An oil-impregnated porous polyimide(PI)retainer is used in space rolling bearings to improve the lubrication performance,which depends on the release of lubricant from the pores,and therefore is closely related to the...An oil-impregnated porous polyimide(PI)retainer is used in space rolling bearings to improve the lubrication performance,which depends on the release of lubricant from the pores,and therefore is closely related to the pore size.To study the effect of pore size,in this work,PI materials with different pore sizes were prepared by preheating the retainer tube billet during the limit pressing process,and then the friction tests were conducted with the ball-on-ring mode.The results show that the applied load deforms the pores,allowing the lubricant to be squeezed out from the pore;the centrifugal effect induced by rotation also makes the lubricant migrate out of the pore.Therefore,for the same pore sizes,the friction coefficients decrease with the increasing loads and rotation speeds.In addition,it was found that there exists an optimal pore size for the best lubrication properties of porous PI material.Furthermore,the optimal pore size should be larger for lubricants with high viscosity.The microscopic mechanism for lubricant outflow from pores is clarified by molecular dynamic simulations.The insights gained in this study can guide the preparation of oil-impregnated porous retainers under different working conditions.展开更多
The laser-induced porous graphene(LIG)prepared in a straightforward fabrication method is presented,and its applications in stretchable strain sensors to detect the applied strain are also explored.The LIGformed on th...The laser-induced porous graphene(LIG)prepared in a straightforward fabrication method is presented,and its applications in stretchable strain sensors to detect the applied strain are also explored.The LIGformed on the polyimide/polydimethylsiloxane(PI/PDMS)composite exhibits a naturally high stretchabil-ity(over 30%),bypassing the transfer printing process compared to the one prepared by laser scribing onPI films.The PI/PDMS composite with LIG shows tunable mechanical and electronic performances withdifferent PI particle concentrations in PDMS.The good cyclic stability and almost linear response of theprepared LIG’s resistance with respect to tensile strain provide its access to wearable electronics.To im-prove the PDMS/PI composite stretchability,we designed and optimized a kirigami-inspired strain sensorwith LIG on the top surface,dramatically increasing the maximum strain value that in linear response toapplied strain from 3%to 79%.展开更多
The architecture and surface modifications have been regarded as effective methods to enhance the bi-ological response of biomaterials in bone tissue engineering.The porous architecture of the implanta-tion was essent...The architecture and surface modifications have been regarded as effective methods to enhance the bi-ological response of biomaterials in bone tissue engineering.The porous architecture of the implanta-tion was essential conditions for bone regeneration.Meanwhile,the design of biomimetic hydroxyap-atite(HAp)coating on porous scaffolds was demonstrated to strengthen the bioactivity and stimulate osteogenesis.However,bioactive bio-ceramics such asβ-tricalcium phosphate(β-TCP)and calcium sili-cate(CS)with superior apatite-forming ability were reported to present better osteogenic activity than that of HAp.Hence in this study,3D-printed interconnected porous bioactive ceramicsβ-TCP/CS scaf-fold was fabricated and the biomimetic HAp apatite coating were constructed in situ via hydrothermal reaction,and the effects of HAp apatite layer on the fate of mouse bone mesenchymal stem cells(mBM-SCs)and the potential mechanisms were explored.The results indicated that HAp apatite coating en-hanced cell proliferation,alkaline phosphatase(ALP)activity,and osteogenic gene expression.Further-more,PI3K/AKT/mTOR signaling pathway is proved to have an important impact on cellular functions.The present results demonstrated that the key molecules of phosphatidylinositol 3-kinase(PI3K),protein kinase B(AKT)and mammalian target of rapamycin(mTOR)were activated after the biomimetic hydrox-yapatite coating were constructed on the 3D-printed ceramic scaffolds.Besides,the activated influence on the protein expression of Runx2 and BMP2 could be suppressed after the treatment of inhibitor HY-10358.In vivo studies showed that the constructed HAp coating promoted bone formation and strengthen the bone quality.These results suggest that biomimetic HAp coating constructed on the 3D-printed bioac-tive composite scaffolds could strengthen the bioactivity and the obtained biomimetic multi-structured scaffolds might be a potential alternative bone graft for bone regeneration.展开更多
基金This work was supported by the National Natural Science Foundation of China(U2141243 and 52175158).
