tail in order to give covalent capture ability for polymerization of the self-assembled structure. The third region is a group of three glycine residues used to make the
hydrophilic head of the peptide flexible. The fourth segment is a single
phosphorylated serine residue that makes the assembled molecules interact strongly
with calcium ions and thus able to nucleate the formation of HA. Finally, since it is
beneficial for biomedical applications if the fibers can promote the adhesion and
growth of cells on their surfaces; the designed peptide also contains a ligand ArgGly-Asp (RGD) at the end of the sequence. According to existing knowledge of
amphiphile assembly, such molecules with an alkyl tail coupled to an ionic peptide
should assemble in water into cylindrical micelles, due to the overall conical shape
of the amphiphiles. TEM examination has indicated that the peptide–amphiphile
assembles into nanofibers, which are stable in alkaline solutions. Moreover,
HRTEM observations have a shown donut-shaped pattern in the cross section of
the fibers, indicating that the hydrophobic alkyl tails pack on the inside of the fiber
micelle and leave the acidic moieties of the peptide exposed to the aqueous
environment. The chemistry of the peptide region is thus repetitively displayed
on the surface. To investigate the mineralization properties of these nanofibers,
mineralization experiments were designed that could be performed directly on
holey, carbon-coated TEM grids. It was thereby shown that the fibers are able to
nucleate HA on their surfaces. The negatively charged surfaces promote mineralization by establishing local ion supersaturation. More significance is the observation that the c-axes of the HA crystals are aligned with long axes of the fibers. This
fact implies that the orientation of the crystalline nuclei and the subsequent crystal
growth are not random but are controlled by the micelles.
The recent development of recombinant protein expression technology provides
a reliable, predictable, and chemically defined source of purified humanlike collagen multi-peptide that is free of animal components. These triple-helical multipeptides have the same amino acid sequence as human tissue-derived collagen and
are free of the concerns related to the use of animal-derived collagen, such as the
risk of causing immunogenic reactions and transmission of infection.
Purified recombinant collagens are capable of undergoing spontaneous alignment to form collagen fibrils and defined features that are characteristic of collagen.
Recent studies (Wang & Cui 2006; Zhai & Cui 2006) have revealed that recombinant humanlike collagen has the same characteristics in the initial minerlization
stage as natural collagen. Additionally, it also can induce the deposition and direct
the growth of HA nanocrystals in vitro, in the form of self-assembly of nanofibrils
of mineralized collagen resembling an extracellular matrix.
Molecular self-assembly is a powerful approach for the synthesis of novel
supramolecular architectures. Zhang et al. (2003a) have focused on the fabrication
of several self-assembling peptides and proteins for a variety of studies of
biomaterials. Their studies have shown that a broad range of peptides and proteins
have the ability to produce very stable nanofibers, which are very well ordered and
possess remarkable regularity and helical periodicity. Moreover, these nanofibers
are similar in scale to the extracellular matrices that are crucial in manufacturing
artificial functional tissues. Furthermore, work in their group has demonstrated that
192
Q. Feng
hydrophilic head of the peptide flexible. The fourth segment is a single
phosphorylated serine residue that makes the assembled molecules interact strongly
with calcium ions and thus able to nucleate the formation of HA. Finally, since it is
beneficial for biomedical applications if the fibers can promote the adhesion and
growth of cells on their surfaces; the designed peptide also contains a ligand ArgGly-Asp (RGD) at the end of the sequence. According to existing knowledge of
amphiphile assembly, such molecules with an alkyl tail coupled to an ionic peptide
should assemble in water into cylindrical micelles, due to the overall conical shape
of the amphiphiles. TEM examination has indicated that the peptide–amphiphile
assembles into nanofibers, which are stable in alkaline solutions. Moreover,
HRTEM observations have a shown donut-shaped pattern in the cross section of
the fibers, indicating that the hydrophobic alkyl tails pack on the inside of the fiber
micelle and leave the acidic moieties of the peptide exposed to the aqueous
environment. The chemistry of the peptide region is thus repetitively displayed
on the surface. To investigate the mineralization properties of these nanofibers,
mineralization experiments were designed that could be performed directly on
holey, carbon-coated TEM grids. It was thereby shown that the fibers are able to
nucleate HA on their surfaces. The negatively charged surfaces promote mineralization by establishing local ion supersaturation. More significance is the observation that the c-axes of the HA crystals are aligned with long axes of the fibers. This
fact implies that the orientation of the crystalline nuclei and the subsequent crystal
growth are not random but are controlled by the micelles.
The recent development of recombinant protein expression technology provides
a reliable, predictable, and chemically defined source of purified humanlike collagen multi-peptide that is free of animal components. These triple-helical multipeptides have the same amino acid sequence as human tissue-derived collagen and
are free of the concerns related to the use of animal-derived collagen, such as the
risk of causing immunogenic reactions and transmission of infection.
Purified recombinant collagens are capable of undergoing spontaneous alignment to form collagen fibrils and defined features that are characteristic of collagen.
Recent studies (Wang & Cui 2006; Zhai & Cui 2006) have revealed that recombinant humanlike collagen has the same characteristics in the initial minerlization
stage as natural collagen. Additionally, it also can induce the deposition and direct
the growth of HA nanocrystals in vitro, in the form of self-assembly of nanofibrils
of mineralized collagen resembling an extracellular matrix.
Molecular self-assembly is a powerful approach for the synthesis of novel
supramolecular architectures. Zhang et al. (2003a) have focused on the fabrication
of several self-assembling peptides and proteins for a variety of studies of
biomaterials. Their studies have shown that a broad range of peptides and proteins
have the ability to produce very stable nanofibers, which are very well ordered and
possess remarkable regularity and helical periodicity. Moreover, these nanofibers
are similar in scale to the extracellular matrices that are crucial in manufacturing
artificial functional tissues. Furthermore, work in their group has demonstrated that
192
Q. Feng