Biodegradable polyurethane and polyurethane ureas

Abstract

This invention relates to biocompatible, biodegradable thermoplastic polyurethane or polyurethane/ureas comprising isocyanate, polyol and a conventional chain extender and/or a chain extender having a hydrolysable linking group and their use in tissue engineering and repair applications, particularly as stents and stent coating.

Claims

1. A tissue engineering scaffold comprising a cured polyurethane or polyurethane/urea, wherein said polyurethane or polyurethane/urea comprises the reaction product of isocyanate, polyol, a chain extender having a hydrolysable linking group and, optionally, a conventional chain extender, said polyol having a molecular weight of 120 to less than 400, said chain extender having a hydrolysable linking group selected from the group consisting of diols and dithiols, the acid number of the polyurethane or polyurethane/urea is about zero, and the tissue engineering scaffold is biocompatible and biodegradable, wherein the polyurethane or polyurethane/urea comprises hard and soft segments and the amount of hard segment is 20 to 70% by weight based on the total weight of the polyurethane or polyurethane/urea; and wherein the soft segment comprises said polyol.

2. A scaffold according to claim 1 wherein said isocyanate is selected from the group consisting of lysine diisocyanate methyl ester, lysine diisocyanate ethyl ester, butane diisocyanate, hexamethylene diisocyanate and 4,4-methylenebis(cyclohexylisocyanate).

3. A scaffold according to claim 1 wherein said polyol is of the formula: ##STR00016## wherein h and/or k can equal 0 or are integers as is j and R and R independently of each other are hydrogen, hydroxy alkyl, aminoalkyl (both primary and secondary) or carboxy alkyl and R and R cannot be hydrogen, but can be a linear or branched alkyl, alkenyl, aminoalkyl, alkoxy or aryl.

4. A scaffold according to claim 3 wherein said polyol is selected from the group consisting of polyglycolic acid, poly (lactic acid) diol, poly (-caprolactone) diol and polyethylene glycol.

5. A scaffold according to claim 3, wherein each occurrence of R is the same.

6. A scaffold according to claim 1 wherein said isocyanate is selected from the group consisting of lysine diisocyanate ethyl ester and hexamethylene diisocyanate; the chain extender having a hydrolysable linking group is ethylene glycol-lactic acid diol; and said polyol is selected from the group consisting of poly (-caprolactone) diol and polyethylene glycol.

7. A scaffold according to claim 3, wherein said polyol comprises a monomer selected from the group consisting of lactic acid, glycolic acid, caprolactone, ethylene glycol, propylene glycol, 4-hydroxybutyrate, 3-hydroxybutyrate, and mixtures thereof.

8. A scaffold according to claim 1, further comprising cells and/or growth factors.

9. A scaffold according to claim 8, wherein the cells are progenitor cells.

10. A scaffold according to claim 1, further comprising pharmaceuticals for use in drug delivery.

11. A scaffold according to claim 1, further comprising drugs.

12. A scaffold according to claim 1 which is a stent or stent coating.

13. A scaffold according to claim 1, further comprising pore sizes in a range of 100-500 microns.

14. A scaffold according to claim 1, further comprising a compressive strength of 0.05-100 MPA.

15. A scaffold according to claim 1, further comprising biological and/or inorganic components selected for their ability to aid tissue repair in vivo or to create physical characteristics for rapid prototyping purposes.

16. The scaffold according to claim 1, which is an in vivo tissue engineering scaffold.

17. A method of repairing tissue comprising inserting into a patient in need of tissue repair a scaffold according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the SEM of a polyurethane scaffold made according to Example 1.

(2) FIG. 2 shows the SEM of a polyurethane scaffold made according to Example 1 but under higher magnification.

(3) FIG. 3 shows the scaffold of Example 1 and demonstrates stratified design and overlap in the z axis.

(4) FIG. 4 shows the scaffold of Example 1 showing the interconnected pores in a regular section.

(5) FIG. 5 shows the scaffold of Example 1 under light microscopy and demonstrates optical clarity and fusion.

(6) FIG. 6 shows the scaffold of Example 1 under light microscopy and demonstrates the proliferation of primary ovine fibroblast therein.

(7) FIG. 7 shows the scaffold of Example 9 under optical microscopy after 9 weeks cell culture.

(8) FIG. 8 shows the scaffold of Example 9 under scanning electron microscopy and demonstrates confluent cell growth.

(9) FIG. 9 shows the scaffold of Example 9 under scanning electron microscopy and demonstrates confluence and some bridging.

