Macrostructuring of emulsion-templated porous polymers by 3D laser patterning

Optimization of a High Internal Phase Emulsion-Based Resin for Use in Commercial Vat Photopolymerization Additive Manufacturing

High internal phase emulsions (HIPEs) are potential stereolithography-based resins for producing innovative lightweight porous materials; however, the use of these resins has only been shown in bespoke stereolithography setups. These studies indicated that HIPEs tend to scatter the light during structuring through stereolithography, and can produce poorly defined and low-resolution structures, but the inclusion of light absorbers can drastically increase the printing resolution. In this study, we focused on the inclusion of biocompatible light absorbers within the resin and the compatibility of those resins with a commercial vat photopolymerization additive manufacturing (or stereolithography) setup. A surfactant (hypermer)-stabilized water-in-oil emulsion based on 2-ethylhexyl-acrylate and isobornyl-acrylate was used. For the light absorbers, both hydrophobic (beta-carotene) and hydrophilic (tartrazine) molecules were used, which dissolve in the organic phase and aqueous phase, respectively. It was found that using a combination of both beta-carotene and tartrazine provided the best stereolithography-based 3D printing resolution. In addition, the emulsion was stable for the duration of the printing process and showed a porous polyHIPE structure with open surface porosity. The formulation of these HIPE-based resins permits them to be used in a wide range of applications since complex structures could be fabricated from HIPEs.

3D printed porous membrane integrated devices to study the chemoattractant induced behavioural response of aquatic organisms

Biological models with genetic similarities to humans are used for exploratory research to develop behavioral screening tools and understand sensory-motor interactions. Their small, often mm-sized appearance raises challenges in the straightforward quantification of their subtle behavioral responses and calls for new, customisable research tools. 3D printing provides an attractive approach for the manufacture of custom designs at low cost; however, challenges remain in the integration of functional materials like porous membranes. Nanoporous membranes have been integrated with resin exchange using purpose-designed resins by digital light projection 3D printing to yield functionally integrated devices using a simple, economical and semi-automated process. Here, the impact of the layer thickness and layer number on the porous properties - parameters unique for 3D printing - are investigated, showing decreases in mean pore diameter and porosity with increasing layer height and layer number. From the same resin formulation, materials with average pore size between 200 and 600 nm and porosity between 45% and 61% were printed. Membrane-integrated devices were used to study the chemoattractant induced behavioural response of zebrafish embryos and planarians, both demonstrating a predominant behavioral response towards the chemoattractant, spending >85% of experiment time in the attractant side of the observation chamber. The presented 3D printing method can be used for printing custom designed membrane-integrated devices using affordable 3D printers and enable fine-tuning of porous properties through adjustment of layer height and number. This accessible approach is expected to be adopted for applications including behavioural studies, early-stage pre-clinical drug discovery and (environmental) toxicology.

Investigating the Potential of Electroless Nickel Plating for Fabricating Ultra-Porous Metal-Based Lattice Structures Using PolyHIPE Templates

The use of polymerized high internal phase emulsions (polyHIPEs) as templates for electroless nickel plating is a promising method for producing ultra-porous metallic lattice structures with consistent wall thickness. These structures have desirable properties such as low density, high specific strength, resilience, and absorbency, making them suitable for various applications including battery electrodes, catalyst supports, and acoustic or vibration damping. This study aimed to optimize and investigate the electroless nickel plating process on polyHIPEs. Initially, a surfactant (Hypermer)-stabilized water-in-oil emulsion based on 2-ethylhexyl-acrylate and isobornyl-acrylate was used as a 3D printing resin to create polyHIPE structures. Then, the electroless nickel plating process was optimized using polyHIPE discs. The study also examined the effects of air, argon, and reducing atmospheres during the heating process to remove the polyHIPE template using metallized 3D-printed polyHIPE lattice structures. The findings indicated that different atmospheres led to the formation of distinct compounds. While nickel-coated polyHIPEs were fully oxidized in an air atmosphere, nickel phosphide (Ni3P) structures occurred in argon and reducing atmospheres along Ni metal. Moreover, in argon and reducing atmospheres, the porous structure of the polyHIPEs was retained as the internal structure was completely carbonized. Overall, the study demonstrated that intricate polyHIPE structures can be used as templates to create ultra-porous metal-based lattices for a wide range of applications.

