Foaming properties of a peptide designed to form stimuli-responsive interfacial films

We have designed an amphipathic peptide, AM1, that can self-assemble at the air-water interface to form an interfacial ensemble capable of switching between a mechanically strong cohesive film state and a mobile detergent state in response to changes in the solution conditions. The mechanical properties of the AM1 ensemble in the cohesive film state are qualitatively equivalent to the protein beta-LG, while in the mobile detergent state they are equivalent to the low molecular weight surfactant, SDS. In this work the foaming properties of AM1 are compared to those of beta-LG and SDS at the same weight concentration and it is found that AM1 adsorbs rapidly to the interface, initially forming a dense foam like that formed by SDS and superior to beta-LG. In addition, under solution conditions where interfacially adsorbed AM1 forms a cohesive film state the foam stability is high, comparable to beta-LG. However when the interfacially adsorbed AM1 forms a foam under detergent-state conditions, the foam stability is poor. We have achieved control of foam stability through the design of a peptide that exhibits stimuli-responsive changes in the extent of intermolecular interactions between peptide molecules adsorbed at the air water interface. These results illustrate the exciting potential of peptide surfactants to form a new class of stimuli-responsive foaming agents.

The effect of energy feedbacks on continental strength

The classical strength profile of continents(1,2) is derived from a quasi-static view of their rheological response to stress-one that does not consider dynamic interactions between brittle and ductile layers. Such interactions result in complexities of failure in the brittle-ductile transition and the need to couple energy to understand strain localization. Here we investigate continental deformation by solving the fully coupled energy, momentum and continuum equations. We show that this approach produces unexpected feedback processes, leading to a significantly weaker dynamic strength evolution. In our model, stress localization focused on the brittle-ductile transition leads to the spontaneous development of mid-crustal detachment faults immediately above the strongest crustal layer. We also find that an additional decoupling layer forms between the lower crust and mantle. Our results explain the development of decoupling layers that are observed to accommodate hundreds of kilometres of horizontal motions during continental deformation.

EFFECT OF FORMULATION ON PHYSICO-CHEMICAL PROPERTIES, WATER STATUS AND STABILITY OF PASTA, TOMATO SAUCE AND READY TO EAT PASTA MEALS

Ready to eat pasta meals are an important segment of convenience food, but these products are subjected to significant changes in physico-chemical properties during storage, which reduce their acceptability at the time of consumption. A deep understanding of the properties of the single phases, their dependence upon formulation, and the changes they undergo during storage is very important to intelligently intervene on products properties to improve their quality at the time of consumer’s consumption. This work has focused on the effect of formulation on physico-chemical properties of pasta and tomato sauce with a special focus on mechanical/rheological attributes and water status. Variable considered in pasta formulation were gluten, glycerol and moisture content and their effect was studied in both freshly cooked or shelf-stable cooked pasta. The effect of multiple hydrocolloids (at different levels) was considered in the case of tomato sauce. In the case of pasta, it was found that water content was indeed a very important variable in defying pasta mechanical properties and water status. Higher moisture contents in pasta resulted in softer samples and reduced the changes in physico-chemical parameters during storage. Glycerol was found to favor water uptake and to soften the pasta matrix, acting as plasticizer and increasing molecular mobility. The addition of gluten hardened pasta but did not affect the water status. The combination of higher amount of gluten (15%, g gluten / 100 g product) with higher moisture content (59-65%, g water / 100 g product) were found to minimize the physico-chemical changes occurring in RTE pasta meals during storage, improving quality at longer storage times. Hydrocolloids added into tomato sauce modulated its mechanical attributes and water status in very different manner, depending on hydrocolloid type and concentration. This may allow to produce tomato sauce for different applications and that are expected to have different performance if placed in contact with pasta in a RTE meal. Future work should include an investigation of how the interaction between the two phases (pasta and sauce) can be modulated and controlled by controlling the properties of the single phases with the goal of obtaining highly acceptable products also at longer storage times.

