WO2012065998A1

WO2012065998A1 - Polyurethane copolymer

Info

Publication number: WO2012065998A1
Application number: PCT/EP2011/070162
Authority: WO
Inventors: Robert S. Ward; Shanger Wang; Li Li; Durgaprasad Chalasani
Original assignee: Dsm Ip Assets B.V.
Priority date: 2010-11-15
Filing date: 2011-11-15
Publication date: 2012-05-24

Abstract

The invention is directed to a polyurethane copolymer, wherein the copolymer has the structure according to formula (I): The invention is further directed to a process for the production of polyurethane copolymers and to drug delivery devices comprising the polyurethane copolymers.

Description

POLYURETHANE COPOLYMER

Background of the invention

The present invention relates to polyurethane copolymers, a process for the production of these copolymers and in drug delivery devices comprising the polyurethane copolymers.

Drug delivery devices are specialized tools for the delivery of a drug or therapeutic agent via a specific route of administration. Such devices are used as part of one or more medical treatments. Examples of drug delivery devices include, but are not limited to, cardiovascular devices, ophthalmic devices, antivirus devices, dialysis devices, contraceptive devices, drug-eluting stents, catheter tubing, transdermal devices, and/or intra-uterine devices.

Drug delivery devices, such as intravaginal drug delivery devices, including intravaginal rings (IVRs), are typically formed from biocompatible polymers and contain a drug released by diffusion through the polymer matrix. The IVR devices may be inserted into the vaginal cavity and the drug may be absorbed by the surrounding body fluid through the vaginal tissue.

Poly(ethylene-co-vinyl acetate), or ethylene vinyl acetate (EVA) (used e.g. in NuvaRing), and poly(dimethyl siloxane), or silicone (used e.g. in Estring, Femring and in Population Councils progesterone-releasing ring), are currently commercially exploited for IVRs. Compared to poly(ethylene-co-vinyl acetate) or ethylene vinyl acetate (EVA), silicone is limited by a lower mechanical stiffness. Therefore, silicone IVRs are fabricated with larger cross-sectional diameters to achieve the retractive forces required for retention in the vaginal cavity, which may affect ring user acceptability. Moreover, the manufacturing costs associated with these IVRs are considerable. Both EVA and silicone have been found particularly useful for the release of a steroid which is a substantially water-insoluble drug.

Polyurethane-containing intravaginal rings have been described (See, Gupta, Kavita M. et all. Journal of Pharmaceutical Sciences (2008), 97(10), 4228-4239 and, and WO2009094573. The known polyurethane-containing IVRs are IVRs containing one single drug. Further, segmented polyurethane IVRs are described in WO2009003125 and WO2009094573.

In addition, the use of polyurethanes for drug delivery devices has been limited in part due to the high processing temperatures required for polyurethanes. These temperatures are often too high for thermolabile drugs. It has also been found that EVA and silicone, which are both hydrophobic polymers, are not able to provide a desired release rate for hydrophilic drugs. So far, no polyurethane material has been developed for the co-delivery of drugs with different hydrophilicity.

This deficiency is remedied by the presently disclosed polyurethane copolymers. Polyurethane copolymers for drug delivery devices, including intravaginal rings are provided.

Unlike a bioresorbable drug delivery device, the device of the invention comprises a biostable polymer used as a matrix to disperse or dissolve the drug within.

An advantage of the polyurethanes according to the invention is that the release characteristics of the polyurethanes can be tailored to accommodate a range of suitable pharmaceutically active substances to be delivered from the drug delivery product, such as an intravaginal drug delivery device.

Another advantage is that the present polyurethane copolymers can have lowered processing temperatures.

A further advantage of the present polyurethane copolymers is that the copolymers can provide adequate release rates for multiple drugs.

A further advantage is that the polyurethane copolymer has a tunable permability to pharmaceutical active compounds which are diffused throughout the polymer matrix. This permability depends on the characteristics of the polymer matrix, such as the hydrophilicity of the various blocks or segments of the co-polymer.

Description of the invention

The present invention relates to polyurethane copolymers and drug delivery devices comprising the copolymer.