Synthesis and Applications of Elastomeric Polymerized High Internal Phase Emulsions (PolyHIPEs)

Polymer foams (PFs) are among the most industrially produced polymeric materials, and they are found in applications including aerospace, packaging, textiles, and biomaterials. PFs are predominantly prepared using gas-blowing techniques, but PFs can also be prepared from templating techniques such as polymerized high internal phase emulsions (polyHIPEs). PolyHIPEs have many experimental design variables which control the physical, mechanical, and chemical properties of the resulting PFs. Both rigid and elastic polyHIPEs can be prepared, but while elastomeric polyHIPEs are less commonly reported than hard polyHIPEs, elastomeric polyHIPEs are instrumental in the realization of new materials in applications including flexible separation membranes, energy storage in soft robotics, and 3D-printed soft tissue engineering scaffolds. Furthermore, there are few limitations to the types of polymers and polymerization methods that have been used to prepare elastic polyHIPEs due to the wide range of polymerization conditions that are compatible with the polyHIPE method. In this review, an overview of the chemistry used to prepare elastic polyHIPEs from early reports to modern polymerization methods is provided, focusing on the applications that flexible polyHIPEs are used in. The review consists of four sections organized around polymer classes used in the preparation of polyHIPEs: (meth)acrylics and (meth)acrylamides, silicones, polyesters and polyurethanes, and naturally occurring polymers. Within each section, the common properties, current challenges, and an outlook is suggested on where elastomeric polyHIPEs can be expected to continue to make broad, positive impacts on materials and technology for the future.

Photoresponsive Emulsion-Templated Porous Materials via Orthogonal Photoclick Chemistry

The functionalization of emulsion-templated porous polymers (polyHIPEs) utilizing modern and efficient chemistries is an important avenue for tailoring the properties of these scaffolds for specific and specialized applications. Herein, tetrazole photoclick chemistry is utilized for the efficient functionalization of polyHIPEs synthesized from various monomer systems and polymerization chemistries. Using both radical polymerization and thiol-ene polymerization, polyHIPEs with well-defined, interconnected open-cell morphologies are synthesized with tetrazole concentrations ranging from 0 to 5 w/v %, with the pore diameters ranging from 3 to 24 μm. Analyzed by fluorescence spectroscopy, FTIR spectroscopy, and confocal microscopy, spatially controlled functionalization to generate photopatterned fluorescent polyHIPEs is demonstrated via the reaction with residual acrylate and thiol groups. In addition, the scaffolds can be readily functionalized with external dipolarophiles such as acrylates to incorporate a functionality onto the polyHIPE surface. With many functional tetrazoles also reported in the literature, a PEG-tetrazole is also used to explore the photoinduced functionalization of polyHIPEs possessing tunable ratios of thiol and acrylate groups, and the effect on fluorescence, wettability, and biocompatibility is analyzed. Overall, the reaction is shown to be a broadly applicable tool for polyHIPE functionalization with many avenues for further development toward specific applications.

Bioceramic scaffolds with triply periodic minimal surface architectures guide early-stage bone regeneration

The pore architecture of porous scaffolds is a critical factor in osteogenesis, but it is a challenge to precisely configure strut-based scaffolds because of the inevitable filament corner and pore geometry deformation. This study provides a pore architecture tailoring strategy in which a series of Mg-doped wollastonite scaffolds with fully interconnected pore networks and curved pore architectures called triply periodic minimal surfaces (TPMS), which are similar to cancellous bone, are fabricated by a digital light processing technique. The sheet-TPMS pore geometries (s-Diamond, s-Gyroid) contribute to a 3‒4-fold higher initial compressive strength and 20%-40% faster Mg-ion-release rate compared to the other-TPMS scaffolds, including Diamond, Gyroid, and the Schoen's I-graph-Wrapped Package (IWP) in vitro. However, we found that Gyroid and Diamond pore scaffolds can significantly induce osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Analyses of rabbit experiments in vivo show that the regeneration of bone tissue in the sheet-TPMS pore geometry is delayed; on the other hand, Diamond and Gyroid pore scaffolds show notable neo-bone tissue in the center pore regions during the early stages (3-5 weeks) and the bone tissue uniformly fills the whole porous network after 7 weeks. Collectively, the design methods in this study provide an important perspective for optimizing the pore architecture design of bioceramic scaffolds to accelerate the rate of osteogenesis and promote the clinical translation of bioceramic scaffolds in the repair of bone defects.