(10) FIG. 10 shows the scaffold of Example 9 under scanning electron microscopy and demonstrates the bridging of a corner of the scaffold by cell growth.

(11) FIG. 11 shows the scaffold of Example 9 under scanning electron microscopy and shows a dose up of unsupported cells demonstrating a fibrous extra-cellular matrix.

DETAILED DESCRIPTION OF THE INVENTION

(12) The present invention provides polyurethanes and polyurethane/ureas which are particularly suited to rapid prototyping techniques such as fused deposition modelling and therefore have specific characteristics as described in the preamble of this specification.

(13) In a preferred form, this invention provides a biocompatible biodegradable polyurethane or polyurethane/urea comprising diisocyanates, polyol of molecular weight 200-600 and a conventional chain extender and/or a chain extender having a hydrolysable linking group.

(14) Isocyanates suitable for preparing polyurethanes and polyurethane/ureas according to the invention include but are not limited to the following:

(15) ##STR00002##
MLDIlysine diisocyanate methyl ester

(16) ##STR00003##
ELDIlysine diisocyanate ethyl ester

(17) ##STR00004##
BDIButane diisocyanate

(18) ##STR00005##
HDIhexamethylene diisocyanate

(19) ##STR00006##
H.sub.12MDI4,4-methylene-bis(cyclohexyl isocyanate)
Polyols or soft segments which may be used to prepare the polyurethanes and polyurethane/ureas of the invention are most preferably those having a molecular weight of 200-400. The structure of the polyol in the present invention is preferably:

(20) ##STR00007##
where h and/or k can equal 0 (as is the case of the dimer, eg, h=0, j=1 and k=1) or are integers as is j and R and R independently of each other are hydrogen, hydroxy alkyl, aminoalkyl (both primary and secondary) or carboxy alkyl and R and R cannot be hydrogen, but can be a linear or branched alkyl, alkenyl, aminoalkyl, alkoxy or aryl. The molecular weight of the entire structure is more preferably 120 to 400. Less preferably the molecular weight can be up to 2000 and much less preferably above 2000. Four examples of suitable soft segments are as follows: Poly(-caprolactone) diol, MW 400 (from Example 1): where R is (CH.sub.2CH.sub.2), R is (CH.sub.2).sub.5, R and R are both H, and j=1 and (h+k)=2.96 (Glycolic acid-ethylene glycol) dimer (from Example 8): where R is (CH.sub.2CH.sub.2), R is (CH.sub.2), R and R are both H, j=1 and (h+k)=1 Poly(ethylene glycol), MW 400 (from Example 4): h=0, k=0, j=13, R is (CH.sub.2CH.sub.2), and R and R are both H Poly(ethylene glycol)bis(3-aminopropyl) terminated (Aldrich): where R is (CH.sub.2CH.sub.2), R and R are both (CH.sub.2).sub.3NH.sub.2, j=34 and (h+k)=0
Either or both of R and R can contain nonlinear structures, for example where R(CH.sub.2CHCH.sub.3) which is lactic acid. However, the R and R should preferably not contain groups such as OH and NH.sub.2 which are likely to cause crosslinking. Suitable compounds include but are not limited to the following polyester polyols:

(21) ##STR00008##
PGAPoly-(glycolic acid) diol, where R is typically (CH.sub.2CH.sub.2)

(22) ##STR00009##
PLAPoly-(lactic acid) diol, where R is typically (CH.sub.2CH.sub.2)

(23) ##STR00010##
PCLPoly-(-caprolactone) diol, where R is typically (CH.sub.2CH.sub.2)

(24) ##STR00011##
PEGPoly-(ethylene glycol)

(25) Examples of other polyols which may act as soft segments include poly-(4-hydroxybutyrate) diol (P4HB diol), poly-(3-hydroxybutyrate) diol (P3HB diol), polypropylene glycol and any copolymers of the aforesaid including PLGA diol, P(LA/CL) diol, P(3HB/4HB) diol.

