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Intergumentary system repair devices (skin focus) - Coggle Diagram
Intergumentary system repair devices (skin focus)
Sutures
been used for thousands of years
billions used anually
hold tissue together to allow healing
application dictates the need to be reabsorbable
failure load controlled by know type and thickness
Suture types
Natural
catgut (ovine-sheep-collagen) (general, subcutaneous)
silk (general suturing, ligation)
Synthetic absorbable
braids PGA/PLLA or PGLA (subcutaneous, peritonial, general)
monofilaments (various)
Synthetic non-absorbable
polyester (PET) (heart valves, vascular prosthesis, general)
polypropylene (general, vascular)
polyamide (nylon) (skin)
stainless steel (sternal closure, tendon repair, orthopedic)
fluorocarbons
Shape
monofilament
very springy, huge recoil
less flexible
braid
cannot move as much
can vary degradation between strands
modern needle and suture bonded together
Physical properties & definitions
Dimensions
(size and length)
tensile strength
(max tensile force that can be applied)
Knot pull strength
(max tensile force that can be applied to know)
needle attachment force
(force required to remove needle from strand)
Knot security
(force before knot slips)
Coefficient of friction
( force required to move strand across itself)
Memory
( tendency of strand to return to original shape)
Creep
(deformation of strand or knot over time under load)
swelling
(tendency of strand to swell in tissues)
Capillarity
(degree to which liquid is transported along a strand)
Handling properties & definitions
Knot tie down
(ease with which a knot can be slid down a strand)
first throw hold
(Force that a surgeon's knot (double turn) can withstand without slipping)
Tissue drag
(force required to pull strand through tissue)
Package memory
(degree to which retains package configuration)
Suppleness
(the feel of a suture)
Biological properties & definitions
Tissue reaction
(cellular response to a strand)
Tensile strength loss
(loss of tensile strength with implantation time)
Absorption
(enzymatic and/or hydrolytic)
Biocompatibility
(degree to which strand and breakdown products affect surrounding tissue)
Reabsorbable sutures
- natural sutures resorb faster than synthetics
Response to sutures
highest 1 day post op
higher for natural materials than synthetics
can allow infections to track into the body
Knot slippage controlled by
number of turns in the knot
friction between suture threads
plastic deformation of the suture thread
Suture failure
is cut through of the tissue
suture diameter has limited effect on initiation of failure (BSS-break starting strength) or final failure (SRS-suture retention strength)
chromic acid cross linking so when applied to sutures they break down and remolds them in a way that is harder to break down
Biomedical use polymers
Polyamides (nylons)
bonds developed between chains increases strength (cross linking)
Aramides- aromatic polyamides (Kevlar) with very high strength to weight
have the form [NH(CH2)_xNHCO(CH)_yCO]_2
easily drawn into fibers
absorb water and proteins easily
loses properties as water acts as plasticiser (reduces stiffness & strength)
polyethylene (HDPE/UHMWPE/XLPE) (orthopaedic sutures)
polyacrylates (PMMA, PEMA ect)
polytetrafluoroethylene (PTFE)
silicones
absorbable
Degradable polymers
types
polylactic acid/polylactide (PLA)
increase lactide to increase absorption time
polyglycolic acid/polyglycolide (PGA)
polycaprolactone (PCL)
polyhydroxybuterate (PHB)/polyhydroxyvalerate (PHV)
various co-polymers
breakdown in the body to water and CO2, excreted by the body
most are polyesters
ester bond is C=O & C-O (same C different O) bonded to R_1 & R_2
produced by acid and alcohol reacting, gives of H2O (condensation reaction)
to break down ester bond water is needed
Polydioxane (PDS)
made by ring opening polymerisation of p-dioxanone
used for monofilament sutures
low modulus
Staples
used for large or heavily loaded closures
quick to apply
can use shape memory alloys (SMA) to apply closure load
do not give good repair aesthetics
can close more after heat treatment
Adhesives
Cynoacrylates
polymerise fast on application
lower strength than sutures so less trauma on really soft tissues (spleen, lungs...)
