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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.

Bacterial Biofilm Resistant Composite Devices Medical implants would benefit from bespoke 3D printing, however microbial infection remains a challenge. By combining functional materials, voxelated manufacturing and algorithmic design, Morgan R. Alexander, Ricky D. Wildman, and co‐workers demonstrate in article number 2100249 a multi‐material inkjet 3D printed device that inhibits the development of bacterial biofilm, while achieving highly customizable geometry and local stiffness, opening further opportunities for biomedical 3D printing. [Image: see text]

The relationship between prepreg tack and the degree of intimate contact (DoIC) between prepreg and a rigid substrate was explored in the context of a continuous application-and-peel test method. Tack for a unidirectional prepreg tape was characterised for different surface combinations and varying test parameters (material feed rate, temperature) at a constant compaction pressure. Application of the prepreg to a transparent rigid substrate (glass), was carried out at matching test conditions to the prepreg tack measurements. Optical microscopy was utilised to acquire images of the contact area at the prepreg-glass interface. Image analysis of the micrographs enabled quantification of the contact area. The time- and temperature-dependent viscoelastic behaviour of the resin was explored directly on the prepreg using oscillatory parallel plate rheometry, and time-temperature superposition was applied to construct both tack and DoIC master curves. The shifted DoIC data showed that true contact area increases with decreasing shifted feed rates, until maximum contact area is achieved. Similarly, tack increases with decreasing shifted feed rates. However, at a critical feed rate, the bond failure mechanism switches from adhesive to cohesive failure. In cohesive failure, tack decreases with decreasing feed rate despite the high levels of DoIC.

As the understanding of disease grows, so does the opportunity for personalization of therapies targeted to the needs of the individual. To bring about a step change in the personalization of medical devices it is shown that multi‐material inkjet‐based 3D printing can meet this demand by combining functional materials, voxelated manufacturing, and algorithmic design. In this paper composite structures designed with both controlled deformation and reduced biofilm formation are manufactured using two formulations that are deposited selectively and separately. The bacterial biofilm coverage of the resulting composites is reduced by up to 75% compared to commonly used silicone rubbers, without the need for incorporating bioactives. Meanwhile, the composites can be tuned to meet user defined mechanical performance with ±10% deviation. Device manufacture is coupled to finite element modelling and a genetic algorithm that takes the user‐specified mechanical deformation and computes the distribution of materials needed to meet this under given load constraints through a generative design process. Manufactured products are assessed against the mechanical and bacterial cell‐instructive specifications and illustrate how multifunctional personalization can be achieved using generative design driven multi‐material inkjet based 3D printing., Multi‐material inkjet‐based 3D printing is used for the design and manufacture of personalized medical devices. A design optimization approach is used to specify the location of two different materials, each with a different moduli, but both with the ability to resist bacterial colonization (up to 75% better than medical silicones), such that they meet user‐defined, complex design constraints.

An adaptable flexural test fixture is proposed to characterise the mechanical properties of miniature beam specimens (≤10 mg) at ambient conditions or in the presence of fluids at elevated temperatures. The fixture is validated using representative amorphous and semi-crystalline polymers. The response of miniature specimens is compared against that of medium-sized specimens (≤1 g) on the same fixture and on conventional test equipment. Good agreement is found between the specimen sizes for all materials, but the comparisons highlight small differences attributed to factors such as specimen dimensional accuracy, crystallinity and span-to-thickness ratios. Flexural tests in water at 37 °C using both specimen sizes were performed to investigate the evolution of mechanical behaviour of hydrolytically degraded polylactides. Here, specimen size influences the diffusion timescale of acidic by-products which can reduce or enhance autocatalysis.

This work investigates the effects of primary compounding temperature and secondary melt processes on the mechanical response and electrical resistivity of polycarbonate filled with 3 wt % multiwalled carbon nanotubes (CNT). Nanocomposites were melt compounded in an industrial setting at a range of temperatures, and subsequently either injection molded or compression molded to produce specimens for the measurement of electrical resistivity, surface hardness, and uniaxial tensile properties. Secondary melt processing was found to be the dominant process in determining the final properties. The effects observed have been attributed to structural arrangements of the CNT network as suggested by morphological evidence of optical microscopy and resistivity measurements. Properties were found to be relatively insensitive to compounding temperature. The measured elastic moduli were consistent with existing micromechanical models.

A method developed in the 1980s for the conversion of linear rheological data to molar mass distribution is revisited in the context of degradable polymers. The method is first applied using linear rheology for a linear polystyrene, for which all conversion parameters are known. A proof of principle is then carried out on four polycarbonate grades. Finally, preliminary results are shown on degradable polylactides. The application of this method to degrading polymer systems, and to systems containing nanofillers, is also discussed. This work forms part of a wider study of bioresorbable nanocomposites using polylactides, novel hydroxyapatite nanoparticles and tailored dispersants for medical applications.