(26) Chain extenders according to the invention are any low molecular weight molecule having two or more functional groups which when reacted with diisocyanates form a urethane or urea linkage. Preferably the chain extender is difunctional and examples of such chain extenders are diols, dithiols, diamines, amino alcohols and dicarboxylic acids. Diols are also relatively non-toxic and can be resorbed or excreted from the body upon degradation and examples include ethylene glycol, diethylene glycol, tetraethylene glycol, 1,3-propane diol, 1,4-butane diol, 1,6-hexane diol, GA-EG dimer, LA-EG dimer, trimers including a combination of LA and/or GA and EG, and oligomeric diols such as dimers and trimers. Examples of amines that may be used are butane diamine, ethanolamine, glycine and lysine. Incorporated into the hard segment, these chain extenders increase degradation. Esters in the hard segment degrade much faster than urethane linkages. The following chain extenders are illustrated:

(27) ##STR00012##
A degradable diol chain extender EG-GA diol, MW120

(28) ##STR00013##
A degradable chain extender EG-LA diol, MW134

(29) ##STR00014##
A degradable diol chain extender EG-4HB diol, MW148

(30) Preferred polyurethane and polyurethane/ureas prepared according to the invention may utilise PCL diol, PGA diol, PLA diol or PEG diol and HDI/EG as the hard segment. Another preferred polyurethane or polyurethane/urea according to the invention includes a diol of poly(4-hydroxybutyrate) or copolymers therewith to give an improved range of properties and degradation rates.

(31) According to the present invention, the monomeric units of the polyurethanes or polyurethane/ureas of the invention are preferably reacted by bulk polymerisation to form a straight-chain poly-(ester-urethane) block copolymer. Catalysts such as titanium butoxide, Tyzor-LA, stannous octoate, ferric acetyl acetonate, magnesium methoxide, zinc octoate, manganese 2-ethyl hexanoate, amine catalyst may, if desired, be used in such polymerisation. The general form of the repeat units in the polymer after polymerisation is:

(32) ##STR00015##
Where R.sub.1 is from the diisocyanate e.g. hexamethylene diisocyanate. R.sub.2 is from a low molecular weight diol chain extender e.g. ethylene glycol. R.sub.3 is from a soft segment diol e.g. PCL diol (MW 400). The pronumeral n represents the average number of repeat units in the hard segment. The pronumeral p is proportional to the molecular weight of the polymer and includes both the hard segment repeat units and the soft segment.

(33) In a preferred embodiment of the invention, the hard segment represents 20 to 100% by weight of the polyurethane/polyurethane/urea. More preferably the hard segment represents 60 to 70% by weight. The polyol and chain extender may be the same compound and this corresponds to the embodiment where the hard segment corresponds to 100% by weight of the polyurethane/polyurethane/urea. It has been found that there must be a reasonably high proportion of hard segment for the materials to have adequate properties to extrude through FDM as well as a reasonably high melt flow index.

EXAMPLES

(34) The following examples are not intended to limit the invention but rather illustrate the nature of the broad invention and its applicability.

Example 1

Preparation of 12TM4 (65% Hard Segment, 35% PCL Diol 400)

(35) Materials: The PCL diol (molecular weight 402.1) from ERA Polymer Pty was dried at 90 C. for 4 hours under vacuum (0.1 torr). Ethylene glycol (Aldrich) was degassed at 90 C. under vacuum (0.1 torr) for three hours and HDI (Aldrich) was used as received. A polyurethane composition based on a mixture of PCL diol, EG and HDI was prepared by a one-step bulk polymerisation procedure. Stannous octoate (Aldrich) was kept moisture-free and used as received.

(36) A mixture of PCL (25.000 g) and EG (9.696 g) and stannous octoate (0.0714 g) was placed in a 100 ml predried polypropylene beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. HDI (36.732 g) was weighed in a separate wet-tared predried polypropylene beaker and added to the PCUEG/stannous octoate beaker and stirred manually until gelation occurred (90 seconds), at which time the viscous mixture was poured onto a Teflon coated metal tray to cure at 100 C. for a period of about 18 hours. The resulting polymer was clear, colourless and tough.

(37) A sample of the polymer after curing was compression moulded at 175 C. to a 1 mm thick flat sheet for tensile testing. Dumbbells punched from the sheet were tensile tested using an Instron Model 5568 Universal Testing Machine.

(38) The mechanical properties of the materials prepared in EXAMPLE 1 were examined and the results are shown in Table 1.

Example 1a

Post-Synthesis Processing

(39) The solid polymer sheet was chopped into about 1 cm.sup.3 pieces with clean tin-snips, cooled in liquid nitrogen and ground into a powder using a cryogrinder. The polymer powder was then dried at 100 C. under vacuum overnight. The polymer was extruded on a mini-extruder equipped with a 1.7 mm die at 180 C. and 40 rpm. The polymer was taken off by a belt conveyor and cooled at ambient temperature in air without water bath. The filament was spooled and kept under nitrogen in a moisture-free environment for at least one week prior to use.