Porous biomaterials for tissue engineering: a review

The field of biomaterials has grown rapidly over the past decades. Within this field, porous biomaterials have played a remarkable role in: (i) enabling the manufacture of complex three-dimensional structures; (ii) recreating mechanical properties close to those of the host tissues; (iii) facilitating interconnected structures for the transport of macromolecules and cells; and (iv) behaving as biocompatible inserts, tailored to either interact or not with the host body. This review outlines a brief history of the development of biomaterials, before discussing current materials proposed for use as porous biomaterials and exploring the state-of-the-art in their manufacture. The wide clinical applications of these materials are extensively discussed, drawing on specific examples of how the porous features of such biomaterials impact their behaviours, as well as the advantages and challenges faced, for each class of the materials.

Emerging porous organic polymers for biomedical applications

This review summarizes and discusses the recent progress in porous organic polymers for diverse biomedical applications such as drug delivery, biomacromolecule immobilization, phototherapy, biosensing, bioimaging, and antibacterial applications.

Interconnectivity and morphology control of poly-high internal phase emulsions under photo-polymerization

We here demonstrate that the interconnectivity and morphology of photo-polymerized HIPEs can be controlled by changing the type of initiators and stabilizers, and the intensity of light.

Thiolene- and Polycaprolactone Methacrylate-Based Polymerized High Internal Phase Emulsion (PolyHIPE) Scaffolds for Tissue Engineering

Highly porous emulsion templated polymers (PolyHIPEs) provide a number of potential advantages in the fabrication of scaffolds for tissue engineering and regenerative medicine. Porosity enables cell ingrowth and nutrient diffusion within, as well as waste removal from, the scaffold. The properties offered by emulsion templating alone include the provision of high interconnected porosity, and, in combination with additive manufacturing, the opportunity to introduce controlled multiscale porosity to complex or custom structures. However, the majority of monomer systems reported for PolyHIPE preparation are unsuitable for clinical applications as they are nondegradable. Thiol-ene chemistry is a promising route to produce biodegradable photocurable PolyHIPEs for the fabrication of scaffolds using conventional or additive manufacturing methods; however, relatively little research has been reported on this approach. This study reports the groundwork to fabricate thiol- and polycaprolactone (PCL)-based PolyHIPE materials via a photoinitiated thiolene click reaction. Two different formulations, either three-arm PCL methacrylate (3PCLMA) or four-arm PCL methacrylate (4PCLMA) moieties, were used in the PolyHIPE formulation. Biocompatibility of the PolyHIPEs was investigated using human dermal fibroblasts (HDFs) and human osteosarcoma cell line (MG-63) by DNA quantification assay, and developed PolyHIPEs were shown to be capable of supporting cell attachment and viability.

Fundamentals and Design-Led Synthesis of Emulsion-Templated Porous Materials for Environmental Applications

Emulsion templating is at the forefront of producing a wide array of porous materials that offers interconnected porous structure, easy permeability, homogeneous flow-through, high diffusion rates, convective mass transfer, and direct accessibility to interact with atoms/ions/molecules throughout the exterior and interior of the bulk. These interesting features together with easily available ingredients, facile preparation methods, flexible pore-size tuning protocols, controlled surface modification strategies, good physicochemical and dimensional stability, lightweight, convenient processing and subsequent recovery, superior pollutants remediation/monitoring performance, and decent recyclability underscore the benchmark potential of the emulsion-templated porous materials in large-scale practical environmental applications. To this end, many research breakthroughs in emulsion templating technique witnessed by the recent achievements have been widely unfolded and currently being extensively explored to address many of the environmental challenges. Taking into account the burgeoning progress of the emulsion-templated porous materials in the environmental field, this review article provides a conceptual overview of emulsions and emulsion templating technique, sums up the general procedures to design and fabricate many state-of-the-art emulsion-templated porous materials, and presents a critical overview of their marked momentum in adsorption, separation, disinfection, catalysis/degradation, capture, and sensing of the inorganic, organic and biological contaminants in water and air.

Development of Photocurable Polyacrylate-Based PolyHIPEs and the Study of the Kinetics of Photopolymerization, and of Their Thermal, Mechanical and Hydrocarbon Absorption Properties

