Models@run.time:foundations, applications, and roadmaps

Traditionally, research on model-driven engineering (MDE) has mainly focused on the use of models at the design, implementation, and verification stages of development. This work has produced relatively mature techniques and tools that are currently being used in industry and academia. However, software models also have the potential to be used at runtime, to monitor and verify particular aspects of runtime behavior, and to implement self-* capabilities (e.g., adaptation technologies used in self-healing, self-managing, self-optimizing systems). A key benefit of using models at runtime is that they can provide a richer semantic base for runtime decision-making related to runtime system concerns associated with autonomic and adaptive systems. This book is one of the outcomes of the Dagstuhl Seminar 11481 on models@run.time held in November/December 2011, discussing foundations, techniques, mechanisms, state of the art, research challenges, and applications for the use of runtime models. The book comprises four research roadmaps, written by the original participants of the Dagstuhl Seminar over the course of two years following the seminar, and seven research papers from experts in the area. The roadmap papers provide insights to key features of the use of runtime models and identify the following research challenges: the need for a reference architecture, uncertainty tackled by runtime models, mechanisms for leveraging runtime models for self-adaptive software, and the use of models at runtime to address assurance for self-adaptive systems.

Sulphonated biomaterials as glycosaminoglycan mimics in wound healing

This chapter considers the available evidence and underlying physicochemical principles that support the proposition that a biomimetic wound dressing based on glycosaminoglycan models offers a potential means of influencing wound bioactivity. Available evidence showing advantages in wound healing for experimental proteoglycanbased dressing materials is described, together with an overview of the bioactive role of sulphated macromolecules. This leads to an assessment of the analogies between the sulphonate group and the sulphate group and an explanation of their unique water binding behaviour. The available information suggests the desirability of an integrated physicochemical, biochemical and biological approach to the design and synthesis of new wound healing biomaterials.

Adhesives and interfacial phenomena in wound healing

This chapter deals initially with the underlying principles of adhesion and adhesives and the understanding of interfacial behaviour. This provides a basis upon which to understand biological interactions (. Chapter 12). The two broad types of adhesive materials encountered in wound healing are pressure-sensitive adhesives (PSA) and tissue sealants. The function of pressure-sensitive adhesives is to form an adhesive bond between tissue and biomaterial under the influence of pressure. Tissue sealants are liquids that convert to solid form at the tissue surface and in so doing form either an effective seal against fluid leakage or a bond between adjacent tissue surfaces. The different requirements and characteristics of these systems are discussed. © 2011 Woodhead Publishing Limited All rights reserved.

Charge-balanced copolymer hydrogels:potential as biomedical materials

Polyzwitterionic-containing hydrogel materials been proposed for use in biomaterial applications. Polyzwitterions contain anions and cations in the same monomeric unit, unlike polyampholytes which contain them in different monomeric units. The use of cationic and anionic monomers in stoichiometrically equivalent proportions produces charge-balanced polyampholytes (PA) copolymers. Membranes prepared using either betaine-containing (BT) polyzwitterionic copolymers or PA copolymers can share similar properties, but the range of EWCs offered by membranes incorporating BT and PA monomers is greater than that for conventional neutral hydrogels and methacrylic acid-based systems. Here we compare properties of BT-containing and PA-containing copolymer membranes, relevant to their potential as biomedical materials. Membranes of the copolymers were prepared as previously described. Surface energy was determined using a GBX Digidrop (GBX Scientific Instruments), with diidomethane and water as probes. The absorption of proteins was determined by soaking the membranes in 1mg/ml protein solutions for a predetermined time, and measuring UV absorption of the membranes at certain wavelengths. The BT and PA copolymer membranes displayed similar values for the polar components and dispersive components of total surface free energy. This was perhaps not surprising when the structures of the monomers were considered. The BT and PA copolymer membranes displayed differences in their protein absorption over time, with the PA demonstrating higher uptake of protein than the BT. In addition to the aforementioned greater EWC range, the use of BT and PA copolymer membranes also avoids some of the problems associated with net anionicity. Comparison of the BT copolymer with the “pseudo” zwitterionic PA copolymers shows that controlled molecular architecture is required to gain the benefits of balancing the charges present in the copolymers in a way that will make them beneficial to hydrogel design.

