Bioresorbable microparticles

Abstract

Polyurethane microparticles are derived from structural units comprising poly(alkylene oxide) moieties, caprolactone moieties and urethane moieties. The microparticles may include an active agent and have a particle size from 0.1 to 100 microns. Microparticles for injection have a particle size of 15 to 80 microns; for use as a aerosol 1 to 3 microns; and for intraocular use 0.02 to 2 microns. Dispersivity is in the range 1 to 3.

Claims

1. Polymer microparticles, the polymer being a polyurethane obtainable by reacting together: (a) a prepolymer comprising co-polymerised units of a caprolactone and poly(alkylene oxide) moieties; (b) a polycaprolactone diol comprising co-polymerised units of a caprolactone and a C.sub.2-C.sub.6 diol; and (c) a diisocyanate; wherein the microparticles have a particle size of from 0.01 to 100 microns, and wherein the microparticles have a dispersivity span in the range from 1 to 3; wherein the dispersivity span is the width of particle size distribution as defined by the formula: $\mathrm{Span}=\frac{D\left[v,0.9\right]-D\left[v,0.1\right]}{D\left[v,0.5\right]}$ wherein: D(v, 0.5) is the median volume diameter wherein 50% of the particle size distribution has a volume-based diameter above the D(v,0.5) value and 50% is below; D(v, 0.9) is the value wherein 90% of the particle size distribution has a volume-based diameter below the D(v, 0.9) value; and D(v, 0.1) is the value wherein 10% of the particle size distribution has a volume-based diameter below the D(v,0.1) value.

2. The microparticles to claim 1, which further comprise an active agent.

3. The microparticles to claim 2, wherein the active agent is a protein or peptide.

4. The microparticles of claim 1, in a formulation suitable for injection, having a particle size of 15 to 80 microns.

5. The microparticles of claim 1, in an aerosolizable formulation that upon aerosolization provides an aerosol having an apparent aerodynamic diameter in the range 1 to 3 microns.

6. The microparticles of claim 1, in a formulation suitable for intraocular use, having a particle size of 0.02 to 2 microns.

7. The microparticles of claim 1, wherein after 1 month at 50 C. in phosphate buffered saline the reduction in average molecular weight of the polymer is 60 to 90%.

8. The microparticles of claim 1, wherein after 6 months at 37 C. in phosphate buffered saline the reduction in average molecular weight of the polymer is 30 to 80%.

9. The microparticles of claim 1, wherein the swellability in phosphate buffered saline at 37 C. is 10-100%.

10. The microparticles of claim 2, wherein the active agent is released by 30 days nominally.

11. The microparticles of claim 1, which become completely resorbed in the body of a human or animal patient.

12. A method for delivering an active agent to a patient comprising administering microparticles according to claim 2 to the patient.

13. The microparticles of claim 8, wherein after 6 months at 37 C. in phosphate buffered saline the reduction in average molecular weight of the polymer is 40 to 70%.

14. The microparticles of claim 1, wherein the dispersivity span is in the range 1.1-2.5.

15. The microparticles of claim 1, wherein the dispersivity span is in the range 1.2-2.0.

16. The microparticles of claim 7, wherein after 1 month at 50 C. in phosphate buffered saline the reduction in average molecular weight of the polymer is 70 to 85%.

17. The microparticles of claim 2, wherein the active agent is released by 60 days nominally.

18. The microparticles of claim 2, wherein the active agent is released by 90 days nominally.

19. The microparticles of claim 2, wherein the active agent is released by 120 days nominally.

20. The microparticles of claim 1, wherein the microparticles degrade in the physiological environment of animals.

21. The microparticles of claim 20, wherein the time taken for the polymer to fully degrade is in the order of from 1 day to 250 weeks.

22. The microparticles of claim 1, wherein the swellability in phosphate buffered saline at 37 C. is in the range from 1 to 500%.

23. The microparticles of claim 2, wherein the overall time to release the active agent is in the order of hours.

24. The microparticles of claim 2, wherein the overall time to release the active agent is in the order of days.

25. The microparticles of claim 2, wherein the overall time to release the active agent is in the order of weeks.

26. The microparticles of claim 2, wherein the overall time to release the active agent is in the order of months.

27. The microparticles of claim 2, wherein the overall time to release the active agent is in the order of years.

28. The microparticles of claim 1, wherein the poly(alkylene oxide) moieties are selected from a poly(C.sub.2-alkylene oxide), a poly(C.sub.3-alkylene oxide), and mixtures thereof.

