Three/Four-Dimensional Printed PLA Nano/Microstructures: Crystallization Principles and Practical Applications.

Compared to traditional methods, three/four-dimensional (3D/4D) printing technologies allow rapid prototyping and mass customization, which are ideal for preparing nano/microstructures of soft polymer materials. Poly (lactic acid) (PLA) is a biopolymer material widely used in additive manufacturing (AM) because of its biocompatibility and biodegradability. Unfortunately, owing to its intrinsically poor nucleation ability, a PLA product is usually in an amorphous state after industrial processing, leading to some undesirable properties such as a barrier property and low thermal resistance. Crystallization mediation offers a most practical way to improve the properties of PLA products. Herein, we summarize and discuss 3D/4D printing technologies in the processing of PLA nano/microstructures, focusing on crystallization principles and practical applications including bio-inspired structures, flexible electronics and biomedical engineering mainly reported in the last five years. Moreover, the challenges and prospects of 3D/4D printing technologies in the fabrication of high-performance PLA materials nano/microstructures will also be discussed.

Cleaning the palate and tongue without nausea: a mixed methods study exploring the appropriate depth and direction of oral care.

BACKGROUND: It is advisable to clean the palate and tongue thoroughly during oral care to protect against nosocomial infections. However, improper cleaning may cause nausea. To date, no robust data are available regarding how to implement this procedure properly. Furthermore, traditional cotton balls, forceps and normal saline are still used in clinical in China. This mixed methods study aimed to explore the appropriate depth and direction of cleaning methods for palates and tongues without causing nausea and the factors influencing cleaning depth and discomfort in traditional oral care. METHODS: Our study recruited students (n = 276) from a medical university. The first phase was a quantitative study, in which forceps were slowly inserted into their throats until the gag reflex was triggered, and then, the insertion depth was measured. After that, participants were randomly divided into two groups. In group A, palates and tongues were cleaned coronally and then sagittally, with the converse order used for group B. The extent of nausea was measured. Additionally, the qualitative data were types of discomfort other than nausea reported by the participants. RESULTS: The tolerable depths (without causing nausea) for cleaning the palate and tongue were 6.75 ± 1.07 cm and 6.92 ± 1.11 cm, respectively. Participants of male sex and with high BMI (overweight/obese) were associated with greater tolerable cleaning depth. The extent of nausea caused by cleaning both the palate and the tongue sagittally was higher than that elicited by coronal cleaning (p = 0.025 and p = 0.003, respectively). Other discomforts included itching, saltiness and coldness. CONCLUSION: It is appropriate to increase the cleaning depth of the palate and tongue for adult males and overweight/obese individuals. Moreover, coronal cleaning causes lower levels of nausea, and traditional oral care appliances should be improved.

G-Quadruplex DNA with an Apurinic Site as a Soft Molecularly Imprinted Sensing Platform.

Molecularly imprinted polymers (MIPs) provide versatile sensor platforms to recognize targets by shape complementarity. However, the rigid structure of the classic MIPs compromises the signal transduction with necessary polymer and target modifications. Herein, we tried to use a flexible DNA that has a perfectly structured folding as the soft molecularly imprinted polymer (SMIP) for a straightforward sensor. As a proof of concept, the guanosine SMIP recognition was achieved by removal of a guanosine from a G-quadruplex-forming sequence (G4). The G4 folding structure with such an apurinic site (AP site) provides a well-defined MIP binding accommodation for guanosine according to the shape complementarity. The guanosine binding at the AP site subsequently leads to a conformation change suitable for remote readout using a G4-specific fluorescent ligand. The G4 sequence and AP site position were optimized for this SMIP behavior. Due to the G4 compact structure and the remaining hydrogen bonding pattern, nucleosides other than guanosine and negatively charged nucleotides exhibit no binding with the AP site, suggesting a high selectivity in the SMIP recognition. The proposed rationale was then convinced by the alkaline phosphatase-catalyzed GMP hydrolysis. Our work will inspire more interest in exploring nucleic acids as the SMIP frameworks due to their variant conformations and well-established molecular engineering.

Thermo Sensitivity of Polysiloxane/Silica Nanocomposites Affected by the Structure of Polymer-Filler Interface.

In this work thermo sensitivity was investigated with the bound rubber theory and thermoelasticity theory of the polymer-filler interface interaction between Polymethylvinylsiloxane (PMVS) and nanofillers (fumed and precipitated silica with the primary particle size of 10 nanometres). Bound rubber (the transition phase between PMVS and silica) content was measured by sol-gel analysis and swelling experiments. Results showed that the amount of bound rubber increases steadily with the increases of filler content. But the increasing rate suddenly decreased at certain silica content (between 40 and 50 phr of precipitated silica and between 30 and 40 phr of fumed silica, respectively), which was constant with the thermoelaticity experiment results. The temperature coefficients in low strain uniaxial extension are found to present sudden changing at the same silica content. This observation shows that thermo sensitivity is closely connected with the structure of polymer-filler interface.

Enhanced catalytic activity and stability of lactate dehydrogenase for cascade catalysis of D-PLA by rational design.

