Thermoresponsive self-assembly and biological application of elastin-block-collagen like peptides
Date
2021
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Elastin-like polypeptides (ELPs) are thermoresponsive biopolymers that undergo an LCST-like phase transition in aqueous solutions. The temperature of this LCST-like transition, Tt, can be tuned by varying the number of repeat units in the ELP, sequence and composition of the repeat units, the solution conditions, and via conjugation to other biomacromolecules. The self-assembly of nanostructures from elastin-like (poly)peptide (ELP) containing block copolymers has been a subject of intense investigation over decades. However, short synthetic ELPs have rarely been used due to their high inverse transition temperature; the use of short ELPs has largely been limited to polymer conjugates. We have sought ways to use these short ELPs in designing versatile, temperature-responsive assemblies. ☐ Collagen is the most abundant protein in mammals that can be widely found in tendon, ligament, skin, cartilage and bone. The high-order structure of collagen is triple helix structure that can provide mechanical strength of a tissue. Collagen-like peptides (CLP) are short synthetic peptides which mimic the triple helical conformation of native collagens. CLPs have been widely used to study the stabilization effect of specific peptide sequences in collagen triple helices as well as to mimic collagen fibril formation. Recent studies have demonstrated that unfolded CLPs are capable of targeting native collagens and collagen substrates via the formation of a triple helix. In spite of these wide applications, the use of CLPs as building blocks for the fabrication of nanostructures for drug delivery has been rarely reported. ☐ Motivated by our previous work in forming nanostructures from ELPs conjugated with a triple helix-forming collagen-like peptide, in these doctoral studies, the ELP library was extended to a series of ELPs equipped with aromatic residues and having sequences as short as four pentapeptide motifs. The resulting elastin-like peptide−collagen-like peptide (ELP−CLP) bioconjugates unexpectedly self-assembled into nanosized platelets likely by forming a bilayer structure. Given the previously demonstrated ability of many other CLP conjugates to target collagens and the potential for encapsulation of hydrophobic drugs in collapsed ELPs, these ELP−CLP nanoplatelets may offer similar opportunities for targeted delivery in biomedical and other arenas. ☐ This observation of the platelet-like nanostructures prompted our investigations of a series of ELP-CLP bioconjugates with tryptophan/phenylalanine-containing ELPs and GPO-based CLPs [W2Fx-b-(GPO)y] with various domain lengths, with an objective to determine the impact of these modifications on the thermoresponsiveness and morphology of the assembly. The lower transition temperature of the conjugates with longer ELP or CLP domains enables the formation of well-defined nanoparticles near physiological temperature. Moreover, a morphological transition between vesicles and platelet-like nanostructures occurred when the ratio of the lengths of ELP/CLP were decreased. ☐ The impact of the distinct morphologies of the bioconjugates on drug release kinetics and collagen targeting has also been investigated. Sustained release of clinically relevant amounts of encapsulated drug is achieved within seven days, followed by a thermally controlled burst release. An unexpected outcome of these studies was the observation of a morphological transformation of nanoparticles depending on the mass of drug loaded, which supported changes in the shape and size of these nanoparticles at various stages of drug release. ☐ Considering the critical role of elastin and collagen peptides in extracellular matrix and the unique dual-themoresponsive ability of the ELP-CLP bioconjugates, our work offers significant opportunities for the design of elastin-collagen-like peptides for targeted application in the biomedical arena.
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Keywords
Elastin-like polypeptides, Thermoresponsive self-assembly, Collagen, Elastin-collagen-like peptides