Carrier-free engineered progesterone microcrystals for controlled release

Abstract

Conventional progesterone formulations often rely on carriers, limiting drug load. This invention presents engineered progesterone microcrystals functioning as carrier-free controlled-release systems, where crystal structure dictates drug release. Distinct microcrystal forms were selectively developed using solvent / antisolvent methods, notably hollow Habit A (from IPA / DDW system) and dense Habit B (from ACN / DDW system). Both Habits A and B are confirmed stable Form 1 polymorphs. Additional habits (e.g., C and D) with diverse morphologies and crystallographic parameters were also produced using other solvent systems (e.g., involving DMSO, acetone, ethanol), demonstrating method versatility. These carrier- free microcrystals exhibit controlled, elongated progesterone release (≥14 days under tested conditions). Crucially, release profiles are tunable based on crystal habit (Habit A releasing faster than Habit B at similar sizes) and particle size, demonstrating suitability for tailored long-term controlled release applications.

Description

CARRIER-FREE ENGINEERED PROGESTERONE MICROCRYSTALS FOR CONTROLLED RELEASEInventors: Shady Farah, Joseph Eldor-ltskovitz, Merna Shaheen-Mualim, Neta Kutner, Edwar OdehTECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates generally to the field of pharmaceutical formulations and drug delivery. More specifically, the invention pertains to engineered crystalline forms of progesterone, carrier-free controlled-release systems comprisingthese microcrystals, methods fortheir preparation, and their use in therapeutic applications.BACKGROUND

[0002] Progesterone, a crucial endogenous 21 -carbon steroid hormone, plays a central role in female reproductive events, including the menstrual cycle and the establishment and maintenance of pregnancy. Beyond reproduction, it exerts vital functions in the central nervous, cardiovascular, and skeletal systems, and in mammary gland preparation. Progesterone is primarily produced by the ovaries, with additional synthesis occurring in the placenta, adrenal glands, and brain, typically via a two-step enzymatic conversion from cholesterol (FIG. 1).

[0003] Given its physiological importance, exogenous progesterone is used in several clinical applications, such as treating recurrent miscarriage, maintaining uterine quiescence in late pregnancy, supporting in-vitro fertilisation (IVF), hormone replacement therapy, and as a contraceptive agent. However, effective controlled release of progesterone presents challenges. As a poorly water-soluble drug, its bioavailability can be low and variable depending on the administration route [1].While oral, transvaginal, and injectable formulations exist, systemic administration can lead to undesirable side effects, and achieving sustained, localised action often requires specialised controlled release strategies [1]. Local administration, where feasible, is often preferred for better bioavailability and reduced systemic exposure [1]-

[0004] Conventional approaches to achieve controlled or sustained release of hydrophobic drugs like progesterone typically rely on formulating the drug within a carrier system. These carriers often include polymers (biodegradable or non- biodegradable), oils, lipids, or other excipients designed to encapsulate the drug and release it over time via diffusion, degradation, or dissolution of the carrier matrix. While widely used, these carrier-based systems suffer from significant limitations:- Limited Drug Loading: The amount of drug that can be incorporated is often restricted by the physical properties and volume of the carrier matrix, typically resulting in formulations with low drug-to-excipient ratios.- Carrier-Related Issues: The carrier materials themselves can elicit adverse biological responses, such as inflammation, foreign body reactions, fibrosis, or toxicity, compromising biocompatibility and therapeutic outcomes.- Complex Formulations: Manufacturing processes can be complex, requiring multiple steps for drug incorporation, potentially affecting drug stability, and making scale-up challenging.- Release Kinetics: Release profiles are often dependent on the carrier's properties (e.g., degradation rate) rather than the drug itself, and can sometimes exhibit undesirable initial burst release followed by unpredictable kinetics.

[0005] Recognising these limitations, an alternative paradigm focuses on developing carrier-free controlled release systems, where the drug's own solid-state properties are engineered to control its release profile. In such systems, the drug is the controlled release system. This approach leverages techniques like controlledcrystallisation to produce drug particles (e.g., microcrystals) with specific sizes, shapes (habits), surface characteristics, and polymorphic forms that inherently dictate the dissolution rate and thus the duration of drug release, eliminating the need for conventional carriers. Prior work by the inventors and others has demonstrated the feasibility and potential benefits of such carrier-free systems for various drugs, including rapamycin and paclitaxel for drug-eluting stents and formulations for reducing implant fibrosis [2-8].

[0006] The carrier-free approach offers several compelling advantages, particularly for sustained and controlled release:- High Drug Loading: Formulations can theoretically achieve up to 100% drug loading, maximising the therapeutic agent delivered per unit volume.- Simplified Formulations: Eliminating carriers simplifies the formulation composition and potentially the manufacturing process.- Improved Biocompatibility: Avoiding exogenous carrier materials reduces the risk of adverse biological reactions associated with those materials.- Direct Release Control: Release kinetics are directly governed by the intrinsic properties of the engineered drug microcrystals (e.g., habit, size, density, porosity, polymorphism), allowing for more precise tuning of the release profile by controlling the crystallisation process.

[0007] Therefore, to enable improved local, long-term, controlled release of progesterone, potentially overcoming the limitations of carrier-based systems, the present inventors sought to engineer and thoroughly characterise novel carrier-free progesterone microcrystals. While progesterone crystallisation and polymorphism have been studied, this work presents, for the first time, the selective development of two distinct carrier-free progesterone microcrystalforms-one exhibitinga hollowlike structure (Habit A) and the other a more condensed structure (Habit B) - using specific solvent / antisolvent systems. This invention details the preparation, detailedcharacterisation, and comparative analysis of these distinct microcrystal habits, demonstrating their potential to function as carrier-free systems providing tuneable, elongated progesterone release suitable for various therapeutic applications requiring controlled release.SUMMARY OF THE INVENTION

[0008] In one aspect, the present invention provides a carrier-free controlled- release system comprising progesterone microcrystals.

[0009] In some embodiments, the progesterone microcrystals comprise microcrystals having crystal habit A. These Habit A microcrystals are characterised as hollow microcrystals, may exhibit morphologies including triangular prism-like or double triangular prism-like shapes, and possess a specific orthorhombic unit cell structure (space group P2i2i2i) with defined lattice parameters and volume as detailed herein.

[0010] In some embodiments, which may be combined with the previous embodiment, the progesterone microcrystals comprise microcrystals having crystal habit B. These Habit B microcrystals are characterised as dense microcrystals, may exhibit morphologies including triangular prism-like, double-sided triangular prismlike, or pyramid shapes, and possess a specific orthorhombic unit cell structure (space group P2i2i2i) with defined lattice parameters and volume as detailed herein.

[0011] In some embodiments, which may be combined with any preceding embodiment, the progesterone microcrystals comprise microcrystals having crystal habit C. These Habit C microcrystals may exhibit morphologies of prism-like shapes and possess a specific orthorhombic unit cell structure (space group P2i2i2i) with defined lattice parameters and volume as detailed herein. In particular embodiments, Habit C microcrystals are obtainable from ethanol / double-distilled water or dimethylsulphoxide / double-distilled water solvent / antisolvent systems.

[0012] In some embodiments, which may be combined with any preceding embodiment, the progesterone microcrystals comprise microcrystals having crystal habit D. These Habit D microcrystals may exhibit morphologies including rod-like or needle-like shapes and possess a specific orthorhombic unit cell structure (space group P2i2i2i) with defined lattice parameters and volume as detailed herein. In particular embodiments, Habit D microcrystals are obtainable from an acetone / double-distilled water solvent / antisolvent system.

[0013] In systems comprising Habit A and Habit B microcrystals, embodiments exist wherein microcrystals of habit A exhibit a faster progesterone release rate than microcrystals of habit B when compared at substantially similar particle sizes under identical accelerated release conditions.

[0014] In particular embodiments, the microcrystals of habits A, B, C, and / or D are further characterised by a calculated density in the range of about 1.140 to about 1.240 g / cm3.

[0015] In embodiments comprising Habit A and / or Habit B microcrystals, these microcrystals correspond to progesterone Form 1 polymorph and are further characterised by a Z-parameter equal to 4.

