Electrochemical biosensors are a rather new class of sensors employed for the detection of analytes in food [Uddin,2008]. They are based on the electrochemical reactivity of biomolecules. Electrochemistry has become a fast growing option in the field of biosensors for a wide range of food, medical, agricultural and environmental analytes with an expanding, multi-billion dollar market [Lee, 2006]. The combination between fast, sensitive, accurately selective, miniaturizable and low cost electrochemistry-based sensing [Uddin,2008*] leads to the evolution of electrochemical sensors of unparalleled selectivity and sensitivity for an enormous variety of analytes or target molecules, if compared to expensive, complicated and slower conventional analytical techniques [Uddin,2008*]. There are virtually inexhaustible opportunities and an immense market potential for the development of electrochemical sensors. Low cost instrumentation and miniaturization can allow the development of portable and easy-to-use microsystems. Today, sensors for food analysis are becoming increasingly essential for many reasons. Still, there are many avenues to be opened in the field of the applications of electrochemical sensors [Volpe, 2006*; Mannino, 1992; Pellegrini, 2004*; Winquist,1997]. The basic principle of electrochemical sensors is the oxidation or reduction reaction of an electroactive analyte species on the surface of an electrode, with the electrode being perturbed by an applied potential or electrical current according to a program provided by a programmable potentiostat. The response is proportional to the analyte concentration and can be an electrical current or a potential depending on the type of perturbation applied. An electrochemical sensor is a self-contained integrated system composed of a recognition interface and a transduction element. The nature of the electrode material is a key factor in the success of the electrochemical measurement. In recent years solid electrodes of platinum, gold, silver, nickel, various doped or undoped forms of carbon and graphite, etc. have replaced the very popular and successful dropping mercury electrode due to the toxicity of Hg. These materials can be either bare or chemically modified for enhanced selectivity, sensitivity and stability [Wang, 1998; Pereira, 1992] mostly by using polymers and/or catalysts of varied characteristics. In recent years, the use of modified electrodes with specific catalysts confined on the surface has gained popularity since surface modification of a cheap material like carbon increases the selectivity of the electrode without the need of using expensive metals. The figure illustrates an electrode, modified with a catalyst such as metallophthalocyanine, accelerating the reduction of an analyte target.
We have considerable experience in designing modified electrodes with selective electrochemical activity for specific targets [Zagal, 2009*, Villagra, 2008; Griveau, 2003]. We have found that the redox potential of a catalyst (like a metallophthalocyanine, see figure above) can be “tuned” [Villagra, 2008] by chemical manipulation to optimize the electrochemical reactivity or response of the modified electrode toward analytes such as l-cysteine, glucose and other relevant molecules in food technology. The activity of such electrodes can be enhanced even further by the use of carbon nanotubes (CNTs). These hybrid materials can be “screen printed” to make disposable low cost electrochemical sensors.
In this project we will develop hybrid molecular electrode materials containing metallomacrocyclic metal complexes, carbon nanotubes, metal nanoparticles and combinations of these, for the electrochemical detection of relevant molecules in food. We will profit from our experience on optimizing the electrocatalytic properties of macrocyclics confined on electrode surfaces to design electrodes with potential applications in the detection of oxygen, sugars, aminoacids, amines and pollutants in foods. We plan to make sensors for real samples based on prototypical non-disposable electrodes successfully tested with glucose, some aminoacids and other molecules. The use of flow injection analysis combined with modified and/or hybrid electrodes and screen-printed disposable electrodes fabricated by us will render more robust systems, faster and capable of yielding more precise results. We anticipate that the envisaged systems described in this project will be of great importance in the potential applications in designing better electrochemical sensors for analytes relevant to food technology. This brief description is a tiny fraction of the potentialities of these electrodes for detecting target molecules in foods. Local opportunities for sensor development, not only electrochemical, will be explored in a tight collaboration with SMAT-C members.
