A MICRO-PARTICLE SUSPENSION

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of U.S. Provisional Patent

Application No. 62/987,794 filed March 10, 2020, which is hereby incorporated by reference in its entirety.

FIELD

[0002] The present disclosure relates to methods and apparatuses for reducing the settling rate of a micro-particle suspension that is suitable for dental or dermatological injection.

BACKGROUND

[0003] The following paragraph is not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art.

[0004] Poly-L-lactic acid (PLLA) can be formulated as an FDA-approved dermal filler for the treatment of facial lipoatrophy or for reducing wrinkles. The delivered PLLA degrades under physiological conditions and stimulates local collagen production.

INTRODUCTION

[0005] The following introduction is intended to introduce the reader to this specification but not to define any invention. One or more inventions may reside in a combination or sub-combination of the apparatus elements or method steps described below or in other parts of this document. The inventors do not waive or disclaim their rights to any invention or inventions disclosed in this specification merely by not describing such other invention or inventions in the claims.

[0006] In contrast to an intravenous injection, a dermal filler is injected into different areas and at different depths of a patient’s skin in order to help fill in facial wrinkles, provide facial volume, or augment a facial feature. The poly-L-lactic acid (PLLA) used in medically-approved dermal fillers is in the form of PLLA micro-particles. The micro-particles are formulated for injection as an aqueous suspension of the microparticles. When PLLA is injected as a dermal filler, it is desirable that the concentration of PLLA being injected at the start of the injection is substantially the same as the concentration of PLLA being injected at the end of the injection. If the concentration of PLLA is not substantially the same over the course of the injection, the amount of PLLA being injected in one area may be different from the amount of PLLA being injected in another area, even if the volumes in both areas are the same.

[0007] One problem associated with PLLA micro-particle suspensions useful as a dermal filler is that the micro-particles exhibit a sedimentation rate that is sufficiently fast that a micro-particle suspension in a 3 mL syringe substantially settles out over the course of 15 minutes, which is the length of time that a medical practitioner may take to fully inject the suspension. This means that, in the absence of any resuspension steps, the concentration of the PLLA suspension in the first portion of injected filler will be higher than the concentration of the PLLA suspension in the last portion of injected filler.

Injecting different amounts of PLLA in different areas of the patient may provide an undesirable aesthetic result, or may result in an adverse reaction.

[0008] Another problem associated with PLLA micro-particle suspensions useful as a dermal filler is that the hydrophobicity and the surface-to-volume ratio of the PLLA can result in at least some micro-particles forming micro-bubble/micro-particle interactions. Interactions with micro-bubbles increases the buoyancy of a micro-particle. As the surface-to-volume ratio of a micro-particle increases, the buoyancy effects of the micro-bubbles decreases. That is, in a PLLA suspension that has been sufficiently agitated or shaken to produce micro-bubble/micro-particle interactions, larger microparticles are less buoyant than smaller micro-particles and so the larger micro-particles have a larger sedimentation rate than the smaller micro-particles. This difference in sedimentation rate may result in unequal amounts, or dissimilar composition of particle sizes of PLLA, or both being injected into the tissue even if the injection is performed correctly.

[0009] One or more of the problems associated with PLLA micro-particle suspensions useful as a dermal filler are also expected to be a problem with a suspension of micro-particles that has a water contact angle of 60° or greater, where the suspension is for injection in a plurality of areas in a patient.

[0010] The author of the present disclosure has found that cooling the microparticle suspension to a temperature of 2 °C or lower can reduce the sedimentation rate sufficiently that the concentration of micro-particles in a well-mixed suspension is substantially the same as the concentration of micro-particles in the suspension after 15 minutes of settling without any resuspension steps.

[0011] One or more described examples attempt to address or ameliorate one or more shortcomings involved with micro-particle formulations useful as a dermal filler. [0012] In one aspect of the present disclosure, a method is provided that includes cooling an aqueous mixture of dermatologically-injectable or periodontally-injectable micro-particles to a temperature of 2 °C or lower, where the aqueous mixture is substantially isotonic to blood or to extracellular fluid, where the micro-particles have a water contact angle of 60° or greater; and where at least a portion of the micro-particles are in suspension.

[0013] The method may additionally include preparing the mixture of microparticles by reconstituting a dried formulation with an aqueous solution.

[0014] The cooled aqueous mixture may be injected into the dermis, the subcutis, or the mucoperiosteum of a subject, such as into the deep dermis, the subcutaneous fat, or the lamina propria of the subject.