The polyurethane copolymers according to the invention are copolymers with a structure according to formula I:

wherein,

SME1 and SME2 can be the same or different and denote a surface modifying end- group, having a number average molecular weight ranging from 200 to 8000, linked to the polymer via a urethane or urea bond resulting from the reaction of an amine- or alcohol-terminated surface modifying end group with an isocyanate group;

SS1 , SS2, and SS3 denote soft-segments, wherein

551 is a polyether diol selected from polyethylene oxide (PEO) diol, polytetramethylene oxide (PTMO) diol, polyhexamethylene oxide diol (PHMO), polypropylene oxide (PPO) diol, copolymer of ethylene glycol and propylene glycol (PEG-co-PPO) diol, and mixtures thereof;

552 is a hydroxyl or amine-terminated silicone polymer having a number average molecular weight ranging from 500 to 5000 g/mol; and

SS3 is a soft-segment selected from polycarbonate diol and polyester diol, and mixtures thereof;

HS denotes a hard-segment prepared from the reaction of one or more diisocyanates and one or more chain extenders,

x, y and z are the same or different and each is an integer equal to or greater than zero and at least one of x, y and z is not zero; and

wherein the copolymer has a number average molecular weight ranging from 50,000 to 350,000 g/mol.

In the present instance, hydrophilicity of a drug or a copolymer block is determined by the solubility in water at 25°C. If a chemical has a solubility value of less than 0.01 mg/ml in water at 25°C, it is considered hydrophobic. If a chemical has a solubility value of above 0.01 mg/ml in water at 25°C, it is considered to be hydrophilic.

The soft segments of the polyurethane copolymer according to the invention comprise a diol. A diol is an alcohol containing at least two hydroxyl groups. A diol is a polymeric soft segment which is distinguished from short chain or low- molecular weight chain extenders. The diols of the soft segments of the polyurethane copolymers of the present invention contain at least two hydroxyl groups. Examples of polyether diols (SS1), which are considered hydrophilic diols, are PEO diol, PTMO diol, PPO diol, copolymer of PPO-co-PEO diol, Examples of hydrophobic diols include silicone diols (SS2), polyester diols, or polycarbonate diols (SS3).

In general the number average molecular weights of the soft segments ranges from 500 to 5000 g/mol.

In the present polyurethane copolymers, there are three blocks which comprise the soft segment; SS1 , SS2, and SS3. The ratio of the soft segments may characterize the structural features of the present polymers. For instance, if x=0, y=1 , and z=2, then SS1 is not present and the ratio of SS3 to SS2 is 2 to 1.

In one embodiment, SS1 is a polyether diol selected from PEO diol, PTMO diol, polyhexamethylene oxide diol (PHMO), PPO diol, copolymer of ethylene glycol and propylene glycol (PEG-co-PPO diol), and mixtures thereof.

The PEO diol may be a linear PEO diol or a side-chain PEO diol. The side-chain PEO diol may be YMERON120.

In one embodiment, SS2 is a hydroxyl or amine-terminated silicone polymer.

The addition of silicone soft segments which are hydrophobic in nature can modify the release characteristics of the drug. Silicone soft segments include silicone diols having a number average molecular weight ranging from 500 to 5000. Examples of which may include silicone polymers prepared by using silicones like ShinEtsu's X22-160AS (Molecular Weight ~ 1000) and MCR-C61 (Molecular Weight ~ 1000 ) or PDS-1615 (Molecular Weight ~ 900-1000) of Gelest.

The percentage of the silicone soft segment can be up to 40 weight%, or more preferably may be up to 20 weight% of the total weight of the polyurethane copolymer.

SS3 is a soft-segment other than polyether and silicone and is selected from polycarbonate diol, polyester diol and mixtures thereof.

In one embodiment the polyurethane copolymer comprises at least two different soft segments.

In the present polymers, the hard segment, HS, can be made from the reaction of diisocyanate and chain extender. For the purpose of the polyurethane copolymers according to formula 1 , a diisocyanate is a molecule with two isocyanate functional groups,

Diisocyanates can be aromatic or aliphatic diisocyanates. Aliphatic diisocyanates are preferably used in the polyurethane copolymers according to the invention. Aliphatic diisocyanates include, but are not limited to hexamethylene diisocyanate (HMDI) and isophorone diisocyanate (IPDI) and combinations thereof.

A chain extender can be selected from short chain diol, diamine, or amino alcohol having a number average molecular weight ranging from 32 to 500, or can be a side chain PEO wherein the diol is on one side of the molecular chain, such as in YMER®N120, having a number average molecular weight ranging from 500 to 3000 g/mol, and mixtures thereof. Examples of the short chain diol include, but are not limited to, ethylene glycol, 1 ,4-butanediol (1 ,4-BDO or BDO), 1 ,6-hexanediol, cyclohexane dimethanol and hydroquinone bis(2-hydroxyethyl) ether (HQEE).