In vivo effects of tailored laminin-332 α3 conjugated scaffolds enhances wound healing:a histomorphometric analysis

Surface modification techniques have been used to develop biomimetic scaffolds by incorporating cell adhesion peptides. In our previous work, we have shown the tethering of laminin-332 α3 chain to type I collagen scaffold using microbial transglutaminase (mTGase), promotes cell adhesion, migration, and proliferation. In this study, we evaluated the wound healing properties of tailored laminin-332 α3 chain (peptide A: PPFLMLLKGSTR) tethered to a type I collagen scaffold using mTGase by incorporating transglutaminase substrate peptide sequences containing either glutamine (peptide B: PPFLMLLKGSTREAQQIVM) or lysine (peptide C: PPFLMLLKGSTRKKKKG) in rat full-thickness wound model at two different time points (7 and 21 days). Histological evaluations were assessed for wound closure, epithelialization, angiogenesis, inflammatory, fibroblastic cellular infiltrations, and quantified using stereological methods (p < 0.05). Peptide A and B tethered to collagen scaffold using mTGase stimulated neovascularization, decreased the inflammatory cell infiltration and prominently enhanced the fibroblast proliferation which significantly accelerated the wound healing process. We conclude that surface modification by incorporating motif of laminin-332 α3 chain (peptide A: PPFLMLLK GSTR) domain and transglutaminase substrate to the laminin-332 α3 chain (peptide B: PPFLMLLKGSTREAQQIVM) using mTGase may be a potential candidate for tissue engineering applications and skin regeneration. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A:2788-2795, 2013. Copyright © 2013 Wiley Periodicals, Inc., a Wiley Company.

Investigating polymer-peptide conjugates and electrospinning for the production of advanced materials

This thesis describes the production of advanced materials comprising a wide array of polymer-based building blocks. These materials include bio-hybrid polymer-peptide conjugates, based on phenylalanine and poly(ethylene oxide), and polymers with intrinsic microporosity (PIMs). Polymer-peptides conjugates were previously synthesised using click chemistry. Due to the inherent disadvantages of the reported synthesis, a new, simpler, inexpensive protocol was sought. Three synthetic methods based on amidation chemistry were investigated for both oligopeptide and polymerpeptide coupling. The resulting conjugates produced were then assessed by various analytical techniques, and the new synthesis was compared with the established protocol. An investigation was also carried out focussing on polymer-peptide coupling via ester chemistry, involving deprotection of the carboxyl terminus of the peptide. Polymer-peptide conjugates were also assessed for their propensity to self-assemble into thixotropic gels in an array of solvent mixtures. Determination of the rules governing this particular self-assembly (gelation) was required. Initial work suggested that at least four phenylalanine peptide units were necessary for self-assembly, due to favourable hydrogen bond interactions. Quantitative analysis was carried out using three analytical techniques (namely rheology, FTIR, and confocal microscopy) to probe the microstructure of the material and provided further information on the conditions for self-assembly. Several polymers were electrospun in order to produce nanofibres. These included novel materials such as PIMs and the aforementioned bio-hybrid conjugates. An investigation of the parameters governing successful fibre production was carried out for PIMs, polymer-peptide conjugates, and for nanoparticle cages coupled to a polymer scaffold. SEM analysis was carried out on all material produced during these electrospinning experiments.