[0016] The controlled-release system of any preceding embodiment may further comprise amorphous progesterone. The controlled-release system of any preceding embodiment may further comprise one or more active pharmaceutical ingredients different from progesterone, incorporated within the microcrystals of progesterone.

[0017] In another aspect, the invention provides methods for preparingthe specified progesterone microcrystals. Embodiments include methods specific for preparing Habit A (using IPA / DDW, with specific concentration ranges), Habit B (using ACN / DDW, with specific concentration ranges), Habit C (using DMSO / DDW or EtOH / DDW), and Habit D (using Acetone / DDW), as detailed in the claims and description.

[0018] In another aspect, the invention provides pharmaceutical compositions comprising the controlled-release system according to any of the system embodiments described above, typically suspended in a pharmaceutically acceptable liquid carrier, optionally with adjuvants like dispersants, wetting agents, stabilizers, or buffering agents.

[0019] In yet another aspect, the invention provides pharmaceutical dosage forms. One category comprises the controlled-release systems containing progesterone microcrystals (Habits A, B, C, D, combinations thereof, optionally with amorphous progesterone). These may be formulated, e.g., as encapsulated beads, dispersions, hydrogels, liposomes, adhesive materials, coatings on medical devices, or as administrable individual microcrystals, optionally with a carrier, suitable for routes like oral, subcutaneous, intravenous, intramuscular, intraperitoneal, or vaginal administration. These dosage forms can be formulated for local and / or controlled release, with tunability based on habit selection and particle size, including embodiments where Habit A provides faster release than Habit B at similar sizes.

[0020] Another category of dosage forms comprises the controlled-release systems containing progesterone microcrystals plus one or more different active pharmaceutical ingredients. These combination therapy dosage forms may be similarly formulated and administered, and can be designed for local, controllable, multifunctional drug release.

[0021] In further aspects, the invention provides the described pharmaceutical compositions or dosage forms for use in therapy, particularly for treating conditions like recurrent miscarriage, maintaining uterine quiescence, supporting IVF, hormone replacement therapy, or contraception. The invention also provides corresponding methods of treatment comprising administering said compositions or dosage forms.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 shows the reaction scheme of progesterone production by the ovaries, adrenal glands, placenta, and brain. Its synthesis by two enzymatic steps: first by conversion of the cholesterol to pregnenolone in the mitochondria via the cholesterol side-chain cleavage enzyme, and then by conversion from pregnenolone to progesterone via the enzyme 30-hydroxysteroid dehydrogenase.FIG. 2 shows SEM images illustrating various microcrystal morphologies obtained during initial screening using different miscible solvent mixtures and ratios (ethanol / DDW, acetone / DDW, DMSO / DDW, ACN / DDW, IPA / DDW).FIGs. 3A-3F show EVOS (FIGs. 3A, 3C and 3E) and SEM (FIGs. 3B, 3D and 3F) images of progesterone microcrystals prepared with the IPA-DDW 1 :2 system (Habit A) at different initial concentrations (12.5, 14.29 and 16.67 mg / ml), showing characteristic hollow morphologies. These morphologies are the typical morphologies that co-form in the IPA-DDW crystallisation system, regardless of the initial solution concentration.FIG. 4 shows the representative SEM image of a progesterone microcrystal (Habit A) from IPA-DDW 1 :2 solvent-antisolvent crystallisation, illustrating maximum and minimum diameter measurements.FIGs. 5A-5D show size distribution histograms for Habit A microcrystals obtained from the solvent IPA-DDW system at different initial concentrations, showing narrower distribution at higher concentrations.❖ FIGs. 5A and 5C show maximum microcrystals diameter by count and percentage of crystallised progesterone in a solution per initial concentration.❖ FIGs. 5B and 5D show the same microcrystals’ minimum diameter by count and percentage of crystallised progesterone in a solution per initial concentration, respectively. The analysis was performed for microcrystals crystallised in a solution with initial drug concentrations of 12.5, 14.29 and 16.67 mg / ml. A higherconcentration of the initial drug solution yielded a narrower microcrystal size distribution.FIG. 6 shows the comparative DSC analysis of Habit A progesterone microcrystals obtained from the IPA-DDW crystallisation system at different initial concentrations (12.5, 14.29 and 16.67 mg / ml), showing a consistent melting peak at 129-131 °C from all the samples indicative of obtaining the stable Form 1 polymorph crystals of progesterone.FIGs. 7A-7D show EVOS (FIGs. 7A and 7C) and SEM (FIGs. 7B and 7D) images of progesterone microcrystals having Habit B, prepared with the ACN-DDW 1 :2 solvent- antisolvent crystallisation system, showing characteristic dense morphologies.FIGs. 7E and 7F showthe corresponding size distribution histograms forthe crystals’ count (FIG. 7E) and percentage (FIG. 7F), as a function of the crystals’ maximum and minimum diameter.FIG. 8 shows the DSC analysis of Habit B progesterone microcrystals obtained from the ACN-DDW crystallisation system, showing a melting peak at 129-1310indicative of obtaining the stable Form 1 polymorph crystals of progesterone.FIGs. 9A-9D show the comparative PXRD analysis of progesterone microcrystals obtained from the ACN-DDW crystallisation system (Habit B, red line) and the IPA- DDW crystallisation system (Habit A, blue line), with an initial drug concentration of 12.5 mg / ml, both consistent with the stable Form 1 polymorph, with the potential preferred orientation indicated for Habit A.❖ FIGs. 9B-9D are the zoom outs from FIG. 9A for three angle regions showing additional peaks for the crystals obtained from the IPA-DDW crystallisation system.FIGs. 10A and 10B show the SXRD structural comparison (FIG. 10A) and crystal lattice packing analysis (FIG. 10B) of progesterone microcrystals obtained from the ACN-DDW crystallisation system (Habit B, red line) and IPA-DDW crystallisationsystem (Habit A, blue line), confirming identical molecular packing and Form 1 polymorph structure. Indeed, the two structures have similar packing with half translation over the a-axis, which is a typical translation due to the symmetry of the 2i a-axis. The 2i-symmetry element means a 180° rotation with 0.5 translation along the axis.FIGs. 10C and 10D show that both ACN-DDW (FIG. 10C) and IPA-DDW (FIG. 10D) are surrounded by 6 molecules with 10 interactions. The supramolecular connectivity and, the number of surrounding molecules and their orientations match perfectly. Also, the selected interactions from both compounds exhibit excellent matching. All these findings support the conclusion that those materials are identical.FIGs. 11 A-11 D show cumulative release profiles (weight and percentage) comparing amorphous progesterone, Habit A microcrystals (IPA-DDW, prepared at 12.5 mg / ml, relatively large size), and Habit B microcrystals (ACN-DDW, prepared at 16.67 mg / ml, relatively smaller size distribution), exhibiting controlled, extended release from both microcrystal habits over 14 days under specific accelerated conditions, compared to the almost immediate release of the amorphous formula over the first day.❖ FIG. 11A shows an averaged cumulative weight release of progesterone from crystals obtained from both crystallisation systems versus amorphous drug, freshly prepared before the release study.❖ FIG. 11 B shows an averaged cumulative weight release of progesterone from crystals obtained from both crystallisation systems versus amorphous drug over the initial 24 hours.❖ FIG. 11C shows a cumulative progesterone release % from crystals obtained from both crystallisation systems versus amorphous drug.❖ FIG. 11 D shows a cumulative progesterone release % from crystals obtained from both crystallisation systems versus amorphous drug over the initial 24 hours.FIG. 12 shows EVOS images monitoring the release and disappearance / shrinkage of amorphous progesterone versus crystalline progesterone (Habit A and Habit B) from alginate capsules over time under accelerated release conditions. The crystalline phase was obtained from the IPA-DDW and ACN-DDW crystallisation systems at 0, 6, and 12 hours, and at 3 and 7 days. The images show that the amorphous formulae has been released promptly, and the capsules were found empty after 3 days. The capsules of the crystalline formulae show the crystal's shrinkage due to the drug release from the crystals' surface with time, maintained throughout the study.FIGs. 13A-13B show EVOS images highlighting microcrystal shrinkage (surface erosion / dissolution) for Habit A from the IPA-DDW crystallisation system during release study in 12 hours (FIG. 13A) and in 7 days (FIG. 13B). The crystal's shrinkage (marked with the arrow) is due to surface release (marked with a dashed line) under accelerated release conditions.FIG. 14 shows additional EVOS and SEM images showing various hollow morphologies of Habit A microcrystals obtained from the IPA-DDW crystallisation system at different concentrations. These morphologies are the common morphologies that co-form in this crystallisation system, regardless of the initial solution concentration.FIG. 15 shows additional EVOS and SEM images showing various dense morphologies and sizes of Habit B microcrystals obtained from the ACN-DDW crystallisation system.FIGs. 16A-16B show molecular structure (FIG. 16A) and unit cell packing (FIG. 16B) of progesterone Form 1 crystal.FIG. 17 shows the SXRD structure representation for Habit A (IPA / DDW) at room temperature.FIG. 18 shows the SXRD structure representation for Habit A (IPA / DDW) at 100 K.FIG. 19 shows the SXRD structure representation for Habit B (ACN / DDW) at room temperature.FIG. 20 shows the SXRD structure representation for Habit B (ACN / DDW) at 100 K.FIG. 21 shows representative microscopy images of progesterone microcrystals obtained using different solvent / antisolvent systems and ratios, including DMSO / DDW (e.g., 30:4:3 and 30:6:3 ratios) and acetone / DDW (e.g., 13:2:3 ratio), illustrating variations in morphology and size distribution compared to Habits A and B.FIGs. 22 shows representative SEM images with detailed morphologies, including prism, needle and rod shapes, of progesterone microcrystals obtained from different solvent-antisolvent systems such as acetone / DDW and DMSO / DDW.FIG. 23 shows representation of SXRD unit cell packing for progesterone microcrystals obtained from the acetone / DDW system (Habit D), indicating a different molecular arrangement compared to Habits A and B.FIG. 24 shows comparative DSC thermograms of progesterone microcrystals obtained from various solvent / antisolvent systems (IPA / DDW, ACN / DDW, DMSO / DDW, acetone / DDW), showing potentially different melting temperatures suggestive of distinct polymorphs beyond Form 1 .FIG. 25 shows comparative PXRD patterns of progesterone microcrystals obtained from various solvent / antisolvent systems, illustrating differences in diffraction peaks potentially indicative of distinct polymorphs or preferred orientations.FIG. 26 shows comparative cumulative release profiles under accelerated conditions for Habit A (IPA / DDW, ~50 pm) and Habit B (ACN / DDW, ~50 pm) microcrystals prepared at approximately 40 mg / ml initial concentration, demonstrating faster release from the hollow Habit A compared to the dense Habit B when particle sizes are substantially similar.DETAILED DESCRIPTION OF THE INVENTION