Design and synthesis of proteoglycan analogues for tissue repair and regeneration

This thesis is concerned with the design and synthesis of a novel, injectable proteoglycan analogue for tissue repair. This is of particular relevance to the restoration of disc height to a degraded nucleus pulposus of the intervertebral disc. The focus is on the use of sulfonate monomers as proteoglycan analogues, in particular sodium 2-acrylamido-2-methylpropane sulfonic acid and the potassium salt of 3-sulfopropyl acrylate. For most biomedical applications, synthetic hydrogels need to show dimensional stability to changes in pH, osmolarity, and temperature. This is readily achieved by neutral structures however ionic sulfonate containing hydrogels are responsive to environmental change which renders them difficult to manage in most tissue replacement applications. In this case osmotic responsiveness rather than stability is desirable. Therefore sulfonate based materials possess advantageous properties. This is a result of the sulfonate becoming an ideal surrogate for the sulfate group present within the structure of natural proteoglycans. This thesis reports polymerisation studies based on the production of a redox initiated copolymer system capable of polymerising in situ within a timescale of circa. 5-7 minutes. The rheological properties, osmotic drive, and residual monomer content of successful compositions is analysed. Properties are adapted to mimic those of the target natural tissue. The adaptation of the material for use as an injectable intra-ocular lens, with hyaluronic acid as an interpenetrate is reported. The synthesis of a radiopaque macromer to allow visibility of the repair system once in situ is investigated and discussed. The results presented in this thesis describe a suitable proteoglycan tissue analogue which is injectable, biomimetic, osmotically responsive and mechanically stable in its desired application.

Characterization of a microbial transglutaminase cross-linked type II collagen scaffold

This study investigated the effect on the mechanical and physicochemical properties of type II collagen scaffolds after cross-linking with microbial transglutaminase (mTGase). It is intended to develop a collagen-based scaffold to be used for the treatment of degenerated intervertebral discs. By measuring the amount of ε-(γ-glutamyl)lysine isodipeptide formed after cross-linking, it was determined that the optimal enzyme concentration was 0.005% (w/v). From the production of covalent bonds induced by mTGase cross-linking, the degradation resistance of type II collagen scaffolds can be enhanced. Rheological analysis revealed an almost sixfold increase in storage modulus (G') with 0.005% (w/v) mTGase cross-linked scaffolds (1.31 ± 0.03 kPa) compared to controls (0.21 ± 0.01 kPa). There was a significant reduction in the level of cell-mediated contraction of scaffolds with increased mTGase concentrations. Cell proliferation assays showed that mTGase cross-linked scaffolds exhibited similar cytocompatibility properties in comparison to non-cross-linked scaffolds. In summary, cross-linking type II collagen with mTGase imparted more desirable properties, making it more applicable for use as a scaffold in tissue engineering applications. © Mary Ann Liebert, Inc.

Enzymatic stabilization of gelatin-based scaffolds

The definitive goal of this research is to develop protein-based scaffolds for use in soft tissue regeneration, particularly in the field of dermal healing. The premise of this investigation was to characterize the mechanical properties of gelatin cross-linked with microbial transglutaminase (mTGase) and to investigate the cytocompatibility of mTGase cross-linked gelatin. Dynamic rheological analysis revealed a significant increase in the storage modulus and thermal stability of gelatin after cross-linking with mTGase. Static, unconfined compression tests showed an increase in Young's modulus of gelatin gels after mTGase cross-linking. A comparable increase in gel strength was observed with 0.03% mTGase and 0.25% glutaraldehyde cross-linked gelatin gels. In vitro studies using 3T3 fibroblasts indicated cytotoxicity at a concentration of 0.05% mTGase after 72 h. However, no significant inhibition of cell proliferation was seen with cells grown on lower concentrations of mTGase cross-linked gelatin substrates. The mechanical improvement and cytocompatibility of mTGase cross-linked gelatin suggests mTGase has potential for use in stabilizing gelatin gels for tissue-engineering applications.

Oxidation and stabilisation chemistry of metallocene-based polyolefins during melt processing

