Biomedical subjects

G Buckton

Publications and source records attributed to G Buckton.

At least 19 recordsLinked to original sources

PubMed2006

Investigation to find a suitable reference material for use as an inverse gas chromatography system suitability test.

The purpose of this study was to find a suitable material for use as a system suitability test material for inverse gas chromatography (IGC). The purpose of a system check is to measure the variability of the instrument being used rather than the material being analysed. Having such a system check for IGC enables a basic GMP requirement to be met. IGC results can then be used in regulatory submissions to support other already established techniques for characterising pharmaceutical materials. Alpha-alumina was chosen because it is inorganic, stable at high temperatures, resistant to hydration and is already established as a system check material for surface area determination by nitrogen adsorption. Two columns (1 and 2) packed from the same reference sample jar of alpha-alumina and analysed under the same conditions yielded dispersive surface energies of 34.8+/-0.8 and 35.3+/-0.8 mJ/m(2), respectively, at 15% RH. Column 1 was analysed on a second IGC system, and gave a dispersive surface energy of 34.7+/-0.2 mJ/m(2). No significant change was evident after 7 months storage under laboratory ambient conditions. Analysis of material from a second reference sample jar of alpha-alumina produced results not noticeably different to those of the first, yielding a dispersive surface energy of 35.3+/-0.1 mJ/m(2). A change was seen to occur in the surface properties alpha-alumina when the humidity was varied, but the change appeared to be consistent across the two columns reported. Based upon the data in this experimental, alpha-alumina appears to be a suitable material for use as a system suitability test material for IGC.

Aluminum Oxide↗

PubMed2005

Calorimetric study of bovine serum albumin dilution and adsorption onto polystyrene particles.

Titration calorimetry was used to investigate the interaction between a model antigen, bovine serum albumin (BSA), and a model particulate carrier, polystyrene (PS). The binding enthalpy was much higher than reported in the literature for a similar system and did not display a sigmoidal binding curve. These experiments may have accessed low coverage surface sites due to the irreversible nature of protein binding and stepwise titration. An important correction is the heat of dilution of the protein solution. Two regimes were observed: at low concentrations of BSA (below ca. 0.3% (w/v)) an exothermic dilution enthalpy of ca. -100 mJ mg-1 was determined, whereas at higher concentrations of BSA values of ca. -20 mJ mg-1 were obtained. Solution rheological data also showed a change at 0.3% (w/v) BSA, so we hypothesise that the fraction of the BSA as monomers, dimers and polymers in solution changes at approximately 0.3% (w/v).

Adsorption↗

PubMed2005

Formation and characterization of porous indomethacin-PVP coprecipitates prepared using solvent-free supercritical fluid processing.

Supercritical carbon dioxide (sc-CO2) was used to prepare coprecipitates of indomethacin (IM) and poly(vinylpyrrolidone) (PVP) with the aim to improve the dissolution rate of IM. The coprecipitates of IM and PVP at various proportions were prepared using a stirred batch reactor containing sc-CO2 as a gas saturated solution (i.e., the compressible CO2 is dissolved in the molten compound). Temperatures between 40 and 90 degrees C and pressure of 150 or 200 bar were employed. The coprecipitates prepared at 75 degrees C and 150 bar were characterized using differential scanning calorimetry (DSC), powder X-ray diffraction (PXD), scanning electron microscopy (SEM), and dissolution testing. The results suggested that IM was totally amorphous at PVP weight fraction of 0.80 and above (indeed, as a molecular composite in which the drug molecules interact with the polymer backbone). As the PVP weight fraction decreased, IM displayed an increasing amount of crystalline material. The SEM photographs of coprecipitates showed a foamed and porous structure. The dissolution rate of IM was increased by incorporation of PVP. IM and PVP at various weight fractions exhibited comparatively higher dissolution rates than that of crystalline IM alone. The sc-CO2 based process produced a solvent free, completely amorphous porous IM solid dispersion with a rapid dissolution rate.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2004

A study of liposome formation using a solution (isoperibol) calorimeter.

