Mythili Prakasam

Fabrication, Properties and Applications of Dense Hydroxyapatite: A Review

In the last five decades, there have been vast advances in the field of biomaterials, including ceramics, glasses, glass-ceramics and metal alloys. Dense and porous ceramics have been widely used for various biomedical applications. Current applications of bioceramics include bone grafts, spinal fusion, bone repairs, bone fillers, maxillofacial reconstruction, etc. Amongst the various calcium phosphate compositions, hydroxyapatite, which has a composition similar to human bone, has attracted wide interest. Much emphasis is given to tissue engineering, both in porous and dense ceramic forms. The current review focusses on the various applications of dense hydroxyapatite and other dense biomaterials on the aspects of transparency and the mechanical and electrical behavior. Prospective future applications, established along the aforesaid applications of hydroxyapatite, appear to be promising regarding bone bonding, advanced medical treatment methods, improvement of the mechanical strength of artificial bone grafts and better in vitro/in vivo methodologies to afford more particular outcomes.

Biodegradable Materials and Metallic Implants—A Review

Recent progress made in biomaterials and their clinical applications is well known. In the last five decades, great advances have been made in the field of biomaterials, including ceramics, glasses, polymers, composites, glass-ceramics and metal alloys. A variety of bioimplants are currently used in either one of the aforesaid forms. Some of these materials are designed to degrade or to be resorbed inside the body rather than removing the implant after its function is served. Many properties such as mechanical properties, non-toxicity, surface modification, degradation rate, biocompatibility, and corrosion rate and scaffold design are taken into consideration. The current review focuses on state-of-the-art biodegradable bioceramics, polymers, metal alloys and a few implants that employ bioresorbable/biodegradable materials. The essential functions, properties and their critical factors are discussed in detail, in addition to their challenges to be overcome.

Continuous cross-over from ferroelectric to relaxor state and piezoelectric properties of BaTiO3-BaZrO3-CaTiO3 single crystals

Optimal properties like piezoelectricity can be found in polarizable materials for which the structure changes sharply under small composition variations in the vicinity of their morphotropic phase boundary or the triple point in their isobaric temperature-composition phase diagram. In the latter, lead-free (Ba0.850Ca0.150)(Ti0.900Zr0.100)O3 ceramics exhibit outstanding piezoelectric coefficients. For the first time, we report the growth of piezoelectric lead-free single crystals in the BaTiO3-BaZrO3-CaTiO3 pseudo-ternary system. The stoichiometry control in the CaO-BaO-TiO2-ZrO2 solid solution led to single crystals with various compositions ranging from (Ba0.857Ca0.143)(Ti0.928Zr0.072)O3 to (Ba0.953Ca0.047)(Ti0.427Zr0.573)O3. We evidenced a continuous cross-over from a ferroelectric state at high titanium content to a relaxor one on increasing the zirconium content. Such a property tuning is rather seldom observed in lead-free ferroelectrics and confirms what was already reported for ceramics. Single crystal with (Ba0.838Ca0.162)(Ti0.854Zr0.146)O3 composition, which has been grown and oriented along [001] crystallographic direction, displayed electromechanical coefficients d31 and k31 of 93 pC.N−1 and 0.18, respectively, near the room temperature (T = 305 K).

Optimal sintering parameters for Al2O3 optoceramics with high transparency by spark plasma sintering

Transparent Polycrystalline Alumina (PCA) optical ceramics were fabricated at a high heating rate and low temperature by spark plasma sintering (SPS). Maximum pressure (100 MPa) at dwell time keeps the grain size small irrespective of the dwell time. A heating and cooling rate of 100°C min−1 at the sintering temperature of 1150°C for a dwell time of 1 h at 100 MPa yielded highly densified samples with the good transparency of 63 and 83% in visible and infra-red region, respectively. Optoceramics yielded a mechanical hardness of (3000 Hv)/ 29.42 GPa and a thermal conductivity of 21 Wm−1 K−1.

