Polypeptide Composition and Topology Affect Hydrogelation of Star-Shaped Poly(L-lysine)-Based Amphiphilic Copolypeptides

In this research, we studied the effect of polypeptide composition and topology on the hydrogelation of star-shaped block copolypeptides based on hydrophilic, coil poly(L-lysine)20 (s-PLL20) tethered with a hydrophobic, sheet-like polypeptide segment, which is poly(L-phenylalanine) (PPhe), poly(L-leucine) (PLeu), poly(L-valine) (PVal) or poly(L-alanine) (PAla) with a degree of polymerization (DP) about 5. We found that the PPhe, PLeu, and PVal segments are good hydrogelators to promote hydrogelation. The hydrogelation and hydrogel mechanical properties depend on the arm number and hydrophobic polypeptide segment, which are dictated by the amphiphilic balance between polypeptide blocks and the hydrophobic interactions/hydrogen bonding exerted by the hydrophobic polypeptide segment. The star-shaped topology could facilitate their hydrogelation due to the branching chains serving as multiple interacting depots between hydrophobic polypeptide segments. The 6-armed diblock copolypeptides have better hydrogelation ability than 3-armed ones and s-PLL-b-PPhe exhibits better hydrogelation ability than s-PLL-b-PVal and s-PLL-b-PLeu due to the additional cation–π and π–π interactions. This study highlights that polypeptide composition and topology could be additional parameters to manipulate polypeptide hydrogelation.

New Survey Questions and Estimators for Network Clustering with Respondent-driven Sampling Data

Respondent-driven sampling (RDS) is a popular method for sampling hard-to-survey populations that leverages social network connections through peer recruitment. Although RDS is most frequently applied to estimate the prevalence of infections and risk behaviors of interest to public health, such as HIV/AIDS or condom use, it is rarely used to draw inferences about the structural properties of social networks among such populations because it does not typically collect the necessary data. Drawing on recent advances in computer science, the authors introduce a set of data collection instruments and RDS estimators for network clustering, an important topological property that has been linked to a network’s potential for diffusion of information, disease, and health behaviors. The authors use simulations to explore how these estimators, originally developed for random walk samples of computer networks, perform when applied to respondent-driven samples with characteristics encountered in realistic field settings that depart from random walks. In particular, the authors explore the effects of multiple seeds, without replacement versus with replacement, branching chains, imperfect response rates, preferential recruitment, and misreporting of ties. The authors find that clustering coefficient estimators retain desirable properties in respondent-driven samples. This work takes an important step toward calculating network characteristics using nontraditional sampling methods, and it expands the potential of RDS to tell researchers more about hidden populations and the social factors driving disease prevalence.

Light Splitting Function of Branched Chains of Microspheres Fabricated by Self-Assembly Process

ABSTRACTUsing a self-assembly process, we fabricated ordered chains of transparent polystyrene microspheres that have 30°- and 60°-branched structures and that act as coupled-resonator optical waveguides (CROWs). We then observed the optical properties of propagation light through the CROWs. The light spectra were directly measured by guide-collection-mode near-field scanning optical microscopy (NSOM) techniques. The spectrum of light propagating to the 60°-branch shows some sharp peaks, which seem to be associated with whispering gallery modes (WGMs). On the other hand, the spectrum of light propagating to the 30°-branch shows rather broad peaks. Moreover, we observed the detailed structures of the CROWs by high-resolution scanning electron microscopy (HR-SEM), and performed a finite-difference time-domain (FDTD) simulation to explain the NSOM spectra. The results suggest that the microspheres’ branching chains themselves have a light-splitting function, which is a kind of wavelength-selective filter.