Coking-Resistant Polyethylene Upcycling Modulated by Zeolite Micropore Diffusion.

Although the mass production of synthetic plastics has transformed human lives, it has resulted in waste accumulation on the earth. Here, we report a low-temperature conversion of polyethylene into olefins. By mixing the polyethylene feed with rationally designed ZSM-5 zeolite nanosheets at 280 °C in flowing hydrogen as a carrier gas, light hydrocarbons (C1-C7) were produced with a yield of up to 74.6%, where 83.9% of these products were C3-C6 olefins with almost undetectable coke formation. The reaction proceeds in multiple steps, including polyethylene melting, flowing to access the zeolite surface, cracking on the zeolite surface, formation of intermediates to diffuse into the zeolite micropores, and cracking into small molecules in the zeolite micropores. The ZSM-5 zeolite nanosheets kinetically matched the cascade cracking steps on the zeolite external surface and within micropores by boosting the intermediate diffusion. This feature efficiently suppressed the intermediate accumulation on the zeolite surface to minimize coke formation. In addition, we found that hydrogen participation in the cracking process could hinder the formation of polycyclic species within zeolite micropores, which also contributes to the rapid molecule diffusion. The coking-resistant polyethylene upcycling process at a low temperature not only overturns the general viewpoint for facile coke formation in the catalytic cracking over the zeolites but also demonstrates how the polyethylene-based plastics can be upcycled to valuable chemicals. In addition to the model polyethylene, the reaction system worked efficiently for the depolymerization of multiple practically used polyethylene-rich plastics, enabling an industrially and economically viable path for dealing with plastic wastes.

Effect of nonionic surfactant Brij 35 on morphology, cloud point, and pigment stability in Monascus extractive fermentation.

BACKGROUND: Nonionic surfactant Brij 35 in submerged fermentation of Monascus can significantly increase Monascus pigment yield. Here, the effects of nonionic surfactant Brij 35 on Monascus pigment secretion in extractive fermentation are discussed in terms of cell morphology, cloud point change, and pigment stability. RESULTS: At Brij 35 concentrations up to 32 g L-1 , the higher concentrations led to the loosening of the network structure on the surface of the fungal wall, enhanced cell wall permeability, and increased abundance of lipid droplets. Alternatively, when the concentration of Brij 35 exceeded 32 g L-1 , a large amount of substances accumulated on the surface of the fungal wall, permeability reduced, and the degree of oil droplet dispersion in cells decreased. Further, during extractive fermentation, Brij 35 induced formation of a grid structure on the fungal wall surface beginning on day 2, increased the number of intracellular lipid droplets, and promoted intracellular pigment secretion into the extracellular environment. When the cloud point temperature in the fermentation system approached that of fermentation, the nonionic surfactant exhibited stronger Monascus pigment extraction capacity, thereby enhancing pigment yield. Hence, Brij 35 can improve pigment stability and effectively reduce damage caused by natural factors, such as light and temperature. CONCLUSION: Brij 35 promotes the secretion of pigment by changing the fungal wall structure and cloud point, as well as by improving pigment stability. © 2020 Society of Chemical Industry.

Analysis of friction between articular cartilage and polyvinyl alcohol hydrogel artificial cartilage.

Many biomaterials are being used to repair damaged articular cartilage. In particular, poly vinyl alcohol hydrogel has similar mechanical properties to natural cartilage under compressive and shearing loading. Here, three-factor and two-level friction experiments and long-term tests were conducted to better evaluate its tribological properties. The friction coefficient between articular cartilage and the poly vinyl alcohol hydrogel depended primarily on the three factors of load, speed, and lubrication. When the speed increased from 10 to 20 mm/s under a load of 10 N, the friction coefficient increased from 0.12 to 0.147. When the lubricant was changed from Ringer's solution to a hyaluronic acid solution, the friction coefficient decreased to 0.084 with loads as high as 22 N. The poly vinyl alcohol hydrogel was severely damaged and lost its top surface layers, which were transferred to the articular cartilage surface. Wear was observed in the surface morphologies, which indicated the occurrence of surface adhesion of bovine cartilage. Surface fatigue and adhesive wear was the dominant wear mechanism.

Bionanomaterials based on protein self-assembly: Design and applications in biotechnology.