Metallocene catalyzed linear low density polyethylene (m-LLDPE) is a new generation of olefin copolymer. Based on the more recently developed metallocene-type catalysts, m-LLDPE can be synthesized with exactly controlled short chain branches and stereo-regular microstructure. The unique properties of these polymers have led to their applications in many areas. As a result, it is important to have a good understanding of the oxidation mechanism of m-LLDPE during melt processing in order to develop more effective stabilisation systems and continue to increase the performance of the material. The primary objectives of this work were, firstly, to investigate the oxidative degradation mechanisms of m-LLDPE polymers having different comonomer (I-octene) content during melt processing. Secondly, to examine the effectiveness of some commercial antioxidants on the stabilisation of m-LLDPE melt. A Ziegler-polymerized LLDPE (z-LLDPE) based on the same comonomer was chosen and processed under the same conditions for comparison with the metallocene polymers. The LLDPE polymers were processed using an internal mixer (torque rheometer, TR) and a co-rotating twin-screw extruder (TSE). The effects of processing variables (time, temperature) on the rheological (MI, MWD, rheometry) and molecular (unsaturation type and content, carbonyl compounds, chain branching) characteristics of the processed polymers were examined. It was found that the catalyst type (metallocene or Ziegler) and comonomer content of the polymers have great impact on their oxidative degradation behavior (crosslinking or chain scission) during melt processing. The metallocene polymers mainly underwent chain scission at lower temperature (<220°C) but crosslinking became predominant at higher temperature for both TR and TSE processed polymers. Generally, the more comonomers the m-LLDPE contains, a larger extent of chain scission can be expected. In contrast, crosslinking reactions were shown to be always dominant in the case of the Ziegler LLDPE. Furthermore, it is clear that the molecular weight distribution (MWD) of all LLDPE became broader after processing and tended generally to be broader at elevated temperatures and more extrusion passes. So, it can be concluded that crosslinking and chain scission are temperature dependent and occur simultaneously as competing reactions during melt processing. Vinyl is considered to be the most important unsaturated group leading to polymer crosslinking as its concentration in all the LLDPE decreased after processing. Carbonyl compounds were produced during LLDPE melt processing and ketones were shown to be the most imp0l1ant carbonyl-containing products in all processed polymers. The carbonyl concentration generally increased with temperature and extrusion passes, and the higher carbonyl content fonned in processed z-LLDPE and m-LLDPE polymers having higher comonomer content indicates their higher susceptibility of oxidative degradation. Hindered phenol and lactone antioxidants were shown to be effective in the stabilization of m-LLDPE melt when they were singly used in TSE extrusion. The combination of hindered phenol and phosphite has synergistic effect on m-LLDPE stabilization and the phenol-phosphite-Iactone mixture imparted the polymers with good stability during extrusion, especially for m-LLDPE with higher comonomer content.

Oral uptake and distribution of microspheres

There is a growing body of experimental evidence suggesting that the gastrointestinal tract (GIT) may be penetrated by sub-micron sized polymeric particles which have the capacity to deliver therapeutic compounds. We investigated this, initially with Fluoresbrite™ carboxylate latex microspheres (0.87 m diameter) which were administered orally to rats. Microsphere numbers within blood samples were then quantified using fluorescence microscopy or FACS technology. These studies were prone to quantitative error, but indicated that increased microsphere translocation occurred if particles were administered in conjunction with large volumes of hypotonic liquid, and that uptake was very rapid. Test particles were detected in blood, only a few minutes after dosing. To improve quantification, GPC technology was adopted. 0.22 m latex particles were found to accumulate in greatest numbers within the Mononuclear phagocyte system tissues after gavage. Again translocation was rapid. The ability of test particles to leave the intestinal lumen and access systemic compartments was found to be highly dependent on their size and hydrophobicity, determined by hydrophobic interaction chromatography. Considerably lower numbers of 0.97 m diameter latex microspheres were detectable within extra-intestinal tissue locations after gavage. Histological studies showed that Fluoresbrite™ microspheres accumulate within the liver, spleen, Mesenteric lymph node and vasculature of rats after oral administration. Fluorescent particles were observed in both the Peyer's patches (PPs), and non lymphoid regions of rat intestinal mucosa after gavage, conductive to the acceptance that more than one mechanism of particle absorption may operate.

