BIODEGRADABLE POLYMER SUBSTRATES LOADED WITH ACTIVE SUBSTANCE SUITABLE FOR THE CONTROLLED RELEASE OF THE ACTIVE SUBSTANCE BY MEANS OF A MEMBRANE

Abstract: Biodegradable hollow fibres with an asymmetric wall, the cavity of which containing an active substance like a drug, hormone etc. or a dilute form of the latter and both ends of the hollow fibre being closed for the controlled re­ lease of the active substance as well as a process for the manufacturing of such hollow fibres.

Description: The invention relates to biodegradable polymer substrates loaded with active substance which are suitable for the controlled release of active substance such as a drug and a hormone. From "Hydrogels and Biodegradable Polymers for the Controlled Delivery of Drugs" by N.B. Graham and D.A. Wood in Polymer News, 1982, volume 8, pages 230-236 all kinds of release systems based on biodegradable polymer substrates loaded with active substance are known which inter alia can be implanted subcutaneously in humans and animals. Such release systems can, for example, have the form of pellets based on a biodegradable polymer which surrounds the active substance as a matrix. Such a release system has, however, the disadvantage that the pellets are not surgically removable or removable with difficulty if it should appear later that the patient does not tolerate the drug. One and the same disadvantage is associated with other release systems mentioned in this article such as microcapsules which have an average size of 10 µm. Apart from the above-mentioned disadvantage the release system based, for example, on pellets has the further disadvantage that if a faster or slower release of the active substance such as a drug is required a different material has always to be used since the rate of release of the active substance is dependent on the breakdown of the polymer matrix. Furthermore, in the above-named article by N.B. Graham and D.A. Wood films are reported as a release system. However, such films have the disadvantage that for them to be used subcutaneously, a surgical operation is necessary, which is found to be cumbersome. Furthermore, in "Sustained Drug Delivery Systems II: Factors Effecting Release Rates from Poly(ε-caprolactone) and Related Biodegradable Polyesters" by Colin G.Pitt et al; in J. Pharm. Sc., vol. 68, no. 12, 1979, pages 1534-1538 films based on homopolymers and copolymers of ε-caprolactone, DL-lactic acid and glycolic acid are described. With regard to the macrocapsules based on poly(ε-caprolactone) described in this article the fact is further brought out in particular that these are prepared by melt extrusion, after which the ends of the hollow tube formed, after filling with the drug, are closed. Of the hollow tubes obtained by means of melt extrusion it is claimed in this article that the external diameter thereof for subcutaneous use in humans and animals can be 2.4 mm max. From the examples given it appears that the external diameter of the hollow tubes has a value between 1.85 and 1.90mm. However, in view of the size of this external diameter, which is considerably greater than 1.3 mm, for human use these macrocapsules should be implanted subcutaneously by means of a surgical operation. Such a surgical operation is, however, found to be cumbersome. In addition these macrocapsules have the disadvantage that the rate of release of the drug per unit surface area, which can be adjusted by varying the wall thickness of the hollow tube, can only be altered to a very limited extent, for example by a factor of 2-3. More especially, with regard to the production technique reported in the last-named literature reference, viz. melt extrusion, the point can be brought out that this technique entails a certain thickness of the membrane, i .e. the wall thickness of the hollow tube to be used for the manufacture of the macrocapsules. In view of the fact that the active substance to be used should be liberated at a certain rate from the macrocapsule provided with a compact wall, the active substance should have both a high solubility in the (co)polymer and also a large diffusion coefficient through the (co)polymer. Since the (co)polymers should in addition also be biodegradable, the choice of the number of suitable (co)polymers to be used for the manufacture of the macrocapsules is very limited and in view of the text of the last-named literature reference, attention being drawn in particular to the passage appearing on page 1534, left-hand column, reading "Release from poly(DL-lactic acid) was very slow when diffusion controlled", is evidently limited to poly(ε-caprolactone). From "Controlled Release Technologies: Methods, Theory and Applications", vol. II by A.F. Kydonieus, page 165 ff, CRC Press Inc. the use of hollow fibres for the release of insect pheromones is known. As, however, specified, such hollow fibres are open at one end so that they are therefore unsuitable for a controlled release of drugs in subcutaneous use in humans and animals. Chemical Abstracts 97 (1982), 188311g refers to substained-release pharmaceutical formulations based on biodegradable chitine hollow fibers that may contain a drug. These chitine hollow fiber, manufactured by coagulation techniques have a symmetrical wall. Therefore the release rate of the drug per unit surface area of the fiber