(40) The polymer filament was fed though the FDM apparatus and a small lattice was made to show that the material was suitable for FDM. The scaffolds were characterised by light microscopy and SEM and were shown to have very good precision and weld. It has been shown to work with a number of commercially available nozzle diameters.

(41) The operating envelope temperature inside the machine was 25 C. and the heating zone was set at 168 C. SEM micrographs and optical microscopy of FDM scaffolds are shown in FIGS. 1-6.

Example 2

Preparation of 12TM1 (a Softer Material than Example 1, 60% Hard Segment, 40% PCL Diol 400)

(42) Materials: The PCL diol (molecular weight 402.1) from ERA Polymer Pty was dried at 90 C. for 4 hours under vacuum (0.1 torr). Ethylene glycol (Aldrich) was degassed at 90 C./0.1 torr for 3 hours and HDI (Aldrich) was used as received. A polyurethane composition based on a mixture of PCL diol, EG and HDI was prepared by a one-step bulk polymerisation procedure. Stannous octoate (Aldrich) was kept moisture-free and used as received.

(43) A mixture of PCL (40.0 g) and EG (11.663 g) and stannous octoate (0.100 g) was placed in a 100 ml predried polypropylene beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. HDI (48.337 g) was weighed in a separate wet-tared predried polypropylene beaker, covered and then added to the PCUEG/stannous octoate beaker and stirred manually until gelation occurred (90 seconds). The viscous mixture was poured onto a Teflon coated metal tray to cure at 70 C. for a period of about 18 hours. The resulting polymer was clear, colourless and tough.

(44) A sample of the polymer after curing was compression moulded at 170 C. to a 1 mm thick flat sheet for tensile testing. Dumbbells punched from the sheet were tensile tested using an Instron Model 5568 Universal Testing Machine.

(45) The mechanical properties of the materials prepared in EXAMPLE 2 were examined and the results are shown in Table 1.

Example 2a

Post-Synthesis Processing

(46) The solid polymer sheet was chopped into about 1 cm.sup.3 pieces with clean tin-snips, cooled in liquid nitrogen and ground into powder using a cryogrinder. The polymer powder was then dried at 70 C. under vacuum overnight. The polymer was extruded on the mini-extruder equipped with a 1.7 mm die at 175 C. and 35-40 rpm. The polymer was taken off on a rotating shaft and cooled at ambient temperature in air without water bath. The filament was spooled and kept under nitrogen in a moisture-free environment for at least one week prior to use.

(47) The polymer filament was fed though the FDM apparatus and a small lattice was made to show that the material was suitable for FDM.

Example 3

Preparation of 12TM6 (a Harder Material than Example 1, 70% Hard Segment, 30% PCL Diol 400)

(48) Materials: The PCL diol (molecular weight 402.1) from ERA Polymer Pty was dried at 90 C. for 4 hours under vacuum (0.1 torr). Ethylene glycol (Aldrich) was degassed at 90 C./0.1 torr for 3 hours and HDL (Aldrich) was used as received. A polyurethane composition based on a mixture of PCL diol, EG and HDI was prepared by a one-step bulk polymerisation procedure. Stannous octoate (Aldrich) was kept moisture-free and used as received.

(49) A mixture of PCL (21.0 g) and EG (10.840 g) and stannous octoate (0.070 g) was placed in a 100 ml predried polypropylene beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. HDI (38.160 g) was weighed in a separate predried polypropylene beaker and added to the PCL/EG/stannous octoate beaker and stirred until gelation occurred (60 seconds), at which time the viscous mixture was poured onto a Teflon coated metal tray to cure at 100 C. for a period of about 18 hours. The resulting polymer was clear, colourless and tough.

(50) A sample of the polymer after curing was compression moulded at 175 C. to a 1 mm thick flat sheet for tensile testing. Dumbbells punched from the sheet were tensile tested using an Instron Model 5568 Universal Testing Machine.

(51) The mechanical properties of the materials prepared in EXAMPLE 3 were examined and the results are shown in Table 1.

Example 3a

Post-Synthesis Processing

(52) The solid polymer sheet was chopped into about 1 cm.sup.3 pieces with clean tin-snips, cooled in liquid nitrogen and ground into powder using a cryogrinder. The polymer powder was then dried at 70 C. under vacuum overnight. The polymer was extruded on the mini-extruder equipped with a 1.7 mm die at 175 C. and 40 rpm. The polymer was taken off on a rotating shaft and cooled at ambient temperature in air without water bath. The filament was spooled and kept under nitrogen in a moisture-free environment for at least one week prior to use.