The aim of food packaging is to extend the shelf-life of the fresh product maintaining its physical, chemical, nutritional and sensorial properties. Among the different materials that are commonly used in food packaging, plastics have presented a great expansion in the recent decades, displacing traditional materials such as glass and tinplate. This growth comes mainly from the properties that plastic materials exhibit, such as mechanical flexibility, low cost, reduced weight and a variety of different formulations. Nevertheless, its use brings concomitant problems related to interaction with food, associated to the spontaneous processes of mass transference from and through the polymeric structure. One of the most important interaction processes that can directly affect a products shelf-life is permeability. Great efforts have been made to control gas transfer through polymer structure in order to develop polymer packaging with barrier properties. Aluminum surface deposition has been developed to reduce gas permeability of polymer films, but in depth studies on polymer surface properties are required giving special notice to chemical composition, hydrophilicity, roughness, crystallinity, conductivity, lubricity and cross-linking. Polymers, very often do not possess all the desired surface properties for these applications. For these reasons, surface modification techniques, which can transform these materials into highly valuable finished products, have become an important part of the plastic industry and otherwise related fields. In recent years, many advances have been made in developing surface treatments to modify chemical and physical properties of polymer surfaces without affecting desired properties. Common surface modification techniques include treatments by flame, corona, plasmas (probably the most versatile), photons, electron beams, ion beams, X-rays, and y-rays. Different types of gases such as argon, oxygen, nitrogen, fluorine, carbon dioxide, and water can produce the unique surface properties required by various applications. Modification by plasma treatment is usually confined to the top several hundred Angströms and does not affect the bulk properties. Thin polymer films with unique chemical and physical properties have been produced by plasma polymerization. This technology is still in its infancy, and the plasma chemical process is not fully understood. The films are prepared by vapor phase deposition and can be formed onto practically any substrate with good adhesion between the film and the substrate. These films, which are usually highly cross-linked and pinhole-free, have very good barrier properties. These patterns can be used to increase the surface roughness of inert polymer therefore generating a surface which will present improved adhesion. Pulsed laser beams can be applied to inert polymer surfaces for increased hydrophilicity and wettability. Polymer surfaces treated by pulsed UV-laser irradiation can be positively or negatively charged to enhance chemical reactivity and processability [Bharadwaj 2001*; Shi, 1996; Koh, 1997; Friedrich, 1993; Lange, 2003*; Ozdemir,1999].
Although aluminum is the mayor metallic component used as a protective barrier in plastic food packaging, its application has an environmental impact related to each stage of aluminum production; from extraction to processing. On the other hand, Chile is the world largest copper producer. Copper could be an alternative to aluminum which may lead to an increase in the protective properties for plastic food packaging, enhancing both packaging aspects and presentation.
The aim of the present study is to determine copper efficiency in polymer surface deposition, evaluating both its properties as a barrier and also its compatibility for the employment in food packaging. Different surface modification techniques and its relationship with barrier properties will be assessed. Our research program involves the expertise of other groups (see work plan for specific objectives). For instance, surface properties of films and novel techniques of metal deposition will be investigated with Profs. Paez and Melo’s research Groups. Further physical evaluation will be conducted in collaboration with physics groups. In addition, the Group will provide the necessary expertise and feedback for sensor assessment
Thin films are ubiquitous examples of soft matter systems; even though they are commonly known as "hard crystalline materials" they behave as soft materials when one of their dimensions is small. It is therefore natural for physicists to present increasing interest in two-dimensional objects [Witten, 2007]. Fruit cuticles, endothelial membranes, vesicles, lipid membranes, nanoparticle films and aggregates, polymer films and silicon nano-membranes show similar mechanical behavior in wrinkling, folding or fracturing phenomena. This discovery has motivated a new research trend which seeks indirect methods to attain material properties of thin films through two dimensional geometry [Huang, 2007; Stafford 2004; Hamm, 2008; Pocivavsek, 2008]. Observation of wrinkling in thin films under different applied loads or the tearing shape when fractured, have given valuable information regarding the film’s stiffness, adhesion, and fracture energy. With the understanding of these phenomena, we expect to provide a basis not only for improving control in the making of films used in applications such as coatings and packages, but also for the design of responsive surfaces [Holmes, 2007; Forterre, 2005].
