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  • 1.
    Ahmed, Hamzah
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Relationship Between Crystal Structure and Mechanical Properties in Cocrystals and Salts of Paracetamol2014Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Oral tablets are convenient and widely administered drugdosage forms.The mechanical properties of a drug substance such as plasticity, ability to cohere into compacts and friction/adhesion are important in the development of a tablet formulation. Crystal engineering is an interesting and viabletool for improving or optimizing these technical properties of a drug substance.The creation of a lternative polymorphic forms, cocrystals, salts or hydrates of a drug substance can result in structural variations in the molecular packing of the crystals and, thereby, can alter the deformation behavior of the materials.Knowledge of the relationships between crystal modifications and the technical properties in multicomponent systems is limited, but represents a possibility to predict mechanical properties based on crystalstructure that facilitates engineering particles for the optimal processing performance. The overall objective of this thesis is thus to gain better understanding of the relationships between the crystal structure features and the mechanical properties of cocrystals and salts. Paracetamol form I, its cocrystals with oxalic acid and 4,4´-bipyridine, and its hydrochloride salt were selected as model systems in the study.The materials were scaled-up using rational crystallization methods and the physical purity was confirmed. The relevant properties of these powders were determined.Tablets were then made at applied pressures of50-250 MPa under controlled conditions.The tabletability and compactability of the powders were determined. The compression mechanics of the powders were the investigated according to a material classification protocol.Slip planes were identified by visually observing the crystal structures and based on the attachment energies calculated using different force fields in the materialsstudio.The tensile strengths of the powders increased with increasing pressure and the tabletability decreased in the order oxalic acid>paracetamol-hydrochloride salt≈paracetamol-oxalic acid>4,4´-bipyridine>paracetamol-4,4´-bipyridine.The tensile strength of the tablets decreased exponentially with increasing porosity,with some exceptions.Ingeneral, the cocrystals and the salt displayed intermediate compression characteristics as compared to the reference substances.The elastic recovery of the cocrystal and salt forms of paracetamol was not markedly different from that of paracetamol.It was found that slip plane prediction based on the attachment energies was not reliable. While it was possible to explain the improved tableting properties of powders based on the crystal features (i.e. the presence of slip planes and flat layers), no clear relationship was found with yield pressure. This may be attributed to possible brittle material characteristics and the surface energies of the crystals,which need to be further studied.Thus, cocrystallization and salt formation introduced structural features that were responsible for changes in the compaction and compression properties of drug substances. In future work, we intend to extend these studies to provide a clear picture of structure-mechanical property relationships in organic molecular crystals over multiple length scales;molecules to crystals to bulk powder.Key words Crystal engineering, solid forms, cocrystals, salts, tableting, crystal structure, mechanical properties, compression analysis

  • 2.
    Ahmed, Hamzah
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Shimpi, Manishkumar R.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Velaga, Sitaram P.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Relationship between mechanical properties and crystal structure in cocrystals and salt of paracetamol2017Inngår i: Drug Development and Industrial Pharmacy, ISSN 0363-9045, E-ISSN 1520-5762, Vol. 43, nr 1, s. 89-97Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives were to study mechanical properties of various solid forms of paracetamol and relate to their crystal structures. Paracetamol Form I (PRA), its cocrystals with oxalic acid (PRA-OXA) and 4,4-bipyridine (PRA-BPY) and hydrochloride salt (PRA-HCL) were selected. Cocrystals and salt were scaled-up using rational crystallization methods. The resulting materials were subjected to differential scanning solid-state characterization. The powders were sieved and 90-360 µm sieve fraction was considered. These powders were examined by scanning electron microscopy (SEM) and densities were determined. Tablets were made at applied pressures of 35-180 MPa under controlled conditions and the tablet height, diameter and hardness were measured. Tensile strength and porosity of the tablets were estimated using well known models. Crystal structures of these systems were visualized and slips planed were identified. Cocrystal and salt of PRA were physically pure. Sieved powders had comparable morphologies and particle size. The apparent and theoretical densities of powders were similar but no clear trends were observed. The tensile strengths of these compacts were increased with increasing pressure whereas tabletability decreased in the order oxalic acid > PRA-HCL ≈ PRA-OXA > BPY > PRA-BPY. Tablet tensile strength decreases exponentially with increasing porosity with the exception of PRY-BPY and BPY. Slip plane prediction based on attachment energies may not be independently considered. However, it was possible to explain the improved mechanical properties of powders based on the crystal structure. Cocrystallization and salt formation have introduced structural features that are responsible for improved tableting properties of PRA.

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