Polyurethanes for contact lenses

Abstract

The present invention provides a poly(ethylene) glycol based polyurethane polymer composition, particularly useful in the production of contact lenses. Generally the reactant mixture used to form the polymer includes a branched chain extender. There is also provided a method of manufacturing a contact lens formed from such a polymer.

Claims

1. A polyurethane xerogel prepared from a mixture consisting essentially of: i) a high molecular weight poly(ethylene glycol) compound having a number average molecular weight of 6000±250, wherein 52 to 53 wt. % of the mixture is formed from the high molecular weight poly(ethylene glycol) compound; ii) a low molecular weight poly(ethylene glycol) compound having a number average molecular weight of about 600, wherein 26 to 27 wt. % of the mixture is formed from the low molecular weight poly(ethylene glycol) compound; iii) dicyclohexylmethane-4,4′-diisocyanate (DMDI), wherein 18-19 wt. % of the mixture is formed from DMDI; iv) trimethylol propane (TMP), wherein 1.2 to 1.3 wt. % of the mixture is formed from TMP; v) poly(ethylene glycol) methyl ether (PEG Me), wherein 0.9 to 1.6 wt. % of the mixture is formed from PEG Me; and vi) butylated hydroxy anisole (BHA), wherein 0.49 to 0.5 wt. % of the mixture is formed from BHA.

2. A process for preparing a polyurethane xerogel in the form of a moulded article, said process comprising the steps of: (i) preparing a mixture as recited in claim 1; (ii) reaction cast moulding the mixture formed in step (i) using substantially anhydrous materials to form a moulded article.

3. A process for preparing a contact lens comprising the steps of: 1. preparing a mixture as recited in claim 1; 2. dispensing the reaction mixture formed in step 1 into a contact lens mould; 3. allowing the reaction mixture to react and cure; and 4. removing the contact lens from the mould; and hydrating the contact lens, in an aqueous fluid.

Description

EXAMPLES

(1) Examples of Embodiments without Silicone Component

Example 1

(2) TABLE-US-00001 Material Mn Mass/g No. of Mols Mol % wt % PEG 6000 5761 12 0.0021 4.5% 39.2695 DPG 134.17 1.5 0.0112 23.9% 4.9087 PEG-PPG-PEG 1100 7 0.0064 13.6% 22.9072 PEG 3350 3447 3.5 0.0010 2.2% 11.4536 BHA 180.24 0.031 0.0002 0.4% 0.1014 TMP 134.17 0.276 0.0021 4.4% 0.9032 DMDI 262.5 6.251 0.0238 51.0% 20.4563 DBTDL 0.10% 0.0306 Total 30.558 NCO:OH = 1:1 Average Results From six Batches Dk = 37 barrers; CA = 57°; % EWC = 69; Transmittance at 550 nm = 97%; Modulus = 0.87 MPa; Extension to break = 565%.

(3) Where CA represents sessile drop contact angle; EWC is equilibrium water content; DMDI=Desmodur W; DBTDL=Dibutyl tin dilaurate the other symbols represent as described in the text.

Example 2 (Less TMP)

(4) TABLE-US-00002 Material Mn Mass/g No. of Mols Mol % wt % PEG 6000 5761 12 0.0021 4.5% 39.4271 DPG 134.17 1.5 0.0112 24.2% 4.9284 PEG-PPG-PEG 1100 7 0.0064 13.8% 22.9992 PEG 3350 3350 3.5 0.0010 2.3% 11.4996 BHA 180.24 0.031 0.0002 0.4% 0.1019 TMP 134.17 0.243 0.0018 3.9% 0.7984 DMDI 262.5 6.162 0.0235 50.9% 20.2455 DBTDL 0.10% 0.0304 Total 30.436 Results From 3 Batches CA = 57°; % EWC = 70; Modulus = 0.63 MPa; Extension to break = 916%

Example 3 (More PEG 6000)

