F/Free Essay-Direct-584.Txt 584

1. Introduction

The four valves in the mammalian heart are responsible for controlling the one-way direction of the blood stream from the heart to body and vice versa [1,2]. For this purpose, the inlet and outlet valves open and close continuously during the cardiac cycles. The malfunction of a valve has resulted in blood circulation disorders and may cause serious heart disease and even death [3]. Currently, when one of the valves malfunctions, the end step of medical choice is to replace it with an artificial one that is state of the art. The drawbacks of artificial valves (either mechanical or biological) such as infection, inflammation, thromboembolic, anticoagulation medication requirement and low durability compel the biomedical engineer to introduce a new concept of tissue engineering heart valve (TEHV) [4]. TEHV is an advanced principle to develop a neo-valvular tissue that can mimic the original tissue characteristics with the capacity to grow, repair and remodel in vivo. Based on tissue engineering (TE) principle, a three-dimensional (3D) scaffold is fabricated using the biomaterials as the initial template for the cells. The shape, structure and mechanical properties of fabricated scaffold should resemble the original aortic heart valve [2,5]. Thus the utilized materials as well as fabrication technique can significantly influence the scaffold properties.

Electrospinning is a versatile method for fabricating high quality of continuous nanofibers. The nanofibers are accumulated over each other and shape the electrospun mats. The mats obtained have hierarchy structure that is suitable for scaffolding engineered tissue. The 3D scaffold is then seeded with proper source of cells and biological behaviors are investigated. The hierarchy structure of the scaffold facilitated the nutrient supply to the cells (particularly those far away from the surface) as well as waste removal. Later, the cell seeded 3D scaffold is developed in a bioreactor (in vitro) prior to implementation into the body (in vivo). Obtaining a proper structure and morphology of the nanofibers mats via electrospinning requires optimum setting for electrospinning parameters involved as well as solution parameters. Previously, initial evaluation of electrospinning process was performed as reported in several publications [6,7,8,9,10]. In our latest publication [10], the parameters involved such as flow rate, voltage, collector rotating speed and solution parameters such as concentration and ratio of compounds were evaluated to determine the process behavior in terms of mechanical strength. The analysis of results indicated significance and importance level of the investigated parameters. The maximum elastic modulus obtained was roughly 20 ± 1.2 MPa in such a way that elasticity was around 20%, which is not quite desirable for heart valve tissue engineering. It is expected that the scaffold may lose mechanical properties after cell seeding when the degradation rate starts (roughly 10–12 MPa loss is expected during one-month incubation of the scaffold in particular condition) [11,12,13]. However, statistical analysis shows the optimum point is achievable somewhere near the selected range. For this purpose, mathematical techniques such as steepest ascent/descent and response surface methodology are useful to explore this region. These methods enable us to move around the previous experimental range to find the optimum point. Furthermore, a quadratic regression model will be obtained that can be used for further point prediction. The advantage of TE concept compared to the current prosthesis is the potential to mimic the original tissue and no further medication treatment, inflammation and reoperation during the long time is required.

A significant difference between the left and right side of the heart is that the left heart distributes blood to a wider part of the body, naturally achieving a peak pressure six times more than the right side. Subsequently, the mitral and aortic valves on the left side of the heart are exposed to much higher pressure than the pulmonary and tricuspid valves. The wall of the left side is thicker than the right side. Generally, the majority of valvular dysfunctions are related to the left heart’s valves [14,15,16]. The aortic heart valve operates under a dynamic tensile–shear–flexural loading, and tolerates an elastic modulus within 10–15 MPa [11,17]. The heart pumps around 3–5 L blood with velocity around 1.35 ± 0.35 m/s every minute [18]. The suggested value for shear stress value for aortic heart valve is approximately 1–8 Pa, while the peak of this value may increase to a range of 3–150 Pa. In heart valve function, elasticity as well as strength are the two undeniable characteristics [19,20].

Several uniaxial tests were performed on both human and animal aortic heart valves to recognize the mechanical behavior. The studies mainly reported an elastic modulus for aortic heart valve in circumferential and radial direction. The reports indicate a much weaker elastic modulus in radial direction compared to circumferential direction. This can be attributed to the direction of collagen fibers that are dispersed circumferentially along the leaflets. In addition, the comparison between human and common animal valves mechanical properties exhibited a much weaker behavior for animals. Balguid and Rubbens [11] reported that the elastic modulus of native human aortic valve to be 15 MPa with ultimate tensile strength of 2.6 MPa and 22% of strain in circumferential direction. In the same report, the elastic modulus in radial direction was measured to be 2 MPa with ultimate tensile strength of 0.4 MPa and strain of 30%. Table 1 lists the related works pertaining to the uniaxial tensile tests of human and animal aortic valve. The average required elastic modulus seems to be approximately 14.5 MPa with at least 22% of elasticity in circumferential direction.