29. The microparticles to claim 1, wherein the C.sub.2-C.sub.6 diol is selected from ethylene glycol and diethylene glycol.

Description

FIGURES

(1) FIG. 1 shows particle size distribution of microparticles prepared in Example 11 as determined by dynamic light scattering; and

(2) FIG. 2 shows an SEM image of microparticles prepared in Example 17.

(3) Synthesis of the polyurethanes is a two-step polymerisation reaction. The first step is ring opening of caprolactone using PEG and stannous octoate as a catalyst, yielding a PCL-PEG-PCL block copolymer, referred to as the pre-polymer. The pre-polymer is then chain extended with polycaprolactone-diol and butane diisocyanate to form the final biodegradable polyurethane. Polycaprolactone-diol is the reaction product of caprolactone and diethylene glycol. The final polymers can be referred to as segmented polyurethanes, as they are believed to undergo microphase separation into hard blocks and soft blocks. In very general terms, the soft block is composed of the pre-polymer and the hard block is composed of the polycaprolactone-diol and urethane moiety (derived from the diisocyanate).

(4) We incorporate bioactive molecules into microspheres made from the biodegradable polyurethane in order to produce a vehicle which allows for controlled release of the bioactive compound from the biodegradable polymer matrix. The aim of this experimental work was to synthesise microparticles using bovine serum albumin (BSA) as a representative protein molecule in either a solid or aqueous form using emulsion solvent evaporation technology. During this process, bioactive molecules can be entrapped in polymer microspheres, which can then be collected. In a water-in-oil-in-water (w/o/w) emulsion, bioactive molecules in the aqueous form are homogenised with polymer dissolved in an organic solvent to form a water-in-oil emulsion. This w/o emulsion is then transferred to a second aqueous phase and homogenised again to form a final w/o/w emulsion.

(5) Bioactive molecules can also be added directly into the polymer phase in a solid form, forming a final solid-in-oil-in-water (s/o/w) emulsion. The bioactive in solid form is homogenised with polymer dissolved in an organic solvent forming a solid-in-oil emulsion. This s/o emulsion is then transferred to an aqueous phase and homogenised to form the final s/o/w emulsion. We tested the particle size and distribution of microparticles containing BSA formed using BSA in the aqueous or the solid form, as recrystallised mono-crystals or co-crystals. The experiments were performed both with and without the presence of surfactants (Tween 80, PEG6000, PVP and PVA,). PVP is polyvinylpyrrolidone; PVA is polyvinyl acetate.

Example 1: Manufacture of Linear Bioresorbable Prepolymers with Different Structure and Block Lengths for Subsequent Polyurethane Synthesis

(6) The length of PEG block (400, 2000 and 8000 g/mol) and caprolactone block (500-3500 g/mol) was changed. The target pre-polymer molecular weight was selected to be between 7000-11 000 g/mol. Pre-polymer batch sizes were about 500-600 g. The pre-polymers were prepared by varying their compositions as follows (see Table 1): Batch A) Prepolymer A made of 32.01 g PEG 400 (16.0 mol-%), 561.58 g caprolactone (98.4 mol-%) and 0.608 g tin(II) octoate (0.03% mol-%), targeting a theoretical molecular weight of 7418 g/mol, Batch B) Prepolymer B made of 149.81 g PEG2000 (2.0 mol-%), 418.84 g caprolactone (97.9 mol-%) and 0.45 g tin(II)octoate (0.03 mol-%), targeting a theoretical molecular weight of 7592 g/mol, Batch C) Prepolymer C made of 461.93 g PEG8000 (10.0 mol-%). 59.30 g caprolactone (90.0 mol-%) and 0.07 g tin(II)octoate (0.03 mol-%), targeting a theoretical molecular weight of 9027 g/mol. Batch D) Prepolymer D made of 394.86 g PEG2000 (2.0 mol-%). 1103.95 g caprolactone (97.97 mol-%) and 1.20 g tin(II) octoate (0.03 mol-%), targeting a theoretical molecular weight of 7592 g/mol.

