APPLICATIONS
OF PSAs
PSA
usd for medical purposes are classified into two application area.
a) Skin
Contact
The
characteristics of a good skin contact adhesive include the absence
pf skin irritating ingredients, a high vapor transmission rate to
decreasing occlusivity, a cohesive stength high enough to allow the
adhesive to be clearly removed from the skin, rheologival properties
to accommodate skin movement without excessive mechanical skin
irritation , and good water resistance.
b)
Non skin contact
Generally
adhesive use for non-skin contact applications should be chemically
inert. Some devices such as diagnositc devices chould be
optically clear, oxygen permeable, water vapor permeable, and should
have excellent adhesion. Silicone polymers meet this
requirement.
SKIN
CONTACT APPLICATION
1.
Electromedical :
Electromedical
devices are designed to provide electrical connections between the
skin and some external equipment. Three types of
electromedical devices are currently in use; disposable EKG
electrodes, TENS electrodes and electrosurgical grounding pads.
a) Disposable EKG (also called
ECG ) electrodes :
These
devices provide a means of monitoring electrophysiological signals
produced by the body. Disposables EKG electordes have replaced
the older, reusable electrodes in most applications as prices have
dropped into the range of a few cent per unit. Design of
disposable EKG electrodes is to a great extent driven by cost
considerations.
b)
Tens electrodes :
The
second product in electromedical class is the TENS (transcutaneous
electrical nerve simulation ) electrodes, used to provide a part for
electrical current into the skin to block nerve impulses and control
pain.
c) Electrpsurgical frounding pads
:
These
devices are applied to the patients' skin during electrosurgery to
provide a continuous circuit with the generating equipment.
Grounding pads often contain conductive gels with some adhesives
properties, but since secure adhesion is critical, the pads are
constructed with a perimeter of more aggressive PSA around the
conductive gel to augment adhesion. Polyethlene foam with
acrylic adhesive is frequently used for this application, but
various occlusive laminates have also been used.
Low
impedance PSA is used for medical electordes. Addition of a
cross-linked poly (N-viny1 lactum) to hydrogel adhesives for
biomedical electordes such as ECG electrode, improves the adhesion
capacity and decrease impedance of the adhesives. An adhesive
comprised acrylic acid 22, benzyl di Me-ketal 0.06, triethylene
glycol bismethylacrylate 0.25, water 24, KOH 6.3, glycerol45,20, and
crosslinked PVP2gm8.
2.
Ostomy Appliances :
Surgical
procedures are sometimes required to create an artifical opening
into the abdomen for the draining of waste from the colon, the ileum
or the ureter. The opening, called a stoma is connected to the
disposable collection device which is typically secured to the body
with pressure sensitive adhesives.
Depending
upon the particular design of the collection appliance, the adhesive
may serve two functions;
a)
Sealing the device to the skin to prevent the leakage of fluids
around the stoma.
b)
Holding the device to the body.
All
the acrylic adhesives may be used for this purpose, their ability to
see around the stoma is marginal. Adhesives such as those
described in the patents assigned to squibb and johnson &
Jpjmspm ,au ne ised to provide sealing property and adhesion to wet
skin. Here adhesives are briegly defined as a blend of
elastomeric materials (preferably polyisobutylene) and water
swellable hydrocolloids ( carboxy methl cellulosem gelatin, pectin).
While adhesives of this type reduce leakage and their ability to
support the weight of the collection appliance is inadequate for
some devices. Case, the device may be designed with perimeter
of tape with the more aggressive adhesive. Non woven fabrics
with porous acrylic adhesives have been used.
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