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

Abstract

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.

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

“…Casting enables the manufacturing of scaffolds in a wide range of shapes and sizes, depending on the mould design ( Paljevac et al, 2018 ; Diez-Ahedo et al, 2020 ; Dikici et al, 2020a ; Owen et al, 2020 ). Recently, Dikici et al (2020a) reported the fabrication of the PolyHIPEs in tubular form by designing a re-usable tubular silicone mould system that, HIPE can be injected into, polymerised, and recovered easily ( Figure 10Ab ).…”

“…Recently, Dikici et al (2020a) reported the fabrication of the PolyHIPEs in tubular form by designing a re-usable tubular silicone mould system that, HIPE can be injected into, polymerised, and recovered easily ( Figure 10Ab ). Also, sacrificial polymer beads made of PDMS ( Paljevac et al, 2018 ) or alginate ( Owen et al, 2020 ) have been incorporated into emulsion composition prior to polymerisation in a mould to simply introduce multiscale porosity to PolyHIPEs.…”

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

“…A hydrophilic material is required to create an open surface with W/O emulsions. This can include hydrophilic glass surface[ 78 - 80 ] or alginate[ 81 ].…”

Design and Evaluation of an Osteogenesis-on-a-Chip Microfluidic Device Incorporating 3D Cell Culture

“…Many different materials have been used for bone tissue engineering, ranging from metals and ceramics to natural and synthetic polymers ( Bose et al, 2012 ; Roseti et al, 2017 ; Owen and Reilly, 2018 ). However, of notable recent interest is the development of polymerized high internal phase emulsion (polyHIPE) materials as polymeric scaffolds for bone tissue engineering ( Robinson et al, 2016 ; Lee et al, 2017 ; Paterson et al, 2018 ; Aldemir Dikici et al, 2019 ; Aldemir Dikici and Claeyssens, 2020 ; Owen et al, 2020b ). PolyHIPEs are inherently porous materials that are formed by emulsion templating; the emulsion consists of a curable continuous phase that encapsulates an immiscible internal droplet phase where the internal phase volume exceeds 74%.…”