In one embodiment the percentage of the hard segment can range from 20 to 45 weight% of the total weight of the polyurethane copolymer.

The polymers according to the invention comprise a surface modifying agent or surface modifying end-group (SME), into the polymer. A surface modifying end group is an endgroup that spontaneously rearranges its positioning in a polymer body to position the endgroup on the surface of the body depending upon the composition of the medium with which the body is in contact.

In one embodiment surface modifying end groups may be selected from amine- or alcohol-terminated polyalkylene oxides, silicones, alkyl, alkylesters, polyalkylene esters and mixtures thereof.

Other surface modifying end-groups include alkyl chains, fluorinated alkyl chains, polyether, fluorinated polyether, silicone, and those described in US 5589563, which is hereby incorporated by reference in its entirety.

A preferred SME group that can be used in the polyurethane copolymers according to the present invention is methyl polyethylene glycol (MPEG).

The end groups migrate to the surface of a device and thereby introduce a biocompatible surface without compromising the bulk properties of the polymer. For example, MPEG dominates the IVR surface which results in a non-fouling surface and facilitates drug release by reducing deposit formation.

x, y and z in Formula 1 are integers equal to or greater than zero. Preferred integers are greater than zero and lower than 700, preferably lower than 200. At least one of x, y and z in formula 1 is not equal to zero.

The hydrophilicity of the polyurethane copolymers according to the invention relates to the ratio of the hydrophilic segment (for instance, polyethylene glycol diol) to the hydrophobic segment (for instance, silicone polymer) of the polyurethane. The hydrophilicity of the polyurethane copolymer can be controlled by using the specific soft segments described in Formula I during the formation of the polyurethane.

The polyurethane copolymer comprises 15-35 weight% of at least one soft segment, 20-40 weight% of at least one hard segment and 0-2 weight% of a surface modifying end group; all related to the total weight of the dry polyurethane copolymer. In an embodiment of the invention the polyurethane copolymers are capable of absorbing water up to 50 weight% related to the total weight of the dry copolymer.

Antioxidants and other additives can be added to the present polyurethane copolymers. Examples of antioxidants include but not limited to octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate (Irganox®),

ethylenediaminetetraacetic acid (EDTA), butylated hydroxytoluene (BHT), citric acid (CA), butylated hydroxyanisole (BHA), tertiary butylhydroquinone (TBHQ), and propyl gallate (PG).

In one embodiment, the polydispersity index (M_w/M_n) of the present urethane copolymers can range from approximately 1.5 to 2.5.

The polyurethanes are biocompatible. By biocompatible it is meant that a biomaterial is able to perform its desired function with respect to a medical therapy, without eliciting any undesirable local or systemic effects in the recipient.

Specifically, the present polyurethanes are non-cytotoxic to a vaginal cell line such as Vk2.

The polyurethane copolymers according to the invention preferably comprise at least one pharmaceutically active substance. Pharmaceutically active substances which can be incorporated into the urethane copolymers and drug delivery devices comprising the copolymers include microbicides, contraceptive agents, estrogen receptor modulators, most-menopausal hormone, antiretroviral, anticancer, therapeutic agents, hormones, and combinations thereof. Examples of hydrophobic pharmaceutically active substances include but are not limited to dapivirine, UC781 , valdecoxib, allopurinol, acetohexamide, benzthiazide, chlorpromazine, chlordiazepoxide, haloperidol, indomethacine, lorazepam, methoxsalen, methylprednisone, nifedipine, oxazepam, oxyphenbutazone, prednisone, prednisolone, pyrimethamine, phenindione, sulfisoxazole, sulfadiazine, temazepam, sulfamerazine, trioxsalen. Examples of hydrophilic pharmaceutically active substances include but are not limited to β-Estradiol, Aciclovir, Estriol, Raloxifene, Atenolol , Pravastatin, aminoglycosides, polysaccharide, cyclodextrins and chitosan.

