Preparation of protein microspheres, films and coatings

Drug – bio-affecting and body treating compositions – Radionuclide or intended radionuclide containing; adjuvant... – Coated – impregnated – or colloidal particulate

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264 41, 264 46, 4242781, 424491, 424492, 42721335, 4274301, 514962, A61K 950, A61K 5112, B01J 1308, B01J 1312

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active

060077913

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BRIEF SUMMARY
The invention relates to micropheres, films and coatings made from proteins or modified proteins and in particular to improvements in the methods of preparation thereof which result in more stable products. The microspheres, films and coatings produced in accordance with the invention are suitable for a variety of biomedical applications.
The term "microspheres" is generally employed to describe colloidal particles which are substantially spherical and have a diameter in the range 10 nm to 2 mm. Particles having a diameter of less than 1 .mu. are sometimes called "nanoparticles". Microspheres made from a very wide range of natural and synthetic polymers have found use in a variety of biomedical applications. They can be labelled with markers (labels or sensing devices) and transported through various media both in-vitro and in-vivo. The labels may be chemical fluorescent, magnetic or radioactive and thus they may, by appropriate sensing equipment, be observed when in use. The sort of applications for which microspheres have been used are diagnostic screening, cell separation, immunoassays, studies of phagocytosis and blood flow, studies of cell motility, haemoperfusion and extracorporeal therapy, drug delivery devices, targeted drug delivery, cell encapsulation and endovasular embolisation.
An important property which microspheres must possess for biomedical applications is biocompatibility. They should be as resistant as possible to attack from the immune system in-vivo. Further, for many applications it is important that the microspheres be biodegradable and/or resorbable in the body once their function has been discharged. Also, in other cases, they should be small enough for easy introduction into the body.
For these reasons, naturally occurring polymer materials such as proteins have been the subject of much study for the preparation of microspheres. Nanoparticles as small as 100 nm can be prepared from, for example, albumin using certain preparation techniques and this is very useful for, among other things, injectable preparations.
Because of their biocompatability some proteins have been used in making coatings for artificial prostheses which will be introduced into the human body and therefore in contact with body fluids. As with microspheres any such coating should be as resistant as possible to attack from the immune system and furthermore should not be thrombolytic i.e. should cause only minimal platelet activation.
It is known that the blood biocompatibility of arterial prostheses is improved by coating the surfaces with albumin as demonstrated by Kottke-Marchant et al in Biomaterials 1989 10 147-155. Indeed albumin has been a particular material of choice for both coatings and microspheres because it is non-antigenic, biodegradable and readily available.
A number of methods are known for preparing protein microspheres and films and protein coatings for prostheses but certain drawbacks are associated with them all.
For example, a well-known method of preparing protein microspheres is suspension cross-linking. In this process an aqueous solution of protein is added to an immiscible liquid or oil phase. Droplets of protein are dispersed by high speed stirring and then hardening or stabilization of the droplets to form microspheres is brought about by heating of the suspension to, for example, a temperature above 80.degree. C. or alternatively by chemical cross-linking employing a cross-linking agent such as glutaraldehyde. Various methods of preparation of albumin microspheres by the suspension cross-linking technique are described by Arshady in Journal of Controlled Release, 14 (1990) 111-131.
A disadvantage of preparing microspheres by the suspension cross-linking technique is that it is difficult to produce microspheres less than 500 nm in size, although nanospheres of about 100 nm diameter have been prepared using high power ultra-sonication. A further disadvantage is that the cross-linking agents used are often toxic which is not conducive to biocompatability.
Apart from suspension cross-li

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