[0015] The method may include cooling the aqueous mixture to freezing, and optionally maintaining the mixture as frozen during distribution.

[0016] The method may include mixing the cooled aqueous mixture in an elongate vessel by rotating the elongate vessel around an axis substantially perpendicular to gravity, where the longitudinal axis of the elongate vessel is (a) substantially parallel to the axis of rotation or (b) substantially equivalent to the axis of rotation.

[0017] In another aspect of the present disclosure, there is provided an apparatus that includes a mixer sized and shaped to accept an elongate vessel, such as a syringe or a vial. The apparatus includes a cooler in thermal communication with the mixer or with an accepted elongate vessel. The cooler is capable of cooling an accepted elongate vessel to a temperature that is from -10 °C to 1 °C. The mixer is rotatable around an axis that is substantially parallel to the longitudinal axis of an accepted elongate vessel, where the axis of rotation of the mixer is substantially perpendicular to gravity when the apparatus is in an operating position.

[0018] In another aspect of the present disclosure, there is provided a syringe or vial that contains a frozen aqueous mixture that includes dermatologically-injectable or periodontally-injectable micro-particles. The frozen aqueous mixture is substantially isotonic to blood or to extracellular fluid. The micro-particles have a water contact angle of 60° or greater, and at least a portion of the injectable micro-particles are in suspension.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures. [0020] Fig. 1 is a flow chart illustrating an exemplary method according to the present disclosure.

[0021] Fig. 2 is a flow chart illustrating an exemplary method according to the present disclosure.

[0022] Fig. 3 is a flow chart illustrating an exemplary mixing method according to the present disclosure.

[0023] Fig. 4 is an perspective view of an exemplary apparatus according to the present disclosure.

[0024] Fig. 5 a front view of the apparatus illustrated in Fig. 4.

[0025] Fig. 6 is a graph illustrating the PLLA micro-particle suspension overtime at 20 °C, 2 °C and -2 °C.

[0026] Fig. 7 is a graph illustrating the PLLA micro-particle suspension overtime at 20 °C and -2 °C for previously frozen suspensions.

DETAILED DESCRIPTION

[0027] In one aspect, the present disclosure provides a method that includes cooling an aqueous mixture that includes dermatologically-injectable or periodontally- injectable micro-particles to a temperature of 2 °C or lower, such as a temperature that is 1.5 °C or lower, 1 °C or lower, 0.6 °C or lower, 0 °C or lower, or -0.5 °C or lower, for example from -0.25 °C to -0.5 °C. At least a portion of the injectable micro-particles are in suspension. For example, at least 90%, such as at least 95% or at least 98%, of the micro-particles are in suspension.

[0028] Cooling the aqueous mixture of micro-particles to a temperature of 2 °C or lower reduces the sedimentation rate of the suspended micro-particles, in comparison to the sedimentation rate of the micro-particles in an otherwise identical aqueous mixture at room temperature. The sedimentation rate may be sufficiently reduced that, at the cooled temperature, at least 85% of the suspended micro-particles remain suspended after 15 minutes.

[0029] The micro-particles have a static water contact angle of 60° or greater. In some examples, the micro-particles have a static water contact angle of 80° or greater. Micro-particles that have a static water contact angle of less than 60° are less likely to form micro-bubble/micro-particle interactions.

[0030] The micro-particles may be at a concentration of about 15 mg/mL to about

30 mg/mL in the aqueous mixture. The micro-particles may have a median size that is from about 1 pm to about 200 pm, such as a median size from about 40 pm to about 75 pm.

[0031] The aqueous mixture is substantially isotonic to blood or to extracellular fluid, and may be dermatologically or periodontally injected into a patient. An aqueous mixture that is substantially isotonic to blood or to extracellular fluid should be understood to mean that dermatological or periodontal injection of the aqueous mixture into a patient would not result in tonicity-related tissue damage. The aqueous mixture may have an osmolarity of from about 280 to about 300 mOsm/liter.

[0032] In some examples, the aqueous mixture includes an excipient such a tonicity agent, a suspending agent, a pH adjusting agent, a preservatives, an anesthetic agent, or any combination thereof in addition to the micro-particles. The tonoxity agent may be mannitol, sodium chloride, dextrose, glycerin, or any combination thereof. The suspending agent may be sodium carboxymethylcellulose, hyaluronic acid, hydrolyzed collagen, methylcellulose, hydroxypropylmethylcellulose, polyvinyl pyrrolidone, or any combination thereof. The pH adjusting agent may be sodium hydroxide, hydrochloric acid, sodium bicarbonate, sodium citrate, sodium phosphate, or any combination thereof. The preservative may be benzyl alcohol, methylparaben, propylparaben, thimerosal, or any combination thereof. The anesthetic agent may be lidocaine hydrocholoride.