The targeting of corticosteroids to inflamed tissues

In recent years, much interest has focused on the beneficial effects of administering potentially harmful therapeutic agents in drug carriers so as to reduce their toxic side effects. Rheumatoid arthritis is a chronic systemic disease with progressive destruction of the Joints and long term patient disability, Corticosteroids have been shown to retard the progression of Joint destruction but are limited in their use due to adverse side effects,This project, following the line of investigation started by other workers, was designed to study the use of microspheres to deliver corticosteroids to inflamed tissues by both the oral and intravenous routes. Hydrocortisone (HC)-loaded albumin microspheres were prepared by three different methods, by direct incorporation of HC within the particles, by indirect incorporation of HC by the enzymatic conversion of hydrocortisone-21-phosphate (H-21-P) to HC within the particles, and by the adsorption of HC onto the surface. HC was also loaded with PLA microspheres. The level of corticosteriod loading and in vitro release from microspheres was determined by HPLC analysis. A reversed-phase, ion-pairing HPLC method was developed to simultaneously measure both HC and H-21-P. The highest level of corticosteroid loading was achieved using the incorporation of H-21-P with enzymatic conversion to HC method. However, HPLC analysis showed only 5% of the incorporated steroid was HC. In vitro release rates of steroid from albumin microspheres showed >95% of incorporated steroid was released within 2 hours of dissolution. Increasing the protein:steroid ratio, and the temperature and duration of microsphere stabilization, had little effect on prolonging drug release. In vivo studies, using the carrageenan-induced rat hind-paw model of inflammation, indicated steroid-incorporated microspheres administered both orally and intraperitoneally were not therapeutically advantageous when compared to equivalent free steroid doses. The ability of orally and intravenously dosed [125I]~albumin microspheres (2.67 μm mean diameter) to accumulate in acutely and chronically inflamed tissues was investigated, The subcutaneous air-pouch was the model of inflammation used, with carrageenan as the inflammatory stimulus. Acute and chronic inflammation was shown to be consistently formed  in pouch tissues in terms of cell infiltration and fluid exudate formation in the pouch cavity. Albumin microspheres were shown to accumulate in the inflamed tissues and pouch fluids after both oral and intravenous administration. Preliminary, confirmatory studies using latex microspheres and quantitation by GPC analysis, also indicated microsphere accumulation in both acutely and chronically inflamed air-pouch tissues. tntl lUr"'poucbtis,sues; The results indicate the uptake and transfer of microspheres across the gastrointestinal tract into the circulation and their migration through disrupted endothelium and basement membranes at the inflamed sites. , .

Polymer film formulations for the preparation of enteric pharmaceutical capsules

Objectives. Standard pharmaceutical capsules are designed to dissolve in the acidic environment of the stomach releasing the encapsulated contents for absorption. When release is required further along the gastrointestinal tract capsules can be coated with acid insoluble polymers to enable passage through the stomach and dissolution in the intestine. This paper describes formulations that have the potential to be used to produce two-piece hard capsules for post-gastric delivery without the requirement of an exterior coat. Methods. The formulation uses three polysaccharides: sodium alginate, hypromellose and gellan gum to provide acid insolubility and the ability to form capsules using standard industrial equipment. Key findings. The rheological profile, on cooling, of the base material, water content and thickness of the films were shown to be comparable with those of commercial capsules. The capsules remained intact for 2 h in 100 mm HCl at pH 1.2, and within 5 min of being removed from the acid and submerged in phosphate-buffered saline at pH 6.8 were ruptured. Conclusions. Selected formulations from this study have potential for use as delayed release capsules.

Steric stabilization and dissolution characteristics of aqueous suspensions of pharmaceutical interest

The adsorption of two qroups of nonionic surface active agents and a series of hiqh molecular weiqht hydrophilic polymer fractions onto a polystyrene latex and a drug substance diloxanide furoate B.P. has been investigated. The presence of pores within the drug surface has been demonstrated and this is shown to increase the adsorption of low molecular weight polymer species. Differences in the maximum amount of polymer adsorbed at both solid-solution interfaces have been ascribed to the different hydrophobicities of the surface as determined by contact angle measurements. Adsorbed layer thicknesses of polymer on polystyrene latex have been determined by three techniques: microelectrophoresis, intensity fluctuation spectroscopy and by viscometric means. These results, in combination with adsorption data, were used to interpret the configuration of the adsorbed polymer molecules at the interface. The type of druq suspension produced on adsorbing the different polymers in the absence of electrostatic stabilization was correlated with theoretical prediuctions of suspension characteristics deduced from potential energy diagrams, The agreement was good for the adsorption of short chain length surfactants, but for the polyvinylalcohols, discrepancies were found between experiment and theory. This was attributed to the inappropriate use of a mean segment density approximation within the adsorbed layer to calculate attractive potentials between particles. A maximum in the redispersibility values for suspensions coated with adsorbed nonylphenylethoxylates was attributed to "partial static stabilization" of the particles in conjunction with the attractive forces operating in the sediment between bare surface patches on neighbouring particles. No significant change in the dissolution of the drug was observed when nonylphenylethoxylates were adsorbed due to desorption upon contact with the dissolution medium. Pluronic F68 and all the polyvinylalcohol fractions caused a reduction in the dissolution rate which is explained by the decreased diffusion of drug' through the adsorbed polymer layer.