Previously, various types of synthetic/natural biomaterials have been used for scaffolding the heart valve. The synthetic/polymeric based materials must be biocompatible, biodegradable and fulfill the required mechanical properties for the dynamic function of heart valve. Synthetic biodegradable polymers such as polyglycolic acid (PGA) [24,25], polycaprolactone (PCL) [26,27], polylactic acid (PLA) [28,29] , and polyglycerol sebacate (PGS) [30,31] have already been reported for TEHV. Sodian et al. [32] engineered tissue scaffolds using PLA and PGA copolymers where the scaffolds obtained were thicker and less flexible than the individual polymers. Scaffolding PLA polymer has been reported by Armentano et al. [29] and, despite the desired tensile strength, it failed during dynamic mechanism of heart valve leaflets due to its high rigidity (brittleness). Van Lieshout et al. [33] reported the application of PCL in TEHV through the electrospinning technique. The biomechanical behavior was good but the low degradation rate of PCL (more than two years) is a hindrance. Masoumi et al. [30] investigated the scaffolding of PGS in TEHV which demonstrates good biodegradability, stiffness and cell adhesion compared to PGA. The PGS tensile strength tests exhibited nonlinear stress–strain behavior. The average elastic modulus of PGS was within the range of 0.025–1.2 MPa, which was not sufficient for heart valve. The main advantage of a synthetic scaffold is the fact that biomechanics and degradation properties can be chemically controlled according to the requirements. Although no biodegradable polymeric materials have been proven to be a desirable substitute for the native valves, work continues to be promising [1,15,24,25,26,27,28,29].

In our previous study [5], maghemite (γ-Fe2O3) loaded thermoplastic polyurethane (TPU)/poly-l-lactic acid (PLLA) was used as a novel mixture for fabricating aortic heart valve’s engineered tissue. The presence of maghemite nanoparticles in the nanofibers latter’s surface improved both cell proliferation rate and also the mechanical properties [10,34]. The elastic modulus of the 50:50% (v/v) neat TPU/PLLA was improved from 3.24 to 4.76 MPa (roughly 32%) when TPU/PLLA was impregnated with γ-Fe2O3. However, it is still far away from the required elastic modulus for a heart valve (around 10–15 MPa). Similarly, the cell viability improved from 72.12% to 95.41% during 72 h of incubation. The results indicated 50:50% TPU/PLLA containing 1% γ-Fe2O3 nanoparticles exhibited overall satisfaction in terms of structural, biological and mechanical properties. The Taguchi analysis was performed to determine the significant parameters influencing the behavior of the selected parameters and the linear regression model was obtained which can only justify the performed experimental range and cannot be generalized for every other process out of that range. In addition, the initial analysis represents half of the curvature (in 3D surface plot) within that range, which means the optimum point is somewhere out of that selected range. Therefore, in this research, the novelty lies in the utilization of initial evaluation and regression model to move from that range to near the optimum point and a second order regression model pertaining to elastic modulus and electrospinning process can be generalized. This was done using the steepest ascent and response surface methodology (RSM). In addition, the cell seeding over the 3D scaffold for 34 days is another novelty of this paper. Besides cell seeding, the new concept is roughness study by AFM techniques for preliminary cell attachment evaluation. Finally, the micro-indentation test was performed after cell seeding to elucidate the elastic modulus loss, which can be attributed to polymer degradation and other factors.

Do you need help with with essay, research paper, homework or even dissertation?

Visit our website – https://goo.gl/HKbmHS (assignmenthelp24.com)