文摘An oil-impregnated porous polyimide(PI)retainer is used in space rolling bearings to improve the lubrication performance,which depends on the release of lubricant from the pores,and therefore is closely related to the pore size.To study the effect of pore size,in this work,PI materials with different pore sizes were prepared by preheating the retainer tube billet during the limit pressing process,and then the friction tests were conducted with the ball-on-ring mode.The results show that the applied load deforms the pores,allowing the lubricant to be squeezed out from the pore;the centrifugal effect induced by rotation also makes the lubricant migrate out of the pore.Therefore,for the same pore sizes,the friction coefficients decrease with the increasing loads and rotation speeds.In addition,it was found that there exists an optimal pore size for the best lubrication properties of porous PI material.Furthermore,the optimal pore size should be larger for lubricants with high viscosity.The microscopic mechanism for lubricant outflow from pores is clarified by molecular dynamic simulations.The insights gained in this study can guide the preparation of oil-impregnated porous retainers under different working conditions.
基金from the National Natural ScienceFoundation of China(Grant No.12072030).
文摘The laser-induced porous graphene(LIG)prepared in a straightforward fabrication method is presented,and its applications in stretchable strain sensors to detect the applied strain are also explored.The LIGformed on the polyimide/polydimethylsiloxane(PI/PDMS)composite exhibits a naturally high stretchabil-ity(over 30%),bypassing the transfer printing process compared to the one prepared by laser scribing onPI films.The PI/PDMS composite with LIG shows tunable mechanical and electronic performances withdifferent PI particle concentrations in PDMS.The good cyclic stability and almost linear response of theprepared LIG’s resistance with respect to tensile strain provide its access to wearable electronics.To im-prove the PDMS/PI composite stretchability,we designed and optimized a kirigami-inspired strain sensorwith LIG on the top surface,dramatically increasing the maximum strain value that in linear response toapplied strain from 3%to 79%.
基金This work was sponsored by the National Science Foundation of China(Nos.32071341,52202358,52003302)The Natural Science Foundation of Guangdong Province(No.2017A030308004)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(No.2021A1515110824)the Science and Technology Project of Guangdong province(No.2018A050506021).
文摘The architecture and surface modifications have been regarded as effective methods to enhance the bi-ological response of biomaterials in bone tissue engineering.The porous architecture of the implanta-tion was essential conditions for bone regeneration.Meanwhile,the design of biomimetic hydroxyap-atite(HAp)coating on porous scaffolds was demonstrated to strengthen the bioactivity and stimulate osteogenesis.However,bioactive bio-ceramics such asβ-tricalcium phosphate(β-TCP)and calcium sili-cate(CS)with superior apatite-forming ability were reported to present better osteogenic activity than that of HAp.Hence in this study,3D-printed interconnected porous bioactive ceramicsβ-TCP/CS scaf-fold was fabricated and the biomimetic HAp apatite coating were constructed in situ via hydrothermal reaction,and the effects of HAp apatite layer on the fate of mouse bone mesenchymal stem cells(mBM-SCs)and the potential mechanisms were explored.The results indicated that HAp apatite coating en-hanced cell proliferation,alkaline phosphatase(ALP)activity,and osteogenic gene expression.Further-more,PI3K/AKT/mTOR signaling pathway is proved to have an important impact on cellular functions.The present results demonstrated that the key molecules of phosphatidylinositol 3-kinase(PI3K),protein kinase B(AKT)and mammalian target of rapamycin(mTOR)were activated after the biomimetic hydrox-yapatite coating were constructed on the 3D-printed ceramic scaffolds.Besides,the activated influence on the protein expression of Runx2 and BMP2 could be suppressed after the treatment of inhibitor HY-10358.In vivo studies showed that the constructed HAp coating promoted bone formation and strengthen the bone quality.These results suggest that biomimetic HAp coating constructed on the 3D-printed bioac-tive composite scaffolds could strengthen the bioactivity and the obtained biomimetic multi-structured scaffolds might be a potential alternative bone graft for bone regeneration.
