Superparamagnetic enhancement of thermoelectric performance.

The ability to control chemical and physical structuring at the nanometre scale is important for developing high-performance thermoelectric materials. Progress in this area has been achieved mainly by enhancing phonon scattering and consequently decreasing the thermal conductivity of the lattice through the design of either interface structures at nanometre or mesoscopic length scales or multiscale hierarchical architectures. A nanostructuring approach that enables electron transport as well as phonon transport to be manipulated could potentially lead to further enhancements in thermoelectric performance. Here we show that by embedding nanoparticles of a soft magnetic material in a thermoelectric matrix we achieve dual control of phonon- and electron-transport properties. The properties of the nanoparticles-in particular, their superparamagnetic behaviour (in which the nanoparticles can be magnetized similarly to a paramagnet under an external magnetic field)-lead to three kinds of thermoelectromagnetic effect: charge transfer from the magnetic inclusions to the matrix; multiple scattering of electrons by superparamagnetic fluctuations; and enhanced phonon scattering as a result of both the magnetic fluctuations and the nanostructures themselves. We show that together these effects can effectively manipulate electron and phonon transport at nanometre and mesoscopic length scales and thereby improve the thermoelectric performance of the resulting nanocomposites.

Corrigendum: Superparamagnetic enhancement of thermoelectric performance.

This corrects the article DOI: 10.1038/nature23667.

Large-Scale Preparation of Hair Follicle Germs Using a Microfluidic Device.

Hair follicle morphogenesis during embryonic development is driven by the formation of hair follicle germs (HFGs) via interactions between epithelial and mesenchymal cells. Bioengineered HFGs are potential tissue grafts for hair regenerative medicine because they can replicate interactions and hair follicle morphogenesis after transplantation. However, a mass preparation approach for HFGs is necessary for clinical applications, given that thousands of de novo hair follicles are required to improve the appearance of a single patient with alopecia. In this study, we developed a microfluidics-based approach for the large-scale preparation of HFGs. A simple flow-focusing microfluidic device allowed collagen solutions containing epithelial and mesenchymal cells to flow and generate collagen microbeads with distinct Janus structures. During the 3 days of culture, the collagen beads contracted owing to cellular traction forces, resulting in collagen- and cell-dense HFGs. The transplantation of HFGs into nude mice resulted in highly efficient de novo hair follicle regeneration. This method provides a scalable and robust tissue graft preparation approach for hair regeneration.

Enhanced Contact Performance and Thermal Tolerance of Ni/Bi2Te3 Joints for Bi2Te3-Based Thermoelectric Devices.

Ni metal has been widely used as a barrier layer in Bi2Te3-based thermoelectric devices, which establishes stable joints to link Bi2Te3-based legs and electrodes. However, the Ni/Bi2Te3 joints become very fragile when the devices were exposed to high temperature, causing severe performance deterioration and even device failure. Herein, stable Ni/Bi2Te3 joints have been established by arc spraying of the Ni barrier layer on the Bi2Te3-based alloys. The interface microstructure and contact performance including the bonding strength and contact resistivity of the arc-sprayed Ni/Bi2Te3 joints are investigated. The results indicate that, as compared with traditional Ni/Bi2Te3 joints, the arc-sprayed Ni/Bi2Te3 joints have comparably low contact resistivity while possessing a 50% higher bonding strength. Aging the joints as an exposure to high-temperature circumstances, the arc-sprayed Ni/Bi2Te3 joints exhibit much better tolerance to the thermal shock with stable bonding strength and contact resistivity. The enhanced interfacial contact performance and thermal tolerance should be attributed to the thick Ni barrier layer and interface reaction layer with good Ohmic contact. This work provides an effective strategy to establish stable joints for the Bi2Te3-based thermoelectric devices with improved thermal stability.

Realizing Excellent Structural and Thermoelectric Performance in Mg3Sb2-Based Alloys by Manipulating Mg Intrinsic Migration Kinetics with Interstitial Ni Doping.

N-type Mg3Sb2 is attracting increasing focus for its outstanding room-temperature (RT) thermoelectric (TE) performance; however, achieving reliable n-type conduction remains challenging due to negatively charged Mg vacancies. Doping with compensation charges is generally used but does not fundamentally resolve the high intrinsic activity and easy formation of Mg vacancies. Herein, a robust structural and thermoelectric performance is obtained by manipulating Mg intrinsic migration activity by precisely incorporating Ni at the interstitial site. Density functional theory (DFT) indicates that a strong performance originates from a significant thermodynamic preference for Ni occupying the interstitial site across the complete Mg-poor to -rich window, which dramatically promotes the Mg migration barrier and kinetically immobilizes Mg. As a result, the detrimental vacancy-associated ionized scattering is eliminated with a leading room-temperature ZT up to 0.85. This work reveals that interstitial occupation in Mg3Sb2-based materials is a novel approach promoting both structural and thermoelectric performance.

