Frederik Claeyssens

Metamaterials provide exceptional properties arising from their well-defined engineered structures in which periodic features ranging from the nanoscale to the macroscale are manufactured to yield the desired characteristics. Recent advances in manufacturing techniques have dramatically expanded the design space and potential applications of metamaterials. Progress in high-resolution additive processes, scalable subtractive techniques, and emerging hybrid and formative approaches has enabled architectures that were previously difficult to realise at meaningful scale. Although challenges remain for scaling production, recent advances are moving metamaterials beyond laboratory-scale demonstrators towards more manufacturable platforms. These developments suggest emerging – though still early – pathways for broader technological deployment, enabling new possibilities for multifunctional devices, large-area metasurfaces, and mechanically robust architected materials. This roadmap explores the current-state-of-the art manufacturing techniques for metamaterials, highlighting key challenges and opportunities in scaling-up production and commercialisation, and outlines potential strategies for overcoming the barriers that currently limit large-scale implementation.

Polymerized high internal phase emulsions (polyHIPEs) offer highly porous and tunable architectures that are promising as templates for functional coatings. In this study, polyHIPE thin films were fabricated using either conventional surfactant-stabilized emulsions (Hypermer B246) or Pickering emulsions stabilized by isobornyl acrylate (IBOA) microparticles, and subsequently subjected to electroless nickel plating to evaluate the effect of emulsion stabilization on metal infiltration. SEM, EDX, and XRD analyses revealed that conventional polyHIPEs featured smaller, more uniform pores, resulting in surface-localized nickel deposition due to rapid pore closure. In contrast, Pickering polyHIPEs displayed larger, irregular pore structures. Although these structures exhibited restricted interconnectivity compared to conventional foams, their macroscopic pore dimensions facilitated deep mass transport, enabling uniform internal metallization. These results highlight that pore size magnitude can override interconnectivity limitations in diffusion-controlled plating processes, offering critical design insights for developing metal–polymer hybrids for applications such as catalysis and Electromagnetic Interference (EMI) shielding.

An electrospun nerve guidance conduit comprised of aligned, growth factor-loaded nanofibres and a fibrin hydrogel promotes peripheral nerve regeneration, demonstrating comparable axonal growth to the nerve graft in a severe injury model.

Corneal impairment is the fourth leading cause of blindness worldwide. Current therapies often use biodegradable amniotic membranes (AMs) to assist in transferring limbal stem cells or explants to the cornea. Surgeons have extensive experience with these, but they are human biological tissue and must be sourced and used under tissue bank conditions to reduce the risk of disease transmission. Thus, accessibility and safety remain concerns in their use. Accordingly, the development of synthetic scaffolds to support limbal tissue outgrowth is an attractive, reproducible and accessible alternative. This group has made good progress towards this membrane design using a Polylactide-co-Glycolide (PLGA) electrospun membrane but has identified problems with handling and integrity of the membrane once wet. Our aim, therefore, is to improve the integrity and pliability of these cell delivery membranes in wet environments without compromising their ability to act as cell carriers for corneal regeneration. Electrospun scaffolds with different mechanical properties were manufactured by blending different concentrations of PLGA and Polycaprolactone (PCL). All the manufactured membranes supported cell outgrowth when tested with porcine and human limbal explants. Scaffolds were characterised under dry and wet conditions using scanning electron microscopy and uniaxial tensile testing. Blends with a relatively high proportion of PCL (30%) were able to maintain their mechanical properties under both dry and wet conditions and were flexible in handling. This study demonstrates that PLGA-PCL electrospun membranes with 30% PCL content retain good mechanical properties in a wet environment, making them easy to handle while retaining the ability to support limbal tissue attachment and cell outgrowth. This makes them a viable synthetic alternative to the AM.

