Fall  2014  

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BIOE  370  Project    Sutures  have  been  applied  for  thousands  of  years  in  the  closure  of  wounds  and  surgical  incisions  to  facilitate  wound   healing.   Over   the   millennia,   a   vast   number   of   suture   materials   and   designs   have   been   explored,  ranging  from  the  heads  of  biting  insects  to  absorbable  synthetic  polymers.  A  number  of  complex  engineering  issues  are  involved  in  selecting  a  material  and  design  for  sutures  for  a  particular  application,  some  of  which  will  be  introduced  and  explored  through  this  project.    You  have  been  contracted  as  a  biomaterials  consultant  to  assist  a  surgeon  in  selecting  a  suture  material  and  design  for  application  in  closing  a  straight  laceration  5-­‐cm  in  length  to  the  latissimus  dorsi  muscle  in  an  adult  human  patient.    

1) List   and   rationalize   three   or   more   numerical   design   requirements   for   sutures   for   the   given  application.    Cite  any  sources  you  use  and  state  your  assumptions.  (6  points)    

2) Sutures   can   be   either   absorbable   or   non-­‐absorbable.   Illustrate   on   a   graph   how   the   percent   initial  mass  and  percent  initial  tensile  strength  of  an  absorbable  suture  would  change  as  a  function  of  time  (plot   time   on   the   x-­‐axis   and   provide   a   scale).   Would   an   absorbable   or   a   non-­‐absorbable   suture  material   be   indicated   for   the   given   application   and   why?   If   absorbable,   then   what   would   be   an  appropriate   time   frame   for   degradation   (provide   numerical   values   and   a   justification   for   your  answer)?  (4  points)    

3) General  material  options  for  production  of  sutures  include  natural  polymers,  synthetic  polymers,  and  metals.   List   a   specific   example   from  each   of   these   general  material   options   (do   not   provide   trade  names,   such  as  Vicryl).  Also,  provide  an  example  of  an  application   for  a  suture   from  each  material  class  and  rationalize  each  example  in  terms  of  the  mechanical  properties  of  the  material  with  respect  to   the   mechanical   requirements   for   the   listed   application.   Support   your   answer   with   numerical  values,  cite  any  sources  you  use,  and  state  your  assumptions.  (10  points)    

4) Sutures  can  be  designed  to  be  either  monofilaments  or  braids  of  several  fibers.  Consider  the  case  of  polymeric   sutures   and   provide   an   advantage   and   a   disadvantage   for   each   suture   design  (monofilament  and  braid).  Would  you  select  a  monofilament  or  a  braid  suture  for  the  latissimus  dorsi  application?  Rationalize  your  selection  in  terms  of  the  properties  of  the  selected  suture  type  and  the  requirements   of   the   application   (include   in   your   rationalization   discussion   of   at   least   three   of   the  numerical  design  requirements  you  listed  in  response  to  Part  1).  Support  your  answer  with  numerical  values,  cite  any  sources  you  use,  and  state  your  assumptions.  (10  points)  

 5) The  manufacturing   of   sutures   requires   a   number   of   steps,   ranging   from   the   synthesis   of   the   raw  

materials   to   the   shipping   of   the   packaged   product   to   the   purchaser.   Consider   the   case   of   a  monofilament   suture   fabricated   from  a   synthetic   polymer  using   an   extrusion  process.  A   simplified  flow  of  the  manufacturing  process  is  as  follows:    

Extrusion   -­‐>   Stretching   of   Fibers   between   Rollers   -­‐>   Annealing   -­‐>   Surface   Coating   (If  Applicable)   -­‐>   Quality   Assurance   Testing   -­‐>   Attachment   to   Pre-­‐fabricated   Needle   (Process  Termed   “Swaging”)   -­‐>   Individual   Packaging   -­‐>   Sterilization   -­‐>   Group   Packaging   -­‐>  Sorting/Shipment    

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Describe  in  terms  of  polymer  chain  orientation  what  occurs  when  the  fibers  are  stretched  between  rollers.  Why   would   this   step   be   important   in   the  manufacturing   process   for   sutures?   Describe   in  terms  of  polymer  crystallinity  the  effects  of  the  annealing  step?  Why  would  this  step  be  important  in  the  manufacturing  process  for  sutures?  The  quality  assurance  testing  typically  involves  verification  of  the   mechanical   properties   of   the   sutures   and   verification   of   the   degradation   kinetics   (if   an  absorbable   suture).   Describe   a   relevant   mechanical   test   that   could   be   applied   in   the   quality  assurance   testing   and   how   it   would   relate   to   the   in   vivo   application.   Identify   the   steps   in   the  simplified  flow  diagram  of  the  manufacturing  process  that  would  be  expected  to  change  the  elastic  modulus  of  the  suture  and  state  and  rationalize  to  what  degree  the  modulus  would  change  (provide  a  numerical  response,  in  terms  of  percent  increase  or  decrease).  For  an  absorbable  suture,  would  an  in   vitro   or   an   in   vivo   (in   this   case   an   animal   model)   assessment   be   more   representative   of   the  degradation  rate  expected  in  the  patient  and  why?  Would  the  site  of  application  of  the  suture  affect  its   absorption   rate?   Why   or   why   not?   List   and   rationalize   a   sterilization   method   for   the   suture  material  you  selected  for  the  given  application.  Would  you  expect  monofilament  or  braided  sutures  to  involve  a  longer  production  time?  Why?  (20  points)    