[0022] In the following description, various aspects of the present application will be described. For purposes of explanation, specific details are set forth to provide a thorough understanding of the present application. However, it will also be apparent to one skilled in the art that the present application may be practiced without the specific details presented herein. Furthermore, well-known features may be omitted or simplified in order not to obscure the present application.

[0023] The terms "comprising" and “comprised of”, used in the claims, are "open ended" and means the elements recited, or their equivalent in structure or function, plus any other element or elements which are not recited. It should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a system comprised of x and z" should not be limited to systems composed of components x and z. Also, the scope of the expression "a method comprisingthe steps x and z" should not be limited to methods consisting only of these steps.

[0024] Unless specifically stated, as used herein, the term "about" is understood as within a range of normal tolerance in the art, for example, within two standard deviations of the mean. In one embodiment, the term "about" means within 10% of the reported numerical value of the number with which it is being used, preferably within 5% of the reported numerical value. For example, the term "about" can be immediately understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1 %, 0.5%, 0.1 %, 0.05%, or 0.01 % of the stated value. In other embodiments, the term "about" can mean a higher tolerance of variation depending on for instance the experimental technique used. Said variations of a specified value are understood by the skilledperson and are within the context of the present invention. As an illustration, a numerical range of "about 1 to about 5" should be interpreted to include not only the explicitly recited values of about 1 to about 5, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4 and sub-ranges, for example from 1 -3, from 2-4, and from 3-5, as well as 1 , 2, 3, 4, 5, or 6, individually. This same principle applies to ranges reciting only one numerical value as a minimum or a maximum.

[0025] Unless otherwise clear from context, all numerical values provided herein are modified by the term "about". Other similar terms, such as "substantially", "generally", "up to" and the like are to be construed as modifying a term or value such that it is not an absolute. Such terms will be defined by the circumstances and the terms that they modify as those terms are understood by those of skilled in the art. This includes, at very least, the degree of expected experimental error, technical error and instrumental error for a given experiment, technique or an instrument used to measure a value.

[0026] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealised or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and / or clarity.

[0027] It will be understood that when an element is referred to as being "on", "attached to", "connected to", "coupled with", "contacting", etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the otherelement or intervening elements may also be present. In contrast, when an element is referred to as being, for example, "directly on", "directly attached to", "directly connected to", "directly coupled" with or "directly contacting" another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed "adjacent" another feature may have portions that overlap or underlie the adjacent feature.

[0028] The term “crystal habit” refers to the characteristic external shape or an external appearance of an individual crystal or aggregate of crystals. The crystal habit is dependent on the crystallographic form and growth conditions of the crystal, and it can be identified, for example as tabular (cuboid), platy (plates), prismatic (rods), acicular (needle), bladed (spatula) etc. Such habits of crystals may be prepared through the modification of crystallisation process parameters, including cooling and stirring rates, the solvent of crystallisation, and the addition of a co-solvent, antisolvent, mixtures of solvents or an additive. It is important to recognise that the different crystal shapes of a material may not necessarily have different physical properties such as melting point, solubility, and dissolution rates. Crystal habit is normally determined by an electron microscope.

[0029] The term “Bravais lattice” refers to the basic building block from which all crystals can be constructed in a particular crystal habit. The concept originated as a topological problem of findingthe number of different ways to arrange points in space where each point would have an identical “atmosphere”. That is each point would be surrounded by an identical set of points as any other point, so that all points would be indistinguishable from each other. Mathematician Auguste Bravais discovered that there were 14 different collections of the groups of points, which are known as Bravais lattices. These lattices fall into seven different "crystal systems”, as differentiated by the relationship between the angles between sides of the “unit cell” and the distance between points in the unit cell

[0030] The term “unit cell” refers to the smallest group of atoms, ions or molecules that, when repeated at regular intervals in three dimensions, will produce the lattice of a crystal system. The “lattice parameter” is the length between two points on the corners of a unit cell. Each of the various lattice parameters are designated by the letters a, b, and c. If two sides are equal, such as in a tetragonal lattice, then the lengths of the two lattice parameters are designated a and c, with b being omitted. The angles are designated by the Greek letters alpha (a), beta (0), and gamma (y), and an angle with a specific Greek letter is not subtended by the axis with its roman equivalent. For example, alpha (a) is the included angle between the b and c axis.

[0031] For instance, a cubic lattice is characterised by a = b = c, a = 0 = y = 90°, which is the most symmetrical of the crystal habits. All the angles are equal to 90°, and all the sides are of the same length. In contrast, an orthorhombic lattice in the crystal habit of the present invention has all of the angles equal to 90°, while all of its sides are of unequal length. In other words, it has three mutually perpendicular axes of different lengths. Thus, the structure of a crystal is defined with respect to a unit cell. As the entire crystal consists of repeating unit cells, this definition is sufficient to represent the entire crystal.

[0032] A space group of a crystal is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that leave it unchanged. In three dimensions, space groups are classified into 219 distinct types, or 230 types if chiralcopies are considered distinct. In crystallography, space groups are also called the crystallographic or Fedorov groups, and represent a description of the symmetry of the crystal. The crystal habit of the present invention is characterised by space group 19, which is known as P 2i 2i 2i having its origin equidistant from all three 2i axes. In most of the cases, this space group belongs to orthorhombic crystal systems.

[0033] The “tap density" of crystals is an increased bulk density attained after mechanically tapping a receptacle containing the crystalline sample. The tapped density is obtained by mechanically tapping a graduated measuring cylinder or vessel containing the crystalline sample.