This article describes a comprehensive study to obtain polymeric porous materials via a photopolymerization technique, using acrylate-based high internal phase emulsions (HIPEs), as a template. The aim of obtaining these polymers was to use them as hydrocarbon absorbing materials. Kinetics of photopolymerization of the acrylate monomers and of the HIPEs were conducted to optimize the process. The obtained monoliths were characterized by thermal analysis such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The morphology and surface area were analyzed by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The compression properties of the materials were determined, as well as their absorption properties of hydrocarbons such as hexane, diesel, toluene and chloroform. The findings show that the acrylate-HIPEs displayed high reactivity photopolymerizing in 20 min. The glass transition temperature of the materials were in the range of 2 to 83 °C, depending on the ratio of acrylates in the photocurable formulation, displaying the characteristic morphology with voids and interconnecting windows. The polyHIPEs exhibited superior properties of absorption of the studied hydrocarbons. The order of capability of absorption was chloroform > toluene > hexane > diesel. The optimum absorbing material was that with trimethylolpropane triacrylate, ethylhexyl acrylate and isobornyl acrylate in a 1:0.9:2.1 ratio, which absorbed 778% of chloroform, 378% of toluene, 306 % of hexane and 236% of diesel.

Attractive Pickering Emulsion Gels

Properties of emulsions highly depend on the interdroplet interactions and, thus, engineering interdroplet interactions at molecular scale are essential to achieve desired emulsion systems. Here, attractive Pickering emulsion gels (APEGs) are designed and prepared by bridging neighboring particle-stabilized droplets via telechelic polymers. In the APEGs, each telechelic molecule with two amino end groups can simultaneously bind to two carboxyl functionalized nanoparticles in two neighboring droplets, forming a bridged network. The APEG systems show typical shear-thinning behaviors and their viscoelastic properties are tunable by temperature, pH, and molecular weight of the telechelic polymers, making them ideal for direct 3D printing. The APEGs can be photopolymerized to prepare APEG-templated porous materials and their microstructures can be tailored to optimize their performances, making the APEG systems promising for a wide range of applications.

Multiscale porosity in a 3D printed gellan-gelatin composite for bone tissue engineering

The aim of this work was to develop a complex-shaped gelatin-gellan composite scaffold with multiscale porosity using a combination of cryogenic 3D printing and lyophilization for bone tissue engineering. Cryogenic 3D printing was used to fabricate a low-concentration composite of complex-shaped macroporous gelatin-gellan structures with a pore size of 919 ± 89 µm. This was followed by lyophilization to introduce micropores of size 20-250 µm and nanometre-level surface functionalities, thus achieving a hierarchical porous structure. These multiscale porous scaffolds (GMu) were compared with two other types of scaffolds having only microporosity (GMi) and macroporosity (GMa) with regard to their physical andin vitrobiological properties. GMu scaffolds were found to be better than GMi and GMa in terms of swelling percentage, degradation rate, uniform pore distribution, cellular infiltration, attachment, proliferation, protein generation and mineralization. In conclusion, we have developed a controlled hierarchical bone-like structure, biomimicking natural bone, together with a reproducible process of manufacture by coupling soft hydrogel 3D printing with lyophilization. This enables the development of complex-shaped patient-specific 3D printed hydrogel scaffolds with enhanced performancein vitroand great potential in the fields of tissue engineering, bioprinting and regenerative medicine.

High Internal Phase Emulsions Synergistically Stabilized by Sodium Carboxymethyl Cellulose and Palm Kernel Oil Ethoxylates as an Essential Oil Delivery System

High internal phase emulsions (HIPEs) with an internal phase fraction of 84 vol % were prepared using carboxymethyl cellulose (CMC) and palm kernel oil ethoxylates (SOE-N-60) as a dual emulsifier. Effects of the oil-phase volume fraction, CMC concentration, and SOE-N-60 concentration on oil-in-water HIPEs stability were systematically studied by a Mastersizer 2000 instrument, Lx POL polarizing microscope, rheometer, etc. The bioavailability of tea tree oil can be effectively protected using HIPEs as a delivery system. The experimental results showed that, with the increase of the concentrations of CMC and SOE-N-60, the droplet size of HIPEs gradually decreases and the HIPEs showed good static stability. In addition, it was observed by scanning electron microscopy that the polyHIPEs materials using HIPEs stabilized by different SOE-N-60 and CMC concentrations as templates had different structures. Moreover, the synergism between CMC and SOE-N-60 surfactants plays a significant role in the preparation and stability of HIPEs.