6) Life-­‐cycle  analysis   involves  the  evaluation  of  the  total  environmental   impact  of  a  product  (from  the  generation   of   the   raw   materials   to   the   disposal   of   the   used   product).   Prior   to   the   wide-­‐spread  application  of  synthetic  polymers   in  the  production  of  absorbable  sutures,  an  absorbable  naturally-­‐derived  polymeric  material  known  as  “catgut”  (derived  from  extracellular  matrix  components  of  the  intestines  of  animals,  but  not  necessarily  cats)  comprised  the  majority  of  sutures.  The  excerpt  below  details  the  production  scale  of  catgut  sutures  at  one  manufacturing  plant  in  Scotland  in  the  1970s.  

 “In  Edinburgh  alone  we  employ  over  a  thousand  people,  use  the  intestines  of  26,000  sheep  per  day  and  manufacture  enough  suture  and  ligature  material  in  a  year  to  stretch  three-­‐quarters  of  the  way  round  the  Equator.  These  materials  comprise  catgut  which  accounts  for  nearly  half  of  all  sutures  and  ligatures,   the   remainder   being   mainly   nonabsorbables…”   from   MacKenzie   D.   The   Twenty-­‐third  Annual  General  Meeting  and   Sixty-­‐eighth  Ordinary  Meeting;   “The  History   of   Sutures.”   The   Scottish  Society  of  the  History  of  Medicine,  1971;  17:  158-­‐168.    Describe  in  400-­‐500  words  the  yearly  environmental  impact  of  the  suture  production  by  the  plant  in  Edinburgh,   given   the   provided   details.   It   is   important   to   think   as   broadly   as   possible.   (20   points)  Support   your   description   with   quantitative   figures   calculated   from   the   information   provided  (calculations  can  be  shown  on  an  additional  page  and  do  not  count  against  the  word  limit).  State  any  assumptions  you  make.  Include  in  your  assessment  the  number  of  sutures  that  reasonably  could  be  produced  (again,  state  your  assumptions).  (10  points)  Also,   include  one  or  two  sentences  providing  your  hypothesis  as  to  whether  or  not  the  development  of  absorbable  synthetic  polymer  sutures  has  an   associated   increased  or   decreased   environmental   impact   relative   to   catgut   sutures.   (10   points)  Support  your  hypothesis  with  at  least  one  major  difference  in  the  production  of  sutures  from  the  two  materials  that  significantly  influences  the  environmental  impact  based  on  your  life-­‐cycle  analysis  and  any  relevant  literature  reports  comparing  the  two  materials.  (10  points)  

Ronal Infante

BIOE 370 Project

Due 11/26/2014

BIOE 370 Project

Objective: Closing a straight laceration 5-cm in length to the latissimus dorsi muscle in an adult human

patient.

1. Assuming that the straight laceration is thin enough to close with sutures, produces tensile forces

able to be countered by the suture material, and has one, if not few, layer(s) that must be closed

(Ethicon 2004:11), the following are three numerical requirements for appropriate sutures:

Low modulus of elasticity of less than 500,000 psi to afford low stiffness and plenty of

flexibility (Broyer 1994).

The ratio of suture length to wound length should be at least 4:1 to avoid complications

(Millbourn 2009). Therefore, at least 20 cm of sutures is required.

High uniform tensile strength that never exceeds the tensile strength of the tissue

(Ethicon 2004:11). In the case of the latissimus dorsi muscle, sutures should never

exceed 490 MPa (Bogduk 1998).

Other requirements lacking numerical data:

Tensile strength retention throughout healing period.

Sterility of suture.

Uniform diameter of suture.

Ronal Infante

BIOE 370 Project

Due 11/26/2014

2. The absorption of a suture and the loss of tensile strength do not directly correspond. A slowly

absorbing suture may quickly develop poor tensile strength and vice versa (Ethicon 2004: 12).