[0033] The micro-particles may include a polymer, such as: poly-L-lactic acid

(PLLA), poly-methylmethacrylate (PMMA), polycaprolactone, polydioxanone, polyglycolic acid, polyglactin, polycaprolate, poliglecaprone polytrimethylene carbonate, polyglytone, or any combination thereof. In some specific examples, the micro-particles are PLLA micro-particles. PLLA microparticles are available in a commercial formulation under the name SCULPTRA™ Aesthetic.

[0034] In specific examples of the disclosed method, the aqueous mixture includes water, sodium carboxymethylcellulose, mannitol, and dermatologically-injectable or periodontally-injectable PLLA micro-particles, and the method includes cooling the mixture to a temperature of 2 °C or lower, such as -0.5 °C or lower.

[0035] In more specific examples, the aqueous mixture that includes the microparticles consists essentially of: water; sodium carboxymethylcellulose; mannitol; dermatologically-injectable or periodontally-injectable PLLA micro-particles; and optionally a local anesthetic such as lidocaine. The components are in a ratio of: about 5 mL of water, to about 90 mg sodium carboxymethylcellulose, to about 127.5 mg mannitol, to about 150 mg of dermatologically-injectable PLLA micro-particles. The exemplary method includes cooling the mixture to a temperature of 2 °C or lower, such as -0.5 °C or lower. [0036] The aqueous mixture of suspended micro-particles may be prepared and frozen for future use. The aqueous mixture may be dispended into a single-use container, such as a syringe, before freezing the mixture. The single-use container may be agitated to maintain the suspension during the cooling step, the freezing step, or both.

[0037] The aqueous mixture may be frozen in a single-use container and distributed from a central manufacturing location to a medical practitioner. During the distribution, the mixture is kept frozen to prevent sedimentation of the micro-particles. The mixture may be stored frozen for future use. Alternatively, the aqueous mixture may be prepared and frozen in a single-use container at a medical clinic.

[0038] A frozen mixture may be thawed before use, such as thawing at a temperature that is 2 °C or lower, for example a temperature that is from about -2.5 °C to about 1.0 °C, for example from about -0.8 °C to about 0 °C, from about 0 °C to about 0.6 °C, or from about 0.6 °C to about 2 °C.

[0039] In some exemplary methods of the present disclosure, the aqueous mixture consists of 5 mL water, about 90 mg sodium carboxymethylcellulose, about 127.5 mg mannitol, and about 150 mg of dermatologically-injectable or periodontally-injectable PLLA micro-particles, and at least 65% of the PLLA micro-particles are in suspension 75 minutes after the frozen mixture has thawed at a temperature of -2.5 °C, as measured by optical transmission.

[0040] Methods according to the present disclosure may include preparing the mixture of micro-particles by reconstituting a dried formulation with an aqueous solution. The aqueous solution may be water, a hypotonic intravenous solution, or a combination thereof. The dried formulation may include the micro-particles, sodium carboxymethylcellulose, and mannitol, where the micro-particles are PLLA microparticles. [0041] Methods according to the present disclosure may include mixing the mixture of micro-particles in an elongate vessel, such as a syringe or vial, where the mixing includes rotating the elongate vessel around an axis substantially perpendicular to gravity, and wherein the longitudinal axis of the elongate vessel is (a) substantially parallel to the axis of rotation or (b) substantially equivalent to the axis of rotation. Agitating the mixture in this manner may help suspend micro-particles in the aqueous solution while reducing the formation of micro-bubble/micro-particle interactions. This agitation may also be referred to as “maintaining the micro-particles in suspension” or “maintaining the suspension of micro-particles” since the micro-particles do not form a sediment during this mixing.

[0042] Without wishing to be bound by theory, when the aqueous mixture is in liquid form, is at a temperature of 2 °C or lower, and is being mixed in this manner, the resulting cooled suspension of micro-particles may (i) have a reduced sedimentation rate in comparison to an otherwise identical mixture at room temperature; and/or (ii) have a more uniform sedimentation rate in comparison to an otherwise identical mixture that is agitated to form micro-bubble/micro-particle interactions.

