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To design effective immunomodulatory implants, innate immune cell interactions at the surface of biomaterials need to be controlled and understood. The architectural design freedom of two-photon polymerization is used to produce arrays of surface-mounted, geometrically diverse 3D polymer objects. This reveals the importance of the interplay between architecture and materials chemistry in determining human macrophage fate in vitro. The ChemoArchiChip identifies key structure-function relationships and design rules from machine learning models to build a mechanistic understanding of cell attachment and polarization. Object shape, vertex/cone angle, and size are key drivers of attachment. Particular shapes are found to heavily modulate pro- or anti-inflammatory cell polarization, while triangular pyramids drastically reduce or even eliminate attachment. Caveola-dependent endocytosis is a principal mechanism by which cells respond to objects with sharp points; i.e., low vertex/cone angles. The discovery of these putative design rules points to surfaces decorated with architectures to augment implant performance.

Wound healing is a complex biological process involving close crosstalk between various cell types. Dysregulation in any of these processes, such as in diabetic wounds, results in chronic non-healing wounds. Fibroblasts are a critical cell type involved in the formation of granulation tissue, essential for effective wound healing. We screened 315 different polymer surfaces to identify candidates which actively drove fibroblasts towards either pro- or anti-proliferative functional phenotypes. Fibroblast-instructive chemistries were identified, which we synthesized into surfactants to fabricate easy to administer microparticles for direct application to diabetic wounds. The pro-proliferative microfluidic derived particles were able to successfully promote neovascularisation, granulation tissue formation and wound closure after a single application to the wound bed. These active novel 3D bio-instructive microparticles show great potential as a route to reducing the burden of chronic wounds. This article is protected by copyright. All rights reserved.

The development of conductive inks is required to enable additive manufacturing of electronic components and devices. A gold nanoparticle (AuNP) ink is of particular interest due to its high electrical conductivity, chemical stability, and biocompatibility. However, a printed AuNP film suffers from thermally induced microcracks and pores that lead to the poor integrity of a printed electronic component and electrical failure under external mechanical deformation, hence limiting its application for flexible electronics. Here, we employ a multifunctional thiol as a cohesion enhancer in the AuNP ink to prevent the formation of microcracks and pores by mediating the cohesion of AuNPs via strong interaction between the thiol groups and the gold surface. The inkjet-printed AuNP electrode exhibits an electrical conductivity of 3.0 × 106 S/m and stable electrical properties under repeated cycles (>1000) of mechanical deformation even for a single printed layer and in a salt-rich phosphate-buffered saline solution, offering exciting potential for applications in flexible and 3D electronics as well as in bioelectronics and healthcare devices.

The field of biofabrication continues to progress, offering higher levels of spatial control, reproducibility, and functionality. However, we remain far from recapitulating what nature has achieved. Biological systems such as tissues and organs are assembled from the bottom-up through coordinated supramolecular and cellular processes that result in their remarkable structures and functionalities. In this perspective, we propose that incorporating such biological assembling mechanisms within fabrication techniques, offers an opportunity to push the boundaries of biofabrication. We dissect these mechanisms into distinct biological organization principles (BOPs) including self-assembly, compartmentalization, diffusion-reaction, disorder-to-order transitions, and out-of-equilibrium processes. We highlight recent work demonstrating the viability and potential of these approaches to enhance scalability, reproducibility, vascularization, and biomimicry; as well as current challenges to overcome.

Biological photovoltaic (BPV) cells are living solar panels capable of producing clean energy by extracting electrons from sunlight (in daytime) and stored carbon in microbial cells (during the night or on cloudy days), irrespective of the organic substrate supply. The physicochemical properties of anode surfaces harbouring microbial communities in BPV systems influence the electrochemical charge transfer rate at the electrode. Hence, these properties play a significant role in regulating the kinetics of metabolic reactions in the biotic compartment while providing an electron transfer path. Various electrically conductive materials have been explored as solid-state anodes to improve the power output and economic viability of BPV systems. However, the current systems still suffer from low power density due to electrodes' electrochemical limitations and a lack of systematic optimization of the device. This review provides a comprehensive insight into the recent developments in different anode materials, their dimensional structure, and their impact on the performance of BPV systems in the last two decades. Moreover, the existing limitations of electrode materials in BPV systems are summarized, and outlooks for future anode advancements are foreseen.

