- Project Title
- Bacterial Cellulose-Made Prosthetic Vascular Grafts
- Project Type
- Nacional / Public
- Funding Body
- Funding Program
- CEB: 120 000,00
- Total: 156 000,00
- Universidade do Minho, Faculdade de Medicina da Universidade do Porto
- External link
A recent review on the state of the art of the prosthetic vascular grafts, entitled “Prosthetic Vascular Grafts: wrong models, wrong questions and no healing” (Zila et al, 2007), pointed the reasons for the failure of the small caliber commercial devices. These authors blame the experimental systems used for the evaluation of the newly developed materials. Thrombogenicity and intimal hyperplasia
remain the most common causes of graft failure. Indeed, there has been little improvement in long term patency of small diameter (< 4mm) prosthetic grafts over the past 100 years. Surprisingly, in humans, neither transmural ingrowth through the graft nor transanastomic ingrowth from the adjacent artery seem to be capable to endothelializing more than a narrow zone confined to the immediate anastomotic area (Brewster et al, 2007). Porosity has long been recognized as a prerequisite for grafts patency. A material with interconnected pores will favor the transmural
ingrowth and ultimately a proper endothelialization of the inner surface. However, the currently used synthetic materials, such as expanded polytetrafluoroethylene (ePTFE), Dacron and Polyurethan, hardly meet these structural properties. Neither of these materials, commonly used in the clinical practice, provides sufficient tissue ingrowth. Furthermore, even after prolonged periods of
implantation, a persistent foreign body reaction is observed.
A literature survey revealed the ongoing efforts in the development of a new generation of prosthetic grafts based in the use of new biomaterials, combined with tissue engineering approaches (Liu and Chang Park, 2008; Heydarkhan-Hgvall et al, 2008; Lovett et al, 2007). However, the beneficts of an off-the shelf approach must be considered, taking into account the massive need for these grafts, that will still be advantageous, over the tissue engineered graft, more time consuming and expensive to produce. The essential problem of producing a long-term fully functional artificial graft is still unsolved.
Bacterial Cellulose is a very promising biopolymer, with exquisite properties based on its 3-D nanofibrilar structure: high water absorption capacity, excellent mechanical properties, elasticity, in situ moldability, nanofiber network and biocompatibility (Czaja et al, 2006; Hsieh et al, 2008). Although a few companies, namely Xylos, are producing BC-based materials for biomedical applications,
it still remains basically an unexploited material. Remarkably, BC induces negligible foreign body reaction and is considered highly biocompatible, a property that has been attributed to the BC nanofibrillar structure (Klemm et al, 2001). Although the use of BC as tubular structures for vascular replacements has been described, it must be stressed that recent results show that the BC porosity is insufficient for tissue ingrowth (Helenius et al, 2005; Schumann, 2009). The in vivo assays to be performed in this projects innovates in several instances: 1) a highly porous and 2) resorbable BC will be developed; 3) long tubes (>4cm) will be used, allowing a proper estimation of endothelialization processes and performance of the material.