[0043] The present disclosure refers to rotating the elongate vessel around an axis substantially perpendicular to gravity while the longitudinal axis of the elongate vessel is substantially parallel or substantially equivalent to the axis of rotation. In the context of the present disclosure, it should be understood that an axis “substantially perpendicular to gravity” and a longitudinal axis that is “substantially parallel” or “substantially equivalent” to the axis of rotation, function together to inhibit or prevent particles from settling into one end of the elongate vessel despite the gentle mixing. In contrast, mixing an elongate vessel using an orbital shaker (i.e. around an axis that is parallel to gravity) at a sufficiently gentle rate to prevent formation of micro-bubble/micro- particle interactions may allow the particles to settle to the bottom of the elongate vessel despite the mixing.

[0044] The longitudinal axis of the elongate vessel may be spaced apart from the axis of rotation by a distance from 0 to 250 cm. The method may include rotating the elongate vessel at a rate from about 1 to about 20 rotations per minute.

[0045] The combination of (a) the distance between the longitudinal axis of the elongate vessel and the axis of rotation, and (b) the rate of rotation of the elongate vessel may be one of the combinations shown in the following table:

Table 1

[0046] The vessel experiences an increase in centripetal force as the distance from the axis of rotation increases, and as the rotations per minute increases. The combinations of RPM and distance shown in the table may suspend the micro-particles while reducing micro-bubble/micro-particle formation.

[0047] The axis substantially perpendicular to gravity may be up to 5 degrees from horizontal, such as up to 3 degrees from horizontal. The longitudinal axis of the elongate vessel may be up to 5 degrees off from parallel to the axis of rotation, such as up to 3 degrees off from parallel. [0048] In some examples, the micro-particles are PLLA micro-particles and the aqueous solution is not frozen, and the method further includes injecting the mixture of PLLA micro-particles into the dermis, the subcutis, or the mucoperiosteum of a subject, such as into the deep dermis, the subcutaneous fat, or the lamina propria of the subject. [0049] The method may include injecting the mixture of PLLA micro-particles into the dermis, the subcutis, or the mucoperiosteum of the subject within 15 minutes, such as within 10 minutes, or within 5 minutes, of the time that the aqueous mixture warms to 3 °C. [0050] The method may include injecting the mixture of PLLA micro-particles into the dermis, the subcutis, or the mucoperiosteum of the subject while the aqueous mixture is at a temperature of 15 °C or lower. [0051] Figure 1 illustrates an exemplary method according to the present disclosure. The exemplary method (100) includes an optional step of reconstituting (102) a dried formulation with an aqueous solution to form an aqueous mixture that includes dermatologically-injectable or periodontally-injectable micro-particles. The aqueous solution is cooled (104) to a temperature of 2 °C or lower. The exemplary method includes a step of suspending (106) the micro-particles in the aqueous mixture. Although not illustrated in Figure 1 , the suspending (106) may be performed before the cooling (104), or at the same time as the cooling (104). In the illustrated method, the cooled suspension is injected (108) into the dermis, the subcutis, or the mucoperiosteum of a subject, such as into the deep dermis, the subcutaneous fat, or the lamina propria of a subject.

[0052] Figure 2 illustrates another exemplary method according to the present disclosure. The exemplary method (200) includes a step of dispensing (202) an aqueous suspension of dermatologically-injectable or periodontally-injectable micro-particles into a single-use container, such as a syringe. The suspension is cooled (204) to freezing. The frozen suspension is thawed (206) and injected (208) while still cold. Although not illustrated in Figure 2, the thawing step (206) may include (i) maintaining the suspension at a temperature of 2 °C or lower, (ii) maintaining micro-particles in suspension, or (iii) both. [0053] Figure 3 illustrates an exemplary method of mixing the mixture of microparticles in an elongate vessel, such as in a single-use container, for example a syringe. The exemplary mixing method may be used to suspend micro-particles in an aqueous solution, such as in step (106) of Figure 1 or in step (206) of Figure 2. This exemplary mixing method may be used in combination with either, or both, of the exemplary methods illustrated in Figure 1 and 2. The exemplary method (300) includes rotating (302) an elongate vessel holding the aqueous mixture around an axis that is substantially perpendicular to gravity. The elongate vessel is positioned such that the longitudinal axis of the elongate vessel is (a) substantially parallel to the axis of rotation or (b) substantially equivalent to the axis of rotation. In the exemplary method, the elongate vessel is cooled (304) to a temperature of 2 °C or lower. The rotating (302) and cooling (304) may be performed at the same time.

