All-Automated Fabrication of Freestanding and Scalable Photo-Thermoelectric Devices with High Performance.

Flexible photo-thermoelectric (PTE) devices have great application prospects in the fields of solar energy conversion, ultrabroadband light detection, etc. A suitable manufacturing process to avoid the substrate effects as well as to create a narrow transition area between p-n modules for high-performance freestanding flexible PTE devices is highly desired. Herein, an automated laser fabrication (ALF) method is reported to construct the PTE devices with rylene-diimide-doped n-type single-walled carbon nanotube (SWCNT) films. The wet-compressing approach is developed to improve the thermoelectric power factors and figure of merit (ZT) of the SWCNT hybrid films. Then, the films are cut and patterned automatically to make PTE devices with various structures by the proposed ALF method. The freestanding PTE device with a narrow transition area of ≈2-3 µm between the p and n modules exhibits a high-power density of 0.32 µW cm-2 under the light of 200 mW cm-2, which is among the highest level for freestanding-film-based PTE devices. The results pave the way for the automatic production process of PTE devices for green power generation and ultrabroadband light detection.

A mechanical and three-dimensional finite element study of the optimum tooth sectioning depth during the extraction of low-level horizontally impacted mandibular third molar.

The present study aims to determine the optimum sectioning depth for the extraction of low-level horizontally impacted mandibular third molar (LHIM3M) using mechanical and finite element analysis. One hundred and fifty extracted mandibular third molars were randomly divided into three groups: 1, 2 or 3 mm of tooth tissue was retained at the bottom of the crown. The breaking force of teeth was tested in a universal strength testing machine. The fracture surface was observed and the type of tooth breakage was recorded. According to the three groups, corresponding 3D finite element models were created. The breaking force obtained in the mechanical study was, respectively, applied and the stress and strain of the teeth and surrounding tissues were analysed. Breaking force decreased as sectioning depth increased. The 2 mm group produced the lowest rate of incomplete breakage (10%). In the 2 mm model, the stresses were evenly distributed in the tooth tissue at the bottom of the fissure, and the maximal stress was located in the tissue close to the root segment. The maximum values of stresses in the bone and of strains in the periodontal ligament of the second molar and bone were lower in the 1 mm model than in other models. Their distribution was similar in the three models. A sectioning depth of 1 mm group saves labour during the extraction of LHIM3M, compared to 2 and 3 mm; 2 mm might be the appropriate sectioning depth in terms of breakage shapes.

Densification Induced Decoupling of Electrical and Thermal Properties in Free-Standing MWCNT Films for Ultrahigh p- and n-Type Power Factors and Enhanced ZT.

Generating sufficient power from waste heat is one of the most important things for thermoelectric (TE) techniques in numerous practical applications. The output power density of an organic thermoelectric generator (OTEG) is proportional to the power factors (PFs) and the electrical conductivities of organic materials. However, it is still challenging to have high PFs over 1 mW m-1  K-2 in free-standing films together with high electrical conductivities over 1000 S cm-1 . Herein, densifying multi-walled carbon nanotube (MWCNT) films would increase their electrical conductivity dramatically up to over 10 000 S cm-1 with maintained high Seebeck coefficients >60 µV K-1 , thus leading to ultrahigh PFs of 7.25 and 4.34 mW m-1  K-2 for p- and n-type MWCNT films, respectively. In addition, it is interesting to notice that the electrical properties increase faster than the thermal conductivities, resulting in enhanced ZT of 3.6 times in MWCNT films. An OTEG made of compressed MWCNT films is fabricated to demonstrate the heat-to-electricity conversion ability, which exhibits a high areal output power of ∼12 times higher than that made of pristine MWCNT films. This work demonstrates an effective way to high-performance nanowire/nanoparticle-based TE materials such as printable TE materials comprised of nanowires/nanoparticles.

Multifunctional Filler-Free PEDOT:PSS Hydrogels with Ultrahigh Electrical Conductivity Induced by Lewis-Acid-Promoted Ion Exchange.