Furthermore, different suture brands will have unique absorption and tensile strength loss profiles

(Ethicon 2004:13). Adapted from Figure 7.4 (Chu 1996: 139), the following graph compares the

percent initial mass and percent initial tensile strength for absorbable plain catgut sutures in the

back of a rabbit as a function of time:

Seroma, or the collection of clear serous fluid underneath surgical skin incisions (Al-Gaithy

2010), is a major complication in suture application to the latissimus dorsi muscle (Shin 2012;

Taghizadeh 2008). Since locations with major fluid accumulation accelerate the absorption of

absorbable sutures (Lai 2013; Ethicon 2004) and surgical procedures to the latissimus dorsi

muscle often result in seroma accumulation, non-absorbable sutures would be required. In this

environment, absorbable sutures prove inadequate since they may degrade before the incised

muscle could recover, possibly leaving the incision open.

0

20

40

60

80

100

0 10 20 30

Per

cent

fro

m I

nit

ial

(%)

Time (days)

Tensile Stength Mass

Ronal Infante

BIOE 370 Project

Due 11/26/2014

3. For the purposes of examining the relative mechanical properties of each of the following general

suture material options, additional criteria such as sterility, cost, and surgeon preference were

assumed negligible. Needle compatibility with the suture and the application was also ignored

assuming that an appropriate needle would exist. It was also assumed that the sutures would be

applied at one or few layer(s), ignoring suture depth due to multiple incision layers. The

following are examples of the three general material options and rationalizations of their

mechanical properties to their applications:

Natural polymers – Surgical Silk Sutures

Useful in oral surgery, maxillofacial surgery, ophthalmology (Serag-Wiessner 2006: 35),

and generally regarded as “the standard of performance (Lai 2013),” this example of a

non-absorbable, natural polymer suture has “superior handling characteristics (Lai

2013),” “high knot stability (Serag-Wiessner 2006: 35),” and “outstanding sliding ability

(Serag-Wiessner 2006: 35).” These properties can be attributed to the material’s low

tenacity (3.43 GPD) and high modulus (79 GPD) (Chu 1996: 107-108), despite its

relatively lower yield stress and breaking stress. This material is ideal for the smaller,

more precise sutures common to the eyes, face, and mouth, since these sutures will

generally require less elongation and more stiffness and tensile strength to keep smaller

surgical incisions shut. This suture material comes in a wide range of sizes from USP 8-0

to 5 or EP 0,4 to 7 and is manufactured as a multifilament, either braided or twisted

(Serag-Wiessner 2006: 35).

Synthetic polymers – Polydioxanone (PDS II) Sutures

Useful in dermatology, vascular surgery, orthopedics, plastic surgery, and urology

(Serag-Wiessner 2006: 27), this example of an absorbable, synthetic polymer suture has a

long, reliable absorption period of 180 – 210 days until full tensile strength loss and a 28-

42 day half-life (Serag-Wiessner 2006: 27). Polydioxanone suture size ranges from USP

7-0 to 2 or EP 0,5 to 5 (Serag-Wiessner 2006: 27). According to the Ethicon Product

Catalog (Ethicon 2014), polydioxanone sutures have the longest absorption period and

are among the absorbable suture materials with the longest strength retention period.

Additionally, since this material is manufactured as a monofilament, it exhibits low

microorganism growth. Since this material retains its mechanical properties for a long

period, it is the ideal absorbable suture to maintain wound closure for tissues with longer

regeneration periods, such as cartilage in orthopedic surgeries (National Health Service

2014).

Ronal Infante

BIOE 370 Project

Due 11/26/2014

Metals – Surgical Steel Sutures

Useful in orthopedics, neurosurgery, trauma surgery, and cardiac surgery (Serag-

Wiessner 2006: 36; Lai 2013), this example of a non-absorbable, metallic suture has the

highest tensile strength among suture materials (Serag-Wiessner 2006: 36). Steel suture

size ranges from USP 5-0 to 8 or EP 1 to 10 (Serag-Wiessner 2006: 36), leaning more

towards the larger suture diameters that produce higher tensile strengths (Chu 1996: 48).

Higher tensile strength ranging from 113 to 116 kgmm-2

(Chu 1996: 110) makes this

material ideal for suturing incisions in locations that experience a lot of movement, and

therefore pressure and tensile forces, such as closing the chest cavity after cardiac surgery

or the skull after neurosurgery. Steel will undergo very little stretch and will effectively

hold the suture shut.

4. Sutures can be manufactured in two designs:

Monofilament:

+ The single filament structure of these sutures encounter less resistance passing through

tissue (Ethicon 2004: 11).

- Because it is comprised of only one filament, any crimping or crushing of the suture will

damage it and create a weak spot that may lead to breakage (Ethicon 2004: 11).

Braided:

+ Braiding of filaments affords higher tensile strength and flexibility (Ethicon 2004: 11).

- Microorganisms may adhere to the crevices of the structure and lead to infection (Ethicon

2004: 11).