(53) The polymer filament was fed though the FDM apparatus and a small lattice was made to show that the material was suitable for FDM.

Example 4

Preparation of 14TM12 (Changing the Soft Segment to PEG Diol

(54) Materials: The PEG diol (molecular weight 394.7) from Aldrich was dried at 90 C. for 4 hours under vacuum (0.1 torr). Ethylene glycol (Aldrich) was degassed at 90 C./0.1 torr for three hours and HDI (Aldrich) was used as received. A polyurethane composition based on a mixture of PCL diol, EG and HDI was prepared by a one-step bulk polymerisation procedure. Stannous octoate (Aldrich) was kept moisture-free and used as received.

(55) A mixture of PEG (20.000 g) and EG (7.715 g) and stannous octoate (0.0571 g) was placed in a 100 ml predried polypropylene beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. HDI (29.428 g) was weighed in a separate predried polypropylene beaker, and added to the PEG/EG/stannous octoate beaker and stirred until gelation occurred (150 seconds), when the viscous mixture was poured onto a Teflon coated metal tray to cure at 70 C. for a period of about 18 hours. The resulting polymer was clear, colourless and tough.

(56) A sample of the polymer after curing was compression moulded at 150 C. to a 1 mm thick flat sheet for tensile testing. Dumbbells punched from the sheet were tensile tested using an Instron Model 4032 Universal Testing Machine.

Example 4a

Post-Synthesis Processing

(57) The solid polymer sheet was chopped into about 1 cm.sup.3 pieces with clean tin-snips, cooled in liquid nitrogen and ground into powder using a cryogrinder. The polymer powder was then dried at 100 C. under vacuum overnight. The polymer was extruded on the mini-extruder equipped with a 1.7 mm die at 150 C. and 40 rpm. The polymer was taken off by a belt conveyor and cooled at ambient temperature in air without water bath. The filament was spooled and kept under nitrogen in a moisture-free environment for at least one week prior to use.

(58) The polymer filament was fed though the FDM apparatus and a small lattice was made to show that the material was suitable for FDM. The scaffolds were characterised by light microscopy and SEM and were shown to have very good precision and weld. It has been shown to work with a number of commercially available nozzle diameters.

(59) The operating envelope temperature inside the machine was 25 C. and the heating zone was set at 168 C.

Example 5

Preparation of 14TM3-1 (Using a Different DiisocyanateMLDI)

(60) Materials: The PEG diol (molecular weight 394.7) from Aldrich was dried at 90 C. for 4 hours under vacuum (0.1 torr). Ethylene glycol (Aldrich) was degassed at 90 C./0.1 torr for 3 hours. Methyl ester of Lysine diisocyanate MLDI (Kyowa Hakko Kogyo CO. Ltd) was used as received. A polyurethane composition based on a mixture of PCL diol, EG and HDI was prepared by a one-step bulk polymerisation procedure. Stannous octoate (Aldrich) was kept moisture-free and used as received.

(61) A mixture of PEG (12.814 g) and EG (16.380 g) and stannous octoate (0.0992 g) was placed in a 100 ml predried polypropylene beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. MLDI (70.00 g) was measured in a separate predried polypropylene beaker and added to the beaker containing mixture of PEG/EG/stannous octoate and stirred until gelation occurred (300 seconds), at which time the viscous mixture was poured onto a Teflon coated metal tray to cure at 70 C. for a period of about 18 hours. The resulting polymer was clear, slightly golden in colour and tough.

(62) A sample of the polymer after curing was compression moulded at 175 C. to a 1 mm thick flat sheet for tensile testing.

Example 6

Preparation of 16TM9 (100% Hard Segment Using MLDI and EG)

(63) Materials: The EG (Aldrich) was degassed at 90 C./0.1 torr for three hours. MLDI (Kyowa Hakko Kogyo CO. Ltd) was used as received. A polyurethane composition based on a 1 to 1 ratio of MLDI and EG was prepared by a one-step bulk polymerisation procedure. Stannous octoate (Aldrich) was kept moisture free and used as received.