Considerations Using Additive Manufacture of Emulsion Inks to Produce Respiratory Protective Filters Against Viral Respiratory Tract Infections Such as the COVID-19 Virus

This review paper explores the potential of combining emulsion-based inks with additive manufacturing (AM) to produce filters for respiratory protective equipment (RPE) in the fight against viral and bacterial infections of the respiratory tract. The value of these filters has been highlighted by the current severe acute respiratory syndrome coronavirus-2 crisis where the importance of protective equipment for health care workers cannot be overstated. Three-dimensional (3D) printing of emulsions is an emerging technology built on a well-established field of emulsion templating to produce porous materials such as polymerized high internal phase emulsions (polyHIPEs). PolyHIPE-based porous polymers have tailorable porosity from the submicron to 100 s of µm. Advances in 3D printing technology enables the control of the bulk shape while a micron porosity is controlled independently by the emulsion-based ink. Herein, we present an overview of the current polyHIPE-based filter applications. Then, we discuss the current use of emulsion templating combined with stereolithography and extrusion-based AM technologies. The benefits and limitation of various AM techniques are discussed, as well as considerations for a scalable manufacture of a polyHIPE-based RPE.

High Internal Phase Emulsion for Food-Grade 3D Printing Materials

Three-dimensional printing (3DP) has attracted significant attention for its use in additive manufacturing techniques because it provides customizability and flexibility for fabricating structures with arbitrary shapes. Certain applications in the food and medicine industries require 3D printable materials that are both biocompatible and biodegradable. Consequently, this study reports 3D printable materials constructed from food-grade high internal phase emulsions (HIPEs). The studied HIPEs (phase ratio 85%) were stabilized by the efficient adsorption behavior of cod proteins (concentration range, 10-50 mg mL^-1) at the oil-water interface. The stability of the oil-in-water HIPEs was improved by the formation of a concentration-dependent percentage of adsorbed proteins and cross-linking networks, and homogeneous and self-supporting structures were generated after 7 days of storage at 4 °C. The gel-like shear thinning rheological behavior induced by the cross-linking networks in the studied HIPEs can be tuned to obtain the desired printability and extrudability during 3DP. In the present study, the HIPEs stabilized with 50 mg mL^-1 of cod proteins exhibited the highest printing resolution, gel strength, hardness, adhesiveness, and chewiness during 3DP. These food-grade HIPE inks have the potential to diversify the applications of 3DP in foods, cosmetics, drug delivery systems, and packaging materials.

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.

3D Two-Photon Microprinting of Nanoporous Architectures

A photoresist system for 3D two-photon microprinting is presented, which enables the printing of inherently nanoporous structures with mean pore sizes around 50 nm by means of self-organization on the nanoscale. A phase separation between polymerizable and chemically inert photoresist components leads to the formation of 3D co-continuous structures. Subsequent washing-out of the unpolymerized phase reveals the porous polymer structures. To characterize the volume properties of the printed structures, scanning electron microscopy images are recorded from ultramicrotome sections. In addition, the light-scattering properties of the 3D-printed material are analyzed. By adjusting the printing parameters, the porosity can be controlled during 3D printing. As an application example, a functioning miniaturized Ulbricht light-collection sphere is 3D printed and tested.

Combined Porogen Leaching and Emulsion Templating to produce Bone Tissue Engineering Scaffolds

Bone has a hierarchy of porosity that is often overlooked when creating tissue engineering scaffolds where pore sizes are typically confined to a single order of magnitude. High internal phase emulsion (HIPE) templating produces polymerized HIPEs (polyHIPEs): highly interconnected porous polymers which have two length scales of porosity covering the 1-100 μm range. However, additional larger scales of porosity cannot be introduced in the standard emulsion formulation. Researchers have previously overcome this by additively manufacturing emulsions; fabricating highly microporous struts into complex macroporous geometries. This is time consuming and expensive; therefore, here we assessed the feasibility of combining porogen leaching with emulsion templating to introduce additional macroporosity. Alginate beads between 275 and 780 μm were incorporated into the emulsion at 0, 50, and 100 wt%. Once polymerized, alginate was dissolved leaving highly porous polyHIPE scaffolds with added macroporosity. The compressive modulus of the scaffolds decreased as alginate porogen content increased. Cellular performance was assessed using MLO-A5 post-osteoblasts. Seeding efficiency was significantly higher and mineralized matrix deposition was more uniformly deposited throughout porogen leached scaffolds compared to plain polyHIPEs. Deep cell infiltration only occurred in porogen leached scaffolds as detected by histology and lightsheet microscopy. This study reveals a quick, low cost and simple method of producing multiscale porosity scaffolds for tissue engineering.