A non-absorbable monofilament suture, such as polypropylene, would be ideal for suturing the

latissimus dorsi muscle. Because of its chemical structure and monofilament design,

polypropylene sutures do not adhere to tissue and are easily applied (Lai 2013). Polypropylene

sutures are “biologically inert (Lai 2013)” and resist microorganism adherence

(Ethicon 2004: 11).

Modulus conversions are calculated below:

Density of polypropylene:

946.00 kgm-³ = 0.946 gcm

-3 (Wikipedia 2014)

Ronal Infante

BIOE 370 Project

Due 11/26/2014

Modulus of elasticity of polypropylene:

15 – 20 GPD (Modrak 1998) = (15 – 20 GPD) * 0.08825 (N/Tex)/GPD [N/Tex = GPa/gcm-3

(Hearle 2001)] = 1.323 – 1.765 GPa/gcm-3

(1.323 – 1.765 GPa/gcm-3

) * 0.946 gcm-3

= (1.252 – 1.669 GPa) * 145037.738 psi/GPa =

181626.046 – 242168.061 psi

The modulus of polypropylene sutures is below the cutoff stated in the aforementioned numerical

requirements. Therefore, the sutures will have enough flexibility for this application.

PROLENE® polypropylene sutures are sold in a variety of lengths, some above the 20 cm

requirement for the latissimus dorsi muscle laceration (Medline 2014). The tensile strength of

PROLENE® polypropylene sutures ranges from 4049.9 – 4657.29 kgcm-2

depending on the

gauge (Von Fraunhofer 1985).

(4049.9 – 4657.29 kgcm-2

) * 9.81 ms-2

= 39729.519 – 45,688.014 Ncm-2

(39729.519 – 45,688.014 Ncm-2

) * 100^2 cm2m

-2 = 397295190 – 45,6880,149 Pa

(397,295,190 – 456,880,149 Pa) / 1000 = 397.295 – 456.880 MPa

Therefore, the tensile strength of PROLENE® polypropylene sutures is an adequate match for the

latissimus dorsi muscle’s tensile strength stated in the numerical requirements. Assuming all of

my calculations are correct, non-absorbable monofilament sutures, such as polypropylene, would

be ideal for suturing the latissimus dorsi muscle.

5. The second step in the flow diagram of the manufacturing process is stretching the synthetic

polymer fibers between rollers. When the polymer fibers are stretched between rollers, the

polymer chains within lamella and otherwise orient themselves along the axis of loading,

increasing the amount of polymer chains per unit area. This stretching (and the resulting polymer

chain alignment) removes misaligned chain kinks in the the polymer material and increases the

material’s crystallinity (Temenoff 2008: 112). Less kinks and higher crystallinity lead to

increased material tensile strength in the direction of loading in order to prevent rupture.

Therefore, stretching between rollers is important because it increases the tensile strength of the

polymer.

The annealing step (a type of thermal processing) increases the crystallinity of the polymer by

using heat to alter the morphological structure of the polymer. Using temperatures above the glass

transition temperature of the material but below melting temperature, the higher energy state

Ronal Infante

BIOE 370 Project

Due 11/26/2014

polymer chains within lamella and otherwise are able to rearrange into more energetically

favorable configurations, increasing crystallites and reducing the size of amorphous regions

(Fischer 1972). As the polymer cools slowly, the polymer chains remain in these configurations

(Temenoff 2008: 209). These energetically favorable configurations feature tightly packed

lamella and higher polymer crystallinity. As aforementioned, an increase in crystallinity of the

polymer relates to an increased the amount of polymer chains per unit area available to resist

tensile forces. Therefore, annealing is important because it also increases the tensile strength of

the material.

Ideally, sutures are meant to seal surgical incisions and provide the necessary tensile strength that

the tissue lacks during tissue regeneration. As a patient moves, tensile forces will be applied to

sutures and they are expected to withstand such forces and resist fracture. Therefore, tensile

testing is imperative for sutures because they must resist the tensile forces they will experience in

in vivo application when a patient moves around. The tensile testing sample is placed on a

mechanical testing frame suited for sutures that features a static grip and a movable platform grip

that provides the testing sample with a load (Temenoff 2008: 133; ADMET 2014). Engineering

stress and strain is calculated from the cross-sectional area, sample lengths, and force applied

across multiple loading cycles (Temenoff 2008: 134). Tensile strength is determined

experimentally right before material failure (Temenoff 2008: 139). Modulus of elasticity is

determined from the relationship between stress and strain throughout testing (Temenoff 2008:

136).

Both the stretching of fibers between rollers and annealing step change the elastic modulus of the

suture because they modify the mechanical properties of the material. As previously discussed,

both steps increase the tensile strength of the material by increasing crystallinity. Since modulus

increases with increasing crystallinity (Ries 2005), both steps thus increase the elastic modulus of

the suture. Annealing produced a 150% increase in the moduli of electrospun poly (L-lactic acid)

nanofibers (Tan 2006). Assuming annealing has the same effect on all polymer moduli, the same

percent increase in moduli is expected. As for the percent increase brought on by stretching the

fibers between rollers, a smaller percent increase is expected because realignment of polymer

chains will not produce as much of an increase in crystallinity as the tight re-packing of lamellar

and amorphous chains brought on by annealing.