A solution (isoperibol) calorimeter has been employed to study the process of formation of phospholipid vesicles from natural and synthetic phospholipid films. Phospholipid films were hydrated in the solution calorimeter at temperatures exceeding the main phospholipid phase transition temperature, with continuous agitation to ensure conversion of the hydrating bilayers into multilamellar liposomes. It was seen that retention of chloroform in phospholipid films altered the apparent enthalpy change of vesicle formation to a far greater extent than would be expected from the contribution of the enthalpy of solution of chloroform; this indicates that chloroform alters the hydration process of the lipid. The overall measured enthalpy change for the formation of egg phosphatidylcholine vesicles was exothermic, whilst that for dimyristoylphosphatidylcholine was endothermic. This difference, it is suggested, results from the influence of the hydrocarbon chains mostly on the hydration process and also on the process of vesicle formation.

Calorimetry↗

PubMed2001

Effects of cyclazocine and scopolamine on swim-to-platform performance in rats.

DL-Cyclazocine (0.5-2.0 mg/kg, i.p.) produced no impairment in rats' acquisition and retention of the behavior of swimming to a large visible platform in a water tank. However, cyclazocine produced a significant enhancement or potentiation of the impairment in swim-to-platform behavior produced by scopolamine. Since cyclazocine has previously been shown to abolish serotonin-dependent electrocortical activation (enabling it, in combination with central muscarinic blockade, to block all cortical activation), the results lend further support to the hypothesis that blockade of electrocortical activation produces dementia rather than sleep or coma as was previously believed.

Acetylcholine↗

PubMed2001

Water sorption/desorption--near IR and calorimetric study of crystalline and amorphous raffinose.

Mass loss at elevated RH is an established method for determining the occurrence of crystallisation of an amorphous material. Through the combination of near infrared spectroscopy and gravimetric vapour sorption, it has been possible to show the transition of raffinose from its spray-dried amorphous form to a crystalline form without this characteristic mass loss. It has also been possible to observe changes in the crystalline material for a period of 30 h subsequent to exposure to elevated relative humidity by near infrared spectroscopy that are not associated with changes in mass, but are related to repacking of hydrate molecules. Drying of the crystalline pentahydrate in the DVS-NIR was seen to show changes in the NIR peak related to -OH. From this, NIR peaks were tentatively ascribed as relating to a penta-, tetra-, tri- and a di-hydrate form, but the sample returned to the amorphous response by the time the water content fell to the equivalent of the monohydrate, indicating that crystallinity had been lost. These observations would be compatible with the hypothesis that lower hydrates of raffinose exist. Due to the absence of mass loss in association with crystallisation, it was found that the enthalpy of crystallisation of amorphous raffinose, as determined by isothermal microcalorimetry, is similar to the enthalpy of fusion determined by differential scanning calorimetry. Finally, it was observed that the early part of the response in the isothermal microcalorimeter was related to mobility of molecules when Tg was above T. This mobility was able to give the bulk morphology of a crystal before the sample developed long range order and crystalline properties.

Calorimetry, Differential Scanning↗

PubMed2001

The influence of incubation temperature and surfactant concentration on the interaction between dimyristoylphosphatidylcholine liposomes and poloxamer surfactants.

Differential scanning calorimetry and photon correlation spectroscopy have been used to study the interaction between poloxamers P338 and P407 and dimyristoylphosphatidylcholine (DMPC) liposomes. The extent of the interaction was found to be dependent on the incubation temperature in addition to the poloxamer concentration. At low poloxamer concentrations (0.1-1.0% w/v) an interaction with the phospholipid bilayer was detected by a reduction of the pre-transition enthalpy of DMPC. At higher concentrations (2.0-5.0% w/v), the main phase transition temperature of the liposomes decreased and the endotherm broadened with a shoulder on the high temperature side, indicative of phase separation. Maximum increases in the diameter of small freeze-thaw extruded liposomes were shown to occur at temperatures close to the poloxamer critical micelle temperatures. At higher temperatures and surfactant concentrations there was evidence of solubilization of phospholipid into mixed micelles.

Calorimetry, Differential Scanning↗

PubMed2001

The use of inverse phase gas chromatography to study the change of surface energy of amorphous lactose as a function of relative humidity and the processes of collapse and crystallisation.