(5) TABLE-US-00003 Material Mn Mass/g No. of Mols Mol % wt % PEG 6000 5761 18 0.0031 6.6% 42.0221 DPG 134.17 1 0.0075 15.7% 2.3346 PEG-PPG-PEG 1100 7 0.0064 13.4% 16.3419 PEG 3350 3447 10 0.0029 6.1% 23.3456 BHA 180.24 0.062 0.0003 0.7% 0.1447 TMP 134.17 0.386 0.0029 6.1% 0.9011 DMDI 262.5 6.387 0.0243 51.3% 14.9099 DBTDL 0.10% 0.0428 Total 42.835 Average Results From 3 Batches CA = 57°; % EWC = 75; Modulus = 0.56 MPa; Extension to break = 245%

Example 4 (More PEG 6000)

(6) TABLE-US-00004 Material Mn Mass/g No. of Mols Mol % wt % PEG 6000 5761 14 0.0024 5.4% 36.3647 DPG 134.17 1 0.0075 16.5% 2.5975 PEG-PPG-PEG 1100 7 0.0064 14.1% 18.1824 PEG 3350 3447 10 0.0029 6.4% 25.9748 BHA 180.24 0.062 0.0003 0.8% 0.1610 TMP 134.17 0.347 0.0026 5.7% 0.9013 DMDI 262.5 6.090 0.0232 51.2% 15.8183 DBTDL 0.10% 0.0385 Total 38.499 Average Results From 3 Batches CA = 64°; % EWC = 76; Modulus = 0.48 MPa; Extension to break = 365%

Example 5 (NCO:OH=1.05:1.0)

(7) TABLE-US-00005 Material Mn Mass/g No. of Mols Mol % wt % PEG 6000 5761 12 0.0021 4.4% 38.9101 DPG 134.17 1.5 0.0112 23.4% 4.8638 PEG-PPG-PEG 1100 7 0.0064 13.3% 22.6976 PEG 3350 3350 3.5 0.0010 2.2% 11.3488 TMP 134.17 0.28 0.0021 4.4% 0.9079 DMDI 262.5 6.560 0.0250 52.3% 21.2719 BHA 0.10% 0.0308 0.0477 DBTDL 0.10% 0.0308 Total 30.840 Average Results Dk = 34.20barrers; % EWC = 67; Modulus = 0.72 MPa; Extension to break = 337%

Example 6 (More TMP)

(8) TABLE-US-00006 Material Mn Mass/g No. of Mols Mol % wt % PEG 6000 5761 20 0.0035 6.1% 49.7283 DPG 134.17 2 0.0149 26.2% 4.9728 PEG-PPG-PEG 1100 4 0.0036 6.4% 9.9457 PEG 3350 3350 6 0.0018 3.1% 14.9185 BHA 180.24 0.04 0.0002 0.4% 0.0995 TMP 134.17 0.483 0.0036 6.3% 1.2009 DMDI 262.5 7.696 0.0293 51.5% 19.1343 DBTDL 0.10% 0.0402 Total 40.219 Results CA = 43°; % EWC = 71; Modulus = 1.08 MPa; Extension to break = 235%

Example 7 (No BHA)

(9) TABLE-US-00007 Material Mn Mass/g No. of Mols Mol % wt % PEG 6000 5761 9 0.0016 2.2% 25.3630 DPG 134.17 2.5 0.0186 26.2% 7.0453 PEG-PPG-PEG 1100 10.25 0.0093 13.1% 28.8856 PEG 3350 3350 3.5 0.0010 1.5% 9.8634 TMP 134.17 0.444 0.0033 4.7% 1.2512 DMDI 262.5 9.791 0.0373 52.4% 27.5915 DBTDL 0.10% 0.0355 Total 35.485 Results CA = 46°; % EWC = 67; Modulus = 0.34 MPa; Extension to break = 216%