Ronal Infante

BIOE 370 Project

Due 11/26/2014

For an absorbable suture, an animal in vivo model would be required to accurately assess the

degradation rate of the material due to chemical and mechanical interactions with surrounding

bodily fluids and tissues (Temenoff 2008: 190). A significantly accurate in vitro model would

need to take into account countless bodily factors and yet not be as representative.

The in vivo model must be site-specific because different parts of the body exhibit different

amounts of water, proteins, inflammatory cells and mechanical stresses, enzyme concentrations,

ion concentrations and pH levels (Temenoff 2008: 190). Therefore, local chemical and

mechanical interactions must be taken into account when determining absorption rate.

Ethylene oxide sterilization is the ideal sterilizing method for polymers (Temenoff 2008: 224).

By permanently altering pathogen nucleic acids and prompting death, it proves to be an effective

method of sterilization. It can sterilize deep within crevices and pores, and it is performed at low

temperatures. However, toxic residues must be monitored. Other sterilization methods prove less

feasible. Steam sterilization is not suitable since it would expose polymer sutures to high

temperatures, likely past the melting temperature, and water, which would degrade an absorbable

polymer. Furthermore, radiation sterilization is very expensive and would expose polymers to

radiation degradation.

I expect the braided sutures would take longer to produce because each strand must undergo the

production and sterilization processes. Then, an additional step of combining/braiding must be

performed.

6. Below are the calculations made in determining the yearly environmental impact of the suture

production using the Edinburgh data (MacKenzie 1971):

Equatorial circumference of the Earth:

40,075 kilometers (National Geographic Society 1989).

Suture and ligature material manufactured in a year:

3

4 ∗ 40,075 𝑘𝑚 = 30056.25 𝑘𝑚

Sheep slaughtered in a year:

26,000𝑠ℎ𝑒𝑒𝑝

𝑑𝑎𝑦 ∗ 365

𝑑𝑎𝑦𝑠

𝑦𝑒𝑎𝑟 = 9.490𝑒6 𝑠ℎ𝑒𝑒𝑝 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟

Suture material per sheep in a year:

Ronal Infante

BIOE 370 Project

Due 11/26/2014

30056.25 𝑘𝑚

9.490𝑒6 𝑠ℎ𝑒𝑒𝑝 = 3.167 𝑚𝑒𝑡𝑒𝑟𝑠 / 𝑠ℎ𝑒𝑒𝑝 ∗ 𝑦𝑒𝑎𝑟

Assuming catgut sutures are of the same length as the ideal latissimus dorsi suture length,

the number of catgut sutures per sheep in a year:

3.167

𝑚𝑒𝑡𝑒𝑟𝑠𝑠ℎ𝑒𝑒𝑝

∗100 𝑐𝑚𝑚𝑒𝑡𝑒𝑟

20 𝑐𝑚= 15.836 𝑐𝑎𝑡𝑔𝑢𝑡 𝑠𝑢𝑡𝑢𝑟𝑒𝑠 / 𝑠ℎ𝑒𝑒𝑝 ∗ 𝑦𝑒𝑎𝑟

30056.25 𝑘𝑚 ∗ 100000𝑐𝑚𝑘𝑚

20 𝑐𝑚= 150,281,250 𝑐𝑎𝑡𝑔𝑢𝑡 𝑠𝑢𝑡𝑢𝑟𝑒𝑠 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟

Assuming the other half of all sutures has the same result (50/50 ratio = 1/1),

150,281,250 non-absorbable sutures are made per year as well.

Sheep are slaughtered when they reach the age of 6 months (Claeys 2003). Assuming all

sheep are slaughtered at the same age:

26,000𝑠ℎ𝑒𝑒𝑝

𝑑𝑎𝑦∗ 30

𝑑𝑎𝑦𝑠

𝑚𝑜𝑛𝑡ℎ∗ 6 𝑚𝑜𝑛𝑡ℎ𝑠

= 4.680𝑒6 𝑠ℎ𝑒𝑒𝑝 𝑚𝑢𝑠𝑡𝑏𝑒 𝑘𝑒𝑝𝑡 𝑜𝑛 𝑎 𝑓𝑎𝑟𝑚 𝑎𝑡 𝑎𝑛𝑦 𝑝𝑜𝑖𝑛𝑡 𝑖𝑛 𝑡𝑖𝑚𝑒

Each sheep eats about 4 lbs of grain a day (University of California 2014). Assuming all

sheep consume the same amount of grain:

