Electrospun scaffolds for regeneration of musculoskeletal interface tissues

L’apparato muscolo scheletrico è composto da strutture muscolari, articolari e ossee. Tali tessuti sono molto diversi tra loro e hanno proprietà meccaniche estremamente variabili, pertanto presentano una transizione graduale in corrispondenza della loro giunzione, onde evitare l’insorgere di concentrazioni di tensione. L’evoluzione ha portato alla formazione di particolari interfacce che permettono la corretta trasmissione dei carichi distribuendo le tensioni su una superficie più ampia in corrispondenza della giunzione. Le interfacce che vanno a inserirsi nell’osso vengono definite entesi e in particolare, in questa review, analizzeremo il caso di quelle tra tendini/legamenti e osso. In questo lavoro ci siamo anche concentrati sulla giunzione miotendinea, ovvero tra muscolo e tendine. Sono numerose le lesioni che riguardano muscoli, ossa, tendini o legamenti e molto spesso l’infortunio avviene a livello della giunzione. Quando ciò accade vi sono diverse strade, ciascuna con i suoi vantaggi e svantaggi: sutura, autograft, allograft o xenograft. Oltre a queste soluzioni si è fatta gradualmente più spazio la possibilità di realizzare degli scaffold che vadano temporaneamente a sostituire la parte danneggiata e a promuovere la sua rigenerazione, degradandosi man mano. L’elettrofilatura (Elettrospinning) è un processo produttivo che negli ultimi decenni si è affermato come tecnica per la fabbricazione di questi scaffold, fino a diventare uno tra i principali processi utilizzati dai ricercatori in questo campo. Questa tecnica infatti permette di realizzare scaffold di nanofibre porose utilizzando polimeri biodegradabili e soprattutto biocompatibili. Lo scopo della review è proprio quello di scoprire tutti i lavori e gli studi che utilizzano l’elettrofilatura per realizzare degli scaffold per interfacce, delineando così lo stato dell’arte sui progressi fatti e sulle varie tecniche utilizzate.

Damping and Thermomechanical behaviour of CFRP laminates modified with rubbery nanofibers

Nanofibrous membranes are a promising material for tailoring the properties of laminated CFRP composites by embedding them into the structure. This project aimed to understand the effect of number, position and thickness of nanofibrous modifications specifically on the damping behaviour of the resulting nano-modified CFRP composite with an epoxy matrix. An improvement of damping capacity is expected to improve a composites lifetime and fatigue resistance by prohibiting the formation of microcracks and consequently hindering delamination, it also promises a rise in comfort for a range of final products by intermission of vibration propagation and therefore diminution of noise. Electrospinning was the technique employed to produce nanofibrous membranes from a blend of polymeric solutions. SEM, WAXS and DSC were utilised to evaluate the quality of the obtained membranes before they were introduced, following a specific stacking sequence, in the production process of the laminate. A suitable curing cycle in an autoclave was applied to mend the modifications together with the matrix material, ensuring full crosslinking of the matrix and therefore finalising the production process. DMA was exercised in order to gain an understanding about the effects of the different modifications on the properties of the composite. During this investigation it became apparent that a high number of modifications of laminate CFRP composites, with an epoxy matrix, with thick rubbery nanofibrous membranes has a positive effect on the damping capacity and the temperature range the effect applies in. A suggestion for subsequent studies as well as a recommendation for the production of nano-modified CFRP structures is included at the end of this document.

Synthesis and characterisation of electrospun gold on ceria catalysts

Cerium oxide in catalysis can be used both as support and as a catalyst itself. Ceria catalyses many oxidations reactions, its excellent catalytic properties are due to its store oxygen storage capacity (OSC) and the reticular defects present on its surface. Different morphologies expose different reticular planes, and different reticular planes can expose different amounts of defects. The preparation method of cerium oxide can influence the surface area, morphology, and the number of defects in the sample. This work is focused on different preparation methods for gold nanoparticles supported on 1D nanostructures of cerium oxide prepared via electrospinning, their XRD, DRUV-Vis and Raman characterizations, and their catalytic performance on the oxidation reaction of HMF to FDCA.