In one embodiment the polyurethane copolymers comprise an anti- HIV agent selected from the group consisting of non-nucleoside reverse transcriptase inhibitors, nucleoside reverse transcriptase inhibitors, and HIV entry inhibitors. Preferably, the non-nucleoside reverse transcriptase inhibitor is UC 781 and/or the nucleoside reverse transcriptase inhibitor is Tenofovir. The present polyurethane copolymers can accommodate two or more pharmaceutically active substances in a single copolymer. In particular they can accommodate two pharmaceutically active substances having contrasting

hydrophilicities. Thus, the polyurethane copolymer has been developed for the co- delivery of pharmaceutically active substances with contrasting hydrophilicity from one polymer. The copolymers can be used for medical devices, such as intravaginal rings. The present polyurethane copolymers are tailored to codeliver pharmaceutically active substances with contrasting hydrophilicity from one polymer which forms a single segment drug delivery device. In the case of intravaginal rings, the single segment IVR device should be more easily-manufactured and less costly than the multisegment IVR (see Todd J. Johnson, et al., "Segmented polyurethane intravaginal rings for the sutained combined delivery of antiretroviral agents dapivirine and tenofovir" European Journal of Pharmaceutical Sciencies 39 (2010) 203-207, which describes two drugs, dapivirine and tenofovir with contrasting hydrophilicity being delivered from a dual segment IVR device. The two drugs were separately formulated into polyurethanes with matching hydrophilicity. The drug loaded rods were then joined together to form dual segment IVRs).

Preferably two or more pharmaceutically active substances are included. In this instance, the pharmaceutically active substances can have the same hydrophilicity or hydrophobicity or different hydrophilicities or hydrophobicities.

In one embodiment, the amount of pharmaceutically active substance to be incorporated into the drug delivery devices ranges from about 0.005 to about 65 weight% related to the total weight of the polyurethane copolymer in the drug delivery device, and more preferably ranges from about 0.2 weight% to about 30 weight% of the polyurethane copolymer in the drug delivery device. The amount of pharmaceutically active substance incorporated can also be calculated as a pharmaceutically effective amount, where the devices of the present polyurethane copolymer comprise a pharmaceutically effective amount of one or more pharmaceutically active substances. By "pharmaceutically effective," it is meant an amount which is sufficient to effect the desired physiological or pharmacological change in subject. This amount will vary depending upon such factors as the potency of the particular pharmaceutically active substance, the desired physiological or pharmacological effect, and the time span of the intended treatment. Those skilled in the pharmaceutical arts will be able to determine the pharmaceutically effective amount for any given pharmaceutically active substance in accordance with the standard procedure. In some embodiments, the pharmaceutically active substance is present in an amount ranging from about 2 mg to about 300 mg of pharmaceutically active substance per gram of polyether urethane. This includes embodiments in which the amount ranges from about 2 mg to about 50 mg, from about 50 mg to about 150 mg, and from about 150 mg to about 300mg of pharmaceutically active substance per gram of polyether urethane.

The present invention also provides a process to produce the polyurethane copolymer and the drug delivery devices disclosed herein. The process involves producing polyurethanes by the polyaddition reaction of one or more diisocyanates with one or more diols, one or more chain extenders and one or more surface modifying end groups in the presence of a catalyst. The reaction product is a polymer containing the urethane linkage, -RNHCOOR'- . A generalized polyurethane reaction is as shown below:

O

R— N=C=O + R₂— OH ^► R— N— C-0-R₂ The catalyst can include organo tin compounds, bismuth compounds, organic and inorganic bases, and combinations thereof. Specific examples include dibutylin dilaurate, stannous octoate, and combinations thereof. The catalyst is preferably stannous octoate.

Preferably, a polyurethane copolymer is mixed or extruded with at least one pharmaceutically active substance or pharmaceutically active substance to form a pharmaceutically active substance-loaded polyurethane copolymer. The methods of mixing include compounding polyurethane with pharmaceutically active substance, dissolving both polyurethane and pharmaceutically active substance in solution followed by evaporation of solvent.

Extrusion conditions of the polyurethane copolymers are below

240°C, preferably below 160 °C and more preferably between 128°C-155°C in order to retain pharmaceutically active substance stability for thermolabile pharmaceutically active substances. Polyurethane copolymers comprising aliphatic diisocyanates can be extruded at these low temperatures.

The pharmaceutically active substance-loaded polyurethane copolymer is formed into shapes suitable for use in drug delivery, wherein a

pharmaceutically effective amount of at least one pharmaceutically active substance is homogeneously distributed throughout the copolymer. This may be carried out under a variety of conditions, including, but not limited to those described in Example 1.