The effect of certain hydrophilic polymers on suspension stability

The adsorption of nonionic surface active agents of polyoxyethylene glycol monoethers of n hexadecanols on polystyrene latex and nonionic cellulose polymers of hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methylcellulose on polystyrene latex and ibuprofen drug particles have been studied. The adsorbed layer thicknesses were determined by means of microelectrophoretic and viscometric methods. The conformation of the adsorbed molecules at the solid-liquid interface was deduced from the molecular areas and the adsorbed layer thicknesses. Comparison of the adsorption results obtained from polystyrene latex and ibuprofen particles was made to explain the conformation difference between these two adsorbates. Sedimentation volumes and redispersibility values were the main criteria used to evaluate suspension stability. At low concentrations of surface active agents, hard caked suspensions were found, probably due to the attraction between the uncoated areas or, the mutual adsorption of the adsorbed molecules on the bare surface of the particles in the sediment. At high concentrations of hydroxypropyl cellulose and hydroxypropyl methylcellulose, heavily caked sediments were attributed to network structure formation by the adsorbed molecules. An attempt was made to relate the characteristics of the suspensions to the potential energy of interaction curves. Generally, the agreement between theory and experiment was good, but for hydroxyethyl cellulose-ibuprofen systems discrepancies were found. Experimental studies showed that hydroxyethyl cellulose flocculated polystyrene latex over a rather wide range of concentrations; similarly, hydroxyethyl cellulose-ibuprofen suspensions were also flocculated. Therefore, it ls suggested that a term to account for flocculation energy of the polymer should be added to the total energy of interaction. A rheometric method was employed to study the flocculation energy of the polymer.

Studies on the anti-inflammatory effect of S-Adenosyl-L-methionine

1. S-adenosyl-L-methionine (SAMe) had no effect on cytochrome C reduction by superoxide generated from xanthine oxidase except at high concentrations. This was due to direct inhibition of the enzyme. 2. SAMe inhibited the neutrophil respiratory burst , measured by luminol enhanced chemiluminescence, to FMLP and zymosan A but not to PMA. 3. Adenosine and methylthioadenosine (MTA) inhibited the respiratory burst elicited by FMLP. 4. SAMe inhibited the phagocytosis of latex particles by neutrophils at high concentrations but methionine and S-adenosyl L-homocysteine had no effect. 5. Treatment with SAMe had no effect on cell infiltration or PGE2 production in 6-day air pouches. 6. Treatment with SAMe at the optimum dose of 50mg/kg inhibited the early phases of carrageenan induced rat hind paw inflammation but had a lesser effect on the secondary response. The antiinflammatory effect was sustained after inhibiton of polyamine synthesis. 7. SAMe increased liver putrescine levels in the presence and absence of inflammation Spermidine levels were increased in the presence of inflammation but spermine levels were unaffected by any of the treatments. 8. MT A and adenosine increased liver putrescine and spermidine levels 9. Treatment with SAMe had no effect on the polyamine status of blood. lO.Treatment with SAMe had no effect on the levels of glutathione in liver or blood. 11.SAMe and MTA inhibited histamine and platelet-activating factor (PAF) induced hind paw inflammation but had no effect on inflammation induced by dextran, zymosan, compound 48/80, 5-hydroxytryptamine, arachidonic acid or glucose oxidase. MTA was more effective than SAMe. 12. PAP-induced rat hind paw inflammation was inhibited by isoprenaline and verapamil. Combinations of these drugs with SAMe or MT A had no further enhancement of effect. 13. Incubation of rat PMNLs with [14c ] SAMe increased the intracellular levels of S-adenosyl-L-homocysteine in a dose dependent manner, but had no effect on the intracellular levels of SAMe, adenosine or MT A. 14. Pharmacokinetic studies of plasma SAMe following a single dose of the drug (50mg/kg) i.p. demonstrated that SAMe is rapidly absorbed and metabolised

