Boosting the Piezoelectric Sensitivity of Amino Acid Crystals by Mechanical Annealing for the Engineering of Fully Degradable Force Sensors.

Biodegradable piezoelectric force sensors can be used as implantable medical devices for monitoring physiological pressures of impaired organs or providing essential stimuli for drug delivery and tissue regeneration without the need of additional invasive removal surgery or battery power. However, traditional piezoelectric materials, such as inorganic ceramics and organic polymers, show unsatisfactory degradability, and cytotoxicity. Amino acid crystals are biocompatible and exhibit outstanding piezoelectric properties, but their small crystal size makes it difficult to align the crystals for practical applications. Here, a mechanical-annealing strategy is reported for engineering all-organic biodegradable piezoelectric force sensors using natural amino acid crystals as piezoelectric materials. It is shown that the piezoelectric constant of the mechanical-annealed crystals can reach 12 times that of the single crystal powders. Moreover, mechanical annealing results in flat and smooth surfaces, thus improving the contact of the crystal films with the electrodes and leading to high output voltages of the devices. The packaged force sensors can be used to monitor dynamic motions, including muscle contraction and lung respiration, in vivo for 4 weeks and then gradually degrade without causing obvious inflammation or systemic toxicity. This work provides a way to engineer all-organic and biodegradable force sensors for potential clinical applications.

Modulating the Electromechanical Response of Bio-Inspired Amino Acid-Based Architectures through Supramolecular Co-Assembly.

Supramolecular packing dictates the physical properties of bio-inspired molecular assemblies in the solid state. Yet, modulating the stacking modes of bio-inspired supramolecular assemblies remains a challenge and the structure-property relationship is still not fully understood, which hampers the rational design of molecular structures to fabricate materials with desired properties. Herein, we present a co-assembly strategy to modulate the supramolecular packing of N-terminally capped alanine-based assemblies (Ac-Ala) by changing the amino acid chirality and mixing with a nonchiral bipyridine derivative (BPA). The co-assembly induced distinct solid-state stacking modes determined by X-ray crystallography, resulting in significantly enhanced electromechanical properties of the assembly architectures. The highest rigidity was observed after the co-assembly of racemic Ac-Ala with a bipyridine coformer (BPA/Ac-DL-Ala), which exhibited a measured Young's modulus of 38.8 GPa. Notably, BPA crystallizes in a centrosymmetric space group, a condition that is broken when co-crystallized with Ac-L-Ala and Ac-D-Ala to induce a piezoelectric response. Enantiopure co-assemblies of BPA/Ac-D-Ala and BPA/Ac-L-Ala showed density functional theory-predicted piezoelectric responses that are remarkably higher than the other assemblies due to the increased polarization of their supramolecular packing. This is the first report of a centrosymmetric-crystallizing coformer which increases the single-crystal piezoelectric response of an electrically active bio-inspired molecular assembly. The design rules that emerge from this investigation of chemically complex co-assemblies can facilitate the molecular design of high-performance functional materials comprised of bio-inspired building blocks.

Effectiveness and safety of retrograde intrarenal surgery (RIRS) vs. percutaneous nephrolithotomy (PCNL) in the treatment of isolated kidney stones.

OBJECTIVE: To compare the effectiveness and safety of retrograde intrarenal surgery (RIRS) and percutaneous nephrolithotomy (PCNL) in the treatment of isolated kidney stones. METHODS: A retrospective analysis was performed on 99 patients with isolated kidney stones treated in our hospital. Patients were divided into a flexible cystoscope group (FCG, n=48, receiving RIRS) and a nephoscopy group (NG, n=51, receiving PCNL) according to the operation methods. The two groups were compared in terms of the operative time, intraoperative bleeding, length of hospitalization, time to bowel function recovery, cost of hospitalization, one-session stone clearance, postoperative incidence of massive hemorrhage, postoperative 1-year recurrence rate, and levels of hemoglobin, urinary kidney injury molecule-1 (Kim-1), cysteine protease inhibitor C (Cys-C), interleukin (IL)-6, IL-10, cortisol (Cor), white blood cells (WBC) and C-reactive protein (CRP). RESULTS: The two groups exhibited significant differences in operation time, intraoperative bleeding, hospital stay, time to bowel function recovery and medical costs (P < 0.05). The NG had a single session stone clearance rate of 88.24% and a total stone clearance rate of 98.04%, which were higher than 70.83% and 83.33%, respectively, in the FCG (P < 0.05). The incidence of postoperative hemorrhage in the NG was 15.69%, which was higher than 2.08% in the FCG (P < 0.05). The postoperative 1-year recurrence rate was 9.80% in the NG and 6.25% in the FCG (P > 0.05). The hemoglobin level of the NG was lower than that of the FCG at 1 day after surgery, and the decrease in the NG were greater than that in the FCG (P < 0.05). The levels of Kim-1 in the NG were higher than those in the FCG at 48 h postoperatively. The levels of Cys-C in the NG were lower than those in the FCG at 12 h, 24 h, 48 h and 72 h postoperatively (P < 0.05). The NG showed higher levels of IL-6, Cor, WBC and CRP, and lower level of IL-10 as compared with the FCG at 6 h, 12 h, 24 h, 48 h, and 72 h postoperatively (P < 0.05). The levels of IL-10 in both groups at different time points after surgery were higher than those before surgery, and the levels of IL-6, Cor, WBC and CRP in both groups at 6 h, 12 h, 24 h, and 48 h after surgery were higher than those before surgery (P < 0.05), whereas there was no significant difference in IL-6, Cor, WBC and CRP at 72 h after surgery as compared with those before surgery (P > 0.05). CONCLUSION: Both RIRS and PCNL were effective in the treatment of isolated kidney stones, so the surgical methods should be specifically selected in clinical practice according to individual patient conditions.

Regulating the Homogeneity of Thiol-Maleimide Michael-Type Addition-Based Hydrogels Using Amino Biomolecules.

Poly(ethylene glycol) (PEG)-based synthetic hydrogels based on Michael-type addition reaction have been widely used for cell culture and tissue engineering. However, recent studies showed that these types of hydrogels were not homogenous as expected since micro domains generated due to the fast reaction kinetics. Here, we demonstrated a new kind of method to prepare homogenous poly(ethylene glycol) hydrogels based on Michael-type addition using the side chain amine-contained short peptides. By introducing such a kind of short peptides, the homogeneity of crosslinking and mechanical property of the hydrogels has been also significantly enhanced. The compressive mechanical and recovery properties of the homogeneous hydrogels prepared in the presence of side chain amine-contained short peptides were more reliable than those of inhomogeneous hydrogels while the excellent biocompatibility remained unchanged. Furthermore, the reaction rate and gelation kinetics of maleimide- and thiol-terminated PEG were proved to be significantly slowed down in the presence of the side chain amine-contained short peptides, thus leading to the improved homogeneity of the hydrogels. We anticipate that this new method can be widely applied to hydrogel preparation and modification based on Michael-type addition gelation.