No abstract

Polyhydroxyalkanoates (PHAs) are natural biopolymers produced by various microorganisms as a reserve of carbon and energy. PHA synthesis generally occurs during fermentation under nutrient limiting conditions with excess carbon. There are two main types of PHAs, short chain length PHAs (scl-PHAs) and medium chain length PHAs (mcl-PHAs). The mechanical and thermal properties of PHAs depend mainly on the number of carbons in the monomer unit and its molecular weight. PHAs are promising materials for biomedical applications because they are biodegradable, non-toxic and biocompatible. The large range of PHAs, along with their varying physical properties and high biocompatibility, make them highly attractive biomaterials for use in drug delivery. They can be used to produce tablets, micro-and nanoparticles as well as drug eluting scaffolds. A large range of different PHAs have been explored and the results obtained suggest that PHAs are excellent candidates for controlled and targeted drug delivery systems.

The only types of polyhydroxyalkanoates (PHAs) that have been explored for use in nerve regeneration are poly(3‐hydroxybutyrate), P(3HB), and poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (P(3HB‐co‐3HHx)). However, nerve regeneration induced by these PHAs is inferior to that of autologous nerve grafting. The aim of this work was to study novel PHA blends as resorbable biomaterials for the manufacture of nerve guidance conduits. PHA blend films with varying ratios of poly(3‐hydroxyoctanoate)/poly(3‐hydroxybutyrate) (P(3HO)/P(3HB)) were produced using the solvent‐casting method. Neat films of P(3HO) and P(3HB), along with 25:75, 50:50, and 75:25 blend films of P(3HO)/P(3HB), were characterized with respect to chemical, material, and biological properties. On surface analysis, the blends exhibited higher values of roughness compared with the neat films. The differential scanning calorimetry characterization of the blends confirmed that P(3HO) and P(3HB) formed immiscible blends. FTIR and XRD analysis of the blends showed a decrease in crystallinity along with an increase of the proportion of P(3HO) . However, an increase in the stiffness of the blends was observed when the proportion of P(3HB) increased. Although all of the blends were biocompatible with NG108‐15 neuronal cells, the 25:75 P(3HO)/P(3HB) blend showed significantly better support for growth and differentiation of these cells. The mechanical properties of PHA blends correspond to the reported properties of peripheral nerves. Therefore, they could serve as base material for the manufacture of nerve guidance conduits.

Surface hydrophobization of cellulose nanomaterials has been used in the development of nanofiller-reinforced polymer composites and formulations based on Pickering emulsions. Despite the well-known effect of hydrophobic domains on self-assembly or association of water-soluble polymer amphiphiles, very few studies have addressed the behavior of hydrophobized cellulose nanomaterials in aqueous media. In this study, we investigate the properties of hydrophobized cellulose nanocrystals (CNCs) and their self-assembly and amphiphilic properties in suspensions and gels. CNCs of different hydrophobicity were synthesized from sulfated CNCs by coupling primary alkylamines of different alkyl chain lengths (6, 8, and 12 carbon atoms). The synthetic route permitted the retention of surface charge, ensuring good colloidal stability of hydrophobized CNCs in aqueous suspensions. We compare surface properties (surface charge, ζ potential), hydrophobicity (water contact angle, microenvironment probing using pyrene fluorescence emission), and surface activity (tensiometry) of different hydrophobized CNCs and hydrophilic CNCs. Association of hydrophobized CNCs driven by hydrophobic effects is confirmed by X-ray scattering (SAXS) and autofluorescent spectroscopy experiments. As a result of CNC association, CNC suspensions/gels can be produced with a wide range of rheological properties depending on the hydrophobic/hydrophilic balance. In particular, sol–gel transitions for hydrophobized CNCs occur at lower concentrations than hydrophilic CNCs, and more robust gels are formed by hydrophobized CNCs. Our work illustrates that amphiphilic CNCs can complement associative polymers as modifiers of rheological properties of water-based systems.

