Catherine A. Kelly

Sustained release hGH microsphere formulation produced by a novel supercritical fluid technology: in vivo studies.

Novel sustained release formulations of hGH prepared by supercritical fluid processing of PLGA/PLA (the CriticalMix process) were produced in the form of microparticles for subcutaneous injection. The basis of the process is that PLGA/PLA polymers liquefy when exposed to supercritical CO(2), thereby allowing the hGH to be mixed efficiently into the polymers at an ambient temperature and in the absence of solvents. The CO(2) was removed from the mixture by depressurisation through a nozzle, resulting in the production of microparticles containing the hGH, which were collected in a cyclone. The best microparticle formulations showed an initial in vitro burst of around 35% and a sustained release over 14 days. When tested in the rat model, which displays a faster clearance rate of hGH than other animal models, two formulations showed prolonged release over 2-3 days with sustained plasma levels at 1-5 ng/ml whereas the soluble hGH formulation was cleared within 24h. Two selected sustained release formulations were tested in cynomolgus monkeys and compared to a single injection of soluble hGH. The burst release from the sustained release formulations was similar in magnitude to a daily dose of hGH and serum hGH levels were maintained for a seven day period. It is probable from the data that the sustained release would have continued for up to 14 days if sampling had been continued. The IGF-1 results showed there was no significant difference between the levels obtained for once daily injection of soluble hGH and the two sustained release formulations.

Stability of Human Growth Hormone in Supercritical Carbon Dioxide

The instability of human growth hormone (hGH) to temperature and interfaces makes its formulation into injectable, sustained-release drug delivery systems challenging. A novel method of encapsulating hGH in polymeric microparticles has been developed using supercritical CO(2) (scCO(2)) technology, but there is limited understanding of the stability of hGH within this system. The aim of this study was to evaluate the stability of hGH in scCO(2) processing. The integrity of the protein was assessed following exposure to scCO(2) using a range of different analytical techniques. Mass spectrometry showed that no peptide cleavage occurred as a result of processing or exposure to scCO(2). Size-exclusion chromatography detected formation of aggregates at high temperatures, but not as a result of the encapsulation process. Reverse-phase chromatography demonstrated that the production of deamidation products occurred as a function of temperature, but only at temperatures higher than those used for the encapsulation process. Circular dichroism and infrared spectroscopy demonstrated that the use of scCO(2) was not detrimental to the secondary molecular structure of hGH. Together, these results show that the structural integrity of hGH is unaffected by scCO(2) processing and that hGH can be successfully encapsulated in polymer microparticles using this technique.

Development of a rapid method to isolate polyhydroxyalkanoates from bacteria for screening studies

We describe a novel method of Polyhydroxyalkanoate (PHA) extraction using dimethyl sulphoxide (DMSO) for use in screening studies. Compared to conventional chloroform extraction, the DMSO method was shown to release comparable quantities of PHA from Cupriavidus necator cells, with comparable properties as determined using Fourier transform infrared spectroscopy and differential scanning calorimetry.

Production of Biodegradable Foams Using Supercritical CO2

A single screw extrusion process in which CO2 is injected into the polymer melt has been utilized to produce low density biodegradable poly(DL-lactic acid) (PDLLA) foams. High pressure differential scanning calorimetry (DSC) and rheology are used to observe the melting point and viscosity depression of PDLLA 3051D in the presence of CO2. Foams of PDLLA 3051D are produced in a static environment under a range of conditions, and these data are utilized to extrude PDLLA 3051D into foamed sheets for packaging applications. The density, crystallinity, mechanical properties and microstructure of these foams are evaluated.

Secondary crystallisation and degradation in P(3HB-co-3HV): an assessment of long-term stability

AbstractThe effect of long-term storage, at a range of temperatures, on the thermal and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) is reported. P(3HB-co-3HV) was stored at −22, 7, 20, 50, 75, 100, 125 and 150 °C for 672 h. Below 100 °C, the observed increase in melting point, glass transition temperature, modulus and strength are due to the development of crystallinity via a secondary process and facilitated by increasing temperature. At 125 °C, the processes of secondary crystallisation and degradation occur in parallel and there is an interplay between these processes, with the effects of degradation masked by the continuation of secondary crystallisation. At 150 °C there is a deterioration in all the properties noted above and given the reduction in molecular weight (and discolouration), this can be attributed to degradation. The significant observation from these results is that the degradation process remains active well below the melting point and long-term stability of P(3HB-co-3HV) is not only affected by secondary crystallisation, but also degradation. In addition, as no significant changes to the thermal or mechanical properties were observed during storage at −22 and 7 °C it suggests that P(3HB-co-3HV) may be a suitable packaging material for frozen or refrigerated products.The effects of long-term storage of poly(3-hydroxbutyrate-co-3-hydroxyvalerate) were evaluated over a range of temperatures. As the storage temperatures were increased towards 100 °C, secondary crystallisation resulted increasing the melting point, Tg, modulus and strength. At 125 and 150 °C secondary crystallisation and degradation occurred simultaneously; the effects of degradation masked by secondary crystallisation. The significant observation is that the degradation process remains active at storage temperatures well below the melting point and long-term stability of P(3HB-co-3HV) is not only affected by secondary crystallisation, but also sub-melting point degradation.

Introducing cryomilling for reliable determination of resin content and degree of cure in structural carbon fibre reinforced thermoset composites

A novel material preparation method is presented that facilitates accurate measurement of the degree of cure and resin content within carbon fibre reinforced polymer composites (CFRPs). When using conventional specimen preparation for standard thermal analysis, it is demonstrated that the experimentally-obtained enthalpy of reaction and resin content varies significantly between analyses. Measurement uncertainties arise because small specimen volumes are extracted from materials that exhibit both macroscopic inhomogeneity and physical discontinuities. To address this issue, representative sample volumes of aligned CFRPs were first cryogenically milled to develop a homogeneous powder before smaller specimens were extracted. The variation in obtained enthalpy of reaction between analyses was reduced from 23% (for conventional specimen extraction) to 1% following cryomilling. The accuracy in measurement of degree of cure for the compression moulding parts was improved 7 times. Further, subsequent FTIR analysis proved that cryomilling did not affect the final chemical structure of the cured material.

Development of partial miscibility in polycarbonate/polypropylene blends via annealing

Abstract The morphology, dynamic mechanical properties and infrared spectra of polycarbonate (PC)/polypropylene (PP) blends were investigated. As expected, PC and PP were immiscible when blended together; however partial miscibility developed following annealing. The miscibility of one polymer in the other was examined using the modified Fox equation and the values of the Flory-Huggins polymer-polymer interaction parameter (χ12) were also calculated following the Kim and Burns approach. Moreover, the possible causes for partial miscibility in the annealed PC/PP blends were explored by infrared spectroscopy. It was concluded that annealing caused degradation of PP, leading to the formation of polar groups which were then able to interact with PC generating regions of partial miscibility.