Elegant protein assembly to generate new biomaterials undergoes extremely rapid development for wide extension of biotechnology applications, which can be a powerful tool not only for creating nanomaterials but also for advancing understanding of the structure of life. Unique biological properties of proteins bestow these artificial biomaterials diverse functions that can permit them to be applied in encapsulation, bioimaging, biocatalysis, biosensors, photosynthetic apparatus, electron transport, magnetogenetic applications, vaccine development and antibodies design. This review gives a perspective view of the latest advances in the construction of protein-based nanomaterials. We initially start with distinguishable, specific interactions to construct sundry nanomaterials through protein self-assembly and concisely expound the assembly mechanism from the design strategy. And then, the design and construction of 0D, 1D, 2D, 3D protein assembled nanomaterials are especially highlighted. Furthermore, the potential applications have been discussed in detail. Overall, this review will illustrate how to fabricate highly sophisticated nanomaterials oriented toward applications in biotechnology based on the rules of supramolecular chemistry.

Influence of dynamic load on friction behavior of human articular cartilage, stainless steel and polyvinyl alcohol hydrogel as artificial cartilage.

Many biomaterials are being developed to be used for cartilage substitution and hemiarthroplasty implants. The lubrication property is a key feature of the artificial cartilage. The frictional behavior of human articular cartilage, stainless steel and polyvinyl alcohol (PVA) hydrogel were investigated under cartilage-on-PVA hydrogel contact, cartilage-on-cartilage contact and cartilage-on-stainless steel contact using pin-on-plate method. Tests under static load, cyclic load and 1 min load change were used to evaluate friction variations in reciprocating motion. The results showed that the lubrication property of cartilage-on-PVA hydrogel contact and cartilage-on-stainless steel contact were restored in both 1 min load change and cyclic load tests. The friction coefficient of PVA hydrogel decreased from 0.178 to 0.076 in 60 min, which was almost one-third of the value under static load in continuous sliding tests. In each test, the friction coefficient of cartilage-on-cartilage contact maintained far lower value than other contacts. It is indicated that a key feature of artificial cartilage is the biphasic lubrication properties.

[Evaluating thrombolytic efficacy and thrombus targetability of RGDS-liposomes encapsulating subtilisin FS33 in vivo].

A novel fibrinolytic enzyme subtilisin FS33, which exhibits much higher activity for decomposing fibrin than urokinase, was purified from Douchi, a traditional soybean-fermented food in China. In order to increase bio-utilization and thrombus targetability of subtilisin FS33 labeled by fluorescein isothiocyanate (FITC), the surface modified liposomes encapsulating subtilisin FS33 and FITC with a synthetic peptide Arg-Gly-Asp-Ser (RGDS), being putatively a specific antagonist of fibrinogen receptor on platelet membrane, were prepared and used to evaluate the therapeutic efficacy in a rat model thrombotic carotid artery. The arterial thrombosis was induced by applying two pieces of filter paper (1 x 2 cm) saturated with 10% of ferric chloride (FeCl3). The rats were infused via the jugular vein with either liposomes carrying BSA (control group) or RGDS-liposomes carrying subtilisin FS33 at doses of 2000 and 4000 U/kg. The plasma of the group infused with RGDS-liposomes showed higher antithrombotic and fibrinolytic activity than did the control group within 15-120 min after infusing. The higher the dose was gived, the higher the activity was shown. APTT(activiated partial thromboplastin time), PT (prothrombin time) and TT (thrombin time) were extended remarkably (P < 0.05, P < 0.01), and FDP (fibrinogen degradation products) also increased greatly (P < 0.01), while ELT (euglobulinlysis time) decreased obviously (P < 0.05). FITC content in heart and brain evidently increased (P < 0.05), and results of D-dimer test were all positive. In addition, the venous thrombi in brain and kidney were dissolved totally or partly as observed by patholgical section. All these indicated that subtilisin FS33 enhanced the antithrombotic and fibrinolytic activities in rat, and RGDS-liposomes improved, in a certain degree, the thrombolytic specificity for targeting to thrombus.

Biomechanical analysis of rapid maxillary expansion in the UCLP patient.

