Biomedical Engineering Reference
In-Depth Information
implants. Therefore, a bone-like surface topography is often regarded as
being of great importance when designing implant materials.
7,105 -109
4.4.1 Nanohydroxyapatite-Cell Interaction
Considering the nanostructured bone surface, it is best to mimic this situ-
ation, thereby invoking the correct proteins to adsorb and avoiding fibrous
tissue encapsulation. Cellular responses to HA particles have been demon-
strated to depend on physical and chemical properties such as particle size,
morphology, crystallinity, and chemical composition. A nanostructured
topography increases the surface space enormously, thereby increasing pro-
tein and cell attachment. Better adherence of osteoblasts was reported with
the use of several types of nanomaterials (i.e., nHA and CNTs) either depos-
ited onto the surface or mixed into composite materials.
53
Regarding particle
size, the ability of nanophase ceramics to promote bone cell function was
found to be limited below 100 nm.
8
The nanometer HA grain size topogra-
phy, in combination with the high surface wettability, promotes increased
selective vitronectin adsorption, and also affects the protein conforma-
tion, thereby enhancing osteoblast functions.
4,8
This conformational change
implies unfolding of the proteins to a greater extent, presenting more epi-
topes for osteoblasts to adhere to. Other proteins that are known to particu-
larly increase osteoblast functions are fibronectin, laminin, and collagen.
7, 8 , 10 4
4.4.1.1
In Vitro
Studies on Nanohydroxyapatite
Many coated and composite bone tissue engineering materials have been
investigated with regard to their
in vitro
and
in vivo
biocompatibility. Here,
some
in vitro
study results of different nHA composite or coated materials
are summarized, starting with a porous chitosan/nHA composite scaf-
fold, seeded with MC 3T3-E1 cells. Compared with a porous chitosan scaf-
fold, the composite scaffold showed a better cytocompatibility, in terms
of cellular proliferation and morphology.
24
Addition of nHA to porous
silk fibroin scaffolds seeded with MG63 cells resulted in an elevated cyto-
compatibility as well, as determined by an MTT assay.
26
The addition of
nHA to collagen scaffolds increased proliferation and redifferentiation
of cells, originating from rat bone fragments, toward osteogenic lineages.
Migration of the cells throughout the network of the porous scaffold was
also increased.
110
Synthetic materials can also be improved by the incorporation of nHA,
as demonstrated by PLGA/nHA and PCL/nHA scaffolds seeded with mes-
enchymal stem cells (MSCs), which obtained better cytocompatibility com-
pared with their counterparts without nHA. They showed a higher alkaline
phosphatase (ALP) activity and an increased rate of matrix mineraliza-
tion.
2 7, 3 0
Seeding polyamide/nHA (PA/nHA) scaffolds with MSCs did not
result in an increase, nor a decrease, in cell proliferation and differentiation.
29
