Biomedical Engineering Reference
In-Depth Information
nanotube) multilayer film. NSCs behaved similarly to those cultured on the standard and
widely used poly(l-ornithine) substratum in terms of cell viability, development of neural
processes, and appearance and progression of neural markers.
In the vascular field, an application of PEM in the endothelialization of vascular grafts
has been investigated. Berthelemy and coworkers (2008) found that endothelial progenitors
differentiated much faster on PSS/PAH multilayer films than on any other extracellular
matrix that had been used up until then, including a layer of jugular venous endothelial
cells. The differentiation occurred in 2 weeks as compared to 2 months for classical coat-
ings, and the cells formed an endothelium-like confluent cellular monolayer. This system
is, of course, extremely relevant for future therapeutic approaches, but it could also pro-
vide a very interesting template for further studies on the mechanisms of endothelial cell
differentiation.
In a recent study describing further efforts for providing stem cells with a biomimetic
niche environment, Nichols et al. (2009) built an elegant scaffold with an inverted colloidal
crystal topography reminiscent of bone marrow architecture, which was further coated
with albumin/PDDA films. Bone marrow stromal cells were first allowed to attach to the
scaffold. Subsequently, CD34+ hematopoietic stem cells were seeded in the scaffold to cre-
ate a three-dimensional coculture. By allowing CD34+ stem cells to self-organize within
this scaffold in the presence of stromal cells, the authors could recreate ex vivo part of the
complexity occurring in vivo. The authors demonstrated that the scaffold supports CD34+
cell expansion and B lymphocyte differentiation with production of antigen specific IgG
antibodies. Finally, implantation of these bone marrow constructs onto the backs of severe
combined immunodeficiency mice proved successful and led to the generation of human
immune cells. In addition to providing a structure that could be used for amplifying a
large part of hematopoietic tissue, this three-dimensional matrix may also be useful for
investigating the complex interactions occurring in bone marrow.
Cell Encapsulation
PEM films can potentially be employed for cell encapsulation as they can coat various cell
types or even be used to build multilayered cell architectures.
One of the first examples was presented by Ai et al. (2002), who reported that plate-
lets can be coated with LbL films and modified with antibodies as a means of investigat-
ing targeted-delivery mechanisms within the walls of blood vessel substitutes. Krol et al.
(2004) later reported that single yeast cells encased within PSS/PAH polyelectrolyte shells
were able to maintain their viability, functionality, and normal exchange of nutrients and
waste. LbL assembly has also been used for encapsulation of
E. coli
cells (Hillberg and
Tabrizian 2006). Later on, Veerabadran et al. coated mesenchymal stem cells with PLL/
HA layers and showed that the cells maintained their shape and viability for up to 1 week
(Veerabadran et al. 2007; Veerabadran et al. 2009). Using platelets as model cells, Fatisson et
al. (2008) detected cytoskeletal changes in blood platelets coated with CHI/HA multilayers
by QCM-D.
Applications for cell coatings in pancreas tissue engineering have also emerged recently.
Krol et al. (2006) applied a nanometer-thick PAH/PSS/PAH coating to cover and protect
human pancreatic islets. Macroscopically, no significant changes in the morphology of the
islets were observed and their functionality was proved by insulin release. In contrast,
however, Wilson et al. (2008) found that these films were cytotoxic to human pancreatic
islets. As an alternative coating, they employed PLL-g-PEG in combination with biotin and
proved cell viability in a coating composed of eight layer pairs.
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