Tarek M. Madkour

The role of the deformational entropy in the miscibility of polymer blends investigated using a hybrid statistical mechanics and molecular dynamics model

To fully understand the thermodynamic nature of polymer blends and accurately predict their miscibility on a microscopic level, a hybrid model employing both statistical mechanics and molecular dynamics techniques was developed to effectively predict the total free energy of mixing. The statistical mechanics principles were used to derive an expression for the deformational entropy of the chains in the polymeric blends that could be evaluated from molecular dynamics trajectories. Evaluation of the entropy loss due to the deformation of the polymer chains in the case of coiling as a result of the repulsive interactions between the blend components or in the case of swelling due to the attractive interactions between the polymeric segments predicted a negative value for the deformational entropy resulting in a decrease in the overall entropy change upon mixing. Molecular dynamics methods were then used to evaluate the enthalpy of mixing, entropy of mixing, the loss in entropy due to the deformation of the polymeric chains upon mixing and the total free energy change for a series of polar and non-polar, poly(glycolic acid), PGA, polymer blends.

Heterocyclic and aromatic based polyurethane scaffolds: morphology and crystallinity studied by X-ray diffraction, small-angle X-ray scattering and differential scanning calorimetry

The morphology, crystallinity and X-ray diffraction of speciality heterocyclic and aromatic based polyurethane and poly(urethane–urea) elastomers synthesized via a one-shot polymerization method were studied. The samples were chain extended by mixtures of aliphatic diols and furanic or aromatic diamine chain extenders. Small-angle X-ray scattering (SAXS) measurements confirmed the results obtained by differential scanning calorimetry (DSC) and revealed the presence of phases with sharp phase boundaries. The SAXS patterns are best fitted with a model that consists of liquid-like ordered polydisperse spheres. Most of the samples were shown to be poorly crystalline, but some soft-phase crystals do exist and these melted at about 353 K as confirmed by DSC and temperature-dependent wide-angle X-ray diffraction. Annealing at 273 K did not affect the thermal stability but influenced the morphology of the samples. The effect of annealing on the samples of poly(urethane–urea) extended using diamine chain extenders was smaller than that for polyurethane samples, which indicates a much higher thermal stability of the poly(urethane–urea) samples owing to the formation of bidentate hydrogen-bond networks across the urea groups.

New polylactic acid/ cellulose acetate-based antimicrobial interactive single dose nanofibrous wound dressing mats

New single dose interactive extracellular matrix (ECM) mimicking nanofibrous wound dressings based on polylactic acid (PLA) and cellulose acetate (CA) were developed, characterized and investigated for wound treatment. The antimicrobial agent, thymoquinone (TQ) was selected and incorporated into the scaffolds for preventing common clinical infections, and to accelerate the rate of wound closure and re-epithelialization. The newly fabricated TQ-loaded PLA/CA wound dressings offered many advantages such as mimicking the ECM via the 3D nanofibrous structure, and promoted the cell proliferation due to the hydrophilicity and bioactivity of CA. The wound dressings also prevented the bacterial infection in the early stages due to presence of TQ, and maintained the minimum possible bacterial load in the wound area through the sustained release of the drug for 9days. In vivo assessment demonstrated that TQ-loaded PLA: CA (7:3) scaffolds significantly promoted the wound healing process by increasing re-epithelialization and controlling the formation of granulation tissue. The obtained results suggest that the developed TQ-loaded PLA/CA nanofibrous mats could be ideal for wound dressing applications.

Influence of Crosslink Characteristics Induced by Aromatic-Based Antioxidants on the Swelling and Stress-Strain Behavior of Natural Rubber Vulcanizates

Stress-strain measurements were performed on dry and swollen natural rubber vulcanizates prepared using both sulfur as the crosslinking agent and aromatic-based bound antioxidants acting as a second crosslinking agent. The aromatic-based antioxidants were synthesized and analyzed spectroscopically in order to relate the final behavior of the vulcanizates to the nature of the crosslink characteristics. The anomalous upturn in the modulus values of these networks in response to the imposed stress was shown to persist in the dry as well as the swollen state. Since the swollen elastomeric chains cannot undergo a strain-induced crystallization, the abnormal upturns in the modulus values in an absence of a filler were explained on the basis of the limited extensibility of the short chains of networks prepared using two different crosslinking agents in line with earlier modeling predictions. Remarkably, the swelling experiments revealed the increase in the crosslink density of the networks in the early stages of the thermal oxidative degradation procedure indicating a post-cure of the chemically bound antioxidants to the elastomeric chains, which incidentally corresponds to a maximum in the modulus values of the networks. The rheological and other mechanical properties such as the hardness were shown not to have been affected as a result of the incorporation of the chemically bound antioxidants.