Co3O4 nanostructures with a high rate performance as anode materials for lithium-ion batteries, prepared via book-like cobalt-organic frameworks

The self-assembly of cobalt coordination frameworks (Co-CPs) with a two-dimensional morphology is demonstrated by a solvothermal method. The morphology of the Co-CPs has been controlled by various solvothermal conditions. The two-dimensional nanostructures agglomerated by Co3O4 nanoparticles remained after the pyrolysis of the Co-CPs. The as-synthesized Co3O4 anode material is characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge measurements. The morphology of Co3O4 plays a crucial role in the high performance anode materials for lithium batteries. The Co3O4 nanoparticles with opened-book morphology deliver a high capacity of 597 mA h g-1 after 50 cycles at a current rate of 800 mA g-1. The opened-book morphology of Co3O4 provides efficient lithium ion diffusion tunnels and increases the electrolyte/Co3O4 contact/interfacial area. At a relatively high current rate of 1200 mA g-1, Co3O4 with opened-book morphology delivers an excellent rate capability of 574 mA h g-1.

Self-assembled SnO2 micro- and nanosphere-based gas sensor thick films from an alkoxide-derived high purity aqueous colloid precursor

Tin oxide is considered to be one of the most promising semiconductor oxide materials for use as a gas sensor. However, a simple route for the controllable build-up of nanostructured, sufficiently pure and hierarchical SnO2 structures for gas sensor applications is still a challenge. In the current work, an aqueous SnO2 nanoparticulate precursor sol, which is free of organic contaminants and sorbed ions and is fully stable over time, was prepared in a highly reproducible manner from an alkoxide Sn(OR)4 just by mixing it with a large excess of pure neutral water. The precursor is formed as a separate liquid phase. The structure and purity of the precursor is revealed using XRD, SAXS, EXAFS, HRTEM imaging, FTIR, and XRF analysis. An unconventional approach for the estimation of the particle size based on the quantification of the Sn-Sn contacts in the structure was developed using EXAFS spectroscopy and verified using HRTEM. To construct sensors with a hierarchical 3D structure, we employed an unusual emulsification technique not involving any additives or surfactants, using simply the extraction of the liquid phase, water, with the help of dry butanol under ambient conditions. The originally generated crystalline but yet highly reactive nanoparticles form relatively uniform spheres through self-assembly and solidify instantly. The spheres floating in butanol were left to deposit on the surface of quartz plates bearing sputtered gold electrodes, producing ready-for-use gas sensors in the form of ca. 50 μm thick sphere-based-films. The films were dried for 24 h and calcined at 300°C in air before use. The gas sensitivity of the structures was tested in the temperature range of 150-400°C. The materials showed a very quickly emerging and reversible (20-30 times) increase in electrical conductivity as a response to exposure to air containing 100 ppm of H2 or CO and short (10 s) recovery times when the gas flow was stopped.

Silica promoted self-assembled mesoporous aluminas. Impact of the silica precursor on the structural, textural and acidic properties

This paper investigates the effect of silica addition on the structural, textural and acidic properties of an evaporation induced self-assembled (EISA) mesoporous alumina. Two silica addition protocols were applied while maintaining the EISA synthesis route. The first route is based on the addition of a Na-free colloidal silica suspension (Ludox®), and the second method consists of the co-hydrolysis of tetraethyl orthosilicate (TEOS) with aluminium tri-sec-butoxide, to favour a more intimate mixing of the Al- and Si-hydrolysed species. The properties of the so derived materials were compared to the SiO2-free counterpart. The SiO2 addition was always beneficial from a structural and textural standpoint. TEOS appears to have a truly promoting effect; the ordering, surface area and pore volume are all improved. For Ludox®, the enhancement comes from the formation of smaller pores by a densification of the structure. The crystallization of γ-alumina depends on the interaction between the Al- and Si-species in the mesophase. Ludox®-based materials achieved crystallization at 750 °C but the intimate mixing in the TEOS-based mesophases shows a suppression of the phase transformation by 50-100 °C, with respect to the SiO2-free counterpart. This reduces the textural features substantially. For all SiO2-modified materials, the enhancement in the surface area is not accompanied by a concomitant improvement of total acidity, and the formation of weak Lewis acid sites was promoted. These effects were ascribed to SiO2 migration to the surface that blocks part of the acidity.

