Biomedical Engineering Reference
In-Depth Information
(A)
(B)
Figure 21.3
The next generation of artificial heart valves. (A) Tri-leaflet heart-valve designed, by
University College London (UCL) with enhanced geometry for improved hemodynamic design. (B) A valve
prototype manufactured using POSS-PCU and Dacron suture ring. Reproduced from [68] with permission
by the International Journal of Nanomedicine.
man who presented with recurrent primary cancer of the distal trachea and main bronchi,
previously treated with debulking surgery and radiation. The nanocomposite POSS-PCU
implant was tailor-made for the patient, seeded with autologous bone-marrow mononuclear
cells and placed in a bioreactor for 36 h before implantation [67]. This is to our knowledge the
only case that has used stem cells on a nanocomposite polymer for clinical application.
One of the most promising areas of application of POSS nanomaterials is the development
of cardiovascular implants [68]. Synthetic heart valves based on POSS-PCU represent an
attractive alternative to the existing devices as they resemble the superior durability of
mechanical valves and enhanced hemodynamic properties of bioprosthetic valves at the
same time [68]. The superior mechanical and chemical properties of POSS-PCU make this
material suitable for developing the next generation of artificial heart valves (Figure 21.3).
Currently, the POSS-PCU nanocomposite is under investigation in our centre for devel-
oping a novel aortic valve suitable for transcatheter aortic valve implantation [68]. Its design
strategy is aimed at achieving high hydrodynamic performances while reducing stress levels
[68]. In this design three polymeric leaflets (POSS-PCU nanocomposite) are attached to a
self-expandable nitinol wire stent, which creates a high expanded/collapsed diameter ratio.
It also improves anchoring by creating sufficient radial and axial forces. What makes this
design even more interesting is that these heart valves are fully retrievable and reposition-
able, two properties that can play a major role in determining the success of the operation.
Tissue-engineering of vascular bypass grafts is another area of research in which the
potential application of POSS-PCU is being investigated (Figure 21.2). To this end,
progenitor cells, extracted from peripheral blood of adult healthy patients, were seeded on a
porous biofunctionalized POSS-PCU nanocomposite under static conditions and endothe-
liazation was evaluated [69]. The results were promising and demonstrated that they have
the ability to promote rapid endotheliazation from progenitor cells [69]. Further studies on
POSS-PCU bypass grafts revealed that they match the viscoelastic properties of the human
arteries, a crucial aspect for the success of the implant in humans.
So far the
in vivo
implantation of the POSS-PCU nanocomposite small diameter bypass
grafts generated favorable outcomes and the human clinical trial of these is due to proceed
