3D/4D printed bio-piezoelectric smart scaffolds for next-generation bone tissue engineering

Piezoelectricity in native bones has been well recognized as the key factor in bone regeneration.Thus,bio-piezoelectric materials have gained substantial attention in repairing damaged bone by mimicking the tissue’s electrical microenvironment(EM).However,traditional manufacturing strategies still encounter limitations in creating personalized bio-piezoelectric scaffolds,hindering their clinical applications.Three-dimensional(3D)/four-dimensional(4D)printing technology based on the principle of layer-by-layer forming and stacking of discrete materials has demonstrated outstanding advantages in fabricating bio-piezoelectric scaffolds in a more complex-shaped structure.Notably,4D printing functionality-shifting bio-piezoelectric scaffolds can provide a time-dependent programmable tissue EM in response to external stimuli for bone regeneration.In this review,we first summarize the physicochemical properties of commonly used bio-piezoelectric materials(including polymers,ceramics,and their composites)and representative biological findings for bone regeneration.Then,we discuss the latest research advances in the 3D printing of bio-piezoelectric scaffolds in terms of feedstock selection,printing process,induction strategies,and potential applications.Besides,some related challenges such as feedstock scalability,printing resolution,stress-to-polarization conversion efficiency,and non-invasive induction ability after implantation have been put forward.Finally,we highlight the potential of shape/property/functionality-shifting smart 4D bio-piezoelectric scaffolds in bone tissue engineering(BTE).Taken together,this review emphasizes the appealing utility of 3D/4D printed biological piezoelectric scaffolds as next-generation BTE implants.

Microstructure evolution and mechanical properties of Al_(2)O_(3)foams via laser powder bed fusion from Al particles

Laser powder bed fusion(LPBF)combined with reaction bonding(RB)of Al particles is an effective method for preparing high-performance 3D Al_(2)O_(3) ceramic foams.However,the indistinct microstructure evolution hinders the regulation of pore features and the improvement of synthetic properties.Herein,the microstructure evolution of the Al_(2)O_(3) ceramic foams during the LPBF/RB process is clarified by various characterization methods,and the corresponding mechanical property modulation is realized by optimizing LPBF parameters,organic binder(E12 epoxy resin)content,heating rate,sintering time,and coral-like Al_(2)O_(3) content.The expansion from Al_(2)O_(3) outward growth and Al granule precipitation counteracts the shrinkage from E12 decomposition and Al_(2)O_(3) sintering,resulting in an ultra-low shrinkage of 0.94%–3.01%.The pore structures of particle packing pores,hollow spheres,and microporous structures allow a tunable porosity of 52.6%–73.7%.The in-situ formation of multi-scale features including hollow spheres,flaky grains,whiskers,nanofibers,and bond bridges brings about a remarkably high bending strength of 6.5–38.3 MPa.Ourfindings reveal the relationship between microstructure evolution and property optimization of high-performance ceramic foams,with potential significance for microstructure design and practical application.

Advances in understanding the mechanisms of Arctic amplification

The near-surface temperatures in the Arctic are increasing at more than twice the global average rate,a phenomenon known as Arctic amplification(AA).In recent years,numerous studies using ground-based and satellite observations,along with model simulations,have explored the potential mechanisms behind AA,offering a variety of observational evidence and theoretical explanations.Although the understanding of AA drivers has improved,significant uncertainties remain in quantifying the contributions of different influential factors.On the basis of the latest research,this article thoroughly examines the factors driving rapid warming in the Arctic,including local feedbacks,atmospheric circulation,ocean currents,and aerosols,and compares quantitative results across studies.The analysis highlights the complex interplay of multiple factors contributing to AA,with no clear consensus on the relative contributions of each driver.Finally,the article underscores key challenges in current research,emphasizing the need for more reliable observational data,a deeper understanding of AA mechanisms,improved model parameterizations,and the disentanglement of interactions among driving factors,all of which are essential for future investigations.

