surgical mesh final report portfolio

8/9/2019 Surgical Mesh Final Report Portfolio

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Light-weight surgical mesh for hernia repair

Lovelady, Robert

[email protected]

EM !"#$ %esign and &election of Materials

%ecember ", #'"$


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(ER)*)+) &EME

ll work presented in this report is of my own/ all information is either i0

original or derived from learned material from my course, or ii0 supported bythe works of other authors who are given proper credit through propercitation. *urthermore, ) hereby verify that ) have not plagiari1ed and that allwork presented is original or cited as to give credit to the work of others.

&ignature2


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Abstract

&urgical meshes are an e3ective method for modern hernia repair, as they close thedefect area in the abdominal muscle and prevent future rupture of the muscle. heyserve to prevent intrusion of intestine through the abdominal void, preventing

damage to the intestinal tissue through poor circulation caused from theconstriction of the intestine through the void. body of research indicates thatthese meshes, which are traditionally made of polymer 4laments, can be designedto reduce chronic pain post-surgery through reducing the weight and si1e of themesh.

light-weight surgical mesh must withstand several conditions within the humanbody. 5rimarily, it must take on any tensile load e6erted by the surroundingabdominal muscle to prevent tearing, and maintain biocompatibility to prompt thecorrect type and e6tent of foreign body reaction and tissue growth. *oreign bodyreactions determine the thickness of the scar tissue developed at the site, and

mesh pore si1e determines how well tissue 4bers can in4ltrate the mesh, using it asa framework for further tissue growth. &ome research can shed light on thecharacteristics of polymers which are more optimal for surgical meshes than others.

7hile material choice is important for a surgical mesh, light-weight meshes can befurther optimi1ed by reducing 4lament diameter. he tensile strength of a speci4cdefect length, or tear, is dependent on both the diameter of the 4lament spanningthe tear, and the number of 4laments spanning the tear. he number of 4lamentsalso correlates to the pore si1e, or gap between 4laments that is necessary fortissue growth. *ilament diameter is important to the weight of the mesh, thoughconsideration for pore si1e and the number of 4laments must be taken into account.

he shape of the mesh or the weave pattern further in8uences the sti3ness andstrength of the overall mesh, and can also in8uence pore si1e.

he material selection, diameter si1e, and mesh weave pattern are all importantfactors for designing a light-weight surgical mesh. 9y utili1ing anthropometric data,tensiometric data, and studies on biocompatible materials, a surgical mesh wasdesigned by reducing the weight of the 4lament while maintaining a safe margin forstrength, minimi1ing density while maintaining 8e6ibility, reducing the 4lamentdiameter, maintaining a minimum pore si1e, and utili1ing a material with idealbiocompatible characteristics. Multiple constraints in the form of biocompatibilitywere considered as priority constraints, as the risk for infection was a high safetyconcern, and optimi1ing factors such as pore si1e and weave pattern weresecondary to minimi1ing diameter si1e and density. material was chosen which iseasily manufactured, safe, strong, and relatively a3ordable from a materialperspective compared to already e6pensive procedures, where cost is mostlyassociated with surgeon:s fees.


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Table of contents

(eri4cationstatement;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;.#

bstract;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;!

)ntroduction;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;.uirements;;;;;;;;;;;;;;;;;;;;;;;;;;;;uences. Light-weight meshes areassociated with lower risk for complications and lower recurrence rates due to theirsmall si1e without a sacri4ce in strength. dditionally, they are found to produce

tissue growth more closely associated with the characteristics of abdominal muscleand reduce chronic pain post operation. +urrent medical e6perts are interested inselecting an ideal light-weight mesh material that will carry the fewestcomplications and lowest chance for hernia recursion. F!G


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Figure 1. Function of a mesh in vivo

Objective and requirements

he ob=ective of this report is to identify an ideal material for a surgical meshthrough material design and analysis, and the recommended selection will be

=usti4ed using shby charts for material indices, and other methods.

*unction

he material function will serve as a light-weight surgical mesh for hernia repair.his report will consider mono4lament weaves and not composite multi4lamentoptions, as they carry a high risk for infection.