[0034] The “Z-parameter” refers to the number of single molecules (orformula units) appearing in the unit cell. It is defined as the number of formula units in the unit cell divided by the number of independent general positions. The Z-parameter is estimated using X-crystallography of the crystal by dividing the unit cell volume by 18 to obtain the number of non-hydrogen atoms in the unit cell. This calculation is based on “Rule of 18” where one assumes that the volume of a non-hydrogen atom is about 18 A3, while hydrogen atoms are ignored. This does not depend directly on crystallographic symmetry.

[0035] In addition to size and purity, the crystal habit represents the most important indicator of the quality of pharmaceutical crystals, which affects the efficiency of subsequent processing steps and the quality of the final drug product. For example, needle-like habit creates problems in pharmaceutical production due to the difficulty of handling them. There is a long-felt need to find new crystal habits that have a positive effect on crystals’ dissolution and release rates, flowability, bioavailability and pharmacokinetic profile. Solvent selection is the most popular strategy for modifying crystal properties, especially for small molecule pharmaceuticals. The effects of crystal habit modification strategies appear to be drug-specific and therefore extremely challenging, requiring careful studies that in most cases yield unpredictable results over broader experimental conditions.

[0036] The present invention focuses on engineering specific solid-state forms of progesterone, namely carrier-free microcrystals, whose inherent physical properties dictate drug release, thereby functioning as a controlled release system without requiring conventional carrier matrices. Several solvent-antisolvent systems (FIG. 2)have been extensively studied by the present inventors and identified specific conditions for selectively producing distinct microcrystal habits with controlled polymorphism and tuneable release profiles. Two primary crystallisation systems, isopropanol-double deionised water (IPA-DDW) yielding hollow microcrystals (Habit A) and acetonitrile-double deionised water (ACN-DDW) yielding dense microcrystals (Habit B), were fully characterised. Furthermore, exploratory studies using dimethylsulphoxide (DMSO)-DDW, acetone-DDW, and ethanol-DDW systems revealed the potential to generate additional progesterone microcrystal morphologies, such as Habit C and Habit D, and potentially different polymorphs, highlighting versatility of solvent-antisolvent crystallisation for tuning progesterone's solid-state form.

[0037] In the context of pharmaceutical formulations, “controlled release” generally refers to a drug delivery approach designed to release a therapeutic agent into the body at a predetermined rate, or over a specified time period, or at a specific location, or according to specific physiological conditions, rather than immediately after administration (as in conventional immediate-release formulations). The primary goals of controlled release often include maintaining drug concentrations within the therapeutic window for an extended duration, reducing dosing frequency, minimising fluctuations in drug levels (peaks and troughs) that can lead to side effects or reduced efficacy, potentially improving patient compliance, and allowing for more efficient use of the drug. Controlled-release profiles (e.g., zero-order, first- order release kinetics) are typically achieved through specialised formulation techniques or delivery system design, often involving polymers, matrices, membranes, or other engineered components.

[0038] As used herein in the context of the present invention, “controlled release” specifically refers to the release of progesterone from the described carrier-free progesterone microcrystals (such as those having Habit A or Habit B, or other habitsdescribed) in a mannerthat is moderated and extended overtime due to the inherent physicochemical properties of the microcrystals themselves. Unlike conventional carrier-based systems, controlled release in this invention is achieved without requiring encapsulation or dispersion within a separate release-controlling matrix (though such formulations are possible dosage forms). Instead, the release rate and duration are governed directly by the engineered characteristics of the progesterone microcrystals, including but not limited to their crystal habit (e.g., hollow vs. dense structure), particle size and size distribution, surface area, porosity, and potentially polymorphism. This inherent control allows for tuneable, sustained release profiles (demonstrated herein for at least 14 days) suitable for localised delivery applications, where the release kinetics can be tailored by selecting or designing microcrystals with specific structural and morphological properties.IPA-DDW Crystallisation System (Habit A - Hollow Microcrystals)

[0039] Utilising isopropyl alcohol (isopropanol, IPA) as the solvent and doubledeionised water (DDW) as the antisolvent, typically in a ratio of about 1 :2 (v / v), yielded progesterone microcrystals designated as Habit A. Experiments were conducted using initial progesterone concentrations primarily in the range of about 12.5 mg / ml to about 16.7 mg / ml. Microscopic analysis (EVOS and SEM) revealed that Habit A microcrystals consistently exhibit hollow structures, often presenting morphologies such as triangular prism-like or double triangular prism-like shapes (FIGs. 3A-3F, 4 and 14). These morphologies appeared common across the tested concentration range (from 12.5 to 16.7 mg / ml). The hollow nature is clearly visible in the SEM images (see FIGs. 3B, 3D, 3F, 4 and 14).

[0040] Size distribution analysis was performed on Habit A microcrystals prepared at 12.5, 14.29, and 16.67 mg / ml. Defining maximum and minimum diameters of the crystal (see FIG. 4) and reviewing histograms (see FIGs. 5A-5D) showed that lowerinitial concentrations (e.g., 12.5 mg / ml) tended to produce a wider size distribution, while higher concentrations (14.29 and 16.67 mg / ml) yielded narrower distributions.

[0041] Another experimental observation is that crystallisation yield also increased with higher initial progesterone concentration, rising from approximately 9% at 12.5 mg / ml to about 23% at 16.67 mg / ml (Table 1).Table 1 : Yield of progesterone crystals in IPA-DDW (1 :2 v / v) crystallisation system, with the different progesterone concentration.

[0042] Experiments conducted using a higher initial concentration of about 40 mg / ml also successfully yielded Habit A microcrystals, demonstrating that the process is applicable across a broader concentration range, although yield and size distribution may vary. Thermal analysis by DSC performed on progesterone Habit A microcrystals (from 12.5 to 16.7 mg / ml preparations) consistently show a single sharp endothermic peak around 130 °C (see FIG. 6), corresponding to the melting point of the known stable polymorph, Form 1. Further crystallographic analysis confirmed this.

[0043] PXRD patterns (FIGs. 9A-9D) are consistent with Form 1 , potentially showing some preferred orientation compared to Habit B. Single crystal X-ray diffraction (SXRD) analysis (see FIGs. 10A-10D, 17 and 18) determined the structure as the orthorhombic space group P2i2i2i with specific lattice parameters:These crystal parameters are characteristic of Form 1 , with Z=4. The calculated density was determined to be in the range of about 1.18-1.21 g / cm (see Table 2).Table 2: Crystal data from SXRD showed the same crystal properties for both crystals obtained by the two crystallisation systems (ACN / DDW and IPA / DDW).ACN-DDW Crystallisation System (Habit B - Dense Microcrystals)

[0044] Using acetonitrile (ACN) as the solvent and DDW as the antisolvent, again typically in a ratio of about 1 :2 (v / v), yielded progesterone microcrystals, which are designated as Habit B. The optimal initial concentration identified in initial studies was about 16.67 mg / ml.

[0045] Microscopic analysis (EVOS and SEM) revealed that the Habit B microcrystals are distinctly dense (non-hollow) structures (see FIGs. 7A-7D and 15). The observed morphologies included triangular prism-like, double-sided triangular prism-like, and pyramid shapes, sometimes formed as individual microcrystals (FIGs. 7B and 15) and sometimes as clusters (FIGs. 7D and 15). Size distribution analysis for the 16.67 mg / ml preparation showed a broad distribution, with a majority of relatively smaller microcrystals (see FIGs. 7E and 7F).

[0046] Similar to the IPA-DDW crystallisation system, experiments with higher initial concentrations of about 40 mg / ml also successfully yielded Habit B microcrystals. Thermal analysis by DSC showed a single sharp endothermic peak around 129.5 °C (FIG. 8), again consistent with the stable Form 1 polymorph. Crystallographic analyses confirmed this.

[0047] PXRD patterns (see FIGs. 9A-9D) matched Form 1 . The SXRD analysis, which is shown in FIGs. 10A-10D, 19 and 20, confirms the orthorhombic P2i2i2i space group with specific lattice parameters:These crystal parameters are characteristic of Form 1 , with Z=4. The calculated density was determined to be in the range of about 1.16-1.21 g / cm (Table 2).