Highly conductive hydrogels with biotissue-like mechanical properties are of great interest in the emerging field of hydrogel bioelectronics due to their good biocompatibility, deformability, and stability. Fully polymeric hydrogels may exhibit comparable Young's modulus to biotissues. However, most of these filler-free hydrogels have a low electrical conductivity of <10 S cm-1 , which limits their wide applications of them in digital circuits or bioelectronic devices. In this work, a series of metal-halides-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hydrogels with an ultrahigh electrical conductivity up to 547 S cm-1 is reported, which is 1.5 times to 104 times higher than previously reported filler-free polymeric hydrogels. Theoretical calculation demonstrated that the ion exchange between PEDOT:PSS and the metal halides played an important role to promote phase separation in the hydrogels, which thus leads to ultrahigh electrical conductivity. The high electrical conductivity resulted in multifunctional hydrogels with high performance in thermoelectrics, electromagnetic shielding, Joule heating, and sensing. Such flexible and stretchable hydrogels with ultrahigh electrical conductivity and stability upon various deformations are promising for soft bioelectronics devices and wearable electronics.

Acid enhanced zipping effect to densify MWCNT packing for multifunctional MWCNT films with ultra-high electrical conductivity.

The outstanding electrical and mechanical properties remain elusive on macroscopic carbon nanotube (CNT) films because of the difficult material process, which limits their wide practical applications. Herein, we report high-performance multifunctional MWCNT films that possess the specific electrical conductivity of metals as well as high strength. These MWCNT films were synthesized by a floating chemical vapor deposition method, purified at high temperature and treated with concentrated HCl, and then densified due to the developed chlorosulfonic acid-enhanced zipping effect. These large scalable films exhibit high electromagnetic interference shielding efficiency, high thermoelectric power factor, and high ampacity because of the densely packed crystalline structure of MWCNTs, which are promising for practical applications.

The radiological and histological investigation of the dental follicle of asymptomatic impacted mandibular third molars.

OBJECTIVES: The indication for removal of asymptomatic fully impacted third molars is still controversial. In this study, radiological and histological investigation of the dental follicle of asymptomatic impacted mandibular third molars was performed, aiming to provide a reference for clinical prophylactic extraction of these teeth. METHODS: Patients with impacted mandibular third molars were included and the maximum width of the dental follicle around the crown was measured in horizontal, sagittal and coronal sections by cone beam computed tomography. The dental follicles were stained with haematoxylin-eosin, analysed by a pathologist and classified as normal, inflammatory or cystic. A Chi-squared test was used to analyse the association of the incidence of inflammation and cysts with the clinical variables of the impacted mandibular third molars. RESULTS: Thirty-seven samples were normal dental follicles; 52 samples showed inflammatory infiltration with an incidence of 57.14%; 2 samples with a maximum dental follicle width of 2-3 mm were diagnosed as odontogenic cysts, and the incidence was 2.20%. There was no significant difference in the incidence of inflammatory and cystic dental follicles between males and females, or between different age groups (P > 0.05). With an increase of the maximum width of the dental follicle, there was a rise in the incidence and degree of infiltration of chronic nonspecific inflammation. CONCLUSION: Asymptomatic impacted mandibular third molars tend to be extracted, especially for teeth with a 2-3 mm maximum width of the dental follicle on radiological examination.

Breakage and displacement of the high-speed hand-piece bur during impacted mandibular third molar extraction: three cases.

BACKGROUND: The high-speed hand-piece bur is one of the methods to perform tooth sectioning during the minimally traumatic extraction of impacted mandibular third molars. During tooth sectioning, the breakage of the bur might take place when it is improperly used. Three cases of the breakage and displacement of a high-speed hand-piece bur during extraction are reported, aiming to remind dental surgeons of this complication. CASE PRESENTATION: The bur fragment in case 1 was embedded in the mandibular bone under the previously removed crown of tooth 48 and distal to tooth 47. The bur fragment in case 2 was embedded in the lingual edge of the socket and partly beneath the mucosa on the lingual side. The position of the bur fragment in case 3 was similar to that of case 1 but was completely embedded in the spongious bone. The three cases were performed by first-year residents, and all of the bur fragments were successfully removed by attending doctors after accurately locating them by radiological examination. CONCLUSIONS: In order to avoid breakage of the high-speed hand-piece bur, the number of uses of the bur should be monitored and the integrity and state of the bur should be carefully checked. Moreover, light pressure with little lateral force should be used during tooth sectioning. If bur breakage and displacement occur, the retrieval protocol should be determined based on the imaging findings and conducted as soon as possible to avoid serious consequences.