(10) Examples of Embodiments that Contain Silicone Macromers

Example 8 (PEG SiHy RCM); NCO:OH=1.02:1.0

(11) TABLE-US-00008 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 7.1% 17.9813 Silsurf 1508 1756.14 54 11 0.0063 10.0% 26.3726 Silsurf 2510 2462.15 60 4 0.0016 2.6% 9.5900 DPG 134.173 0.7 0.0052 8.3% 1.6783 PEG 2050 2050 7 0.0034 5.4% 16.7826 PEG 3350 3350 1.2 0.0004 0.6% 2.8770 TMP 134.17 1.05 0.0078 12.5% 2.5174 DMDI 262.5 8.849 0.0337 53.6% 21.2148 BHA 1.00% 0.4113 0.0628 DBTDL 0.05% 0.0209 Total 41.710 0.001406 28.45 Average Results From two Batches Dk = 50.62 barrers; % EWC = 45; Transmittance at 550 nm = 98%; Modulus = 1.05 MPa; Extension to break = 305%

Example 9 (PEG SiHy RCM); NCO:OH=1.03:1.0

(12) TABLE-US-00009 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 7.0% 17.9440 Silsurf 1508 1756.14 54 11 0.0063 9.9% 26.3178 Silsurf 2510 2462.15 60 4 0.0016 2.6% 9.5701 DPG 134.173 0.7 0.0052 8.3% 1.6748 PEG 2050 2050 7 0.0034 5.4% 16.7477 PEG 3350 3350 1.2 0.0004 0.6% 2.8710 TMP 134.17 1.05 0.0078 12.4% 2.5122 DMDI 262.5 8.935 0.0340 53.9% 21.3783 BHA 1.00% 0.4113 0.0632 DBTDL 0.05% 0.0209 0.1219 Total 41.797 0.001406 28.39 Average Results from 3 Batches Dk = 54.02 barrers; % EWC = 44; Modulus = 1.09 MPa; Extension to break = 227%

Example 10 (PEG SiHy RCM) No BHA

(13) TABLE-US-00010 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 7.1% 18.2370 Silsurf 1508 1756.14 54 11 0.0063 10.1% 26.7476 Silsurf 2510 2462.15 60 4 0.0016 2.6% 9.7264 DPG 134.173 0.7 0.0052 8.4% 1.7021 PEG 2050 2050 7 0.0034 5.5% 17.0212 PEG 3350 3350 1.2 0.0004 0.6% 2.9179 TMP 134.17 1.05 0.0078 12.6% 2.5532 DMDI 262.5 8.675 0.0330 53.1% 21.0946 DBTDL 0.05% 0.0206 Total 41.125 28.85 Results Dk = 52.70 barrers; CA = 81°; % EWC = 53; Modulus = 0.72 MPa; Extension to break = 228%

Example 11 (PEG SiHy RCM) More TMP

(14) TABLE-US-00011 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 6.8% 17.9451 Silsurf 1508 1756.14 54 11 0.0063 9.6% 26.3195 Silsurf 2510 2462.15 60 4 0.0016 2.5% 9.5707 DPG 134.173 0.7 0.0052 8.0% 1.6749 PEG 2050 2050 7 0.0034 5.2% 16.7488 PEG 3350 3350 1.2 0.0004 0.5% 2.8712 TMP 134.17 1.22 0.0091 13.9% 2.9191 DMDI 262.5 9.174 0.0349 53.5% 21.9507 DBTDL 0.05% 0.0209 Total 41.794 28.39 Average Results from 2 Batches Dk = 70.31 barrers; CA = 73°; % EWC = 44; Transmittance at 550 nm = 99%; Modulus = 1.21 MPa; Extension to break = 247%

Example 12 (PEG SiHy RCM) with 4% PEGdme 1000 NCO:OH=1.03:1.0)

(15) TABLE-US-00012 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 7.0% 17.9440 Silsurf 1508 1756.14 54 11 0.0063 9.9% 26.3178 Silsurf 2510 2462.15 60 4 0.0016 2.6% 9.5701 DPG 134.173 0.7 0.0052 8.3% 1.6748 PEG 2050 2050 7 0.0034 5.4% 16.7477 PEG 3350 3350 1.2 0.0004 0.6% 2.8710 TMP 134.17 1.05 0.0078 12.4% 2.5122 DMDI 262.5 8.935 0.0340 53.9% 21.3783 BHA 1.00% 0.4113 0.0632 PEG dme 1000 4.00% 1.6719 DBTDL 0.05% 0.0209 Total 41.797 0.001406 28.39 Average Results from 2 Batches Dk = 45.70 barrers; CA = 75°; % EWC = 43%; Transmittance at 550 nm = 98%; Modulus = 1.23 MPa; Extension to break = 332%

