Novel hypercrosslinking approach toward high surface area functional 2-hydroxyethyl methacrylate-based polyHIPEs

RAFT Polymerisation and Hypercrosslinking Improve Crosslink Homogeneity and Surface Area of Styrene Based PolyHIPEs

The influence of a polymerisation mechanism (reversible addition-fragmentation chain transfer; RAFT vs. free radical polymerisation; FRP) on the porous structure of highly porous poly(styrene-co-divinylbenzene) polymers was investigated. The highly porous polymers were synthesised via high internal phase emulsion templating (polymerizing the continuous phase of a high internal phase emulsion), utilising either FRP or RAFT processes. Furthermore, residual vinyl groups in the polymer chains were used for the subsequent crosslinking (hypercrosslinking) applying di-tert-butyl peroxide as the source of radicals. A significant difference in the specific surface area of polymers prepared by FRP (between 20 and 35 m²/g) and samples prepared by RAFT polymerisation (between 60 and 150 m²/g) was found. Based on the results from gas adsorption and solid state NMR, it could be concluded that the RAFT polymerisation affects the homogeneous distribution of the crosslinks in the highly crosslinked styrene-co-divinylbenzene polymer network. During the initial crosslinking, RAFT polymerisation leads to the increase in mesopores with diameters between 2 and 20 nm, resulting in good accessibility of polymer chains during the hypercrosslinking reaction, which is reflected in increased microporosity. The fraction of micropores created during the hypercrosslinking of polymers prepared via RAFT is around 10% of the total pore volume, which is up to 10 times more than for polymers prepared by FRP. Specific surface area, mesopore surface area, and total pore volume after hypercrosslinking reach almost the same values, regardless of the initial crosslinking. The degree of hypercrosslinking was confirmed by determination of the remaining double bonds by solid-state NMR analysis.

Metallic Nanoparticles Adsorbed at the Pore Surface of Polymers with Various Porous Morphologies: Toward Hybrid Materials Meant for Heterogeneous Supported Catalysis

Hybrid materials consisting of metallic nanoparticles (NPs) adsorbed on porous polymeric supports have been the subject of intense research for many years. Such materials indeed gain from intrinsic properties, e.g., high specific surface area, catalytic properties, porous features, etc., of both components. Rational design of such materials is fundamental regarding the functionalization of the support surface and thus the interactions required for the metallic NPs to be strongly immobilized at the pore surface. Herein are presented some significant scientific contributions to this rapidly expanding research field. This contribution will notably focus on various examples of such hybrid systems prepared from porous polymers, whatever the morphology and size of the pores. Such porous polymeric supports can display pores with sizes ranging from a few nanometers to hundreds of microns while pore morphologies, such as spherical, tubular, etc., and/or open or closed, can be obtained. These systems have allowed some catalytic molecular reactions to be successfully undertaken, such as the reduction of nitroaromatic compounds or dyes, e.g., methylene blue and Eosin Y, boronic acid-based C–C homocoupling reactions, but also cascade reactions consisting of two catalytic reactions achieved in a row.

Porous polycaprolactone and polycarbonate poly(urethane urea)s via emulsion templating: structures, properties, cell growth

Macroporous, emulsion-templated, linear poly(urethane urea) elastomers were synthesized from polyols (poly(ε-caprolactone)s or polycarbonates) and a diisocyanate. Growing cells adhered to the walls, spread, and penetrated into the porous structures.

Basic Principles of Emulsion Templating and Its Use as an Emerging Manufacturing Method of Tissue Engineering Scaffolds

Tissue engineering (TE) aims to regenerate critical size defects, which cannot heal naturally, by using highly porous matrices called TE scaffolds made of biocompatible and biodegradable materials. There are various manufacturing techniques commonly used to fabricate TE scaffolds. However, in most cases, they do not provide materials with a highly interconnected pore design. Thus, emulsion templating is a promising and convenient route for the fabrication of matrices with up to 99% porosity and high interconnectivity. These matrices have been used for various application areas for decades. Although this polymer structuring technique is older than TE itself, the use of polymerised internal phase emulsions (PolyHIPEs) in TE is relatively new compared to other scaffold manufacturing techniques. It is likely because it requires a multidisciplinary background including materials science, chemistry and TE although producing emulsion templated scaffolds is practically simple. To date, a number of excellent reviews on emulsion templating have been published by the pioneers in this field in order to explain the chemistry behind this technique and potential areas of use of the emulsion templated structures. This particular review focusses on the key points of how emulsion templated scaffolds can be fabricated for different TE applications. Accordingly, we first explain the basics of emulsion templating and characteristics of PolyHIPE scaffolds. Then, we discuss the role of each ingredient in the emulsion and the impact of the compositional changes and process conditions on the characteristics of PolyHIPEs. Afterward, current fabrication methods of biocompatible PolyHIPE scaffolds and polymerisation routes are detailed, and the functionalisation strategies that can be used to improve the biological activity of PolyHIPE scaffolds are discussed. Finally, the applications of PolyHIPEs on soft and hard TE as well as in vitro models and drug delivery in the literature are summarised.

