Biofunctional polymers prepared in supercritical fluid

Details Biofunctional polymers prepared in supercritical fluid Biofunctional polymers prepared in supercritical fluid

2002-06-10

2003-12-30

Cain, Edward J. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C424S001290, C424S200100, C424S469000

Reexamination Certificate

active

06670407

ABSTRACT:

The present invention relates to a process for the preparation of a biofunctional polymer composition comprising biofunctional material adapted for use in or in association with a biolocus such as the human or animal body or cultivated or uncultivated living matter, the polymer compositions, and apparatus for the preparation thereof. More particularly the present invention relates to the process, the polymer compositions, and their polymer compositions, and apparatus for the preparation thereof, wherein biofunctional material is adapted for release of biofunctional material into the human or animal body or living matter and/or adapted for insertion into human or animal host structures.
The use of supercritical fluids in the production of polymers as a swelling, foaming or purification agent is known from various sources. Supercritical fluid serves to increase resin mobility thereby improving mixing and processing, to reduce the polymer glass transition temperature by swelling, and enabling processing at lower temperatures, and acts as a solvent for impurities (including unreacted monomer and residual conventional solvents) which may be removed during the processing to give high purity products. Moreover the fluid can be used to aerate the polymer by transition to non-critical gaseous state whereby a porous material may be obtained. Supercritical fluid has found application in incorporation of dyes and other inorganic materials which are insoluble in the supercritical fluid, for example inorganic carbonates and oxides, into polymers with a good dispersion to improve quality, in particular dispersion in products such as paints for spray coating and the like.
Polymers have also been used in biomedical applications to develop materials in which biocompatibility can be influenced to promote favourable tissue responses whilst also producing materials with acceptable mechanical and surface properties. Biofunctional composite materials e.g. calcium hydroxyapatite dispersed in various polymers are well established for orthopaedic, dental and other applications. These materials are prepared with very high loadings of biofunctional inorganic solid, of up to 80%, in the form of a powder, and a composite is formed either by vigorous mixing of the powdered material into the solid or molten polymer, or by polymerisation of the monomers in the presence of suspended inorganic powders. In both cases, the material becomes entrapped within the polymer matrix. Particle size is selected for higher mechanical strength (ca. 25 m) or surface polishing finishing (ca. 1-8 m). These methods for preparation however are prone to insufficient and uncontrolled mixing of material leading to large aggregate formation whereby the composite is prone to fracture and may not be suitable for commercial processing.
The processes have moreover found limited application in incorporating materials which are limited by solubility constraints and sensitivity to process conditions into polymers.
Accordingly there is a need for a process for the preparation of biofunctional polymers having the desired properties for commercial processing and for use in or in association with the human or animal body or living matter as a biofunctional material release agent or a toxicity shielding or barrier agent, or as an implant into a human or animal host structure such as bone or cartilage, dental and tissue structures into which they are surgically implanted for orthopaedic bone and implant, prosthetic, dental filling or restorative applications and the like.
Moreover there is a need for biofunctional polymers having the desired mechanical properties both for commercial processing and for implant into a human or animal host structure such as bone or cartilage, dental and tissue structures into which they are surgically implanted for orthopaedic bone and implant, prosthetic, dental filling or restorative applications and the like.
We have now surprisingly found that the properties of supercritical fluids may be employed to further advantage in the preparation of biofunctional polymers for the improved processing and quality thereof, in a process which is notably independent of solubility constraints and sensitivity of biofunctional materials.
Accordingly in a first aspect of the invention there is provided a process for the preparation of a composition comprising a biofunctional polymer substrate and biofunctional material substrate adapted for use in or in association with the human or animal body, cultivated or uncultivated living matter, wherein the biofunctional material substrate is optionally substantially insoluble in the polymer substrate and/or a supercritical fluid, wherein the process comprises contacting a mixture of the substrates or their precursors with a supercritical fluid under supercritical conditions and conditions of reduced viscosity and physical blending to plasticise and swell the polymer and distribute the biofunctional material substrate throughout the polymer, and releasing the fluid under subcritical conditions, wherein the substrates are adapted to be isolated in form of a solid admixture comprising the biofunctional material substrate in substantially unchanged chemical form, and optionally in substantially unchanged physical form.
Reference herein to precursors of polymer and/or material substrates, is to components thereof which may be combined in the process of the invention, together with supercritical fluid under the defined process conditions, whereby the precursors react to form the substrate(s) in situ. For example functional or non functional component precursors of the biofunctional material may be simultaneously reacted and admixed according to the process of the invention.
Reference herein to a solid admixture is to any desired morphology. For example the biofunctional material substrate may be encapsulated by the biofunctional polymer substrate in the form of a coating, resembling a particulate morphology or may be distributed throughout the biofunctional polymer substrate resembling a (co-)continuous morphology.
In some cases the transition from coated or encapsulated particles to distributed mixtures is merely a gradation of order of magnitude, whereby particles, pellets, monoliths and the like may effectively comprise a plurality of biofunctional material particles independently coated with or encapsulated by a continuous phase of polymer. This is conveniently termed particulate morphology.
It has surprisingly been found that according to the present invention a process is provided which may be suited to the preparation of composition comprising any biofunctional polymer and material substrates, irrespective of the chemical or physical nature thereof, whereby classical processing requirements such as matching solubilities, melt extrusion, mechanical mixing and the like to obtain a suitable blend are found to be not essential to the successful processing of the composition avoiding solvent poisoning and monomer residues.
The process may therefore be carried out in the presence or absence of additional carriers or solvents, and by selection of biofunctional material substrate which is optionally insoluble in the polymer substrate and/or the supercritical fluid.
Preferably however, where it is desired to obtain a composition comprising a solid admixture comprising the biofunctional material substrate in substantially unchanged chemical and physical form the process is operated in the substantial absence of the additional carrier or solvent, and with use of biofunctional material substrate which is substantially insoluble in the polymer substrate and the supercritical fluid. By this means it is found that biofunctional material in the form to provide the required bioactivity or like performance, for processing thereof to form the composition, will retain that form in the processed composition.
Preferably the process is carried out in the substantial absence of solvent or carrier, by mixing of solid phase material substrate into fluid or solid phase polymer and fluid phase supercritical fluid,

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