Effect of the Dianhydride/Branched Diamine Ratio on the Architecture and Room Temperature Healing Behavior of Polyetherimides.

Traditional polyetherimides (PEIs) are commonly synthesized from an aromatic diamine and an aromatic dianhydride (e.g., 3,4'-oxidianiline (ODA) and 4,4'-oxidiphtalic anhydride (ODPA)) leading to the imide linkage and outstanding chemical, thermal and mechanical properties yet lacking any self-healing functionality. In this work, we have replaced the traditional aromatic diamine by a branched aliphatic fatty dimer diamine (DD1). This led to a whole family of self-healing polymers not containing reversible chemical bonds, capable of healing at (near) room temperature yet maintaining very high elastomeric-like mechanical properties (up to 6 MPa stress and 570% strain at break). In this work, we present the effect of the DD1/ODPA ratio on the general performance and healing behavior of a room temperature healing polyetherimide. A dedicated analysis suggests that healing proceeds in three steps: (i) an initial adhesive step leading to the formation of a relatively weak interface; (ii) a second step at long healing times leading to the formation of an interphase with different properties than the bulk material and (iii) disappearance of the damaged zone leading to full healing. We argue that the fast interfacial adhesive step is due to van der Waals interactions of long dangling alkyl chains followed by an interphase formation due to polymer chain interdiffusion. An increase in DD1/ODPA ratio leads to an increase in the healing kinetics and displacement shift of the first healing step toward lower temperatures. An excess of DD1 leads to the cross-linking of the polymer thereby restricting the necessary mobility for the interphase formation and limiting the self-healing behavior. The results here presented offer a new route for the development of room temperature self-healing thermoplastic elastomers with improved mechanical properties using fatty dimer diamines.

Afterload sensitivity of nonlinear end-systolic pressure-volume relation vs preload recruitable stroke work in conscious dogs.

The observations in vivo of a non-linear, afterload-sensitive end-systolic pressure-volume relation (ESPVR) and a linear, load-insensitive preload recruitable stroke work (PRSW) relation may be reconciled by considering the PRSW as a product of both the ventricular ESPVR and the arterial elastance (Ea). We obtained pressure-volume data from eight conscious dogs. The ESPVR was nonlinear, and its trajectory was afterload-dependent. The PRSW was linear and load-independent. Arterial elastance changed with both acute reductions in preload and steady-state changes in afterload. The PRSW relation thus describes both myocardial function and ventricular-arterial interaction and is a useful index of cardiovascular performance in patients.

Changes in muscle mechanics during chronic conditioning for cardiomyoplasty.

Chronic repetitive stimulation of skeletal muscle causes significant changes in contractile mechanics and makes the muscle fatigue resistant. The purpose of this study was to quantify the magnitude and time course of these changes. One latissimus dorsi muscle from each of 28 mongrel dogs was stimulated in situ at 1 Hz for 0, 3, 7, 14, 21, 42, or 70 days. Changes in isometric and isotonic mechanical performance were measured as a function of conditioning time. Isotonic force and velocity data were fitted to the Hill equation to obtain Vmax. The most striking early change was a 30 and 26% decline in muscle mass and cross-sectional area, respectively. Coincident with this was an approximate 40% decline in tetanic and twitch tension. There was a similar decline in the rates of rise and fall of twitch and tetanus tensions (+dT/dt and -dT/dt). The decline in tetanus +dT/dt and -dT/dt followed a similar time course, suggesting that these muscle functions were under similar influences. Calculation of the isometric force data per unit of cross-sectional area minimized the effect of stimulation on isometrically measured muscle function but did not eliminate it. Fusion frequency declined 52% with conditioning. The increases in time-to-peak twitch tension and half-relaxation time were independent of cross-sectional area. Time-to-peak twitch tension and half-relaxation time increased after 7 days of stimulation and became maximal after 42 or 70 days, respectively. Time-to-peak tetanus tension was unchanged by muscle conditioning. Changes in the force-velocity relationship began after 3 days of stimulation, changed very little between 3 and 21 days of stimulation, and showed another change after 42 and 70 days of stimulation. It may be possible to better modify the muscle for dynamic cardiomyoplasty by pharmacological or stimulation regimens once the mechanism of fiber switching is better understood.