In the domain of biological systems, protective coatings such as fruit cuticles, byssal threads, endothelium and epithelial linings of living tissues, have surprising properties in comparison to artificial coatings. One of the definitions of a good coating [Holten-Andersen, 2007], is that it must adhere well to the substrate and at the same time be hard enough to protect the underlying material. However, increasing the hardness of a coating makes the material less resilient and more likely to fracture. In addition, different responses between the coating and substrate produce stress concentration at the interface, leading to blistering and separation of the two materials. Biological coatings seem to have found the formula for better design of protective and, at the same time, extensible coatings. Some biological coatings reach 80% of strain before rupture [Holten-Andersen, 2007]. We believe that part of the large extensibility of such coatings is due to their highly convoluted shape. Most of our internal vessels that transport blood (arteries), air (bronchi), or food (esophagus) have elements of wrinkles and folds [Lambert, 1991; Jeffery, 2006] that we plan to study with physical models and numerical simulations. Following our previous work using geometry as a tool for studying the behavior of elastic interfaces [Pocivavsek, 2009], we aim to find new assessment methods to evaluate the mechanical properties of living tissues in their in vivo state and complex coatings developed by the teams of Prof. Páez and Prof. Osorio. Similarly, experiments with Langmuir-Blodgget troughs will give information about the mechanical properties of other interfaces such as lung surfactant, lipid and nanoparticle monolayers, and ultrathin polymer films [Huang, 2007; Pocivavsek, 2009]. The experimental capabilities developed by the team of Prof. Melo will be crucial to study these nanomembranes.
Packaging is the engineering counterpart of the biological protective coating. Food products must be packed in such a way that they are attractive to the consumer and at the same time protected from physical damage caused by vibrations, temperature variations, consumer handling, inappropriate manipulations, etc. However, packages must also be easy to open and close by the consumer. Designing an enclosure satisfying these ambivalent features is challenging. The process of opening a package, in scientific terms, corresponds to the propagation of a fracture that too frequently moves along an unexpected trajectory [Hamm, 2008; Audoly, 2005; Ghatak, 2003; Atkins, 1994]. Guiding the opening process with designed tear lines (perforated lines) weakens the enclosure and, as common experience reveals, frequently fails. We have built a traction machine that allows the simultaneous measurement of a pulling force and the determination of the fracture trajectories induced by that force. We will investigate the natural propagation of a fracture in specific geometries and study the potential applications of our findings to packaging. We also aim to explore the effect of artificially generated tear lines on fracture propagation by using a Cutting Plotter available in our group. The analysis of the mechanisms of tearing will help us understand the failure in the opening process of typical packages. We will also study the conditions under which an opening system based on natural fracture paths is an improvement to tear lines. Although our main focus will be to study tearing in brittle films, we also plan to study tearing in materials that are not necessarily brittle, but important in the packaging industry as plastic, paper or metal films, or textile sheets. We also plan to study the fracture properties of the new films developed by our colleagues in SMAT-C.
