Key Engineering Materials Vol. 441

Abstract: In the recent years the driving force for technological change in many respects has shifted towards the design and process of materials that offer a set of responses to external stimuli or environmental conditions. These materials are called “smart materials”. Such responses are designed to fulfil the range of scenarios to which a material or structure may be exposed providing them with a particular functionality. These materials are not only useful because of their structural, chemical, physical or mechanical properties; they can also perform an action within a process. It has been described that smart structures exhibit one or more of the following features; they can act as sensors or actuators within a structural material or bonded in the surface; or they have controllable capabilities that permit to respond to the stimuli according to a prescribed function. These materials become intelligent when they have the ability to respond intelligently and autonomously to changing conditions. There are lots of possibilities within the term functional “smart materials” but in all of them, the term is used to describe systems which respond to a stimulus in a useful and predictable manner. Nowadays it is widely known the useful capability of, piezoelectric, electro-optic, magnetic, electro-mechanic materials, etc…that respond to stimuli such as, electric or magnetic fields, stress, temperature, moisture or pH. These multifunctional character and capability of biomaterials makes them suitable for a big number of applications in every order of human activity, from photochromic lenses for sunglasses to military and aerospace uses. They are already a big part of the market in the engineering industry.

Abstract: Carbon nanotubes (CNTs) are composed of two-dimensional hexagonal graphite sheets rolled up to form into a seamless hollow tube or cylinder of diameters ranging from 0.7 to 100 nm and length of several micrometres up to several millimetres [1, 2]. CNTs can be synthesised in two configurations, as single-walled nanotubes (SWCNTs) and multi-walled nanotubes (MWCNTs). Whereas SWCNTs are made of one tubular structure, MWCNTs consist of concentrically arranged carbon tubes with a typical spacing of ≈ 0.34 nm between the different layers. Owing to their remarkable structural characteristics (light weight, high aspect ratio, high specific surface area), as well as attractive mechanical (high stiffness and strength), electrical (high conductivity) and chemical (versatile surface chemistry, easily to functionalise) properties [2], there is increasing interest in biomedical applications of CNTs.

Abstract: Many recently designed drug delivery systems have been constructed from nano-sized components that serve as the carrier or targeting ligand for a therapeutic agent. Even though these materials have been regarded previously as inert or non-active components of dosage forms, they are now recognized as sometimes being even more important than the drug itself. Hence, it is becoming increasingly imperative that the pharmaceutically relevant properties, including identity, physicochemical characteristics, purity, solubility and toxicity, of these functional nano-excipients be fully characterized. Carbon nanotubes (CNTs) are novel nanomaterials made of carbon atoms that have wide application potential in many areas of nanomedicine. However, because of their significant potential, CNTs, as building blocks for nanomedicines, need to be characterized more fully. Studies to date indicate that both physical and chemical properties of CNTs play an important role in their interactions with cells. Therefore, a full understanding of the physical properties of CNTs, such as identity, chirality, particle size, aspect ratio, morphology and dispersion state, as well as chemical properties such as purity, defect sites and types and functional groups, will be essential to develop a full characterization panel of these versatile nanomaterials.

Abstract: Different strategies used to biofunctionalize CNTs with proteins, from direct physical adsorption on pristine CNTs to chemical treatments to achieve covalent interaction, are described. The discussion is focused on the consequences of the adsorption process on the structure and properties of both proteins and CNTs. On this base, recent developments in CNTs-proteins based biosensors (electrochemical and optical) and drug delivery systems are reviewed.

Abstract: On the landscape of the nanoscience and nanothecnology carbon nanotubes (1) have played an important role on the development of 1D materials. They consist of single (SWCNT) or multi (MWCNT) layers of graphene cylinders arranged around a central hollow. In the case of the SWCNT the size distribution is narrow (1-2 nm) while it is broader for MWCNT (2-25 nm) exhibiting a constant separation between layers, nearly equal to that of graphite-layer spacing (0.34 nm). In both cases, the length extends up to several microns. These characteristics provide large external and internal surfaces making both functionalization and filling processes very attractive for potential performances in several areas like electronic, spintronic, or drug release

