In this thesis, we present the results of our explorations into how the use of additive manufacturing (AM) or 3D printing as a production method can contribute to design in a circular economy. The aim of design in a circular economy is to preserve the value of products and materials by keeping them in the economic system, either by lengthening their lifetime or through high value reuse and recovery. Design in a circular economy needs to account for both product integrity and material integrity, which represent the quality of products and materials to remain whole and complete over time. AM is an emerging technology and is viewed as a promising production process for the circular economy because of its unique additive and digital character. The papers and chapters making up this thesis answer the following two research questions:
1. How can additive manufacturing support product integrity in a circular economy?
2. How can additive manufacturing support material integrity in a circular economy?
We addressed these questions by performing a literature and design review followed by experimental studies using “research through design” (RtD) as a research method. In RtD, design plays a formative role to generate knowledge by iteratively developing prototypes and framing, reflecting on, and communicating insights from these. We used the prototyping process to develop the emerging AM technology in the new context of a circular economy. The main contributions can be summarised as following:
• We helped establish of a new research direction by exploring design approaches for product integrity and material integrity in a circular economy.
• We developed a circular AM process flow for product integrity. This is demonstrated by showing that the digital and additive character of AM can be harnessed to develop reversible connections that enable products to be disassembled and reassembled without loss of quality. We developed reversible joints and demonstrated these with a proof-of-concept of a lamp and vase (figure 5 and 6 in this document).
• We established a design approach for developing reprintable materials. This was demonstrated by producing reprintable materials from locally available bio-based resources, i.e. ground mussel shells with two different binders (sugar and alginate). We designed a lampshade and hairpin and 3D printed them using these materials (figure 2,3 and 4 in this document).
We contributed to the domain of ‘research through design’ by using the prototyping process for knowledge generation; a less common use. The design goal in the prototyping process was used to obtain relevant information (from other disciplines) for developing technology in a new context. This resulted in an iterative process between experimental prototyping processes and scientific knowledge generation.

The thesis includes a number of published and submitted articles: chapters 2, 3 and 5 have been published, chapter 4 is under review, and chapter 6 is accepted for publication at the time of writing.
In chapter 2, the use of annotated portfolios was extended to analyse qualitative interview data. With this development, interview data can now be visually analysed, which is valuable when designers are interviewed about their design projects. The visual overview of images with annotations led to fruitful discussions and contributed to a deeper understanding of the subject. We applied this novel approach in chapter 3.
In chapter 3, we explored to what extent the opportunities that AM offers for sustainable design are also useful when designing in a circular economy. we performed a literature review and held qualitative interviews with five designers about their sustainable 3D printing projects. The interviews were analysed using the extended annotated portfolios. Our results present opportunities (adapting digital design files for changing needs and using complex structures for recycling) and challenges (complex geometries can hamper disassembly and reassembly, and designers request for renewable materials) for how AM can support design in a circular economy. Based on these findings, we defined two areas for exploration in our experimental studies: ‘pursuing high value reuse with reversible connections for product integrity’ (Chapter 4) and ‘the development of reprintable materials from bio-based resources for material integrity’ (Chapter 5 and 6).
In chapter 4, a theoretical framework is presented for a circular AM process flow that considers high value reuse by including both materials and physical parts directly in the digital production process. The process flow is demonstrated with a prototyping process resulting in prototypes with reversible 3D printed joints and laser cut panels that can be both disassembled and reassembled.
In chapter 5 and 6, we established a design approach for the development of reprintable materials. Reprintable materials can be reconstituted to their original properties in terms of printability and functionality. A full material life cycle is described for the development of these materials. In chapter 5, we explore this approach by using locally sourced bio-based waste streams. This resulted in a material for extrusion paste printing from ground mussel shells and sugar that can be dissolved in water after use to retain a printable paste. In chapter 6, we further elaborate on the design approach and developed a reprintable bio-based composite material from ground mussel shells and alginate. This new material can be recovered based on reversable ion cross-linking resulting in water-resistant materials.
In Chapter 7, we describe the insights gained about product integrity and material integrity with AM for design in a circular economy. Furthermore, we evaluate our research process with ‘research through design’ and present practical insights for design as well as share directions for future research.

We would like to conclude by nothing that, in spite of all the optimism about the way the use of AM can accelerate the transition to a circular economy, there are currently few AM applications that actually support and enable the circular economy. Our exploration shows that to successfully print for product integrity and material integrity, both in-depth knowledge and understanding of the AM production technique is required.