Isotropic thermal expansion in anisotropic thermal management composites filled with carbon fibres and graphite

Light materials with high thermal conductivity and low thermal expansion have a wide application potential for the thermal management of high-performance electronics, in particular in mobile and aerospace applications. We present here metal matrix composites with a mixture of graphite flakes and pitch-based carbon fibres as filler. The production by spark plasma sintering orients the filler particles on to a plane perpendicular to the pressing axis. The obtained materials have lower density than aluminium combined with a thermal conductivity significantly outperforming the used metal matrix. Depending on the ratio of the filler components, a low thermal expansion along the pressing direction (high graphite flakes content) or across the pressing direction (high carbon fibre content) is achieved. For a 1:3 ratio of carbon fibres to graphite, we measured an isotropic reduction of the thermal expansion of the matrix by up to 55%. We present a detailed characterisation of composites with two aluminium alloys as matrix and an overview of the properties for six different metal matrices including magnesium and copper. With the goal of a technical application, we show that the described properties are intrinsic to the material compositions and are achieved with a wide spectrum of production methods.

Modern Preservation Tools Through Packaging for High Hydrostatic Pressure Processing

Abstract High hydrostatic pressure (HHP) processing is a well-known method for processing by nonthermal means for various applications in food, pharmaceutical, and biological industries. The products are enveloped in a packaging material before subjecting to HHP. Extensive research has proved that HHP has no negative impact created when subjecting the food material to high pressure. Physical and chemical compatibility of the packaging material is mandatory to retain hermetical properties. Any negative influence of HHP on packaging material could cause adverse effects on the shelf life, quality, and safety of the food product. Essential properties of the packaging materials such as barrier and mechanical properties have to be investigated before usage. Influence on the packaging material by high pressure is vital for study of sterilization effect. Multilayers in the packaging material could lead to adhesion and a loss of structural integrity. In this chapter, various characteristics of the packaging materials required for HHP and their application in various domains utilizing packaging materials for HHP of biomaterials and their influence will be discussed in this chapter alongside the new developments in this domain.

Fabrication and Multiscale Structural Properties of Interconnected Porous Biomaterial for Tissue Engineering by Freeze Isostatic Pressure (FIP)

Biomaterial for tissue engineering is a topic of huge progress with a recent surge in fabrication and characterization advances. Biomaterials for tissue engineering applications or as scaffolds depend on various parameters such as fabrication technology, porosity, pore size, mechanical strength, and surface available for cell attachment. To serve the function of the scaffold, the porous biomaterial should have enough mechanical strength to aid in tissue engineering. With a new manufacturing technology, we have obtained high strength materials by optimizing a few processing parameters such as pressure, temperature, and dwell time, yielding the monolith with porosity in the range of 80%–93%. The three-dimensional interconnectivity of the porous media through scales for the newly manufactured biomaterial has been investigated using newly developed 3D correlative and multi-modal imaging techniques. Multiscale X-ray tomography, FIB-SEM Slice & View stacking, and high-resolution STEM-EDS electronic tomography observations have been combined allowing quantification of morphological and geometrical spatial distributions of the multiscale porous network through length scales spanning from tens of microns to less than a nanometer. The spatial distribution of the wall thickness has also been investigated and its possible relationship with pore connectivity and size distribution has been studied.

Flexible packaging for nonthermal decontamination by high hydrostatic pressure

High hydrostatic pressure (HHP) is an emerging technology in biosciences including foods, pharmaceutical products, cosmetics, and medicine. Nonthermal decontamination, in particular cold decontamination (Pascalization), using pressure treatment (high-pressure processing, HPP) permits preservation of the inherent property of the material. Main applications of HHP are for the decontamination and at the same time preserve the properties of raw material. HHP is done by packing in flexible polymer film to avoid the contact with media and for pressure transmission. Film packaging has to be flexible, easily sealable, or closed by physical assembling. Packaging must present good mechanical properties, absent polymer complex migration to the product, and act as a barrier during HPP and to be leak-proof, which also helps in food security. The various parameters influencing flexible polymer behavior due to HHP and their aspects on food products are explained in detail in this chapter.