1,056 research outputs found
Trabecular coating on curved alumina substrates using a novel bioactive and strong glass-ceramic
Optical Nanoantennas for Energy Harvesting
In the last decade, the increasing demand for renewable energy has been leading to the
development of new devices, which overcome the disadvantages of the traditional
photovoltaic conversion and exploit the thermal radiation created by the Sun, that is
transferred in the form of electromagnetic waves into free space and finally absorbed by the
surface of the Earth [1-2]. These new devices, called nanoantennas, have only recently been
considered thanks to the development of electron beam lithography and similar techniques.
Nanoantennas operate at nanometers wavelengths and their dimensions range from a few
hundred nanometres to a few microns. They exhibit potential advantages in terms of
polarization, tunability, and rapid time response. Furthermore, the nanoscale dimensions,
combined with the high electric field enhancement in the antenna gap, enable a small device
footprint, making it compact enough to be monolithically integrated with electronics and
auxiliary optics [3]. Similar to traditional RF antennas, nanoantennas capture the incident
visible or infrared electromagnetic wave causing an AC current onto the antenna surface, such
that it oscillates at the same frequency of that of the wave. The movement of the electrons
produces an alternating current in the antenna circuit. A proper rectifier coupled with
nanoantenna is used in order to produce a DC power [3]. This rectifier contains one or more
diodes whose power loss and fast response can influence the whole device efficiency. This
circuit is known as rectenna and the typical block diagram and the equivalent circuit are
shown in figure 1-2 [3-4]. Infrared nanoantennas are also coupled to a metallic thermocouple.
The rectification mechanism is based on the Seebeck effect, a thermoelectric voltage
generation due to the infrared irradiation induced currents in the antenna. Figure 3 shows the
electric equivalent circuit of the antenna-coupled thermocouples [5]. The purpose of this
contribution is to critically compare advantages and disadvantages of new optical
nanoantennas for energy harvesting, focusing on the state of the art and its perspectives.
Nanoantennas for visible radiation reveal better upper bound limits in terms of efficiency and
available power density, table 1 [4]. Infrared nanoantennas can work even in the absence of
solar radiation, but the efficiency is still very low. Some technological issues have to be taken
into account before these commercial devices are put on the market. They mainly regard the
circuits between the antenna and the load. Nonetheless, they show a greater efficiency than
traditional PV solar cells and could be an alternative to the latter in the energy harvesting
process in the next future
Bioceramics and scaffolds: a winning combination for tissue engineering
In the last few decades we have assisted to a general increase of elder population worldwide with associated age-related pathologies. Therefore, there is the need for new biomaterials that can substitute damaged tissues, stimulate the body’s own regenerative mechanisms and promote tissue healing. Porous templates referred to as scaffolds are thought to be required for three-dimensional tissue growth. Bioceramics, a special set of fully, partially or non-crystalline ceramics (e.g. calcium phosphates, bioactive glasses and glass-ceramics) that are designed for the repair and reconstruction of diseased parts of the body, have high potential as scaffold materials. Traditionally, bioceramics have been used to fill and restore bone and dental defects (repair of hard tissues). More recently, this category of biomaterials has also revealed promising applications in the field of soft tissue engineering. Starting with an overview of the fundamental requirements for tissue engineering scaffolds, this article provides a detailed picture on recent developments of porous bioceramics and composites, including a summary of common fabrication technologies and a critical analysis of structure-property and structure-function relationships. Areas of future research are highlighted at the end of this review, with special attention to the development of multifunctional scaffolds exploiting therapeutic ion/drug release and emerging applications beyond hard tissue repair
Extrusion 3D printing of a multiphase collagen-based material: An optimized strategy to obtain biomimetic scaffolds with high shape fidelity
Extrusion printing represents one of the leading additive manufacturing techniques for tissue engineering purposes due to the possibility of achieving accurate control of the final shape and porosity of the scaffold. Despite many polymeric materials having already been optimized for this application, the processing of biopolymer-based systems still presents several limitations mainly ascribed to their poor rheological properties. Moreover, the introduction of inorganic components into the biomaterial formulation may introduce further difficulties related to system homogeneity, finally compromising its extrudability. In this context, the present study aimed at developing a new multi-phase biomaterial ink able to mimic the native composition of bone extracellular matrix, combining type-I-collagen with nano-hydroxyapatite and mesoporous bioactive glass nanoparticles. Starting from a comprehensive rheological assessment, computational-fluid-dynamics-based models were exploited to describe the material flow regime and define the optimal printing process planning. During printing, a gelatin-based bath was exploited to support the deposition of the material, while the gelation of collagen and its further chemical crosslinking with genipin enabled the stabilization of the printed structure, characterized by high shape fidelity. The developed strategy enables the extrusion printing of complex multi-phase systems and the design of high-precision biomimetic scaffolds with great potential for bone tissue engineering
Collagen and non-collagenous proteins molecular crosstalk in the pathophysiology of osteoporosis.