(7) TABLE-US-00001 TABLE 1 Synthesised prepolymers for the present invention Number of CL Theoretical Theoretical units in Reaction Prepolymer MW of MW of PCAP Temperature Name PEG prepolymer PCAP block black ( C.), time Prepolymer 400 7418 3509 31 155, 5 h A Prepolymer 2000 7592 2796 24.5 155, 6 h B Prepolymer 8000 9027 514 4.5 155, 5 h C Prepolymer 2000 7592 2796 24.5 155, 5 h D

(8) The molecular weights (Mn and Mw) and molecular weight distributions were measured for various prepolymers by a triple angle light scattering combined with size exclusion chromatography (SEC) system, see Table 2.

(9) TABLE-US-00002 TABLE 2 Prepolymers were characterised using SEC coupled with light scattering. Mn (g/mol) Prepolymer Name SEC MWD SEC Prepolymer A 10,711 1.34 Prepolymer B 9,072 1.27 Prepolymer C 10,525 1.00 Prepolymer D 13,731 1.43

Example 2: Manufacture of a Linear Bioresorbable Hydrogel Prepolymer and Polymer (Prepolymer A and Polymer 1)

(10) Into a stirred tank reactor 32.01 g (16.0 mol-%) of dried PEG400 (MW 400 g/mol), 561.58 g caprolactone (98.4 mol-%) and 0.608 g (0.03 mol-%) tin(II) octoate were fed in that order. Dry nitrogen was continuously purged into the reactor. The reactor was pre-heated to 155 C. using an oil bath and a mixing speed of 60 rpm. PEG400 was dried and melted in a rota-evaporator prior to being added into the reactor. Then, -caprolactone was added and finally the catalyst tin(II) octoate. Prepolymerisation time for the PEG-PCL prepolymer was 5 hours. The theoretical molecular weight of the prepolymer was 7418 g/mol.

(11) For the polymer preparation 6.60 g of low molecular weight poly(-caprolactone)diol (MW 530 g/mol) (PCLDI) and 90.2 g of the above mentioned prepolymer were dried and melted in a rota-evaporator prior to being added into the reactor. Dry nitrogen was continuously purged into the reactor. The reactor was pre-heated to 110 C. using an oil bath and a mixing speed of 75 rpm. 2.21 ml of 1,4-butane diisocyanate (BDI), at a molar ratio of 1:1:2 PEG-PCL prepolymer: PCLDI: BDI, were fed into the reactor. Polymerisation time was 6 minutes. Polymer was scraped into an aluminium pan and stored in a desiccator for further testing. (Polymer 1)

(12) DSC analysis revealed that the glass transition temperature (T.sub.g) and the melting point (T.sub.m) were 57.1 and 52.2 C. respectively.

Example 3: Manufacture of a Linear Bioresorbable Polymer with a Different Structure

(13) Prepolymer B (Table 1 in Example 1), and polycaprolactone diol (MW 530 g/mol) were mixed, dried and melted under vacuum at 90 C. for at least one hour prior to feeding them into the preheated (110 C.) reactor. Reaction mixture was mixed (75 rpm) under nitrogen. 1,4-butane diisocyanate was fed into the reactor. The molar ration between prepolymer, poly(-caprolactone)diol and BDI was 1:1:2. The reaction times was 13 minutes.

(14) DSC analysis revealed that there were two glass transition temperatures (T.sub.g) at 53.7 and 1.6 C. and the melting point (T.sub.m) was 51.3 C.

Example 4: Manufacture of a Linear Bioresorbable Polymer with a Different Structure

(15) The chain extending polymerisation was performed as in Example 3, except the prepolymer was Prepolymer C in Table 1 in Example 1. The reaction time was 15 minutes.

(16) DSC analysis revealed that the glass transition temperature (T.sub.g) and the melting point (T.sub.m) were 59.1 and 53 C. respectively.

Example 5: Manufacture of a Linear Bioresorbable Polymer with a Different Structure

(17) The chain extending polymerisation was performed as in Example 3, except the prepolymer was Prepolymer C in Table 1 in Example 1 and the molar ratio between pre-polymer, poly(-caprolactone)diol and BDI was 0.25:1.75:2. The reaction time was 12 minutes.

(18) DSC analysis revealed that the glass transition temperature (T.sub.g) was 38.6 C. and there were two melting endotherms (T.sub.m) at 51.1 and 95.9 C.

Example 6: Manufacture of a Linear Bioresorbable Polymer with a Different Structure

(19) The chain extending polymerisation was performed as in Example 3, except the prepolymer was Prepolymer C in Table 1 in Example 1 and the molar ration between pre-polymer, poly(-caprolactone)diol and BDI was 0.05:1.95:2. The reaction time was 20 minutes.