[0054] In another aspect, the present disclosure provides and apparatus that includes: a mixer sized and shaped to accept an elongate vessel, such as a syringe or a vial; and a cooler in thermal communication with the mixer or with an accepted elongate vessel. The cooler is capable of cooling an accepted elongate vessel to a temperature that is from -10 °C to 1 °C. The mixer is rotatable around an axis that is substantially parallel, or substantially equivalent, to the longitudinal axis of an accepted elongate vessel. The axis of rotation of the mixer is substantially perpendicular to gravity when the apparatus is in an operating position. As discussed above, it should be understood that an axis “substantially perpendicular to gravity” and a longitudinal axis that is “substantially parallel” or “substantially equivalent” to the axis of rotation, function together to inhibit or prevent particles from settling into one end of the elongate vessel despite the gentle mixing. [0055] The axis of rotation may be up to about 5 degrees, such as up to about 3 degrees, off from parallel to the longitudinal axis of an accepted elongate vessel. The axis of rotation may be up to about 5 degrees, such as up to about 3 degrees, from horizontal when the apparatus is in an operating position. [0056] The mixer may define an aperture that is sized and shaped to accept the elongate vessel, or may define an aperture that is sized and shaped to accept an insert that defines an aperture that is sized and shaped to accept the elongate vessel. The aperture that is sized and shaped to accept the elongate vessel may be sized and shaped to be in thermal communication with at least 80% of the surface area of an accepted elongate vessel.

[0057] The longitudinal axis of an accepted elongate vessel may be spaced apart from the axis of rotation by a distance from 0 to 250 cm. The mixer may be rotatable at an rate of from about 1 to about 20 rotations per minute.

[0058] The apparatus may be configured to operate using a combination of (a) the distance between the longitudinal axis of the elongate vessel and the axis of rotation, and (b) the rate of rotation of the elongate vessel that is shown in the following table:

Table 2

[0059] The mixer may be a heat transfer body and the cooler may be in thermal communication with the heat transfer body. The heat transfer body may be configured to use a solid, a liquid, a gas, or a combination thereof, in the transfer of heat from the accepted elongate vessel to the cooler.

[0060] The cooler may be a thermoelectric cooler, such as a Peltier cooler, or a vapor-compression refrigeration cooler.

[0061] The apparatus may also include a light source, and photon detector; where the light source and photon detector are configured to detect a solid-liquid phase change in an accepted elongate vessel. The light source may be a laser or a light emitting diode. [0062] The apparatus may include a temperature sensor and an electrical power meter detector; where the temperature sensor and the power meter detector are configured to detect: a solid-liquid phase change, a supercooling condition in the accepted elongate vessel, a superheating condition in the accepted elongate vessel, or any combination thereof.

[0063] The apparatus may additionally include a level sensor configured to detect a deviation between the axis of rotation and an axis perpendicular to gravity.

[0064] An exemplary apparatus according to the present disclosure is illustrated in

Figure 4. The apparatus (400) includes a mixer (402) defining a plurality of apertures (404) sized to accept syringes. The mixer (402) is in thermal communication with a cooler (406). In the illustrated apparatus, the cooler (406) is a Peltier cooler that draws thermal energy from the mixer (402), which acts as a heat transfer body for the accepted syringes in the apertures (404). In this manner, the apparatus is capable of cooling the accepted syringes to a temperature that is 2 °C or lower.

[0065] As may be seen in Figure 4, the apertures (404) position the accepted syringes such that the longitudinal axis of an accepted syringe (illustrated by the dashed line, 408) is substantially parallel to, or substantially equivalent to, the axis of rotation (illustrated by the dashed line, 410). When the apparatus is in an operating position, the axis of rotation is substantially perpendicular to gravity (illustrated by the dashed line, 412). [0066] Figure 5 is a front view of the apparatus illustrated in Figure 4. In Figure 5, the longitudinal axis 408 and the axis of rotation 410 are illustrated using an “x” in a circle to indicate they are entering the page. [0067] In another aspect, the present disclosure provides a syringe or vial that includes a frozen aqueous mixture that includes dermatologically-injectable or periodontally-injectable micro-particles. The frozen aqueous mixture is substantially isotonic to blood or to extracellular fluid. The micro-particles have a water contact angle of 60° or greater, and at least a portion of the injectable micro-particles are in suspension. For example, at least 90%, such as at least 95% or at least 98%, of the micro-particles are in suspension. In the context of the present disclosure, it should be understood that a frozen mixture has micro-particles in suspension if the micro-particles were in suspension at the time the liquid mixture froze.

