114 results found
Parambil JV, Poornachary SK, Heng JYY, et al., 2019, Template-induced nucleation for controlling crystal polymorphism: from molecular mechanisms to applications in pharmaceutical processing, CRYSTENGCOMM, Vol: 21, Pages: 4122-4135, ISSN: 1466-8033
Lapidot T, Matar OK, Heng JYY, 2019, Calcium sulphate crystallisation in the presence of mesoporous silica particles: experiments and population balance modelling, Chemical Engineering Science, Vol: 202, Pages: 238-249, ISSN: 0009-2509
A population balance model is used to investigate the effect of mesoporous silica particles on calcium sulphate crystallisation in a stirred batch crystalliser. The model accounts for nucleation, growth, agglomeration, breakage, and particle-assisted nucleation, and the model equations are solved numerically using the method of classes over a logarithmic, non-uniform mesh. The crystallisation process is characterized experimentally using electrical conductivity to track the ion concentration and laser diffraction to measure the steady-state crystal size distribution obtained at the end of the experiments. The experiments are carried out over a range of temperatures, initial supersaturations, particle pore diameters, and particle loadings. The model is first fitted to experimental data obtained in the absence of particles to determine kinetic parameters of the nucleation, growth, agglomeration, and breakage for pure calcium sulphate crystallisation. Varying pore diameter did not influence the catalytic effect of the particles, however, particle loading was found to significantly decrease the nucleation induction time. The model was extended to account for the presence of particles by fitting two additional mechanisms. The first proposed a particle-assisted nucleation where nuclei are produced via heterogeneous crystallisation, then detach by particle-particle collision that is second-order with respect to particle loading. The second proposed that the crystal breakage frequency increases linearly with particle loading. Good agreement with the experimental data is demonstrated over the range of conditions examined.
Ouyang J, Zhou L, Liu Z, et al., 2019, Solubility determination and modelling of benzamide in organic solvents at temperatures from 283.15 K and 323.15 K, and ternary phase diagrams of benzamide-benzoic acid cocrystals in ethanol at 298.15 K, JOURNAL OF MOLECULAR LIQUIDS, Vol: 286, ISSN: 0167-7322
Yang H, Belviso BD, Li X, et al., 2019, Optimization of Vapor Diffusion Conditions for Anti-CD20 Crystallization and Scale-Up to Meso Batch, CRYSTALS, Vol: 9, ISSN: 2073-4352
Zhang B, Wang Y, Thi S, et al., 2019, Enhancement of lysozyme crystallization using DNA as a polymeric additive, Crystals, Vol: 9, ISSN: 2073-4352
This study reports the first experimental evidence of using DNA as a polymeric additive to enhance protein crystallization. Using three kinds of DNA with different molecular weights—calf DNA, salmon DNA, and herring DNA—this study showed an improvement in the success rate of lysozyme crystallization, as compared to control experiments, especially at low lysozyme concentration. The improvement of crystallization is particularly significant in the presence of calf DNA with the highest molecular weight. Calf DNA also speeds up the induction time of lysozyme crystallization and increases the number of crystals per drop. We hypothesized the effect of DNA on protein crystallization may be due to the combination of excluded volume effect, change of water’s surface tension, and the water competition effect. This work confirms predications of the potential use of DNA as a polymeric additive to enhance protein crystallization, potentially applied to systems with limited protein available or difficult to crystallize.
Zou J, Wu J, Wang Y, et al., Synergistic effect of graphene oxide and different valence of cations on promoting catalase crystallization, Crystal Growth & Design, ISSN: 1528-7483
This study tests the effect of using the combination of graphene oxide (GO) with different valence cations as a heterogeneous nucleant on promoting catalase crystallization. By using GO and three types of salts with different valences, NaCl, MgCl2, and YCl3, the addition of GO with all three salts resulted in an increase in the percentage of crystal drops and a decrease in induction time. The experimental results further verified that there is a synergistic effect of GO and cations as the percentage of crystal drops was higher when GO with cations was added compared to control experiments where only GO or cations presented. It was also observed that the improvement in crystallization became more significant when cations with higher valence were utilized. It is believed that the enhancement in crystallization was due to the synergistic effect arising from the cation-π and electrostatic interactions between GO sheets and cations. These interactions subsequently contributed to the positively charged salt, which adsorbed and connected both negatively charged catalase molecules and the GO surfaces, increasing the local protein concentration and leading to crystallization. In addition, we compared LaCl3 and CeCl3 with YCl3 to verify the effect of the same valence salt on catalase crystallization and found that the higher the charge density, the more pronounced the promotion effect. This study provides a new protein crystallization methodology by exploiting GO with cations as heterogeneous nucleant to promote catalase crystallization and brings about a new model for investigating protein crystallization mechanisms.