Tuning Thermoelectric Conversion Performance of BiSbTe/Epoxy Flexible Films with Dot Magnetic Arrays.

Embedding of magnetic functional units into the thermoelectric (TE) materials has been demonstrated to be an effective way to enhance the TE conversion performance. However, the magnetic functional units in TE materials are all randomly distributed. In this paper, to explore the effect of the ordering of the magnetic functional units on TE conversion performance, a series of BiSbTe/epoxy flexible thermoelectromagnetic (TEM) films with dot magnetic arrays were successfully prepared by a two-step screen printing combined with a hot pressing process. TEM films with dot magnetic arrays can achieve high carrier mobility, while the carrier concentration increases due to large coercivity. Therefore, its electrical conductivities are significantly improved on the condition that it maintains a high Seebeck coefficient. The TEM film with hexagonal-dot magnetic arrays exhibits the best electrical transport properties, for which the room-temperature power factor reaches 1.51 mW·m-1·K-2, increased by 33.6 and 36.1% as compared with those of the pristine TE film and the TEM film with a continuous magnetic layer, respectively. This work provides a new way to enhance the TE conversion performance of flexible TEM films through the ordered magnetic arrays.

[Synthesis of particle-free silver conductive ink and investigation of fabrication of conductive film by printing].

Particle-free conductive ink was prepared, taking silver citrate as conductive metal precursor, sec-butylamine as complexing agent and ethanol as media adjusting the viscosity and wettability. The ink could be printed on PET substrate by gravure printing, and silver conductive film with high electrical conductivity was obtained after thermal treated at low temperature. Silver citrate, silver citrate based conductive ink and silver conductive film were characterized with EDS, STA, IR, XRD, SEM and four point probe method. The results of STA showed that the mass of the conductive ink came to constant at 132 degrees C which is much lower than that of silver citrate (210 degrees C); the results of SEM and XRD showed that the silver conductive film cured at 150 C was constituted by compact silver nano particles with high purity; the result of four point probe method showed that its sheet resistance was 1.83 omega x square(-1).

High Transverse Thermoelectric Performance and Interfacial Stability of Co/Bi0.5Sb1.5Te3 Artificially Tilted Multilayer Thermoelectric Devices.

Artificially tilted multilayer thermoelectric devices (ATMTDs) have attracted extensive attention because of their numerous advantages, such as high integration, great structural freedom, and large transverse Seebeck coefficients. ATMTDs are composed of numerous alternating stackings of two types of materials with large differences in electrical and thermal transport. Therefore, it is of great interest to find ATMTDs with both high transverse thermoelectric performance and good interfacial stability to develop their practical application. In this work, cobalt (Co) and Bi0.5Sb1.5Te3 (BST) are chosen to prepare Co/BST ATMTDs. The interfacial structure and composition of Co/BST are characterized, and its interfacial stability and transverse thermoelectric performance are evaluated. The results show that the thickness of the Co/BST interfacial reaction layer is about 4 µm. Annealing at 473 K for 32 h does not increase the thickness, which indicates better interfacial stability than Ni/BST. After structure optimization, Co/BST ATMTD has ZTzx = 0.41, which is second only to YbAl3/BST ATMTDs. Meanwhile, the transverse Seebeck coefficient reaches -120.38 µV/K. The outstanding interfacial stability and transverse thermoelectric performance promise excellent thermal response and refrigeration performance with Co/BST ATMTDs.

Fabrication and Excellent Performances of Bismuth Telluride-Based Thermoelectric Devices.

The barrier layer between thermoelectric (TE) legs and electrodes has crucial impact on the electrothermal conversion efficiency of the TE device; however, the interfacial reaction of the Ni metal barrier layer with TE legs in traditional Bi2Te3-based devices is harmful to the device performance. Herein, a high-quality barrier layer of a Ni-based alloy has been fabricated on both n-type and p-type Bi2Te3-based TE legs by the electroplating method. The in situ XRD results indicate that the as-prepared Bi2Te3-based TE legs with a Ni-based alloy barrier layer remain stable even at 300 °C. The high-resolution high-angle annular dark field scanning transmission electron microscopy images reveal that the Ni-based alloy barrier layer has more excellent stability than that of the Ni metal barrier layer. The Bi2Te3-based TE devices with excellent structural and performance stabilities were assembled with the as-grown high-performance n-type and p-type Bi2Te3-based leg with a Ni-based alloy barrier layer, which have lower internal resistance and higher cooling and power generation performances. A maximum cooling temperature difference over 65 K and a maximum cooling capacity of 55 W were obtained for the high-performance Bi2Te3-based TE devices. This work provides a new strategy for high-temperature applications of commercial Bi2Te3-based TE devices.

Targeting angiogenesis for fracture nonunion treatment in inflammatory disease.