This study was designed to investigate the biomechanical effects of rapid maxillary expansion (RME) in the patient with unilateral cleft lip and palate (UCLP). A finite element model of a patient's craniofacial complex with UCLP was created using data from spiral computed tomographic (CT) scanning. A transversal displacement with a magnitude of 5mm was applied on the maxillary premolar and first permanent molar crown of the model simulating the clinical situation. The stress and deformation within the craniofacial complex were then calculated and analyzed during 0.25- and 5-mm expansions. The corresponding orthodontic forces on each loaded tooth were also calculated. Obtained results revealed the biomechanical performance of the craniofacial complex with UCLP undergoing RME, including the distribution pattern of the stress and displacement, the transmission and dissipation of the orthodontic force, the stress level and the magnitude of the orthodontic force. All these findings could help us better comprehend the biomechanical mechanism of RME in the UCLP patient and provided theoretic data for optimizing surgical assisted RME in clinic.

Degradation of anthocyanins and polymeric color formation during heat treatment of purple sweet potato extract at different pH.

Purple sweet potato anthocyanins are common natural pigments widely used in food industry, while they are often thermally processed in application. Degradation of anthocyanins, formation of polymers and color changes of purple sweet potato extract (PSPE) were investigated at 90 °C in the range of pH 3.0-pH 7.0. Data analysis indicated a first-order reaction for anthocyanins degradation in solutions with pH 3.0, 5.0 and 7.0 have half-lives of 10.27, 12.42 and 4.66 h, respectively. The polymeric color formation followed zero-order kinetics, progressively increasing with pH values. The color of PSPE were changed with heating time and pH value through visual observation and colorimetric characterization. Analysis by UV-Vis spectrophotometry and HPLC indicated that anthocyanins in solution with pH 3.0 changed from monomeric anthocyanin into new polymers during heat treatment. Degradation of anthocyanins was accompanied by an increase in polymeric color index, due to the formation of melanoidin pigments and condensation reactions.

[Bionic design of articular cartilage].

Natural articular cartilage is well known as a special connective tissue with multiple effects and functions, which are important and irreplaceable, in human synovial joints. Biomedical, histological and pathological characteristics of articular cartilage, as well as biomaterial, biomechanical and bio-tribological properties thereof, are summarized from a novel aspect of bionics. Bionic design of articualr cartilage at macro-level and micro-level is carried out from three aspects, i.e., structure, material, and function; and a bionic design model of articular cartilage is set up. As a result, this basic research would be helpful to providing theoretical and practical basis for innovational design and manufacturing of new-style artificial joint with "soft-cushion bearing", and of bionic artificial cartilage.

[Research on the development of image guided oral implant system].

In this paper is introduced an image guided oral implant system (IGOIS), including the 3D surface-model generation through Marching Cubes algorithm and large-scale triangular mesh simplification, the realization of pre-operative planning module with computer graphics and image processing technology, the non-invasive point-to-point registration with the fabrication of tooth-supported polymer resin templates and ICP algorithm, and the development of the real-time navigation system software by programming in VTK and VC+ +6.0. The experimental test for a patient's rapid prototype model shows that with the support of IGOIS, the precision achieved in the planning phase can be transferred to the patient so that the accuracy of the oral implant surgery under difficult conditions is improved.

[A mathematical model of 3-dimensional excursive movement of the mandible on Hanau articulator].

Aiming at filling the vacancy in the study about mandibular movement, which mainly focuses on the field of biology at present, this study builds a mathematical model of 3-dimensional excursive movement of the mandible on Hanau articulator from the viewpoint of spatial mechanisms and analytical geometry. On the basis of the theory of spatial mechanisms, the freedom of motion of Hanau articulator is analyzed, and a hypothesis of constraints is presented, the objective of which is to restrict the mandibular movement. Based on the theory of analytical geometry, a series of mathematical expressions are derived to describe the 3-dimensional movement of the mandible mounted on the articulator. With the geometrical parameters of the articulator, these mathematical equations are solved by programming in Matlab 6.5 (a language for technical computing) and VC + +6.0. Therefore, the spatial path of the arbitrary point on the mandible can be precisely described when the upper body of Hanau articulator is guided along a specific direction. This study proves that the included angle between the plane of orientation and occlusal plane is positively related to the inclination of condylar guidance and incisal guidance, therefore, provides a theoretical foundation for Hanau's laws of articulation and the Hanau Quint. The future of dentistry is basically connected with the use of computer technology. This study will be useful for the further research of the dynamic occlusion to improve dental restorative procedures by realizing future replacement of the mechanical articulator with a virtual one.