Nanostructured piezoelectric materials for the design and development of self-sensing composite materials and energy harvesting devices

The work activities reported in this PhD thesis regard the functionalization of composite materials and the realization of energy harvesting devices by using nanostructured piezoelectric materials, which can be integrated in the composite without affecting its mechanical properties. The self-sensing composite materials were fabricated by interleaving between the plies of the laminate the piezoelectric elements. The problem of negatively impacting on the mechanical properties of the hosting structure was addressed by shaping the piezoelectric materials in appropriate ways. In the case of polymeric piezoelectric materials, the electrospinning technique allowed to produce highly-porous nanofibrous membranes which can be immerged in the hosting matrix without inducing delamination risk. The flexibility of the polymers was exploited also for the production of flexible tactile sensors. The sensing performances of the specimens were evaluated also in terms of lifetime with fatigue tests. In the case of ceramic piezo-materials, the production and the interleaving of nanometric piezoelectric powder limitedly affected the impact resistance of the laminate, which showed enhanced sensing properties. In addition to this, a model was proposed to predict the piezoelectric response of the self-sensing composite materials as function of the amount of the piezo-phase within the laminate and to adapt its sensing functionalities also for quasi-static loads. Indeed, one final application of the work was to integrate the piezoelectric nanofibers in the sole of a prosthetic foot in order to detect the walking cycle, which has a period in the order of 1 second. In the end, the energy harvesting capabilities of the piezoelectric materials were investigated, with the aim to design wearable devices able to collect energy from the environment and from the body movements. The research activities focused both on the power transfer capability to an external load and the charging of an energy storage unit, like, e.g., a supercapacitor.

Electrospun hierarchical artificial muscle for soft robotics applications

Nowadays, one of the most ambitious challenges in soft robotics is the development of actuators capable to achieve performance comparable to skeletal muscles. Scientists have been working for decades, inspired by Nature, to mimic both their complex structure and their perfectly balanced features in terms of linear contraction, force-to-weight ratio, scalability and flexibility. The present Thesis, contextualized within the FET open Horizon 2020 project MAGNIFY, aims to develop a new family of innovative flexible actuators in the field of soft-robotics. For the realization of this actuator, a biomimetic approach has been chosen, drawing inspiration from skeletal muscle. Their hierarchical fibrous structure was mimicked employing the electrospinning technique, while the contraction of sarcomeres was designed employing chains of molecular machines, supramolecular systems capable of performing movements useful to execute specific tasks. The first part deals with the design and production of the basic unit of the artificial muscle, the artificial myofibril, consisting in a novel electrospun core-shell nanofiber, with elastomeric shell and electrically conductive core, coupled with a conductive coating, for the realization of which numerous strategies have been investigated. The second part deals instead with the integration of molecular machines (provided by the project partners) inside these artificial myofibrils, preceded by the study of several model molecules, aimed at simulating the presence of these molecular machines during the initial phases of the project. The last part concerns the realization of an electrospun multiscale hierarchical structure, aimed at reproducing the entire muscle morphology and fibrous organization. These research will be joined together in the near future like the pieces of a puzzle, recreating the artificial actuator most similar to biological muscle ever made, composed of millions of artificial myofibrils, electrically activated in which the nano-scale movement of molecular machines will be incrementally amplified to the macro-scale contraction of the artificial muscle.

Nanostructured smart materials as functional components of medical devices

The field of medical devices has experienced, more than others, technological advances, developments and innovations, thanks to the rapidly expanding scientific knowledge and collaboration between different disciplines such as biology, engineering and materials science. The design of functional components can be achieved by exploiting composite materials based on nanostructured smart materials, that due to the inherent characteristics of single constituents develop unique properties that make them suitable for different applications preserving excellent mechanical proprieties. For instance, recent developments have focused on the fabrication of piezoelectric devices with multiple biomedical functions, as actuation and sensing functions in one component for monitoring pressure signals. The present Ph.D. Thesis aims at investigating nanostructured smart materials embedded into a polymeric matrix to obtain a composite material that can be used as a functional component for medical devices. (i) Nanostructured piezoelectric material with self-sensing capability was successfully manufactured by using ceramic (i.e. lead zirconate titanate (PZT)) and (ii) polymeric (i.e. poly(vinylidene fluoride-trifluoro ethylene (PVDF-TRFE)) piezoelectric materials. PZT nanofibers were obtained by sol-gel electrospinning starting from synthetized PZT precursor solution. Synthesis, sol-gel electrospinning process, and thermal treatment were accurately controlled to obtain PZT nanofibers dimensionally stable with densely packed grains in the perovskite phase. To guarantee the impact resistance of the laminate, the morphology and size of the hosting filler were accurately designed by increasing the surface area to volume ratio. Moreover, to solve the issue relative to the mechanical discrepancy between rigid electronic materials/soft human tissues/different material of the device (iii) a nanostructured flexible composite material based on a network of Poly-L-lactic acid (PLLA) made of curled nanofibers that present a tuneable mechanical response as a function of the applied stress was successful fabricated.