Atrophic fracture nonunion poses a significant clinical problem with limited therapeutic interventions. In this study, we developed a unique nonunion model with high clinical relevance using serum transfer-induced rheumatoid arthritis (RA). Arthritic mice displayed fracture nonunion with the absence of fracture callus, diminished angiogenesis and fibrotic scar tissue formation leading to the failure of biomechanical properties, representing the major manifestations of atrophic nonunion in the clinic. Mechanistically, we demonstrated that the angiogenesis defect observed in RA mice was due to the downregulation of SPP1 and CXCL12 in chondrocytes, as evidenced by the restoration of angiogenesis upon SPP1 and CXCL12 treatment in vitro. In this regard, we developed a biodegradable scaffold loaded with SPP1 and CXCL12, which displayed a beneficial effect on angiogenesis and fracture repair in mice despite the presence of inflammation. Hence, these findings strongly suggest that the sustained release of SPP1 and CXCL12 represents an effective therapeutic approach to treat impaired angiogenesis and fracture nonunion under inflammatory conditions.

Excellent Thermoelectric Performance from In Situ Reaction between Co Nanoparticles and BiSbTe Flexible Films.

Low-cost flexible thermoelectric (TE) films with excellent cooling performance are critical for the in-plane heat dissipation application based on the TE film refrigeration technology. In this work, a flexible film epoxy/Bi0.5Sb1.5Te3 is developed by the incorporation of ferromagnetic Co nanoparticles to improve the electrical transport and cooling performance. The magnetic properties and microstructures clearly indicate that part of Co nanoparticles in situ reacts with Te from Bi0.5Sb1.5Te3 to form CoTe2, as well as BiTe' antisite defects. The electric conductivity is greatly enhanced because of the increased carrier density, while a large Seebeck coefficient is well maintained because of the extra magnetic scattering. The power factor of the flexible film with 0.2 wt % Co nanoparticles reached 2.28 mW·m-1·K-2 at 300 K, increased by 34% compared to the epoxy/Bi0.5Sb1.5Te3 film. The maximum cooling temperature difference is 1.5 times higher compared with the epoxy/Bi0.5Sb1.5Te3 film. This work provides a general method to improve the electrothermal conversion performance of BiSbTe-based flexible films through in situ reaction.

Interactions at engineered graft-tissue interfaces: A review.

The interactions at the graft-tissue interfaces are critical for the results of engraftments post-implantation. To improve the success rate of the implantations, as well as the quality of the patients' life, understanding the possible reactions between artificial materials and the host tissues is helpful in designing new generations of material-based grafts aiming at inducing specific responses from surrounding tissues for their own reparation and regeneration. To help researchers understand the complicated interactions that occur after implantations and to promote the development of better-designed grafts with improved biocompatibility and patient responses, in this review, the topics will be discussed from the basic reactions that occur chronologically at the graft-tissue interfaces after implantations to the existing and potential applications of the mechanisms of such reactions in designing of grafts. It offers a chance to bring up-to-date advances in the field and new strategies of controlling the graft-tissue interfaces.

Autologous cell membrane coatings on tissue engineering xenografts for suppression and alleviation of acute host immune responses.

Xenogeneic extracellular matrix (ECM) based tissue engineering graft is one of the most promising products for transplantation therapies, which could alleviate the pain of patients and reduce surgery cost. However, in order to put ECM based xenografts into clinical use, the induced inflammatory and immune responses have yet to be resolved. Cell membrane is embedded with membrane proteins for regulation of cell interactions including self-recognition and potent in reducing foreign body rejections. In this study, a novel and facile method for evasion from immune system was developed by coating autologous red blood cell membrane as a disguise on xenogeneic ECM based tissue engineering graft surface. Porcine source Living Hyaline Cartilage Graft (LhCG) and decellularized LhCG (dLhCG) established by our group for cartilage tissue engineering were chosen as model grafts. The cell membrane coating was quite stable on xenografts with no obvious decrease in amount for 4 weeks. The autologous cell membrane coated xenograft has been proved to be recognized as "self" by immune system on cell, protein and gene levels according to the 14-day lasting in vivo study on rats with less inflammatory cells infiltrated and low inflammation-related cytokines gene expression, showing alleviated acute immune and inflammatory responses.

Decellularized tissue engineered hyaline cartilage graft for articular cartilage repair.