Example 7: Manufacture of a Linear Bioresorbable Polymer with a Different Structure

(20) The chain extending polymerisation was performed as in Example 3, except the prepolymer was Prepolymer D in Table 1 in Example 2. The reaction time was 20 minutes.

(21) DSC analysis revealed that the polymer had a glass transition temperatures (T.sub.g) of 62.5 and 10.6 C. and the melting point (T.sub.m) was 52.3 C.

(22) TABLE-US-00003 TABLE 3 Synthesised bioresorbable polymers for the present invention. Theoretical Theoretical CAP- Reaction Polymer Prepolymer MW of MW of diol BDI Temperature Name PEG Name prepolymer CAP block Prepolymer Mol Ratio ( C.), time Polymer 1 400 Prepolymer A 7418 3509 1 1 2 110, 6 min Polymer 2 2000 Prepolymer B 7592 2796 1 1 2 110, 13 min Polymer 3 8000 Prepolymer C 9027 514 1 1 2 110, 15 min Polymer 4 8000 Prepolymer C 9027 514 0.25 1.75 2 110, 12 min Polymer 5 8000 Prepolymer C 9027 514 0.05 1.95 2 110, 20 min Polymer 6 2000 Prepolymer D 7592 2796 1 1 2 110, 20 min

Example 8

(23) Molecular weight determination was carried out for a selected number of bioresorbable polymers, which are shown in Table 4. The molecular weight of the polymer will determine its mechanical properties and have an impact on its degradation properties; therefore the importance of determining molecular weight values is evident.

(24) These types of polymers are expected to have a molecular weight of 100,000 (M.sub.n) in the best of cases. The minimum value for the M.sub.n to have reasonable mechanical properties or to consider the compound a polymer is 30,000. In the present invention molecular weight values of M.sub.n exceeded our expectations and values of around 80,000 were obtained in most cases.

(25) TABLE-US-00004 TABLE 4 Molecular weight analyses for selected bioresorbable polymers. Mw Mn Example Polymer Prepolymer (g/mol) (g/mol) MWD Number Name PEG Name SEC SEC SEC 2 Polymer 400 Prepolymer 158,124 88,428 1.79 1 A 3 Polymer 2000 Prepolymer 132,328 77,345 1.71 2 B 4 Polymer 8000 Prepolymer 100,009 83,869 1.19 3 C 5 Polymer 8000 Prepolymer 116,019 94,375 1.24 4 C 6 Polymer 2000 Prepolymer 80,992 56,215 1.45 6 D

Example 9: Processing of Thermoplastic Polymers by Using a Hot-PressFilm Production

(26) Bioresorbable Polymers 1, 2, 3, 4 and 6 from Table 3 were dried under vacuum over night prior to processing them using the hot-press. Upper and lower plate temperatures were set at 160 C. Two Teflon sheets were placed between the mould and the hot plates. The melting time was 2 min followed by a 30 second holding under pressure (170 bar). An exact amount of polymer was used to fill the mould. After cooling to room temperature samples were mechanically punched out and kept in the freezer for further analysis.

Example 10: Polymer Degradation and Swelling Investigation at 37 C. and 50 C. in Phosphate Buffered Saline Solution

(27) In order to prove the bioresorbability of synthesised polymers and their potential to release bioactive agents, a number of polymers were selected to carry out biodegradation and swelling studies.

(28) Polymer samples for degradation studies and swelling were made from the biodegradable polymers by hot-pressing films and punching specimens out of it. There were two different types of degradation studies: one at 37 C. in phosphate buffered saline solution pH 7.4 for twelve months and an accelerated study at 50 C. in phosphate buffered saline solution pH7.4 for twelve months where applicable. At the beginning samples were taken every week and after one month once a month or even less frequently.

(29) The degradation and swelling results at for Polymer 1 can be seen in Table 5.

(30) TABLE-US-00005 TABLE 5 Swelling and erosion of Polymer 1 incubated in PBS buffer at 37 C. and 50 C. Average Average mass swelling (%) remaining (%) Incubation time 37 C. 50 C. 37 C. 50 C. One day 1 2 99 99 One week 0 1 99 99 One month 1 0 99 99 Two months 1 1 97 99 Three months 0 1 98 98 Six months 1 0 99 98 Twelve months 98 87

(31) The degradation and swelling results at for Polymer 2 can be seen in Table 6.