Preparation of porous adsorbent via Pickering emulsion template for water treatment: A review

Porous materials as emerging potential adsorbents have received much more attention because they are capable of capturing various pollutants with fast adsorption rate, high adsorption capacity, good selectivity and excellent reusability. In order to prepare porous materials with decent porous structure, Pickering emulsion template method has been proved to be one of the most effective technologies to create pore structure. This paper reviewed comprehensively the latest research progress on the preparation of porous materials from various Pickering emulsions and their applications in the decontamination of pollutants (e.g., heavy metal ions, organic pollutants) and in the oil/water separation. It was expected that the summaries and discussions in this review will provide insights into the design and fabrication of new efficient porous adsorbents, and also give us a better understanding of the subject.

Assessment of the Angiogenic Potential of 2-Deoxy-D-Ribose Using a Novel in vitro 3D Dynamic Model in Comparison With Established in vitro Assays

Angiogenesis is a highly ordered physiological process regulated by the interaction of endothelial cells with an extensive variety of growth factors, extracellular matrix components and mechanical stimuli. One of the most important challenges in tissue engineering is the rapid neovascularization of constructs to ensure their survival after transplantation. To achieve this, the use of pro-angiogenic agents is a widely accepted approach. The study of angiogenesis has gained momentum over the last two decades. Although there are various in vitro, ex vivo, and in vivo angiogenesis models that enable testing of newly discovered pro-angiogenic agents, the problem with researching angiogenesis is the choice of the most appropriate assay. In vivo assays are the most representative and reliable models, but they are expensive, time-consuming and can cause ethical concerns whereas in vitro assays are relatively inexpensive, practical, and reproducible, but they are usually lack of enabling the study of more than one aspect of angiogenesis, and they do not fully represent the complexity of physiological angiogenesis. Therefore, there is a need for the development of an angiogenesis model that allows the study of angiogenesis under physiologically more relevant, dynamic conditions without causing ethical concerns. Accordingly, in this study, we developed 3D in vitro dynamic angiogenesis model, and we tested the angiogenic potential of 2-deoxy-D-ribose (2dDR) in comparison with vascular endothelial growth factor (VEGF) using newly developed in vitro 3D dynamic model and well-established in vitro models. Our results obtained using conventional in vitro assays demonstrated that 2dDR promoted proliferation, migration and tube formation of human aortic endothelial cells (HAECs) in a dose-dependent manner. Then, the angiogenic activity of 2dDR was further assessed using the newly developed 3D in vitro model, which enabled the monitoring of cell proliferation and infiltration simultaneously under dynamic conditions. Our results showed that the administration of 2dDR and VEGF significantly enhanced the outgrowth of HAECs and the cellular density under either static or dynamic conditions.

Amphiphobic polyHIPEs with pH-triggered transition to hydrophilicity–oleophobicity for the controlled removal of water from oil–water mixtures

Amphiphobic polyHIPEs with pH-triggered transition to hydrophilicity–oleophobicity were templated from high internal phase emulsions for the controlled removal of water from oil–water mixtures.

A Novel Bilayer Polycaprolactone Membrane for Guided Bone Regeneration: Combining Electrospinning and Emulsion Templating

Guided bone regeneration is a common dental implant treatment where a barrier membrane (BM) is used between epithelial tissue and bone or bone graft to prevent the invasion of the fast-proliferating epithelial cells into the defect site to be able to preserve a space for infiltration of slower-growing bone cells into the periodontal defect site. In this study, a bilayer polycaprolactone (PCL) BM was developed by combining electrospinning and emulsion templating techniques. First, a 250 µm thick polymerised high internal phase emulsion (polyHIPE) made of photocurable PCL was manufactured and treated with air plasma, which was shown to enhance the cellular infiltration. Then, four solvent compositions were investigated to find the best composition for electrospinning a nanofibrous PCL barrier layer on PCL polyHIPE. The biocompatibility and the barrier properties of the electrospun layer were demonstrated over four weeks in vitro by histological staining. Following in vitro assessment of cell viability and cell migration, cell infiltration and the potential of PCL polyHIPE for supporting blood vessel ingrowth were further investigated using an ex-ovo chick chorioallantoic membrane assay. Our results demonstrated that the nanofibrous PCL electrospun layer was capable of limiting cell infiltration for at least four weeks, while PCL polyHIPE supported cell infiltration, calcium and mineral deposition of bone cells, and blood vessel ingrowth through pores.

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.