+onstraints

he surgical mono4lament mesh material will need to withstand a minimal tensilestrength that will correspond to intra-abdominal pressure, and withstand thispressure for the lifetime of a patient. he material also need to be physically andchemically inert Hbiocompatible0, and should be 8e6ible and elastic to a limitede6tent.

b=ective

he ob=ective would be to minimi1e the 4lament si1e to reduce weight, withoutcompromising the strength of the material to withstand abdominal pressures.

*ree variables

*ree variables for the selection process are primarily the material choice, the4lament diameter, and additionally, the type of the weave.


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Figure 2. Surgical meshes of dierent shaes and si!es for dierent rocedures.

"oading conditions

he mesh material would be placed on the anterior abdominal muscle near thedefect area, and would have to assume all loads on the muscle surrounding it toprevent future rupture of the muscle. he cross sectional area of a human abdomencan be treated as a simple pressure vessel, with the hoop stress being the greateststress on a IcrackJ or abdominal rupture. nthropometric data maintains that intra-abdominal pressure in the supine Hlying down0 position is around ".


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Figure #. $uman ressure vessel model

he radius of the human Ipressure vesselJ was obtained from the average malewaist circumference Has hernias are most common in men0 from the +%+:santhropometric data from "DDD-#''$ F


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o further e6plore what materials could best suit the needs for this load, materialindices were derived for a round mono4lament line that a surgical mesh iscomprised of.

he derived indices M" and M# correlated to the Modulus-Elasticity and Modulus-&trength indices in 4gure $ and


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Figure ( )oung*s modulus versus strength

Figure + )oung,s modulus versus densit-

sing the material indices, polymers were selected for their suCcient strength,which far e6ceed the necessary stress endurances, and can provide a family ofbiocompatible materials. n ideal material selected should be biocompatible- that

&earch area

&earch area


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5olyethylene terephthalate H5E0 was reported to degrade after an unspeci4edamount of time, and resulted in some mesh ruptures. F"!G

5olytetra8uoroethylene H5*E0 was found to fail in integrating surrounding tissuenecessary for in4ltration, and is suspected to lose stability over time. F"$G

5olyvinylidene 8uouriode H5(%*0 is a thermally stable and is used in some suturesfor orthopedic surgery. )t induces minimal cellular response and is resistant todegradation. he material also e6hibited lower bending sti3ness and aging does notappear to increase this sti3ness. F"


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any odd numbered turn0, where outgoing strands in the pattern did not deviate fromtheir ingoing paths. )t was found that strands that crossed the pattern of the meshHfour half-turn0 diagonally resulted in higher tensile strength of the pattern andreacted better than three half-turn patterns when one strand was cut. F"DG nepotential problem of this weave is that the edges may unravel depending on the

sti3ness of the 5(%*. More research should be done to determine what is done tostabili1e the boundaries of meshes before implantation.

9iocompatibility was the largest con8icting constraint in the material selectionprocess, as many metals that could provide suitable strength and 8e6ibility in theform of wire were e6cluded due to their microstructure. &uch wires could also becomplicated and sti3ened by being woven into a mesh pattern, and result in lessbiocompatible implants.

Shae ecienc-/ 'lament diameter

o carry out calculations for 4lament diameter, the defect si1e and tensile strengthwas needed. aking the mean defect si1e in the abdomen to be $$cm #, translatingto a ?.?! cm wide defect gap F#'G, and the hoop stress of the abdominal pressurevessel model earlier, the re>uired tensile strength under calculated conditions wasfound to be about "D Ocm.

9ased on the tensile strength in Om, the total force on a defect area of ?.?!cm wascalculated. sing the e>uation for elongation, this force was correlated to an area ofn filaments of area QH%O#0S#. his combined area of n filaments would endure theload * under "'T elongation. he unknowns of this relation were the diameter % ofthe mono4laments, and the number of 4laments, n, to span the width of the defect.

he force across a ?.?! cm defect was calculated to be ""B?. , so the e>uationfor force was re-arranged to solve for diameter as a function of number of 4laments,


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to satisfy the calculated force. his function was plotted to choose a diameter andnumber of 4laments.

he relation showed that a diameter between .# and .B mm was ideal, provided thatfor a ?.?!cm defect, a mesh with a smaller diameter would need increasingly more4laments and meshes larger than "mm were undesirable. 4lament number of !'was chosen, yielding a necessary diameter of .#$?!mm. o meet the curve at !'4laments, a diameter of .!mm was chosen.


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