(32) TABLE-US-00006 TABLE 6 Swelling and erosion of Polymer 2 incubated in PBS buffer at 37 C. and 50 C. Average Average mass swelling (%) remaining (%) Incubation time 37 C. 50 C. 37 C. 50 C. One day 17 30 98 99 One week 18 31 99 99 One month 19 21 99 99 Two months 17 29 99 99 Three months 17 31 99 97 Six months 20 30 99 96 Twelve months ND ND 98 91

(33) The degradation and swelling results for Polymer 3 can be seen in Table 7. The dissolution of this polymer in PBS was rapid and therefore swelling measurements were only possible in the first 5 minutes of the study.

(34) TABLE-US-00007 TABLE 7 Swelling and erosion of Polymer3 incubated in PBS buffer at 37 C. and 50 C. Average Average mass swelling (%) remaining (%) Incubation time 37 C. 50 C. 37 C. 50 C. One minute 91 ND ND ND Two minute 108 ND ND ND Three minutes 107 ND ND ND Four minutes 164 ND ND ND Five minutes 212 ND ND ND

(35) The degradation and swelling results for Polymer 4 can be seen in Table 8. The dissolution of this polymer in PBS was rapid and therefore swelling and erosion measurements were only possible in the first six hours of the study.

(36) TABLE-US-00008 TABLE 8 Swelling and erosion of Polymer 4 incubated in PBS buffer at 37 C. and 50 C. Average Average mass swelling (%) remaining (%) Incubation time 37 C. 50 C. 37 C. 50 C. One hour 150 143 91 91 Two hours 221 231 88 88 Three hours 254 234 84 91 Four hours 237 244 83 79 Six hours 282 244 81 63

(37) The degradation and swelling results at for Polymer b can be seen in Table 9.

(38) TABLE-US-00009 TABLE 9 Swelling and erosion of Polymer 6 incubated in PBS buffer at 37 C. and 50 C. Average Average mass swelling (%) remaining (%) Incubation time 37 C. 50 C. 37 C. 50 C. One day 18 33 98 99 One week 18 33 99 99 One month 18 38 99 99 Two months 19 43 99 99 Three months 19 45 99 97 Six months ND ND 99 96

Example 11: Preparation of Microparticles Using a 5% Polymer in Dichloromethane (DCM) Solution with Tween 80 as a Surfactant

(39) 0.5 g of Polymer 6 was dissolved in 10 g DCM, forming an oil phase (O). 0.1 g of bovine serum albumin (BSA) was dissolved in 0.5 g of distilled water (dH.sub.2O) forming the inner aqueous phase (W.sub.1). 1.5 g Tween 80 was dissolved in 48.5 g of dH.sub.2O to form the outer aqueous phase (W.sub.2). W.sub.1 and O were homogenised at 4000 rpm for 5.5 min, using a high shear mixer to form a water-in-oil (W.sub.1/O) emulsion. 5 g of the resulting W.sub.1/O emulsion was transferred to the outer aqueous phase (W.sub.2) and homogenised at 7000 rpm to form the final water-in-oil-in-water (W.sub.1/O/W.sub.2) emulsion. The emulsion was stirred at 650 rpm for 24 hours, using a magnetic stirrer, in order to remove the solvent from the oil phase.

Example 12: Preparation of Microparticles Using a 5% Polymer in DCM Solution without Surfactant

(40) The formulation was prepared as in Example 11, except that the outer aqueous phase consisted of 50 g of dH.sub.2O only.

Example 13: Preparation of Microparticles Using a Solid Protein Formulation, a 5% Polymer in DCM Solution with Tween 80 as a Surfactant

(41) The formulation was prepared as in Example 11, except that BSA was used in a solid formulation (as a co-crystal with valine) as opposed to an aqueous phase. 0.1 g of this solid BSA formulation was added directly to the oil phase and homogenised, forming a solid-in-oil (s/o) emulsion.

Example 14: Preparation of Microparticles Using a Solid Protein Formulation, a 5% Polymer in DCM Solution without a Surfactant

(42) The formulation was prepared as in Example 11, except that BSA was used in a solid formulation (as a co-crystal with valine) as opposed to an aqueous phase. 0.1 g of this solid BSA formulation was added directly to the oil phase and homogenised, forming a solid-in-oil (s/o) emulsion. The outer aqueous phase consisted solely of 50 g of dH.sub.2O.