The purpose of this study was to assess the effect of relative humidity (RH) on the surface energy of amorphous lactose. Two samples of amorphous lactose were investigated; a spray dried 100% amorphous material and a ball milled sample of crystalline lactose. The milled sample had less than 1% amorphous content by mass, but on investigation at 0% RH, yielded surface energies comparable to those obtained from the 100% amorphous material, indicating that the surface was amorphous. The effect of increasing humidity was to reduce the dispersive surface energy of the two samples from 36.0 +/- 0.14 and 41.6 +/- 1.4 mJ m(-2) at 0% RH for the spray dried and milled samples respectively, to a value comparable to that obtained for the crystalline alpha-lactose monohydrate of 31.3 +/- 0.41 mJ m(-2). The change in surface energy due to water sorption was only reversible up to 20% RH; after exposure to higher RH values subsequent drying did not result in a return to the original surface energy of the amorphous form. This shows that the surface is reorganising as the glass transition temperature (Tg) is reduced, even though the sample has not collapsed or crystallised. It was possible to follow the collapse behaviour in the column with ease, using a number of different methods.

Absorption↗

PubMed2001

The effect of co-spray drying with polyethylene glycol 4000 on the crystallinity and physical form of lactose.

The effect of spray drying lactose alone and in the presence of polyethylene glycol 4000 was investigated. Lactose was added to distilled water to give concentrations of 10, 20, 30 and 40g/100ml at room temperature and each spray dried in turn. Identical samples were prepared to which polyethylene glycol (PEG) 4000 was added (12% by weight of lactose) prior to spray drying. Microcalorimetric and X-ray diffraction studies showed that spray drying lactose solutions produced completely amorphous material due to rapid solidification during the spray drying process, whereas lactose suspensions yielded partially crystalline products due to crystalline material that remained in suspension. However, all the PEG/lactose (12%w/w) co-spray dried products were found to be crystalline. It can be inferred that the solidification rates of the lactose in the presence of PEG must have been slower than that of lactose alone which allowed PEG and lactose to crystallize. The PEG/lactose products that were spray dried from solution consisted of alpha-anhydrous, alpha-monohydrate, beta-lactose and PEG extended chain polymorph, whereas those formed from suspension PEG/lactose samples consisted of only alpha-anhydrous, alpha-monohydrate and extended chain PEG crystals. PEG probably caused the more concentrated lactose suspensions to crystallize slowly due to the strong hydrogen bonding between PEG and water, which allowed growth on the alpha-lactose seed crystals.

Calorimetry, Differential Scanning↗

PubMed2001

The use of inverse phase gas chromatography to measure the surface energy of crystalline, amorphous, and recently milled lactose.

PURPOSE: To assess differences in surface energy due to processing induced disorder and to understand whether the disorder dominated the surfaces of particles. METHODS: Inverse gas chromatography was used to compare the surface energies of crystalline, amorphous, and ball milled lactose. RESULTS: The milling process made ca 1% of the lactose amorphous, however the dispersive contribution to surface energy was 31.2, 37.1, and 41.6 mJ m(-2) for crystalline, spray dried and milled lactose, respectively. A physical mixture of crystalline (99%) and amorphous (1%) material had a dispersive surface energy of 31.5 mJ m(-2). CONCLUSION: Milling had made the surface energy similar to that of the amorphous material in a manner that was very different to a physical mixture of the same amorphous content. The milled material will have similar interfacial interactions to the 100% amorphous material.

Algorithms↗

PubMed2001

The application of near infrared spectroscopy and dynamic vapor sorption to quantify low amorphous contents of crystalline lactose.