气溶胶直接辐射强迫研究进展

近年来,气溶胶直接辐射强迫(aerosol direct radiative forcing,ADRF)的不确定性逐渐减少,但由于缺乏大范围、高精度气溶胶光学特征的观测,并且模式对气溶胶光学特性和物理化学过程的描述不够准确,ADRF的不确定性相比温室气体依然很大.本文首先回顾了气溶胶光学厚度(aerosol optical depth,AOD)和单次散射反照率(single scattering albedo,SSA)两种气溶胶光学特性及其相应ADRF时空分布的相关研究.AOD和SSA在不同的时空尺度上差异明显,在经济快速发展的地区(如印度),AOD呈现增长的趋势且平均值较高,而受环境保护政策影响的地区如北美和欧洲呈现下降的趋势且平均值较低.根据站点观测,大多数欧洲、北美洲、非洲和亚洲站点的SSA呈显著增长的趋势,而在生物质燃烧频繁或沙尘爆发的季节,部分地区如深秋和初春的华南和西南地区、春季的华北和西北地区,SSA会下降.未来在全球及大部分区域,随着气溶胶及其前体物排放的下降,ADRF也随之减弱,但减弱的趋势取决于各个区域的发展水平和发展路径.随后,本文系统总结了气溶胶光学特征如AOD、SSA、非对称因子(asymmetry factor,ASY)以及环境因素如地表反照率(surface albedo,SA)、气溶胶高度、气溶胶与云之间的相对位置、不同类型气溶胶之间的相对位置、太阳天顶角(solar zenith angle,SZA)等对ADRF的影响,并梳理了ADRF对不同影响因素的敏感性及不同影响因素对ADRF评估不确定性贡献的相关研究.研究发现,多数情况下SSA是ADRF不确定性最大的来源;而在污染严重的地区,SA和ASY造成的误差也不容忽视.最后,本文从观测和模式两个角度对提升ADRF评估的精确性作了简要展望.未来需要充分结合各种先进的观测和模式,如多角度、多(高)光谱、偏振的遥感观测、精细的原位测量和地球系统模式,获取更精确的气溶胶和环境信息,改进气溶胶及其前体物的模拟.随着对气溶胶与辐射相互作用机制理解的加深,以及相应观测技术和模式模拟能力的进步,ADRF的评估将更加精确.

Ultra-lightweight ceramic scaffolds with simultaneous improvement of pore interconnectivity and mechanical strength

The high porosity and interconnectivity of scaffolds are critical for nutrient transmission in bone tis-sue engineering but usually lead to poor mechanical properties.Herein,a novel method that combines acid etching(AE)with selective laser sintering(SLS)and reaction bonding(RB)of Al particles is pro-posed to realize highly improved porosity,interconnectivity,mechanical strength,and in vitro bioactivity in 3D Al_(2)O_(3) scaffolds.By controlling the oxidation and etching behaviors of Al particles,a tunable hol-low spherical feature can be obtained,which brings about the distinction in compressive response and fracture path.The prevention of microcrack propagation on the in situ formed hollow spheres results in unique near elastic buckling rather than traditional brittle fracture,allowing an unparalleled compressive strength of 3.72±0.17 MPa at a high porosity of 87.7%±0.4%and pore interconnectivity of 94.7%±0.4%.Furthermore,scaffolds with an optimized pore structure and superhydrophilic surface show excellent cell proliferation and adhesion properties.Our findings offer a promising strategy for the coexistence of out-standing mechanical and biological properties,with great potential for tissue engineering applications.

Development of Fe-Mn-Si-Cr-Ni shape memory alloy with ultrahigh mechanical properties and large recovery strain by laser powder bed fusion

This work systematically studied the effect of volumetric energy density E on the densification,mi-crostructures,tensile mechanical properties,and shape memory performance of a Fe-Mn-Si-Cr-Ni shape memory alloy(SMA)fabricated by laser powder bed fusion(L-PBF).An E of 90-265 J/mm3 is suggested to fabricate the Fe-Mn-Si-Cr-Ni SMA with minor metallurgical defects and a high relative density of above 99%.The increase in E can promote the formation of the primaryγaustenite and the solid phase trans-formation from the primaryδferrite to theγaustenite,which helps to achieve a nearly complete y austenitic microstructure.The increase in E also contributes to fabricating the Fe-Mn-Si-Cr-Ni SMA with superior comprehensive mechanical properties and shape memory performance by L-PBF.The Fe-Mn-Si-Cr-Ni SMA with a combination of good ductility of around 30%,high yield strength of above 480 MPa,an ultrahigh ultimate tensile strength of above 1 GPa,and large recovery strain of about 6%was manu-factured by L-PBF under a high E of 222-250 J/mm^(3).The good shape memory effect,excellent compre-hensive mechanical properties,and low cost of Fe-Mn-Si-Cr-Ni SMAs,as well as the outstanding ability to fabricate complex structures of L-PBF technology,provide a solid foundation for the design and fabri-cation of novel intelligent structures.