Example 15: Preparation of Microparticles Using a 2.5% Polymer in DCM Solution with Tween 80 as a Surfactant

(43) The formulation was prepared as in example 11, except that 0.25 g of polymer was dissolved in 10 g DCM in order to form a 2.5% polymer solution.

Example 16: Preparation of Microparticles Using a 5% Polymer in DCM Solution with Tween 80 as a Surfactant

(44) The formulation was prepared as in example 11 except the rate of addition of the (W.sub.1/O) emulsion to W.sub.2 was decreased.

Example 17: Preparation of Microparticles Using a 1% Polymer in Ethyl Acetate (EA) Solution with Tween 80 as a Surfactant

(45) The formulation was prepared as in Example 11, except that 0.1 g of polymer was dissolved in 10 g EA.

Example 18: Preparation of Microparticles Using a 2.5% Polymer in EA Solution with Tween 80 as a Surfactant

(46) The formulation was prepared as in Example 11, except that 0.25 g of polymer was dissolved in 10 g EA.

Example 19: Preparation of Microparticles Using a 5% Polymer in EA Solution with Tween 80 as a Surfactant

(47) The formulation was prepared as in Example 11, except that 0.5 g of polymer was dissolved in 10 g EA.

Example 20: Preparation of Microparticles Using a 1% Polymer in EA Solution with PEG6000 as a Surfactant

(48) The formulation was prepared as in Example 11, except that 0.1 g of polymer was added to 10 g EA and the outer aqueous phase consisted of 1.5 g of PEG6000 in 48.5 g dH.sub.2O.

Example 21: Preparation of Microparticles Using a 1% Polymer in EA Solution with PVP as a Surfactant

(49) The formulation was prepared as in Example 11, except that 0.1 g of polymer was added to 10 g EA and the outer aqueous phase consisted of 1.5 g of PVP in 48.5 g dH.sub.2O.

Example 22: Preparation of Microparticles Using a 1% Polymer in EA Solution with PVA as a Surfactant

(50) The formulation was prepared as in Example 11, except that 0.1 g of polymer was added to 10 g EA and the outer aqueous phase consisted of 1.5 g of PVA in 48.5 g dH.sub.2O.

Example 23: Particle Size Determination of Microparticles

(51) Dynamic light scattering is a method that can be used to determine the particle size distribution of the microparticles formed. In dynamic light scattering particle sizing the volume median diameter D(v,0.5) is the diameter where 50% of the particle size distribution is above and 50% is below. The D(v,0.9), is the value where 90% of the volume distribution is below this value. The D(v,0.1), is the value where 10% of the volume distribution is below this value. The span is the width of the distribution based on the 10%, 50% and 90% quantile as shown in the equation below:

(52) $\mathrm{Span}=\frac{D\left[v,0.9\right]-D\left[v,0.1\right]}{D\left[v,0.5\right]}$

(53) Various microparticle preparations were collected after solvent removal and centrifugation and added directly to dH.sub.2O (acting as the dispersing medium) in the Malvern Mastersizer, stirring at 2000 rpm and sized. FIG. 1 shows a typical size distribution curve obtained from Microparticles prepared in Example 11.

(54) Table 10 summarises the average particle size (D(v, 0.5) and the size distribution (Span) for microparticles prepared in Example 11, Example 12, Example 13, Example 14, Example 15, Example 16, Example 18, Example 19, Example 20, Example 21, Example 22.

(55) TABLE-US-00010 TABLE 10 The D(v, 0.5) and Span for various microparticles preparations prepared in Example 11 to Example 22. Batch no. Microparticles D(v, 0.5) Span Example 11 39.8 1.5 Example 12 68.9 1.3 Example 13 26.8 2.3 Example 14 117.3 3.5 Example 15 98.3 6.8 Example 16 71.2 1.8 Example 18 23.2 7.1 Example 19 50.8 2.7 Example 20 1621.5 1.3 Example 21 31.2 8.2 Example 22 23.9 8.0

Example 24: Image Analysis of Microparticles

(56) Scanning Electron Microscopy (SEM) is a technique commonly used to study particle morphology. Microparticles prepared in Example 17 were gold-coated before imaging using a Polaron SC515 SEM coating system. They were then viewed on a JEOL 6400 scanning electron microscope. Images were captured using Scandium software. FIG. 2 shows the formation of generally spherical particles with an average particle size less than 10 microns in size.