PURPOSE: To explore the use of a combined near infrared spectroscopy and gravimetric sorption apparatus in providing an accurate quantification of amorphous contents of predominantly crystalline lactose. METHODS: Key wavelengths on the near infrared spectra of amorphous and crystalline lactose were used to construct a calibration plot of spectral fit to amorphous content. The extent of water sorption and desorption at 75% relative humidity (RH) was used to quantify the amount of amorphous material in the sample. RESULTS: Near infrared spectroscopy was used to quantify the amorphous contents of a set of 10 partially amorphous lactose samples using a calibration equation generated from an independent set of 17 samples. The results were found to be accurate to within 1% w/w amorphous content. Dynamic vapor sorption quantification relates the mass of water sorbed and subsequently desorbed during the crystallization process with the amount of amorphous material originally contained within the sample. It was possible to quantitatively detect as little as 1 mg of amorphous content in the sample. The percent amorphous content determination will thus be sample mass dependent, however, assuming a sample mass of 150 mg, the best detection would be ca. 0.7%. CONCLUSIONS: It has been found that both techniques may be used to quantify small quantities of amorphous material. The combination of the two techniques lends itself to added verification of results and thus increased reliability.

Crystallization↗

PubMed2000

The quantification of small degrees of disorder in lactose using solution calorimetry.

There is a realisation that small quantities of amorphous material can have a significant impact on the properties of crystalline solids. Consequently there is a growing interest in quantifying the amount of amorphous material that is present in "crystalline powders". Success has been reported when using isothermal microcalorimetry and vapour sorption techniques, however, the use of solution calorimetry has largely been ignored. In this study the enthalpies of solution of mixtures of amorphous and crystalline lactose are reported concentrating on the range 0-10% w/w amorphous content. It was found that there was a possible error due to water vapour penetration into the ampoule, resulting in crystallisation of the amorphous content, however this was overcome by double sealing the ampoules with wax. Subsequently there was a good correlation between the enthalpy of solution and the amorphous content, which was not adversely affected by stirring rate used during the experiment. Over the range from 0 to 10% amorphous content, quantification of the amorphous content of an unknown would be good to +/-0.5%. The effects of residual moisture retained within a sample were also investigated. Storage at 33% or 43% RH resulted in a much reduced wetting (exothermic) response compared with that seen for completely dry samples, which in turn led to a higher net enthalpy of solution.

Calorimetry↗

PubMed2000

The novel combination of dynamic vapour sorption gravimetric analysis and near infra-red spectroscopy as a hyphenated technique.

The novel combination of an environmental controlled gas flow microbalance (Dynamic Vapour Sorption, Surface Measurement Systems, UK) with a NIR spectrometer (Foss NIR Systems) is described. The study follows the gravimetric changes and the spectroscopic changes in the amorphous and crystalline states of lactose at 298 K. NIR spectra and gravimetric water sorption were recorded simultaneously for the same sample. Differentiation of the amorphous and crystalline states of lactose was possible from the evaluation of peak intensity and shifts in the known fingerprint regions of the NIR spectra, i.e. 1350-1510 and 1825-1975 nm which correspond to water changes, and 2075-2160 nm which tends to illustrate changes in the organic/structural backbone character. Gravimetric analysis confirmed that the amorphous lactose crystallised, as weight changes can be linked to structural changes. The combined technique maintains the high performance of the DVS microbalance for gravimetric analysis but also provides a preset, regulated and controllable environment for studies using NIR spectroscopy probes, which was previously not possible. The results obtained agree with accepted data, and therefore provide validation for the hyphenation technique. The use of the combined DVS-NIR instrument has indicated two new pieces of information, firstly the amorphous form loses some water before the crystallisation is detectable. This indicates that water desorption may precede crystallisation, rather than the other way around, and secondly, the sample has completed crystallisation before water desorption has ended.

Crystallization↗

PubMed2000

An exploration of inter-relationships between contact angle, inverse phase gas chromatography and triboelectric charging data.

Surfaces of pharmaceutical powders have been assessed using contact angle, inverse phase gas chromatography (IGC) and triboelectric (electrostatic) charging techniques. The suitability of the Dynamic Angle Tester (DAT), an instrument based on the sessile drop technique, in determining contact angles and then the surface energy of pharmaceutical powders was assessed. The dispersive components of the surface energy of powders determined from the DAT and IGC method ranked the powders in the same order. The dispersive component values obtained by IGC were, as expected, higher than those from the DAT, due to IGC probing the highest energy sites on the powder surface. IGC and triboelectric studies allow materials to be characterised in terms of their electron donating-accepting tendencies, so inter-relationships between the data from the two techniques were explored. Although the data set was limited, there appeared to be a correlation between the charges developed by the powders on contact with stainless steel and the ratio of the electron-donating to electron-accepting tendencies of the materials as obtained from IGC.