Abstract Collagenous and non-collagenous proteins (NCPs) in the extracellular matrix, as well as the coupling mechanisms between osteoclasts and osteoblasts, work together to ensure normal bone metabolism. Each protein plays one or more critical roles in bone metabolism, sometimes even contradictory, thus affecting the final mechanical, physical and chemical properties of bone tissue. Anomalies in the amount and structure of one or more of these proteins can cause abnormalities in bone formation and resorption, which consequently leads to malformations and defects, such as osteoporosis (OP). The connections between key proteins involved in matrix formation and resorption are far from being elucidated. In this review, we resume knowledge on the crosstalk between collagen type I and selected NCPs (Transforming Growth Factor-β, Insulin-like Growth Factor-1, Decorin, Osteonectin, Osteopontin, Bone Sialoprotein and Osteocalcin) of bone matrix, focusing on their possible involvement and role in OP. The different elements of this network can be pharmacologically targeted or used for the design/development of innovative regenerative strategies to modulate a feedback loop in bone remodelling
Composite biomaterials based on sol-gel mesoporous silicate glasses: a review
Bioactive glasses are able to bond to bone and stimulate the growth of new tissue while dissolving over time, which makes them ideal materials for regenerative medicine. The advent of mesoporous glasses, which are typically synthesized via sol-gel routes, allowed researchers to develop a broad and versatile class of novel biomaterials that combine superior bone regenerative potential (compared to traditional melt-derived glasses) with the ability of incorporating drugs and various biomolecules for targeted therapy in situ. Mesoporous glass particles can be directly embedded as a bioactive phase within a non-porous (e.g., microspheres), porous (3D scaffolds) or injectable matrix, or be processed to manufacture a surface coating on inorganic or organic (macro)porous substrates, thereby obtaining hierarchical structures with multiscale porosity. This review provides a picture of composite systems and coatings based on mesoporous glasses and highlights the challenges for the future, including the great potential of inorganic–organic hybrid sol-gel biomaterials
Synthesis and incorporation of rod-like nano-hydroxyapatite into type I collagen matrix: A hybrid formulation for 3D printing of bone scaffolds
Abstract Over the recent years, nanometric hydroxyapatite (HA) has gained interest as constituent of hybrid systems for bone scaffold fabrication, due to its biomimicry and biocompatibility. In this study, rod-like nano-HA particles were introduced in a type I collagen matrix to create a composite mimicking the bone composition. HA nano-rods (40−60 nm × 20 nm) were synthesised by hydrothermal method involving the use of an ammonium-based dispersing agent (Darvan 821-A) and fully characterised. The homogeneous dispersion of HA nanoparticles throughout the final hybrid formulation was achieved through their suspension in a collagen solution in presence of Darvan 821-A. The resulting homogeneous collagen/nano-HA suspension proved to be suitable for extrusion printing applications, showing shear thinning and sol-gel transition upon simil-physiological conditions. Furthermore, mesh-like structures were printed in a gelatine-supporting bath by means of a commercial bioprinter further demonstrating the potential of the designed hybrid system for the fabrication of 3D bone-like scaffolds
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