In some embodiments, a pharmaceutically active substance-loaded polyurethane copolymer is formed into a shape suitable for use in intravaginal drug delivery, wherein a pharmaceutically effective amount of at least one vaginally administrable pharmaceutically active substance is compounded with the polyurethane copolymer. In some embodiments in which the device is an intravaginal ring, the step of forming the pharmaceutically active substance-loaded polyether urethane copolymer into the shape of the device involves extruding the pharmaceutically active substance- loaded polyurethane copolymer into a rod and joining the ends of the extruded rod to form a ring. The ends of the ring may be joined together via a variety of biocompatible adhesives, including, but not limited to molten pharmaceutically active substance-free or pharmaceutically active substance-loaded polyurethane. Each of these steps may be carried out under a variety of conditions.

In a further embodiment the invention is directed to drug delivery devices comprising the polyurethane copolymer.

The drug delivery devices generally may include, but are not limited to, cardiovascular devices, ophthalmic devices, contraceptive devices, antivirus devices, drug-eluting stents, transdermal devices, and/or intrauterine devices. More specifically, the devices may include intravaginal rings, artificial hearts, catheter tubing, feeding tubes, surgical drains, intra-aortic balloon pumps, patches, and dialysis devices.

The polyurethane copolymer for devices of the present invention may encompass a variety of shapes and sizes provided the device is compatible with internal administration to the subject and with the requirements imposed by drug delivery kinetics. The dimensions of the of the device may vary depending upon the mode of administration, anatomy of the subject, the amount of pharmaceutically active substance to be delivered to the patient, the time over which the pharmaceutically active substance is to be delivered, the diffusion characteristics of the pharmaceutically active substance and other manufacturing considerations. In some embodiments, the device is for intravaginal administration. This includes embodiments, where the device is in the form of an intravaginal ring (IVR) or is in annular form. The IVR should be flexible enough to enable bending and insertion inside the vaginal cavity and rigid enough to withstand the expulsive forces of the vaginal musculature without causing abrasion to the vaginal epithelium. In some embodiments, the cross-sectional diameter of the IVRs may range, e.g., from about 3 mm to about 10 mm. Other intravaginal devices include tablets, pessaries, rods and films for adhesion to the mucosal epithelium as disclosed in U.S. Patent Number 6, 951 , 654, which is hereby incorporated by reference in its entirety.

In one embodiment, the pharmaceutically active substance is uniformly dispersed, diffused, or dissolved throughout the polyurethane copolymer.

The polyurethane copolymer forms a polymer matrix and preferably, the polymer matrix forms a monolithic system. In this way a single segment drug delivery device can be formed from the polyurethane copolymer.

The present polyurethane drug delivery devices demonstrate release characteristics which are tailored to accommodate a range of suitable pharmaceutically active substances, to provide sustained release of pharmaceutically effective amounts of pharmaceutically active substances in the desired length of usage. Specifically pharmaceutically active substances can include UC781 , Tenofovir (TFV), and

Levonorgestrel (LNG) alone or in combination, including combination of

pharmaceutically active substances with contrasting hydrophilicity, (e.g. UC781 and Tenofovir) to be delivered from an intravaginal drug delivery device and provide a range of delivery rates for a particular pharmaceutically active substance. The release rate can be controlled through the percentage of hard segment, ratio of the hydrophilic segment to the hydrophobic segment of the polyurethane and the selection of diisocyanate.

In an embodiment the release rate of a pharmaceutically active substance is determined by a daily flux value. Preferably, the mean daily flux of at least one of the pharmaceutical active substances is greater than 0.1 μg/mm²/d.

Unlike a bioresorbable drug delivery device, the device of the invention comprises a biostable polymer used as a matrix to disperse or dissolve the drug within. The polymer thus needs to support mechanical integrity and physical stability.

Properties which are desired for intravaginal drug delivery devices include mechanical properties, drug release properties, biostability and biocompatibility for the intended implantation duration.

