Charge Density as a Molecular Modulator of Nanostructuration in Intrinsically Disordered Protein Polymers.

Intrinsically disordered protein polymers (IDPPs) have attracted a lot of attention in the development of bioengineered devices and for use as study models in molecular biology because of their biomechanical properties and stimuli-responsiveness. The present study aims to understand the effect of charge density on the self-assembly of IDPPs. To that end, a library of recombinant IDPPs based on an amphiphilic diblock design with different charge densities was bioproduced, and their supramolecular assembly was characterized on the nano-, meso-, and microscale. Although the phase transition was driven by the collapse of hydrophobic moieties, the hydrophilic block composition strongly affected hierarchical assembly and, therefore, enabled the production of new molecular architectures, thus leading to new dynamics that govern the liquid-gel transition. These results highlight the importance of electrostatic repulsion for the hierarchical assembly of IDPPs and provide insights into the manufacture of supramolecular protein-based materials.

Hydrophobic Cholesteryl Moieties Trigger Substrate Cell-Membrane Interaction of Elastin-Mimetic Protein Coatings in Vitro.

A cellular coating based on hydrophobic interactions of an elastin-like recombinamer (ELR) with the cell membrane is presented. It is well-documented that biophysical properties such as net charge, hydrophobicity, and protein-driven cell-ligand (integrin binding) interactions influence the interaction of polymers, proteins or peptides with model membranes and biological cells. Most studies to enhance membrane-substrate interactions have focused on the introduction of positively charged groups to foster electrostatic interactions with the negatively charged membrane. Herein, we present an antagonistic approach based on ELRs with varying amounts of hydrophobic cholesteryl groups (ELRCTAs). The ability of the membranes to stabilize cholesteryl groups is hypothesized to assist the coordination of hydrophobic ELRs with the membrane. The main objective was to generate a defined cellular coating of a recombinant protein that allows for total sequence control and less host, or batch-to-batch, variation as a substitute for the existing coatings like alginate, polyelectrolytes, collagens, and fibronectin. We used an in vitro cell-binding assay to quantify cell-substrate interactions, showing enhanced cellular recognition and matrix distribution with an increasing number of cholesteryl groups incorporated. These novel materials and the versatile nature of their protein sequence have great potential as cellular markers, drug carriers, or hydrophobic cell-binding domains.

In vitro degradation and mechanical properties of PLA-PCL copolymer unit cell scaffolds generated by two-photon polymerization.

The manufacture of 3D scaffolds with specific controlled porous architecture, defined microstructure and an adjustable degradation profile was achieved using two-photon polymerization (TPP) with a size of 2 × 4 × 2 mm(3). Scaffolds made from poly(D,L-lactide-co-ɛ-caprolactone) copolymer with varying lactic acid (LA) and ɛ -caprolactone (CL) ratios (LC16:4, 18:2 and 9:1) were generated via ring-opening-polymerization and photoactivation. The reactivity was quantified using photo-DSC, yielding a double bond conversion ranging from 70% to 90%. The pore sizes for all LC scaffolds were see 300 µm and throat sizes varied from 152 to 177 µm. In vitro degradation was conducted at different temperatures; 37, 50 and 65 °C. Change in compressive properties immersed at 37 °C over time was also measured. Variations in thermal, degradation and mechanical properties of the LC scaffolds were related to the LA/CL ratio. Scaffold LC16:4 showed significantly lower glass transition temperature (T g) (4.8 °C) in comparison with the LC 18:2 and 9:1 (see 32 °C). Rates of mass loss for the LC16:4 scaffolds at all temperatures were significantly lower than that for LC18:2 and 9:1. The degradation activation energies for scaffold materials ranged from 82.7 to 94.9 kJ mol(-1). A prediction for degradation time was applied through a correlation between long-term degradation studies at 37 °C and short-term studies at elevated temperatures (50 and 65 °C) using the half-life of mass loss (Time (M1/2)) parameter. However, the initial compressive moduli for LC18:2 and 9:1 scaffolds were 7 to 14 times higher than LC16:4 (see 0.27) which was suggested to be due to its higher CL content (20%). All scaffolds showed a gradual loss in their compressive strength and modulus over time as a result of progressive mass loss over time. The manufacturing process utilized and the scaffolds produced have potential for use in tissue engineering and regenerative medicine applications.