Properties
very low viscosity
brittle and toxic
poor application ease
short set time
good tissue bonding
poor pliability
medium toxicity
poor reabsorbability
poor cell infiltration
spread well over the surface
initially methyl isobutyl and n-butyl were used
2-octylcyanoacrylate gained FDA apporval in 1998 with lower toxicity
strengthened with polymer mesh
addition polymerisation
Fibrin
more recently used more
based on fibrin involvement in clotting
higher strength than cynoacrylates
used for nerves anastomoses, micrograft surgery and bone grafts
developed in WW2 to stop bleeding
use synthetic fibrin clot as an adhesive wound covering agent
fibrin conc. much higher than in the blood
can be modified to promote homeostasis
Properties
excellent ease of application
medium set time
poor tissue bonding
excellent pliability
low toxicity
good reabsorbability
excellent cell infiltration
quick and will naturally be degraded
Hydrogels
block co-polymerisation
can be photopolymerised
photoinitiated addition polymerisation
block co-polymers of PEG, poly(lactic acid) and acrylate esters
GRF glue
gelatin, resorcinol and formaldehyde
condensation polymerisation
Properties
poor application ease
medium set time
excellent tissue bonding
poor pliability
high toxicity
poor reabsorbability
poor cell infiltration
required to flow over a wet surface
can be used for drug delivery
Skin Scaffolds
used for burns or trauma where large areas of skin damaged leading to potential bacterial ingress
scar tissue inclined to contract so can limit movement
skin can be grafted but limited amounts available
Burns
1st degree
mild pain
redness (no blistering)
skin functions normally
Treatment
flush with cold water, cover with dressing/membrane
Heals
3-4 days
Example
sun burn
only epidermis
2nd degree
pain
redness
blistering (epidermis separates from underlying layers and fluid fills void)
oedema
some skin function lost
treatment
if no infection no need for grafting just cover with dressing/membrane
heals
3-4 weeks
on epidermis and dermis
3rd degree
severe pain (burnt region is numb due to nerve damage)
marked oedema
marble white to black skin colour
most skin functions are lost
tissue damage
susceptible to infection
slow healing
treatment
requires skin/auto graft to promote healing and prevent scaring
epidermis, dermis and subcutaneous layer all effected
need to prevent excessive fluid loss, electrolytes etc but prevent wound getting "soggy"
tissue needs oxygen to repair
material needs to degrade as underlying tissue repairs
tissue engineering beneficial as it can bring in cells
ideal qualities of burn dressing/skin substitutes
inexpensive
single application
bacterial barrier/microbicidal
semipermeable to water vapour
conformable and elastic
easy to apply and remove
reduces pain
non-immunogenic and non-toxic
extended shelf life
maintains moisture and limits drainage
promotes tissue restoration and limits scar
ensure air pockets removed
similar mechanical properties between dressing and skin
resist shear forces
resist peel off
allow some moisture release to prevent oedema
split skin graft
outer layer of skin take from donor site on patient and meshed so covers defect area
avoids rejection process
removes risk of transmitted disease
Xenografts
taken from another species (typically porcine)
Xeno=foreign
split thickness grafts taken, sterilized then frozen
provides
temporary
coverage of 2nd degree burns
addition of silver to reduce microbial infections
some reconstituted fish skin also used
burn dressing and grafts/skin substitutes are an area that has
massively
developed over 20 years
dressings in 2004 were not positively benefiting the patient, now they do
Biobrane
not biodegradable so only
temporary
barrier
Combines
silicon outer layer -> prevent fluid loss & bacterial ingress
3D membrane -> encourage clotting mechanism thus regrowth of skin
silicon rubber, nylon mesh & collagen peptide makes up
fabric side towards wound
Dermagraft
cryopreserved dermal substitute
used for burns & diabetic ulcers
scaffold is polyglactin (co-polymer of glycolide and l-lactide)
scaffold also contains fibroblasts and extracellular matrix
Tissue engineered skin
can treat full thickness skin wounds
stem cells can differentiate into different cell types
collect cells and expand then seed onto scaffold
place on burn and allow healing
stem cells accelerate healing
takes time to produce skin cover but very effective
Percutaneous devices
permanent or semi-permanent entry to body required
need to take load without allowing bacteria entry
problems
extrusion
body trying to force implant out
down-growth of epithelium
invagination
over-growth of epithelium
both occur at skin device interface
unhelpful pathological responces
Interface requirements
epidermis & device
seal against bacteria
dermis & device
seal against bacteria and mechanical stress
hypodermis & device
seal against bacteria and mechanical stress
1st layer=epidermis, 2nd layer=dermis, 3rd layer=hypodermis, 4th layer=facia
implant material must be compatible with skin and bioactive for skin cells
Branemark Osseointegrated prostheses
1969 noted cpTi becomes strongly grown in bone
initially used in tooth root replacements
since 2000 used for amputes
improves propeoseption as directly through bone
need to be very careful of infection moving through skin
no weight on soft skin -> more comfortable
use factors
Data:
biopotentials, temperature, pressure, blood flow, etc
Energy:
electrical stimulation, power for cardiac assist devices, cochlear implants, etc
Material Transport:
kidney dialysis, blood infusion
Load Bearing:
prosthesis attachment
Blood gas monitoring
Measures
efficiency of pulmonary gas exchange
transport of blood gases
tissue oxygenation
non-invasive option contrasting to invasively taken blood samples
Pulse oximetry
monitors
pH
tc pO2
tc pCO2
oxygen saturation (sO2)
ratio oxygenated hemoglobin to deoxygenated
function
light passing through skin absorbed by
skin
soft tissue
venous blood
arterial blood (higher absorption in oxygenated hemoglobin)
2 modes
Transmission:
through pinna (lobe) of ear or finger tip
(classic method)
Reflection:
any convenient area of skin
use light at 660 and 805 nanometers -> measure difference in transmitted/reflected light
applications
neonates
intensive care
sleep apnea studies
during surgery
covid-19/pneumonia & other lung infections
not good at measuring methemoglobin
How effective?
overestimates change in arterial O2 and more slowly than other methods
reflectance picks up issues quicker than transmission
nail polish effects results (colour matters)
recent studies show skin colour also has large effects
relatively simple and effective
systematic errors must be considered
transcutaneous (non-invaisive)