Serving as a vital medical intermediate and an environmentally-friendly preservative, D-PLA exhibits substantial potential across various industries. In this report, the urgent need for efficient production motivated us to achieve the rational design of lactate dehydrogenase and enhance catalytic efficiency. Surprisingly, the enzymatic properties revealed that a mutant enzyme, LrLDHT247I/D249A/F306W/A214Y (LrLDH-M1), had a viable catalytic advantage. It demonstrated a 3.3-fold increase in specific enzyme activity and approximately a 2.08-fold improvement of Kcat. Correspondingly, molecular docking analysis provided a supporting explanation for the lower Km and higher Kcat/Km of the mutant enzyme. Thermostability analysis exhibited increased half-lives and the deactivation rate constants decreased at different temperatures (1.47-2.26-fold). In addition, the mutant showed excellent resistance abilities in harsh environments, particularly under acidic conditions. Then, a two-bacterium (E. coli/pET28a-lrldh-M1 and E. coli/pET28a-ladd) coupled catalytic system was developed and realized a significant conversion rate (77.7%) of D-phenyllactic acid, using 10 g/L L-phenylalanine as the substrate in a two-step cascade reaction.

Mechanical properties and osteoblast proliferation of complex porous dental implants filled with magnesium alloy based on 3D printing.

In this paper, a complex porous dental implant with biodegradable magnesium alloy was designed based on selective laser melting (SLM). Finite element analysis (FEA) was used to simulate the stress distribution of dental implant and alveolar bone in two models of preliminary and later stages of implant. The stress concentration area of dental implants was found not in the porous structure, and the weak part of mechanical properties accords with the work requirements. The porous structure of dental implants can promote the function of cancellous bone in the process of conducting the stress of the dental implant, thus improving the bearing capacity of dental implants. In vitro fatigue experiments were carried out on the experimental samples produced by 3D printing. Through the cell contrast experiment, it was proved that the decomposed Mg2+ could reach the titanium surface smoothly through the porous structure and complete the proliferation of osteoblasts.

Study on statics and fatigue analysis of dental implants in the descending process of alveolar bone level.

Alveolar bone atrophy can directly cause a decrease in bone level. The effect of this process on the service life of dental implants is unknown. The aim of this study was to determine the failure forms of the two-piece dental implants in the descending process of alveolar bone level, and the specific states of the components during the failure process. The CAD software SolidWorks was used to establish the model of alveolar bone and dental implants in this article. The finite element analysis was used to analyze the statics of the dental implants in the host oral model. The finite element analysis results showed that the stress concentration point of the implant and abutment in the implant system has changed greatly during the descending process of alveolar bone level, and indirectly increased the fatigue life of the same fatigue risk point. At the same time, the dental implants were tested in vitro in the descending process of alveolar bone level. Then, the fracture of the implant system was scanned by scanning electron microscope. The fatigue test results proved the finite element analysis hypothesis the central screw first fractured under fatigue and then caused an overload break of the implant and abutment.

High-intensity focused ultrasound ablation around the tubing.

High-intensity focused ultrasound (HIFU) has been emerging as an effective and noninvasive modality in cancer treatment with very promising clinical results. However, a small vessel in the focal region could be ruptured, which is an important concern for the safety of HIFU ablation. In this study, lesion formation in the polyacrylamide gel phantom embedded with different tubing (inner diameters of 0.76 mm and 3 mm) at varied flow speeds (17-339 cm/s) by HIFU ablation was photographically recorded. Produced lesions have decreased length (~30%) but slightly increased width (~6%) in comparison to that without the embedded tubing. Meanwhile, bubble activities during the exposures were measured by passive cavitation detection (PCD) at the varied pulse repetition frequency (PRF, 10-30 Hz) and duty cycle (DC, 10%-20%) of the HIFU bursts. High DC and low flow speed were found to produce stronger bubble cavitation whereas no significant influence of the PRF. In addition, high-speed photography illustrated that the rupture of tubing was produced consistently after the first HIFU burst within 20 ms and then multiple bubbles would penetrate into the intraluminal space of tubing through the rupture site by the acoustic radiation force. Alignment of HIFU focus to the anterior surface, middle, and posterior surface of tubing led to different characteristics of vessel rupture and bubble introduction. In summary, HIFU-induced vessel rupture is possible as shown in this phantom study; produced lesion sizes and shapes are dependent on the focus alignment to the tubing, flow speed, and tubing properties; and bubble cavitation and the formation liquid jet may be one of the major mechanisms of tubing rupture as shown in the high-speed photography.

Targeted long-term venous occlusion using pulsed high-intensity focused ultrasound combined with a pro-inflammatory agent.

Esophageal and gastric varices are associated with significant morbidity and mortality for cirrhotic patients. The current modalities available for treating bleeding esophageal and gastric varices, namely endoscopic band ligation and sclerotherapy, require frequent sessions to obtain effective thrombosis and are associated with significant adverse effects. A more effective therapy that results in long-term vascular occlusion has the potential to improve patient outcomes. In this study, we investigated a new potential method for inducing long-term vascular occlusion by targeting segments of a rabbit's auricular vein in vivo with low-duty-cycle, high-peak-rarefaction pressure (9 MPa), pulsed high-intensity focused ultrasound in the presence of intravenously administered ultrasound microbubbles followed by local injection of fibrinogen and a pro-inflammatory agent (ethanol, cyanoacrylate or morrhuate sodium). The novel method introduced in this study resulted in acute and long-term complete vascular occlusions when injecting a pro-inflammatory agent with fibrinogen. Future investigation and translational studies are needed to assess its clinical applicability.