Ngeow YW, Heng JYY, Williams DR, et al., 2019, TEM observation of silane coupling agent in silica-filled rubber tyre compound, Journal of Rubber Research, Vol: 22, Pages: 1-12, ISSN: 1511-1768
The microdispersion of silica in filled elastomer vulcanisates was evaluated by transmission electron microscopy (TEM)—network visualisation analysis. In this study, the silica is modified with a wide range of coupling and non-coupling silanes. The silica-filled elastomer samples were microtomed using a glass knife. The resulting TEM micrographs were interpreted and characterised based on aggregates with a cross-sectional area larger than 100 nm2. The study showed that silica surface modification has reduced the silica aggregate size by approximately 30–40% compared to an untreated silica-filled elastomer vulcanisate. The TEM micrographs showed evidence of coupling between silica and the elastomer phase and demonstrated a good estimation of silica microdispersion in the elastomer phase. This study has shown that the presence of different surface functionalities has an effect on the silica microdispersion.
Zhang R, Liao W, Sun Y, et al., 2019, Investigating the Role of Glass and Quartz Substrates on the Formation of Interfacial Droplets, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 123, Pages: 1151-1159, ISSN: 1932-7447
Yang H, Chen W, Peczulis P, et al., The development and workflow of a continuous protein crystallisation process: A case of lysozyme, Crystal Growth & Design, ISSN: 1528-7483
In the present work, a workflow on the development of a continuous protein crystallisation is introduced, with lysozyme as a model protein, from micro L screening experiments, to small scale batch crystallisation experiments in a shaking crystallisation platform, and to batch and continuous crystallisation experiments in an oscillatory flow platform. The lysozyme crystallisation investigated were for a concentration range from 30 to 100 mg/mL, shaking conditions from 100 to 200 rpm in the batch shaking crystallisation platform, and oscillatory conditions with amplitude (x) from 5 to 30 mm and frequency (f) from 0.1 to 1.0 Hz in the batch oscillatory flow crystallisation platform. We propose the use of the Reynold’s number (Re) for scaling up of the process from the shaking batch to the continuous oscillatory flow platform. Additionally, it is shown that the nucleation rate increased with increase in concentration of initial lysozyme solution, or increase in shear rate, inducing smaller size of lysozyme crystals. These indicate that continuous crystallisation platforms may offer advantages to the downstream bioprocessing of proteins.
Burnett DJ, Karde V, Heng J, 2019, Surface energy of albumins and the effect of relative humidity, ISSN: 1526-7547
© 2019 Omnipress - All rights reserved. Statement of Purpose: Mositure can greatly affect the structure, stability, folding and activity of protein molecules. The interactions of the sorbed moisture with the proteins can make them susceptible to undergo physico-chemical changes under humid conditions. These protein-water interactions get influenced by the number of polar and non-polar groups and their arrangement along the protein molecule. Water also plays an important role in hydrogen bonded networks and various hydrophilic and hydrophobic interactions. Although an important contributor for protein functionality, these water–protein interactions are still far from being fully understood. Surface energy could be employed as a potential descriptor for investigating these interactions.