We will also explore “packaging” at a smaller scale. Nature has found ways to design responsive enclosures that can rapidly react to changes in the environment. The carnivorous plant Venus Fly trap [Forterre, 2005], for instance, has a rapid closing mechanism to prey on small flies and other insects. The open andclosed states correspond to two isometric states of equivalent Gaussian curvature separated by a high-energy barrier. The plant snaps between these two states to minimize the elastic energy. A different example is provided by pollen grains [Katifori, 2009]. Pollen grains close to accommodate the decrease in cellular volume due to water loss when freed from the flower stamen. It allows large deformations of the pollen wall while preserving the integrity of the plasma membrane. Recently, there have been important developments showing how these elements can be used to design responsive surfaces with high potential for technological applications [Holmes, 2007]. Active surfaces that can snap between two or more configurations could be used for rapid opening and closing devices, chemical sensing, and switchable optical systems. This proposal aims to explore new patterns of deformation and study for their applicability as responsive devices and packaging enclosures at the microscale. We plan to study these new patterns at the macroscale using numerical simulations and physical models generated by 3D printers. We also plan to study enclosures at the microscale by fabricating polymer shells and lipid vesicles in the laboratory. Specifically, we aim to mimic pollen grain behavior and snapping shells by using similar techniques to those applied in reference [Holmes, 2007].
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 Huang J., Juszkiewicz M., De Jeu W.H., Cerda E., Emrick T., Menon N., and Russell T.P., Capillary Wrinkling of Floating Thin Polymer Films, Science, 317, 650 (2007).
 Stafford C., et al., A buckling-based metrology for measuring the elastic moduli of polymeric thin films, Nature Materials, 3, 545 (2004).
 Hamm E., Reis P., LeBlanc M., Roman B., and Cerda E., Tearing as a Test for Mechanical Characterization of Thin Adhesive Films, Nature Materials, 7, 386 (2008).
 Pocivavsek L., Dellsy R., Kern A., Johnson S., Lin B., Lee K.Y., and Cerda E., Stress and Fold Localization in Thin Elastic Membranes, Science, 320, 912 (2008).
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 Forterre Y., Skotheim J. M., Dumais J., and Mahadevan L., How the Venus fly trap snaps, Nature, 433, 421 (2005).
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 Pocivavsek L., Leahy B., Holten-Andersen N., Lin B., Lee K.Y., and Cerda E., Geometric tools for complex interfaces: from lung surfactant to the mussel byssus, Soft Matter, 5, 1963 (2009).
 Audoly B., Reis P., and Roman B., Cracks in thin sheets: when geometry rules the fracture path, Phys. Rev. Lett., 95, 025502 (2005).
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 Katifori E., Alben S., Cerda E., Nelson D., and Dumais J., Foldable Structures and the Natural Design of Pollen Grains, PNAS, 107, 7635 (2010).
Fruits and aerial green parts of plants are protected by a cuticle. The cuticular membrane (CM) is a non-cellular polymeric thin layer which covers the outer cell layer; it consists of a matrix membrane (MX) made of polysaccharide microfibrils and lipophilic polymers and waxes. The cuticle is not only exposed to abiotic factors such as solar radiation, wind or rain, but it also interacts with microbes and insects. Attending to its importance as a protective layer, we are interested both in the characterization of the cuticle as well as improving its defending properties by using state-of-the-art agrochemical compounds.
A mismatch of fruit surface expansion and cuticle deposition at late stages of fruit development, the cuticle can lead to fruit cracking. Although the mechanical properties of some cuticles have already been measured, the deformation mechanisms of cuticles have yet to be studied for further understanding. One third of the earth’s terrestrial area has a rain deficit, which affects quantity and quality of agricultural products. Under water stress, plants react closing their stomata, after which water loss is mostly dependent on the cuticle. Although, efforts have been conducted towards assessing water cuticular permeability and developing cuticular antitranspirants, further research is required in order to understand the determining factors which influence the performance of antitranspirant compounds (i.e. compound dispersion and coverage). Water stress is not the only threat to current agriculture and horticulture. Although by midcentury the ozone-depleting gases should fall, other major parameters determining the surface UV radiation (clouds, aerosols and albedo) are likely to change as a consequence of climate change. Exposure to solar UV radiation may affect the reactions of polymerization and/or degradation of lipophilic polymers ofthe matrix membranes (MX) leading in turn to changes in the mechanical and optical properties of the cuticle. No studies on UV-induced changes in these optical properties have been performed.