Introduction: Polycaprolactone (PCL) and poly (glycerol sebacate) (PGS) are biodegradable polymers with which high internal phase emulsion (HIPE) templating may be used to create highly porous structures. Although both polymers have been reported for a wide range of hard- and soft-tissue applications, several challenges remain. For example, PCL structures require surface treatment to allow for efficient cell infiltration, which becomes difficult with thick, complex geometries, and PGS is a soft polymer which results in the collapse of its porous structure during necessary processing steps. Methods: Here, we demonstrate how methacrylated forms of PCL (PCL-M) and PGS (PGS-M) can be blended to create highly tailorable porous structures that support cell growth and overcome the limitations of the two polymers individually. Material properties were characterised via mechanical testing, porous structures were imaged via scanning electron microscopy, and biological properties were investigated by resazurin assay and fluorescent staining. Results and Discussion: Mechanical testing of bulk blends of PCL-M and PGS-M demonstrated that the polymers mix together uniformly to provide predictable properties at different weight:weight ratios. PolyHIPEs formed of PCL-M and PGS-M were stable and exhibited highly interconnected porosity. Further investigation was undertaken on the 50:50 blend due to its favourable viscosity and rounded porous structure. Adjusting the synthesis parameters of the 50:50 PCL-M:PGS-M blend demonstrated that a wide range of porous structures can be fabricated, with average pore size ranging from 10–69 μm. The blend was demonstrated to be cell compatible, and collagen staining demonstrated that extracellular matrix adhered to the material. Blend-based scaffolds did not require surface treatment to maintain long term cell adhesion, unlike PCL-M-only controls. Overall, this study demonstrated that highly tuneable porous structures for a wide variety of tissue engineering applications can be created by blending PCL-M and PGS-M to form a composite that exhibits tailorable properties in between those currently known for PCL-M and PGS-M alone.

A key challenge in bone tissue engineering (BTE) is designing structurally supportive scaffolds, mimicking the native bone matrix, yet also highly porous to allow nutrient diffusion, cell infiltration, and proliferation. This study investigated the effect of scaffold interconnectivity on human bone marrow stromal cell (BMSC) behaviour. Highly interconnected, porous scaffolds (polyHIPEs) were fabricated using the emulsion templating method from 2-ethylhexyl acrylate/isobornyl acrylate (IBOA) and stabilised with ∼200 nm IBOA particles. Pore interconnectivity was tuned by varying the internal phase fraction from 75%–85% and characterised by the degree of openness, Euler number, frequency, and size of pore interconnects. The attachment, proliferation, infiltration, and osteogenic differentiation of the BMSC cell line (Y201) were evaluated on these scaffolds. Results showed that high pore interconnectivity facilitated diffusion and cell infiltration throughout the scaffolds. Furthermore, the most interconnected scaffolds enhanced osteogenic differentiation of Y201 cells, as evidenced by elevated alkaline phosphatase activity and increased calcium and collagen production compared to less interconnected scaffolds. These findings emphasise the importance of scaffold interconnectivity in BTE for efficient nutrient transport, facilitating cell migration and infiltration, and supporting the development of interconnected cell networks that positively influence osteogenic differentiation.

1. The periosteum is the connective tissue that envelopes bone and contributes to the normal bone healing process. Periosteal grafts have shown excellent success in the treatment of nonunion bone defects but surgical challenges such as donor site morbidity and graft availability have limited their clinical use. Artificial periosteal membranes are being explored as off-the-shelf alternatives, with several groups investigating the use of decellularized tissues or extracellular matrix (ECM)-based strategies for this purpose. In this study, we investigate the use of in vitro -generated, fibroblast-derived ECM to decorate porous biodegradable scaffolds for use as synthetic periosteal grafts. Scaffolds were fabricated using an emulsion templating technique from a blend of polycaprolactone methacrylate (PCL-M) and poly(glycerol sebacate) methacrylate (PGS-M), resulting in membranes with large, interconnected pores (average pore size = 49.6 ± 40.9 µm, average window size = 12.6 ± 6.1 µm) and structural characteristics suitable for soft tissue applications. The BJ5ta fibroblast cell line was cultured on scaffolds for 14 days to deposit ECM, after which constructs were decellularized. When tested in vitro , periosteal-typical cells exhibited a significantly higher growth rate on ECM-decorated scaffolds compared to controls. Additionally, the chick chorioallantoic membrane (CAM) demonstrated that ECM decoration had a positive angiogenic effect. This proof-of-concept study highlights a promising approach to enhance the biological properties of synthetic membranes, while avoiding challenges associated with decellularizing whole tissues.