DESIGN STRATEGIES AND ADDITIVE MANUFACTURING OF 3D CUSTOMIZED SCAFFOLDS WITH OPTIMIZED PROPERTIES FOR CRANIOFACIAL TISSUE ENGINEERING

3D customized scaffolds for craniofacial tissue engineering were designed using advanced strategies and technologies. Specifically, reverse engineering, additive manufacturing, material selection, experimental and theoretical analyses were properly integrated. The focus was on: i) design strategies of 3D customized nanocomposite scaffolds for hard tissue regeneration; ii) an engineered design of 3D additive manufactured nanocomposite scaffolds with optimized properties; iii) an approach toward the design of 3D customized scaffolds for large cranial defects

Integrated Methodologies and Technologies for the Design of Advanced Biomedical Devices

Biomedical devices with tailored properties were designed using advanced methodologies and technologies. In particular, design for additive manufacturing, reverse engineering, material selection, experimental and theoretical analyses were properly integrated. The focus was on the design of: i) 3D additively manufactured hybrid structures for cranioplasty; ii) technical solutions and customized prosthetic devices with tailored properties for skull base reconstruction after endoscopic endonasal surgery; iii) solid-lattice hybrid structures with optimized properties for biomedical applications. The feasibility of the proposed technical solutions was also assessed through virtual and physical models

3D Engineered Peripheral Nerve: Towards A New Era of Patient-Specific Nerve Repair Solutions

Reconstruction of peripheral nerve injuries (PNIs) with substance loss remains challenging because of limited treatment solutions and unsatisfactory patient outcomes. Currently, nerve autografting is the first-line management choice for bridging critical-sized nerve defects. The procedure, however, is often complicated by donor site morbidity and paucity of nerve tissue, raising a quest for better alternatives. The application of other treatment surrogates, such as nerve guides remains questionable, and inefficient in irreducible nerve gaps. More importantly, these strategies lack customization for personalized patient therapy, which is a significant drawback of these nerve repair options. This negatively impacts the fascicle-to-fascicle regeneration process, critical to restoring the physiological axonal pathway of the disrupted nerve. Recently, the use of additive manufacturing (AM) technologies has offered major advancements to the bioengineering solutions for PNI therapy. These techniques aim to reinstate the native nerve fascicle pathway using biomimetic approaches, thereby augmenting end-organ innervation. AM-based approaches, such as 3D bioprinting, are capable of biofabricating 3D engineered nerve graft scaffolds in a patient-specific manner with high precision. Moreover, realistic in vitro models of peripheral nerve tissues that represent the physiologically and functionally relevant environment of human organs could also be developed. However, the technology is still nascent and faces major translational hurdles. In this review, we spotlighted the clinical burden of PNIs and most up-to-date treatment to address nerve gaps. Next, a summarized illustration of the nerve ultrastructure that guides research solutions is discussed. This is followed by a contrast of the existing bioengineering strategies used to repair peripheral nerve discontinuities. In addition, we elaborated on the most recent advances in 3D printing (3DP) and biofabrication applications in peripheral nerve modeling and engineering. Finally, the major challenges that limit the evolution of the field along with their possible solutions are also critically analyzed

Design and Analysis of 3D Customized Models of a Human Mandible

Polymer-based composites are ideal for applications where high strength-to-weight and stiffness-to-weight ratios are required. In the biomedical field, fiber-reinforced polymers have replaced metals, emerging as suitable alternative. Reverse engineering and additive manufacturing methods are required to achieve the design of customized devices with specific shape and size. At the same time, micromechanics and macro-mechanics play an important role in the development of highly functional composite materials. The aim of this research is to develop customized 3D models of a human mandible using reverse engineering, additive manufacturing and composite material technology. Experiments were carried out by loading the models through the condyles and the results show the potential to reproduce the mechanical behavior of a human mandible. Taking into account the curves of the load-arch width decrease, the stiffness of the 3D composite model was 14.1± 1.9 N/mm, which is close to the tested human mandible (17.5 ± 1.8 N/mm)

State of the art in the use of bioceramics to elaborate 3D structures using robocasting

