent, and 
cutting away the polymeric preform according to lines adapted to permit its 
opening, and 
securing to the preform quick closure means. 
The polymeric composition for making a preform useful in the process 
comprises at least one elastomer and one polycaprolactone diluted in a 
composition of solvents suitable for dissolving at least one and the other 
of the polymers. 
More particularly, the elastomer is polyurethane. 
As to the composition of the solvents, they comprise dimethylformamide to 
dissolve the polyurethane, toluene to dissolve the polycaprolactone, and 
methylethylketone as a buffer.

The invention is described hereafter according to a particular non-limiting 
example. 
There should first of all be produced a preform of a polymeric material 
having shape memory. These preforms are made from templates, if desired of 
special sizes without it being necessary to spend important sums for the 
production of these templates. These templates are generally made as a 
function of known size graduations to permit adaptation to each of the 
sizes or a series of sizes of the range of non-orthopaedic shoes, but 
often beyond that range to take account of extreme cases. There can thus 
be provided a range of preforms according to a particular scale. 
These preforms are made by immersing the templates in baths of polymer with 
shape memory, diluted in a solvent, or by spraying of this polymer with 
shape memory. 
Once the solvent has evaporated, the polymeric shell is cut away so as to 
be able to permit its withdrawal. 
In line with these cuts, there should be integrated closure means such as 
quick closure strips of hook-and-eye material. This integration can be 
carried out after but preferably at the same time as for example the 
spraying or other coating of the template. 
There is thus obtained a preform having a substantially standard profile, 
with sizes varying as a function of the usual range of sizes. 
When the podo--orthesist desires to take an imprint of the foot of a 
person, he chooses from among the preforms that which most closely 
approaches the foot in question and performs a further step of the process 
according to the invention. 
He raises the temperature of the preform to a temperature suitable for its 
deformation. He opens the closure means to permit fitting the preform like 
a boot on the foot and then the closure means are closed. 
The temperature of the preform is of course bearable by the skin of the 
patient. For example, the preform can be heated solely by immersing it in 
a bath at 60.degree. C. or better still in a hot air oven thermostatically 
controlled, which avoids handling water thereby avoiding the risk of 
staining or splashing in the vicinity of the operation, as was the case 
with plaster. 
The preform thus being emplaced, is deformed manually if necessary, in 
addition to its own elasticity, to ensure that it matches well the contour 
of the foot and particularly the part of the foot which gives rise to the 
problem. 
Very quickly, the cooling of the preform gives rise to sufficient 
rigidification so that it is possible to withdraw this preform by opening 
the closure means. 
If the impression is not satisfactory, the same preform is again raised to 
its working temperature and then the operation repeated, which requires 
only several seconds. 
If the impression is satisfactory, a positive shape is cast in 
polyurethane, but in this case, machining and correction are not needed 
because the surface condition of the preform is such that it gives a 
positive shape directly usable for production of the shoe. 
The polymerization reaction of the polyurethane is only slightly exothermic 
so that the preform faithfully keeps the impression. 
The preform, once the shoes has been produced, is returned to its original 
profile by raising its temperature. In the absence of forced deformation 
by the introduction of a solid element into its interior, the preform 
returns to the original profile it had after evaporation of the solvents, 
which is to say that of the template, thanks to its shape memory. 
More particularly, a material usable for practicing this process is a 
composition of an elastomer and a polycaprolactone. 
Thus, the elastomer ensures the elastic effect to match the contours and 
the polycaprolactone ensures the effect of rigidification and blocking the 
deformation of the elastomer at ambient temperature with sufficient 
softening for a small temperature elevation. 
A material which is satisfactory for producing such preforms comprises two 
polymers in a composition of solvents. 
The first polymer is polyurethane and the second polymer is 
polycaprolactone. 
The composition of solvents comprises three solvents: dimethylformamide, 
methylethylketone, and toluene, serving respectively as solvent for the 
polyurethane, buffer, and solvent for the polycaprolactone. 
Thus it is necessary to avoid bubbles during evaporation of the solvent, 
segregation and other parasitic effects whilst ensuring rapid evaporation 
of the solvents. 
According to a further advantage of the invention, there can be integrated 
into the preform temperature indication means by pigments sensitive to 
heat and whose color varies as a function of the temperature, such that 
for a given color, one knows that the temperature of the preform is at the 
softening temperature sufficient for taking an imprint or on the contrary 
that the preform is at the rigidification temperature permitting its 
removal. 
There can also be envisaged providing information elements such as sizes 
for example within the thickness of the preform and also germicidal and 
fungicidal elements to ensure permanent treatment of the preform. 
According to other desirable features of the invention, there can also be 
provided a supplemental internal layer to avoid the preform sticking 
tightly to the skin during fitting. 
A treatment by radiation can also permit the decrease of this property of 
sticking, whilst increasing the elastic capabilities of the preform when 
it is brought to its working temperature. 
All the description has been given with respect to an orthopaedic product 
so as to give all the details of the process according to the invention, 
but this embodiment must not be considered limitative. 
Thus, such a material is itself adapted to find important applications in 
medical fields such as post-traumatic support, surgical, or orthotic 
compression devices for burns. 
For physical therapy, there can be produced suitable splints.