4.680𝑒6 𝑠ℎ𝑒𝑒𝑝 ∗ 4 𝑙𝑏𝑠 𝑜𝑓 𝑔𝑟𝑎𝑖𝑛/𝑠ℎ𝑒𝑒𝑝 ∗ 𝑑𝑎𝑦 ∗ 365 𝑑𝑎𝑦𝑠/𝑦𝑒𝑎𝑟

= 6.833𝑒9 𝑙𝑏𝑠 𝑜𝑓 𝑔𝑟𝑎𝑖𝑛 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟

One acre of land produces 60 lbs of grain (Funderburg 2008). Assuming this number is

consistent for all acres of land:

6.833𝑒9 𝑙𝑏𝑠 𝑜𝑓 𝑔𝑟𝑎𝑖𝑛 ∗1 𝑎𝑐𝑟𝑒

60 𝑙𝑏𝑠= 1.139𝑒8 𝑎𝑐𝑟𝑒𝑠 𝑜𝑓 𝑙𝑎𝑛𝑑 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟 𝑡𝑜 𝑚𝑎𝑘𝑒 𝑔𝑟𝑎𝑖𝑛

Each acre requires 16 acre-inches of water (Bauder 2005). Assuming every acre uses the

same amount of water:

1.139𝑒8 𝑎𝑐𝑟𝑒𝑠 𝑜𝑓 𝑙𝑎𝑛𝑑 ∗16 𝑎𝑐𝑟𝑒 𝑖𝑛𝑐ℎ𝑒𝑠

𝑎𝑐𝑟𝑒∗

27154.286 𝑔𝑎𝑙𝑙𝑜𝑛𝑠

𝑎𝑐𝑟𝑒 𝑖𝑛𝑐ℎ

= 4.948𝑒13 𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟 𝑡𝑜 𝑚𝑎𝑘𝑒 𝑔𝑟𝑎𝑖𝑛

Each sheep requires 1.5 gallons of water per day (Ingram 2014).

4.680𝐸𝑒6 𝑠ℎ𝑒𝑒𝑝 ∗ 1.5 𝑔𝑎𝑙/𝑠ℎ𝑒𝑒𝑝 ∗ 𝑑𝑎𝑦 ∗ 365 𝑑𝑎𝑦𝑠/𝑦𝑒𝑎𝑟

= 2.562𝑒9 𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟

Every 6 sheep need 1 acre of land (Schindler 2014). Assuming this is true for all sheep:

4.680𝑒6 𝑠ℎ𝑒𝑒𝑝 ∗ 1 𝑎𝑐𝑟𝑒/6 𝑠ℎ𝑒𝑒𝑝 = 7.8𝑒5 𝑎𝑐𝑟𝑒𝑠 𝑜𝑓 𝑙𝑎𝑛𝑑 𝑓𝑜𝑟 𝑠ℎ𝑒𝑒𝑝 𝑜𝑛 𝑎 𝑓𝑎𝑟𝑚

Ronal Infante

BIOE 370 Project

Due 11/26/2014

Each sheep produces 5.0e-3 Tg of methane per year (Lerner 1988). Assuming all sheep

produce the same amount of methane:

4.680𝑒6 𝑠ℎ𝑒𝑒𝑝 ∗ 5.0𝑒 − 3 𝑇𝑔 𝑚𝑒𝑡ℎ𝑎𝑛𝑒

𝑠ℎ𝑒𝑒𝑝 ∗ 𝑦𝑒𝑎𝑟∗

1 𝑔𝑟𝑎𝑚

1.0𝑒 − 12 𝑇𝑔

= 23.4𝑒15 𝑔𝑟𝑎𝑚𝑠 𝑜𝑓 𝑚𝑒𝑡ℎ𝑎𝑛𝑒 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟

Producing catgut sutures from the intestines of sheep has a large yearly environmental impact. In

order to keep up the 26,000 sheep slaughter rate, at least 4.680e6 sheep must be bred and raised

continuously because it takes 6 months for a lamb to reach slaughter age. It takes 7.8e5 acres of

land to comfortably house this amount of sheep. Maintaining this amount of sheep takes 6.833e9

lbs of grain and 2.562e9 gallons of water per year. Furthermore, to produce the grain that feeds

the sheep, an additional 1.139e8 acres of land and 4.948e13 gallons of water per year is needed.

In addition to the environmental impacts to sustain the sheep, the sheep release 23.4e15 grams of

methane gas into the atmosphere per year. This contributes to the detrimental effects of

greenhouse gases and global warming. After all of this effort and environmental impact,

150,281,250 sheep catgut sutures are produced per year, 12,351,884 per month, and 411,730 per

day, assuming a constant rate over the entire year.