The mechanical properties (dry and swollen hardness, tensile strength, modulus, percentage elongation at break) of an IVR material are crucial to the IVR's efficacy and acceptability in vivo. An IVR that is too stiff may be difficult to insert and could cause tissue damage and inflammation. (See, Bounds, W., Szarewski, A., Lowe, D., Guillebaud, J., 1993. Preliminary report of unexpected local reactions to a progestogen-releasing contraceptive vaginal ring. Eur. J. Obstet. Gynecol. Reprod. Biol. 48, 123-125 and Weisberg, E., Fraser, I.S., Baker, J., Archer, D., Landgren, B.M., Killick, S., Soutter, P., Krause, T., D'arcangues, C, 2000 A randomized comparison of the effects on vaginal and cervical epithelium of a placebo vaginal ring with non-use of a ring. Contraception 62, 83-89.) Whereas a ring that is too soft may lack retention and thus slip or be expelled from the vagina (Koetsawang, S., Ji, G., Krishna, U., Cuadros, A., Dhall, G.I., Wyss, R., Rodriquez La Puenta, J., Andrade, AT., Khan, T., Kononova, E.S., et al., 1990. Microdose intravaginal levonorgestrel contraception: a multicentre clinical trial. III. The relationship between pregnancy rate and body weight. World Health Organization. Task force on long-acting systemic agents for fertility regulation. Contraception 41 , 143-150). Since the device is used in vaginal environment it is important for the polymer to show desired mechanical properties after the polymer is swollen by vaginal fluid. Therefore, swollen hardness (in pH 4.0 buffer simulating the vaginal environment) of the polymer was also one of the design criteria.

The intravaginal devices should be capable of providing sustained delivery of one or more pharmaceutically active substances for the desired length of usage. The drug release rate is affected by the percent equilibrium swelling of the polymer. For example, for a hydrophilic pharmaceutically active substance, the release rate should increase with the increase of percentage of equilibrium swelling of the polymer.

The invention will now be illustrated by the following, non-limiting examples. EXAMPLES

Mechanical properties which are desired for medical devices in general include hardness, tensile strength, modulus, percentage elongation at break.

Hardness may be measured either dry, or with swollen polymers. In any case, the hardness should be at least 30A. Dry hardness may preferably range from 40A-45D. Swollen hardness may preferably range from 30A to 90A. The hardness of the polymer is measured by the Shore® test. The Shore hardness is measured with an apparatus known as a Durometer and consequently is also known as 'Durometer hardness'. The hardness value is determined by the penetration of the Durometer indenter foot into the sample. The tensile strength of the present polymers may range from 1 15.0 psi to 5400.0 psi. A preferred tensile strength is at least 500 psi.

A measurement of the stiffness may be the Young's modulus.

Properties which are desired for intravaginal drug delivery devices include mechanical properties, drug release properties, biostability and biocompability for the intended implantation duration.

Example 1 : Synthesis of polyurethanes

Several batches of polyurethane material are synthesized by varying the formulation of each batch (Table 1). The compositional changes made in the various batches include 1) using either isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HMDI) as the aliphatic isocyanate, 2) changing the percentage hard segment, 3) using different amounts of methoxy polyethylene glycol (MPEG) soft segment, 4) inclusion of silicone soft segment, and 5) varying the catalyst.

Polyurethane was synthesized in a batch reactor. A batch synthesis of the polyurethane material involved adding the required quantity of polyols, aliphatic diisocyanate and catalyst to a glass quart jar equipped with a mechanical stirrer, heating the jar to 100°C for 3 hours followed by addition of required quantity of a surface modifying end-group and continuing heating at same temperature for 2 hours. Chain extension was achieved by addition of butanediol after which the polymeric material was poured into plastic trays and cured at 100°C for 24 hours. The hardened polymer slab is then grinded into smaller granules for compounding with pharmaceutically active substances. Example 2: Mw, Swelling, mechanical, process temperature of polyurethanes

The analytical results for the various polyurethane batches are summarized in Table 1. It was found that most polyurethane batches met the criteria for Mw, swelling, and dry mechanical properties that is desirable for IVR devices. The polyurethanes were compounded with 20% tenofovir (TFV) and 5% UC781. Most batches compounded with TFV and UC781 show a 2-3 fold reduction in elastic modulus when hydrated. In addition, results also showed that polyurethanes according to lot# 1100032, 1100235, 1100048, and 1100234 could be used to design a IVR that has mechanical properties (force @ 25% IVR compression) similar to IVRs already in use such as NuvaRing with acceptable IVR cross-sectional diameter (~5-9mm). Example 3: Compounding of TFV and UC781 loaded polvurethanes matrices

