Biomechanics and mechanobiology of the bone matrix

The bone matrix plays an indispensable role in the human body,and its unique biomechanical and mechanobiological properties have received much attention.The bone matrix has unique mechanical anisotropy and exhibits both strong toughness and high strength.These mechanical properties are closely associated with human life activities and correspond to the function of bone in the human body.None of the mechanical properties exhibited by the bone matrix is independent of its composition and structure.Studies on the biomechanics of the bone matrix can provide a reference for the preparation of more applicable bone substitute implants,bone biomimetic materials and scaffolds for bone tissue repair in humans,as well as for biomimetic applications in other fields.In providing mechanical support to the human body,bone is constantly exposed to mechanical stimuli.Through the study of the mechanobiology of the bone matrix,the response mechanism of the bone matrix to its surrounding mechanical environment can be elucidated and used for the health maintenance of bone tissue and defect regeneration.This paper summarizes the biomechanical properties of the bone matrix and their biological significance,discusses the compositional and structural basis by which the bone matrix is capable of exhibiting these mechanical properties,and studies the effects of mechanical stimuli,especially fluid shear stress,on the components of the bone matrix,cells and their interactions.The problems that occur with regard to the biomechanics and mechanobiology of the bone matrix and the corresponding challenges that may need to be faced in the future are also described.

Effect of transcatheter aortic valve replacement on bicuspid coronary hemodynamics:A numerical study

To investigate the effects of transcatheter heart valve(THV)poses and bicuspid aortic valve(BAV)subtypes on coronary hemodynamics after transcatheter aortic valve replacement(TAVR).The computational models for BAV included left-right fusion(LR),non-coronary-left fusion(LN)and non-coronary-right fusion(RN).THV deployment height is defined as the distance below the aortic annulus of the lowest point of the stent,H_(1)=2mm,H_(2)=5mm and H_(3)=8mm,Orientations include O_(1)(one commissure is aligned with the raphe)and O_(2)(one commissure is aligned with the axis of non-fused leaflet symmetry).The maximum flow velocity(Vmax),mean wall shear stress(mWSS)and coronary perfusion pressure(CPP)of coronary were obtained by computational fluid dynamics(CFD)simulation.The CPP was 59%in left coronary and 82%in right coronary higher than that before deployment.At O_(1),the CPP of the LN left coronary and the RN right coronary was 74%and 79%higher than that before deployment.At O_(2),the CPP of the LN right coronary and the RN left coronary was 83%and 82%higher than that before deployment.When the THV deployment height is less than 2​mm,Vmax and CPP of coronary arteries do not return to healthy TAV levels or changed weakly.The overlap of the THV commissure with the coronary ostium makes the coronary CPP so large that it exceeds the level of a healthy TAV.

Bioinspired mineralized collagen scaffolds for bone tissue engineering

Successful regeneration of large segmental bone defects remains a major challenge in clinical orthopedics,thus it is of important significance to fabricate a suitable alternative material to stimulate bone regeneration.Due to their excellent biocompatibility,sufficient mechanical strength,and similar structure and composition of natural bone,the mineralized collagen scaffolds(MCSs)have been increasingly used as bone substitutes via tissue engineering approaches.Herein,we thoroughly summarize the state of the art of MCSs as tissue-engineered scaffolds for acceleration of bone repair,including their fabrication methods,critical factors for osteogenesis regulation,current opportunities and challenges in the future.First,the current fabrication methods for MCSs,mainly including direct mineral composite,in-situ mineralization and 3D printing techniques,have been proposed to improve their biomimetic physical structures in this review.Meanwhile,three aspects of physical(mechanics and morphology),biological(cells and growth factors)and chemical(composition and cross-linking)cues are described as the critical factors for regulating the osteogenic feature of MCSs.Finally,the opportunities and challenges associated with MCSs as bone tissue-engineered scaffolds are also discussed to point out the future directions for building the next generation of MCSs that should be endowed with satisfactorily mimetic structures and appropriately biological characters for bone regeneration.

Model construction and numerical simulation of arterial remodeling after stent implantation with variations of cell concentration

Differences in concentration of molecules can cause different molecular diffusion.This issue has not been well studied in the vascular remodeling process with regards to is-stent restenosis.This study designed and built a model to explore the effect of differences in vascular cell concentration on vascular remodeling.Finite element analysis(FEA)models and the agent-based models(ABMs)were established to simulate the damage and proliferation process of vascular smooth muscle cells(VSMCs)caused by coronary artery stent implantation.The FEA model simulated the expansion of the stent in the coronary artery,the tensile stress was captured and imported into the ABM,and the damaged VSMCs proliferated to reduce their damage level.VSMCs were randomly distributed within a defined domain,and the number of VSMCs in a unit volume(or area)was defined as the concentration of VSMCs.VSMCs with the smallest concentration of VSMCs will preferentially proliferate,which simulates the cell proliferation affected by the concentration of VSMCs.The results showed that after stent implantation,VSMCs proliferated gradually from the severely damaged stent area to the lumen until the artery reached a steady state.By comparison,the loss of arterial lumen and the number of newly grown VSMCs were greater in the presence of the concentration than in its absence.Cells made full use of the lumen space under the influence of concentration differences,so the concentration was of great significance to vascular remodeling.