Zhang B, Mei AR, Isbell MA, et al., 2018, DNA origami as seeds for promoting protein crystallization, ACS Applied Materials & Interfaces, Vol: 10, Pages: 44240-44246, ISSN: 1944-8244
This study reports the first experimental evidence of DNA origami as a seed resulting in the increase in probability of protein crystallization. Using DNA origami constructed from long single-stranded M13 DNA scaffolds folded with short single-stranded DNA staples, it was found that the addition of the DNA origami in concentrations of 2-6 nM to mixtures of a well-characterized protein (Catalase) solution (1.0-7.0 mg/mL) resulted in a higher proportion of mixtures with successful crystallization, up to 11x greater. The improvement to crystallization is evident particularly for mixtures with low concentrations of Catalase (< 5 mg/mL). DNA origami in different conformations: a flat rectangular sheet and a tubular hollow cylinder, were examined. Both conformations improved crystallization as compared to control experiments without M13 DNA or non-folded M13 DNA, but exhibited little difference in the extent of protein crystallization improvement. This work confirms predictions of the potential use of DNA origami to promote protein crystallization, with potential application to systems with limited protein available or difficult to crystallize.
Morgeneyer M, Ramirez A, Poletto M, et al., 2018, Particle technology as a uniform discipline? Towards a holistic approach to particles, their creation, characterisation, handling and processing!, Chemical Engineering Research and Design, ISSN: 0263-8762
Yang H, Peczulis P, Inguva P, et al., 2018, Continuous protein crystallisation platform and process: Case of lysozyme, Chemical Engineering Research and Design, Vol: 136, Pages: 529-535, ISSN: 1744-3598
In this work, we designed and built a continuous crystallisation oscillatory flow platform. The lysozyme crystallisation behaviours were investigated at concentrations from 30 to 100 mg/mL, under oscillatory conditions with amplitude (x0) from 10 to 25 mm and frequency (f) from 0.05 to 0.25 Hz in a batch oscillatory flow crystallisation platform. The nucleation rate increased with increase in concentration of initial lysozyme solution, and was also found to increase with increase in shear rate. By learning the thermodynamics and kinetics of lysozyme crystallisation in batch oscillatory flow, the batch crystallisation process was successfully transferred to a continuous oscillatory flow crystallisation process. The equilibrium state of continuous crystallisation reached at residence time 200 min, and the final product crystals shape and size were consistent during the continuous process. This work demonstrates the feasibility of oscillatory flow based platforms for the development of continuous protein crystallisation as for downstream bioseparation.
Yao Z, Wu D, Heng JYY, et al., 2018, Surface characterization of bio-fillers from typical mollusk shell using computational algorithms, International Journal of Adhesion and Adhesives, Vol: 84, Pages: 48-53, ISSN: 0143-7496
The generation of surface free energy parameters calculated from contact angle data is a burdensome and time-consuming process. To facilitate these calculations, computational algorithms using three different programming languages—MATLAB, C and Python—were developed and validated by surface properties determination of PO and CPO. The results indicated that the surface free energy parameters calculated using the three algorithms were consistent. The unknowns were obtained directly from within the C and Python programs, however, indirectly from within MATLAB function. In addition, the assembly statements of the C function were longer than those of the other two. The obtained results were also compared with those from an IGC analysis. It showed that the values determined using the contact angle methods were consistent, although lower than those obtained by IGC analysis. Compared to , the component contributed less to . The lower and values for CPO which added up to a lower value, could reduce filler particle/particle interactions, allowing a better dispersion in a polymer matrix.
Ngeow YW, Chapman AV, Heng JYY, et al., Characterization of silica modified with silanes by using thermogravimetric analysis combined with infrared detection, Rubber Chemistry and Technology, ISSN: 0035-9475
Tire treads with reduced rolling resistance and increased wet grip can be achieved by coupling hydrophilic silica to hydrocarbon rubber by using an alkoxysilane. The silica surface was modified by reaction with a wide range of coupling and non-coupling silanes. The chemistry and extent of these silanizations were elucidated using thermogravimetric analysis (TGA) combined with infrared detection. The silane grafting efficiencies were typically 52–72%, but efficiencies were lower in the bulkier [3-(di-(tridecyloxypenta(ethyleneoxy))ethoxysilyl]propyl mercaptan. However, the silica surface coverage increases with increasing size of the silane. Grafting efficiencies were lower with higher silane loadings. In the TGA, ethoxy and methoxy groups are displaced from the grafted silanes mainly at moderate temperatures (up to about 495 °C) to form siloxane bridges. Over a similar temperature range, the weaker S–S bonds present in bis(3-triethoxysilylpropyl) tetrasulfide (TESPT)- or bis[3-(triethoxysilyl)propyl] disulfide (TESPD)-modified silica are cleaved, leading to weight losses from TESPT or TESPD bound at one end to the silica and from TESPT bound at both ends. The remaining weight losses from bound silanes occurred mainly at higher temperatures. In the commercial silanized silica Coupsil 8113, TGA indicates that about two of three ethoxy groups in each triethoxysilane were lost during the silanization process.