(64) EG (22.000 g) and stannous octoate (0.0972 g) were weighed into a 100 ml predried polypropylene beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. MLDI (75.214 g) was measured in a separate predried polypropylene beaker, covered with aluminium foil and also heated under nitrogen at 70 C. before being added to the EG/stannous octoate and stirred until gelation occurred (700 sec), at which time the viscous mixture was poured onto a Teflon coated metal tray to cure at 70 C. overnight for a period of about 18 hours. The resulting polymer was clear, golden in colour, very hard and brittle.

Example 6a

Post-Synthesis Processing

(65) The melt flow index of the material prepared was measured to be 136 g/10 min with a 2.16 kg load.

Example 7

Preparation of 12TM19 Illustrating Shape Memory Effects (100% Hard Segment Using MLD1 and 2-ethyl-1,3-hexanediol)

(66) Materials: The 2-ethyl-1,3-hexanediol (Fluka) was degassed at 90 C./0.1 torr for 3 hours. MLDI (Kyowa Hakko Kogyo CO. Ltd) was used as received. A polyurethane composition based on a 1 to 1 ratio of MLDI and 2-ethyl-1,3-hexanediol was prepared by a one-step bulk polymerisation procedure. Stannous octoate (Aldrich) was kept moisture free and used as received.

(67) 2-ethyl-1,3-hexanediol (8.269 g) and stannous octoate (0.021 g) were weighed into a 100 ml predried polypropylene beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. MLDI (12.000 g) was measured in a separate predried polypropylene beaker, covered with aluminium foil and also heated under nitrogen at 70 C. before being added to the 2-ethyl-1,3-hexanediol/stannous octoate and stirred until gelation occurred (30 min), at which time the viscous mixture was poured onto a Teflon coated metal tray to cure at 70 C. overnight for a period of about 18 hours. The resulting polymer was clear, golden in colour, very hard and brittle.

Example 7a

Post-Synthesis Processing

(68) DSC was taken on a Mettler DSC 30 and showed the Tg to be 30 C. When left at room temperature it was hard and brittle but it reversibly softened in the hand and became elastic.

Example 8

Preparation of a Hydrolysable Chain Extender (15TM7, GA-EG Diol)

(69) 22.19 g of glycolic acid (GA) (Sigma) was heated at 200 C. under nitrogen outgassing in a round bottomed flask equipped with a stillhead sidearm and condenser to collect the water runoff. After 18 hours the nitrogen was stopped and vacuum applied (0.1 torr), by which stage the GA had polymerised to a white solid (PGA). Dry ethylene glycol (EG) (Aldrich) (106 g) was added to the PGA in an approximate ratio of 5:1 in order to transesterify the polymer. This was refluxed for a period of 8 hours in total and was followed by GPC until there were three major products: EG, EG-GA and some EG-GA-GA. The EG was removed under vacuum and heat and the resulting chain extender was used to make a polyurethane (16TM7).

Example 8a

Preparation of a Polyurethane Using a Hydrolysable Chain Extender (16TM7 from Example 8)

(70) Materials: The 15TM7 (GA-EG diol chain extender) was degassed at 90 C./0.1 torr for three hours, as was the PCL diol (MW400). HDI (Aldrich) was used as received. A polyurethane composition based on an 80% hard segment composition was prepared by a one-step bulk polymerisation procedure. Stannous octoate (Aldrich) was kept moisture free and used as received.

(71) 15TM7 (30.73 g) and PCL diol (MW402.099) (20.05 g) and stannous octoate (0.100 g) were weighed into a 100 ml predried polypropylene beaker, covered with aluminium foil and heated to 70 C. under nitrogen in. a laboratory oven. HDI (49.47 g) was measured in a separate predried polypropylene beaker, covered with aluminium foil and also heated under nitrogen at 70 C. before being added to the PCL diol/15TM7/stannous octoate mixture and stirred until gelation occurred when the viscous mixture was poured onto a Teflon coated metal tray to cure at 70 C. overnight for a period of about 18 hours. The resulting polymer was slightly cloudy, hard but flexible.