Robocasting, também conhecido como Direct Ink Writing, é uma técnica de fabricação aditiva (AM), que inclui extração direta de sistemas coloidais, que consiste na exposição de camadas e um controlador controlado por computador de uma mídia altamente concentrada nesta extrusão. Este artigo apresenta uma visão geral das contribuições e desafios no desenvolvimento de biomateriais cerâmicos tridimensionais (3D) por esse método de impressão. O estado da arte em diferentes biocerâmicas como alumina, zircônia, fosfato de vidro, vidro / vitrocerâmica e compostos é avaliado e discutido em relação a suas aplicações e comportamento biológico, em uma pesquisa que produziu desde uma produção de próteses dentárias personalizadas a biofabricantes 3D humanos tecidos.Embora o robocasting represente uma interrupção na fabricação de estruturas porosas, como os andaimes para a Engenharia de Tecidos (TE), muitas vantagens ainda são necessárias, mas ainda são divulgadas, essa técnica já está usando a utilização de peças densas. Assim, são necessárias estratégias para a fabricação de biocerâmica densificada, com o objetivo de ampliar as possibilidades dessa técnica de AM. As vantagens e desvantagens e também perspectivas futuras da aplicação do robocasting no processamento biocerâmico também são exploradas

Layer manufacturing for in vivo devices

Traditional in vivo devices fabricated to be used as implantation devices included sutures, plates, pins, screws, and joint replacement implants. Also, akin to developments in regenerative medicine and drug delivery, there has been the pursuit of less conventional in vivo devices that demand complex architecture and composition, such as tissue scaffolds. Commercial means of fabricating traditional devices include machining and moulding processes. Such manufacturing techniques impose considerable lead times and geometrical limitations, and restrict the economic production of customized products. Attempts at the production of non-conventional devices have included particulate leaching, solvent casting, and phase transition. These techniques cannot provide the desired total control over internal architecture and compositional variation, which subsequently restricts the application of these products. Consequently, several parties are investigating the use of freeform layer manufacturing techniques to overcome these difficulties and provide viable in vivo devices of greater functionality. This paper identifies the concepts of rapid manufacturing (RM) and the development of biomanufacturing based on layer manufacturing techniques. Particular emphasis is placed on the development and experimentation of new materials for bio-RM, production techniques based on the layer manufacturing concept, and computer modelling of in vivo devices for RM techniques

Recent advances in melt electro writing for tissue engineering for 3D printing of microporous scaffolds for tissue engineering

Melt electro writing (MEW) is a high-resolution 3D printing technique that combines elements of electro-hydrodynamic fiber attraction and melts extrusion. The ability to precisely deposit micro- to nanometer strands of biocompatible polymers in a layer-by-layer fashion makes MEW a promising scaffold fabrication method for all kinds of tissue engineering applications. This review describes possibilities to optimize multi-parametric MEW processes for precise fiber deposition over multiple layers and prevent printing defects. Printing protocols for nonlinear scaffolds structures, concrete MEW scaffold pore geometries and printable biocompatible materials for MEW are introduced. The review discusses approaches to combining MEW with other fabrication techniques with the purpose to generate advanced scaffolds structures. The outlined MEW printer modifications enable customizable collector shapes or sacrificial materials for non-planar fiber deposition and nozzle adjustments allow redesigned fiber properties for specific applications. Altogether, MEW opens a new chapter of scaffold design by 3D printing

Development of metallic functionalized biomaterials with low elastic modulus for orthopedic applications

