Dural Sub v Sealant – Can one product really be both?

A surgical sealant is a surgical sealant. A tissue replacement is a tissue replacement. Can one product fulfil both functions without compromise?

Repairing the Dura Mater offers two challenges to the neurosurgeon. Where dural tissue is missing or inadequate it requires replacement with a so-called dural substitute. A dural substitute needs to have the potential to bridge gaps and regenerate dural tissue.

In contrast, routine closure of intact Dura, especially in high leak-risk areas, demands a tight seal. A dural sealant needs to be strongly adherent and resist physiological pressure.

Whether one product solution can address these dual demands remains open to question. Authors affiliated to a well-known sealant manufacturer seek the answer in an article recently published in Neurosurgery.

In an industry-funded study, Baxter Healthcare’s Kevin Lewis and co-workers describe an in vivo study comparing the merits of a ‘hybrid’ product, Hemopatch for use as a dural substitute and a sealant. This product combines a collagen-based dural substitute with a Polyethylene glycol (PEG) sealant surface.

It’s almost a decade since Tissuemed launched its revolutionary sealant film. The company’s scientists possess a wealth of experience in the field of tissue sealing and especially dural closure. The key parameter that originally drove Tissuemed towards a covalent bonding adherent film was physiological fluid pressure. The company rejected PEG-based sealants in the past for reasons of burst pressure resistance. Tissuemed concluded that polymers that physically adhered to the tissue surface offered a better solution, especially in situations where burst pressure risk is greatest. That view is still held today.

One key feature of the Lewis study is that it involves lower risk/pressure ‘supratentorial’ surgery.  Reading further, the authors report that the average maximum pressure of Hemopatch is 12.3mmHg, claiming it is ‘effective over the range of normal human CSF pressure, 7-15mmHg’. From the data presented we would challenge this conclusion.  It’s worth bearing in mind that the upper limit of normal CSF pressure can range from 20-25mmHg, almost twice the maximum pressure this hybrid product can withstand.

Continuing this theme, in destructive testing the Hemopatch product’s ‘mode of failure’ was cohesive. CSF ‘weeping through the collagen [component]’** is a common failure of collagen dural substitutes.

In conclusion, the data presented suggests the product will not be effective when faced with anything other than routine, low leak-risk conditions. The burst pressure data suggests it falls short in the face of physiological pressures encountered in the more challenging cases. These cases are also likely to be those in which leak risk is greater and its prevention more important.

Tissuemed introduced TissuePatchDural to the neurosurgical community back in 2007, ensuring it was presented to neurosurgeons as an effective dural sealant. Although TissuePatchDural can be used to close small gaps – up to 5mm, it is not indicated or promoted as a dural replacement.

David Mandley, Tissuemed’s CEO commented, “Comparative burst pressure data in the literature* reveals that the sealing strength of TissuePatchDural is more than 3 times that of Hemopatch. TissuePatchDural achieves consistent sealing performance in high pressure areas, where CSF leaks increase postoperative risks for complications.”

*summarised in the latest TissuePatchDural brochure, here.

**Application of a hydrogel sealant improves watertight closures of duraplasty onlay grafts in a canine craniotomy model. Preul MC1, Campbell PK, Bichard WD, Spetzler RF., J Neurosurg. 2007 Sep;107(3):642-50.