To produce these figures, assumptions were made to generalize the measurements that were

found. For example, it is not likely all sheep consume the same amount grain per day, despite it

being an average value, but the assumption had to be made in order to produce a general

calculated result. Also, only sheep were assumed to be used when calculating catgut sutures,

despite catgut sutures being able to be made by other animals as well.

Since we’ve calculated that a large amount of resources are required to produce cat gut sutures

and we know that synthetic polymers may be synthesized in labs through polymerization

reactions involving common carbon-based molecules, I would hypothesize that that the

development of absorbable synthetic polymers would produce a relative decrease in

environmental impact. Once removed from the sheep, natural sheep catgut sutures are processed

by removing intestinal contents and certain intestinal membranes (ROAP 2008). Then they are

cut, stretched, twisted and turned into sutures of varying size (Terhune 2014). Some types of

catgut are treated with chromium salts and heat to decrease tissue reactivity and increase tensile

strength respectively (Terhune 2014). While natural catgut sutures take time, money, and

Ronal Infante

BIOE 370 Project

Due 11/26/2014

environmental resources to produce, absorbable synthetic polymers form from reactions

involving organic molecules in labs. The process of polymerization joins basic organic mers into

longer polymer chains through repeated chemical reactions that usually involve free radicals

(Temenoff 2008: 64). Furthermore, synthetic polymers prove advantageous because you may use

copolymers to improve mechanical and chemical properties of the suture (Temenoff 2008: 66). It

should be mentioned that non-degradable synthetic polymers are of environmental concern due to

various forms of pollution (King 2014; Vroman 2009). However, absorbable synthetic sutures are

degradable and contribute minimal environmental pollution. After polymerization, processing

techniques, such as annealing, may be used to further improve suture mechanical, chemical, and

degradative bulk properties (Temenoff 2008: 218). While both natural and synthetic sutures

require additional processing to achieve satisfactory suture properties, producing a small amount

of pollution, the resources used in the synthesis of catgut sutures produce an overwhelmingly

larger environmental impact.

Ronal Infante

BIOE 370 Project

Due 11/26/2014

References

ADMET.

2014 “Suture tensile strength test.” ADMET Materials Testing System Manufacturer.

Publisher: ADMET.

Al-Gaithy, Z. K., Ali, S. S., Al-Sawy, N., and Ayuob, N. N.

2010 “Local and systemic TNF-α level correlation to histopathology in post-mastectomy

seroma in rabbits.” Surgery Journal, 5(2): 17-21.

Bogduk, N., Johnson, G., and Spalding, D.

1998 “The morphology and biomechanics of latissimus dorsi.” Clinical Biomechanics, 13(6),

377-385.

Bauder, J.W.

2005 “Wheat Irrigation.” Montana State University.

<http://waterquality.montana.edu/docs/irrigation/wheatirrigation.shtml>.

Broyer, E.

1994 “Thermal treatment of theraplastic filaments for the preparation of surgical sutures.”

Google Patents, US Patent 5,294,395.

<http://www.google.com/patents/US5294395>

Chu, C.C., von Fraunhofer, J.A., and Greisler, H.P.

1996 Wound Closure Biomaterials and Devices. Publisher: Taylor & Francis.

ISBN: 9780849349645.

<http://books.google.com/books?id=oFlXOeHboL8C>. *

Claeys M.C., S.B. Rogers

2003 “Sheep Facts” North Carolina State University.

<http://www.cals.ncsu.edu/an_sci/extension/animal/4hyouth/sheep/sheepfacts.htm>.

Ethicon, Inc.

2004 Ethicon Wound Closure Manual. Publisher: Ethicon, Incorporated.

<http://academicdepartments.musc.edu/surgery/education/resident_info/supplement/sutur

e_manuals/ethicon_wound_closure_manual.pdf>.

Ethicon US, LLC.

2014 “Sutures: Absorbable” Ethicon Product Catalog. Publisher: Ethicon US, LLC.

< http://www.ecatalog.ethicon.com/sutures-absorbable>.

Ronal Infante

BIOE 370 Project

Due 11/26/2014

Fischer, E. W.

1972 “Effect of annealing and temperature on the morphological structure of polymers.” Pure

and applied chemistry, 31(1-2), 113-132.

Funderburg, E. and D. Oswald

2008 “Profit Potential in Wheat for Grain” The Samuel Roberts Noble Foundation. Publisher:

The Samuel Roberts Noble Foundation, Inc.

<http://www.noble.org/ag/economics/profitinwheat/>.

Hearle, J. W. (Ed.).

2001 High-performance fibres. Elsevier.

Ingram, Roger.

2014 “How Much Water Do My Animals Need Each Day?” University of California Division

of Agriculture and Natural Resources. PDF.

<http://ucanr.edu/sites/placernevadasmallfarms/files/90846.pdf>.

King, J.

