Self-Assembled Hydrogel Membranes with Structurally Tunable Mechanical and Biological Properties.

Using supramolecular self-assembled nanocomposite materials made from protein and polysaccharide components is becoming more popular because of their unique properties, such as biodegradability, hierarchical structures, and tunable multifunctionality. However, the fabrication of these materials in a reproducible way remains a challenge. This study presents a new evaporation-induced self-assembly method producing layered hydrogel membranes (LHMs) using tropocollagen grafted by partially deacetylated chitin nanocrystals (CO-g-ChNCs). ChNCs help stabilize tropocollagen's helical conformation and fibrillar structure by forming a hierarchical microstructure through chemical and physical interactions. The LHMs show improved mechanical properties, cytocompatibility, and the ability to control drug release using octenidine dihydrochloride (OCT) as a drug model. Because of the high synergetic performance between CO and ChNCs, the modulus, strength, and toughness increased significantly compared to native CO. The biocompatibility of LHM was tested using the normal human dermal fibroblast (NHDF) and the human osteosarcoma cell line (Saos-2). Cytocompatibility and cell adhesion improved with the introduction of ChNCs. The extracted ChNCs are used as a reinforcing nanofiller to enhance the performance properties of tropocollagen hydrogel membranes and provide new insights into the design of novel LHMs that could be used for various medical applications, such as control of drug release in the skin and bone tissue regeneration.

The Effects of the Deacetylation of Chitin Nanowhiskers on the Performance of PCL/PLA Bio-Nanocomposites.

The multiple roles of organic nanofillers in biodegradable nanocomposites (NC) with a blend-based matrix is not yet fully understood. This work highlights combination of reinforcing and structure-directing effects of chitin nanowhiskers (CNW) with different degrees of deacetylation (DA), i.e., content of primary or secondary amines on their surface, in the nanocomposite with the PCL/PLA 1:1 matrix. Of importance is the fact that aminolysis with CNW leading to chain scission of both polyesters, especially of PLA, is practically independent of DA. DA also does not influence thermal stability. At the same time, the more marked chain scission/CNW grafting for PLA in comparison to PCL, causing changes in rheological parameters of components and related structural alterations, has crucial effects on mechanical properties in systems with a bicontinuous structure. Favourable combinations of multiple effects of CNW leads to enhanced mechanical performance at low 1% content only, whereas negative effects of structural changes, particularly of changed continuity, may eliminate the reinforcing effects of CNW at higher contents. The explanation of both synergistic and antagonistic effects of structures formed is based on the correspondence of experimental results with respective basic model calculations.

Effect of Polydopamine Coating of Cellulose Nanocrystals on Performance of PCL/PLA Bio-Nanocomposites.

In bio-nanocomposites with a poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) matrix with neat and polydopamine (PDA)-coated cellulose nanocrystals (CNCd), the use of different mixing protocols with masterbatches prepared by solution casting led to marked variation of localization, as well as reinforcing and structure-directing effects, of cellulose nanocrystals (CNC). The most balanced mechanical properties were found with an 80/20 PLA/PCL ratio, and complex PCL/CNC structures were formed. In the nanocomposites with a bicontinuous structure (60/40 and 40/60 PLA/PCL ratios), pre-blending the CNC and CNCd/PLA caused a marked increase in the continuity of mechanically stronger PLA and an improvement in related parameters of the system. On the other hand, improved continuity of the PCL phase when using a PCL masterbatch may lead to the reduction in or elimination of reinforcing effects. The PDA coating of CNC significantly changed its behavior. In particular, a higher affinity to PCL and ordering of PLA led to dissimilar structures and interface transformations, while also having antagonistic effects on mechanical properties. The negligible differences in bulk crystallinity indicate that alteration of mechanical properties may have originated from differences in crystallinity at the interface, also influenced by presence of CNC in this area. The complex effect of CNC on bio-nanocomposites, including the potential of PDA coating to increase thermal stability, is worthy of further study.

Synergistic effects in Methylcellulose/Hydroxyethylcellulose blend: Influence of components ratio and graphene oxide.