Imide-Based Polymers of Intrinsic Microporosity: Probing the Microstructure in Relation to CO2 Sorption Characteristics

A range of microporous, imide-based polymers were newly synthesized using two-step poly-condensation reactions of bis(carboxylic anhydride) and various aromatic diamines for CO2 gas capture and storage applications. In this report, we attempted to assess the relative significance of molecular structural aspects through the manipulation of the conformational characteristics of the building blocks of the polymeric structures, the spiro-containing acid anhydride and the aromatic amines, to induce greater intrinsic microporosity and higher surface areas for the resulting solids. Results obtained from this study were thus used to outline a working relationship between the structural diversity of the constructed porous solids and their performance as CO2 sorbents.

Biodegradable biorenewable polymeric nano composites for food packaging applications

T phytochemical quercetin is one of the most abundant dietary flavonoids widely present in many fruits and vegetables. Previous in vitro studies has shown that quercetin acts as an antioxidant and anti-inflammatory agent and it has potential anti-carcinogenic properties as an apoptosis inducer. In this study, it was examined apoptotic effects of quercetin on the K562 erythroleukemia cell line. K562 cells were induced to undergo apoptosis by hydrogen peroxide. Cell viability and apoptosis level were assessed by annexin V and PI staining methods using flow cytometry. Viability of K562 cells was increased by low dose of quercetin (5-100 μM) for 3 hours. Meanwhile, the toxicity of high doses of quercetin utilizing was proved in the conditions of 100-500 μM, 24 hours and resulted in decreasing of K562 cell viability as expected (p<0.01). As a result, 100 μM quercetin was defined as a protective dose. Also, K562 cell apoptosis due to hydrogen peroxide was decreased in a dose dependent manner. As indicated in previous studies, reduction of superoxides by free radical scavengers like quercetin could be beneficial for prevention of cancer but consumption of such flavonoids during cancer treatment may weaken effects of chemotherapeutics and radiotherapy. Especially cancer patients should be carefully considered for traditional phytotherapy during cancer treatment which can lead to controversial results.N a decrease in blood selenium levels in the UK and other European countries has raised great interest about possible health implications especially regarding cancer and cardiovascular diseases. Furthermore, the increase of blood LDL cholesterol has been associated with the modern way of life which is strongly related to consumption of foods with high levels of saturated fats. Therefore, Aggelakis S A has developed a method of producing high quality chicken with high levels of organic selenium and oleic acid. Starting from the poultry growth, the company has changed the usual vegetable chicken feed program and it has turned it into an enriched one, consisted of naturally grown grains, fortified with 2.2% w/w olive oil and 0.02% w/w organic selenium. Using Cobb and Ross broilers and starting this fortified program on the 28th day of their growth, Aggelakis SA achieves to grow poultry which 44% of their rearing and 50% of their body mass is strongly associated with this poultry feed program. In the end of the growth period, functional chickens are produced with average net weight of 1.85 kg, when its fortified feed for 18 days weighs about 2.78 kg, the 59% of their total feed. The final result shows a substantial nutritional value because 100 gr of chicken meat is consisted of 7 gr fats, 40.3% oleic acid (of total fats) and 33 mg (60% of RDA) organic selenium when a conventional chicken is comprised with at least 14 gr fats per 100 gr of chicken meat, 39.3 % oleic acid (of total fats) and 16 mg of organic selenium. A product like OliV Chicken is a functional food which is able to protect people against selenium deficiency, cancer appearance and cardiovascular diseases.B polymers may provide an excellent alternative to petroleum-based polymers but their poor mechanical, thermal and barrier performance may form an obstacle to their full utilization as food packaging materials. In the current work, bionanocomposites were prepared with various nanofiller particles in order to improve their overall performance as food packaging and storage materials. Both the biopolymeric matrix and the reinforcement agents are based on natural renewable materials namely poly lactic acid (PLA) and functionalized and non-functionalized carbon nanotubes and graphene nanoplatelets, respectively. Use of the bionanocomposites comes with the advantage of sustainable development from shifting the dependency of using the limited supply of fossil fuel resources for the production of the packaging materials to using renewable natural resources for the production of biodegradable materials that can break down easily and diffuses naturally back into the environment. The addition of nano-sized fillers has efficiently improved the mechanical and barrier properties of the materials provided that the nanofiller particles are well dispersed into the matrix. It was observed that the incorporation of functionalized nanofillers into the PLA matrix enhanced its rate of degradation and hence markedly decreased the thermal