may be adjusted by varying of the wall thickness of the hollow fiber. The non-timely published EP-A- 0.126.827 relates to a controlled release, biologically active agent containing composition for use in an aquatic environment comprising strands of polymeric fiber containing a biologically effective amount of a biologically active agent which is effective for the treatment of plants in an aquatic environment. A specific type of strands of polymeric fiber for the controlled release is mentioned in the paragraph on page 12, lines 7-11 of said EP-A stating: "In another method of preparing polymeric fibers containing biologically active agent the polymeric fiber may be extruded as a hollow fiber. The fiber is then filled with an active agent or active agent formulation in its inner core". A search has been made for biodegradable substrates loaded with an active substance such as a drug based on polymer compositions which have an easily adjustable rate of release for the active substance by means of a simple change in the release characteristics of the substrate, only degrade after the active substance has been fully released from the substrate, and can contain any desired active substance such as a drug. In addition, if used subcutaneously, such substrates should be easy to implant subcutaneously by means of injection so that a surgical operation is superfluous and be easily removable if it later appears that the patient does not tolerate the drug. It was found that the above-named object can be achieved by means of a biodegradable polymer hollow fibre substrate for the controlled release of an active substance, present as such or in a dilute form thereof in the inner core of this substrate wherein this hollow fibre substrate, which both ends are closed, has an asymmetric structure consisting of a porous wall provided with a compact skin and manufactured by wet spinning or dry-wet spinning techniques. More in particular the invention relates to hollow fibres with closed ends filled with an active substance for the controlled release of the active substance, the permeability of the wall of the hollow fibres is adjustable by means of coagulation techniques in such a way that hollow fibres based on one type of material may always have a good permeability for any type of active substance. The above mentioned term "asymmetric wall" relates to the variation of the porosity across the wall of the hollow fibres according to the invention from low (outer or top layer) to high (inner layer). In view of the above it is stated that the porosity of the wall of the hollow fibres is in fact determined by the porosity of the outer or top layer and that in this respect the wall thickness as such does only play a neglectable part. Such an asymmetric wall is elucidated by figure 1, illustrating a cross-section of a wall of a hollow fibre according to the invention. The following may be mentioned as biodegradable polymer materials to be used for the hollow fibres: polyhydroxy acids like poly(hydroxyvalerate), poly(ε-caprolactone) and also copolymers derived therefrom as well as poly(α-amino acids) like polyglutamic acid and copolymers derived therefrom. For subcutaneous use of the substrates according to the invention in humans and animals (co)polymers are preferably used which generate no exogenous products after degradation. Examples of these are polylactic acid, poly(β-hydroxybutyrate), polydepsipeptide, poly(α-amino acids), and also copolymers derived therefrom. The hollow fibres used according to the invention have an external diameter of 1.3 mm max. when they are used subcutaneously in humans. Because of this external diameter the substrates according to the invention can be injected so that a cumbersome surgical operation can be omitted. Since the substrates according to the invention can have a length even of centimetres, preferably of 1-2 cm, they are easily traceable if the patient does not tolerate the implanted drug. For veterinary use both the external diameter of the hollow fibres and also their length can, of course, be considerably larger, for example an external diameter of approximately 3 mm and a length advantageously of 2-5 cm. In the hollow cavity of the hollow fibres any desired active substances can be used such as drugs and hormones. The polymer substrates according to the invention, when implanted, release the active substance to the body over a certain time which can vary, for example, from one week to one year, after which the closed hollow fibre which has acted as a reservoir for the active substance degrades to products which can be excreted from the body. The release period referred to above as well as the rate of release of the active substance used associated with it can be adjusted in a simple manner by adjusting the production conditions in the manufacture of the hollow fibres. The biodegradable polymer substrates loaded with active substance according to the invention can, moreover, be used in agriculture and horticulture, insecticides, pheromones, repellants and related products being suitable for use as the active substance. In this use, too, the biodegradable, i.e. capable of being broken down by hydrolysis, polymer substrates according to the invention break down after the active substance has been released to the surroundings. Examples of