Assessment of Shape Memory Alloy Stent Deployment in a Stenosed Artery

Linxia Gu,Shijia Zhao,Stacey R. Froemming 대한의용생체공학회 2011 Biomedical Engineering Letters (BMEL) Vol.1 No.4

Purpose Shape memory alloy (SMA) stents have been used increasingly for the treatment of complex arterial occlusions. There is an immediate need to quantify the mechanical performance of SMA stents to open occluded arteries. Methods The stent crimping and expanding process was assessed through both numerical modeling and in-vitro studies. The implantation of a SMA stent in curved arteries with eccentric stenosis were simulated to evaluate the effect of artery curvature on arterial mechanics. Results The crimping process stored a considerable amount of strain energy in the stent, which were then released through self-expansion until a balance between the stent and stenosed artery was achieved. The deployed SMA stent exhibited a dog-bone shape, where the longitudinal ends of the stent penetrated into the artery causing arterial stress concentrations. However, the maximum arterial stress was observed at the central portion of artery contacting the thin side of the plaque. Furthermore, stent-induced arterial mechanics were more pronounced in the curved artery than the straight artery. The maximum Von Mises stress in the curved artery with a curvature of 0.05 mm-1 was 37% larger than that found in the straight artery. The percentage of the intimal area at higher stress level (> 0.05 MPa) is 5.51% in the curved artery, compared to 1.76% in the straight artery. Conclusions This work provided a fundamental understanding of the behavior of SMA stent and its impact on the vascular wall, and illuminated the possibilities for exploiting their potential to alleviate arterial injury.

Numerical and Experimental Investigation of Vascular Suture Closure

Linxia Gu,Ananth Ram Mahanth Kasavajhala,Haili Lang,James M. Hammel 대한의용생체공학회 2012 Biomedical Engineering Letters (BMEL) Vol.2 No.1

Purpose In order to optimize the performance of the suture for tissue closure, it is essential to develop strategies for devising new and improved techniques that can visualize and compare various suturing techniques. This paper describes an experimental and numerical investigation on the performance of sutured tissue. Methods In the experiments, two pieces of glutaraldehyde cross-linked bovine pericardium were sutured together through simple running suture and tensioned to study the performance of the sutured tissue. During testing, the tension load and the total displacement of the specimen were recorded. The strain field of the specimen was simultaneously captured using two high speed cameras and post processed using its associated image processing software. In addition, nonlinear hyperelastic material models for Shelhigh patch and cryopreserved human aorta were derived through least-square fitting into the tensile testing data. Three dimensional finite element models were developed to replicate the behavior of wound closure. Results The effect of tissue material mismatch, and stiffness of the suture thread on the mechanical behavior of sutured tissue was examined. The stain distributions obtained from simulation agrees with the captured surface strain map from experiments. A relative softer suture thread could reduce the peak stress concentrations at the knotting location. Conclusions The mechanical performance of sutured tissue depends on the level of mismatch in material stiffness between the native tissue and the replacement material.

An efficient method to improve the stability of submerged functionally graded cylindrical shell

Rong Li,Linxia Liu,Bin Liang,Meng Yang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.6

An efficient method is presented to improve the stability of a submerged functionally graded (FG) cylindrical shell which is subjected to external hydrostatic pressure. To improve stability while satisfying the application requirements for shell thickness, we focused on the optimum value of the power-law exponent to maximize the critical hydrostatic pressure. The optimum value of the power-law exponent is obtained from an analysis of the influence factors on critical pressure. The results show that the critical pressure can be greatly increased by using the optimum value of the power-law exponent, and the growth rate of critical pressure is almost constant independent of the shell geometry and boundary condition. The advantage of the present method in reducing the shell thickness is illustrated by examples. In addition, the present method is applicable to all kinds of material combinations.

Effects of Arterial Strain and Stress in the Prediction of Restenosis Risk: Computer Modeling of Stent Trials

Shijia Zhao,Linxia Gu,Stacey R. Froemming 대한의용생체공학회 2012 Biomedical Engineering Letters (BMEL) Vol.2 No.3

