I – Aim of the work

47

I – Aim of the work

Tissue engineering (TE) aims to the development of temporary replacement structures to be used in the human body in order to improve healing and reduce pain when a traumatic injury or disease affects the normal function of a tissue or organ. The new approaches developed within the TE domain are aimed to overcome the shortcoming of current surgical strategies involving auto-, allo- and xeno-grafts transplantation. Scaffold-guided TE approach involves the use of a temporary porous template, referred to as scaffold, which serves as temporary template to fill the tissue defect and to promote cell-cell interaction and extracellular formation. A wide range of natural and synthetic polymers in combination with bioactive molecules and cells have been proposed for the development of TE scaffolds with different physical and chemical properties. The fabrication techniques proposed in the last two decades to obtain scaffolds with different microstructures and external shapes can be divided into conventional and additive manufacturing (AM) techniques.

Conventional techniques present several drawbacks, including poor control over pore architecture, porosity, pore interconnectivity, and complex manufacturing procedures. Inversely, AM techniques allow to produce rapidly complex three-dimensional (3D) models with controlled internal architecture (porosity, pore size and pore distribution) and external geometry.

The present PhD work is part of a research program in the TE field performed at the Laboratory of Polymeric Materials for Biomedical and Environmental Applications (BIOLab) of the Department of Chemistry and Industrial Chemistry of the University of Pisa, specifically regarding the development of 3D scaffolds of synthetic and/or natural origin. In this context the processing of biodegradable and bioactive polymers as well as the development of new fabrication techniques for the obtainment of customised scaffolds that can meet the specific microstructure and anatomical requirements for a given clinical application are key factors for the development of a rational approach to the design of biomimetic TE constructs.

The aim of this PhD research program was the development for novel manufacturing techniques for

the obtainment of 3D polymeric constructs suitable as scaffold for TE. Innovative approaches to

conventional techniques, i.e. electro- and wet-spinning, were investigated in order to enhance their

application to scaffold fabrication process and to allow their combination with AM techniques with

the aim of obtaining multi-scale scaffold structures. The development of dual-scale scaffolds

consisting of 3D constructs of aligned poly(ε-caprolactone) (PCL) microfilaments, fabricated by

melt extrusion-based AM techniques, and electrospun poly(lactic-co-glycolic acid) (PLGA) fibres

was investigated. Moreover, wet-spinning was applied for the development of 3D microfibrous

meshes of a star poly(ε-caprolactone) (*PCL) endowed with antimicrobial activity suitable as

scaffolds for the regeneration of bone defects in the presence of infections.

I – Aim of the Work

48 A further aspect that was addressed concerned the computer-controlled automation of the wet- spinning process permitting scaffold fabrication following AM principles. For such purpose, the assembling, validation and employment of a novel AM technology enabling to obtain 3D scaffolds composed of wet-spun fibres made of different polymeric materials, i.e. PCL, *PCL and poly(3- hydroxybutyrate-co-3-hydroxyhexanoate), were investigated. Adopting the same rationale, the technological solutions allowing for a computer-control over melt-electrospinning process were studied in order to develop a novel technique for the obtainment of 3D microfibrous meshes made of *PCL. Finally, innovative approaches for the fabrication of microstructured, anatomically- shaped poly[poly(ethylene oxide) terephthalate-co-butylene terephthalate] scaffolds for middle-ear TE, by means of melt extrusion-based AM techniques or electrospinning, were developed.

This PhD thesis is divided into eight chapters reporting on the different topics investigated during the implementation of the research activities:

Development of Advanced Technologies for Manufacturing of Tissue Engineering Scaffolds;

Dual-Scale Polymeric Constructs as Scaffolds for Tissue Engineering;

Development of 3D Wet-spun Polymeric Scaffolds Loaded with Antimicrobial Agents for Bone Engineering;

Additive Manufacturing of Wet-spun Polymeric Scaffolds for Bone Tissue Engineering;

Additive Manufacturing of Star Poly(ε-caprolactone) Wet-spun Scaffolds for Tissue Engineering Applications;

Additive Manufacturing of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Scaffolds for Engineered Bone Development;

Additive Manufacturing of 3D Melt-electrospun Star Poly(ε-caprolactone) Scaffolds

Development of novel scaffolds for otologic surgery applications;