[0048] Comparison of SXRD data for Habits A and B confirmed they share the same fundamental molecular packing corresponding to Form 1 (FIGs.10A-10D). Essentially, the yield obtained with the ACN-DDW system (at 16.67 mg / ml) was substantially higher (around 49%) compared to the IPA-DDW system under similar conditions (around 23% at 16.67 mg / ml) (Table 3), making the ACN-DDW system potentially more efficient for producing these carrier-free Form 1 microcrystals.Table 3: Yield of progesterone microcrystals at IPA-DDW crystallisation system versus ACN-DDW system at initial drug concentration 16.67 mg / ml.Other Solvent-Antisolvent Systems

[0049] Exploratory crystallisation experiments were also conducted using other solvent systems, including dimethylsulphoxide (DMSO)-DDW, acetone-DDW, and ethanol-DDW, with varying solvent / antisolvent ratios and initial progesterone concentrations (see FIGs. 21 and 22). Specifically, these included:1) A colourless needle obtained from acetone / DDW (2:3)2) A colourless prism obtained from ethanol / DDW (1 :2)3) A colourless prism obtained from DMSO / DDW (2:1)

[0050] Each selected crystal was immersed in Paratone-N oil and mounted on a Rigaku Oxford Diffraction - XtaLAB Synergy-S diffractometer. Data collection was performed at 100 K using monochromate Cu Ka radiation (A = 1 .54184 A). Standard 4> and UJ scans were used to cover the Ewald sphere. Accurate unit cell parameters were determined based on the indicated reflections. Structure solution and refinement were carried out using Olex2. The structure was solved using the olex2. solve program employing Charge Flipping and refined against F using the ShelXL refinement package via Least Squares minimisation (see Examples below). All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed in calculated positions and refined using a riding model; their isotropic displacement parameters (UiS0) were constrained to 1.5 times the Ueqof their parent atom for terminal sp carbons and 1.2 times Ueqfor all other carbon atoms. Moleculargraphics were generated using Mercury software (version 2022.3.0).

[0051] All three analysed single crystals exhibited an orthorhombic unit cell structure belonging to the P2i2i2i space group, with a = 0 = y = 90° (Table 3). Specific morphologies and lattice parameters were determined as follows:❖ Acetone / DDW System: Characterised as colourless needle microcrystals. Lattice parameters: a = 6.2129 A, b = 12.5886 A, c = 22.1829 A. Unit cellO Q volume: 1734.96 A .❖ Ethanol / DDW System: Characterised as colourless prism microcrystals. Lattice parameters: a = 10.2561 A, b = 12.4994 A, c = 13.6480 A. Unit cellO Q volume: 1749.60 A .❖ DMSO / DDW System: Characterised as colourless prism microcrystals. Lattice parameters: a = 10.2545 A, b = 12.4970 A, c = 13.6534 A. Unit cellO Q volume: 1749.68 A .

[0052] Thes crystallisation experiments yielded progesterone microcrystals with diverse morphologies distinct from Habits A and B, such as rod-like and different prism shapes, particularly noted from the acetone-DDW system (see FIG. 22). Preliminary characterisation suggested these alternative crystallisation systems might produce different progesterone polymorphs or crystal packings. For instance, SXRD analysis of microcrystals from the acetone-DDW system indicated a potentially different unit cell packing compared to Habits A and B (see FIG. 23).Table 3: SXRD crystal data of other solvent systems, including DMSO-DDW, acetone- DDW and ethanol-DDW, showing the crystal properties for other progesterone crystals different from those of Habit A or Habit B.

[0053] While both Habits A (hollow prisms, Form 1) and B (dense prisms and pyramids, Form 1 ) represent well-characterised carrier-free microcrystals selectively produced using IPA / DDW and ACN / DDW systems respectively, further exploration revealed that alternative solvent-antisolvent systems can yield progesterone microcrystals with distinct characteristics.

[0054] For example, crystallisation using DMSO / DDW, acetone / DDW, and ethanol / DDW systems (as described in Examples) generated microcrystals exhibiting different morphologies, such as Habits C and D having different crystallographic parameters compared to Habits A and B.

[0055] Microscopy (see FIGs. 21 and 22) revealed morphological diversity. For instance, the acetone / DDW system produced mixtures including distinct needle- shaped microcrystals alongside prisms of Habit D, differing significantly from the generally prismatic / pyramidal shapes of Habits A and B (see FIGs. 3, 7, 14 and 15).

[0056] The DMSO / DDW and ethanol / DDW systems tended to produce prismatic microcrystals of Habit C (see FIGs. 21 and 22), appearing morphologically similar to some crystals observed in Habit B preparations, although potentially differing in density or other fine features not fully assessed. This demonstrates that the choice of solvent system provides a powerful tool to control not only density (hollow vs. dense, as seen in A vs. B) but also the fundamental crystal shape (e.g., needles vs. prisms).

[0057] Single crystal X-ray diffraction (SXRD) analysis was successfully performed on representative crystal samples, which were obtained from acetone / DDW (needle), ethanol / DDW (prism) and DMSO / DDW (prism) systems (SXRD analysis in Examples and FIG. 23 for acetone / DDW packing example). Interestingly, all three samples were found to crystallise in the same orthorhombic system and P2i2i2i space group as Habits A and B. However, their lattice parameters revealed significant differences, particularly for the acetone / DDW system (Habit D), which resulted in a crystal exhibiting the following lattice parameters: a ~ 6.2 A, b ~ 12.6 A, c ~ 22.2 A and a unit cell volume ~ 1735 A . These parameters are markedly different from the lattice parameters of Habits A and B having a ~ 10.2 A and c ~ 13.6 A, as mentioned above.

[0058] The substantially different dimensions, especially 'a' and 'c', despite a similar overall volume and the same space group, strongly indicate a different molecular packing arrangement, suggesting these needles represent a distinct polymorph or solvate of progesterone compared to the Form 1 identified for Habits A and B.

[0059] The ethanol / DDW and DMSO / DDW systems (Habit C) yielded microcrystals with lattice parameters a ~ 10.25 A, b ~ 12.5 A, c ~ 13.65 A and volume ~ 1750 A that are very similarto each other and also fall within the range observed for Habits A and B (Form 1). This suggests that, despite using different solvent systems, these conditions predominantly produced prisms of the known stable Form 1 polymorph, similar to Habits A and B.

[0060] Comparative DSC thermograms (FIG. 24) and PXRD patterns (FIG. 25) across the various systems (IPA-DDW, ACN-DDW, DMSO-DDW and acetone-DDW) revealed differences in melting peaks and diffraction patterns and provided further evidence for polymorphic diversity. Different melting points were observed via DSC for samples prepared from different solvent systems. Similarly, PXRD patterns showed distinct differences in peak positions and intensities, particularly comparing the acetone / DDW product with the others. These thermal and diffraction differences align with the SXRD findings (especially the unique structure from acetone / DDW) and support the conclusion that the solvent-antisolvent crystallisation method can access multiple polymorphic forms of progesterone.

[0061] In other words, these differences suggest the existence of polymorphs other than Form 1 or variations in crystal structure / packing achievable using these alternative solvent systems. While Habits A and B (Form 1) are the primary focus of this invention due to their full characterisation and controlled formation, these results for other systems, such as Habits C and D, highlight the broad potential of solvent-antisolvent crystallisation to generate a diverse range of carrier-free progesterone microcrystal forms, potentially offering further options for tuning controlled release properties.

[0062] In summary, while Habits A and B represent distinct hollow and dense morphologies of the well-characterized progesterone Form 1 (P2i2i2i), altering the solvent system (e.g., using acetone, DMSO, ethanol) allows for the generation of carrier-free progesterone microcrystals with alternative morphologies (e.g., needles, rods or prisms) and potentially different polymorphic forms, as evidenced strongly by the distinct crystallographic parameters of the acetone / DDW product (Habit D). Indeed, the ethanol / DDW and DMSO / DDW systems appeared to yield primarily the Form 1 polymorph (Habit C), similar crystallographically to Habits A and B, but potentially offering alternative routes or minor morphological variations. This l ' lhighlights the versatility of the described carrier-free crystallisation approach to access a range of progesterone solid-state forms with potentially diverse physicochemical properties and release profiles.Release Profile Analysis: Tuneability via Habit and Size

[0063] A key aspect of this invention is the demonstration that the engineered carrier-free progesterone microcrystals provide controlled, extended release, and that this release can be tuned by modulating the microcrystal's physical properties, particularly habit and size.