stability of the resulting nanocomposites. Control of the thermal degradation of the biopolymer nanocomposites was also achieved by controlling the amount and type of the nanofillers. Good quality bionanocomposite films with low porosity and well dispersed nanofiller particles were obtained as indicated from the scanning electron microscopy micrographs.T effects of various co-pigment sources (gallic acid and water extracts obtained from green tea, pomegranate rind and rose petal) and various sweeteners (sucrose, honey and maltose syrup) on anthocyanins stability were investigated in sour cherry nectars. Water extracts of green tea, pomegranate rind and rose petal were added to sour cherry nectars to form co-pigmentation with anthocyanins. Sour cherry nectars were then sweetened by sucrose, honey and maltose syrup. In the nectar samples, the pigment vs. co-pigment ratio was 1:10 (w/w), the pH values were 3.2-3.5 and the temperature was at 20°C. Co-pigmentation was measured by the shift in absorbance (hyperchromic effect, ΔAmax) and the shift in the wavelength of the maximum absorbance of the anthocyanins (bathocromic shift, Δλmax). The addition of rose petal and green tea extracts and gallic acid led to significantly increase in ΔAmax value while there was no significant co-pigmentation effect of the sweeteners (sugar, honey and maltose syrup) added. In contrast, the combination of phenolic extracts and sweeteners resulted in the increase in ΔAmax value and this significant increase clearly showed the synergistic effect for co-pigmentation when these two added together. The maximum co-pigmentation effect was observed after the addition of rose petals extract including honey as sweetener. This addition resulted in bathochromic shift up to 4.1 nm and increase in absorbance up to 4%. Results demonstrated that gallic acid and rose petal extracts had co-pigmentation effect and increased the stability of anthocyanins in sour cherry nectars containing various sweeteners.I would be scientifically and commercially valuable to understand how external mechanical damage to fruit causes internal cellular damage and other changes that lead to bruising. This requires multi-scale geometrical modelling and FEA simulations linking the macroscopic (whole fruit) scale through the mesoscopic (tissue) scale to the microscopic (cellular) scale. As a first step in such modelling, the anatomical characteristics of a commercial tomato variety were reviewed. Subsequently, some key technologies to simplify an anatomical model of a real tomato fruit for geometrical modelling are discussed in detail. It mainly includes: 1. What components should be included in a multiscale geometrical model of whole fruit? 2. How to create the asymmetric and irregular structure and curved contour line of fruit at different scales, 3. How to connect the boundaries between different tissues in a whole fruit models, 4. How best to represent the cells in specific tissues, this relates to the vibration in tissue thickness, cell size, shape and arrangement, cell wall thickness and protoplast and 5. How to handle the effect of locular cavity and some spaces between the cells on the simulation results in FEA. In summary, it is important to simplify an anatomical model of a real tomato fruit for geometrical modelling. A more complex model might be more accurate but take a long time to compute using FEA. Using these new simplifications a potential improvement in model accuracy would be achieved within existing computing power. Those simplified methods might also be suitable for geometrical modelling of other fruits.A Jamaica is a highly fruitful country, many of its fruit species are unknown by the masses resulting in their exclusion from the diet and their non-exploitation with respect to cultivation and use in research and food and nutraceutical product development. The goal of our research therefore is to conduct research on uncommon Jamaican plant species including fruits, aimed at investigating their health-beneficial properties including antioxidant, anti-inflammatory, anti-diabetic and anticancer properties. This is done with a view of promoting productive utilization of the island’s plant resources. Studies have been done on four berries species from the Rubus genus (R. rosifolius, R. racemosus, R. ellipticus and R. jamaicensis, three raspberry and one blackberry species respectively). Our results revealed that the Jamaican berries possess high antioxidant activities and levels of anthocyanins comparable to those found in similar commercial varieties sold worldwide. Extracts of the Jamaican berries demonstrated superior anti-inflammatory and anticancer properties compared to their counterparts. Additionally, extracts and compounds from the red and yellow raspberries (respectively R. rosifolius and R. ellipticus) showed anti-proliferative activity against several cancer cell lines including colon, breast and stomach cancers. Rubus leaf extracts have demonstrated high antioxidant activity and are good sources α-linolenic acid, an essential fatty acid. Phenolics including gallic acid, 3-0-methyl catechin and epicatechin have been isolated from Rubus leaf extracts which significantly account for their antioxidant activity. These results prove that these uncommon fruit species represent a valuable natural resource which may be productively harnessed for their health-promoting properties.