Hadjittofis E, Isbell M, Karde V, et al., 2018, Influences of crystal anisotropy in pharmaceutical process development, Pharmaceutical Research, Vol: 35, ISSN: 0724-8741
Crystalline materials are of crucial importance to the pharmaceutical industry, as a large number of APIs are formulated in crystalline form, occasionally in the presence of crystalline excipients. Owing to their multifaceted character, crystals were found to have strongly anisotropic properties. In fact anisotropic properties were found to be quite important for a number of processes including milling, granulation and tabletting. However, an understanding of crystal anisotropy and an ability to control and predict crystal anisotropy are mostly subjects of interest for researchers, as they can have a profound influence on the development of more efficient process development approaches. A number of studies dealing with the aforementioned phenomena are grounded on over-simplistic assumptions, neglecting key attributes of crystalline materials, most importantly the anisotropic nature of a number of their properties. Moreover, concepts such as the influence of interfacial phenomena in the behaviour of crystalline materials during their growth and in vivo, are still poorly understood. The review aims to address concepts from a molecular perspective, focusing on crystal growth and dissolution. It begins with a brief outline of fundamental concepts of intermolecular and interfacial phenomena. The second part discusses their relevance to the field of pharmaceutical crystal growth and dissolution. Particular emphasis is given to works dealing with mechanistic understandings of the influence of solvents and additives on crystal habit. Furthermore, comments and perspectives, highlighting future directions for the implementation of fundamental concepts of interfacial phenomena for the rational understanding of crystal growth and dissolution processes, have been provided.
Yao Z, Wu D, Heng JYY, et al., 2017, Comparative study of surface properties determination of colored pearl-oyster-shell-derived filler using inverse gas chromatography method and contact angle measurements, International Journal of Adhesion and Adhesives, Vol: 78, Pages: 55-59, ISSN: 0143-7496
Mollusk shells, such as clam, mussel, oyster and pearl oyster shells, are potential candidates for commercial calcium carbonate-based fillers. In this work, the surface properties of colored pearl-oyster-shell-derived filler (CMF) were investigated with comparison to those of pearl oyster shell powder (MSP), using an inverse gas chromatography (IGC) method and contact angle measurements. A developed computational model for the interpretation of surface free energy heterogeneity distributions was applied to both samples. The contact angle measurements revealed an amphiphilic nature. The dispersion component of surface free energy for both samples calculated using the Owens–Wendt–Kaelble (OWK), van Oss–Chaudhury–Good (vOCG) and Wu methods were consistent with those determined using the IGC method. The deconvolution of surface energetic sites confirmed their energetic heterogeneity. The CMF displayed lower work of cohesion, which could be beneficial to the fabrication of polymer composites, as typically reduced filler particle-particle interactions would result.
Yang H, Song C, lim Y, et al., 2017, Selective Crystallisation of Carbamazepine Polymorphs on Differing Surface Properties, CrystEngComm, Vol: 19, Pages: 6573-6578, ISSN: 1466-8033
Surface-induced nucleation of carbamazepine (CBZ) in ethanol was investigated with different surface materials: glass, polytetrafluoroethylene (PTFE) and tin. The introduction of foreign surfaces with different areas and surface chemistries into the solution has an impact on the crystal morphology and polymorphic form (Form II or III). With an increase in supersaturation, a higher possibility of crystallisation of CBZ metastable Form II was observed, as expected. Increasing the number of inserts resulted in a direct increase in the surface area available for heterogeneous nucleation. The increase in surface area resulted in the greater possibility of obtaining the metastable Form II of CBZ. The stable Form III preferred to nucleate on tin rather than on glass and PTFE. The results indicate that the two different polymorphs of CBZ can be selectively crystallised out from solution with the aid of a foreign surface. The kinetic mechanism of heterogeneous nucleation of the different polymorphs induced by foreign surfaces was discussed. The potential applications will be used to control and design the crystallisation process.
