Fabrication of Highly Uniform Nanoparticles from Recombinant Silk-Elastin-like Protein Polymers for Therapeutic Agent Delivery

Abstract

Here we generate silk-elastinlike protein (SELP) polymeric nanoparticles and demonstrate precise control over their dimensions using an electrospray differential mobility analyzer (ES-DMA). Electrospray produces droplets encompassing several polymer strands. Evaporation ensues, leading polymer strands to accumulate at the droplet interface forming a hollow nanoparticle. The resulting nanoparticle size distributions which govern particle yield, depend on buffer concentration to the −1/3 power, polymer concentration to the 1/3 power, and ratio of silk to elastin blocks. Three recombinantly tuned ratios of silk to elastin blocks, 8:16, 4:8, and 4:16, respectively named SELP-815K, SELP-47K, and SELP-415K, are employed with the latter ratio resulting in a thinner shell and larger diameter for the nanoparticles than the former. The DMA narrows the size distribution by electrostatically classifying the aerosolized nanoparticles. These highly uniform nanoparticles have variations of 1.2 nm and 1.4 nm for 24.0 nm and 36.0 nm particles, respectively. Transmission electron microscopy reveals the nanoparticles to be faceted, as a buckling instability releases compression energy arising from evaporation after the shell has formed by bending it. A thermodynamic equilibrium exists between compression and bending energies, where the facet length is 1/2 the particle diameter, in agreement with experiments. Rod-like particles also formed from polymer stabilized filaments when the viscous length exceeds the jet radius at higher solution viscosities. The unusual uniformity in composition and dimension indicates the potential of these nanoparticles to deliver bioactive and imaging agents.

Rapid Nanoparticle Characterization

“…Indeed, Figure 7b shows two histograms of SELP particles nominally 24.0 nm and 36.0 nm in diameter, each assembled from nearly 200 nanoparticle TEM images. Statistical compilation shows the standard deviation on the diameter of these purified particles to be 1.2 nm and 1.4 nm for the two sizes, respectively, leading to coefficients of variation of <5% [Anumolu et al, 2011]. This manufacturing precision meets or exceeds that of metallic nanoparticles and rivals that of biologically assembled particles such as viruses [Cole et al, 2009;Lute et al, 2008;Pease, 2011a;Pease et al, 2007].…”

“…The electrical force acting on the particles carrying n e electron charges of magnitude e (=1.602 x 10 -19 C) through an electric field, E s , is given by F E = n e eE s . The mobility of the particle, Z p , is then defined as the ratio of the particle's velocity v to the force giving rise to that velocity [Anumolu et al, 2011;Knutson & Whitby, 1975]. This force gives rise to a resulting radial drag force acting on the particle, F D = 3 µ g vd p /C c , where d p is the spherically equivalent particle mobility diameter and g is the gas viscosity.…”

“…Similarly, Tsai, et al, used planar p-n junction patterned substrates to generate an array of tunable electric fields [Park & Phaneuf, 2003;Tsai et al, 2005]. Several other substrates are used for electrostatic deposition such as TEM grids (~3 mm in diameter) with thin holey carbon films [Anumolu et al, 2011], silicon wafers, and glass substrates pretreated in KOH and UVO-cleaner [Kang et al, 2011[Kang et al, , 2012. The optimum deposition time onto holey carbon TEM grids requires the product of the aerosol number density and time to exceed 3000 particle .…”

“…These highly uniform nanoparticles may be developed into carriers of therapeutic agents [Anumolu et al, 2011]. Simply including the therapeutic agent in the polymer solution to be electrosprayed, leads to incorporation within the nanoparticle.…”

Effect of noncovalent interaction on the self-assembly of a designed peptide and its potential use as a carrier for controlled bFGF release

“…30 Poly-(GVGV), poly-(GVGVA), and poly-(GGVGV) are ambivalent sequences that form amyloid fibers under certain conditions, 31 whereas poly-(GVGVP) adopts a β-sheet structure in the folded state and can be used as building blocks to create elastin-like polypeptides (ELPs) 32,33 and silk-elastinlike protein polymers (SELPs). 34,35 In this study, the GVGV tetrapeptide was incorporated into the RADA16-I sequence to evaluate the effects of weak interactions on the folding and self-assembly of the peptide. Figure 1 Figure 1 amino acid sequences of the designed peptides 1-4 used in this study.…”