3D printing of tissue engineering scaffolds:a focus on vascular regeneration

Tissue engineering is an emerging means for resolving the problems of tissue repair and organ replacement in regenerative medicine.Insufficient supply of nutrients and oxygen to cells in large-scale tissues has led to the demand to prepare blood vessels.Scaffold-based tissue engineering approaches are effective methods to form new blood vessel tissues.The demand for blood vessels prompts systematic research on fabrication strategies of vascular scaffolds for tissue engineering.Recent advances in 3D printing have facilitated fabrication of vascular scaffolds,contributing to broad prospects for tissue vascularization.This review presents state of the art on modeling methods,print materials and preparation processes for fabrication of vascular scaffolds,and discusses the advantages and application fields of each method.Specially,significance and importance of scaffold-based tissue engineering for vascular regeneration are emphasized.Print materials and preparation processes are discussed in detail.And a focus is placed on preparation processes based on 3D printing technologies and traditional manufacturing technologies including casting,electrospinning,and Lego-like construction.And related studies are exemplified.Transformation of vascular scaffolds to clinical application is discussed.Also,four trends of 3D printing of tissue engineering vascular scaffolds are presented,including machine learning,near-infrared photopolymerization,4D printing,and combination of self-assembly and 3D printing-based methods.

Modelling of the In uence of Tool Runout on Surface Generation in Micro Milling

Micro milling is a flexible and economical method to fabricate micro components with three-dimensional geometry features over a wide range of engineering materials. But the surface roughness and micro topography always limit the performance of the machined micro components. This paper presents a surface generation simulation in micro end milling considering both axial and radial tool runout. Firstly, a surface generation model is established based on the geometry of micro milling cutter. Secondly, the influence of the runout in axial and radial directions on the surface generation are investigated and the surface roughness prediction is realized. It is found that the axial runout has a significant influence on the surface topography generation. Furthermore, the influence of axial runout on the surface micro topography was studied quantitatively, and a critical axial runout is given for variable feed per tooth to generate specific surface topography. Finally, the proposed model is validated by means of experiments and a good correlation is obtained. The proposed surface generation model o ers a basis for designing and optimizing surface parameters of functional machined surfaces.

Micro Model of Carbon Fiber/Cyanate Ester Composites and Analysis of Machining Damage Mechanism

Machining damage occurs on the surface of carbon fiber reinforced polymer (CFRP) composites during processing. In the current simulation model of CFRP, the initial defects on the carbon fiber and the periodic random distribution of the reinforcement phase in the matrix are not considered in detail, which makes the characteristics of the cutting model significantly different from the actual processing conditions. In this paper, a novel three-phase model of carbon fiber/cyanate ester composites is proposed to simulate the machining damage of the composites. The periodic random distribution of the carbon fiber reinforced phase in the matrix was realized using a double perturbation algorithm. To achieve the stochastic distribution of the strength of a single carbon fiber, a novel method that combines the Weibull intensity distribution theory with the Monte Carlo method is presented. The mechanical properties of the cyanate matrix were characterized by fitting the stress-strain curves, and the cohesive zone model was employed to simulate the interface. Based on the model, the machining damage mechanism of the composites was revealed using finite element simulations and by conducting a theoretical analysis. Furthermore, the milling surfaces of the composites were observed using a scanning electron microscope, to verify the accuracy of the simulation results. In this study, the simulations and theoretical analysis of the carbon fiber/cyanate ester composite processing were carried out based on a novel three-phase model, which revealed the material failure and machining damage mechanism more accurately.

Fabrication of Periodic Nanostructures Using AFM Tip-Based Nanomachining:Combining Groove and Material Pile-Up Topographies

This paper presents an atomic force microscopy(AFM)tip-based nanomachining method to fabricate periodic nanostructures.This method relies on combining the topography generated by machined grooves with the topography resulting from accumulated pile-up material on the side of these grooves.It is shown that controlling the distance between adjacent and parallel grooves is the key factor in ensuring the quality of the resulting nanostructures.The presented experimental data show that periodic patterns with good quality can be achieved when the feed value between adjacent scratching paths is equal to the width between the two peaks of material pile-up on the sides of a single groove.The quality of the periodicity of the obtained nanostructures is evaluated by applying one-and two-dimensional fast Fourier transform(FFT)algorithms.The ratio of the area of the peak part to the total area in the normalized amplitude–frequency characteristic diagram of the cross-section of the measured AFM image is employed to quantitatively analyze the periodic nanostructures.Finally,the optical effect induced by the use of machined periodic nanostructures for surface colorization is investigated for potential applications in the fields of anti-counterfeiting and metal sensing.

Epigenetic and transcriptional landscapes during cerebral cortex development in a microcephaly mouse model

The cerebral cortex is a pivotal structure integral to advanced brain functions within the mammalian central nervous system.DNA methylation and hydroxymethylation play important roles in regulating cerebral cortex development.However,it remains unclear whether abnormal cerebral cortex development,such as microcephaly,could rescale the epigenetic landscape,potentially contributing to dysregulated gene expression during brain development.In this study,we characterize and compare the DNA methylome/hydroxymethylome and transcriptome profiles of the cerebral cortex across several developmental stages in wild-type(WT)mice and Mcph1 knockout(Mcph1-del)mice with severe microcephaly.Intriguingly,we discover a global reduction of 5′-hydroxymethylcytosine(5hmC)level,primarily in TET1-binding regions,in Mcph1-del mice compared to WT mice during juvenile and adult stages.Notably,genes exhibiting diminished 5hmC levels and concurrently decreased expression are essential for neurodevelopment and brain functions.Additionally,genes displaying a delayed accumulation of 5hmC in Mcph1-del mice are significantly associated with the establishment and maintenance of the nervous system during the adult stage.These findings reveal that aberrant cerebral cortex development in the early stages profoundly alters the epigenetic regulation program,which provides unique insights into the molecular mechanisms underpinning diseases related to cerebral cortex development.