Yao Z, Heng JYY, Lanceros-Mendez S, et al., 2017, Surface free energy and mechanical performance of LDPE/CBF composites containing toxic-metal free filler, International Journal of Adhesion and Adhesives, Vol: 77, Pages: 58-62, ISSN: 0143-7496
Heavy-metal contamination in children's toys is a widespread problem, and the international community has issued a series of safety standards to restrict and control the use of toxic metals in toys. In this work, a colored filler (CBF) was prepared using pearl oyster shell (POS) as the green raw material and azo dye as the colorant. Its surface properties were subsequently studied in comparison to those of POS powder using the inverse gas chromatography method. The dispersion surface free energy profiles for both CBF and POS showed that this component contributed the major part (>70%) to the total surface free energy. The CBF possessed lower polar surface free energy and was relatively more hydrophobic. It also showed a lower thermodynamic work of cohesion, allowing its better dispersion in a low density polyethylene (LDPE) matrix. Mechanical performance studies showed that adding CBF could significantly increase the tensile strength, elastic modulus, flexural strength and flexural modulus of LDPE composites. The absence of toxic metals coupled with excellent mechanical performance makes the CBF an ideal candidate as a filler for children's toys fabrication.
Li Y, Yang Q, Mei RA, et al., 2017, Controlling the Accumulation of Water at Oil-Solid Interfaces with Gradient Coating, Journal of Physical Chemistry B, Vol: 121, Pages: 6766-6772, ISSN: 1520-5207
In this work, we demonstrate a strategy to control the accumulation of water in the oil–solid interface using a gradient coating. Gradient chemistry on glass surface is created by vapor diffusion of organosilanes, leading to a range of contact angles from 110 to 20°. Hexadecane is placed on the gradient substrate as an oil layer, forming a “water/hexadecane/gradient solid substrate” sandwich structure. During incubation, water molecules spontaneously migrate through the micrometer-thick oil layer and result in the formation of micrometer-sized water droplets at the oil–solid interface. It turns out that water droplets at more hydrophobic regions tend to be closer to a regular spherical shape, which is attributed to their higher contact angle with the hydrophobic substrate. However, along the gradient from hydrophobic to hydrophilic, the water droplets gradually form more irregular shapes, as hydrophilic surfaces pin the edges of droplets to form a distorted morphology. It indicates that more hydrophilic surfaces containing more Si–OH groups lead to a higher electrostatic interaction with water and a higher growth rate of interfacial water droplets. This work provides further insights into the mechanism of spontaneous water accumulation at oil–solid interfaces and assists in the rational design for controlling such interfacial phenomenon.
Lee MY, Tan J, Heng JYY, et al., 2017, A comparative study of production of glass microspheres by using thermal process, The 2nd International Conference on Materials Engineering and Nanotechnology, ISSN: 1757-8981
Microspheres are spherical particles that can be distinguished into two categories; solid or hollow. Microspheres typical ranges from 1 to 200 μm in diameter. Microsphere are made from glass, ceramic, carbon or plastic depending on applications. Solid glass microsphere is manufactured by direct burning of glass powders while hollow glass microspheres is produced by adding blowing agent to glass powder. This paper presented the production of glass microspheres by using the vertical thermal flame (VTF) process. Pre-treated soda lime glass powder with particle sized range from 90 to 125μm was used in this work. The results showed that glass microspheres produced by two passes through the flame have a more spherical shape as compared with the single pass. Under the Scanning Electron Microscope (SEM), it is observed that there is a morphology changed from uneven surface of glass powders to smooth spherical surface particles. Qualitative analysis for density of the pre-burned and burned particles was performed. Burned particles floats in water while pre-burned particles sank indicated the change of density of the particles. Further improvements of the VTF process in terms of the VTF set-up are required to increase the transformation of glass powders to glass microspheres.