Purpose In-stenting restenosis is one of the major complications after stenting. Clinical trials of various stent designs have reported different restenosis rates. However,quantitative correlation between stent features and restenosis statistics is scant. In this work, it is hypothesized that stress concentrations on arterial wall caused artery injury, which initiates restenosis. The goal is to assess the correlation between stent-induced arterial stress and strain and the documented restenosis rates. Methods Six commercially available stents, including balloon-expandable stents and self-expanding stents, were virtually implanted into the arteries through finite element method. The resulted peak Von Mises stress, principal stress,principal logarithm strain, as well as percentage of intimal area with abnormal higher stress were monitored. Results Positive correlation between arterial stress and strain after stent implantations and the documented restenosis rates from the corresponding clinical trials was found regardless of stent types. No statistical significant difference was observed for various stress or strain parameters serving as indicators of artery injury. Conclusions In-stent restenosis are less likely to occur as arterial mechanics are least altered by stent implantations. Optimization of stent designs to minimize the stent-induced arterial stresses and strains can reduce the arterial injury, and thus reduce the occurrence of restenosis. This work improved our understanding of the stent-lesion interactions that regulate arterial mechanics and demonstrated that arterial stress and strain could predict the risk of in-stent restenosis.

Primary blast waves induced brain dynamics influenced by head orientations

Yi Hua,Yugang Wang,Linxia Gu 대한의용생체공학회 2017 Biomedical Engineering Letters (BMEL) Vol.7 No.3

There is controversy regarding the directionaldependence of head responses subjected to blast loading. The goal of this work is to characterize the role of headorientation in the mechanics of blast wave-head interactionsas well as the load transmitting to the brain. A three-dimensionalhuman head model with anatomical details wasreconstructed from computed tomography images. Threedifferent head orientations with respect to the oncomingblast wave, i.e., front-on with head facing blast, back-onwith head facing away from blast, and side-on with rightside exposed to blast, were considered. The reflected pressureat the blast wave-head interface positively correlatedwith the skull curvature. It is evidenced by the maximumreflected pressure occurring at the eye socket with the largestcurvature on the skull. The reflected pressure patternalong with the local skull areas could further influence theintracranial pressure distributions within the brain. We didfind out that the maximum coup pressure of 1.031 MPa inthe side-on case as well as the maximum contrecoup pressureof -0.124 MPa in the back-on case. Moreover, themaximum principal strain (MPS) was also monitored due toits indication to diffuse brain injury. It was observed that thepeak MPS located in the frontal cortex region regardless ofthe head orientation. However, the local peak MPS withineach individual function region of the brain depended on thehead orientation. The detailed interactions between blastwave and head orientations provided insights for evaluatingthe brain dynamics, as well as biomechanical factors leadingto traumatic brain injury.

Comparative transcriptome analysis in the hepatopancreas of Helice tientsinensis exposed to the toxic metal cadmium

Zhengfei Wang,Dan Tang,Linxia Sun,Xueling Shi,Ruobing Liu,Huayun Guo,Bo-Ping Tang 한국유전학회 2019 Genes & Genomics Vol.41 No.4

Background The mudflat crab Helice tientsinensis is one of the most commercially valuable species for crabmeat production due to its delicious taste. These crabs are mainly found in coastal wetland where they are seriously threatened by toxic heavy metal pollution. In crustaceans, the hepatopancreas is an important organ for detoxification, and metal toxic substances can be converted to non-toxic or less toxic compounds in this organ. Objective To develop a better understanding of the molecular response of H. tientsinensis to the toxic metal cadmium (Cd) and provide a molecular basis for the toxic metal tolerance of H. tientsinensis. Methods In this study, we performed comparative hepatopancreas transcriptome analysis between H. tientsinensis unexposed (as control) and exposed to the toxic metal Cd for 48 h. Results We identified 1089 Cd stress significantly-upregulated and 1560 Cd stress significantly-downregulated unigenes. Functional categorization and annotation of these differentially-expressed genes (DEGs) demonstrated that the response to Cd stress in the hepatopancreas of H. tientsinensis mainly involves “antioxidant activity”, “detoxification”, “toxin degradation activity” and “immune system process”. In addition, five genes (ABCC1, NDUFAF5, ASTL, DES1, CYP27A) were identified as possible major targets for toxic metal tolerance. Conclusion This is the first time reporting that the response of H. tientsinensis to Cd exposure at the transcriptome level, and it lays the foundation for understanding the molecular mechanisms of the response of H. tientsinensis to environmental toxic metal stress.