A robust processing of polymers into antimicrobial materials is introduced using polymer/clay nanotechnology. Antimicrobial activity of commercially available organoclays modified with cationic surfactants has been screened in tests against gram-negative Escherichia coli and gram-positive Staphylococcus aureus bacteria. Despite the leaching biocidal surfactants, cell interactions with organoclay surface have been identified to be responsible for antimicrobial activity of organoclays. Distribution of clay platelets within polymer matrix by melt extrusion process resulted in polymer/clay nanocomposites active against both gram-positive and gram-negative bacteria by contact. The study discloses a much overlooked function of organoclays modified with cationic surfactants for nanocomposite application, i.e., the ability of organoclays to render polymer nanocomposites biocidal.

Cellulose nanocrystals (CNCs) that bind to each other through associative hydrophobic interactions have been synthesized by modifying sulfated CNCs (sCNCs) with hydrophobic moieties. These octyl-CNCs form gels at significantly lower concentrations than parent sCNCs, producing extremely strong hydrogels. Unlike sCNCs, these octyl-CNCs do not form ordered liquid crystalline phases indicating a random association into a robust network driven by hydrophobic interactions. Furthermore, involvement of the octyl-CNCs into multicomponent supramolecular assembly was demonstrated in combination with starch. AFM studies confirm favorable interactions between starch and octyl-CNCs, which is thought to be the source of the dramatic increase in gel strength.

Here, we report a nanoplatform based on iron oxide nanocubes (IONCs) coated with a bioresorbable polymer that, upon exposure to lytic enzymes, can be disassembled increasing the heat performances in comparison with the initial clusters. We have developed two-dimensional (2D) clusters by exploiting benchmark IONCs as heat mediators for magnetic hyperthermia and a polyhydroxyalkanoate (PHA) copolymer, a biodegradable polymer produced by bacteria that can be digested by intracellular esterase enzymes. The comparison of magnetic heat performance of the 2D assemblies with 3D centrosymmetrical assemblies or single IONCs emphasizes the benefit of the 2D assembly. Moreover, the heat losses of 2D assemblies dispersed in water are better than the 3D assemblies but worse than for single nanocubes. On the other hand, when the 2D magnetic beads (2D-MNBs) are incubated with the esterase enzyme at a physiological temperature, their magnetic heat performances began to progressively increase. After 2 h of incubation, specific absorption rate values of the 2D assembly double the ones of individually coated nanocubes. Such an increase can be mainly correlated to the splitting of the 2D-MNBs into smaller size clusters with a chain-like configuration containing few nanocubes. Moreover, 2D-MNBs exhibited nonvariable heat performances even after intentionally inducing their aggregation. Magnetophoresis measurements indicate a comparable response of 3D and 2D clusters to external magnets (0.3 T) that is by far faster than that of single nanocubes. This feature is crucial for a physical accumulation of magnetic materials in the presence of magnetic field gradients. This system is the first example of a nanoplatform that, upon exposure to lytic enzymes, such as those present in a tumor environment, can be disassembled from the initial 2D-MNB organization to chain-like assemblies with clear improvement of the heat magnetic losses resulting in better heat dissipation performances. The potential application of 2D nanoassemblies based on the cleavable PHAs for preserving their magnetic losses inside cells will benefit hyperthermia therapies mediated by magnetic nanoparticles under alternating magnetic fields.

Polyhydroxyalkanoates, a broad family of natural biodegradable and biocompatible polymers, have emerged as highly promising biomaterials both for bulk and biomedical applications. Here we describe an approach to tune the mechanical properties of stiff and brittle poly(3-hydroxybutyrate) and thereby to expand its potential biomedical applications. Plasticisation, a common practice in the plastic industry to modify polymer mechanical properties, has been used very cautiously for biomedical applications due to plasticiser toxicity and migration. We have developed a plasticiser for poly(3-hydroxybutyrate) based on a structurally related but softer and pliable medium chain length polyhydroxyalkanoate. Additives of oligomeric derivatives of this polymer improved ductility of poly(3-hydroxybutyrate), greatly widening the future applicability of this well-established biomaterial. In parallel, the binary polyhydroxyalkanoate materials also exhibited improved cell attachment and proliferation, a highly desirable outcome.