Example 13 (PEG SiHy RCM) with 6% PEGdme 1000 NCO:OH=1.03:1.0)

(16) TABLE-US-00013 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 7.0% 17.9440 Silsurf 1508 1756.14 54 11 0.0063 9.9% 26.3178 Silsurf 2510 2462.15 60 4 0.0016 2.6% 9.5701 DPG 134.173 0.7 0.0052 8.3% 1.6748 PEG 2050 2050 7 0.0034 5.4% 16.7477 PEG 3350 3350 1.2 0.0004 0.6% 2.8710 TMP 134.17 1.05 0.0078 12.4% 2.5122 DMDI 262.5 8.935 0.0340 53.9% 21.3783 BHA 1.00% 0.4113 0.0632 PEG dme 1000 6.00% 2.5078 DBTDL 0.05% 0.0209 Total 41.797 0.001406 28.39 Average Results from 2 Batches Dk = 48 barrers; CA = 85°; % EWC = 47; Transmittance at 550 nm = 96%; Modulus = 1.24 MPa; Extension to break = 317%

Example 14 (PEG SiHy RCM) Less DPG; NCO:OH=1.03:1.0)

(17) TABLE-US-00014 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 7.2% 18.0919 Silsurf 1508 1756.14 54 11 0.0063 10.2% 26.5348 Silsurf 2510 2462.15 60 4 0.0016 2.6% 9.6490 DPG 134.173 0.6 0.0045 7.3% 1.4474 PEG 2050 2050 7 0.0034 5.6% 16.8858 PEG 3350 3350 1.2 0.0004 0.6% 2.8947 TMP 134.17 1.04 0.0078 12.6% 2.5087 DMDI 262.5 8.704 0.0332 53.9% 20.9955 BHA 1.00% 0.4113 0.0615 DBTDL 0.05% 0.0207 Total 41.455 0.001406 28.62 Average Results from 2 Batches Dk = 59.5 barrers; CA = 70°; % EWC = 47; Transmittance at 550 nm = 98%; Modulus = 1.28 MPa; Extension to break = 185%

Example 15 (PEG SiHy RCM) Less DPG and More PEG 2050; NCO:OH-1.03:1.0)

(18) TABLE-US-00015 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 7.0% 17.5613 Silsurf 1508 1756.14 54 11 0.0063 9.9% 25.7566 Silsurf 2510 2462.15 60 4 0.0016 2.6% 9.3660 DPG 134.173 0.6 0.0045 7.1% 1.4049 PEG 2050 2050 8 0.0039 6.2% 18.7320 PEG 3350 3350 1.2 0.0004 0.6% 2.8098 TMP 134.17 1.07 0.0080 12.7% 2.5054 DMDI 262.5 8.926 0.0340 53.9% 20.9009 BHA 1.00% 0.4113 0.0630 DBTDL 0.05% 0.0214 Total 42.708 0.001406 27.78 Average Results from 2 Batches Dk = 45.5 barrers; CA -= 65°; % EWC = 46%; Transmittance at 550 nm = 96%; Modulus = 1.4 MPa; Extension to break = 294%

Example 16 (PEG SiHy RCM) Half the Amount of BHA:NCO:OH=1.02:1.0)

