Properties Of Available Materials Research Articles

Multifunctional Scaffolds Based on Emulsion and Coaxial Electrospinning Incorporation of Hydroxyapatite for Bone Tissue Regeneration

Tissue engineering is nowadays a powerful tool to restore damaged tissues and recover their normal functionality. Advantages over other current methods are well established, although a continuous evolution is still necessary to improve the final performance and the range of applications. Trends are nowadays focused on the development of multifunctional scaffolds with hierarchical structures and the capability to render a sustained delivery of bioactive molecules under an appropriate stimulus. Nanocomposites incorporating hydroxyapatite nanoparticles (HAp NPs) have a predominant role in bone tissue regeneration due to their high capacity to enhance osteoinduction, osteoconduction, and osteointegration, as well as their encapsulation efficiency and protection capability of bioactive agents. Selection of appropriated polymeric matrices is fundamental and consequently great efforts have been invested to increase the range of properties of available materials through copolymerization, blending, or combining structures constituted by different materials. Scaffolds can be obtained from different processes that differ in characteristics, such as texture or porosity. Probably, electrospinning has the greater relevance, since the obtained nanofiber membranes have a great similarity with the extracellular matrix and, in addition, they can easily incorporate functional and bioactive compounds. Coaxial and emulsion electrospinning processes appear ideal to generate complex systems able to incorporate highly different agents. The present review is mainly focused on the recent works performed with Hap-loaded scaffolds having at least one structural layer composed of core/shell nanofibers.

Tensile and Fatigue Analysis of 3D-Printed Polyethylene Terephthalate Glycol

This paper investigates the tensile and fatigue behavior of polyethylene terephthalate glycol (PETG) parts manufactured by fused filament fabrication (FFF). PETG is a thermoplastic polyester that is available as a filament for commercial desktop 3D printers. As the functionality of 3D printing components for end-part use grows, it is essential to characterize mechanical properties of available materials in a quasistatic and dynamic loading condition. One of the main issues of FFF components is the anisotropy of mechanical properties that is induced by part-build orientation and raster orientation. The objective of this study was to quantify anisotropy of PETG coupons by testing against four raster orientations—longitudinal, transversal, diagonal and crosshatched. Quasistatic tensile tests were performed on two specimen types that yielded the highest ultimate tensile strength and modulus of elasticity for longitudinal specimens. Measured strength varied from 41.58 to 48.04 MPa for the weakest and strongest orientations which correspond to 83–96% of PETG strength processed by injection molding. Tensile–tensile fatigue tests with a stress ratio of R = 0.1 were performed at 90, 80, 70 and 60% of nominal UTS of each specimen type. S–N curves displayed the highest fatigue life of the longitudinal specimen followed by the crosshatched specimen at 80–90% UTS stress level that were both eventually outperformed by the diagonal specimen at the 60% UTS stress level. Finally, a fractography analysis conducted on fatigued specimens displayed signs of plastic failure for all orientations. This paper provides an experimental analysis of PETG tensile and fatigue properties that have not been found in the literature. Results show that PETG is a good candidate for FFF technology because of the competitive mechanical properties and lesser anisotropy.

Resonant meta-atoms with nonlinearities on demand

Nonlinear light-matter interactions and their applications are constrained by properties of available materials. The use of metamaterials opens the way to achieve precise control over electromagnetic properties at a microscopic level, providing tools for experimental studies of complex nonlinear phenomena in photonics. Here, a doubly resonant nonlinear meta-atom is proposed, analyzed, and characterized in the GHz spectral range. The underlying structure is composed of a pair of split rings, resonant at both fundamental and nonlinear frequencies. The rings share a varactor diode, which serves as a microscopic source of nonlinearity. Flexible control over the coupling and near- and far-field patterns are reported, favoring the doubly resonant structure over other realizations. Relative efficiencies of the second and third harmonics, generated by the diode, are tailored by dint of the double-ring geometry, providing a guideline for selecting one frequency against another, using the design of the auxiliary structures. The on-demand control over the microscopic nonlinear properties enables developing a toolbox for experimental emulation of complex nonlinear phenomena.

Hygromorphic materials for sustainable responsive architecture

Contemporary smart building systems typically aim to reduce building energy use by means of technologically enabled climate-responsiveness; however, these technologies lack the efficiency and elegance of naturally responsive mechanisms employing the inherent properties of available materials, such as the moisture-induced opening and closing of conifer cones. This mechanism can be replicated to produce low-tech low-cost hygromorphic (moisture-sensitive) materials with the response driven by shrinkage and swelling wood. This paper explores the possibility of adaptive building systems based on incorporation of hygromorphic materials and argues that they present opportunities for architecture that is passively attuned to the variable natural rhythms of the internal and external environments, and that addresses a wide range of sustainability considerations.