[Design and biomechanical evaluation of obturator prostheses with removable partial denture].

The closed palate and obturator prostheses with bar clasp and attachment retention were designed and modeled for repairing the unilateral defect maxillary, and then they were analyzed using finite element method. Under simulated muscle restriction and masticating force boundary, the strength of four maxillary prostheses, the attachment, base plate, bar clasp, denture, obturator et cetera, were considered, and the stress dimension and tendency of the rest living teeth and prostheses were studied. According to the studies on stress, the optimized structure and biomechanical evaluation have a role in the repairs to maxillary defect. The results of analysis are as follows: The stresses of each part of the prostheses were all in the strength range of the materials. The stress distribution on the rest living teeth and alveolar bone was reasonable; the biting force was effectively transferred by the prostheses. As to the obturator prostheses, the materials properties were similar to those of alveolar bone or a bit lower than those, and the obturator structure filled in the cavum of maxillary bone to increase the touch area in the structure was more reasonable than the palate closed structure. The stress and displacement results of living teeth showed that the attachment retention and obturator prostheses could avoid the stress concentration on living teeth and could benefit the retention and power support.

[A rapid prototype fabrication method of dental splint based on 3D simulation and technology].

The conventional design and fabrication of the dental splint (in orthognathic surgery) is based on the preoperative planning and model surgery so this process is of low precision and efficiency. In order to solve the problems and be up to the trend of computer-assisted surgery, we have developed a novel method to design and fabricate the dental splint--computer-generated dental splint, which is based on three-dimensional model simulation and rapid prototype technology. After the surgical planning and simulation of 3D model, we can modify the model to be superior in chewing action (functional) and overall facial appearance (aesthetic). Then, through the Boolean operation of the dental splint blank and the maxillofacial bone model the model of dental splint is formed. At last, the dental splint model is fabricated through rapid prototype machine and applied in clinic. The result indicates that, with the use of this method, the surgical precision and efficiency are improved.

[Study of biomechanical effects on the reconstruction of mandible defect with autogenous bone grafts].

The biomechanical effects of the reconstructed mandible with autogenous bone grafts were analyzed and evaluated, under simulated mechanical environment of occlusion. Based on anatomical feature of the human skeleton, muscle system and the clinical B, BS"S" and RB"S"defect patterns, the modularized model of mandible and the three finite element models of the fibula grafts and iliac crest grafts reconstruction mandible were made. The stress state calculations under bite force were also processed. The findings are as follows: Along the right connection area to left connection area (corresponding to far-end of the molar teeth alveolar ridge and the chin section respectively), the stress state on the various grafted bone all changes from compression stress to tensile stress. There is obvious change on the stress distribution between the fibula type reconstruction mandible and normal one. The stress on the grafted bone which is mainly made up of cortical bone is approximately 5 times higher than that of normal, which indicates the obvious stress shielding effect; the stress distribution of the iliac crest type reconstruction mandible is close to the normal mandible, the iliac crest used is mainly made up of cancellous. Therefore, the mechanical properties of the reconstructed mandible with iliac crest are more similar to normal mandible, which is beneficial to wound healing and further functional reconstruction.

[Digital geometry processing and its applications in maxilla and mandible reconstruction surgery].

A new method to fabricate exact-fit medical implants is proposed. Medical image processing and digital geometry processing are adopted for bone triangular mesh modeling from CT image series. After geometric operations such as decimation, defragmentation, cutting and mirroring are applied to the original triangular mesh, an RP model of same size as the bone is fabricated with LOM method. RP models are used for manufacturing exact-fit implants and they also serve surgery-guiding purpose. This novel technique has been applied in over 30 clinical cases, and it is proven to be practicable.

[Rolling friction: a desing of artificial knee joint].

Resorption and osteolysis of periimplant bones resulting from the wear debris of artificial joint will cause long-term loosening. A new type of rolling knee artificial joint without UHMWPE based on the mechanics of rolling friction is designed for alleviating this problem. Because of low friction force, the resistance of extension and flexion is reduced strikingly and the stress on the interface between prosthesis and bone is reduced evidently. In addition, the bio-toxicity caused by the wear debris of UHMWPE will not occur absolutely. In consequence, the rolling artificial joint can prevent the trend of long-term loosening of the prosthesis efficiently.