We are studying the underlying mechanisms that influence the optical and mechanical properties of cuticles, and also to investigate the cuticular permeability of economically important species. Fruit cracking-related studies require mechanical tests involving CM and MX of fruits frequently affected by this problem, such as tomato (Lycopersicon esculentum), grape (Vitis vinifera), and cherry (Prunus avium). Research regarding both permeability and optical properties are being conducted with CM and MX sampled from leaves of both citrus (Citrus lemon) and apples (Malus domestica). The CM is being isolated by using an enzymes containing aqueous solution; organic solvents is used to isolate the MX.
The mechanical properties of the cuticle is being assessed by subjecting isolated samples of CM and MX to tensile tests. The whole-field deformation is being monitored by using high sensitivity optical techniques. The permeability assessment involves measuring the water loss rates of cuticles mounted on transpiration chambers. Studies on the optical properties require measuring the spectrum of light scattered by isolated samples of both CM and MX.
It is expected that by monitoring the deformation progression, we will be able to characterize the deformation mechanisms of fruit cuticles and to understand the role of the cellulose fibril. Strategies for avoiding the macroscopic fruit cracking by preventing the development of microcracks are also likely results. Moreover, we argue that the planned permeability tests will lead to a better understanding of the mechanism of water diffusion through the matrix membrane, the definition of a protocol for antitranspirant testing, as well as the assessment of the driving mechanisms determining the performance of these compounds. The potential of developing new antitranspirant is being also tested. Finally, it is expected that by comparing permeabilities, mechanical properties and absorption coefficients, between cuticles that were exposed to different UV doses, we will be able to assess some of the UV-linked effects. The use of UV-counteracting compounds is being also evaluated.
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For the past 10 years, research on edible films for food has increased as a result of the growing demand of consumers for longer shelf–life and higher quality of fresh food, and also due to the rise in awareness that has lead to the preference of environmentally friendly packaging [Cha, 2004; Siracusa, 2008*]. Films can mechanically protect food, prevent contamination with microorganisms and prevent food quality loss due to mass transfer (e.g. moisture, gases, flavors, etc.). Moreover, edible films can be used for incorporating natural or chemical antimicrobial agents, antioxidants, enzymes or functional ingredients such as probiotics, minerals and vitamins. The objectives of our research group are: quality optimization of edible films by control of their nano-microstructures, investigation of the relationship between macroscopic properties of edible films (thermal, mechanical, rheological, appearance, stability) and nano-microscopic properties of their components, and study of the aging effect on the functional properties of edible films.
Nanocomposite edible films could have properties superior than conventional microscale composites. However, in food engineering, very little has been investigated (Vargas, 2008). Nanocomposite edible films can be constituted by two or more organic layers of material with dimensions in the scale of nanometers (10–100 nm per layer). Organic layers can be formed by polyelectrolytes (proteins and polysaccharides), charged lipids and colloidal particles. The physical properties of these new edible films will be dictated by their architectural complexity at the nanoscale and microscale. The adsorption (electrostatic attraction) of each of its layers will be characterized using a Fourier transfer infrared spectrophotometer (FT-IR). The adhesion of edible films on food substrates will be measured with atomic force microscopy (AFM), and their maximum storage and loss values shall be assessed with dynamic mechanical analysis (DMA). Moreover, a clever choice of components for the elaboration of an edible film could limit for instance its destruction at high temperatures. Nano-micro composite films could also include various functional agents. The advantages are mainly for food-industry applications: provide food with specific protection, improve food’s textural properties, promote film transparency, optimize barriers against oxygen and carbon, and present optimal adhesion to the food product, among others.
It is also important to study the biopolymeric constituents of edible films (type of hydrocolloid, carbohydrate, proteins, plasticizer, and functional agents) which determine their mechanical properties. When polymers are tested by varying the shear rate, four rheological problems are important in film solutions [Macosko, 2007*]: (1) polymer shear thinning, (2) normal forces under shear, (3) time dependence of material properties and (4) extensional thickening of melt [Tirrel, 1996].
