PEPTIDE SELF-ASSEMBLY BIOMATERIALS DESIGN AND APPLICATION - Biologically-Responsive Hybrid Biomaterials - page 78

One of the Lego peptides, RADA16-I, now called PuraMatrix for its single
component purity, is commercially available for research (BD Bioscience).
PuraMatrix has been used to culture diverse types of tissue cells including stem
and progenitor cells, as well as differentiated cell types and tissues. The
examples of cell types cultured in PuraMatrix are listed in Table 1 and the list is
rapidly expanding as more and more people use such scaffolds for their research
and clinical tissue repair studies [7~10] .

5. Peptide Surfactants or Detergents

Inspired from building blocks of cell membranes using Nature's lipids as a guide,
a class of peptide surfactants containing hydrophobic tails and hydrophilic heads
has been designed by taking advantage of their self-assembly properties in water.
These peptides have a hydrophobic tail with various degrees of hydrophobicity
and a hydrophilic head, either negatively charged aspartic and glutamic acids or
positively charged lysine or histidine. These peptide monomers contain 7~16
amino acid residues and have a hydrophilic head composed of aspartic acid and a
tail of hydrophobic amino acids, such as alanine, valine or leucine. The length of
each peptide is Ä 2 nm, similar to that of biological phospholipids. The length can
also be varied by adding more amino acids, one at a time to a desired length as
shown in Figure 5.
Although individually these peptide surfactants have completely different
composition and sequences, they share a common feature: the hydrophilic heads
have 1~2 charged amino acids and the hydrophobic tails have four or more
consecutive hydrophobic amino acids. For example, A6K (AAAAAAK), A6K ±
(AAAAAAK ± ) peptide has six hydrophobic alanine residues from the N-
terminus followed by a positive charged lysines acid residue, thus having two
negative charges, one from the side chain and the other from the C-terminus
[11, 12]

. Likewise, G8DD (GGGGGGGGDD) has eight glycines following by two
asparatic acids with three negative charges. By contrast, K2V6 (KKVVVVVV)
has two positively charged lysines as the hydrophilic head, followed by six
valines as the hydrophobic tail [11~15] .
These peptides undergo self-assembly in water to form nanotubes and
nanovesicles with an average diameter of 30-50 nm. The tails consisting of
alanines and valines produce more homogeneous and stable structures than those
of glycines, isoleucine and leucine. This property might be due to their
hydrophobic and hydrophilic ratios. Besides, the surfactant peptides were used
for molecular modeling and data suggest that they form tubular and vesicle