(72) TABLE-US-00001 TABLE 1 Mechanical properties of some PCL-based polyurethanes with different hard segment percentages Hard segment Y. Mod UTS Shore Code (Wt %) Elong (%) (MPa) (MPa) (D) 12TM1 60 899 189 103 5 41 1 44 12TM4 65 1300 42 112 3 54 5 52 12TM6 70 1537 141 143 7 56 6 57

(73) TABLE-US-00002 TABLE 2 Melt flow index of various materials The Melt Flow Index of various materials according to the present invention was calculated, along with the readily available commercial materials: acrylonitrile butadiene styrene (ABS), polyamide and investment casting wax (ICW). In order to be suitable for FDM, the materials of the present invention preferably should have a MFI which is similar or higher than that of the commercial samples, without significant degradation of the material. MFI (g/10 min), 2.16 kg Material Temperature ( C.) weight ABS 270 8.5 Polyamide 140 75 ICW 73 9.5 14TM3-1 160 7.64 12TM4-6 165 10.43 16TM9 160 136
It will be appreciated that the scope of the invention is not limited to the specific examples described herein but extends to the general inventive concepts defined. None of the examples should be considered limiting.

Example 9

Cell Compatibility of Scaffolds

(74) This example illustrates the cell compatibility of scaffolds fabricated using polymers prepared according to the invention.

(75) Polymers were prepared according to the procedure disclosed in Example 1 and 3D scaffolds were fabricated using the procedure described in EXAMPLE 1A.

(76) Three dimensional scaffolds similar to those shown in FIGS. 1 to 3 were seeded with primary ovine fibroblasts explanted from the aortic heart-valve leaflet. The cells were grown in Dulbecco's Modified Eagle's Medium (DMEM) in static culture for a period of nine weeks. The temperature was 37 C. and incubator contained 5% CO.sub.2(g). The DMEM was replaced every five days. At the end of the nine weeks the scaffolds were cross linked using glutaraldehyde and then dehydrated progressively through ethanol and dried.

(77) SEM micrographs and optical microscopy of the cell-seeded FDM scaffolds are shown in FIGS. 7-11.

Example 10

(78) This example illustrates the preparation of polyurethanes by varying the weight percentage of hard segment, the molecular weight of the soft segment polyol and the type of polyol. The quantities of the diisocyanate, polyol and the chain extender used are summarised in Table 3. The following example illustrates the procedure used in making sample with code TM1-9 in Table 3. Other materials in the Table were prepared accruing the same one-step polymerisation procedure.

(79) Preparation of TM1-9 (50% Hard Segment, 50% PCL Diol 1000).

(80) Materials: The PCL diol (molecular weight 1000) from ERA polymer Pty Ltd was dried at 90 C. for four hours under vacuum (0.1 torr). Ethylene glycol (Aldrich) was distilled and degassed at 90 C. under vacuum (0.1 torr) for three hours. Ethyl-LDI was distilled before use. Stannous octoate (Aldrich) was used as received. A polyurethane composition based on a mixture of PCL diol, EG and eLDI was prepared by a one-step bulk polymerisation procedure.

(81) A mixture of PCL diol (20.000 g) and EG (3.336 g) and stannous octoate (0.040 g) were placed in a 100 ml predried glass beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. ELDI (16.665 g) was weighed in a separate wet-tared predried polypropylene beaker and added to the PCL/EG/stannous octoate beaker, covered with aluminium foil and heated to 70 C. under nitrogen in a laboratory oven. ELDI was then added to the PCL/EG/stannous octoate beaker and stirred manually until gelation occurred at which time the viscous mixture was poured onto Teflon coated metal tray to cure at 100 C. for a period of about 18 hours. The resulting polymer was clear, colourless and rubbery. The molecular weight of the polymer was determined by gel permeation chromatography and the results reported in Table 3 are relative to polystyrene standards.

(82) TABLE-US-00003 TABLE 3 Formulation details of various polyurethanes prepared. Soft Segments Hard Diisocyanate Chain Extenders PCL PCL PEG Segment eLDI HDI EG EG-LA TETEG 1000 2000 1000 GPC Results (in THF) Code (%) (g) (g) (g) (g) (g) (g) (g) (g) Mn Mw PD TM1-11 30 10.778 1.222 28.000 58,758 97,196 1.65 TM1-9 50 16.665 3.336 20.000 94,673 172,649 1.82 TM1-14 70 22.551 5.449 12.000 55,398 92,696 1.67 TM1-15 70 18.587 9.413 12.000 57,847 115,357 1.99 TM1-16 100 25.111 14.889 28,242 51,038 1.81 TM1-22 50 15.305 1.266 3.429 20.000 56,742 94,031 1.66 TM1-23 50 13.889 2.584 3.527 20.000 39,369 73,452 1.87 TM1-24 50 12.846 7.154 20.000 53,266 96,737 1.82 TM1-25 70 16.313 11.687 12.000 50,059 89,809 1.79 TM1-27 33.33 11.759 1.574 13.333 13.333 55,398 97,045 1.75 TM1-28 33.33 9.410 3.923 13.333 13.333 47,625 63,464 1.33 TM1-30 50 16.665 3.335 10.000 10.000 43,770 72,845 1.66 TM1-31 50 14.238 5.762 10.000 10.000 30,631 50,196 1.64 TM1-29 50 16.178 3.822 20.000 59,057 101,750 1.72 TM1-32 50 13.397 6.603 20.000 36,466 61,103 1.68 Abbreviations: eLDI: lysine diisocyanate ethyl ester, HDI: hexamethylene diisocyanate, EG-LA: ethylene glycol-lactic acid ester diol: TETEG: tetraethylene glycol, PCL: polycaprolactone diol, PEG: poly(ethylene glycol), PD: polydispersity.