Abstract: Bone tissue has evolved into hierarchical three-dimensional structures with dimensions ranging from nanometres to metres. The structure varies depending on the site in the body, which is dictated by the loading environment. Medically, bone is one of the most replaced body parts (second only to blood) but replicating these complex living hierarchical structures for the purpose of regenerating defective bone is a challenge that has yet to be overcome. A temporary template (scaffold) is needed that matches the hierarchical structure of native bone as closely as possible that is available ‘off the shelf’ for surgeons to use. After implantation the scaffold must bond to bone and stimulate not only three dimensional (3D) bone growth, but also vascularisation to feed the new bone. There are many engineering design criteria for a successful bone scaffold and bioactive glass foam scaffolds have been developed that can fulfil most of them, as they have a hierarchical porous structure, they can bond to bone, and they release soluble silica species and calcium ions that have been found to up-regulate seven families of genes in osteogenic cells. Other ions have also been incorporated to combat infection and to counteract osteoporosis. Their tailorable hierarchical structure consists of highly interconnected open spherical macropores, further, because the glass is sol-gel derived, the entire structure is nanoporous. The macropores are critical for bone and blood vessel growth, the nanopores for tailoring degradation rates and protein adsorption and for cell attachment. This chapter describes the optimised sol-gel foaming process and how bone cells respond to them. Whatever type of scaffold is used for bone regeneration, it is critically important to be able to quantify the hierarchial pore structure. The nanopore size can be quantified using gas sorption, but to obtain full information of the macropore structure, imaging must be done using X-ray microtomography and the resulting images must be quantified via 3D image analysis. These techniques are reviewed.

Abstract: Mesoporous materials synthesized using a polymer templating route have attracted considerable attention in the field of bone tissue regeneration because their unique pore textural properties (high specific surface area, pore volume and controllable mesopore structure) can promote rapid bone formation. In addition, their potential use as a drug delivery system has been highlighted. The scaffolds in bone tissue regeneration should contain 3D interconnected pores ranging in size from 10 to 1000 μm for successful cell migration, nutrient delivery, bone in-growth and vascularization. Meso-sized pores are too small to carry out these roles, even though mesoporous materials have attractive functionalities for bone tissue regeneration. Therefore, a technique linking mesoporous materials with the general scaffolds is required. This paper reviews recent studies relating the development of new porous scaffolds containing mesopores for using in bone tissue regeneration. All the suggested methods, such as a combination of polymer templating methods and rapid prototyping technique can provide hierarchically 3D porous bioactive scaffolds with well interconnected pore structures in the nano to macro size range, good molding capability, biocompatibility, and bioactivity. The new fabrication techniques suggested can potentially be used to design ideal scaffolds in bone tissue regeneration.

Abstract: For tissue regeneration in medicine three-dimensional scaffolds with specific characteristics are required. A very important property is a high, interconnecting porosity to enable tissue ingrowth into the scaffold. Pore size distribution and pore geometry should be adapted to the respective tissue. Additionally, the scaffolds should have a basic stability for handling during implantation, which is provided by ceramic scaffolds. Various methods to produce such ceramic 3D scaffolds exist. In this paper conventional and new fabrication techniques are reviewed. Conventional methods cover the replica of synthetic and natural templates, the use of sacrificial templates and direct foaming. Rapid prototyping techniques are the new methods listed in this work. They include fused deposition modelling, robocasting and dispense-plotting, ink jet printing, stereolithography, 3D-printing, selective laser sintering/melting and a negative mould technique also involving rapid prototyping. The various fabrication methods are described and the characteristics of the resulting scaffolds are pointed out. Finally, the techniques are compared to find out their disadvantages and advantages.

Abstract: The use of bone grafts is constantly increasing, their employ is principally linked to bone trauma, prosthesis revision surgery, and arthrodesis applications. In the case of biological bone grafts and depending on the origin of the graft, these grafts are classified as autografts, allografts, or xenografts. The autograft is the most commonly used and corresponds to a fresh bone graft harvesting taken from a second operating site, i.e. iliac crest, parietal bone, tibial plateaux or the fibula. The autograft has many advantages in terms of biotolerance and osteogenic potential, which justify its widespread utilization in reconstructive surgery[1]. From a practical point of view, sampling and grafting take place during the same surgical session. However, the longer exposure to the anesthetic and the surgical operation per se increases the risk of complications. For example, this procedure results in sever post-operation pain, iliac hernias, or even haemorrhages[2]. Furthermore, the volume of the bone graft taken is generally limited to 20 cm3. In the case of allografts, it generally leads to an acute inflammatory reaction which participates to the resorption/substitution process. Xenografts are less used since it involves a donor and a recipient from different species.