The polyurethanes were compounded with 20% TFV and 5% UC781. As an example, batches 1100234 and 1100235 were compounded with 20% TFV and 5% UC781 and extruded in to 5 mm cross-section cylindrical strands. Extrusion temperatures for 1 100234 and 1100235 were 128 °C and 134 °C, respectively. Approximately 10-20 mm long segments were incubated in 25 mM sodium acetate buffer with 2% Solutol HS-15 (pH=4.2) (changed daily) at 37°C and 80 rpm in a heated shaker for 7 days. Samples of release media, taken after 24 ± 1 hrs. incubation were taken and stored at -80°C. Samples were analyzed utilizing a 25-minute gradient (pH=6 potassium phosphate and acetonitrile) HPLC method. Using the model y=a*(1 +x)^Ab, release data were fitted to a continuous profile, the equation of which was used to determine the average daily flux. Release data represent N=3 rods, mean ± standard deviation (SD). Example 4: drug release studies of TFV and UC781 loaded polvurethanes

Approximately 15 mm long segments were incubated in 25 mM sodium acetate buffer with 2% Solutol HS-15 (pH=4.2) (changed daily) at 37°C and 80 rpm in a heated shaker for 30 days. Samples of release media, taken after 24 ± 1 hrs. incubation were taken and stored at -80°C. For lots '68' and '40' equal volumes of each aliquot were mixed in an HPLC vial to represent the average daily concentration of each analyte. For all other materials, aliqouts from three timepoints throughout the release study were analyzed by HPLC. Using the model y=a*(1 +x)^Ab, release data was fitted to a continuous profile, the equation of which was used to determine the average daily flux. Release data represent N=3 rods, mean ± SD.

Results showed that UC781 fl ux is 2-3 μg/mm²/d and minimally impacted by polymer composition; TFV flux ranged from 2-23 μg/mm²/d and was correlated with 1) degree of swelling, 2) hard segment percentage, and 3) silicone content. It was found that initial drug burst release increased with increasing hardness of the polyurethane material. This was both surprising and unexpected. In general, the initial drug burst release was expected to decrease with increasing hardness of polyurethane.

Example 5 Processing stability and accelerated stability study of TFV and UC781 loaded polvurethanes Lot# 1 100032 was compounded with TFV and UC781 and it was found that Mw decreased to 58% of the original value after extrusion (Table 2). The decrease in the molecular weight of Lot# 1 100032 may be mainly caused by the relatively high water content of the polymer before being extruded and the TFV (20 wt% in PU) being a monohydrate which tends to facilitate the hydrolysis of the PU material. Various antioxidants were incorporated into lot# 1 100032 in order to improve the process stability, and it was found that Mw still reduced to 39-61 % of the original value with antioxidants (Table 2). The results suggest that antioxidants do not improve the process stability of the polyurethanes compounded with drugs.

In addition to the processing stability studies, accelerated stability study was also performed on Lot# 1100032 compounded with TFV and UC781 , with various antioxidants added. Samples were pulled after -2.5 month and stability of Lot# 1 100032 was evaluated by Mw analyses. It was found that the Mw hardly changed after the -2.5 months' accelerated stability study compared to the control (t=0) for all antioxidants. The results suggest that Lot# 1 100032 was stable in the accelerated storage conditions in the presence of the drugs and antioxidants.

Example 6 Drug stability in TFV and UC781 loaded polyurethanes

The drug stability in compounded lot# 1100032 was also studied after extrusion and under accelerated storage conditions, with and without various antioxidants (Table 3). The results suggest that the process flow temperature (128°C- 155°C) of the polyurethanes were low enough to retain UC781 stability after the extrusion. The 4-5 week, 60°C data showed that Irganox is incompatible with UC781. UC781 showed the best stability with BHT, EDTA or without any additives.

Example 7 Cytotoxicity of polyurethanes

50±5 mg of extruded polymer rod segments (single extrusion, no cryogrinding, no drying) were dipped in 70% isopropanol for 5 seconds and air dried for about an hour in a laminar flow hood. Rods were transferred to microcentrifuge tubes and incubated in 1.5 ml of Keratinocyte-SF cell media. The tubes were allowed to rotate in the microcentrifuge at setting "8" for 24 hrs at room temperature. Pieces of latex (6-7 per tube measuring 5mm x 2mm) were also incubated in 1.5 ml media/ tube. N-9 (49.6μΜ cone.) was made in media. Vk2 cells were plated at a density of 40,000 cells per well (96-well format) and incubated for 24 hrs (37C, 5% C0₂). 300μΙ of media from each rod-containing and latex-containing centrifuge tube is added to the cells (N=6). 300μ of N-9 in media was also added to cells (N=6). The cells were incubated for 24hrs. A cell viability analysis using the Cell Titer 96 Aqueous Non-Radioactive Cell Proliferation Assay (MTS assay) was performed.

