Intelligent Vascularized 3D/4D/5D/6D‑Printed Tissue Scaffolds

Blood vessels are essential for nutrient and oxygen delivery and waste removal.Scaffold-repairing materials with functional vascular networks are widely used in bone tissue engineering.Additive manufacturing is a manufacturing technology that creates three-dimensional solids by stacking substances layer by layer,mainly including but not limited to 3D printing,but also 4D printing,5D printing and 6D printing.It can be effectively combined with vascularization to meet the needs of vascularized tissue scaffolds by precisely tuning the mechanical structure and biological properties of smart vascular scaffolds.Herein,the development of neovascularization to vascularization to bone tissue engineering is systematically discussed in terms of the importance of vascularization to the tissue.Additionally,the research progress and future prospects of vascularized 3D printed scaffold materials are highlighted and presented in four categories:functional vascularized 3D printed scaffolds,cell-based vascularized 3D printed scaffolds,vascularized 3D printed scaffolds loaded with specific carriers and bionic vascularized 3D printed scaffolds.Finally,a brief review of vascularized additive manufacturing-tissue scaffolds in related tissues such as the vascular tissue engineering,cardiovascular system,skeletal muscle,soft tissue and a discussion of the challenges and development efforts leading to significant advances in intelligent vascularized tissue regeneration is presented.

Application of bi-directional static loading test to deep foundations

Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.

Lotus seedpod-inspired internal vascularized 3D printed scaffold for bone tissue repair

In the field of bone defect repair,3D printed scaffolds have the characteristics of personalized customization and accurate internal structure.However,how to construct a well-structured vascular network quickly and effectively inside the scaffold is essential for bone repair after transplantation.Herein,inspired by the unique biological structure of“lotus seedpod”,hydrogel microspheres encapsulating deferoxamine(DFO)liposomes were prepared through microfluidic technology as“lotus seeds”,and skillfully combined with a three-dimensional(3D)printed bioceramic scaffold with biomimetic“lotus”biological structure which can internally grow blood vessels.In this composite scaffold system,DFO was effectively released by 36%in the first 6 h,which was conducive to promote the growth of blood vessels inside the scaffold quickly.In the following 7 days,the release rate of DFO reached 69%,which was fundamental in the formation of blood vessels inside the scaffold as well as osteogenic differentiation of bone mesenchymal stem cells(BMSCs).It was confirmed that the composite scaffold could significantly promote the human umbilical vein endothelial cells(HUVECs)to form the vascular morphology within 6 h in vitro.In vivo,the composite scaffold increased the expression of vascularization and osteogenic related proteins Hif1-α,CD31,OPN,and OCN in the rat femoral defect model,significantly cutting down the time of bone repair.To sum up,this“lotus seedpod”inspired porous bioceramic 3D printed scaffold with internal vascularization functionality has broad application prospects in the future.

Experimental study on pile-end post-grouting piles for super large bridge pile foundations

The application of pile-end post-grouting piles for super-large bridge pile foundations in some important projects was introduced in this paper.There are totally 21 test piles.The maximum pile diameter varies from 2.5 m to 3 m,and the maximum length is 125m;the bearing capacity of the post-grouting piles is over ten thousands tons.Based on the test results,the bearing capacity,displacement,and beating characteristics before and after grouting were analyzed.The results show that the beating capacity of the piles is increased in different degrees after grouting although the technical parameters,including the patterns of grouting pipes,pressure,dosages of cement,duration of grouting lasting time,are different.However,the obtained values are very discrete.In addition,the calculation formula for the post-grouting piles under specified grouting condition was deduced based on the statistics analysis results of 57 test piles.The research results have been applied in the design of bridge foundation.