Supramolecular interactions provide 3D printable materials with noncovalent cross-linking and stimuli-responsive properties to improve their processability and functionality. Here, we developed photoprintable acrylate polymer networks that contain pendant aliphatic or aromatic urea groups at different molar ratios to improve their toughness and enable self-healing ability via hydrogen bonding. We synthesized two methacrylate monomers containing either an aliphatic or an aromatic urea motif, and we formulated them in liquid photoreactive resins. We 3D printed these formulations and evaluated their tensile mechanical strength, elongation, toughness, and self-healing properties. By increasing the supramolecular cross-linking density provided by the urea groups, we improved the mechanical strength up to 119%, and the toughness up to 205%, compared to the control, in formulations with 10% molar ratio of the aromatic urea monomer, without sacrificing the elongation of the printed parts. Physical evidence for the presence of hydrogen bonding was provided with variable temperature Fourier transform infrared (VT-ATR-FTIR) spectroscopy and van’t Hoff analysis. The self-healing efficiency of these formulations was characterized by measuring the recovery of their tensile mechanical properties. Resins that contained 10 mol % of the aliphatic or aromatic urea monomers recovered more than 100% of their original mechanical strength. These results show the ability of supramolecular cross-linking via urea hydrogen bonding in improving the toughness, tuning the mechanical properties, and imparting stimuli-responsiveness in materials that are compatible with photoprinting methods.

The carbonyl stretching modes have been widely used in linear and two-dimensional infrared (IR) spectroscopy to probe the conformation, interaction, and biological functions of nucleic acids. However, due to their universal appearance in nucleobases, the IR absorption bands of nucleic acids are often highly congested in the 1600–1800 cm–1 region. Following the fruitful applications in proteins, 13C isotope labels have been introduced to the IR measurements of oligonucleotides to reveal their site-specific structural fluctuations and hydrogen bonding conditions. In this work, we combine recently developed frequency and coupling maps to develop a theoretical strategy that models the IR spectra of oligonucleotides with 13C labels directly from molecular dynamics simulations. We apply the theoretical method to nucleoside 5′-monophosphates and DNA double helices and demonstrate how elements of the vibrational Hamiltonian determine the spectral features and their changes upon isotope labeling. Using the double helices as examples, we show that the calculated IR spectra are in good agreement with experiments and the 13C isotope labeling technique can potentially be applied to characterize the stacking configurations and secondary structures of nucleic acids.

The level of interest in probing the strength of noncovalent interactions in DNA duplexes is high, as these weak forces dictate the range of suprastructures the double helix adopts under different conditions, in turn directly impacting the biological functions and industrial applications of duplexes that require making and breaking them to access the genetic code. However, few experimental tools can measure these weak forces embedded within large biological suprastructures in the native solution environment. Here, we develop experimental methods for detecting the presence of a single noncovalent interaction [a hydrogen bond (Hbond)] within a large DNA duplex in solution and measure its formation enthalpy (ΔH f ). We report that introduction of a H-bond into the TC2�O group from the noncanonical nucleobase 2-aminopurine produces an expected decrease ∼10 ± 0.76 cm −1 (from ∼1720 cm −1 in Watson−Crick to ∼1710 cm −1 in 2-aminopurine), which correlates with an enthalpy of ∼0.93 ± 0.066 kcal/mol for this interaction.