Macroporous beads were fabricated from a mixture of
alginate, surfactant, and a gas-generating component.
The method utilized was based on the creation of gas
pockets and their subsequent removal from the hydrogel
beads. The matrices possessed an interconnected pore
P. Eiselt et al. / Biomaterials 21 (2000) 1921}1927 1925
Fig. 5. In vivo response to implantation of porous alginate beads into
a subcutaneous pocket. Photomicrographs of tissue cross-section after
2 weeks of implanation at magni"cations of (a) 100] and (b) 400].
Photomicrographs have labels for alginate and (A) granulation tissue
(G), and blood vessels (arrows).
structure and su$ciently sized pores to allow cellular
invasion in vitro and in vivo. This method was also
adapted for the formation of matrices with low molecular
weight alginates ((50 kDa), obtained by the controlled
c-irradiation of high molecular weight alginate, which
potentially allows for renal clearance. Furthermore,
other surfactants (i.e., Pluronics) proved to be very suitable
replacements for the BSA.
Porous structures have been prepared adapting an
approach to form and subsequently remove gas bubbles
from alginate gels. This general method has been previously
described [10] but did not lead to the formation
of structures with a highly interconnected pore structure.
Additionally, there is no quanti"cation of porosity in the
previous studies. The modi"cation of this process described
here results in matrices that have a macroporous,
interconnected pore structure. BSA served as a surfactant
to stabilize the air bubbles created during vigorous agitation
of the solution. Several factors a!ect foam stability,
including the viscosity of the surface "lm. In order for
foaming to occur, the solute must be able to resist the
forces that rupture the lamellae long enough to form
a network of bubbles. The Ca2`-ions in the gelling solution
served to ionically cross-link alginate, while the
acetic acid reacted with the sodium bicarbonate to release
CO2
. Initially, the CO2 created gas bubbles in the
bead, and exposure of the beads to vacuum drew entrapped
gas bubbles out and created a highly interconnected
matrix. The openings on the surface of the matrix allowed
for cellular invasion, which is important for the
intended function in tissue engineering.