Responsive peptide surfaces

Responsive peptide surfaces may originate from biologically inspired peptide sequences or they may be artificially designed based on our knowledge of the interactions of amino acids within a peptide chain. Both classes will be discussed here. Naturally inspired responsive peptide surfaces are based either on a protein mimic (a long peptide sequence that mimics the properties of a responsive protein) or on 

Elastin-like polypeptides (ELPs) have been extensively studied due to the fact that they combine similar stimulus response properties to other artificial polymers such as poly(A-isopropylacrylamide) (pNIPAM) with the advantages of a biologically derived material, that is, it is biocompatible, modular in its composition, and can be obtained by biological processes. ELPs are polypeptides that contain a short, repetitive peptide sequence, most commonly (VPGXG) that is derived from tropoelastin, the precursor of elastin. In this sequence, X represents any amino acid sequence except proUne. Polypeptides composed of the pentapeptide repeat unit VPGXG possess a reversible lower critical solution temperature (LCST). Below the LCST, the peptide is soluble 

Switchable and Responsive Surfaces and Materials for Biomedical Applications 

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When preparing responsive peptide surfaces, a number of points need to be considered to ensure functionality and compatibility with the response mechanism and the application. These considerations are laid out first before introducing the various fabrication strategies that have been used to prepare responsive peptide surfaces. 

Figure 3.1 Strategies for the preparation of responsive peptide surfaces—gold-based self-assembled monolayers (SAMs), (a) Direct attachment and (b) pre-functionalisation.

Figure 3.2 Strategies for the preparation of responsive peptide surfaces—silanisation. (a) Activation, (b) functionalisation, and (c) direct build-up.

Figure 3.3 Strategies for the preparation of responsive peptide surfaces—adsorption.

The characterisation of a stimulus responsive surface in general includes two aspects verification of the surface composition and evaluation of the materials response due to the presence of the stimulus. Although a variety of techifiques are available to characterise peptides and their stimulus-responsive properties in solution and in bulk, many of these are not compatible with surface-immobilised peptides. Hence, a common approach is to characterise the peptide material in solntion before attachment to the surface. UV-based turbidity measurements (Lee et al., 2(X)9 Nath Chilkoti, 2003 Teeuwen et al., 2009) and calorimetry (Barbosa et al., 2009) are used to determine the LCST of ELPs. The isomerisation of azobenzene can be studied with UV absorption, nuclear magnetic resonance spectroscopy, and high-performance Uqnid chromatography (Anemheimer et al., 2005 Hayashi et al., 2007), and CD is nsed to determine the presence of helices in a peptide (Minelli et al., 2013 Yasntomi et al., 2005). Non-solution-based methods that can be used to characterise responsive peptide surfaces will be discussed in more detail below. 

Cyclic voltammetry (C V) is the method of choice for electrochemically responsive peptide surfaces. It provides evidence of the presence of redoxactive compounds at the surface (Lamb Yousaf, 2011 Yeo Mrksich, 2006 Yeo et al., 2003 Yeung et al., 2010) and can be used to demonstrate the reversibility of the responsive reaction (Blonder et al., 1997 Wang et al., 2010). If CV data are collected at specific time points, kinetic information about the response time becomes available (Chan et al., 2008 Wang et al., 2010). 

Topographical changes caused by temperature-induced phase changes (Barbosa et al., 2009 Hyun et al., 2004) or by the adsorption of compounds on the surface in response to a stimulus (Koga et al., 2006) can be monitored by atomic force microscopy (AFM). Altered adhesion properties of a responsive peptide surface can also be probed by AFM force measurements (Hyun et al., 2004). 

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