One-step Preparation of Monodisperse Multifunctional Macroporous Particles through a Spontaneous Physical Process

Macroporous particles that combine the property features of spherical structures and porous materials are expected to find use over micro- and macroscopic length scales from miniaturized systems such as cell imaging, drug and gene delivery to industrial applications. However, the capacity for de novo design of such materials is still limited. Here, a spontaneous process to fabricate monodisperse multifunctional macroporous particles (MMMPs) by high internal phase emulsion templating is reported. An interesting physical phenomenon involving self-emulsification and synergistic effects between nanoparticles and amphiphilic diblock copolymers is observed in this process. These MMMPs, featured with tailor-made pore structures, pH responsiveness, and magnetic response, could be used as stimuli-responsive carriers for multiple functional molecules with a high loading and releasing efficiency. This new understanding regarding the underlying phenomena that control self-emulsification behavior and synergistic action in emulsion systems provides a unique outlook and a novel approach to the design of potentially multifunctional porous materials for controllable release and delivery processes.

Synthesis and Concentration of Organosols of Silver Nanoparticles Stabilized by AOT: Emulsion Versus Microemulsion

In this work, we tried to combine the advantages of microemulsion and emulsion synthesis to obtain stable concentrated organosols of Ag nanoparticles, promising liquid-phase materials. Starting reagents were successively introduced into a micellar solution of sodium bis-(2-ethylhexyl)sulfosuccinate (AOT) in n-decane in the dynamic reverse emulsion mode. During the contact of the phases, Ag⁺ passes into micelles and Na⁺ passes into emulsion microdroplets through the cation exchange AOTNa^Org + AgNO₃^Aq = AOTAg^Org + NaNO₃^Aq. High concentrations of NaNO₃ and hydrazine in the microdroplets favor an osmotic outflow of water from the micelles, which reduces their polar cavities to ∼2 nm. As a result, silver ions are contained in the micelles, and the reducing agent is present mostly in emulsion microdroplets. The reagents interact in the polar cavities of micelles to form ∼7 nm Ag nanoparticles. The produced nanoparticles are positively charged, which permitted their electrophoretic concentration to obtain liquid concentrates (up to 30% Ag) and a solid Ag-AOT composite (up to 75% Ag). Their treatment at 250 °C leads to the formation of conductive films (180 mOhm per square). The developed technique makes it possible to increase the productivity of the process by ∼30 times and opens up new avenues of practical application for the well-studied microemulsion synthesis.

Multiple-Level Porous Polymer Monoliths with Interconnected Cellular Topology Prepared by Combining Hard Sphere and Emulsion Templating for Use in Bone Tissue Engineering

A combination of hard sphere and high internal phase emulsion templating gives a platform for synthesizing hierarchically porous polymers with a unique topology exhibiting interconnected spherical features on multiple levels. Polymeric spheres are fused by thermal sintering to create a 3D monolithic structure while an emulsion with a high proportion of internal phase and monomers in the continuous phase is added to the voids of the previously constructed monolith. Following polymerization of the emulsion and dissolution of the templating structure, a down-replicating topology is created with a primary level of pores as a result of fused spheres of the 3D monolithic structure, a secondary level of pores resulting from the emulsion's internal phase, and a tertiary level of interconnecting channels. Thiol-ene chemistry with divinyladipate and pentaerythritol tetrakis(3-mercaptopropionate) is used to demonstrate the preparation of a crosslinked polyester with overall porosity close to 90%. Due to multilevel porosity, such materials are interesting for applications in bone tissue engineering, possibly simulating the native sponge like bone structure. Their potential to promote ossteointegration is tested using human bone derived osteoblasts. Material-cell interactions are evaluated and they reveal growth and proliferation of osteoblasts both on surface and in the bulk of the scaffold.

Emulsion templated scaffolds with tunable mechanical properties for bone tissue engineering

Polymerised High Internal Phase Emulsions (PolyHIPEs) are manufactured via emulsion templating and exhibit a highly interconnected microporosity. These materials are commonly used as thin membranes for 3D cell culture. This study uses emulsion templating in combination with microstereolithography to fabricate PolyHIPE scaffolds with a tightly controlled and reproducible architecture. This combination of methods produces hierarchical structures, where the microstructural properties can be independently controlled from the scaffold macrostructure. PolyHIPEs were fabricated with varying ratios of two acrylate monomers (2-ethylhexyl acrylate (EHA) and isobornyl acrylate (IBOA)) and varying nominal porosity to tune mechanical properties. Young's modulus, ultimate tensile stress (UTS) and elongation at failure were determined for twenty EHA/IBOA compositions. Moduli ranged from 63.01±9.13 to 0.36±0.04MPa, UTS from 2.03±0.33 to 0.11±0.01MPa and failure strain from 21.86±2.87% to 2.60±0.61%. Selected compositions were fabricated into macro-porous woodpile structures, plasma treated with air or acrylic acid and seeded with human embryonic stem-cell derived mesenchymal progenitor cells (hES-MPs). Confocal and two-photon microscopy confirmed cell proliferation and penetration into the micro- and macro-porous architecture. The scaffolds supported osteogenic differentiation of mesenchymal cells and interestingly, the stiffest IBOA-based scaffolds that were plasma treated with acrylic acid promoted osteogenesis more strongly than the other scaffolds.