Enterotoxigenic Escherichia coli infection of pigs: expression, extraction, purification and the adhesive properties of the K88 fimbrial adhesin

The ability of Escherichia coli to express the K88 fimbrial adhesin was satisfactorily indicated by the combined techniques of ELISA, haemagglutination and latex agglutination. Detection of expression by electron microscopy and the ability to metabolize raffinose were unsuitable. Quantitative expression of the K88 adhesin was determined by ELISA. Expression was found to vary according to the E.coli strain examined, media type and form. In general it was found that the total amount was greater, while the amount/cfu was less on agar than in broth cultures. Expression of the K88 adhesin during unshaken batch culture was related to the growth rate and was maximal during late logarithmic to early stationary phase. A combination of heat extraction, ammonium sulphate and isoelectric precipitation was found suitable for both large and small scale preparation of purified K88ab adhesin. Extraction of the K88 adhesin was sensitive to pH and it was postulated that this may affect the site of colonisation of by ETEC in vivo. Results of haemagglutination experiments were consistent with the hypothesis that the K88 receptor present on erythrocytes is composed of two elements, one responsible for the binding of K88ab and K88ac and a second responsible for the binding of the K88ad adhesin. Comparison of the haemagglutinating properties of cell-free and cell-bound K88 adhesin revealed some differences probably indicating a minor conformational change in the K88 adhesin on its isolation. The K88ab adhesin was found to bind to erythrocytes over a wide pH range (PH 4-9) and was inhibited by αK88ab and αK88b antisera. Inhibition of haemagglutination was noted with crude heparin, mannan and porcine gastric mucin, chondrosine and several hexosamines, glucosamine in particular. The most potent inhibitor of haemagglutination was n-dodecyl-β-D-glucopyranoside, one of a series of glucosides found to have inhibitory properties. Correlation between hydrophobicity of glucosides tested and degree of inhibition observed suggested hydrophobic forces were important in the interaction of the K88 adhesin with its receptor. The results of Scatchard and Hill plots indicated that binding of the K88ab adhesin to porcine enterocytes in the majority of cases is a two-step, three component system. The first K88 receptor (or site) had a K2. of 1.59x1014M-1 and a minimum of 4.3x104 sites/enterocyte. The second receptor (or site) had a K2 of 4.2x1012M-1 with a calculated 1.75x105 sites/enterocyte. Attempts to inhibit binding of cell-free K88 adhesin to porcine enterocytes by lectins were unsuccessful. However, several carbohydrates including trehalose, lactulose, galactose 1→4 mannopyranoside, chondrosine, galactosamine, stachyose and mannan were inhibitory. The most potent inhibitor was found to be porcine gastric mucin. Inhibition observed with n-octyl-α-D-glucopyranose was difficult to interpret in isolation because of interference with the assay, however, it agreed with the results of haemagglutination inhibition experiments.

Stabilisation of metallocene ethylene-1-octene copolymers during multiple extrusions

The melt stabilising efficiency of antioxidants with different structures based on hindered phenols, phosphite esters, phosphonite and a lactone was examined during multi-pass extrusions at 265 °C in three metallocene ethylene-1-octene copolymers (m-LLDPE) having different extent of short chain branching (SCB) and one Zeigler copolymer (z-LLDPE) containing the same level of SCB corresponding to one of the m-LLDPE polymers. The effect of the different antioxidants, when used separately and in combination, was investigated by characterising the changes in the polymer's rheological behaviour, colour formation and structural changes based on unsaturated groups and carbonyl content during five multi-pass extrusions. The results showed that all stabilisation systems examined offered higher efficiency in the metallocene polymers compared to the Zeigler. The effect of the extent of SCB in the metallocene polymers on the stabilising efficacy of the antioxidant systems was also examined, and it was shown that it had a significant effect, with both single and combinations of antioxidants giving higher efficiency in the m-LLDPE polymer containing higher extent of SCB. The presence of the lactone HP136 in mixtures containing hindered phenol–phosphite antioxidant systems gave a higher melt stabilisation efficiency than in its absence and this has been attributed to a co-operative antioxidant reaction steps that take place between the antioxidants resulting in the possible regeneration of the lactone antioxidant through a redox reaction. In all the metallocene PE polymers examined, the biologically hindered phenol, Irganox E, was shown to be more effective than the conventionally hindered phenol Irganox 1076, when examined alone or in combination with phosphite esters.