Kontturi KS, Biegaj K, Mautner A, et al., 2017, Noncovalent Surface Modification of Cellulose Nanopapers by Adsorption of Polymers from Aprotic Solvents, LANGMUIR, Vol: 33, Pages: 5707-5712, ISSN: 0743-7463
Basic adsorption of hydrophobic polymers from aprotic solvents was introduced as a platform technology to modify exclusively the surfaces of cellulose nanopapers. Dynamic vapor sorption demonstrated that the water vapor uptake ability of the nanopapers remained unperturbed, despite strong repellency to liquid water caused by the adsorbed hydrophobic polymer on the surface. This was enabled by the fact that the aprotic solvents used for adsorption did not swell the nanopaper unlike water that is generally applied as the adsorption medium in such systems. As case examples, the adsorptions of polystyrene (PS) and poly(trifluoroethylene) (PF3E) were followed by X-ray photoelectron spectroscopy and water contact angle measurements, backed up with morphological analysis by atomic force microscopy. The resulting nanopapers are useful in applications like moisture buffers where repellence to liquid water and ability for moisture sorption are desired qualities.
Biegaj KW, Rowland MG, Lukas TM, et al., 2017, Surface Chemistry and Humidity in Powder Electrostatics: A Comparative Study between Tribocharging and Corona Discharge, ACS Omega, Vol: 2, Pages: 1576-1582, ISSN: 2470-1343
In the present study, the correlation between surface chemical groups and the electrostatic properties of particulate materials was studied. Glass beads were modified to produce OH-, NH2-, CN-, and F-functionalized materials. The materials were charged separately both by friction and by conventional corona charging, and the results were compared. The results obtained from both methods indicated that the electrostatic properties are directly related to the surface functional group chemistry, with hydrophobic groups accumulating greater quantities of charge than hydrophilic groups. The fluorine-rich surface accumulated 5.89 times greater charge upon tribocharging with stainless steel than the hydroxyl-rich surface. However, in contrast to the tribocharging method, the charge polarity could not be determined when corona charging was used. Moreover, discharge profiles at different humidity levels (25% RH, 50% RH, and 75% RH) were obtained for each modified surface, which showed that higher humidity facilitates faster charge decay; however, this enhancement is surface chemistry-dependent. By increasing the humidity from 25% RH to 75% RH, the charge relaxation times can be accelerated 1.6 times for fluorine and 12.2 times for the cyano group. These data confirm that surface functional groups may dictate powder electrostatic behavior and account for observed charge accumulation and discharge phenomena.
Yang H, Heng J, 2017, Template assisted and continuous crystallisation: Control of polymorphs, protein crystallisation and bioseparation, 253rd National Meeting of the American-Chemical-Society (ACS) on Advanced Materials, Technologies, Systems, and Processes, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Yang H, Heng J, 2017, Effects of flow and seeding on the crystallisation of immunoglobulin G, 253rd National Meeting of the American-Chemical-Society (ACS) on Advanced Materials, Technologies, Systems, and Processes, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Kontturi K, Biegaj K, Mautner A, et al., 2017, Exclusive surface modification of cellulose nanopapers by adsorption of polymers from non-aqueous solvents, 253rd National Meeting of the American-Chemical-Society (ACS) on Advanced Materials, Technologies, Systems, and Processes, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Yao Z, Wu D, Heng JYY, et al., 2017, Solids surface characterization using computational algorithms: A case study for talc fillers, Applied Clay Science, Vol: 141, Pages: 212-218, ISSN: 0169-1317
The solid surface characterization using contact angle measurement is complicated and time-consuming. In this work, two computational algorithms in MATLAB and C were developed and validated by the surface properties determination of talc filler (TCF) and colored talc filler (CTCF). The results indicated that, the surface free energy parameters calculated using the two algorithms for both samples were consistent. As compared to the MATLAB function, the assembly statements of C function were longer, although the unknowns can be directly obtained using this toolbox. The γSD values determined by the Owens-Wendt-Kaelble (OWK), van Oss-Chaudhury-Good (vOCG) and Wu methods were consistent and contributed a major part of the γST. Compared to γSD, the γSSP component contributed less to γST, implying a lower polarity for both samples. The lower γSD and γSSP for CTCF added up to a lower γST value, which could reduce filler particle-particle interactions. The mechanical properties study of acrylonitrile-butadiene-styrene (ABS) matrix filled with the two fillers showed that the incorporation of them played mainly a reinforcing role, and a better performance for CTCF was observed.