Condensation-enhanced self-assembly as a route to high surface area α-aluminas

High surface area nanosized α-alumina has been obtained by thermally treating a sol-gel-derived mesophase at 1200 C; the mesophase was synthesized by a sol-gel route involving evaporation induced self-assembly (EISA) of a hydrolyzed gel from Al-tri-sec-butoxide in s-BuOH in the presence of a nonionic surfactant (EO20PO70EO20), HCl as catalyst, and water (H2O/Al = 6). The activated material renders moderate surface areas of about 8.4-10 m2 g-1, associated with significant crystallite coarsening. The key aspect to produce smaller crystallites is making the mesophase more resistant to coarsening. This was achieved by enhancing the condensation step by treating the hydrolyzed gel with tetrabutyl ammonium hydroxide (TBAOH) before evaporation. The characteristics of the mesophase indicate condensation of the primary particles with less AlO5 unsaturated sites, at the expense of a lower solid yield due to small crystallites dissolution. The activated TBAOH condensed EISA material is composed of α-alumina aggregated crystallites of about 60-100 nm, and the material possesses surface areas ranging from 16 to 24 m2 g -1 due to the improved resistance to coarsening. At least two aspects are suggested to play a role in this. The worm-hole morphology of the mesophase aggregates yields high particle coordination, which favors densification rather than coarsening. Furthermore, the decrease of the AlO5 defect sites by the TBAOH condensation makes the mesophase less reactive and consequently more resistant to coarsening. © 2013 American Chemical Society.

Stabilization of self-assembled alumina mesophases

An efficient route to stabilize alumina mesophases derived from evaporation-induced self-assembly is reported after investigating various aspects in-depth: influence of the solvent (EtOH, s-BuOH, and t-BuOH) on the textural and structural properties of the mesophases based on aluminum tri-sec-butoxide (ATSB), synthesis reproducibility, role of nonvolatile acids, and the crystallization and thermal stability of the crystalline counterparts. Mesophase specific surface area and pore uniformity depend notably on the solvent; s-BuOH yields the highest surface area and pore uniformity. The optimal mesophase synthesis is reproducible with standard deviations in the textural parameters below 5%. The most pore-uniform mesophases from the three solvents were thermally activated at 1023 K to crystallize them into γ-alumina. The s-BuOH mesophase is remarkably thermally stable, retaining the mesoscopic wormhole order with 300 m2/g (0.45 cm3/g) and an increased acidic site density. These features are not obtained with EtOH or t-BuOH, where agglomerated γ-Al2O3 crystallites are formed with lower surface areas and broader pore size distributions. This was rationalized by the increase of the hydrolysis rate using EtOH and t-BuOH. t-BuOH dehydrates under the synthesis conditions or reacts with HCl, situations that increase the water concentration and rate of hydrolysis. It was found that EtOH exchanges rapidly, producing a highly reactive Al-ethoxide, thus enhancing the hydrolysis rate as well. Particle heterogeneity with random packing of fibrous and wormhole morphologies, attributed to the high hydrolysis rate, was observed for mesophases derived from both solvents. Such a low particle coordination favors coarsening with enlargement of the pore size distribution upon thermal treatment, explaining the lower thermal stability. Controlled hydrolysis and formation of low-polymerized Al species in s-BuOH are possibly responsible for the adequate assembly onto the surfactant. This was verified by the formation of a regular distribution of relatively size-uniform nanoparticles in the mesophase; high particle coordination prevents coarsening, favors densification, and maintains a relatively uniform pore size distribution upon thermal treatment. The acid removal in the evaporation is another key factor to promote network condensation in this route. © 2013 American Chemical Society.