In-situ uniaxial drawing of poly-L-lactic acid (PLLA): Following the crystalline morphology development using time-resolved SAXS/WAXS

Facet Engineering Boosts Interfacial Compatibility of Inorganic-Polymer Composites

The interfacial compatibility between inorganic particles and polymer is crucial for ensuring high performance of composites. Current efforts to improve interfacial compatibility preferentially rely on organic modification of inorganic particles, leading to their complex process, high costs, and short lifespans due to aging and decomposition of organic modifiers. However, the fabrication of inorganic particles free from organic modification that is highly compatible in polymer still remains a great challenge. Herein, a novel facet-engineered inorganic particle that exhibit high compatibility with widely used polymer interface without organic modification is reported. Theoretical calculations and experimental results show that (020) and (102) facets of inorganic particles modulate local coordination environment of Ca atoms, which in turn regulate d-orbital electron density of Ca atoms and electron transfer paths at interfaces between polymer and inorganic particles. This difference alters the molecular diffusion, orientation of molecular chains on surface of inorganic particles, further modulating interfacial compatibility of composites. Surprisingly, the facet-engineered inorganic particles show exceptional mechanical properties, especially for tensile strain at break, which increases by 395%, far superior to state-of-the-art composites counterparts. Thus, the method can offer a more benign approach to the general production of high-performance and low-cost polymer-inorganic composites for diverse potential applications.

Investigating Cross-Linking Parameters and Molecular Arrangement in Liquid Crystalline Epoxy Monomer with Aromatic Diamine: DSC-TOPEM® and WAXS Analysis

This study presents the characterization of cross-linking parameters of a liquid crystalline epoxy monomer with an aromatic diamine as a curing agent. The mixture tested consisted of bis [4-(10,11-epoxyundecanoyloxy)benzoate] p-phenylene (LCEM) and 1,3-phenylenediamine (1,3-PDA). This paper focuses on the structural characterization of such systems using X-ray analysis. To investigate this, a comprehensive analysis was conducted using Differential Scanning Calorimetry (DSC) and Wide-Angle X-ray Scattering (WAXS). Through DSC analysis, the curing behavior and transition temperature of the liquid crystal epoxy system were established. To fully characterize the cross-linking of the system, a novel technique called DSC-TOPEM® was employed. The use of this technique enabled real-time monitoring of the curing process and provided precise information on the cross-linking energy, which resulted in the finding that the mixture was cross-linking faster than expected. WAXS analysis was performed to assess the structural changes formed during the cross-linking. The results of this analysis confirm that lower cross-linking temperatures of the mixture cause better ordering of mesogens than higher ones.

Bionic structure and biocompatibilities of long chain branched poly(L-lactic acid) oriented microcellular foaming material

In order to solve the problem of uneven microporous structure of Poly(L-lactic acid) (PLLA) bulk orientation by using biological safety multi-functional plant oil as chain extenders (CE), multi-armed flexible chains were introduced into PLLA through reactive processing to prepare long chain branched PLLA (LCB-PLLA). When the total content of the CE was 6.15 wt%, PLLA and the CE reacted most fully, while maintaining the tensile strength of PLLA and improving toughness. After introducing the LCB structure, the presence of multi-armed flexible chains increased the mobility of the molecular chains, resulting in a significantly lower degree of crystallinity. When the draw ratio up to 900 %, the crystallinity of LCB-PLLA-F-900 % was only 45.15 %, lower than that of PLLA-F-900 %. Thanks to the mobility of polymer chains can be enhanced, which reduces the degree of crystallinity while promoting the uniform growth of oriented microporous structures. Finally, an oriented micro-porous biomimetic LCB-PLLA material with an average cell diameter of 540 nm was prepared, and the results of in vitro cell culture showed that the oriented micro-porous LCB-PLLA biomimetic material was more conducive to cell proliferation.