Towards a sustainable approach for Cultural Heritage Conservation: developing micro-structured green materials and analytical protocols for their performance assessment

Cleaning is one of the most important and delicate procedures that are part of the restoration process. When developing new systems, it is fundamental to consider its selectivity towards the layer to-be-removed, non-invasiveness towards the one to-be-preserved, its sustainability and non-toxicity. Besides assessing its efficacy, it is important to understand its mechanism by analytical protocols that strike a balance between cost, practicality, and reliable interpretation of results. In this thesis, the development of cleaning systems based on the coupling of electrospun fabrics (ES) and greener organic solvents is proposed. Electrospinning is a versatile technique that allows the production of micro/nanostructured non-woven mats, which have already been used as absorbents in various scientific fields, but to date, not in the restoration field. The systems produced proved to be effective for the removal of dammar varnish from paintings, where the ES not only act as solvent-binding agents but also as adsorbents towards the partially solubilised varnish due to capillary rise, thus enabling a one-step procedure. They have also been successfully applied for the removal of spray varnish from marble substrates and wall paintings. Due to the materials' complexity, the procedure had to be adapted case-by-case and mechanical action was still necessary. According to the spinning solution, three types of ES mats have been produced: polyamide 6,6, pullulan and pullulan with melanin nanoparticles. The latter, under irradiation, allows for a localised temperature increase accelerating and facilitating the removal of less soluble layers (e.g. reticulated alkyd-based paints). All the systems produced, and the mock-ups used were extensively characterised using multi-analytical protocols. Finally, a monitoring protocol and image treatment based on photoluminescence macro-imaging is proposed. This set-up allowed the study of the removal mechanism of dammar varnish and semi-quantify its residues. These initial results form the basis for optimising the acquisition set-up and data processing.

Analysis of the state of the art of the biofabrication strategies for the regeneration of the myotendinous junction

La giunzione miotendinea (MTJ) è una struttura anatomica specializzata che collega il muscolo al tendine. La sua funzione è quella di permettere la trasmissione della forza generata dal muscolo al tendine, permettendo il movimento. Essendo una struttura di interfaccia che funge da raccordo tra due tipi di tessuti molto differenti, tende a risentire di una forte concentrazione di tensione, questo la rende fortemente suscettibile a rottura. Le tecniche ad oggi utilizzare per riparare lesioni alla MTJ risultano inadatte ad una completa ed ottimale ripresa meccanica. Al fine di trovare una soluzione a questo problema, l’ingegneria tissutale sta lavorando alla fabbricazione di strutture tridimensionali che siano in grado di imitare al meglio la struttura nativa della MTJ. Le tecniche utilizzate per la produzione di tali strutture sono, principalmente, stampa 3D ed elettrofilatura. Il vantaggio di queste tecniche è la loro elevata risoluzione, che permette di controllare finemente l’architettura di tali strutture artificiali. Nella seguente tesi verrà presentato lo stato dell’arte sulle tecniche utilizzate per la fabbricazione di scaffolds per la rigenerazione della MTJ, soffermandosi in particolare sui metodi di fabbricazione e sulle prestazioni morfologiche, meccaniche e cellulari effettuando un confronto tra i diversi studi che se ne sono occupati, individuandone punti di forza, debolezze e possibili studi futuri che potranno essere effettuati su tali scaffolds. In questo modo, sarà possibile rendersi conto di quale di queste tecniche risulti essere più promettente per il futuro.

CFRP modificati con membrane elettrofilate per il self-healing: ottimizzazione delle condizioni di cura e test di delaminazione

I compositi a matrice polimerica rinforzati con fibre di carbonio (Carbon fiber reinforced polymers, CFRP) posseggono proprietà meccaniche uniche rispetto ai materiali convenzionali, ed un peso decisamente inferiore. Queste caratteristiche, negli ultimi decenni, hanno determinato un crescente interesse nei confronti dei CFRP che ha portato a numerose applicazioni in settori come l’industria aerospaziale e l’automotive. Le sollecitazioni cui i CFRP laminati sono soggetti durante la vita d’uso possono causare fenomeni di delaminazione che, portando ad una drastica riduzione delle proprietà meccaniche del materiale, ne compromettono l’integrità strutturale. Nel presente lavoro di tesi, sono state integrate in laminati CFRP membrane elettrofilate da blend polimeriche con capacità di self-healing. Le migliori condizioni da applicare in fase di cura del composito sono state approfonditamente investigate mediante analisi termica (DSC). Per verificare la capacità di autoriparazione dei laminati modificati, è stata valutata la tenacità a frattura interlaminare in Modo I e Modo II prima e dopo il trattamento di attivazione del self-healing.