The stability of biopolymers as structuring matrix in films, is mainly dependent on the glass transition temperature (Tg) of the amorphous fraction present [Roos, 1995*]. At temperatures above Tg, a highly mobile structure will facilitate changes in the molecular order toward lower energy levels leading to a re-crystallization of the polymer chains resembling its native configuration [Green et al., 2007]. At temperatures below Tg a reduction in the thermodynamic quantities (enthalpy and entropy) occur [Liu et al., 2007], generating changes in mechanical properties of the matrix characterized by a decrease in specific volume [Liu et al., 2007]. The research goal aims to improve the understanding of the aging mechanisms and its kinetics in the rubbery and glassy state of single and combination of biopolymers (hydrocolloids) at a macro, micro and nano scale using DSC, DMA, FT-IR and AFM techniques. These studies will give new insights of the structure of these coatings and how variations in their configuration at the molecular level can affect their nano and macroscopic properties.
On the other hand, application of image analysis in the food industry has increased in the last decade, involving several complex techniques such as artificial neural networks, multivariate image analysis along with traditional imaging analysis methods. These methods have been applied to grain classification, fruit handling and sorting, detection of food defects, automatic fruit recognition, determination of the state of maturity of a fruit, texture analysis and many others [Sun & Chu, 2004*], contributing to industrial process control. Two central aims have been considered in using the image analysis methodology on images obtained from nano, micro and macroscopic techniques. First, is to assist in predicting food's macroscopic properties such as color, geometry, appearance, crispness and texture characteristics; and, second, to study the effects introduced by coatings on food's microstructure and how these coatings affect food visual appeal.
Most biological membranes respond to environmental stimuli with the purpose to satisfy a particular requirement of the organism. Therefore, the concept of “intelligence” is often attributed to biological membranes due to their ability to respond, e.g. to a change in pH, variation in salt concentration, and physical or chemical damage, among others. The so-called smart materials are inspired in the natural intelligence of living systems.
For corrosion-protection of metals,. Aluminum alloys of the 2000 and 7000 series are widely used in structural applications, particularly in the aircraft industry due to their remarkable weight / mechanical resistance ratio and to the well defined physical properties of these materials. The presence of alloying elements and the thermal treatment that these alloys are subjected to, make them highly susceptible to corrosion, that is, they experience damage in moist environments of varied composition [Hatch 1984, Chen 1996]. Although the traditional method of aluminum protection has been anodizing, the methodology is restricted to the local and global behavior of the alloying elements constituents from the 2000 and 7000 series during the electrolytic process [Páez 1996, Habazaki 1996 a, Páez 2000*, Zhou 2000, Habazaki 1996 b]. Such behavior gives rise to fragile anodic films associated with pore branching during film growth. Indeed, these alloys are protected by the multilayer paint system [Hatch 1984], where the first and second layers are chromate-based. Since the process is currently under scrutiny, an alternative methodology to protect alloy materials is of an utmost importance. Also worth mentioning are the costs associated to waste disposal of current metal coating processes which present a constant issue for the industry.