Example 11

Use as Stent Coatings

(83) This example illustrates that the polymers could be easily dissolved in solvents such as tetrahydrofuran and coated on stainless steel surfaces.

(84) The polymers TM1-9, TM1-11, TM1-14, TM1-15 and TM1-16 were dissolved separately in tetrahydrofuran to make 5%, 10% and 20% solutions. The solutions were used to coat stainless steel coupons by dip-coating and by spin coating (Spin coater: Model WS-400B-6NPP/Lite, Laurell Technologies Corporation). The coatings adhered well to the stainless steel showing their suitability for coating metallic surfaces. These polymers were also soluble in solvents such as chloroform, dichloromethane, dimethyl formamide and dimethyl acetamide.

Example 12

(85) The following example illustrates the preparation of strands, fibres and tubes using a reactive extruder (Prism Model)

(86) Polyurethanes were produced on a Prism 16 mm twin screw extruder of L/D=26:1 via liquid feed of the diisocyanate, polyester polyol, ethylene glycol and catalyst.

(87) Methyl ester Lysine diisocyanate (m-LDI), polycaprolactone diol GMW 426 (ERA 2043), chain extender ethylene glycol, and catalyst stannous 2 ethyl hexanoate were used as reagents to prepare polyurethanes with hard segment weight percentage of 65 and 95%.

(88) The ratio of isocyanate to hydroxyl was kept at 1:1 and the catalyst loading was 0.1 wt %. The throughput rate was 2 g/min and the reaction was controlled via extruder screw speed (for mixing control) and via the temperature settings across the 6 individual barrel sections and the dies. Materials based on 95 and 65% hard segment produced good tubes and filaments. A cross-linked polyurethane was produced using this technique by replacing 40% of the ethylene glycol with trimethylol propane in the 65% hard segment polyurethane formulation.

Example 13

15RA40: ELDI/PEG/EG/TMP 80% Hs

(89) A cross linked polyurethane material was produced following a one-step procedure as described below.

(90) A mixture of pre-dried (degassed) macrodiol PEG (2.5 g, MW 394.75), Ethylene glycol (18.77 g), Trimethylol propane (1.50 g, 40 mol % of EG) and catalyst Dibutyltin dilaurate (0.1 wt %) were weighed in a polypropylene beaker. The polymer mixture was then degassed at 70 C. for about an hour under a vacuum of 1 torr at 70 C. ELDI (7.10 g) was weighed in a syringe and added to the polyol mixture and stirred rapidly for about 3 minutes and then poured into a Teflon-coated metal pan and pressed under a nominal load of 8 tonn for 2 hours at 100 C. followed by further curing in a nitrogen-circulating oven 16 hours. The polymer showed maximum tensile stress (343 MPa), Youngs Modulus (1.0+0.2 MPa) and elongation at break 15632%).

Example 14

(91) A mixture of pre-dried (degassed) macrodiol PEG (10.0 g, MW 394.75); Ethylene glycol (7.17 g) and catalyst Dibutyltin dilaurate (0.1 wt %) was weighed in a polypropylene beaker. The polymer mixture was then degassed at 70 C. for about an hour under a vacuum of 1 torr at 70 C. ELDI (32.82 g) was weighed in a syringe and added to the polyol mixture and stirred rapidly for about 3 minutes and then poured into a Teflon-coated metal pan and pressed under a nominal load of 8 tonne for 2 hours at 100 C. followed by further curing in a nitrogen-circulating oven 16 hours. GPC showed molecular weight (MP) 112,000 and had maximum tensile stress (100.5 MPa), Young's Modulus (3.7+0.4 MPa) and elongation at break 3016%).