Isorefractive high internal phase emulsion organogels for light induced reactions

We report the fabrication of isorefractive high internal phase emulsion (HIPE) organogels and the as-prepared transparent HIPE organogels can be used for various light induced reactions.

Preparation of hybrid thiol-acrylate emulsion-templated porous polymers by interfacial copolymerization of high internal phase emulsions

Emulsion-templated highly porous polymers (polyHIPEs), containing distinct regions differing in composition, morphology, and/or properties, are prepared by the simultaneous polymerization of two high internal phase emulsions (HIPEs) contained within the same mould. The HIPEs are placed together in the mould and subjected to thiol-acrylate photopolymerization. The resulting polyHIPE material is found to contain two distinct semicircular regions, reflecting the composition of each HIPE. The original interface between the two emulsions becomes a copolymerized band between 100 and 300 μm wide, which is found to be mechanically robust. The separate polyHIPE layers are distinguished from one another by their differing average void diameter, chemical composition, and extent of contraction upon drying.

Mesoporous inorganic salts with crystal defects: unusual catalysts and catalyst supports

We proposed a strategy to synthesize mesoporous inorganic salt particles using the special properties of ionic liquid (IL) mixtures, and hollow mesoporous LaF3, NdF3, and YF3 particles were synthesized and characterized using different techniques. The size of the mesopores in the salt particles was about 4 nm, and the materials were full of crystal defects. The LaF3, NdF3 and YF3 particles were used as the catalysts for the cyanosilylation reaction of benzaldehyde using trimethylsilyl cyanide, and Ru/LaF3 and Ru/NdF3, in which Ru nanocatalysts were supported on the LaF3 and NdF3 particles with mesopores, were used to catalyze hydrogenations of benzene to cyclohexane and levulinic acid (LA) to γ-valerolactone (GVL). It was discovered that the activities of these catalysts were unprecedentedly high for these reactions. Detailed study showed that both the crystal defects and the mesopores in the salt particles played crucial roles for the extremely high catalytic activity.

Functional nanoparticle-decorated graphene oxide sheets as stabilizers for Pickering high internal phase emulsions and graphene oxide based foam monoliths

A facile and versatile approach was developed for the preparation of graphene oxide sheet-based Pickering high internal phase emulsions by nanoparticle decoration.

Nitrogen-rich and fire-resistant carbon aerogels for the removal of oil contaminants from water

Effective removal of crude oils, petroleum products, organic solvents, and dyes from water is of significance in oceanography, environmental protection, and industrial production. Various techniques including physical and chemical absorption have been developed, but they suffer from problems such as low separation selectivity, a complicated and lengthy process, as well as high costs for reagents and devices. We present here a new material, termed nitrogen-rich carbon aerogels (NRC aerogels,) with highly porous structure and nitrogen-rich surfaces, exhibiting highly efficient separation of specific substances such as oils and organic pollutants. More importantly, we demonstrate that the fabricated NRC aerogels can also collect micrometer-sized oil droplets from an oil-water mixture with high efficiency that is well beyond what can be achieved by most existing separation methods, but is extremely important in practical marine oil-spill recovery because a certain amount of oils often shears into many micrometer-sized oil droplets by the sea wave, resulting in enormous potential destruction to marine ecosystem if not properly collected. Furthermore, our fabricated material can be used like a recyclable container for oils and chemicals cleanup because the oil/chemical-absorbed NRC aerogels can be readily cleaned for reuse by direct combustion in air because of their excellent hydrophobicity and fire-resistant property. We demonstrate that they keep 61.2% absorption capacity even after 100 absorption/combustion cycles, which thus has the highest recyclability of the reported carbon aerogels. All these features make these fabricated NRC aerogels suitable for a wide range of applications in water purification and treatment.

Macroporous antibacterial hydrogels with tunable pore structures fabricated by using Pickering high internal phase emulsions as templates

Pickering-based antibacterial hydrogels with tunable pore structures were fabricated by using high internal phase emulsion templates.