Coating processes – Foraminous product produced – Microporous coating
Reexamination Certificate
2001-07-27
2003-09-30
Yoon, Tae H. (Department: 1714)
Coating processes
Foraminous product produced
Microporous coating
C427S002310, C428S423100, C523S332000, C523S105000, C528S495000, C528S499000, C528S503000
Reexamination Certificate
active
06627258
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a film for medical use, which film consists of linear block polymers of polyurethane and urea containing groups which can behydrolyzed. More particularly, the present invention relates to a porous film, and is designed to be used as a temporary implant after operations on, or damage to, a human body or a mammal. More particularly, the present invention relates to a procedure for obtaining the desired porosity.
BACKGROUND OF THE INVENTION
The healing of living tissue after an operation or damage incorporates complicated processes which are set in motion, involving a range of different cell types. In rough outline, the following processes take place in the following order: first a matrix of fibrin is formed, then the epicells begin to divide and bridge over the injury. Under the epithelial layer fibroblasts are already beginning to build connective tissue consisting of collagen and base substances. The connective tissue is gradually vascularized and condensed into scar tissue.
In other cases, for example in the healing of broken bones, the formation of the matrix is followed by the growth of stem cells, which are categorized as chondroblasts. These form soft callus, consisting of cartilage, in the fracture. Fibroblasts migrate into the cartilage and form zones of collagen. Then osteoblasts enter and form new spongy bone. The final phase in the healing process consists of the conversion to hard bone and restoration of the remaining structure. This can take years before it is completed.
Even if the healing process goes generally well, its complicated course creates many possibilities for going wrong. For example, micro-organisms can affect it or a wounded area can act together with wrong “neighboring areas” and form a joint growth. Often there are fibroblasts which grow quickly and are a source of unwanted connective tissue formation. This can prevent reconstruction of bone tissue or other desired tissue.
Therefore, there has long been a wish to be able to assist the self-healing process and overcome the problems set forth above.
SUMMARY OF THE INVENTION
This and other objects have now been realized by the invention of a porous film for medical use comprising a linear block polymer of polyurethane and urea containing hydrolyzable ester groups and having a carbon chain backbone, the hydrolyzable ester groups being spaced along the carbon chain backbone a predetermined distance such that upon hydrolysis of the ester groups fragments of the polymer are formed having a size which can be secreted from the body of a mammal, the porous film including pores having an average pore size of up to 600 &mgr;m. In a preferred embodiment, the porous film has a predetermined thickness, and the porosity of the film varies across the thickness. Preferably, the porosity of the film is asymmetric across the thickness of the film.
In accordance with one embodiment of the porous film of the present invention, a mesh of biodegradable material is laminated to the porous film.
In accordance with another embodiment of the porous film of the present invention, the film forms a coating on individual threads of a biodegradable fabric.
In accordance with the present invention, a method has also been devised for the preparation of a porous film for medical use comprising preparing a solution of a linear block polymer of polyurethane and urea containing hydrolyzable ester groups at a concentration of between 5% and 30% in a solvent, applying a thin layer of the solution onto a surface, and treating the coated surface by evaporating the solvent or treating the layer with a polymer precipitating agent. In a preferred embodiment, the concentration of the polymer in the solvent is between 10% and 20%.
In accordance with one embodiment of the method of the present invention, the polymer precipitating agent is water, methanol or acetone.
In accordance with another embodiment of the method of the present invention, the method includes controlling the size of pores of the porous film. In a preferred embodiment, controlling of the size of the pores comprises adjusting the polymer concentration, selecting the solvent having a predetermined volatility, selecting the temperature during the process, or selecting the time of the process of evaporating and treating.
In accordance with one embodiment of the method of the present invention, the solvent comprises a mixture of a plurality of solvents. In a preferred embodiment, the method includes controlling the size of the pores by selecting the plurality of solvents having a corresponding plurality of volatilities.
In accordance with another embodiment of the method of the present invention, the method includes adjusting the pore size of the pores by conditioning the porous film during the carrying out of the method. In a preferred embodiment, the conditioning comprises immersion of the porous film in at least one solvent or thermal treatment of the porous film. Preferably, the method includes immersion of the porous film in a mixture of solvents and anti-solvents.
According to the present invention, a porous film has been provided which can be used for medical purposes consisting of linear block polymers of polyurethane and urea containing hydrolyzable ester groups at such a spacing in the carbon chain that on hydrolysis of the ester groups such small fragments are formed that they can be secreted from a human body, or that of a mammal, which film is characterised in that it is porous with an average pore size up to 600 &mgr;m.
According to the present invention, the film is further characterized in that the porosity can be varied across the thickness of the film.
According to the present invention, the porosity through the thickness of the film can be asymmetric, i.e. a thin outer layer has lower porosity.
According to the present invention, it is often appropriate that the film is laminated with a mesh of biodegradable material.
According to the present invention, the film can be made up of a coating on the individual threads in a biodegradable mesh or the like.
The present invention also includes a method for the production of a porous film for medical use consisting of linear block polymers of polyurethane containing hydrolyzable ester groups, in which procedure a solution of the polymers with a concentration of 5 to 30% is applied in a thin layer on a surface, after which the solvent is evaporated and/or the layer is treated with a polymer-precipitating agent.
According to the present invention, the precipitating agent can be best chosen from the group consisting of water, methanol and acetone.
According to the present invention, the porosity is adjusted by means of the polymer concentration, where high concentrations give small pores, by means of the solvent, where highly volatile solvents give small pores, by means of temperature, where high temperatures give small pores and/or time, where short evaporation or precipitation times, as appropriate, give small pores.
According to the present invention, a mixture of two or more solvents with different volatilities can be used to effect variable porosity through the film thickness.
According to the present invention, the porosity of the film can also be adjusted by the conditioning of an already-formed film by immersing it in a solvent or a mixture of solvents and non-solvents and/or by heat treatment.
Porous films can assist in preventing undesired growth of cells by acting as a barrier over a wound area. In addition, porous films can be used to repair or replenish a periosteum in the case of transplants of e.g. cartilage. The porosity allows transport of dissolved substances, such as metabolites and/or proteins through the film. If the pore size is sufficient certain cell types can also grow in the film. Films with very large pores can also permit vascularization. For these various processes the following limiting values for the average pore sizes can be given:
<1 &mgr;m diffusion of dissolved components and growth of collagen,
<5 &mgr;m no growth of fibrous ti
Flodin Per
Gisselfält Katrin
Artimplant AB
Lerner David Littenberg Krumholz & Mentlik LLP
Yoon Tae H.
LandOfFree
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