Rapid fabrication of modular 3D paper-basedmicrofluidic chips using projection-based 3D printing

Paper-based microchips have different advantages,such as better biocompatibility,simple production,and easy handling,making them promising candidates for clinical diagnosis and other fields.This study describes amethod developed to fabricate modular three-dimensional(3D)paper-based microfluidic chips based on projection-based 3D printing(PBP)technology.A series of two-dimensional(2D)paper-based microfluidic modules was designed and fabricated.After evaluating the effect of exposure time on the accuracy of the flow channel,the resolution of this channel was experimentally analyzed.Furthermore,several 3D paper-based microfluidic chips were assembled based on the 2D ones using different methods,with good channel connectivity.Scaffold-based 2D and hydrogel-based 3D cell culture systems based on 3D paper-based microfluidic chips were verified to be feasible.Furthermore,by combining extrusion 3D bioprinting technology and the proposed 3D paper-based microfluidic chips,multiorgan microfluidic chips were established by directly printing 3D hydrogel structures on 3D paperbased microfluidic chips,confirming that the prepared modular 3D paper-based microfluidic chip is potentially applicable in various biomedical applications.

Printability during projection-based 3D bioprinting

Since projection-based 3D bioprinting(PBP)could provide high resolution,it is well suited for printing delicate structures for tissue regeneration.However,the low crosslinking density and low photo-crosslinking rate of photocurable bioink make it difficult to print fine structures.Currently,an in-depth understanding of the is lacking.Here,a research framework is established for the analysis of printability during PBP.The gelatin methacryloyl(GelMA)-based bioink is used as an example,and the printability is systematically investigated.We analyze the photo-crosslinking reactions during the PBP process and summarize the specific requirements of bioinks for PBP.Two standard quantized models are established to evaluate 2D and 3D printing errors.Finally,the better strategies for bioprinting five typical structures,including solid organs,vascular structures,nerve conduits,thin-wall scaffolds,and micro needles,are presented.

Rapid printing of 3D porous scaffolds for breast reconstruction

Prosthesis implantation and fat transplantation are common breast reconstructionmethods.In general,prosthesis implantation alone does not achieve a realistic enough appearance,and fat transplantation alone is difficult to achieve in the correct capacity.To date,no reports have focused on methods of combining fat with implanted prostheses for breast reconstruction.Using a newly designed bionic ink(i.e.,polyether F127 diacrylate(F127DA)&poly(ethylene glycol)diacrylate(PEGDA))and projection-based three-dimensional bioprinting(PBP),we report the development of a new method for printing porous prostheses.PEGDA was used to improve the printing precision of the prosthesis by increasing the gel point of F127DA and reducing the impact of external temperature.The compression modulus of the printed prosthesis was very close to that of prostheses currently used in clinical practice and to that of natural breasts.Finally,stromal vascular fraction gel(SVF-gel),a human fat extract,was injected into the pores of the synthesized prostheses to prepare a prosthesis mixed with adipose tissue.These were implanted subcutaneously in nude mice to observe their biological performance.After 14 and 28 days of observation,the prosthesis showed good biocompatibility,and adipose tissues grew well in and around the prosthesis.This result shows that a porous prosthesis containing pre-placed adipose tissues is a promising breast reconstruction material.

Towards development of enhanced fully-Lagrangian mesh-free computational methods for fluid-structure interaction

Simulation of incompressible fluid flow-elastic structure interactions is targeted by using fully-Lagrangian mesh-free computational methods. A projection-based fluid model（moving particle semi-implicit（MPS）） is coupled with either a Newtonian or a Hamiltonian Lagrangian structure model（MPS or HMPS） in a mathematically-physically consistent manner. The fluid model is founded on the solution of Navier-Stokes and continuity equations. The structure models are configured either in the framework of Newtonian mechanics on the basis of conservation of linear and angular momenta, or Hamiltonian mechanics on the basis of variational principle for incompressible elastodynamics. A set of enhanced schemes are incorporated for projection-based fluid model（Enhanced MPS）, thus, the developed coupled solvers for fluid structure interaction（FSI） are referred to as Enhanced MPS-MPS and Enhanced MPS-HMPS. Besides, two smoothed particle hydrodynamics（SPH）-based FSI solvers, being developed by the authors, are considered and their potential applicability and comparable performance are briefly discussed in comparison with MPS-based FSI solvers. The SPH-based FSI solvers are established through coupling of projection-based incompressible SPH（ISPH） fluid model and SPH-based Newtonian/Hamiltonian structure models, leading to Enhanced ISPH-SPH and Enhanced ISPH-HSPH. A comparative study is carried out on the performances of the FSI solvers through a set of benchmark tests, including hydrostatic water column on an elastic plate,high speed impact of an elastic aluminum beam, hydroelastic slamming of a marine panel and dam break with elastic gate.

A note on diagnosis and performance degradation detection in automatic control systems towards functional safety and cyber security

This note addresses diagnosis and performance degradation detection issues from an integrated viewpoint of functionality maintenance and cyber security of automatic control systems.It calls for more research attention on three aspects:(i)application of control and detection uni ed framework to enhancing the diagnosis capability of feedback control systems,(ii)projection-based fault detection,and complementary and explainable applications of projection-and machine learning-based techniques,and(iii)system performance degradation detection that is of elemental importance for today's automatic control systems.Some ideas and conceptual schemes are presented and illustrated by means of examples,serving as convincing arguments for research e orts in these aspects.They would contribute to the future development of capable diagnosis systems for functionality safe and cyber secure automatic control systems.

Fourier Collocation and Reduced Basis Methods for Fast Modeling of Compressible Flows

A projection-based reduced order model(ROM)based on the Fourier collocation method is proposed for compressible flows.The incorporation of localized artificial viscosity model and filtering is pursued to enhance the robustness and accuracy of the ROM for shock-dominated flows.Furthermore,for Euler systems,ROMs built on the conservative and the skew-symmetric forms of the governing equation are compared.To ensure efficiency,the discrete empirical interpolation method(DEIM)is employed.An alternative reduction approach,exploring the sparsity of viscosity is also investigated for the viscous terms.A number of one-and two-dimensional benchmark cases are considered to test the performance of the proposed models.Results show that stable computations for shock-dominated cases can be achieved with ROMs built on both the conservative and the skew-symmetric forms without additional stabilization components other than the viscosity model and filtering.Under the same parameters,the skew-symmetric form shows better robustness and accuracy than its conservative counterpart,while the conservative form is superior in terms of efficiency.