Jakubec M, Klimsa V, Hanus J, et al., 2017, Formation of multi-compartmental drug carriers by hetero-aggregation of polyelectrolyte microgels, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, Vol: 522, Pages: 250-259, ISSN: 0927-7757
The formation of drug carriers able to incorporate multiple molecular payloads in separate compartments was investigated, using the hetero-aggregation of oppositely charged hydrogel microparticles as the building blocks. The primary particles – negatively charged alginate and positively charged chitosan microgels with a mean diameter of 6–7 μm – were produced by spray drying with in situ cross-linking. The kinetics of their hetero-aggregation was measured on-line by static light scattering. The effects of the starting stoichiometry (positive:negative particle ratio), hydrodynamic conditions (agitation intensity), and pre-conditioning (dry vs. pre-hydrated primary particles) on the aggregate growth rate were systematically investigated. An optimum stoichiometric ratio of the primary particles was found in each case. The structure of the resulting hetero-aggregates was characterised by laser scanning confocal microscopy and found to strongly depend on the pre-conditioning of the primary particles. While dry primary particles resulted in open, floccular structures, pre-hydrated primary particles gave rise to relatively dense, compact aggregates. The ability to incorporate multiple molecular payloads was demonstrated, providing a platform for the formation of well-defined structures that can be further used in applications such as the encapsulation and release of multiple actives from a single carrier.
Shah UV, Karde V, Ghoroi C, et al., 2017, Influence of particle properties on powder bulk behaviour and processability, International Journal of Pharmaceutics, Vol: 518, Pages: 138-154, ISSN: 1873-3476
Understanding interparticle interactions in powder systems is crucial to pharmaceutical powder processing. Nevertheless, there remains a great challenge in identifying the key factors affecting interparticle interactions. Factors affecting interparticle interactions can be classified in three different broad categories: powder properties, environmental conditions, and powder processing methods and parameters. Although, each of these three categories listed is known to affect interparticle interactions, the challenge remains in developing a mechanistic understanding on how combination of these three categories affect interparticle interactions. This review focuses on the recent advances on understanding the effect of powder properties, particularly particle properties, its effect on interparticle interactions and ultimately on powder bulk behaviour. Furthermore, this review also highlights how particle properties are affected by the particle processing route and parameters. Recent advances in developing a particle processing route to prepare particles with desired properties allowing desired interparticle interaction to deliver favoured powder bulk behaviour are also discussed. Perspectives for the development of potential particle processing approaches to control interparticle interaction are presented.
Hadjittofis E, Zhang GGZ, Heng JYY, 2017, Influence of sample preparation on IGC measurements: the cases of silanised glass wool and packing structure, RSC Advances, Vol: 7, Pages: 12194-12200, ISSN: 2046-2069
Inverse Gas Chromatography (IGC) is an established technique for the determination of the surface energy heterogeneity of various types of materials, including particulate and fibrous materials. However, variability in sample and column preparation may lead to low reproducibility of data. In this work, the influence of two aspects of chromatographic column preparation; the amount of silanised glass wool and the packing structure of mixtures of particulate materials, on IGC measurements were investigated using a combined experimental and modelling approach. In silico experiments were used to examine these factors for a range of materials with different surface energy. We report here, that the packing structure of particulate materials in the column does not significantly affect the measurements and the results. However, the contribution of the silanised glass wool needs to be corrected, particularly for materials of low surface area or low surface energy. This work demonstrates the importance of column preparation and the need for standardisation of packing protocols for robust experimental determination of surface energy heterogeneity.
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