This article was published as part of the Peptide- and protein-based materials themed issue Guest editors Rein Ulijn and Dek Woolfson Please take a look at the issue 9 2010 table of contents to access other reviews in this themed issue Published on 02 August 2010. Downloaded by University of Bristol on 12/10/2015 14:30:42. View Article Online / Journal Homepage / Table of Contents for this issue
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This article was published as part of the
Peptide- and protein-based materials themed issue
Guest editors Rein Ulijn and Dek Woolfson
Please take a look at the issue 9 2010 table of contents to access other reviews in this themed issue
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View Article Online / Journal Homepage / Table of Contents for this issue
3464 Chem. Soc. Rev., 2010, 39, 3464–3479 This journal is c The Royal Society of Chemistry 2010
More than just bare scaffolds: towards multi-component and decorated
fibrous biomaterialsw
Derek N. Woolfson*ab and Zahra N. Mahmouda
Received 4th July 2010
DOI: 10.1039/c0cs00032a
We are entering a new phase in biomaterials research in which rational design is being used to
produce functionalised materials tailored to specific applications. As is evident from this Themed
Issue, there are now a number of distinct types of designed, self-assembling, fibrous biomaterials.
Many of these are ripe for development and application for example as scaffolds for 3D cell
culture and tissue engineering, and in templating inorganic materials. Whilst a number of groups
are making headway towards such applications, there is a general challenge to translate a wealth
of excellent basic research into materials with a genuine future in real-life applications.
Amongst other contemporary aspects of this evolving research area, a key issue is that of
decorating or functionalising what are mostly bare scaffolds. There are a number of hurdles to
overcome to achieve effective and controlled labelling of the scaffolds, for instance: maintaining
biocompatibility, i.e., by minimising covalent chemistry, or using milder bioconjugation methods;
attaining specified levels of decoration, and, in particular, high and stoichiometric labelling;
introducing orthogonality, such that two or more functions can be appended to the same scaffold;
and, in relevant cases, maintaining the possibility for recombinant peptide/protein production.
In this critical review, we present an overview of the different approaches to tackling these
challenges largely for self-assembled, peptide-based fibrous systems. We review the field as it
stands by placing work within general routes to fibre functionalisation; give worked examples on
our own specific system, the SAFs; and explore the potential for future developments in the area.
Our feeling is that by tackling the challenges of designing multi-component and functional
biomaterials, as a community we stand to learn a great deal about self-assembling biomolecular
systems more broadly, as well as, hopefully, delivering new materials that will be truly useful in
biotechnology and biomedical applications (107 references).
1. Introduction
1.1 Rationale for and objectives of this review
This review does not focus on any one class of biomaterial
per se—there are excellent articles on these throughout this
a School of Chemistry, University of Bristol, Cantock’s Close, Bristol,UK BS8 1TS. E-mail: [email protected]
bDepartment of Biochemistry, University of Bristol, Medical School,University Walk, Bristol, UK BS8 1TD
w Part of the peptide- and protein-based materials themed issue.
Derek N. Woolfson
Dek Woolfson received hisPhD from the University ofCambridge, UK, working withProf Dudley Williams FRSand Dr Phil Evans onproblems in peptide andprotein folding. He did shortpost-doctoral stints with ProfJanet Thornton FRS(UC London), and Prof TomAlber (UC Berkeley), wherehe honed skills in bio-informatics and biophysics tostudy sequence-to-structurerelationships in proteins. Forthe past 15 years his indepen-
dent group at the University of Sussex, and, since 2005, at theUniversity of Bristol, has focussed on protein design and itsapplication to bionanotechnology and synthetic biology. Hisgroup takes a multidisciplinary approach to its work.
Zahra N. Mahmoud
Zahra Mahmoud received herPhD from the University ofHull, where she was alsoinvolved in the develop-ment of a second-generationtracheo-oesophageal fistulaspeech valve. She currentlyworks as a research associatewith Professor Dek Woolfsonat the University of Bristol;her research interests includedesign and functionalisationof self-assembling coiled-coilbiomaterials.
CRITICAL REVIEW www.rsc.org/csr | Chemical Society Reviews
This journal is c The Royal Society of Chemistry 2010 Chem. Soc. Rev., 2010, 39, 3464–3479 3477
Nonetheless, we find this analysis useful, and we hope that
others will find it helpful too.
During the course of our reading and writing, it became
clear that common themes, approaches and methods that
represent best practice are emerging in the field. For example:
(1) the exploitation of natural self-assembling systems, or
peptides derived from these often present a good starting
point. However, this can present restrictions in terms of
control over self-assembly, and also asks the question, just
how does one functionalise materials pre- or post-assembly
without interfering with the self-assembly process itself? This
raises the next two key points from our perspective. (2) That
the design or engineering of the self-assembling and functional
components of the system should be orthogonal. And, related
to this, (3) that this orthogonality should be designed or
engineered into the system, or at least considered, from the
outset of materials development. Perhaps the best examples
that illustrate these two points to date are the peptide amphi-
philes from Stupp and colleagues. (4) Rational peptide design
also represents a good approach in these respects, but it does
rely on having good rules that relate sequence, structure and
assembly. Our understanding for certain protein-folding
motifs, such as the coiled coil, is headed in the right direction,
but this is by no means the case universally for protein folding.
Finally (5) there are now many examples of designed and
engineered self-assembled systems, and it is likely that some
will be better suited to appending certain functions and in
specific applications than others. It would seem prudent, to
choose the right tool for the job in this respect, and not to be
wedded to any one material type. Ideally, as the field develops
we would have an open-source or synthetic-biology ethos, and
a toolkit of basic materials with which to build will emerge.
Somewhat related to this, it is quite understandable that
different groups have adopted similar strategies to demon-
strate that they have achieved decoration. The common
methods are ‘‘functionalisation’’ with a fluorophore of some
description followed by visualisation using light microscopy;
or the addition of gold nanoparticles (GNPs) followed by
visualisation using electron microscopy. Clearly, these are the
best options for demonstrating that decoration has been
achieved, but usually they do not represent functionalisations
in themselves; though examples such as the formation of
metallic nanowires following the recruitment of gold nano-
particles are cases where functional materials are being
developed in this way. Nonetheless, true functionalisation
would be to impart some biological activity such as cell-
binding properties onto the scaffolds. Of course, there is strong
research in this endeavour. However, this is and must remain
one of the tenets of both materials science and synthetic
biology: that is, whilst as a community we must develop the
very best understanding of natural and design self-assembling
systems, as materials scientist and/or synthetic biologists, we
must consider applications that put our materials to use.
In the case of soft fibrous biomaterials, the key applications
areas that are being explored here are scaffolds for 3D cell
culture and tissue engineering, and as sacrificial templates for
the organisation of functional, often hard, materials that are
less readily self-assembled. In many respects, the studies that
we have highlighted have laid the groundwork for this
development, and it is now time to translate further this basic
research and deliver functionalised materials for specific real-
life applications. There are many challenges ahead, including
issues of large-scale materials production, biocompatibility of
methods used in functionalisation, and, for tissue engineering,
immunogenicity of the final materials. However, we feel that
these and other issues are being tackled and will be surmounted.
In summary, the current state of basic research in functional
fibrous biomaterials is buoyant, and provides a strong basis
for translation into real-life applications.
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