[0068] The micro-particles may have a water contact angle of 80° or greater. The micro-particles may be at a concentration of about 15 mg/ml_ to about 30 mg/ml_. The micro-particles may have a median size that is from about 1 pm to about 200 pm, such as a median size from about 40 pm to about 75 pm.

[0069] The aqueous mixture may have an osmolarity of from about 280 to about

300 mOsm/liter. The aqueous mixture may include an excipient such a tonicity agent, a suspending agent, a pH adjusting agent, a preservatives, an anesthetic agent, or any combination thereof in addition to the micro-particles. The tonoxity agent may be mannitol, sodium chloride, dextrose, glycerin, or any combination thereof. The suspending agent may be sodium carboxymethylcellulose, hyaluronic acid, hydrolyzed collagen, methylcellulose, hydroxypropylmethylcellulose, polyvinyl pyrrolidone, or any combination thereof. The pH adjusting agent may be sodium hydroxide, hydrochloric acid, sodium bicarbonate, sodium citrate, sodium phosphate, or any combination thereof. The preservative may be benzyl alcohol, methylparaben, propylparaben, thimerosal, or any combination thereof. The anesthetic agent may be lidocaine hydrocholoride.

[0070] The micro-particles may include a polymer, such as: poly-L-lactic acid

(PLLA), poly-methylmethacrylate (PMMA), polycaprolactone, polydioxanone, polyglycolic acid, polyglactin, polycaprolate, poliglecaprone polytrimethylene carbonate, polyglytone, or any combination thereof. The micro-particles may be PLLA micro-particles.

[0071] The aqueous mixture may include water, sodium carboxymethylcellulose, mannitol, and dermatologically-injectable or periodontally-injectable PLLA micro-particles. The aqueous mixture may consists essentially of: water; sodium carboxymethylcellulose; mannitol; dermatologically-injectable or periodontally-injectable PLLA micro-particles; and optionally a local anesthetic such as lidocaine, where these components are in a ratio of: about 5 mL of water, to about 90 mg sodium carboxymethylcellulose, to about 127.5 mg mannitol, to about 150 mg of dermatologically-injectable PLLA micro-particles. [0072] Methods

[0073] The measured optical transmission reflects the amount of micro-particles in suspension. The more micro-particles in suspension, the lower optical transmission. The optical transmission of PLLA micro-particle suspensions in a 3 mL polypropylene syringe or a 3 mL glass vial was measured. The PLLA micro-particle suspensions were Sculptra™ (150 mg PLLA, 90 mg Sodium CMC, 127.5 mg manitol) reconstituted in 5cc sterile water for injection (Hospira, QC) and homogenized using an exemplary method according to step (302) of Figure 3. The syringes and vials were positioned with their longitudinal axis substantially parallel to gravity. The syringes and vials were maintained at the test temperature in a temperature control cabinet (IVXY Scientific 5L Lab Incubator). The incubator's heat radiator was actively cooled with Zimmer Cryo mini as necessary. The optical transmission was measured using a Philips Lighting TL Mini Blacklight Blue (4W BLB 1FM/10X25CC) which transmits UV-A radiation, primarily within the range of 350 to 400 nm, in combination with a UV340 UV light meter from Lutron Electric Enterprice Co. Ltd. to measure the amount of transmitted light. The UV340 light meter detects light in the spectrum of 290 nm to 390 nm.

[0074] Example 1. PLLA micro-particle suspensions at a constant temperature overtime.

[0075] The measured optical transmission for each sample over 60 minutes was plotted in a graph, shown in Figure 6. The sample kept at -2 °C showed reduced settling in comparison to the samples kept at 20 °C or 2 °C.

[0076] Example 2. Previously frozen PLLA micro-particle suspensions at a constant temperature overtime.

[0077] The measured optical transmission for both samples over 60 minutes was plotted in a graph, shown in Figure 7. The sample kept at -2 °C showed reduced settling in comparison to the samples kept at 20 °C, and showed a substantially identical settling profile as the never frozen sample used in Example 1.

[0078] In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the examples. However, it will be apparent to one skilled in the art that these specific details are not required. Accordingly, what has been described is merely illustrative of the application of the described examples and numerous modifications and variations are possible in light of the above teachings. [0079] Since the above description provides examples, it will be appreciated that modifications and variations can be effected to the particular examples by those of skill in the art. Accordingly, the scope of the claims should not be limited by the particular examples set forth herein, but should be construed in a manner consistent with the specification as a whole.