[0064] Initial release studies compared amorphous progesterone, Habit A microcrystals (prepared at 12.5 mg / ml, resulting in relatively larger hollow microcrystals), and Habit B microcrystals (prepared at 16.67 mg / ml, resulting in a distribution skewed towards smaller, dense microcrystals) under accelerated conditions using an alginate bead encapsulation model for testing (see FIGs. 11A-11D). As it was expected, the amorphous form released very rapidly, essentially completing the drug release within approximately 50 hours. Both Habit A and Habit B microcrystals exhibited significantly prolonged and controlled release extending over the full 14- day study period. In this specific experiment (FIG. 11), the smaller, dense Habit B microcrystals showed a somewhat faster release rate compared to the larger, hollow Habit A microcrystals. Microscopic monitoring confirmed the gradual shrinkage of microcrystals within the test capsules over time due to surface dissolution / erosion (see FIG. 12, 13A and 13B).

[0065] This initial study demonstrated the fundamental principle of achieving sustained release using these carrier-free microcrystals and suggested that particle size plays a significant role, consistent with Noyes-Whitney dissolution principles.

[0066] To specifically isolate the effect of crystal habit (hollow vs. dense) independent of the significant size difference in the first study, a second releaseexperiment was conducted (see FIG. 26). In this study, Habit A (hollow) and Habit B (dense) microcrystals were prepared using about 40 mg / ml initial concentrations and selected to have substantially similar particle sizes (about 50 pm). Under identical accelerated release conditions, the hollow Habit A microcrystals exhibited a distinctly faster release profile compared to the dense Habit B microcrystals.

[0067] This surprising finding strongly suggests that for a given particle size, the increased surface area and porosity of the microcrystals associated with the hollow structure of Habit A facilitate more rapid dissolution and drug release compared to the dense structure of Habit B. This demonstrated difference in release kinetics between Habit A and Habit B, when particle size is controlled, offers significant therapeutic flexibility. For instance, the relatively faster release profile observed for the hollow Habit A microcrystals (at similar sizes compared to Habit B) could be advantageous in clinical scenarios requiring a more rapid establishment of therapeutic progesterone levels, such as providing immediate luteal phase support following assisted reproductive procedures like IVF, while still maintaining a controlled release over an extended period.

[0068] Conversely, the inherently slower and more prolonged release profile exhibited by the dense Habit B microcrystals (at similar sizes compared to Habit A) may be particularly beneficial for applications demanding long-term maintenance therapy with minimal fluctuations, potentially including certain hormone replacement regimens or long-acting injectable contraceptives where release over many weeks or months is desired. The ability to select between these intrinsically different release profiles, based on crystal habit alone, adds another dimension to the tunability previously discussed based on particle size, further empowering the design of optimised carrier-free progesterone therapies tailored to specific patient needs and clinical indications.

[0069] Taken together, these release studies (FIGs. 11A-11D and 26) powerfully illustrate the tuneability afforded by this carrier-free microcrystal technology. Drug release duration and rate can be controlled by selecting: a) Crystal Habit: Hollow Habit A provides inherently faster release than dense Habit B at similar sizes; and b) Particle Size: Larger microcrystals provide slower release than smaller microcrystals of the same habit.

[0070] By controlling the crystallisation process (solvent system choice, concentration, ratios, time) to target specific habits and size distributions, the release profile of progesterone can be tailored for different therapeutic needs - for example, using larger Habit B microcrystals for very long-term, slow release, or smaller Habit A microcrystals for a more rapid onset or moderately sustained release. This ability to tune release directly via crystal engineering is a major advantage of the carrier-free approach.EXAMPLESMaterials and Methods

[0071] Progesterone (>98%) was purchased from Acros Organics. Isopropyl alcohol (IPA) was purchased from Bio-Lab Ltd. Acetonitrile (AON) was purchased from J.T. Baker. Dimethyl sulfoxide (DMSO), acetone, and ethanol (EtOH) were analytical grade and purchased from Sigma-Aldrich. PRONOVA UP MVG sodium alginate was purchased from NovaMatrix, Norway. Barium chloride and other standard chemicals were analytical grade from Sigma-Aldrich. Double-deionised water (DDW) was used throughout.Crystallisation of Progesterone Microcrystals

[0072] General Procedure: Progesterone stock solutions were prepared by dissolving the required amount of progesterone powder in the selected solvent (IPA,ACN, DMSO, acetone, or ethanol) in a suitable vial to achieve the target initial concentration (% w / v). The mixture was vortexed until a clear, homogenous solution was obtained.

[0073] Optionally, the solution was filtered through a sterilising filter (e.g., 0.22 pm). Subsequently, DDW (antisolvent) was added dropwise or using a micropipette while potentially mixing gently, to achieve the desired solvent / antisolvent volume ratio (v / v). The vials were typically covered (e.g., with aluminium foil) and left undisturbed at approximately room temperature (e.g., 25°C) for a set duration, typically about 5 hours, to allow for microcrystal formation and growth.

[0074] Following the crystallisation period, the supernatant (solvent-antisolvent mixture) was carefully aspirated. The resulting microcrystals were washed several times with DDW and then typically left to dry overnight in a chemical hood or under vacuum at ambient conditions.Specific Examples:Habit A (IPA / DDW): Prepared using IPA:DDW ratio of approx. 1:2 (v / v) with initial progesterone concentrations ranging from about 12.5 mg / ml to about 16.7 mg / ml, and also at approx. 40 mg / ml.Habit B (ACN / DDW): Prepared using ACN:DDW ratio of approx. 1 :2 (v / v) with initial progesterone concentrations of about 16.67 mg / ml and also at approx. 40 mg / ml.Other Systems (Habits C and D): Examples include DMSO / DDW at ratios like 4:3 or 6:3 (v / v solvent-antisolvent) with initial progesterone concentration ~30 mg / ml (in DMSO); acetone / DDW at ratio ~2:3 with initial concentration ~13 mg / ml (in acetone); ethanol / DDW at ratio ~1 :2 with initial concentration ~15 mg / ml (in ethanol).Microcrystal Characterisation: Morphology and Size

[0075] EVOS Microscope: Brightfield microscopy (EVOS M5000 Invitrogen by Thermo Fisher Scientific) using LED illumination was employed to observe general micro-crystal morphology, shape, and estimate size distributions directly in suspension or after drying.

[0076] Scanning Electron Microscope (SEM): Detailed morphology, surface features (e.g., hollowness, density), and size analysis of dried microcrystals were obtained using a Thermo ScientificTM XL G2 Phenom Desktop SEM. Samples were mounted on carbon tape and sputter-coated with a thin layer of gold (~7 nm) to prevent charging. Images were typically acquired using the backscattered electron detector (BSD) with appropriate settings for magnification, beam intensity, and working distance. Size measurements (e.g., maximum / minimum diameters) were performed on multiple microcrystals per sample using image analysis software.Microcrystal Characterisation: Polymorphism and Thermal Properties

[0077] Powder X-ray Diffraction (PXRD): Polymorphism and crystal structure were assessed using PXRD. Measurements were typically performed on dried microcrystal powder using an instrument like a Rigaku Labview 2 9kW diffractometer (Cu Ka radiation, e.g., 45kV, 200mA). Data was collected over a 20 range (e.g., 4° to 60°) with a small step size (e.g., 0.01°).

