We report on fundamental aspects of spin dynamics in heterostructures of graphene and transition metal dichalcogenides (TMDCs). By using realistic models derived from first principles we compute the spin lifetime anisotropy, defined as the ratio of lifetimes for spins pointing out of the graphene plane to those pointing in the plane. We find that the anisotropy can reach values of tens to hundreds, which is unprecedented for typical 2D systems with spin-orbit coupling and indicates a qualitatively new regime of spin relaxation. This behavior is mediated by spin-valley locking, which is strongly imprinted onto graphene by TMDCs. Our results indicate that this giant spin lifetime anisotropy can serve as an experimental signature of materials with strong spin-valley locking, including graphene/TMDC heterostructures and TMDCs themselves. Additionally, materials with giant spin lifetime anisotropy can provide an exciting platform for manipulating the valley and spin degrees of freedom, and for designing novel spintronic devices. PACS numbers: 72.80.Vp, 72.25.Rb, 71.70.Ej Introduction. Following the discovery of graphene in 2004 [1], a host of other two-dimensional (2D) materials have been synthesized and studied, each demonstrating unique properties and showing promise for technological applications [2]. Currently, there is a great deal of interest in layered heterostructures of these materials [3, 4], where the combined system might be engineered for specific applications [5] or might enable the exploration of new phenomena [6, 7]. In the field of spintronics, graphene has exceptional charge transport properties but weak spin-orbit coupling (SOC) on the order of 10 µeV [8], which makes it ideal for long-distance spin transport [9-11] but ineffective for generating or manipulating spin currents. To advance towards spin manipulation, recent work has focused on heterostructures of graphene and magnetic insulators [12-16] or strong SOC materials such as transition metal dichalcogenides (TMDCs) and topo-logical insulators [17-19]. The SOC induced in graphene by a TMDC could enable phenomena such as topological edge states [20] or the spin Hall effect [21-23]. To this end, a variety of recent experiments have explored spin transport in graphene/TMDC heterostruc-tures [21, 24-29]. Magnetotransport measurements revealed that graphene in contact with WS 2 exhibits a large weak antilocalization (WAL) peak, revealing a strong SOC induced by proximity effects [24-26, 30]. Fits to the magnetoconductance yielded spin lifetimes τ s ≈ 5 ps, which is two to three orders of magnitude lower than graphene on traditional substrates [10, 31]. It was later asserted that after the removal of a temperature-independent background, τ s becomes at most only a few hundred femtoseconds [26]. Nonlocal Hanle measurements , meanwhile, have revealed spin lifetimes up to a few tens of picoseconds [27-29] that can be tuned by a back gate [28, 29]. Finally, charge transport measure
Bovine xenograft materials, followed by synthetic biomaterials, which unfortunately still lack documented predictability and clinical performance, dominate the market for the cranio‐maxillofacial area. In Europe, new stringent regulations are expected to further limit the allograft market in the future. Aim Within this narrative review, we discuss possible future biomaterials for bone replacement. Scientific Rationale for Study Although the bone graft (BG) literature is overflooded, only a handful of new BG substitutes are clinically available. Laboratory studies tend to focus on advanced production methods and novel biomaterial features, which can be costly to produce. Practical Implications In this review, we ask why such a limited number of BGs are clinically available when compared to extensive laboratory studies. We also discuss what features are needed for an ideal BG. Results We have identified the key properties of current bone substitutes and have provided important information to guide clinical decision‐making and generate new perspectives on bone substitutes. Our results indicated that different mechanical and biological properties are needed despite each having a broad spectrum of variations. Conclusions We foresee bone replacement composite materials with higher levels of bioactivity, providing an appropriate balance between bioabsorption and volume maintenance for achieving ideal bone remodelling.
Background and Aims To review the regenerative technologies used in bone regeneration: bone grafts, barrier membranes, bioactive factors and cell therapies. Material and Methods Four background review publications served to elaborate this consensus report. Results and Conclusions Biomaterials used as bone grafts must meet specific requirements: biocompatibility, porosity, osteoconductivity, osteoinductivity, surface properties, biodegradability, mechanical properties, angiogenicity, handling and manufacturing processes. Currently used biomaterials have demonstrated advantages and limitations based on the fulfilment of these requirements. Similarly, membranes for guided bone regeneration (GBR) must fulfil specific properties and potential biological mechanisms to improve their clinical applicability. Pre‐clinical and clinical studies have evaluated the added effect of bone morphogenetic proteins (mainly BMP‐2) and autologous platelet concentrates (APCs) when used as bioactive agents to enhance bone regeneration. Three main approaches using cell therapies to enhance bone regeneration have been evaluated: (a) “minimally manipulated” whole tissue fractions; (b) ex vivo expanded “uncommitted” stem/progenitor cells; and (c) ex vivo expanded “committed” bone‐/periosteum‐derived cells. Based on the evidence from clinical trials, transplantation of cells, most commonly whole bone marrow aspirates (BMA) or bone marrow aspirate concentrations (BMAC), in combination with biomaterial scaffolds has demonstrated an additional effect in sinus augmentation and horizontal ridge augmentation, and comparable bone regeneration to autogenous bone in alveolar cleft repair.
Biomedical scientists use chemistry-driven processes found in nature as an inspiration to design biomaterials as promising diagnostic tools, therapeutic solutions, or tissue substitutes.
Etching is used for the surface modification of titanium to improve the implant performance in bone. In this study, pure titanium implants were surface modified by a cathodic reduction process by using hydrofluoric acid (HF) at various concentrations (0.001, 0.01, and 0.1 vol %) and a constant current of 1 mA/cm(2). The resulting surface microtopographies were analyzed by atomic force microscopy, scanning electron microscopy, and profilometry, while the surface chemical contents were evaluated by time of flight secondary ion mass spectrometry. The competitive forces between ionic surface implementation induced by the current direction and the HF etching effect on titanium were highlighted. The implant performance was evaluated in an in vivo rabbit model by using a pull-out test method. The group of implants modified with 0.01% HF showed the highest retention in bone. Fluoride and hydride amounts measured in the surfaces, as well as surface skewness (S(sk)), kurtosis (S(ku)), and core fluid retention (S(ci)) were positively correlated to the implant's retention in bone in vivo. Frequently used parameters for characterizing the implant, such as oxide content and the average height deviation from the mean plane (S(a)), were not correlated to implant performance, suggesting that these parameters are not the most important in predicting the implant performance.
Highly porous and well interconnected titanium dioxide (TiO2) scaffolds with compressive strength above 2.5 MPa were fabricated without compromising the desired pore architectural characteristics, such as high porosity, appropriate pore size, surface-to-volume ratio, and interconnectivity. Processing parameters and pore architectural characteristics were investigated in order to identify the key processing steps and morphological properties that contributed to the enhanced strength of the scaffolds. Cleaning of the TiO2 raw powder removed phosphates but introduced sodium into the powder, which was suggested to decrease the slurry stability. Strong correlation was found between compressive strength and both replication times and solid content in the ceramic slurry. Increase in the solid content resulted in more favourable sponge loading, which was achieved due to the more suitable rheological properties of the ceramic slurry. Repeated replication process induced only negligible changes in the pore architectural parameters indicating a reduced flaw size in the scaffold struts. The fabricated TiO2 scaffolds show great promise as load-bearing bone scaffolds for applications where moderate mechanical support is required.
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