Replacement of chromate-based coatings is a noteworthy challenge, since these coatings have the ability of self-healing in case of chemical or mechanical damage of the film. Furthermore, chromate based coatings inhibit bacterial proliferation, which has been found to influence corrosion processes (Microbiological Influenced Corrosion, MIC). For the aforementioned reasons, an alternative type of coating, which would effectively replace those chromate based, should be ideally compact, with self-healing abilities and resistant to biocorrosion. Recently, the development of a new generation of self-repairing coatings and bulk materials [Andreeva 2008*] has driven investigations on future high-tech functional surfaces for corrosion protection of aluminum alloys. These smart coatings have both passive mechanical characteristics originated from matrix material (mainly polymeric matrixes of organic-inorganic sol-gel type) and an active response sensitive to changes in the local environment or to the integrity of the passive matrix. The progress in this area of research is in resonance with the advances that nanotechnology has generated in the development of such coatings. Indeed, nowadays coatings can be generated with specific properties in relation to their particular application. The main concept is to modify polymer hybrid coatings through nanoparticle incorporation, which requires the investigation of synthesis combination and modification that will ultimately enable the generation of a film with high-quality mechanical properties. Another important concept is the nanoparticle functionalization to be incorporated in the coating. In this case, both the type of interaction between the nanoparticle and the functionalizing species, and between the modified nanoparticle and the polymer matrix, are determinant for the properties conferred to the coating [Feng 2007].
In the present proposal, the different functionalities and specificities that can be accomplished with the incorporation of nanoparticles to films shall be applied to develop smart coatings for the protection of aluminum alloys. To simulate the bactericidal property of chromate species, the present project, based on preliminary investigations of our laboratory, proposes the study of the incorporation of copper and silver nanoparticles into inorganic-organic hybrid sol-gel type polymers. The metallic nanoparticles will be directly or, through prior encapsulation with silica, incorporated into the polymeric matrix. Recent advances in different types of nanomaterials [Gu 2003; Gong, 2007*] have shown that silver nanoparticles have antibacterial, antiviral and antimycotic properties [Gong, 2007*; Rai 2009]. Even though silver nanoparticles have been incorporated in coatings designed for medical equipment, clothing and textile fabrics [Gong, 2007*; Rai,2009], there is no information of their incorporation in anti-corrosion hybrid coatings of the sol-gel type. On the other hand, for introducing self-healing properties to the coating, incorporation of inorganic nanoparticles doped with corrosion inhibitors into the polymeric matrix will be also considered. Incorporation of both types of nanoparticles (functionalized inorganic and silver) in hybrid polymeric films are expected to reproduce the performance of chromate base coatings as starting point.
In addition to the properties already mentioned, several aspects such as extensibility, adherence, and coating tension are also addressed with the purpose of ensuring the operative life of the coated material. The combination between specific and mechanical properties, which are required for a great deal of material applications, constitute a permanent challenge. In consequence, the necessity to develop new effective and environmentally friendly coatings has significantly increased. The mechanical resistance will be used as a parameter to study the coatings for their potential application in material protection. Coating adherence, thickness, fracture resistance, hardness, residual tension and ageing are key features that critically determine the final efficiency of these films. Regardless of the significance of evaluating these mechanical behaviors, the existing methods for their assessment are limited by resolution or they require film destruction. This collaboration project aims to connect investigators that use non-destructive methods to obtain mechanical characterization of thin films with investigators who are developing new types of coatings.
Atomic force microscopy applied to food rheology. Interface operating forces, electrical double layers present in charged interfaces and structure of water layers adjacent to biomolecules among other concepts, constitute the basis for understanding a wide variety of surface and soft matter properties in food processing, medicine, biotechnology and environmental sciences, to mention a few[Fragneto 2009]. On the other hand, although atomic force (AFM) is a widespread technique for the analysis of bio-related surfaces [Morris 2008], only a few groups in Chile have developed research on this field. Indeed, over the last five years our group has been studying the crystal growth mediated by organic molecules (Dermatan Sulfate, DS) by the use of this technique. Main achievements include surface charge measurements by colloidal probes and mechanical characterization of single DS molecules. Experimental work was carried out to elucidate the selective role of molecules treated with Dermatan Sulfated on step roughness, step density, and step speed and also evaluating step-step interaction as a function of DS concentration [Gonzalez 2009]. Further experiments employing suitable functionalized nanoparticles should provide notions for elucidating the role of functional DS groups in eliminating acute steps (see figure). Our expertise on gold functionalized nanoparticles of potential therapeutic applications, [Guerrero 2009*], will provide the methodological basis for this investigation.
