Demonstration of Heparin Coating in Tubing

(by J.J.G. Bos)

Click HERE for background information on heparin coatings.

PVC Tubing for Blood Transfusion
Nylon Tubing for Endovascular Catheters
High-density Polyethylene Tubing
Silicone Tubing

Here are some photographs of PVC tubing with the EMPEH heparin coating applied to the inner surface. The inner diameter of the tubing amounts 3.0 mm. The coating is stained with toluidine blue O, which gives it a nice violet color in the presence of heparin. The first picture shows, from left to right, (1) the uncoated tubing, (2) the EMPEH-coated tubing, and (3) the toluidine-stained EMPEH coating. The second picture shows results from artificial aging by subjecting the samples to elevated temperatures. The PVC material that was used here, tends to sweat low-molecular components that might cover/disable the heparin. However, the toluidine staining clearly shows that the heparin remains fully accessible. It must be noted though, that low-molecular sweating of the PVC during real-time aging will eventually put a limit on the shelf life of this type of samples. Artificial (accelerated) aging indicated a shelf life of more than 3 years. However, real-time aging of the same samples set the limit at 1 - 5 years, depending on the utilized coating application technique and the storage method. It was found that silicone tubing that had been coated with EMPEH proved to be (very) much less limited regarding shelf life.

The last picture in this section shows 4 meters of the same PVC tubing, coated with the EMPEH heparin coating and stained with toluidine blue O. It demonstrates suitability of this coating for application to PVC infusion/transfusion tubing, even if lenght matters. The CovHep and IoHep are not suited for application to PVC tubing. [Refer to the PRODUCTS page for more information related to the EMPEH, IoHEP and CovHEP coatings].

The pictures below show nylon tubing coated with the IoHep heparin coating. The inner diameter of the tubing amounts approximately 1.2 mm. The samples on the left, in the first picture, were stained with toluidine blue O on the inside. This clearly reveals the presence of heparin there. The second photograph shows a detail of the same stained tubes. The other samples in the first picture are (1) coated with the IoHep heparin coating, but not stained, and (2) uncoated tubes (control). The uncoated tubing does not pick up any significant amount of toluidine blue O.

The coated samples generally show a silk gloss, whereas the original samples had more shine to them. However, the difference is small and can hardly be noticed from the picture. These samples age very well - many many years of shelf life. Similar results regarding heparin staining are obtained with the EMPEH coating. In turn, the EMPEH coating is able to significantly reduce the coefficient of friction, whereas the IoHep coating is not. However, both coatings are anti-thrombogenic and thus prevent thrombus formation when in contact with blood.

The picture below-left shows the results from application of the IoHep heparin coating to high-density polyethylene tubing. The inner diameter amounts approximately 4.5 mm, the outer approx. 6 mm. The lower tubing has not been coated, whereas the upper three samples carry a monomolecular heparin layer on both the in- and outside. The second sample from the top is stained with toluidine blue O on the inside only. The uppermost sample was stained on the inside and outside. Without staining, this coating is hard to detect visually. However, originally shiny surfaces will have become somewhat duller after coating with this particular recipe. Similar results are obtained by application of the EMPEH coating, as can be seen in the second picture. Here, the coating was applied to the inside only. The EMPEH layer, as stated before, also reduces the friction coefficient of the samples. Note that the top sample of the second photograph is only partly stained, in order to show the contrast with the unstained part.

The picture below shows silicone tubing with the inner surface heparinized. The inner diameter of the tubing amounts 2.0 mm. Again, toluidine blue O treatment of the coating convincingly indicates the presence of the heparin. The tubing in this picture was coated and stained some six years before the picture was taken! The toluidine would have turned blue if sweating of low-molecular silicone components had reached and isolated the heparin (this happens with aging heparin-coated PVC tubing). Apparently, the coating is still in perfect condition!