Crucial Differences in the Hydrolytic Degradation between Industrial Polylactide and Laboratory-Scale Poly(L-lactide)

The rate of degradation of large-scale synthesized polylactide (PLA) of industrial origin was compared with that of laboratory-scale synthesized poly­(L-lactide) (PLLA) of similar molar mass. The structural discrepancy between the two material types resulted in a significant difference in degradation rate. Although the hydrolysis of industrial PLA was substantially faster than that of PLLA, the PLA material became less brittle and fragmented to a lesser extent during degradation. In addition, a comprehensive picture of the degradation of industrial PLA was obtained by subjecting different PLA materials to hydrolytic degradation at various temperatures and pH’s for up to 182 days. The surrounding environment had no effect on the degradation rate at physiological temperature, but the degradation was faster in water than in a phosphate buffer after prolonged degradation at temperatures above the <i>T</i>_g. The degree of crystallinity had a greater influence than the degradation environment on the rate of hydrolysis. For a future use of polylactide in applications where bulk plastics are generally used today, for example plastic packages, the appropriate PLA grade must be chosen based on the conditions prevailing in the degradation environment

Homocomposites of Polylactide (PLA) with Induced Interfacial Stereocomplex Crystallites

The demand for “green” degradable composite materials increases with growing environmental awareness. The key challenge is achieving the preferred physical properties and maintaining their eco-attributes in terms of the degradability of the matrix and the filler. Herein, we have designed a series of “green” homocomposites materials based purely on polylactide (PLA) polymers with different structures. Film-extruded homocomposites were prepared by melt-blending PLA matrixes (which had different degrees of crystallinity) with PLLA and PLA stereocomplex (SC) particles. The PLLA and SC particles were spherical and with 300–500 nm size. Interfacial crystalline structures in the form of stereocomplexes were obtained for certain particulate-homocomposite formulations. These SC crystallites were found at the particle/matrix interface when adding PLLA particles to a PLA matrix with d-lactide units, as confirmed by XRD and DSC data analyses. For all homocomposites, the PLLA and SC particles acted as nucleating agents and enhanced the crystallization of the PLA matrixes. The SC particles were more rigid and had a higher Young’s modulus compared with the PLLA particles. The mechanical properties of the homocomposites varied with particle size, rigidity, and the interfacial adhesion between the particles and the matrix. An improved tensile strength in the homocomposites was achieved from the interfacial stereocomplex formation. Hereafter, homocomposites with tunable crystalline arrangements and subsequently physical properties, are promising alternatives in strive for eco-composites and by this, creating materials that are completely degradable and sustainable

Highlighting the Importance of Surface Grafting in Combination with a Layer-by-Layer Approach for Fabricating Advanced 3D Poly(l‑lactide) Microsphere Scaffolds

A combined surface treatment (i.e., surface grafting and a layer-by-layer (LbL) approach) is presented to create advanced biomaterials, i.e., 3D poly­(l-lactide) (PLLA) microsphere scaffolds, at room temperature. The grafted surface plays a crucial role in assembling polyelectrolyte multilayers (PEMs) onto the surface of the microspheres, thus improving the physicochemical properties of the 3D microsphere scaffolds. The grafted surface of the PLLA microspheres demonstrates much better PEM adsorption, improved surface coverage at low pH, and smoother surfaces at high pH compared with those of nongrafted surfaces of PLLA microspheres during the assembly of PEMs. They induce more swelling than nongrafted surfaces after the assembly of the PEMs and exhibit blue emission after functionalization of the microsphere surface with a fluorescent dye molecule. The 3D scaffolds functionalized with and without nanosheets not only exhibit good mechanical performance similar to the compressive modulus of cancellous bone but also exhibit the porosity required for cancellous bone regeneration. The magnetic nanoparticle-functionalized 3D scaffolds result in an electrical conductivity in the high range of semiconducting materials (i.e., 1–250 S cm^–1). Thus, these 3D microsphere scaffolds fabricated by surface grafting and the LbL approach are promising candidates for bone tissue engineering

Nondestructive Covalent “Grafting-from” of Poly(lactide) Particles of Different Geometries

A nondestructive “grafting-from” method has been developed using poly­(lactide) (PLA) particles of different shapes as substrates and three hydrophilic monomers as grafts. Irregularly shaped particles and spheres of PLA were covalently surface functionalized using a versatile method of photoinduced free radical polymerization. The preservation of the molecular weight of the PLA particle bulk and the retention of the original particle shape confirmed the negligible effect of the grafting method. The changes in surface composition were determined by FTIR for both spherical and irregular particles and by XPS for the irregular particles showing the versatility of the method. Changes in the surface morphology of the PLA spherical particles were observed using microscopy techniques showing a full surface coverage of one of the grafted monomers. The method is applicable to a wide set of grafting monomers and provides a permanent alteration of the surface chemistry of the PLA particles creating hydrophilic PLA surfaces in addition to creating sites for further modification and drug delivery in the biomedical fields

Force Interactions of Nonagglomerating Polylactide Particles Obtained through Covalent Surface Grafting with Hydrophilic Polymers

Nonagglomerating polylactide (PLA) particles with various interaction forces were designed by covalent photografting. PLA particles were surface grafted with hydrophilic poly­(acrylic acid) (PAA) or poly­(acrylamide) (PAAm), and force interactions were determined using colloidal probe atomic force microscopy. Long-range repulsive interactions were detected in the hydrophilic/hydrophilic systems and in the hydrophobic/hydrophilic PLA/PLA-<i>g</i>-PAAm system. In contrast, attractive interactions were observed in the hydrophobic PLA/PLA and in the hydrophobic/hydrophilic PLA/PLA-<i>g</i>-PAA systems. AFM was also used in the tapping mode to determine the surface roughness of both neat and surface-grafted PLA film substrates. The imaging was performed in the dry state as well as in salt solutions of different concentrations. Differences in surface roughness were identified as conformational changes induced by the altered Debye screening length. To understand the origin of the repulsive force, the AFM force profiles were compared to the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory and the Alexander de Gennes (AdG) model. The steric repulsion provided by the different grafted hydrophilic polymers is a useful tool to inhibit agglomeration of polymeric particles. This is a key aspect in many applications of polymer particles, for example in drug delivery