16 Nov 2015
New design of catheter and customized adhesive points towards less invasive methods of tissue repair.
Representing a potentially radical change in the way such cardiac problems might be addressed, the new device has been developed by researchers from Boston Children's Hospital; the Wyss Institute for Biologically Inspired Engineering at Harvard University; the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS); and the Karp Lab at Brigham and Women’s Hospital.
The work, published in Science Translational Medicine, builds on the earlier development of a light-activated adhesive based on poly(glycerol sebacate acrylate), a material which demonstrated all the necessary hydrophobic and biodegradable properties to function as a means of rapidly sealing defects in heart tissue and vessels.
To exploit this material properly, a method was needed of first getting the patch to the area to be treated and then applying the UV light needed to cure it - and preferably doing so without the invasive and potentially problematic open surgery techniques often involved in treating cardiac defects.
"The adhesive had been shown to be a way to seal vessels and cardiac defects, but what was missing was a device to deliver the light in a minimally invasive way," commented Ellen Roche, co-lead author on the paper. "A large light-guide attached to a UV source had been tried, but that is quite bulky, and putting it directly into the heart is not ideal."
So the team conceived an instrument able to deliver both the adhesive patch and the UV light, and then be removed back through a minimal aperture in the patch to leave the tissue tear sealed.
The procedure employs a catheter-based device that first unfolds the adhesive-loaded elastic patch in position and then deploys a double-balloon design - one small balloon on each side of the tear to be closed, so as to apply pressure to the patch against the tissue defect when the balloons are inflated. A fiber-optic system within the catheter then delivers the ultraviolet light needed to activate the adhesive.
"The design proved to be a challenge, even though we ultimately simplified it as much as possible while still meeting the criteria," said Roche. "It became an authentically multi-disciplinary effort, involving all the project partners, along with medical device specialists Vention Medical."
Part of that effort involved ensuring that enough of the UV light delivered down an optical fiber within the catheter successfully hits the uncured adhesive patch positioned across the damaged area. The eventual solution involved using one of the balloons pressing on the patch as a reflective chamber: UV emerges from the optical fiber into the balloon on the distal side of the tear, and is reflected back towards the adhesive thanks to a 100 nm metallic coating deposited on the inside of the balloon for this purpose.
By carefully shaping the tip of the optical fiber and adjusting its position within the reflective distal balloon, the pattern of reflected light could be controlled and optimized. Moving the fiber within the balloon allows a uniform spread of UV light to be effectively "painted" onto the patch, and completely cures the adhesive.
In ex vivo trials on tissues from pigs, the new system successfully treated defects in the abdominal wall, the stomach and the heart. Further testing in vivo showed its ability to seal tissues in rat hearts, and close what the STM paper describes as a challenging cardiac septal defect in a porcine animal model.
"Translation to human clinical trials may take a little time, given the novel nature of the approach and the need to do multiple lab and large animal trials first," commented Roche. "We have patented the technology and are looking to license it. A Paris-based company, Gecko Biomedical, will work on demonstrating the suitability of the adhesive for use in humans as we determine the strategy for going forward into new applications."
Alongside its clear step forward in tissue repair, the system demonstrates the advantages available from incorporating optical technologies into advanced catheter designs. Catheter-based biophotonic devices are currently making significant progress in bioimaging and optical biopsy fields, among others.
"Advances in optical technology and in the biophotonics space have certainly played a part in enabling this development in tissue repair, and there are several other applications where advanced optical fibers could be used," said Roche. "It's an exciting area, and could lead to a lot of different applications."
About the Author
Tim Hayes is a contributor to Optics.org.
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