Bioprinting suffers from several limitations when considering its clinical application, such as scaffold handling difficulty, risk of contamination, need of a maturation period in a bioreactor and shape/morphology of the bioprinted construct not perfectly matching with the defect site. For these reasons, in situ bioprinting has emerged as a promising alternative. It consists in the direct deposition of biological material into the patient, following the complex geometry of the anatomical defect. This approach guarantees an enhancement in the maturation and differentiation of the bioprinted constructs since the patient body itself works as a bioreactor. Currently, the most promising approach consists of the use of a robotic manipulator since it involves less human intervention and guarantees higher precision thus allowing the regeneration of complex defects.

With the aim of investigating the potential and limitations of this promising technology we developed and validated IMAGObot, a 5-axis open-source robotic-arm purposely re-engineered in both hardware and software for in situ bioprinting applications. Considering a standardized operating workflow, we identified four main steps: i) acquisition of the anatomical defect 3D digital model, ii) path planning, iii) path registration in the robot workspace, and iv) in situ bioprinting. IMAGObot was designed to manage all the previous steps, thanks to the availability of different tools and printheads. The acquisition of the geometry of the anatomical defect is performed using a touch probe, that also allows to evaluate the mechanical properties of the involved biological tissues. Based on the acquired geometry, the printing path is planned using an in-house developed Matlab^® algorithm, that is capable of computing non-planar trajectories and slice highly geometrically complex objects. This path is then registered on the patient using anatomical reperii or artificial fiducial markers, always exploiting the available touch probe. The in situ bioprinting step can finally be performed using all the technologies available on the platform (e.g., pneumatic extrusion-based bioprinting, valve-jet bioprinting, inkjet bioprinting). IMAGObot features a fully automatic tool change allowing the use of all these technologies alone or in combination favouring the in situ fabrication of multiscale and multimaterial tissue substitutes.

Considering the need of obtaining highly stable structures in a physiological environment, the path-planning algorithm also enables the management of a purposely developed photo-crosslinking device installed on the pneumatic extruder. The system consists of a support adjustable in height (to modulate the substrate exposure) which allows the direct accommodation of 8 LEDs. To minimise the light exposure of the needle, and avoid its clogging, only the LEDs opposite to the printing direction are switched on to irradiate the newly deposited filament.

IMAGObot was successfully tested on different anthropomorphic phantoms, highlighting the potential that a robotic platform can have for in situ bioprinting. This approach opens the way to a number of possibilities in the field of tissue engineering, especially for the easiest accessible organs such as skin, bone and cartilage.

All the details about IMAGObot open-source project and a standalone Matlab® app for management of the operating workflow are available at https://github.com/CentroEPiaggio/IMAGObot.

In 2013 Dr. Skylar Tibbits introduced the term “4D printing” to denote the fabrication via 3D printing of structure able to shape-transform overtime when exposed to an external stimulus, such as heat, pH, and light. 4D printing relies on the patterning in space of smart materials, namely materials that undergo to useful, predictive, reproducible, and macroscopic physical/chemical changes in their properties as a consequence of an environmental stimuli. Impactfully, 4D printed structures achieve their functions through this pre-determined property change, that usually display macroscopically as a shape changing, thus possessing several advantages over traditional static structures and funding application in multiple fields of biomedical interest, such as tissue engineering, drug delivery systems and medical devices.

Our goal is the expansion and consolidation of 4D printing as an enabling manufacturing technology to program the environmental-triggered physical evolution of structures of biomedical interest. With this aim, in the recent years, we fabricated by 4D printing several devices of biomedical interest, such as scaffolds for trachea engineering and neural tube modeling and medical devices to perform intestinal anastomosis and for the treatment of the short bowel syndrome. These studies were conducting in collaboration with bio-materialists, biologists, and physicians from all over the world. Our approach in the design and fabrication of 4D (bio)printed devices is systematic and relies on the use of mathematical models, both analytical and computational, to investigate the desired property modification/shape morphing of the structures according to the material properties and their patterning in the 3D space. Moreover, we focus on the characterization and optimization of smart materials, with the aim to make the 4D printable.

Concurrently, we are also focusing on the formalization of the 4D printing approach, by means of systematic methodologies for engineering design and artificial intelligent.