Bone-Like Mineral and Organically Modified Bone-Like Mineral Coatings - Biological and Biomedical Coatings: Processing and Characterization - page 20

receptors, increasing the likelihood of cell-specific responses (Lebaron and Athanasiou
2000; Segvich, Smith, and Kohn 2009; Hersel, Dahmen, and Kessler 2003).
Noncollagenous proteins found in bone, such as osteopontin, osteonectin, and bone sia-
loprotein, bind strongly to hydroxyapatite and are thought to be involved in nucleation
and growth of crystals during mineralization in vivo (Hunter, Kyle, and Goldberg 1994;
Hunter and Goldberg 1994; Fujisawa et al. 1997). These proteins are made up of several
regions of acidic amino acids, which are believed to interact with hydroxyapatite crys-
tals. Peptides designed to adhere to hydroxyapatite-based materials have been inspired by
these acidic amino acid regions. Peptides consisting of consecutive glutamic acid residues
derived from osteonectin bind strongly to hydroxyapatite. The type of acidic amino acid
present in these peptides affects mineralization in vitro. For example, polyglutamic acid
residues (Glu6) enhanced mineralization, whereas polyaspartic acid residues (Asp6) had
an inhibitory effect (Fujisawa et al. 1996). Hence, during the peptide designing process,
it is important to understand the contribution of each amino acid to the entire peptide's
properties.
ECM proteins are usually multifunctional, containing several domains, allowing them
to influence attachment to both materials and cells. Peptidomimetics capable of mediating
binding to both hydroxyapatite and cells have been designed using bone sialoprotein as
a model. This peptide (EEEEEEEPRGDT) contains a glutamic acid-rich (E7) sequence and
the ubiquitous cell binding Arg-Gly-Asp (RGD) domain and binds well to hydroxyapatite,
as well as mediates osteoblast attachment and osteogenesis in vitro (Fujisawa et al. 1997;
Itoh et al. 2002).
Peptide sequences capable of binding specifically to BLM have recently been identified
using a unique combination of phage display and computational modeling techniques
(Segvich, Smith, and Kohn 2009) (Figure 1.4). Phage display is a powerful tool as it allows
for a wide range of peptides (~10 9 ) to be panned against any substrate, including natural

APWHLSSQYSRT
VTKHLNQISQSY
STLPIPHEFSRE

Peptides identified as having highest potential (3)

Top phage
sequences from
RELIC INFO
(49)

ELISA
(10)

Model
(19)

Phage identified via DNA sequencing from
repeated experiments
(243)

Original phage library (~10 9 )

FIGURE 1.4
Schematic displaying the trifold analysis approach used to identify peptides that preferentially bind to BLM
and HA. (Reprinted from Segvich, H.J., Smith, H.C., and Kohn, D.H., Biomaterials, Vol. 30, pp. 1287-1298, 2009,
with permission from Elsevier.)