Thiol-yne-methacrylate and thiol-yne-acrylate ternary systems were investigated for polymerization kinetics and material properties and compared to the analogous pure thiol-yne and (meth)acrylate systems. Both thiol-yne-methacrylate and thiol-yne-acrylate systems were demonstrated to reduce polymerization induced shrinkage stress while simultaneously achieving high glass transition temperatures (Tg) and modulius. Formulations with 70 wt% methacrylate increased the Tg from 51 ± 2 to 75 ± 1 °C and the modulus from 1800 ± 100 to 3200 ± 400 MPa (44% increase) over the pure thiol-yne system. Additionally, the shrinkage stress was 1.2 ± 0.2 MPa, which is lower than that of the pure methacrylate, binary thiol-yne and thiol-ene-methacrylate control systems which are all > 2 MPa. Interestingly, with increasing methacrylate or acrylate concentration, a decrease and subsequent increase in the shrinkage stress values were observed. A minimum shrinkage stress value (1.0 ± 0.2 MPa) was observed in the 50 wt% methacrylate and 70 wt% acrylate systems. This tunable behavior results from the competitive reaction kinetics of the methacrylate or acrylate homopolymerization versus chain transfer to thiol and the accompanying thiol-yne step-growth polymerization. The crosslinking density of the networks and the amount of volumetric shrinkage that occurs prior to gelation relative to the total volumetric shrinkage were determined as two key factors that control the final shrinkage stress of the ternary systems.

Serving as a decades old answer to synthetic proteins, polypeptides possess beneficial chemical and mechanical characteristics as well as secondary structure that can lead to the formation of complex nanostructures. Utilizing these characteristics, scientists have strived toward developing "smart" materials to aid in drug delivery, wound healing, and tissue engineering. In this Perspective, we discuss some aspects of the current state of oligopeptide and polypeptide research and highlight important fields relating to the self-assembly of traditional polypeptides, peptide amphiphiles, hydrogels, protein−polypeptide conjugates, and multiarm or branched systems. This Perspective serves to highlight the recent (2015−present) advances in block oligo/polypeptides, specifically self-assembly of NCA-derived polypeptides, peptide amphiphiles, hydrogels, protein conjugation, and dendrimer/ star polymers. Our primary focus is to outline the importance of oligo/polypeptide structure and nanoarchitecture and how these parameters dictate self-assembly and/or function.

Objective Fillers are widely utilized to enhance the mechanical properties of polymer resins. However, polymerization stress has the potential to increase due to the higher elastic modulus achieved upon filler addition. Here, we demonstrate a hyperbranched oligomer functionalized glass filler UV curable resin composite which is able to reduce the shrinkage stress without sacrificing mechanical properties. Methods A 16-functional alkene-terminated hyperbranched oligomer is synthesized by thiol-acrylate and thiol-yne reactions and the product structure is analyzed by 1H-NMR, mass spectroscopy, and gel permeation chromatography. Surface functionalization of the glass filler is measured by thermogravimetric analysis. Reaction kinetics, mechanical properties and shrinkage stress are studied via Fourier transform infrared spectroscopy, dynamic mechanical analysis and a tensometer, respectively. Results Silica nanoparticles are functionalized with a flexible 16-functional alkene-terminated hyperbranched oligomer which is synthesized by multistage thiol-ene/yne reactions. 93% of the particle surface was covered by this oligomer and an interfacial layer ranging from 0.7 – 4.5 nm thickness is generated. A composite system with these functionalized silica nanoparticles incorporated into the thiol-yne-methacrylate resin demonstrates 30% reduction of shrinkage stress (from 0.9 MPa to 0.6 MPa) without sacrificing the modulus (3100 ± 300 MPa) or glass transition temperature (62 ± 3 °C). Moreover, the shrinkage stress of the composite system builds up at much later stages of the polymerization as compared to the control system. Significance Due to the capability of reducing shrinkage stress without sacrificing mechanical properties, this composite system will be a great candidate for dental composite applications.

The relative hydrophilicity at the interface of a nanoparticle was measured utilizing electron paramagnetic resonance (EPR) spectroscopy. The supramolecular structure was assembled from spin-labeled peptide amphiphiles (PA) derived from N-carboxy anhydrides (NCA). Cyanuric chloride, or 2,4,6-trichloro-1,3,5-triazine (TCT), was used as a modular platform to synthesize the spin-labeled, lipidmimetic macroinitiator used for the ring-opening polymerization of γ-benzyl-L-glutamic acid NCA to produce polyglutamate-b-dodecanethiol 2 . Through static and dynamic light scattering, as well as transmission electron microscopy, PAs with DP of 50 and 17 were shown to assemble into stable nanoparticles with an average hydrodynamic radius of 117 and 84 nm, respectively. Continuous wave EPR spectroscopy revealed that the mobility parameter (h −1 /h 0 ) and 2A iso of the nitroxide radical increased with increasing pH, in concert with the deprotonation of the PE side chains and associated helix−coil transition. These results are consistent with an increase in the relative hydration and polarity at the nanoparticle interface, which would be dependent on the secondary structure of the polypeptide. This research suggests that a pH stimulus could be used to facilitate water diffusion through the membrane.

The advances of serial crystallography techniques at synchrotron and X-ray free electron laser facilities have made possible the acquisition of useable data sets to determine 3-dimensional structures of macromolecules from micro- to nanosized crystals. In addition, the same technological hallmarks have contributed significantly to the field of time-resolved crystallography. However, the production of usable crystalline slurries for serial crystallographic experiments has been one of the limiting factors and contributes to an alternative sample “bottleneck” in crystal growth. In this study, we propose a method: labeled microbatch mixing (MBM), which has the capability to produce large quantities of microcrystals of macromolecules suitable for serial crystallographic experiments. This is shown to be successful for producing lysozyme, carbonic anhydrase, and adeno-associated virus crystals. MBM takes advantage of secondary nucleation induced by mixing via the application of steady agitation during the crystallization process. This leads to excessive nucleation, resulting in large quantities of well-diffracting microcrystals. MBM therefore presents a method that can potentially be applied to a range of macromolecules and a possible simple protocol to produce microcrystals for serial crystallographic experiments.