A specific feature of water-soluble polysaccharides is formation of organized structures in solutions. This study deals with an unexpected effect of 2-hydroxyethylcellulose (HEC) on structure and mechanical performance of methylcellulose (MC) films. The values of modulus with 5 and 10 % HEC content exceed those of the linear model, which indicates synergistic effect consisting in formation of ordered structures. However, higher content of HEC leads to worse properties corresponding to contribution of its lower parameters. The structural transformations are confirmed by XRD and polarized-light microscopy. Ability of HEC to support formation of ordered structures in MC solutions is indicated by rheology. Important fact is that low graphene oxide (GO) content has a high reinforcing effect on neat MC or HEC, but its presence in blends is accompanied by elimination of HEC-induced structural transformations. The results confirm complex effect of blending and GO on structure and properties of the MC/HEC system.

Nano-modified epoxy: the effect of GO-based complex structures on mechanical performance.

The application of nanofillers (NFs) in multicomponent polymer systems is accompanied by important structure-directing effects that are more marked in partially miscible systems, such as polymer-modified epoxy. This study deals with rubber-modified epoxy using different combinations of GO and amine-terminated butadiene-acrylonitrile copolymer (ATBN), including in situ and pre-made grafting. Moreover, GO grafted via planar epoxy groups or solely edge-localized carboxyls was used. It is shown that the grafted ATBN chains promote the assembly of GO-g-ATBN into nacre-mimicking lamellar structures instead of usual exfoliation in thermoplastics. This complex structure of elastically embedded GO leads to the best mechanical performance. It is obvious that a small concentration of the grafted polymer exceeds the contribution of a higher concentration of separately added ATBN. The results highlight the important effect of the degree of grafted chains and geometry of the internal structure of the self-assembled arrays and their effect on the mechanical performance.

Facile preparation of biocompatible poly (lactic acid)-reinforced poly(ε-caprolactone) fibers via graphite nanoplatelets -aided melt spinning.

Addition of high-aspect-ratio (AR) nanofillers can markedly influence flow behavior of polymer systems. As a result, application of graphite nanoplatelets (GNP) allows preparation of microfibrillar composites (MFC) based on PCL matrix reinforced with in-situ generated PLA fibrils. This work deals, for the first time, with preparation of analogous melt-drawn fibers. Unlike other blend-based fibers, the spinning and melt drawing leads to structure of deformed inclusions due to unfavorable ratio of rheological parameters of components. Subsequent moderate cold drawing of the system with dissimilar deformability of components causes strengthening with PLA fibrils. Unexpectedly, high velocity and extent of cold drawing leads to structure with low-AR inclusions, similar to the original melt-drawn blend. Extensive fast deformation of the soft PCL matrix does not allow sufficient stress transfer to rigid PLA. In spite of peculiarities found, the GNP-aided melt spinning allows facile preparation of biodegradable biocompatible fibers with wide range of diameters (80-400 µm) and parameters (2.35-18 cN/tex).

Graphite nanoplatelets-modified PLA/PCL: Effect of blend ratio and nanofiller localization on structure and properties.

Structure and properties of poly(lactic acid) (PLA)/poly (ɛ-caprolactone) (PCL) influenced by graphite nanoplatelets (GNP) were studied in dependence on blend composition. Electron microscopy indicates predominant localization of GNP in PCL. GNP-induced changes in viscosity hinder refinement of PCL inclusions, support PCL continuity in the co-continuous system, and lead to reduction of PLA inclusions size without GNP being present at the interface in the PCL-matrix blend. Negligible differences in crystallinity of both phases indicate that mechanical behaviour is mainly influenced by reinforcement and GNP-induced changes in morphology. Addition of 5 parts of GNP leads to ~40% and ~25% increase of stiffness in the PCL- and PLA-matrix systems, respectively, whereas the reinforcing effect is practically eliminated in the co-continuous systems due to GNP-induced lower continuity of PLA which enhances toughness. Impact resistance of the 80/20 blend shows increase with 5 parts content due to synergistic effect of PCL/GNP stacks, whereas minor increase in the blend of the ductile PCL matrix with brittle PLA inclusions is caused by GNP-modification of the component parameters. Results indicate high potential of GNP in preparing biocompatible systems with wide range of structure and properties.