Method of producing a microstructure in a bioresorbable element

Details Method of producing a microstructure in a bioresorbable element Method of producing a microstructure in a bioresorbable element

1994-02-07

1996-01-23

Clark, W. Robinson

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

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

522 2, 264482, C08G 6302

Patent

active

054865468

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method of producing microstructures in a bioresorbable element to be used for medical applications in a living organism. The element could be used e.g. to selectively influence the healing process by separating and guiding the tissues surrounding the element in such a way that regeneration is achieved, as described in WO 90/07308. Typically, the bioresorbable materials used for the elements are made from homopolymers or copolymers that have been formed by polymerization of monomers such as hydroxy acids, hydroxy ether acids, lactones and cyclic dimers thereof, or cyclic carbonates. Examples of such monomers are glycolic acid, lactic acid, .epsilon.-caprolactone, trimetylene carbonate, paradioxanone, 1,5-dioxepan-2-one, valerolactone and .beta.-butyrolactone. The element may also be made from the naturally occurring polymer known as hydroxy butyrate or any copolymer of hydroxy butyrate and hydroxy valerate. The use of such materials in said element is preferred because these materials degrade in contact with water and thereby disintegrate into smaller molecules that are metabolized or excreted from the body. The tissue an then heal without disturbances, and no foreign material is left in the body after complete healing, which eliminates the long term risks for e.g. infections and other complications.
An element that is to be used in the process of regeneration of living tissues, also should have certain properties which are not related to the material. Such properties may include: and thereby allow for an early integration or a pre-programmed initial period of total separation before integration of two different tissues; longer period of time.
Said properties can be achieved by incorporation of a microstructure into the element or the surface thereof. Typically, this microstructure could have dimensions as large as several square millimeters and as small as a few square micron and could cover the surface from 0 to 80%, preferably in the range of 2 to 50%. The microstructure may form a continuous pattern or a discontinuous pattern including microstructure areas positioned close to each other or further away from each other. The microstructure could take different shapes such as apertures e.g. in the form of circles or rectangles, grooves, and indentations, e.g. blind holes.
Prior art technique that can be used for the purpose of obtaining related or comparable microstructures includes mechanical punching, freeze drying, extraction or sublimation of pre-placed crystals, and infrared laser technology.
Mechanical punching is difficult to perform if the transverse dimension of the aperture to be punched is smaller than 70 .mu.m, and will be difficult also in case of larger dimension is many apertures are to be made within a small area. The success of mechanical punching is depending extensively on the mechanical properties of the material in which the apertures shall be made, and the three-dimensional design of the element. An obvious limitation of this technique is the fact that only through apertures can be made in the element.
By the freeze drying technique only random patterns of pores or textures can be produced within or on the surface of the element. The same is true also for the extraction and sublimation technique where it is difficult to position crystals in a structured, planned fashion. The sublimation method may result in difficulties during the sublimation procedure to remove all of the preplaced crystals, and the extraction method may result in retention of water or organic solvent in the element after the extraction procedure that could be delicate to remove. Moreover, it is difficult to remove the crystals completely by extraction or sublimation without at the same time damaging or destroying the element.
Infrared laser technology has been used for many years in the form of CO.sub.2 and Nd:YAG lasers. Typical use of these lasers, operating at a wave-length of 10.6 and 1.06 .mu.m, respectively, is for cutting or drilling purposes, the materials hit by the beam b

REFERENCES:
patent: 4417948 (1983-11-01), Mayne-Banton et al.
patent: 4824699 (1990-04-01), Woo et al.
patent: 5017423 (1991-05-01), Bossmann et al.
patent: 5207955 (1993-05-01), Esrom et al.

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