such polymers which can be broken down by hydrolysis are polyhydroxy acids like polylactic acid, polyglycolic acid, poly(β-hydroxybutyrate), polycaprolactone, and also copolymers derived therefrom as well as poly(α-amino acids) like polyglutamic acid and copolymers derived therefrom. The manufacture of hollow fibres with an asymmetric wall having an adjustable wall permeability for the controlled release of an active substance introduced in such hollow fibres can be carried out by means of coagulation techniques. More in particular the hollow fibres can be manufactured by means of the following techniques: a) wet spinning or coagulation spinning and b) "dry-wet" spinning. Re a): In wet spinning or coagulation spinning a polymer solution is fed via a spinning pump toga spinning head in which a spinning plate or spinneret is mounted. In the spinning head the polymer solution is spun through a ring-shaped channel. The inside of this channel consists of a hollow needle through which an injection medium is metered in via a separate feed system. This injection medium can, for example, consist of a coagulant or a coagulant/solvent combination. The spun fibre is introduced directly into a coagulant. In this process the solvent is displaced by the coagulant. The fibre then obtained is no longer fluid or sticky and can be dried and wound. The choice of the solvent or of the coagulant (non-solvent combination) is important because it determines the molecular conformation in the solvent system and the rate of coagulation. This last aspect again has an influence on the porous structure of the fibre wall and consequently on its permeability. Re b): The "dry-wet" spinning differs from the wet spinning or coagulation spinning dealt with under a) in that in "dry-wet" spinning the polymer solution which emerges from the spinning head first passes an air slit before it comes into contact with the coagulant. This spinning method has the advantage that the fibre can be stretched in the air slit, which is generally not possible with a coagulated fibre without damaging the fibre wall. By means of this method a larger range of spinning speeds can be achieved. In addition to the fact that the wall thickness and fibre diameter are more readily adjustable with this "dry-wet" spinning method than in the case of wet spinning, this technique also has as an important advantage the fact that the skin formation occurring in the process can better be influenced. Specifically, with this method it is possible to manufacture fibres with a porous wall which are provided with a very thin but adjustable compact skin. In this respect it is mentioned that in addition to the above indicated spinning parameters the temperature as well as the composition of the polymer solution, of the coagulating medium and of the injection medium, as well as additives introduced into the polymer solution like polyvinylpyrrolidone or lactide, which normally have a porosity-increasing effect determine the permeability of the fibre wall. The rate of release of the active substance per unit surface area of the wall of the hollow fibre can be substantially altered by means of the spinning techniques mentioned under a) and b); if cresyl violet acetate is used as a standard, the release rate can be varied by a factor of approximately 1000. This is considerably more than is possible with the hollow tubes obtained by means of melt extrusion which can only be varied as regards the wall thickness, viz. by a factor of 2-3. The hollow fibres manufactured in the embodiments below have been manufactured by means of the technique mentioned under b), viz. "dry-wet" spinning. To determine the release characteristics of the hollow fibres use is made of cresyl violet acetate (9-amino-5-imino-5H-benzo[α]-phenoxazine-acetic acid salt; molecular weight 321; Sigma) which is a dyestuff which as regards molecular weight and structure to some extent resembles oestrogen hormones. The values for the release of cresyl violet acetate reported in the Examples below were determined as follows. The hollow fibres were cut into lengths of 25 cm and filled with a 2% (w/w) solution of cresyl violet acetate in water. The filled fibres were sealed with silicone rubber glue (Dow Corning) and then placed in glass vessels which were filled with 25 ml of distilled water. The release of the dyestuff was determined spectrophotometrically. The test method was carried out at room temperature, the content of the glass vessels being stirred one to two times per day. The spectrophotometric absorption took place at 650 nm (zero) and 585 nm (peak). Aftr the measurement the samples were again returned to the glass vessels. The following examples serve to illustrate the invention. In the spinning head the internal diameter of the ring-shaped channel was 1.0 mm and the external diameter of the hollow needle present therein was 0.6 mm. Example I Spinning conditions: 20% w/w solution of poly-lactic acid (MW = 450,000) in N-methylpyrrolidone; temperature: 80°C; rate: 2 ml/min. Injection fluid: water; flow rate: 40 ml/h Spinning bath: water; temperature: 20°C Spinning speed: 4 m/min. Spin height: 1, 2 and 8 cm with respect to spinning bath. Release of cresyl violet acetate from the hollow fibres manufactured with an external diameter of approximately 650 µm and an internal