Chemistry, Pharmaceutical↗

PubMed2000

Near IR spectroscopy to quantify the silica content and difference between silicified microcrystalline cellulose and physical mixtures of microcrystalline cellulose and silica.

Silicified microcrystalline cellulose (SMCC) has been shown to have advantages over conventional microcrystalline cellulose (MCC). These advantages are (i) improved tablet strength compared to that achieved with MCC, (ii) the retention of compressibility after wet granulation, whereas MCC produces weaker tablets after wet granulation, and (iii) superior flow properties than MCC. In this study near IR spectroscopy has been used to study MCC, SMCC (with different loadings of colloidal silicon dioxide, CSD) and physical mixtures of MCC and CSD. It was found that even though SMCC and MCC were very similar, there was a region of the near IR spectra (second derivative peak at 2194 nm) where a distinctive response was seen for SMCC. The size of the peak was proportional to the CSD content for the co-processed SMCC samples. The peak was not present to the same extent for physical mixtures. A combination of near IR and a test for total silica content would make it possible to discern whether microcrystalline cellulose samples were SMCC material or simple physical mixtures.

Cellulose↗

PubMed1999

Isothermal microcalorimetry and inverse phase gas chromatography to study small changes in powder surface properties.

It is known that processing can alter the surface energetics of powders. In this study a sample of drug has been processed by use of different drying techniques. The samples were then assessed using inverse phase gas chromatography. It was seen that the original material had a highest surface energy and the tray-dried sample had the lowest energy surface, other samples were intermediate. The use of isothermal microcalorimetry to study water sorption to the powders revealed that the surface of the original material was unstable, as the water sorption response changed on repeat cycling. The tray-dried sample did have a stable surface which gave the same sorption response on repeat exposure to water vapour. It was concluded that the drug had minor variations in surface energy, with the as received material being in a high energy unstable state, which could be due to it being partially amorphous. The tray-dried sample had a lower energy stable surface. In certain applications differences in surface energetics could be expected to lead to changes in processing nature of the powder, so these vapour sorption techniques offer a good way of providing an assurance of the same surface energy between batches of nay material which may be at risk.

Adsorption↗

PubMed1999

A high sensitivity differential scanning calorimetry study of the interaction between poloxamers and dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine liposomes.

High sensitivity differential scanning calorimetry (HSDSC) has been used to measure the thermal behaviour of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) liposomes to which poloxamer surfactants P338 or P407 had been added during or after preparation. The phospholipid pre-transition was more sensitive than the main transition to the association of poloxamers with liposomal bilayers. Poloxamers reduced the enthalpy of the pre-transition of liquid-crystalline state DMPC and DPPC MLVs but not that of gel state DPPC MLVs. Freezing and thawing DMPC and DPPC liposomes in the presence of poloxamers was shown to increase their interaction with the liposomal bilayers.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1999

Water sorption and near IR spectroscopy to study the differences between microcrystalline cellulose and silicified microcrystalline cellulose before and after wet granulation.

Silicified microcrystalline cellulose (SMCC) has been shown to have advantages over conventional microcrystalline cellulose (MCC). These advantages are (i) improved tablet strength compared to that achieved with MCC, (ii) the retention of compressibility after wet granulation, whereas MCC produces weaker tablets after wet granulation, and (iii) superior flow properties than MCC. In this study gravimetric and calorimetric vapour sorption data and near IR spectroscopy have been used to study MCC and SMCC before and after wet granulation. It was found that MCC, SMCC and wet granulated SMCC had essentially identical physical structures (except for a size increase due to granulation). Wet granulated MCC had a different enthalpy of water sorption at low RH, and its near IR spectrum was different from the other samples in the region which relates to C-H bonding. It can be concluded that MCC and SMCC are of very similar structures, thus these analytical techniques cannot provide an explanation for the improvements in compressibility. However the change in compressibility in MCC after wet granulation may relate to the observed differences in internal bonding in this sample.

Absorption↗