An accurate higher order displacement model with shear and normal deformations effects for functionally graded plates

Functionally graded materials (FGMs) are the potential candidates under consideration for designing the first wall of fusion reactors with a view to make best use of potential properties of available materials under severe thermo-mechanical loading conditions. A higher order shear and normal deformations plate theory is employed for stress and free vibration analyses of functionally graded (FG) elastic, rectangular, and simply (diaphragm) supported plates. Although FGMs are highly heterogeneous in nature, they are generally idealized as continua with mechanical properties changing smoothly with respect to spatial coordinates. The material properties of FG plates are assumed here to vary through thickness of plate in a continuous manner. Young's modulii and material densities are considered to be varying continuously in thickness direction according to volume fraction of constituents which are mathematically modeled here as exponential and power law functions. The effects of variation of material properties in terms of material gradation index on deformations, stresses and natural frequency of FG plates are investigated. The accuracy of present numerical solutions has been established with respect to exact three-dimensional (3D) elasticity solutions and the other models’ solutions available in literature.

Aesthetic resin onlay restorations: ‘rationale and methods’

Resin composite restorations have gained increasing popularity over the past two decades. This has been largely driven by a patient-orientated demand for the use of aesthetic restorative materials. It has occurred concomitantly with an improvement in the mechanical properties of available materials, and advances in our knowledge of resin bonding. Onlay restorations are advocated for a plethora of clinical applications. This paper considers the role of adhesive onlay restorations fabricated in resin composite in contemporary restorative practice, including the presentation of two case reports. This case report describes a minimally invasive, aesthetic solution to provide cuspal coverage by means of either a direct or indirect resin composite onlay restoration, respectively.

Materials for intraocular lenses (IOLs): Review of developments to achieve biocompatibility

AbstractIt is true that the developments in material sciences along with the improvements in various aspects of technology involved in transforming materials into products, over the years, have been responsible for making many of the impossible-looking devices possible. It is also a fact that the demand for a new, improved and better material has never ended; in fact it has been increasing to a greater degree and with bigger dimensions than ever before, especially in recent times. As a matter of fact, for certain advanced applications, the need for efforts to have new materials can never be over emphasized; for example, in the area of biomedical devices such as intraocular lens (IOL). The advances in the field of bio-medical applications require the materials of high quality meeting stringent norms of performance. For implants such as the ones like IOL used for correction of vision of the eyes, besides the quality and performance of materials, biocompatibility is an issue of major concern. The material scientists have been working on the development of materials for IOLs targeting the needs arising out of the developing countries. The challenges include not only to bring down the cost of the materials used for IOLs but also to increase the biocompatibility of IOLs. For making the development process easy and bringing the state-of-the- art of knowledge to those looking for new materials, it is thought necessary to review various facets of IOLs in the present paper. Not only the aspects related to the recent developments in biomedical devices of eye care but also related to the properties of available materials vis a vis the deficiencies in properties of existing materials have been covered in this review. The aim has been to bring out the gap areas at various levels of process of product chain starting from the monomer to polymer, blank to IOL, insertion of IOL into eyes to life cycle of IOLs, mainly to provide certain possible and feasible leads to meet the challenges of making new and more biocompatible materials.

Design research programs and the logic of their development

Design research programs attempt to bring together the properties of available materials and the demands derived from intended applications. The logic of problem states and state transitions in such programs, including assessment criteria and heuristic principles, is described in settheoretic terms, starting with a naive model comprising an intended profile and the operational profile of a prototype. In a first concretization the useful distinction between structural and functional properties is built into the model. In two further concretizations the inclusion of potential applications is motivated and described for the case of drug research as well as the inclusion of potential realizations for the case of complex products. Next, another line of concretization of the naive model, the incorporation of potentially relevant properties, is sketched. Then the partial analogy between “product-” and “truth-approximation” is indicated. We conclude with some remarks about the usefulness of our models for products reaching the market in comparison to the the so-called social construction of technology approach.

Scientific consultancy

Scientific consultancy applied to the electrical and electronics industry invokes academic skills over a wide range of disciplines. These skills need to be complemented by others involved in project preparation and in project management. The limits of design are frequently set by the properties of available materials or combination of materials, with the result that a large part of scientific consultancy is materials-related in some way. Staff expertise profiles need to be carefully supervised and modified by appropriate recruitment policies and comprehensive training schemes to keep abreast of a rapidly changing technological scene. The intellectual capital of the consultancy must be maintained at a high level, and, to ensure this, the ratio of skill-enhancing to skill-depleting activity must be maximised. Short-term work, although frequency quite lucrative, is on the whole a skill-depleting activity and ways must be found to engage in longer-term investigational activity. Consultancy related to a basic problem which is common to the activities of several clients, usually involves long-term skill-enhancing research and development. Consultancy can operate quite successfully with a management structure based on a division/project matrix. Examples of typical consultancy projects indicate the wide range of problems arising in the electrical and electronics industries.

Practical selection of elastomer materials for vacuum seals

Proper selection of polymer seal materials must consider restraints imposed by the application and the properties of available materials. Data and concepts presented enable the working vacuum technician to make an educated selection considering chemical and mechanical properties, outgassing, permeation, and nuclear radiation damage. Early reports on the new perfluoroelastomer Kalrez have shown problems with compression set and adhesion, but these difficulties may have resulted from improper groove design.