ABSTRACT
The clinical use of pro-angiogenic growth factors could greatly impact the treatment of critical limb ischemia
(CLI), a condition characterized by arterial blockages in the extremities. With CLI, 40% of patients are ineligible
for available therapies and even with intervention, the 6-month risk of limb amputation is 25-40% with an
annual mortality of 20%. In preclinical models of CLI, collateral blood vessel formation and perfusion
restoration are observed in the ischemic limb following the administration of angiogenic growth factors.
However, attempts at clinically translating these promising preclinical results, via the use of at-site or systemic
injections of angiogenic growth factors, has remained a challenge. The delivery of growth factors via injection
or using conventional scaffold-based approaches does not afford active control of the dose, timing, or spatial
localization at the intended site of collateral vessel formation. Furthermore, no consensus exists regarding
what range of these parameters, including what combination of growth factors, are required for effective
therapeutic angiogenesis. Thus, there is an urgent need to develop a safe and effective delivery system for
multiple angiogenic growth factors that recapitulates critical aspects of endogenous growth factor signaling and
facilitates identification of these crucial parameters. Our long-term goal is to develop implantable biomaterials
for the delivery of regenerative molecules, where delivery can be manipulated spatiotemporally in an
externally-regulated, on-demand manner. The modulating mechanism is megahertz-range ultrasound, which is
clinically translatable since it can be applied non-invasively, focused with sub-millimeter precision, and
delivered in a spatiotemporally defined manner to sites deep within the body. The objective of this proposal is
to develop an implantable scaffold where the released dose, sequence, and localization of two growth factors
involved in angiogenesis - basic fibroblast growth factor (bFGF) and platelet derived growth factor-BB (PDGF-
BB) - are non-invasively controlled. The scaffold, termed an acoustically-responsive scaffold (ARS), is doped
with two ultrasound-sensitive emulsions that each contain a growth factor. The central hypothesis driving this
project is that ultrasound can spatiotemporally pattern angiogenesis in and around an ARS by controlling the
sequential release of bFGF and PDGF-BB. The rationale for the proposed research is that an ARS enables
the study of how various doses and spatiotemporal gradients of bFGF and PDGF-BB affect the development of
blood vessels, which can be used in the translation of therapeutic angiogenesis for the treatment of CLI. The
hypothesis will be tested via three specific aims: 1) enhance selective release of growth factors from the ARS;
2) use an ARS to demonstrate the impact of spatiotemporally-generated gradients of bFGF on angiogenesis;
and 3) demonstrate restoration of perfusion in a murine hind limb ischemia model using an ARS. Successful
completion of the proposed research is significant since it will elucidate how microenvironmental factors – such
as growth factor doses, spatiotemporal profiles, and sequence – affect angiogenesis.