It was found that (see Table 1) the preliminary batches prepared with dibutyltin dilaurate as catalyst were cytotoxic to a vaginal cell line (e.g., lot# 1 100032). In later batches (e.g., lot# 1100121), dibutyltin dilaurate was replaced by stannous octoate and the batches were found to be non-cytotoxic. The results suggest that dibutyltin dilaurate is the cause of cytotoxicity for the batches which use this catalyst and stannous octoate should be used as the catalyst.

Table 1. Comparison of polyurethane batches. *Dailv drug flux calculated using the mixing method, all others using the curve-fitting method

Table 2. Process stability and accelerated stability study of lot#100032 + drugs with and without various antioxidants added based on M measured by GPC. Accelerated stability measured after 2.5 month.

EDTA = ethylenediaminetetraacetic acid

CA = citric acid

IRGANOX = octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate

BHT = butylated hydroxytoluene

Table 3. UC781 stability in Lot#1100032 with and without additives

Claims

1) A polyurethane copolymer, wherein the copolymer has the structure according to formula (I):

wherein,

SME1 and SME2 can be the same or different and denote a surface modifying end-group, having a number average molecular weight ranging from 200 to 8000, linked to the polymer via a urethane or urea bond resulting from the reaction of an amine- or alcohol-terminated surface modifying end group with an isocyanate group;

SS1 , SS2, and SS3 denote soft-segments, wherein

553 is a soft-segment selected from polycarbonate diol and polyester diol, and mixtures thereof;

Polyurethane copolymer according to claim 1 , further comprising at least one pharmaceutically active substance.

Polyurethane copolymer according to claim 1 , wherein the diisocyanate is selected from the group consisting of isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HMDI) and combinations thereof.

Polyurethane copolymer according to claim 1 , wherein the surface modifying end group is selected from an amine- or alcohol-terminated polyalkylene oxide, silicone, alkyl, alkylester, polyalkylene ester and mixtures thereof. Polyurethane copolymer according to any one of claims 1-16, wherein the percentage of hard segment in the copolymer ranges from 20 - 45 weight% related to the total weight of the copolymer.

Polyurethane copolymer according to claim 1 , wherein the dry hardness of the polyurethane copolymer ranges from 40A - 45D and the swollen hardness of the copolymer ranges from 30A - 90A.

Polyurethane copolymer according to claim 1 , wherein the polydispersity index (Mw/Mn) of the copolymer is in the range 1.5 - 2.5.

Polyurethane copolymer according to claim 1 , wherein the tensile strength of the copolymer varies from 1 15 psi - 5400 psi.

Polyurethane copolymer according to claim 2, wherein the pharmaceutically active substance is selected from a group of microbicides, contraceptive agents, estrogen receptor modulators, post-menopausal hormone, antiretroviral agents, anticancer agents, therapeutic agents, hormones, and combinations thereof.

Polyurethane copolymer according to claim 2, wherein the pharmaceutically active substance is an anti-HIV agent selected from the group consisting of non-nucleoside reverse transcriptase inhibitors, nucleoside reverse transcriptase inhibitors, and HIV entry inhibitors.

Polyurethane copolymer according to claim 10, wherein the non-nucleoside reverse transcriptase inhibitor is UC 781 and/or the nucleoside reverse transcriptase inhibitor is Tenofovir.

Process to produce a polyurethane copolymer according to claim 1 , comprising a polyaddition reaction of one or more diisocyanates with one or more diols, one or more chain extenders and one or more surface modifying end groups in the presence of a catalyst.

Process according to claim 12, wherein the polyurethane copolymer is further compounded with a pharmaceutically active substance at a temperature below 240 °C.

Process according to claim 12, wherein the catalyst is stannous octoate.

Process according to claim 12, wherein the process further comprises adding at least one antioxidant.

A drug delivery device comprising the polyurethane copolymer according to any one of claims 1-8. The device according to claim 16, wherein the device is selected from cardiovascular devices, ophthalmic devices, contraceptive devices, antivirus devices, drug-eluting stents, transdermal devices, and/or intrauterine devices. The device according to claim 16, wherein at least one pharmaceutically active substance is uniformly dispersed, diffused, or dissolved throughout the polyurethane copolymer.

The device according to claim 16, wherein the polyurethane copolymer forms a single segment drug delivery device.

The device according to claim 16, wherein the mean daily flux of at least one of the pharmaceutically active substances is greater than 0.1 μg/ mm²/d.