Poly(vinylbenzyl chloride-co-divinyl benzene) polyHIPE monolith-supported o-hydroxynaphthaldehyde propylenediamine Schiff base ligand complex of copper(ii) ions as a catalyst for the epoxidation of cyclohexene

Poly(vinylbenzyl chloride-co-divinyl benzene)-based polyHIPE monoliths of different porosities were prepared using high-internal-phase emulsions (HIPEs) containing a fixed amount of vinylbenzyl chloride (VBC, 6.0 g, 0.0393 mol) and divinyl benzene (DVB 4.0 g, 0.0308 mol) as the oil phase and different volume ratios of aqueous calcium chloride as the internal phase. Span-80 (2.0 g (4.67 mmol))-stabilized HIPEs were polymerized at 60 °C using potassium persulfate (0.4 g, 1.48 mmol) as the initiator. Upon varying the volume ratio of aqueous calcium chloride from 80 to 90%, the prepared polyHIPE monoliths have shown significant variations in their surface morphology, specific surface area (SA), and pore volumes (V p) as confirmed by scanning electron microscopy (SEM) and a gas adsorption (BET) method. The prepared polyHIPE monoliths were anchored with o-hydroxynaphthaldehyde propylenediamine Schiff base ligand (HNPn) and then loaded with copper(ii) ions (HNPn-Cu) to act as a catalyst. The structural information of unsupported HNPn-Cu complexes was obtained by recording its FT-IR and UV-visible spectra. The amount of copper(ii) ions loaded onto HNPn ligand-anchored polyHIPE monoliths was determined by atomic absorption spectroscopic analysis. In comparison to unsupported HNPn-Cu catalyst, the polyHIPE monolith-supported HNPn-Cu catalyst has shown high catalytic activity (66.8%), product selectivity for epoxycyclohexane (ECH) (94.8%), high turn over number (0.028 mol mol-1 h-1) and low energy of activation (22.4 kJ mol-1) in the epoxidation of cyclohexene in the presence of hydrogen peroxide (H2O2) as an oxidant at 40 °C. The polyHIPE-supported HNPn-Cu catalyst also shows high reuse applications. Studies show that there is sufficient scope to develop polyHIPE monoliths with various properties for specific applications.

Covalent Attachment of Fibronectin onto Emulsion-Templated Porous Polymer Scaffolds Enhances Human Endometrial Stromal Cell Adhesion, Infiltration, and Function

A novel strategy for the surface functionalization of emulsion-templated highly porous (polyHIPE) materials as well as its application to in vitro 3D cell culture is presented. A heterobifunctional linker that consists of an amine-reactive N-hydroxysuccinimide ester and a photoactivatable nitrophenyl azide, N-sulfosuccinimidyl-6-(4'-azido-2'-nitrophenylamino)hexanoate (sulfo-SANPAH), is utilized to functionalize polyHIPE surfaces. The ability to conjugate a range of compounds (6-aminofluorescein, heptafluorobutylamine, poly(ethylene glycol) bis-amine, and fibronectin) to the polyHIPE surface is demonstrated using fluorescence imaging, FTIR spectroscopy, and X-ray photoelectron spectroscopy. Compared to other existing surface functionalization methods for polyHIPE materials, this approach is facile, efficient, versatile, and benign. It can also be used to attach biomolecules to polyHIPE surfaces including cell adhesion-promoting extracellular matrix proteins. Cell culture experiments demonstrated that the fibronectin-conjugated polyHIPE scaffolds improve the adhesion and function of primary human endometrial stromal cells. It is believed that this approach can be employed to produce the next generation of polyHIPE scaffolds with tailored surface functionality, enhancing their application in 3D cell culture and tissue engineering whilst broadening the scope of applications to a wider range of cell types.