[0078] Single CrystalX-ray Diffraction (SXRD): For definitive structure determination, suitable single microcrystals were selected, mounted (e.g., in Paratone-N oil on a loop), and analysed using a single-crystal diffractometer (e.g., Rigaku Oxford Diffraction - XtaLAB Synergy-S) typically using Mo Ka or Cu Ka radiation at room temperature and / or low temperature (e.g., 100K). Data collection involved appropriate scans (e.g., 4> and UJ) to cover the Ewald sphere. Structure solution and refinement were performed using standard crystallographic software (e.g., Olex2,SHELXL) to determine unit cell parameters, space group, atomic coordinates, and calculated density. Molecular graphics were generated using software like Mercury. Differential

[0079] Scanning Calorimetry (DSC): Thermal properties, including melting point and phase transitions indicative of polymorphism, were analysed using DSC (e.g., Mettler Toledo DSC3+). Samples of dried microcrystals were heated in sealed pans (e.g., aluminium) under a nitrogen atmosphere over a defined temperature range (e.g., 0 °C to 150 °C or higher) at a controlled heating rate (e.g., 10°C / min). Endothermic and exothermic events were recorded.In Vitro Release Studies

[0080] Progesterone Encapsulation (for Testing): To facilitate handling and maintain sink conditions during release testing, carrier-free progesterone microcrystals were often encapsulated as an exemplary administration / testing format.

[0081] Microcrystals (specific habit and size / batch noted for each study) were suspended uniformly in an alginate solution (e.g., 2% w / v MVG alginate) to achieve a target concentration (e.g., 10 mg / ml). Alginate capsules / beads containing the microcrystals were then formulated using techniques like micro-electro-encapsulation (e.g., ~7.5 kV voltage, ~1 ml / min flow rate) and crosslinked using a suitable salt solution (e.g., barium chloride).

[0082] Amorphous progesterone control capsules were prepared by first dissolving progesterone (e.g., in ethanol) and mixing this solution with the alginate before encapsulation and immediate testing.

[0083] Release Conditions: A known amount of encapsulated progesterone (determined by dissolving representative capsules and quantifying drug content via HPLC) was placed in a defined volume of release medium, ensuring sink conditions (e.g., 12 ml PBS with 0.2% SDS for accelerated release, based on progesteronesolubility at 37°C). Studies were conducted typically at 37°C with appropriate shaking / agitation.

[0084] At predetermined time points (e.g., ranging from minutes to 14 days), the entire release medium was collected and replaced with fresh medium. Collected samples were stored for analysis. Triplicate samples per formulation were typically tested.

[0085] Progesterone Quantification (HPLC): Progesterone concentration in the collected release samples was quantified using High-Performance Liquid Chromatography (HPLC) (e.g., Waters e2695 system with 2998 Photodiode Array Detector). Separation was achieved using a suitable column (e.g., XSelect HSS T3, 3.5 pm) with an appropriate mobile phase (e.g., ACN / Water gradient). Progesterone was detected by UV absorbance (e.g., at its Amax), and concentration was determined based on peak area relative to a standard calibration curve. Cumulative drug release (amount and percentage) was calculated over time.CONCLUSION

[0086] This work successfully demonstrates the engineering of novel carrier-free progesterone microcrystals functioning as their own controlled release systems, offering significant advantages over conventional carrier-based formulations. The present inventors have developed and optimised distinct solvent / antisolvent crystallisation methods to selectively produce two well-characterised progesterone microcrystal habits:1 . Habit A: Hollow microcrystals, exhibiting morphologies like triangular prisms, reliably produced using an IPA / DDW system.2. Habit B: Dense microcrystals, with morphologies including dense prisms and pyramids, reliably produced using an ACN / DDW system, notably with higher yield compared to the IPA / DDW system under tested conditions.

[0087] Both Habit A and Habit B were confirmed through careful and comprehensive characterisation (DSC, PXRD, SXRD) to be the stable Form 1 polymorph with an orthorhombic P2i2i2i crystal structure.

[0088] Crucially, these carrier-free microcrystals demonstrated controlled and significantly elongated progesterone release, extending for at least 14 days under accelerated in vitro conditions. This sustained release profile is an inherent property of the engineered microcrystalline structure, eliminating the need for external polymeric or lipidic carriers.

[0089] Furthermore, this invention reveals key principles for tuning the drug release kinetics from these carrier-free systems: Influence of Habit: At substantially similar particle sizes, the hollow Habit A microcrystals provide a faster release rate compared to the dense Habit B microcrystals, likely attributable to increased surface area and porosity. Influence of Size: Consistent with dissolution principles, larger microcrystals exhibit slower release compared to smaller microcrystals of the same habit.

[0090] This dual control mechanism - tuning via both crystal habit selection and particle size control - offers significant versatility in tailoring progesterone release profiles for specific therapeutic needs, ranging from faster onset to very prolonged release, directly through crystal engineering.

[0091] In addition, exploratory studies utilising other solvent systems successfully generated distinct progesterone microcrystal habits, including Habit C (prism-like microcrystals obtained from DMSO-DDW or ethanol-DDW systems, appearing crystallographically similar to Form 1) and Habit D (needle / rod-like microcrystals obtained from the acetone-DDW system, exhibiting unique lattice parameters suggesting a different polymorph or packing). The successful generation of these varied morphologies and structures indicates the broad applicability of this solvent-antisolvent crystallisation approach to create diverse solid-state forms of progesterone beyond the primary Habits A and B.

[0092] In conclusion, this invention provides novel, well-characterised, carrier-free progesterone microcrystals (including Habits A, B, C, and D) and methods for their selective production. These microcrystals function as effective controlled release systems offering high drug loading, controlled elongated release over weeks, and uniquely tuneable release kinetics based on inherent structural properties (habit and size). This technology holds significant promise for developing improved controlled release formulations for various clinical applications of progesterone, potentially enhancing efficacy and patient compliance while avoiding carrier-related complications.REFERENCES[1] Sarkar, A., Ragab, D., & Rohani, S. (2014). Polymorphism of progesterone: A new approach for the formation of form li and the relative stabilities of form i and form IL Crystal Growth & Design, 14(9}, 4574-4582.[2] Farah, S., Doloff, J. C., Muller, P., Sadraei, A., Han, H. J., Olafson, K.s... & Anderson, D. G. (2019). Long-term implant fibrosis prevention in rodents and non-human primates using crystallised drug formulations. Nature materials, 18(8), 892-904.[3] Kutner, N., Kunduru, K. R., Rizik, L., & Farah, S. (2021). Recent advances for improving functionality, biocompatibility, and longevity of implantable medical devices and deliverable drug delivery systems. Advanced Functional Materials, 31(44), 2010929.[4] Farah, S. (2018). Protective layer development for enhancing stability and drugdelivery capabilities of des surface-crystallised coatings. ACS applied materials & interfaces, 10( 0), 9010-9022.[5] Farah, S., & Domb, A. J. (2018). Crystalline paclitaxel coated DES with bioactive protective layer development. Journal of Controlled Release, 271 , 107-117.[6] Khan, W., Farah, S., Nyska, A., & Domb, A. J. (2013). Carrier free rapamycin loaded drug eluting stent: in vitro and in vivo evaluation. Journal of Controlled Release, 768(1), 70-76.[7] Farah, S., Khan, W., & Domb, A. J. (2013). Crystalline coating of rapamycin onto a stent: Process development and characterisation. International journal of pharmaceutics, 445(1-2), 20-28.[8] Levy, Y., Khan, W., Farah, S., & Domb, A. J. (2012). Surface crystallisation of rapamycin on stents using a temperature induced process. Langmuir, 28(15), 6207-6210.[9] Sundstrom-Poromaa, Inger, et al. "Progesterone-Friend or foe?." Frontiers in Neuroendocrinology 59 (2020): 100856.