Additive Manufacturing (AM) techniques have gained extensive attention recently as they are able to directly produce 3D parts utilising a layer-by-layer manner. Inkjet printing is one such technique which can produce micron-scale features but is generally constrained to liquid viscosities of less than 30 mPa·s, therefore available materials are limited. A 3D reactive inkjet printing (3DRIJP) approach to deposit low viscosity monomers and polymerise in-situ to form polymer parts is emerging. In this work, a 3DRIJP approach has been developed to fabricate bisphenol A-polycarbonate (BPA-PC) for the first time by using a low viscosity reactive ink containing monomers, catalyst and solvent. A set of processing parameters were explored and optimised including temperature of droplet formation, substrate temperature and droplet spacing to print films. With a thermal post-curing process, BPA-PC was formed successfully with a molecular weight comparable to those which were manufactured by the conventional melt transesterification process. The thermal properties were evaluated suggesting good thermal resistance characteristics. Finally, a 3D ziggurat structure was printed to demonstrate the capability to fabricate BPA-PC by an AM method, thus broadened the library of AM materials to include engineering grade polymers via 3DRJIP. This approach was innovative in both the BPA-PC material formulation and the 3DRIJP process development from traditional inkjet printing methods, where a single printable formulation of monomers for thermoplastic optical-clear BPA-PC was able to be printed using one printhead to form 3D structures.

Inkjet printing of metal nanoparticles (MNPs) allows for design flexibility, rapid processing and enables 3D printing of functional electronic devices through co-deposition of multiple materials. However, the performance of printed devices, especially their conductivity, is lower than those made by traditional manufacturing methods and is previously not fully understood. Here, we revealed that anisotropic electrical conductivity of printed MNPs is caused by organic residuals from MNPs inks. We employed a combination of electrical resistivity tests, morphological analysis and novel 3D nanoscale chemical analysis of printed devices using silver nanoparticles (AgNPs) to show that the polymer stabiliser polyvinylpyrrolidone (PVP) tends to concentrate between vertically stacked AgNPs layers as well as at dielectric/conductive interfaces. The understanding of organic residues behaviour in printed nanoparticles reveal potential new strategies to improve nanomaterial ink formulations for functional printed electronics.

As our understanding of disease grows, it is becoming established that treatment needs to be personalized and targeted to the needs of the individual. In this paper we show that multi-material inkjet-based 3D printing, when backed with generative design algorithms, can bring a step change in the personalization of medical devices. We take cell-instructive materials known for their resistance to bacterial biofilm formation and reformulate for multi-material inkjet-based 3D printing. Specimens with customizable mechanical moduli are obtained without loss of their cell-instructive properties. The manufacturing is coupled to a design algorithm that takes a user-specified deformation and computes the distribution of the materials needed to meet the target under given load constraints. Optimisation led to a voxel map file defining where different materials should be placed. Manufactured products were assessed against the mechanical and cell-instructive specifications and ultimately showed how multifunctional personalization emerges from generative design driven 3D printing.

Controlling the microstructure of materials by means of phase separation is a versatile tool for optimizing material properties. In this study, we show that ink jet 3D printing of polymer blends gives rise to controllable phase separation that can be used to tailor the release of drugs. We predicted phase separation using high throughput screening combined with a model based on the Flory-Huggins interaction parameter, and were able to show that drug release from 3D printed structures can be predicted from observations based on single drops of mixtures. This new understanding gives us hierarchical compositional control, from droplet to device, allowing release to be ‘dialed up’ without any manipulation of geometry. This is an important advance for implants that need to be delivered by cannula, where the shape is highly constrained and thus the usual geometrical freedoms associated with 3D printing cannot be exploited, bringing a hitherto unseen level of understanding to emergent material properties of 3D printing.

