Pressure-Sensitive Adhesives (PSA) & Coatings :
Medical Device Applications

PSAs with Added Functionality
 

a) Conductivity : Electrodes, dispersive pads Drug delivery (iontophoresis) Electrochemical diagnostic tests	b) Hydrophilic/Hydrophobic Moisture barriers Moisture absorption Enhanced wetting (wound care, capillary flow diagnostic strips)
c) Permeability and Porosity Enhanced MVTR allowing longer term, safer wear of the item Controlled diffusion/penetration of liquids and gases in system	d) Hydrogels Biocompatible Ionically conductive

Typical Chemistries used in PSA

The typical chemistries that are used in pressure sensitive adhesives are as follows:

a) Elastomer: Different kind of elastomers are NR, Block polymer, PIB & SBR
b) Silicone: Various structures are used in PSA
c) Acrylic: By far it is most versatile because depending on what kind of monomers are used, you can tailor made a co-polymer of desired property.

Characterization of PSA

The PSA can be characterized in following ways:

• Surface Energy : It is an important property to characterize Pressure Sensitive Adhesives. All surfaces are not bond alike and the bond to one surface is different then the bond to other surface. For example Polypropylene bond is weaker bond and polyester bond is stronger bond and it all depends on surface energy. So tailoring a surface energy of pressure sensitive adhesive by using either chemistry route to do it or formulation route.

• Viscoelastic properties: Basically it determines the hardness of the material or cold flow material. This is very important property for diagnostic devices as in diagnostic devices it is required that material should not ooze out or there should not be filling up of capillary or clogging of filter paper.

• Tack : It is the measure of quick stick and it determines how well a material sticks and how quickly it sticks.

• Peel Strength: It is the measure of adhesion strength of adhesive.

• Shear Strength : It defines how much of weight can a material hold and what kind of temperature can it be subjected to before it slides.

• Residual solvent/extractable levels: This is very important with diagnostic devices because in diagnostic devices there should not be any residual solvent or any extractable coming out and interacting with ace chemistry and messing up with the result.

 Applications of Pressure Sensitive Adhesives

I. Biosensors in the market place.

Fig. 4 : Blood Glucose Monitor

Figure-2 shows glucose monitoring strips. These two strips are made out of several layers of materials and to bond these layers together one would use pressure sensitive adhesive in the final process. As shown in fig-5 , there is also electrode involved , transport of fluid is also involved from the sample area to the detection area. The flow of fluid depends on the kind of adhesive that is used.

As shown in Fig.-9 , Continuous glucose monitoring system, in which the adhesive used is not only used to hold the monitor to the body but it also plays the active role in performing chemistry for sensing glucose.
 

Fig. 5 : HemoSense INRatioTM system	Fig. 6 : NanoChip® Electronic	Fig. 7 : Amersham BioSciences CodelinkTM
Fig. 8 : Fig - 5 : i-STAT® Portable Analyzers	Fig. 9 : Medtronic Minimed Guardian® Continuous Glucose Monitoring System

Technology Overview& Related Applications

Competencies :

Adhesives research has several competencies in various fields like Medical , Pharmaceutical , Electronic Business , Engineered Tapes & Splicing Business.

I. Hydrophilic Films & PSA’s
 

A lateral flow device is built up with a stack of several layers and as marked in the fig-10 there is a layer of adhesive that is used to bond all the subsequent layers to the bottom substrate. And the top cover is also of pressure sensitive adhesive layer.

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