Bioscaffolds embedded with regulatory modules for cell growth and tissue formation:A review

The demand for artificial organs has greatly increased because of various aging-associated diseases and the wide need for organ transplants.A recent trend in tissue engineering is the precise reconstruction of tissues by the growth of cells adhering to bioscaffolds,which are three-dimensional(3D)structures that guide tissue and organ formation.Bioscaffolds used to fabricate bionic tissues should be able to not only guide cell growth but also regulate cell behaviors.Common regulation methods include biophysical and biochemical stimulations.Biophysical stimulation cues include matrix hardness,external stress and strain,surface topology,and electromagnetic field and concentration,whereas biochemical stimulation cues include growth factors,proteins,kinases,and magnetic nanoparticles.This review discusses bioink preparation,3D bioprinting(including extrusion-based,inkjet,and ultraviolet-assisted 3D bioprinting),and regulation of cell behaviors.In particular,it provides an overview of state-of-the-art methods and devices for regulating cell growth and tissue formation and the effects of biophysical and biochemical stimulations on cell behaviors.In addition,the fabrication of bioscaffolds embedded with regulatory modules for biomimetic tissue preparation is explained.Finally,challenges in cell growth regulation and future research directions are presented.

Experimental and modeling study of surface topography generation considering tool-workpiece vibration in high-precision turning

High-precision turning(HPT)is a main processing method for manufacturing rotary high-precision components,especially for metallic parts.However,the generated vibration between tool tip and workpiece during turning may seriously deteriorate the surface integrity.Therefore,exploring the effect of vibration on turning surface morphology and quality of copper parts using 3D surface topography regeneration model is crucial for predicting HPT performance.This developed model can update the machined surface topology in real time.In this study,the effects of tool arc radius,feed rate,radial vibration,axial vibration and tangential vibration on the surface topography and surface roughness were explored.The results show that the effect of radial vibration on surface topography is greater than that of axial vibration and tangential vibration.The radial vibration frequency is also critical.When vibration frequency changes,the surface topography profile presents three different types:the standard sinusoidal curve,the sinusoidal curve whose lowfrequency signal envelopes high-frequency signal,and the oscillation curve whose low-frequency signal superimposes high-frequency signal.In addition,HPT experiment was carried out to validate the developed model.The surface roughness obtained in the experiment was Ra=53 nm,while the roughness obtained by the simulation was Ra=46 nm,achieving a prediction accuracy of 86.7%.Received 4 September 2022;revised 3 October 2022;accepted 17 October 2022.

Bacterial diacetyl suppresses abiotic stress-induced senescence in Arabidopsis

Premature plant senescence induced by abiotic stresses is a major cause of agricultural losses worldwide. Tools for suppressing stress-induced plant senescence are limited. Here, we report that diacetyl, a natural compound emitted by the plantbeneficial bacterium Bacillus amyloliquefaciens,suppresses abscisic acid-mediated foliar senescence in Arabidopsis thaliana under various abiotic stress conditions. Our results establish diacetyl as an effective protector against stressinduced plant senescence and reveal a molecular mechanism for bacteria-enhanced plant stress resistance.

Field-scale spatial variability of soil calcium in a semi-arid region:Implications for soil erosion and site-specific management

Excess calcium(Ca)in soils of semi-arid and arid regions has negative effects on soil structure and chemical properties,which limits the crop root growth as well as the availability of soil water and nutrients.Quantifying the spatial variability of soil Ca contents may reveal factors influencing soil erosion and provide a basis for site-specific soil and crop management in semi-arid regions.This study sought to assess the spatial variability of soil Ca in relation to topography,hydraulic attributes,and soil types for precision soil and crop management in a 194-ha production field in the Southern High Plains of Texas,USA.Soils at four depth increments(0-2,0-15,15-30,and 30-60 cm)were sampled at 232 points in the spring of 2017.The Ca content of each sample was determined with a DP-6000 Delta Premium portable X-ray fluorescence(PXRF)spectrometer.Elevation data was obtained using a real-time kinematic GPS receiver with centimeter-level accuracy.A digital elevation model(DEM)was derived from the elevation data,and topographic and hydraulic attributes were generated from this DEM.A generalized least-squares model was then developed to assess the relationship between soil Ca contents of the four layers and the topographic and hydraulic attributes.Results showed that topographic attributes,especially slope and elevation,had a significant effect on soil Ca content at different depths(P<0.01).In addition,hydraulic attributes,especially flow length and sediment transport index(STI),had a significant effect on the spatial distribution of soil Ca.Spatial variability of soil Ca and its relationships with topographic and hydraulic attributes and soil types indicated that surface soil loss may occur due to water or wind erosion,especially on susceptible soils with high slopes.Therefore,this study suggests that the application of PXRF in assessing soil Ca content can potentially facilitate a new method for soil erosion evaluation in semi-arid lands.The results of this study provide valuable information for site-specific soil conservation and crop management.