Ultra-High Electrical Conductivity in Filler-Free Polymeric Hydrogels Toward Thermoelectrics and Electromagnetic Interference Shielding.

Conducting hydrogels have attracted much attention for the emerging field of hydrogel bioelectronics, especially poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) based hydrogels, because of their great biocompatibility and stability. However, the electrical conductivities of hydrogels are often lower than 1 S cm-1 which are not suitable for digital circuits or applications in bioelectronics. Introducing conductive inorganic fillers into the hydrogels can improve their electrical conductivities. However, it may lead to compromises in compliance, biocompatibility, deformability, biodegradability, etc. Herein, a series of highly conductive ionic liquid (IL) doped PEDOT:PSS hydrogels without any conductive fillers is reported. These hydrogels exhibit high conductivities up to ≈305 S cm-1 , which is ≈8 times higher than the record of polymeric hydrogels without conductive fillers in literature. The high electrical conductivity results in enhanced areal thermoelectric output power for hydrogel-based thermoelectric devices, and high specific electromagnetic interference (EMI) shielding efficiency which is about an order in magnitude higher than that of state-of-the-art conductive hydrogels in literature. Furthermore, these stretchable (strain >30%) hydrogels exhibit fast self-healing, and shape/size-tunable properties, which are desirable for hydrogel bioelectronics and wearable organic devices. The results indicate that these highly conductive hydrogels are promising in applications such as sensing, thermoelectrics, EMI shielding, etc.

Lateral Fully Organic P-N Diodes Created in a Single Donor-Acceptor Copolymer.

P-N junctions exist in many solid-state organic devices, such as light-emitting diodes, solar cells, and thermoelectric devices. Creating P-N junctions by bulk chemical doping in a single organic material (like silicon doped by boron and phosphorus) may capitalize the vast scientific and technological groundwork established in the inorganic semiconducting field. However, high-performance single-organic-material P-N junctions are seldom reported, because the diffusion of the dopant counterions often leads to transient rectification properties. Herein, a new type of lateral fully organic diodes created in single donor-acceptor (D-A) copolymer films with only one P-type dopant is reported. The achieved lateral devices exhibit high current densities of ≈3.83 A cm-2 and a high rectification ratio of ≈2100, which are beyond the requirements for high-frequency identification tags. The P- to N-type polarity switching mechanism is proposed after spectroscopic and structural tests. Decent stability of the organic diode is obtained, which is due to the long channel length and low diffusion speed of the large size of dopants. This work opens the opportunities to create P-N junctions in ways of silicon-based inorganic semiconductors and promises new opportunities for integrating organic materials for flexible and printable organic devices.

Functionalized starch as a novel eco-friendly vulcanization accelerator enhancing mechanical properties of natural rubber.

A novel eco-friendly vulcanization accelerator, starch supported sodium isobutyl xanthate (SSX) has been synthesized firstly. The modification of starch using sodium isobutyl xanthate (SIBX) has improved the thermal stability significantly, and the vulcanization process of natural rubber (NR) could be accelerated by SSX at 145 ℃ accordingly. More importantly, SSX can be dispersed into NR matrix uniformly along with the strong interfacial interaction between SSX and NR, as evidenced by the constrained rubber chains around SSX surface. In addition, mechanical properties of the obtained NR have been enhanced remarkably, showing a 22.4 % increase in tensile strength when compared with traditional vulcanization accelerator. Laying on the fact that a novel vulcanization accelerator has been fabricated successfully using SIBX functionalized starch, new strategies for the preparation of green vulcanization accelerators and the functional application of biopolymers can be provided.