(19) TABLE-US-00016 Material Mn % Si Mass/g No. of Mols Mol % wt % % Si Silsurf 1010 1692.56 47 7.5 0.0044 7.1% 18.1604 Silsurf 1508 1756.14 54 11 0.0063 10.0% 26.6352 Silsurf 2510 2462.15 60 4 0.0016 2.6% 9.6855 DPG 134.173 0.7 0.0052 8.3% 1.6950 PEG 2050 2050 7 0.0034 5.4% 16.9497 PEG 3350 3350 1.2 0.0004 0.6% 2.9057 TMP 134.17 1.05 0.0078 12.5% 2.5425 DMDI 262.5 8.849 0.0337 53.6% 21.4261 BHA 0.50% 0.2065 0.0628 DBTDL 0.05% 0.0206 Total 41.299 0.001406 28.73 Average Results from 3 Batches Dk = 52 barrers; CA = 77°; % EWC = 46%; Modulus = 1.55 MPa; Extension to break = 325%

Example 17

(20) TABLE-US-00017 Material Mn Mass No. of Mols Mol % wt % PEG 6000 5761 20 0.0035 6.7% 52.5343 PEG 600 600 10.1163 0.0169 32.5% 26.5726 PEG Me 550 0.38 0.0007 1.3% 0.9982 BHA 180.24 0.19 0.0011 2.0% 0.4991 TMP 134.17 0.462 0.0034 6.6% 1.2135 DMDI 262.5 6.922 0.0264 50.8% 18.1823 DBTDL 0.10% 0.0381 Total 38.070 Average Results from 6 Batches % EWC = 72%, Modulus = 0.67 MPa, Extension to break = 137%

Example 18

(21) TABLE-US-00018 Material Mn Mass No. of Mols Mol % wt % PEG 6000 5761 20 0.0035 7.0% 53.5845 PEG 600 600 10.1163 0.0169 34.0% 27.1038 BHA 180.24 0.19 0.0011 2.1% 0.5091 TMP 134.17 0.392 0.0029 5.9% 1.0503 DMDI 262.5 6.626 0.0252 50.9% 17.7524 DBTDL 0.10% 0.0373 Total 37.324 Average Results from 6 Batches % EWC = 70%, Modulus = 0.92 MPa, Extension to break = 137%

Comparative Example 19

(22) The reactant mixture as detailed in Table X was formed. Using a Mettler Toledo (AG 285) analytical balance the following (for each experiment) were weighed into a quickfit 250 ml flask:

(23) TABLE-US-00019 TABLE X Material Mn % Si Mass Mass (*1.3) Actual (g) Mass (*4.3) Actual No. of Mols wt % % Si Silsurf 2510 2409.79 60 22 28.6 94.6 94.614 0.0091 76.5560 TEG 150.17 0 0 0 0.0000 0.0000 PEG 6000 6000 2.5 3.25 10.75 10.7569 0.0004 8.6995 TMP 134.17 0.44 0.572 1.892 1.896 0.0033 1.5311 DMDI 262.5 3.797 16.328 0.0145 13.2133 DBTDI 0.05% 0.0144 0.019 0.0618 0.0640 0.0345 0.0500 Total 28.737 0.0273 45.93 100% NCO Code Master batch weight Actual TEG Actual Des W Actual RCM Moulds Syringes % Si Bsi Hy 215 24.9414 24.945 0 0 3.797 3.799 18 2 45.93 Opaque Bsi Hy 216 24.9414 24.943 3 3.038 9.041 9.095 18 2 35.69 Opaque Bsi Hy 217 24.9414 24.949 6 6 14.285 14.274 18 2 29.19 Opaque Bsi Hy 218 24.9414 24.948 10 10.036 21.277 21.267 18 2 23.48 Clear

(24) Silsurf (Silsurf 2510 being an example) is of Formula A above where each R group represents a methyl group, x is 25 and p is 10.

(25) The flask was attached to a rotary evaporator with an oil bath temperature of 95° C. and the contents of the flask were dried/dehydrated for 2 hr. The moisture content of mixture was checked by Karl Fisher and if the water content was <0.05% then these materials were considered to be substantially anhydrous and used without further dehydration, otherwise these were further dehydrated under vacuum until the moisture content was <0.05%. The reactants were transferred to separate preheated polypropylene tubs.