2014 “Environmental Problems Caused by Synthetic Polymers” seattlepi. Publisher: Hearst

Seattle Media, LLC.

<http://education.seattlepi.com/environmental-problems-caused-synthetic-polymers-

5991.html>.

Lai, Stephen Y, Daniel G Becker, and Richard F Edlich.

2013 “Sutures and Needles” Medscape Drugs & Diseases. Publisher: WebMD LLC.

<http://emedicine.medscape.com/article/884838-overview>.

Lerner, J., Matthews, E., & Fung, I.

1988 “Methane emission from animals: A Global High‐Resolution Data Base.” Global

Biogeochemical Cycles, 2(2), 139-156.

MacKenzie D.

1971 “The Twenty-third Annual General Meeting and Sixty-eighth Ordinary Meeting; ‘The

History of Sutures.’” The Scottish Society of the History of Medicine, 17: 158-168

Medline

2014 “Prolene Sutures by Ethicon.” Medline. Publisher: Medline Industries, Inc.

<http://www.medline.com/product/Prolene-Sutures-by-Ethicon/Z05-PF45417>.

Ronal Infante

BIOE 370 Project

Due 11/26/2014

Millbourn, D., Cengiz, Y., and Israelsson, L. A.

2009 “Effect of stitch length on wound complications after closure of midline incisions: a

randomized controlled trial.” Archives of Surgery, 144(11), 1056-1059.

Modrak, J.P.

1998 “High tenacity, high elongation polypropylene fibers, their manufacture, and use.”

Google Patents. US Patent 5,846,654.

<http://www.google.com/patents/US5846654>.

National Geographic Society.

1989 Exploring Your World: The Adventure of Geography. Publisher: National Geographic

Society. ISBN: 9780870447266.

<http://books.google.com/books?id=oFlXOeHboL8C>.

National Health Service

2014 “Cartilage damage” NHS Choices. Publisher: gov.uk.

<http://www.nhs.uk/conditions/Cartilage-damage/Pages/Introduction.aspx >.

Ries, M. D. and Pruitt, L.

2005 “Effect of cross-linking on the microstructure and mechanical properties of ultra-high

molecular weight polyethylene.” Clinical orthopaedics and related research, 440, 149-

156.

ROAP

2008 “Casings” Regional Office for Asia and the Pacific. Publisher: Food and Agriculture

Organzation of the United Nations.

<http://www.fao.org/docrep/010/ai407e/ai407e20.htm>.

Schindler, Melissa

2014 “The Pasture Size for Sheep” Pawnation. Publisher: Demand Media.

<http://animals.pawnation.com/pasture-size-sheep-5103.html>.

Serag-Wiessner KG

2006 Pocket Guide to Suture Materials, Techniques and Knots. 4th revised edition. Copyright

held by Serag-Wiessner KG, Naila, Germany.

<http://www.fmdental.pl/uploads/20110107131642.pdf>.

Shin, In Soo, Dong Won Lee, and Dae Hyun Lew.

2012 “Efficacy of quilting sutures and fibrin sealant together for prevention of seroma in

extended latissimus dorsi flap donor sites.” Archives of Plastic Surgery, 39(5): 509-513.

Ronal Infante

BIOE 370 Project

Due 11/26/2014

Taghizadeh, R., Shoaib, T., Hart, A. M., & Weiler-Mithoff, E. M.

2008 "Triamcinolone reduces seroma re-accumulation in the extended latissimus dorsi donor

site." Journal of Plastic, Reconstructive & Aesthetic Surgery, 61(6): 636-642.

Tan, E. P., & Lim, C. T.

2006 “Effects of annealing on the structural and mechanical properties of electrospun

polymeric nanofibres.” Nanotechnology, 17(10), 2649.

Temenoff, J. S. and Mikos, A. G.

2008 Biomaterials: the intersection of biology and materials science. Upper Saddle River, NJ,

USA: Pearson/Prentice Hall. *

Terhune, Margaret

2014 “Materials for Wound Closure” Medscape Drugs & Diseases. Publisher: WebMD LLC.

<http://emedicine.medscape.com/article/1127693-overview>.

University of California

2014 “Sheep: From the Animal’s Point of View” University of California. Publisher: ANR

Publication.

<http://anrcatalog.ucdavis.edu/pdf/8476.pdf >.

Von Fraunhofer, J. A., Storey, R. S., Stone, I. K., & Masterson, B. J.

1985 “Tensile strength of suture materials.” Journal of biomedical materials research, 19(5),

595-600.

Vroman, I., & Tighzert, L.

2009 “Biodegradable polymers.” Materials, 2(2), 307-344.

Wikipedia

2014 “Polypropylene” Wikipedia. Publisher: Wikimedia Foundation.

< http://en.wikipedia.org/wiki/Polypropylene>.

* In-text Page Reference: (AUTHOR DATE: PAGE #)