diameter of approximately 400 µm injection fluid (ml/h) 40 40 40 spin height (cm) 1 2 8 release (µg/cm of fibre/day) 2 10 15 Example II Spinning conditions 15% w/w solution of poly-lactic acid (MW = 125,000) and 5% w/w poly(vinylpyrrolidone) (MW = 50,000) in chloroform; temperature: 45°C; speed: 0.6 ml/min. injection fluid: ethanol; flow rate: 10 and 20 ml/h spinning bath: methanol; temperature: 20°C spinning speed: 1 m/min. spin height: 0 and 1 cm with respect to spinning bath. Release of cresyl violet acetate from the hollow fibres manufactured with an external diameter of approximately 800 µm and an internal diameter of approximately 600 µm injection fluid (ml/h) 10 20 20 spin height (cm) 1 0 1 release (µg/cm of fibre/day) 0.1 1.1 2.3 Example III Spinning conditions 15% w/w solution of poly-lactic acid (MW = 125,000) and 5% w/w poly(vinylpyrrolidone) (MW = 50,000) in chloroform; temperature: 45°C, speed: 0.6 ml/min. injection fluid: ethanol; flow rate: 20 ml/h spinning bath: ethanol; temperature: 20°C spinning speed: 1 m/min. spin height: 0.1 and 5 cm with respect to spinning bath. Post-extraction of the spun hollow fibres in methanol for three days at a temperature of 20°C to remove poly(vinylpyrrolidone). Release of cresyl violet acetate from the hollow fibres manufactured with an external diameter of approximately 750 µm and an internal diameter of approximately 500 µm injection fluid (ml/h) 20 20 20 spin height (cm) 0 1 5 release (µg/cm of fibre/day) 0.07 0.04 0.03 Example IV Spinning conditions 13% w/w solution of poly-lactic cid (MW = 95,000) and 4% w/w lactide in dioxane; temperature: 50°C, speed: 1 ml/min. injection fluid: water; 20 ml/h spinning bath: water; temperature: 20°C spinning speed: 1 m/min. spin height: 1 and 10 cm with respect to spinning bath. Release of cresyl violet acetate from the hollow fibres manufactured with an external diameter of approximately 720 µm and an internal diameter of approximately 620 µm injection fluid (ml/h) 20 20 spin height (cm) 1 10 release (µg/cm of fibre/day) 0.05 2 Example V Spinning conditions 12% w/w solution of γ-ethyl-L-glutamate-co- γ-piperonyl-L-glutamate (MW = 205,000) in N-methyl-pyrrolidone; temperature: 45°C; speed: 1 ml/min. injection fluid: water/N-methyl-pyrrolidone 1:3 v/v; 20 ml/h spinning bath: water; temperature: 20°C spinning speed: 2 m/min. spin height: 2 and 5 cm with respect to spinning bath. Release of cresyl violet acetate from the hollow fibres manufactured with an external diameter of approximately 640 µm and an internal diameter of approximately 560 µm injection fluid (ml/h) 20 20 spin height (cm) 2 5 release (µg/cm of fibre/day) 0.04 0.08

Claims: Biodegradable polymer hollow fiber substrate for the controlled release of an active substance, present as such or in a dilute form thereof in the inner core of this substrate wherein this hollow fiber substrate, which both ends are closed, has an asymmetric structure consisting of a porous wall provided with a compact skin and manufactured by wet spinning or dry-wet spinning techniques. Polymer substrate according to Claim 1, wherein the biodegradable polymer is a polyhydroxy acid like polylactic acid, polyglycolic acid, poly(β-hydroxybutyrate), poly(hydroxyvalerate), poly(ε-caprolactone) or a copolymer derived therefrom or a poly(α-amino acid) like polyglutamic acid or a copolymer derived therefrom. Polymer substrate according to Claim 2, wherein the biodegradable polymer is poly-lactic acid. Polymer substrate according to Claim 2, wherein the biodegradable polymer is poly-γ-ethyl-L-glutamate-co-γ-piperonyl-L-glutamate. Polymer substrate according to one or more of Claims 1-4, wherein the active substance is a drug, a hormone, an insecticide, a feromone or a repellant. Polymer substrate according to one or more of Claims 1-5, wherein for human use the external diameter of the hollow fibre is 1.3 mm max. and the length of the hollow fibre is 1-2 cm. Polymer substrate according to one or more of Claims 1-5, wherein for veterinary use the external diameter of the hollow fibre is 3 mm max. and the length of the hollow fibre is 2-5 cm. Biodegradable polymer hollow fibre substrate suitable for use for the controlled release of an active substance introduced therein, wherein the hollow fibre substrate has an asymmetric structure consisting of a porous wall provided with a compact skin and manufactured by wet spinning or dry-wet spinning techniques. Polymer substrate according to Claim 8, wherein the biodegradable polymer is a polyhydroxy acid like poly-lactic acid, polyglycolic acid, poly(β-hydroxybutyrate), poly(hydroxyvalerate), poly(ε-caprolactone) or a copolymer derived therefrom or a poly-α-amino acid like polyglutamic acid or a copolymer derived therefrom. Polymer substrate according to Claim 9, wherein the biodegradable polymer is polylactic acid. Polymer substrate according to Claim 9, wherein the biodegradable polymer is poly-γ-ethyl-L-glutamate-co-γ-piperonyl-L-glutamate.

Inventors: ALBERS, JAN HENDRIK MARIA, EENINK, MARINUS JAN DIRK, FEIJEN, JAN, GREIDANUS, PIETER JAN, OLIJSLAGER, JAN, RIEKE, JOHANNES CORNELIS
Applicants: NEDERLANDSE ORGANISATIE VOOR TOEGEPAST-NATUURWETENSCHAPPELIJK ONDERZOEK TNO
Application year: 1985
Main classification: A61K9
IPC codes: A61K9, C07K19, D01F6, C08L101, A01N25, C12N11, C07K14, C07K17, B01J4, D01F4