(26) The reactants were thoroughly mixed using an overhead Hiedolph mixer fitted with a helical ribbon stirrer. Part of the mixture was then dispensed into lens moulds and the moulds closed. A proportion of the material was transferred into a 5 ml polypropylene syringe. The remaining material in the polypropylene cup was covered by a screw cap lid and both the lens moulds and the polypropylene cup were placed in an oven at 95° C. and reacted for 5 hours. The resulting products form cast moulded lenses. The lenses, the syringe were demoulded by chilling in a freezer at −80° C. over 30 minutes. The lenses were placed directly into glass vials containing saline. These lenses were left for 24 hours to fully hydrate.

(27) The compositions containing higher content of silicone tended to have an increased risk of some opacity.

Example 20

(28) The method of comparative Example 19 above was repeated for the reactant mixture shown in Table Y.

(29) TABLE-US-00020 TABLE Y Material Mn % Si Mass Mass (*1.3) Actual Mass (*4.3) Actual No. of Mols wt % % Si Silsurf 2510 2409.79 60 20 90 90.0161 0.0083 50.9915 DPG 134.17 0 2.5 11.25 11.3045 0.0186 6.3739 TEG 150.17 2.5 11.25 11.2687 0.0166 6.3739 PEG 6000 5767 1.25 5.625 5.6251 0.0002 3.1870 TMP 134.17 0.375 1.6875 0.0028 0.9561 DMDI 262.5 12.597 56.69 0.0480 32.1176 DBTDL 0.05% 1.0196 0.09 0.0780 0.1186 0.0500 Total 39.222 0.0946 30.59 100% NCO Code Master batch weight Actual TMP Actual Des W Actual RCM Moulds Syrings % Si Clarity BSi Hy 246 26.269 26.284 0.385 0.39 12.627 12.67 36 2 30.56 Clear BSi Hy 247 26.269 26.276 0.385 0.386 12.374 12.395 36 2 30.56 Clear BSi Hy 248 26.269 26.285 0.375 0.372 12.597 12.622 36 2 30.59 Clear BSi Hy 249 26.269 26.268 0.375 0.373 12.345 12.353 36 2 30.59 Clear

(30) All lenses appeared transparent following hydration, and contained over 30 wt % silicone.

(31) Method of Manufacture for Producing Polymer Compositions Both with and without Silicone Component

(32) Compositional detail for several embodiments are provided in tables above, these are not exhaustive and details for only a few are provided merely to exemplify the present invention.

(33) The reactants as per listed for each embodiment in each table are accurately weighed into a round bottom flask and dehydrated using a rotary evaporator under reduced pressure at 95° C. for at least 3-4 hours until the moisture content of the dehydrated mixture falls below 0.05 wt %. The moisture content is measured by Carl Fischer Titrator.

(34) A known weight of this mixture is weighed into a clean preheated polypropylene tub and a lid was placed on the tub to prevent moisture entering the system. Isocyanate (typically Desmodur W) as required is then added through a syringe while the contents of the mixture in the tub are being stirred by an overhead stirrer. A small amount of this overall mixture is then degassed using the rotary evaporator and dispensed into contact lens moulds which are then closed and allowed to cure in an oven at 95° C. for 8-16 hours until the reaction completes. This is indicated by the disappearance of NCO peak at ˜2260 cm.sup.−1. The tub was lidded and also placed in the same oven for curing. The mixing, dispensing and curing was done in a fume hood and operators wear appropriate protective clothing, gloves and respirators that are suitable to handle the isocyanate. The dehydration of selected components may be carried out separately where required.

(35) Testing for Contact Lens Attributes

(36) The lens attributes, namely equilibrium water content, DK, Modulus, UV Transmission, Extension to break and Contact angle were measured by standard methods used by the industry.

(37) Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

(38) Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

(39) Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, mean “including but not limited to”, and are not intended to (and do not) exclude other moieties, additives, components, integers or steps. All documents referred to herein are incorporated by reference. The word copolymer and block copolymer is used to describe either.

(40) Various modifications and variations of the described aspects of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the Invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes of carrying out the invention which are obvious to those skilled in the relevant fields are intended to be within the scope of the following claims.