[Three-dimensional finite element analysis of the biomechanical effects of multiloop edgewise archwire (MEAW)].

This study is designed to theoretically evaluate the treatment effects of MEAW with tip back bends on the mandible dentition when used as a finishing archwire without elastic and with long class III elastics respectively, and to compare them with those of stainless-steel wire and shape-memory wire. The finite element analysis (FEA) method was adopted and the findings were as follows: (1) In the case of no elastics, the MEAW rotates the second premolar, the first molar and the second molar distally while rotating other teeth mesially, and depresses anterior teeth. However, the stainless-steel wire and the shape-memory wire rotate molars distally while rotating other teeth mesially. Furthermore, they extrude anterior teeth and depress posterior teeth. (2) The MEAW with tip back bends and long class III elastics inclines and rotates posterior teeth more distally than the MEAW with only tip back bends does. In the case of tip back bends and long class III elastics loaded together, the shape-memory wire inclines teeth in greater strength as compared with the stainless-steel wire. (3) The stress level of tooth root is the lowest with MEAW, the highest with stainless-steel wire, and is middle with the shape-memory wire. From these results, it is suggested that: (1) The MEAW therapy technique is effective for leveling the curve of Spee and regulating tooth respectively. (2) The MEAW therapy technique can transfer therapy force efficiently. (3) The MEAW is considered to be suitable for treating openbite malocclusion to make the posterior teeth upright because it effectively rotates teeth distally through the force of posterior bends and long class III elastics. (4) The loaded force on the teeth is more soft and permanent in the MEAW than in the stainless-steel wire and the shape-memory wire.

[Fabricating facial prostheses using CAD/CAM and rapid prototyping technique].

At present, the treatments of hemifacial microsomia such as the missing of ear and eye still rely on the skill of technician to make the wax model of contralateral apparatus of patient in China. In this paper, CAD/CAM and rapid prototyping (RP) techniques are integrated to successfully create a silastic prosthesis by using the patient's data of CT or laser scanning. The clinical results suggest that a high accuracy has been achieved in shape, size, and protrusion of the facial prostheses, which indicates that the application of RP techniques in conjunction with CAD/CAM is a suitable approach for fabricating facial prosthesis.

[Study on the 3D mathematical mode of the muscle groups applied to human mandible by a linear programming method].

Four types of 3D mathematical mode of the muscle groups applied to the human mandible have been developed. One is based on electromyography (EMG) and the others are based on linear programming with different objective function. Each model contains 26 muscle forces and two joint forces, allowing simulation of static bite forces and concomitant joint reaction forces for various bite point locations and mandibular positions. In this paper, the method of image processing to measure the position and direction of muscle forces according to 3D CAD model was built with CT data. Matlab optimization toolbox is applied to solve the three modes based on linear programming. Results show that the model with an objective function requiring a minimum sum of the tensions in the muscles is reasonable and agrees very well with the normal physiology activity.

A virtual training system for maxillofacial surgery using advanced haptic feedback and immersive workbench.

BACKGROUND: VR-based surgery simulation provides a cost-effective and efficient method to train novices. In this study, a virtual training system for maxillofacial surgery (VR-MFS), which aims mainly at the simulation of operations on mandible and maxilla, was developed and demonstrated. METHODS: The virtual models of the anatomic structures were reconstructed from CT data, and the virtual instruments were built from laser scanning data using reverse engineering technology. For collision detection, axis aligned bounding boxes (AABBs) were constructed for the anatomic models. Then, the simulation algorithms were developed, and the haptic force feedback was consequently calculated based on regression equations. Finally, the vivid 3D stereo effect was implemented with the use of an immersive workbench. RESULTS: A virtual training system for maxillofacial surgery was developed; in particular, the application for Le-Fort I osteotomy was implemented. The tactile, visual and aural effects were highly integrated, making the virtual surgical environment vivid and realistic. CONCLUSIONS: The VR-MFS provides an effective approach in terms of helping novices to become familiar with maxillofacial surgery procedures. The same method can also be applied to other bone simulations.