Our proposal is to apply AFM for the study and understanding of food properties with the purpose of solving problems related to this area. Reviews on the field have pointed out promising directions [Kirby 1995, Shimori 2008*, Morris 2004*] (see for instance [Morris 2008] for experimental methods), some of which we intend to explore. For instance, in a tight interaction with Prof. Osorio´s group, we will use AFM to investigate polysaccharides which are mainly used as thickeners through the observation of relevant parameters in structural changes, aiming at providing valuable insight onto the mechanics and self-organization properties of these molecules. Optical and magnetic [Celedon, 2009*] tweezers will be developed to investigate the mechanical properties of single molecules of our interest.
-Wetting of fruit surfaces. To avoid bursting, and even cracking of the fruit cuticle, we propose to improve the mechanical properties of the surface by adding protective or edible films whose suitability requires knowledge of surface chemistry to improve/inhibit adhesion or wetability. In the same fashion, we will undertake studies of surface topology and interactions by AFM techniques. Dynamics of micro and nanodrops on top of such surfaces will be investigated. This study aims at producing relevant information for edible film optimization.
-Vesicles for micropackaging: Vesicles have been widely studied in the last ten years as model systems for drug delivery and mimicry of cellular agglomerates. A method for generating these structures is through the combination ternary lipids which result in enhanced giant unilamellar vesicles (GUVs). At the laboratory of BioPhysics we plan to mechanically test bilayered vesicles that incorporate biopolymers such as f-actin and tubulin to enhance vesicle wall properties. Addition of ligand proteins at the vesicle´s outer wall is also being considered for improving the membrane’s adhesion to specific targets. Another topic being addressed as an option for food innovation is the incorporation of functional natural products, such as phenolic compounds that act as natural antioxidants and also provide with antimicrobial activity [Manach et al, 2004]. The use of these compounds would not only provide protection towards cardiovascular diseases, age-related degenerative diseases and cancer, but would also generate a decrease in the use of artificial additives as antioxidants [Seeram, 2008; Wang, 2000]. Phenolic compounds are being targeted for the design of conventional food with additional health benefits (functional foods). Such value-added food is needed for dietary support to manage major oxidation-linked diseases. In this proposal, we will explore the potential of vesicles in selective encapsulation and delivery of phenolic compounds, antibiotics and proteins among others. The methodological aspects of this investigation will be optimized in collaboration with food groups.
-Bio mineralization based degradable films. Nanostructured materials not only add value to traditional materials but also enhance their mechanical strength, superconductivity, and ability to incorporate and efficiently deliver active substances into biological systems, food included, at low costs and with limited environmental impact. In addition, it is possible to incorporate sensing properties to the nanostructured packaging materials that, for example, change color in the presence of harmful microorganisms or toxins. Biomineralization-inspired nanocomposites are a promising class of new materials with nanoscale structure and that present morphology and interfacial properties which give them novel desirable characteristics. An example of this, is packaging material made out of potato starch and calcium carbonate that form lightweight foam material with increased toughness, good thermal insulation properties, and biodegradability (see [Moraru, 2003]. Our expertise in biomineralization is a source of inspiration for producing micro- and nanocomposites biomimetically, and will set the basis for scaling our research efforts towards the design, characterization and production of novel nanocomposite material for food packaging and technology (see [Arias, 2007; Arias, 2008; Toro, 2007; Neira-Carrillo, 2007, Neira-Carrillo, 2008]). Nanocomposites will be designed by combining natural (i.e. starch, chitosan, cellulose) or synthetic polymers (i.e.polyethylene, polyesters) with calcium carbonate or other inorganic salts or oxides of different particle sizes and by using different compatibilizers when needed to produce variable films with taylored mechanical properties [Srinivasa, 2002; Rahmat, 2009]. This development of these structures will be carried out in collaboration with Prof. Guarda´s Group.