Blast-induced Mild Traumatic Brain Injury through Ear Canal: A Finite Element Study

Praveen Akula,Yi Hua,Linxia Gu 대한의용생체공학회 2015 Biomedical Engineering Letters (BMEL) Vol.5 No.4

Purpose The role of ear canal in transmitting blast waves tothe brain is not clear. The goal of this work is to characterizethe influence of ear canal on blast-induced mild traumaticbrain injury through a computational approach. Methods A three-dimensional human head model withsingle-side ear canal details was reconstructed from computedtomography images. The ear canal was positioned eitherfacing the incident blast wave or facing away from the blastwave. Results The blast wave-head interaction has demonstratedthat the overpressure within the ear canal was substantiallyamplified when the ear directly faced the blast wave. Whenit faced away from the blast wave, the overpressure withinthe ear canal was less than the actual incident blast pressure. Regardless of the substantial pressure differences within theear canal induced by the blast wave, the resulting intracranialpressures were almost the same for both cases. Conclusions The blast wave-head interaction has demonstratedthat the role of the ear canal in brain dynamics, and thusbrain injury, was negligible. However, the peak overpressurewithin the ear canal exceeded the documented tympanicmembrane rupture and inner ear damage thresholds. Thiswas speculated to cause the degeneration of axons along theauditory pathway up to the midbrain. This work providedfundamental understanding of the load transmission throughthe ear canal and could serve as a platform for designingbetter protective armors.

Evolution of mitochondrial energy metabolism genes associated with hydrothermal vent adaption of Alvinocaridid shrimps

Zhengfei Wang,Daizhen Zhang,Xuejia Shi,Linxia Sun,Yuze Bai,Bo-Ping Tang 한국유전학회 2017 Genes & Genomics Vol.39 No.12

Most of Alvinocaridid shrimps live in hydrothermal vents, where is a wicked environment with highly toxic chemistry, hypoxia, acidic pH, and sulfide deposits. In order to adapt to this environment, change in energy metabolism may be one of the primary factors. However, the genetic basis of energy metabolism underlying this environment remains unexplored. Here, we present the first systematic investigation of mitochondrial genes in Alvinocarididae. The analysis demonstrated that ATP6, ND4 and ND6 were subjected to strong positive selection leading to last common ancestors of Alvinocarididae, and ATP8, ND5, COX1 and COX2 were determined to have undergone positive selection in the interior lineages of Alvinocarididae. Considering that about 95% of ATP is supplied by mitochondria via oxidative phosphorylation, and body detoxification process associated with cytochrome c. Positive selection in these genes suggested that Alvinocaridid shrimps might have acquired an enhanced capacity for energy metabolism and detoxification in extreme hydrothermal vent field.

The complete mitochondrial genomes of Tarsiger cyanurus and Phoenicurus auroreus: a phylogenetic analysis of Passeriformes

Huabin Zhang,Yuze Bai,Xuejia Shi,Linxia Sun,Zhengfei Wang,Xiaobing Wu 한국유전학회 2018 Genes & Genomics Vol.40 No.2

Passeriformes is the largest group within aves and the phylogenetic relationships between Passeriformes have caused major disagreement in ornithology. Particularly, the phylogenetic relationships between muscicapoidea and sylvioidea are complex, and their taxonomic boundaries have not been clearly defined. Our aim was to study the status of two bird species: Tarsiger cyanurus and Phoenicurus auroreus. Furthermore, we analyzed the phylogenetic relationships of Passeriformes. Complete mitochondrial DNA (mtDNA) sequences of both species were determined and the lengths were 16,803 (T. cyanurus) and 16,772 bp (P. auroreus), respectively. Thirteen protein-coding genes, 22 tRNA genes, two rRNA genes, and one control region were identified in these mtDNAs. The contents of A and T at the base compositions was significantly higher than the content of G and C, and this AT skew was positive, while the GC skew was negative. The monophyly of Passeriformes is divided into four major clades: Corvoidea, Sylvioidea, Passeroidea, and Musicicapoidea. Paridae should be separated from the superfamily Sylvioidea and placed within the superfamily Muscicapoidea. The family Muscicapidae and Corvida were paraphyly, while Carduelis and Emberiza were grouped as a sister taxon. The relationships between some species of the order passeriformes may remain difficult to resolve despite an effort to collect additional characters for phylogenetic analysis. Current research of avian phylogeny should focus on adding characters and taxa and use both effectively to obtain a better resolution for deeper and shallow nodes.

Exploring the Vitreoretinal Interface: A Key Instigator of Unique Retinal Hemorrhage Patterns in Pediatric Head Trauma

Helen H. Song,Wallace B. Thoreson,Pengfei Dong,Yasin Shokrollahi,Linxia Gu,Donny W. Suh 대한안과학회 2022 Korean Journal of Ophthalmology Vol.36 No.3