The 3D spatial structure of porous polyethylene particles was reconstructed from their X‐ray micro‐tomography images. Several polyolefin particles with an artificial granular structure were generated. Transport in reconstructed particles was calculated for the case of a monomer diffusing through both the pores and the polymer. The calculated degassing characteristics of reconstructed polyolefin particles can be compared to experiments. Monomer mass transport limitations are important not only in the early stage of particle growth, but also in fully‐developed polyolefin particles. The problems and limitations of the developed method are discussed. The method developed allows prediction of the effect of particle structure on mass transport limitations for real particle structures.
Advanced models of penetrant transport and reaction in spatially 3D porous polyolefin particles reconstructed from X‐ray µCT images require proper determination of particle morphology. Moreover, polyolefins exhibit a relatively low absorptivity for X‐rays, therefore their investigation using µCT can be difficult. In this paper, a low‐resolution µCT built into an SEM is used to examine how the µCT resolution and several user‐selected parameters associated with the scanning/reconstruction affect the resulting particle morphology. Using samples with known morphology and independent imaging techniques, the performance of the µCT device is critically assessed. Finally, a method suitable for the reliable reconstruction of polyolefin particles using low‐resolution µCT is proposed.
The diffusion of liposomes and PL/DNA complexes in mucin and collagen solutions, considered to model ‘in vivo’ colloidal gene delivery vector transport, is studied with FCS. The diffusion of defined liposomes is investigated as a function of particle size, surface charge, and the deviation from the Stokes‐Einstein behavior. In all cases the self‐diffusion coefficient decreases exponentially with polymer concentration. The same surface charge dependence of diffusion is observed in mucin for PL/DNA complexes with either positive or negative excess charge. Incubation of positively‐charged PL/DNA complexes in a natural lung surfactant lipid increases the diffusion coefficients to almost the same as for the negatively‐charged PL/DNA complexes.
Mucoadhesive NP drug carriers have attracted substantial interest as a potential treatment for anterior eye diseases. NPs composed of PLA‐Dex surface functionalized with a mucoadhesive ligand, PBA, were developed as drug carriers with particle sizes ranging from 25 to 28 nm. Using CycA as a model drug, we showed that NPs encapsulated up to 13.7 wt% CycA and exhibited sustained release for up to 5 d in vitro at a clinically relevant dose. We fine‐tuned the PBA density on the NP surface to maximize the mucin‐NP interaction without compromising the particle stability in vitro. This block copolymer conjugate may be useful to improve the bioavailability of topical formulations.
The transport of reaction species in polyolefin particles affects both the polymerization and the degassing of the powder in the down‐stream processing. The morphology of particles – that is, the distribution of polymer and pore phases – predetermines their degassing behavior. We utilize gravimetric measurements to obtain the dynamics of degassing and to determine morphology characteristics of porous poly(propylene) particles. We found that Fick's diffusion model is not generally capable of fitting the shape of degassing curves of porous particles. Therefore we propose a particle model including two sizes of compact polymer granules and demonstrate that the degassing can be described by this model and that the model is capable of estimating fractions of large and small compact zones and the size of large compact zones.
In order to impart antibacterial properties to microfibrous electrospun materials from styrene/maleic anhydride copolymers, quaternized chitosan derivatives (QCh) containing alkyl substituents of different chain lengths are covalently attached to the mats. A complete inhibition of the growth of bacteria, S. aureus (Gram‐positive) and E. coli (Gram‐negative), for a contact time of 30–120 min or a decrease of the bacterial titer by 2–3 log units is observed depending on the quaternization degree, the chain length of the alkyl substituent, and the molar mass of QCh. The modified mats are also effective in suppressing the adhesion of pathogenic S. aureus bacteria.
Silk fibroin is a useful protein polymer for biomaterials and tissue engineering. In this work, porogen leached scaffolds prepared from aqueous and HFIP silk solutions were reinforced through the addition of silk particles. This led to about 40 times increase in the specific compressive modulus and the yield strength of HFIP‐based scaffolds. This increase in mechanical properties resulted from the high interfacial cohesion between the silk matrix and the reinforcing silk particles, due to partial solubility of the silk particles in HFIP. The porosity of scaffolds was reduced from ≈90% (control) to ≈75% for the HFIP systems containing 200% particle reinforcement, while maintaining pore interconnectivity. The presence of the particles slowed the enzymatic degradation of silk scaffolds.
Aromatic polyamide particles were prepared by reacting diamines and diacid chlorides in a reaction solution containing water. They consisted of submicron‐sized pie‐shaped or rugged spherical particles with a narrow size distribution. The surface morphology of these particles was found to vary with the volume of water added, the reaction solvent, and the monomer concentration, but the degree of crystallinity of the particles obtained was almost the same. In addition, the molecular weight of the resulting material depended on the volume of water added and the monomer concentration. During the particle formation process, the degree of crystallinity was set at the initial stage, and thereafter the morphology and the molecular weight changed gradually with reaction time.
Three types of aromatic polyamide particles have been prepared from reacting diamines and diacid chlorides in an acetone or dioxane solution that includes water, using the precipitation polymerization method employing ultrasonic irradiation. The particle diameters were in the range from 300 nm to 1.2 µm with a narrow size distribution. The surface morphology and crystallinity differed greatly among the particles. They began to degrade at temperatures above 400 °C. Also the morphology depended on the ultrasonic frequency. The addition of water was essential to form particles using this polymerization method. Further it was useful to increase the molecular weights of polyamide products.
