Engineering complex tissues such as the tendon-to-bone insertion sites require a strong and tough biomimetic material system that incorporates both mineralized and unmineralized tissues with different strengths and stiffnesses. However, increasing strength without degrading toughness is a fundamental challenge in materials science. Here, we demonstrate a promising nanofibrous polymer-hydroxyapatite system in which, a continuous fibrous network must function as a scaffold for both mineralized and unmineralized tissues. It is shown that the high toughness of this material system could be maintained without compromising on the strength with the addition of hydroxyapatite mineral. Individual electrospun poly(lactide-co-glycolide) (PLGA) nanofibers demonstrated outstanding strain-hardening behavior and ductility when stretched uniaxially, even in the presence of surface mineralization. This highly desirable hardening behavior which results in simultaneous nanofiber strengthening and toughening was shown to depend on the initial cross-sectional morphology of the PLGA nanofibers. For pristine PLGA nanofibers, it was shown that ellipsoidal cross-sections provide the largest increase in fiber strength by almost 200% compared to bulk PLGA. This exceptional strength accompanied by 100% elongation was shown to be retained for thin and strongly bonded conformal mineral coatings, which were preserved on the nanofiber surface even for such very large extensions.

In polymer nanocomposites (PNCs), the physical and chemical interactions at the polymer matrix–filler interface lead to local variations in polymer properties over a substantial “interphase” region in the vicinity of the interface. Characterization of mechanical properties in the polymer interphase region is essential for informed modeling and design of advanced PNCs. Direct contact measurement of the mechanical properties in the interphase region has been performed via high-resolution scanning probe nanoindentation experiments on model polymer–substrate samples. However, the force–displacement data from indentation experiments are affected by the interaction of the elastic stress field with the substrate, which limits determination of the interphase properties close to the polymer–substrate boundary. To extract the mechanical properties of the interphase from experimentally measured data, three-dimensional finite element analysis (3D FEA) models are developed in this study to simulate the indentation experiments on model nanocomposites samples. The simulation results quantify the substrate effects and allow them to be excluded from experimental data analysis. The results also provide insight into the role of tip deformation and tip radius during the measurement of the modulus profile of the interphase.

Nanoindentation was used to evaluate the mechanical properties of commercial float glass surfaces that were subjected to various surface cleaning treatments and other short‐term corrosion conditions. The changes in the plane strain elastic modulus , where νs and Es are the Poisson ratio and Young modulus of the specimen, respectively) and hardness after exposure to dilute hydrochloric acid (pH 0.9), reverse osmosis water (pH 7.1), and commercial cleaning solutions (pH 9.5) were found to be 0.5%–9% and 2%–35%, respectively. Similarly, weathering in a humid atmosphere and leaching in hot deionized water also had a distinct effect on the measured properties of the float glass surfaces. Moreover, both the surface cleaning treatments and the short‐term corrosion exposures affected the tin side of the float glass differently than the air side. This work suggests that many of the discrepancies in the literature on the effect of tin concentration on the nanomechanical properties of float glass surfaces are likely due to variability in the surface cleaning and exposure history of the samples and calibration glasses that have been used.

An atomic force microscope (AFM) based fast dynamic scanning indentation (DSI) nano-DMA method, which relies only on the commonly available capabilities of commercial AFMs to provide quantitatively accurate high-resolution (∼15 nm) spatial maps of local viscoelastic mechanical properties (E′, E″, and tan ϕ) in heterogeneous soft adhesive material systems, is described. The versatility of the DSI approach is demonstrated by successfully employing it on three industry-leading commercial AFMs/modules (Asylum’s Cypher ES and MFP-3D Infinity AFMs with the FastForceMapping module, and Bruker’s Dimension Icon AFM with the PeakForce QNM module). Frequency sweep thermorheological DSI experiments were performed to generate quantitatively accurate nano-DMA master curves spanning an unprecedented frequency range of 5 decades. Quantitative agreement between DSI nano-DMA and bulk DMA measurements is demonstrated for two different homogeneous elastomers (styrene butadiene rubber, SBR, and synthetic natural rubber, SNR). The capability of the DSI methodology in acquiring quantitatively accurate viscoelastic property maps of heterogeneous soft solids was validated through experiments on an SBR-SNR blend sample. Experimental factors affecting DSI data quality (e.g., shift factor and AFM tip size) are also discussed.