=================>>>CLICK HERE<<<=================

=================>>>CLICK HERE<<<=================

=================>>>CLICK HERE<<<=================

=================>>>GET ASSIGNMENT HELP<<<=================

=================>>>GET ASSIGNMENT HELP<<<=================

=================>>>GET ASSIGNMENT HELP<<<=================

gitam cdl assignments results of michigan

describe your 15 minutes of fame essay

ptlls level 4 assignments meaning

what is core critical thinking skills

appreciating nature essay emerson

essay paper on identity theft

good science research paper topics

essay grading machine

type of classroom observation essay

mehnat ki azmat essay in sindhi language in india

hijrat e madina essay in urdu

300-500 word essay is how many pages

essays on all quiet on the western front theme

essay on sustainable development and environment

art and society essays in marxism aesthetics training

e214 essays for scholarships

2000 word essay ideas for imagination

persuasive research paper topics about animals

free essay accountability

financial crisis causes and effects essay of smoking

business continuity research paper

law essay questions

essay on subhash chandra bose birthday express

cllege essays

advanced higher biology 2006 marking scheme for essay

clausewitz on war bibliography

port gamble s’klallam housing assignment map

oil crisis 1973 essay outline

incompatibilism free will and determinism essay

essay on taras shevchenko

practice makes perfect essay writing

aging theories essay

northern lights book trailer assignment

asking question in essay cite

young goodman brown annotated bibliography

thailand essays

structure source based history essays

musician cv personal statement

media tv drama essay

wild cards 4 aces abroad assignment

high school personal statement prompts

response essays on at a slaughterhouse some things never die

People Who Do Homework for Money gcse maths higher non calculator topics for persuasive essays

retroaction descriptive essays

personal essay for college application samples

essays ethics of abortion

critical essays for king lear

5jg homework assignments

plan dialectique dissertation introduction

definition of micro environment essay pollution

dissertationsvorhaben tum

hr advisor cover letter uk example

okonkwo and nwoye essay writing

indenting on common app essay 2016-2017

endocrine system essay questions

baroque music song names in essays

romeo and juliet in class People Who Do Homework for Money essay prompts for sat

semialgebraic descriptive essay

People Who Do Homework for Money hies admissions essay

purpose of a cover letter resume

poetry essays sample

online free essay tutor online

graduating high school senior scholarship essay

essay alice walker’s beauty

where i lived and what i lived for essay summary sample

magical realism in a very old man with enormous wings essays

soil conservation essay writing

truth always wins essay scholarships

cieh level 4 food safety assignments

vg wort dissertation frist funeral home

red badge of courage conflict essay

necessity is the mother of invention essay free

term paper on the pacific gyre trash

do not litter essay contest

what is a periodical essay

cross country trav corps assignment

iapmo scholarship essay contest for adults

pixmap assignment sheet

brain tumor research papers

make an outline for research paper

are taxes fair essay

fruitless love definition essay

heroism definition essay on freedom

kashmir earthquake case study a2 exam

southwest airlines case study 2010

nature essayist’s initials

sample personal statement for graduate school in special education

earning and spending money essay writing

coca cola advertisement essay paper

sample cover letter for beer sales rep

mississippi burning summary essay sample

sothy eng dissertation defense

climax in hamlet essay ideas

latex bibliography und statt and

sta1501 assignment management

definitions of abnormality essay writer

philip roth essay

am proud american essay examples

entry level firefighter cover letter samples

over dependence on technology essay

romanticism history historicism essays on an orthodoxy chesterton

school board meeting essay topics

persuasive essay topics pdf producer

revision of an essay

insead essay word limits

our government today essay examples

film la belle et la bete critique essay

sky pilot the animals explication essay

jimmy santiago baca essay

essay marketplaces

expository essay scoring rubric

young love sweet love essay

causes of the protestant reformation essays

reflective essay definition origin

earth essay in pakistan quake

melbourne uni school of culture and communication essay writing guide

zomerland michael chabon bibliography

my favourite season rainy essay writing

mastering chemistry online homework access code

honesty is the best policy essay pdf sample

unemployment in lebanon essay

children essay on my parents

print media analysis essay

helpfulness essay

electrolux terms company material zanussi acquiring site web essays acquisitions

get homework done online

economics essay example free

requiem dream essay topics

5 paragraph essay on hobbies

f/free essay-direct-584.txt 584

admission essay examples undergraduate engineering

need motivation to do my homework

ban homework petition

archaeology dissertation pottery blog

intro paragraph examples essay for oral presentation

bibliography of the song of roland

example of medical case study People Who Do Homework for Money format

rbgh free definition essay

boy in striped pyjamas essay plan

collected essays ralph waldo emerson

republic day india essay hindi

research paper on working capital management

simlock research paper

ismael mallari essayist lamb

People Who Do Homework for Money am i essay tumblr wallpapers

literary device glossary assignment satisfaction

People Who Do Homework for Money nuclear weapons essay thesis writing

maria belon family interview essay

writing bibliography of books

resume cover letter example 2014

About The Author

0 thoughts on “F/Free Essay-Direct-584.Txt 584”

    -->

Leave a Comment

Your email address will not be published. Required fields are marked *