Claims

CLAIMS1. A carrier-free controlled release system comprising progesterone microcrystals having a crystal habit selected from the group consisting of crystal habit A, crystal habit B, and a combination thereof, wherein the microcrystals of said habit A are characterised as hollow microcrystals, exhibiting morphologies including triangular prism-like or double triangular prism-like shapes, and having an orthorhombic unit cell structure, space group P2i2i2i, lattice parameter a in the range of about 10.20 - 10.30 A, b in the range of about 12.44 - 12.54 A, c in the range of about 13.58 - 13.77 A, alpha equal to 90, beta equal to 90, gamma equal to 90, and unit cell volume in the range of about 1730 - 1770 A3; and wherein the microcrystals of said habit B are characterised as dense microcrystals, exhibiting morphologies including triangular prism-like, doublesided triangular prism-like or pyramid shape, and having an orthorhombic unit cell structure, space group P2i2i2i, lattice parameter a in the range of about 10.20 - 10.38 A, b in the range of about 12.44 - 12.58 A, c in the range of about 13.57 - 13.83 A, alpha equal to 90, beta equal to 90, gamma equal to 90 and unit cell volume in the range of about 1730 - 1795 A3.2 The system of claim 1 , wherein microcrystals of habit A exhibit a faster progesterone release rate than microcrystals of habit B when compared at substantially similar particle sizes under identical accelerated release conditions.3 The system of claim 1 , further comprising progesterone microcrystals having crystal habit C, exhibiting morphology of prism-like shapes, and having an orthorhombic unit cell structure, space group P2i2i2i, lattice parameter a in therange of about 10.25 - 10.26 A, b in the range of about 12.49 - 12.50 A, c in the range of about 13.64 - 13.66 A, alpha equal to 90, beta equal to 90, gamma equal to 90, and unit cell volume in the range of about 1749 - 1750 A3. The system of claim 3, wherein the microcrystals having crystal habit C are obtainable from a solvent / antisolvent system selected from ethanol / double- distilled water or dimethylsulphoxide / double-distilled water. The system of claim 1 or 3, further comprising progesterone microcrystals having crystal habit D, exhibiting morphology of rod-like or needle-like shapes, and having an orthorhombic unit cell structure, space group P2i2i2i, lattice parameter a of about 6.21 A, b of about 12.50 A, c of about 22.18 A, alpha equal to 90, beta equal to 90, gamma equal to 90, and unit cell volume of about 1735 A3. The system of claim 5, wherein the microcrystals having crystal habit D are obtainable from a solvent / antisolvent system of acetone / double-distilled water. The system of any one of claims 1 to 6, wherein the microcrystals of said crystal habits A, B, C, and D are further characterised by a calculated density in the range of about 1 .140 to about 1 .240 g / cm3. The system of claims 1 or 2, wherein the microcrystals of habit A and habit B correspond to progesterone Form 1 polymorph and are further characterised by a Z-parameter equal to 4.

9. The system of any one of claims 1 to 8, further comprising amorphous progesterone.

10. The system of any one of claims 1 to 9, further comprising one or more active pharmaceutical ingredients different from progesterone, incorporated within the microcrystals of progesterone.

11. A method for preparing the progesterone microcrystals having crystal habit A of claim 1 , said method comprisingthe steps:Step 1 : Dissolving amorphous or crystalline progesterone in isopropanol solvent to obtain a clear and homogenous solution of progesterone;Step 2: Optionally filtering the solution of Step 1 through a sterilising filter;Step 3: Adding double-distilled water anti-solvent to the progesterone solution prepared in Step 1 or 2 in a ratio of about 1 :2 (v / v) of solvent / anti-solvent to initiate crystallisation;Step 4: Leaving the solution obtained in Step 3 for about 2 to 8 hours at about room temperature to allow crystallisation;Step 5: Aspirating the solution of Step 4, followed by collecting the obtained microcrystals, washing the collected microcrystals with double-distilled water, and drying the microcrystals.

12. The method of claim 11 , wherein the concentration of the dissolved progesterone in isopropanol solvent in Step 1 is from about 10 mg / ml to about 20 mg / ml.

13. The method of claim 11 , wherein the concentration of the dissolved progesterone in isopropanol solvent in Step 1 is about 40 mg / ml.

14. A method for preparing the progesterone microcrystals having crystal habit B of claim 1 , said method comprisingthe steps:Step 1 : Dissolving amorphous or crystalline progesterone in acetonitrile solvent to obtain a clear and homogenous solution of progesterone;Step 2: Optionally filtering the solution of Step 1 through a sterilising filter;Step 3: Adding double-distilled water anti-solvent to the progesterone solution prepared in Step 1 or 2 in a ratio of about 1 :2 (v / v) of solvent / anti-solvent to initiate crystallisation;Step 4: Leaving the solution obtained in Step 3 for about 2 to 8 hours at about room temperature to allow the crystallisation;Step 5: Aspiration of the solution of Step 4, followed by collecting the obtained microcrystals, washing the collected microcrystals with double-distilled water and drying the microcrystals.

15. The method of claim 14, wherein concentration of the dissolved progesterone in acetonitrile solvent is from about 15 mg / ml to about 20 mg / ml.

16. The method of claim 14, wherein the concentration of the dissolved progesterone in acetonitrile solvent is about 40 mg / ml.

17. A method for preparing progesterone microcrystals havingcrystalhabitC of claim 3, said method comprising the steps: (1) Dissolving progesterone in a solvent selected from the group consisting of dimethylsulphoxide and ethanol; (2) Adding double-distilled water anti-solvent to the progesterone solution; (3) Allowing microcrystals to form; and (4) Collecting the obtained microcrystals.

18. A method for preparing progesterone microcrystals having crystal habit D of claim 5, said method comprising the steps: (1) Dissolving progesterone in acetone solvent; (2) Adding double-distilled water anti-solvent to the progesterone solution; (3) Allowing microcrystals to form; and (4) Collecting the obtained microcrystals.

19. A pharmaceutical composition comprising the controlled-release system of any one of claims 1 to 10 suspended in double-distilled water, saline, phosphate buffer, phosphate buffer saline, or other physiologically relevant buffers, optionally with stabilisers or organic solvents.

20. The pharmaceutical composition of claim 19, further comprising one or more pharmaceutically acceptable adjuvants.

21. The pharmaceutical composition of claim 20, wherein said one or more pharmaceutically acceptable adjuvants are selected from the group consisting of dispersants, wetting agents, stabilisers, and buffering agents.

22. A pharmaceutical dosage form comprising the controlled release system of any one of claims 1 to 9, wherein the system is encapsulated in barium-alginate or calcium-alginate beads, dispersed in oil, incorporated into a hydrogel capsule, formulated as liposomes, included in adhesive materials, coated on a medical device, or present as individual microcrystals or mixtures thereof, optionally comprising a pharmaceutically acceptable carrier, wherein the dosage form is suitable for oral, subcutaneous, intravenous, intramuscular, intraperitoneal or vaginal administration.

23. The pharmaceutical dosage form of claim 22, formulated to locally release progesterone.

24. The pharmaceutical dosage form of claim 22 or 23, formulated to controllably release progesterone, wherein the release profile is tuneable based on the selected ratio of habit A and habit B microcrystals and / or the particle size distribution.

25. The pharmaceutical dosage form of claim 24, wherein selecting microcrystals predominantly comprising habit A results in a faster initial release compared to a formulation comprising microcrystals predominantly comprising habit B of substantially similar particle size.

26. A pharmaceutical dosage form comprising the controlled release system of claim 10, wherein the system is encapsulated in barium-alginate or calcium-alginate beads, dispersed in oil, incorporated into a hydrogel capsule, formulated as liposomes, included in adhesive materials, coated on a medical device, or present as individual microcrystals or mixtures thereof, optionally comprising a pharmaceutically acceptable carrier, wherein the dosage form is suitable for oral, subcutaneous, intravenous, intramuscular, intraperitoneal or vaginal administration.

27. The pharmaceutical dosage form of claim 26, formulated for local multifunctional drug release.

28. The pharmaceutical dosage form of claim 26 or 27, formulated for controllable multifunctional drug release.

9. The pharmaceutical composition of any one of claims 19 to 21 , or the pharmaceutical dosage form of any one of claims 22 to 25, orthe pharmaceutical dosage form of any one of claims 26 to 28, for use in treating recurrent miscarriage, maintaining uterine quiescence in late pregnancy, supporting in- vitro fertilisation (IVF), as part of hormone replacement therapy, or as a contraceptive agent for birth control.

0. A method of treating or supporting a condition selected from the group consisting of late pregnancy maintenance, recurrent miscarriage, in-vitro fertilisation (IVF), hormone replacement therapy need, and need for birth control, the method comprising administering to a patient in need thereof a therapeutically effective amount of the pharmaceutical composition of any one of claims 19 to 21 , or the pharmaceutical dosage form of any one of claims 22 to 25, orthe pharmaceutical dosage form of any one of claims 26 to 28.

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