Key Factors of Mechanical Strength and Toughness in Oriented Poly(l-lactic acid) Monofilaments for a Bioresorbable Self-Expanding Stent

The investigation of the strength and toughness of poly(l-lactic acid) (PLLA) monofilaments is essential as the fundamental element of a biodegradable braided stent. However, the determining factor remains poorly addressed with respect to influencing the mechanical behavior of PLLA monofilaments. In this work, the electron beam (EB) with different radiation doses was utilized to sterilize PLLA monofilaments. Properties of the monofilaments, including the breaking strength, elongation at break, molecular weight, orientation, and microstructure of the fracture, were characterized. Results showed that a random chain scission of PLLA resulting from EB during this process could cause the decrease in molecular weight, which led to the decline in breaking strength. Meanwhile, the irradiated monofilaments were found to have almost the same elongation at break below a dose of 30 kGy and declined by 71.41% up to a dose of 48 kGy. It was also found that the ductile fracture connection of the monofilament translated to the brittle fracture by comparing the microstructure without and with sterilization. These phenomena could originate from the destruction of the long molecular chains connecting the crystal plates into shorter ones by radiation. PLLA monofilaments with 0, 30, and 48 kGy were used to braid carotid stents. Compared with a carotid Wallstent, the PLLA stent can better provide radial supporting to the carotid lesion. This study provides preliminary experimental references to evaluate and predict the mechanical performance of PLLA braided stents.

Polylactic Acid Piezo-Biopolymers: Chemistry, Structural Evolution, Fabrication Methods, and Tissue Engineering Applications

Polylactide acid (PLA), as an FDA-approved biomaterial, has been widely applied due to its unique merits, such as its biocompatibility, biodegradability, and piezoelectricity. Numerous utilizations, including sensors, actuators, and bio-application-its most exciting application to promote cell migration, differentiation, growth, and protein-surface interaction-originate from the piezoelectricity effect. Since PLA exhibits piezoelectricity in both crystalline structure and an amorphous state, it is crucial to study it closely to understand the source of such a phenomenon. In this respect, in the current study, we first reviewed the methods promoting piezoelectricity. The present work is a comprehensive review that was conducted to promote the low piezoelectric constant of PLA in numerous procedures. In this respect, its chemistry and structural origins have been explored in detail. Combining any other variables to induce a specific application or to improve any PLA barriers, namely, its hydrophobicity, poor electrical conductivity, or the tuning of its mechanical properties, especially in the application of cardiovascular tissue engineering, is also discussed wherever relevant.

An investigation into the polylactic acid texturization through thermomechanical processing and the improved d33 piezoelectric outcome of the fabricated scaffolds

The bio/sensors performance has been established to be significantly affected through partially or entirely alignment of nano/microfibrous in polymeric mats. The matter of crystalline/amorphous proportion in semicrystalline polymers is another factor that can affect the application of the piezoelectric patches. The present work deals with fabricating the scaffolds of micro/nanofibers through a modified electrospinning procedure. The ratio of the relevant organic and polar solvents, the beading, the degree of fiber alignment, and fiber thickness have been intentionally elaborated. An unaligned unbeaded nanofibrous mat has been fabricated after tuning the solvents to poly-lactic acid ratio. This paper, for the first time, deals with the calculation of the value of d₃₃ value of a commercial PLA and its improvement, it has been revealed that the d₃₃ piezoelectric property is improved as a consequence of the thermo-mechanical processing above the cold crystallization temperature. The applied thermo (mechanical) processing causes the structural evolution from amorphous to crystallized states. Formation of the α and α' crystalline phases is introduced as the main responsible for the improvement of the piezoelectric property. This improvement not only is correlated with the degree of crystallinity, but also the orientation and alignment of the crystallites is known to be influential. In this respect, the complex helical chain structural evolution of poly-lactic acid has been analyzed through Herman's orientation function. It has been found that, besides the characterized disorder-to-order phase transformation, the C=O branched out dipoles interactions significantly affects by the texturization of the aligned polymeric chains in the direction of the electrospinning which is known as the main factor to promote the piezoelectric property of processed mat.