Articular cartilage repair has been a long-standing challenge in orthopaedic medicine due to the limited self-regenerative capability of cartilage tissue. Currently, cartilage lesions are often treated by microfracture or autologous chondrocyte implantation (ACI). However, these treatments are frequently reported to result in a mixture of the desired hyaline cartilage and mechanically inferior fibrocartilage. In this study, by combining the advantages of cartilage tissue engineering and decellularization technology, we developed a decellularized allogeneic hyaline cartilage graft, named dLhCG, which achieved superior efficacy in articular cartilage repair and surpassed living autologous chondrocyte-based cartilaginous engraftment and ACI. By the 6-month time point after implantation in porcine knee joints, the fine morphology, composition, phenotype, microstructure and mechanical properties of the regenerated hyaline-like cartilaginous neo-tissue have been demonstrated via histology, biochemical assays, DNA microarrays and mechanical tests. The articular cartilaginous engraftment with allogeneic dLhCG was indicated to be well consistent, compatible and integrated with the native cartilage of the host. The successful repair of articular chondral defects in large animal models suggests the readiness of allogeneic dLhCG for clinical trials.

Full-Scale Osteochondral Regeneration by Sole Graft of Tissue-Engineered Hyaline Cartilage without Co-Engraftment of Subchondral Bone Substitute.

In this study, full-scale osteochondral defects are hypothesized, which penetrate the articular cartilage layer and invade into subchondral bones, and can be fixed by sole graft of tissue-engineered hyaline cartilage without co-engraftment of any subchondral bone substitute. It is hypothesized that given a finely regenerated articular cartilage shielding on top, the restoration of subchondral bones can be fulfilled via spontaneous self-remodeling in situ. Hence, the key challenge of osteochondral regeneration lies in restoration of the non-self-regenerative articular cartilage. Here, traumatic osteochondral lesions to be repaired in rabbit knee models are endeavored using novel tissue-engineered hyaline-like cartilage grafts that are produced by 3D cultured porcine chondrocytes in vitro. Comparative trials are conducted in animal models that are implanted with living hyaline cartilage grafts (LhCG) and decellularized LhCG (dLhCG). Sound osteochondral regeneration is gradually revealed from both LhCG and dLhCG-implanted samples 50-100 d after implantation. Quality regeneration in both zones of articular cartilage and subchondral bones are validated by the restored osteochondral composition, structure, phenotype, and mechanical property, which validate the hypothesis of this study.

Engineering a multiphasic, integrated graft with a biologically developed cartilage-bone interface for osteochondral defect repair.

Tissue engineering is a promising approach to repair osteochondral defects, yet successful reconstruction of different layers in an integrated graft, especially the interface remains challenging. The multiphasic, functionally integrated tissue engineering graft described herein mimics the entire osteochondral tissue in terms of structure and composition at the cartilage, bone and cartilage-bone interface layer to repair osteochondral defects. In this manuscript, we report the fabrication of a multiphasic graft via bonding of a cartilaginous hydrogel and a sintered poly(lactic-co-glycolic acid) microsphere scaffold by an endogenous fibrotic cartilaginous extracellular matrix. We demonstrated that culturing chondrocytes within the alginate hydrogel conjugated to the poly(lactic-co-glycolic acid) scaffold allows for (i) gradient transition and integration from the cartilage layer to the subchondral bone layer as assessed by scanning electron microscopy, histology and biochemistry, and (ii) superior tissue repair efficacy in a rabbit knee defect model. Industrialization of the graft remains an unsolved challenge as after decellularization the tissue repair efficacy of the graft decreased. Taken together, the multiphasic osteochondral graft repaired the osteochondral defects successfully and has the potential to be applied clinically as an implant in orthopaedic surgery.

Recognition of plastic nanoparticles using a single gold nanopore fabricated at the tip of a glass nanopipette.

A single gold nanopore with high surface enhanced Raman spectroscopy (SERS) activity is fabricated on the tip of a glass nanopipette. Polystyrene (PS) nanospheres can be recognized from the SERS spectrum while passing through the single nanopore.

Decellularized orthopaedic tissue-engineered grafts: biomaterial scaffolds synthesised by therapeutic cells.

In orthopaedic surgery, the reconstruction of musculoskeletal defects is a constant challenge. Biomaterials in tissue engineering are utilized as scaffolds which serve as templates for cell proliferation and secretion as well as guides for new tissue formation. The extracellular matrix (ECM) is a desirable biological scaffold due to its complex composition and three-dimensional ultrastructure, which drive the homeostasis and regeneration of tissues. Successfully used in a variety of regenerative medicine applications, ECM scaffolds can be achieved by decellularization of engineered tissue. In addition to using decellularized grafts directly as scaffolds, decellularized grafts can also be coated on or incorporated into synthetic biomaterials to substantially enhance their biological performance regarding integration into the surrounding tissue and bioactivity for neo-tissue generation. However, at present, the most widely adopted decellularized scaffolds are decellularized native scaffolds, which have the limitations of inherent heterogeneity, fixed shapes and insufficient sources. Decellularized tissue-engineered scaffolds are promising to avoid these restrictions and are receiving attention in the regenerative medicine field. This review describes the rationale of using decellularized tissue-engineered grafts for different regenerative purposes and details their application in the repair of orthopaedic defects.