1. Research field
This research falls within the scope of computational design and digital fabrication, focusing on 4D printing tools, techniques and materials.
Starting from the definition of 4d printing the aim is to identify the best combination of stimulus-responsive materials behavior and its potential for architectural applications.
1.1 Current scenario
The last decade set a wide range of urgent and inescapable imperatives: greater awareness of environmental responsibility, energy use and its impact on global warming, the need to take ethical account of materials origin, depletion of resources and building waste \cite{2017}. After 200 years of industrial activities climate change is ravaging the planet with soil degradation, biodiversity loss, global warming and consequent aggravation of the urban heat island effect \cite{Taha_1997}, rising
sea levels, drought, and ocean acidification \citep{zapata-marti2007}. Buildings worldwide account for 40% of global energy consumption\citep*{2012a}, at the same time the building sector is expected to reduce consumptions up to 53% by 2030.
Furthermore the global economy is in crisis, GDP is slowing all over the world due to the inability of the infrastructure (both digital and physical) to adapt to society demands: in the last 20 years productivity has been declining \cite{rifkin2011}. Thermodynamic laws have been neglected: energy changes form in only one direction and at every step of conversion some energy is lost. Improving the system with better machines and better workers doesn't affect productivity anymore because machines and workers accounts for only 40% of productivity while the rest 60% occurs as a result of aggregate efficiency. However aggregate efficiency has now reached its ceiling in many countries (Japan is leading the world with a mere 20%) because the business is still plugged into a second industrial revolution infrastructure \cite{rifkin2014}. Therefore according to Jeremy Rifkin the key for a new sustainable growth is to raise aggregate efficiency trough the convergence of digitalization, automation and renewability in terms of communication, transportation, energy \cite{economy2018}.
Indeed the digital revolution is the enabler of a new era of intelligent, automated, ubiquitous, interactive systems able to sense, manage and compute data and adapt themselves to the environment optimizing resources.
1.2 Problem statement
Coming to the architectural world, computational design and digital fabrication are offering an unseen opportunity for redemption in the field of construction, the flexible nature of advance manufacturing technology is more than just an enabler of formal complexity; it is rather leveraged as a chance to replan the whole design-to-production chain \cite{2014}. We often hear about "re-thinking" or "re-inventing" building sector because conventional processes are no more sustainable, not only environmentally but socially and economically as well.
Indeed in the broaden context of Industry 4.0, the construction field is implementing its adaptivity trough parametric performative design based on data and digital fabrication machines and tools. The 4th industrial revolution is providing a wide contamination of knowledge in the “age of entanglement” \cite{oxman2016}: the multidisciplinary, or better, according to \citet{ito2016} antidisciplinary approach breaks the boundaries between disciplines. This allows an extraordinary understanding of the entire construction process: as in the Renaissance the designer has the chance to access, control and manage a large amount of knowledge in the form of data. For instance materials or structural properties are fundamentally embedded in the design phase. Furthermore it is challenging the assumptions that underly mass production allowing “individuals to design and produce tangible objects on demand” \cite{gershenfeld2012} offering then a democratic advanced customization.
However, even though the digital revolution is having a deep impact on architecture and construction we are still attached to conventional methods, we 3D print bricks in clay or concrete houses with the same shape we did with traditional architecture, automation is employed as a working force just for its precision and complexity-enabling skills but still we are not fully exploiting such technologies.
A new approach is based on material as active generator of architecture materialism \cite{naboni2017}, programmable materials can offer a new paradigm for construction \cite{Tibbits_2012} and hybrid additive processes, according to \citet{Tibbits_2016}, are the future of this field.
1.3 Informed matter
In conventional design methodology material is often considered as a subordinate attribute of form, \citet{oxman2010} claims it rather represents its progenitor. In fact natural processes such as growth, evolution and self-organisation instead of being considered just as metaphors or digital simulations, they can be employed in physical materials and fabricated systems \cite{Papadopoulou_2017}. This defines generative materiality, material system carries its own inherent genotypic information as well as phenotypic procedural characteristics of joining or assembly \cite{perez2008}. Procedural integration already exists in nature: "The human bone re-accommodates its formal organization (“geometry”),
through material distribution (material) according to the magnitude and direction of loads applied
to it at any given moment (structure)."
\cite{Oxman2010}
2. State of art
4D printing, at the time it was firstly brought to life by Skylar Tibbits, was defined as 3D printing with the addition of time, meaning featuring transformation by time in the object manufactured \cite{hirsch2014} . The last researches on the field have emphasized the importance of materials in the process, hence a more accurate formulation could be: "additive manufacturing of stimulus-responsive materials".