Droplet microfluidics can produce highly tailored microparticles whilst retaining monodispersity. However, these systems often require lengthy optimisation, commonly based on a trial-and-error approach, particularly when using bio-instructive, polymeric surfactants. Here, micropipette manipulation methods were used to optimise the concentration of bespoke polymeric surfactants to produce biodegradable (poly(d,l-lactic acid) (PDLLA)) microparticles with unique, bio-instructive surface chemistries. The effect of these three-dimensional surfactants on the interfacial tension of the system was analysed. It was determined that to provide adequate stabilisation, a low level (0.1% (w/v)) of poly(vinyl acetate-co-alcohol) (PVA) was required. Optimisation of the PVA concentration was informed by micropipette manipulation. As a result, successful, monodisperse particles were produced that maintained the desired bio-instructive surface chemistry.

Purpose This paper aims to print 3D structures from polymers that resist bacterial attachment by reactive jetting of acrylate monomers. Design/methodology/approach The first step towards printing was ink development. Inks were characterised to carry out an estimation of their potential printability using the Z parameter to predict stable jetting conditions. Printability conditions were optimised for each ink using a Dimatix DMP-2800, which enabled 3D structures to be fabricated. Findings UV photo-initiated polymers, which resist bacterial attachment, were found to be printable using piezo-based inkjet printers. The waveform required for each ink depends on the value of the Z parameter. Once the waveform and the printability parameters were optimised, 3D objects were fabricated. Research limitations/implications This methodology has been confirmed as an effective method to 3D print materials that have been demonstrated to be bacteria resistant. However, ink curing depends on modification of some parameters (such as photoinitiator concentration or UV exposure time) which would result in an improvement of the curing process post jetting. Social implications The combination of inkjet based 3D printing with new materials resistant to bacterial attachment means the possibility of building customised medical devices with a high level of complexity and bespoke features can be fully realised. The scope and variability of the devices produced will exceed what can be achieved using standard fabrication methodologies and can be applied to reduce the incidence of device associated infections and to address increased morbidity, mortality and health care costs associated with nosocomial infections. Originality/value In this paper, the novel use of materials that resist bacterial attachment has been described to build 3D structures using material jetting. Its value lies on the potential impact this methodology could produce in the biomedical device and research fields.

A robust methodology is presented to identify novel biomaterials suitable for three-dimensional (3D) printing. Currently, the application of additive manufacturing is limited by the availability of functional inks, especially in the area of biomaterials; this is the first time when this method is used to tackle this problem, allowing hundreds of formulations to be readily assessed. Several functional properties, including the release of an antidepressive drug (paroxetine), cytotoxicity, and printability, are screened for 253 new ink formulations in a high-throughput format as well as mechanical properties. The selected candidates with the desirable properties are successfully scaled up using 3D printing into a range of object architectures. A full drug release study and degradability and tensile modulus experiments are presented on a simple architecture to validating the suitability of this methodology to identify printable inks for 3D printing devices with bespoke properties.

The aim of this paper is to investigate the design optimization and additive manufacture of automotive components. A Titanium brake pedal processed through Selective Laser Melting (SLM) is considered as a test case. Different design optimisation techniques have been employed including topology optimization and lattice structure design. Rather than using a conventional topology optimization method, a recently developed topology optimization method called Iso-XFEM is used in this work. This method is capable of generating high resolution topology optimised solutions using isolines/isosurfaces of a structural performance criterion and eXtended Finite Element Method (XFEM). Lattice structure design is the other technique used in this work for the design of the brake pedal. The idea is to increase the stability of the brake pedal to random loads applied to the foot pad area of the pedal. The use of lattice structures can also significantly reduce the high residual stress induced during the SLM process. The results suggest that the integration of the design optimization techniques with a metal additive manufacturing process enables development of a promising tool for producing lightweight energy efficient automotive components.

Additive manufacturing (AM) is expanding the range of designable geometries, but to exploit this evolving design space new methods are required to find optimum solutions. Finite element based topology optimisation (TO) is a powerful method of structural optimization, however the results obtained tend to be dependent on the algorithm used, the algorithm parameters and the finite element mesh. This paper will discuss these issues as it relates to the SIMP and BESO algorithms. An example of the application of topological optimization to the design of improved structures is given.