Tesi per compendi de publicacionsTitanium (Ti) and Ti alloys have been used for decades for bone implants and prostheses due to its mechanical reliability and good biocompatibility. However, implant-related infections, lack of osseointegration with the surrounding bone, and the mismatch of mechanical properties between implant and bone, remain among the leading reasons for implant failure. In the present PhD thesis, two strategies have been studied to increase implant viability: fabrication of porous Ti structures and surface functionalization. The stiffness mismatch between titanium implant and bone can cause significant bone resorption, which can lead to serious complications such as periprosthetic fracture during or after revision surgery. Titanium surface plays a major role in the bone prosthesis interactions, not only to promote initial cell adhesion but also to avoid bacterial adhesion. One strategy studied in the thesis has been the development and manufacturing of porous Ti structures. A scaffold with a porosity of 75% has been prepared by direct ink writing, with the objective of reducing the apparent modulus elasticity of Ti prostheses. In this work, porous Ti structures with a stiffness and compressive strength of 2.6 GPa and 64.5 MPa respectively has been manufactured. To this end, a new ink formulation was designed based on the mixture of a thermosensitive hydrogel with Ti irregular powder particles with a mean particle size of 22.45 μm. A thermal treatment was optimized to ensure the complete elimination of the binder before the sintering process, in order to avoid contamination of the titanium structures. The understanding of infections is closely linked to the concept of the “race for the surface”. The winner of this race (cell versus bacteria) decides if a solid anchoring between implant and bone will be achieved or if bacterial growth will lead to a periprosthetic infection. Another strategy studied on this thesis focuses on the functionalization of the Ti surface. First, surface of Ti scaffolds were functionalized with a cell adhesion fibronectin recombinant fragment for optimizing cell adhesion. Additionally, a multifunctional coating based on the potential of calcium phosphate coatings to be used as carriers for drug delivery was also studied to achieve a balance between cell attachment and reduction of bacterial adhesion. Porous Ti structures have been successfully coated with a one-step pulsed electrodeposition process achieving a uniform calcium phosphate layer both on the inner and outer the surface of the scaffold, with adhesion strengths over 22 MPa. The codeposition of an antibacterial agent with a pulsed and reverse pulsed electrodeposition was achieved on both smooth and open-cell Ti surfaces. The release rate of the antibacterial agent can be modulated within hours or days timeframe by adjusting the coating conditions and without altering the antimicrobial potential of the loaded antibacterial agent itself. The biofunctionalized coatings exhibited a noteworthy in vitro antibacterial activity against S. aureus and E. coli bacteria strains, with a significant decrease of viable attached bacteria to the treated surfaces. Cell culture tests also showed that Ti structures loaded with the antibacterial agent presented an improved cell adhesion compared to that of untreated Ti. Therefore, the proposed strategies can efficiently improve orthopedic implants in terms of improving biointegration and microbial adhesion resistance.El titani (Ti) i els seus aliatges s'han emprat durant dècades per a implants i pròtesis òssies a causa de la seva fiabilitat mecànica i bona biocompatibilítat. Tanmateix, les infeccions relacionades amb els implants, la manca d'osteointegració amb l'os circumdant i el desajust de les propietats mecàniques entre l'implant i l'os, continuen sent els principals motius de fallida de l'implant En la present tesi doctoral, s'han estudiat dues estratègies per augmentar la viabilitat de l'implant fabricació d'estructures poroses de Ti i funcionalització superficial. El desajust de la rigidesa entre l'implant de titani i l'os pot causar una reabsorció òssia important, que pot provocar complicacions greus com la fractura periprotètica durant o després de la cirurgia de revisió . La superfície del titani té un paper important en les interaccions os-pròtesi, no només per promoure l'adhesió inicial de les cèl·lules, sinó també per evitar l'adhesió bacteriana. Una estratègia estudiada a la tesi ha estat el desenvolupament i fabricació d'estructures poroses de Ti. S'ha preparat un andamiatge amb una porositat del 75% mitjançant Direct lnk Writing, amb l'objectiu de reduir l'elasticitat del mòdul aparent de les pròtesis de Ti. En aquest treball, s'han fabricat estructures poroses de Ti amb una rigidesa i resistència a la compressió de 2,6 GPa i 64,5 MPa respectivament. Per això, es va dissenyar una nova formulació de tinta basada en la barreja d'un hidrogel termosensible amb partícules de pols irregulars de Ti amb una mida mitjana de partícula de 22,45 µm. Es va optimitzar un tractament tèrmic per assegurar l’eliminació completa de l'aglutinant abans del procés de sinterització, per evitar la contaminació de les estructures de titani. La lluita contra les infeccions està estretament lligada al concepte de "carrera per la superfície". El guanyador d'aquesta carrera (cèl·lula contra bacteris) decideix si s'aconseguirà un ancoratge sòlid entre l'implant i l'os o si el creixement bacterià conduirà a una infecció periprotètica. Una altra estratègia estudiada en aquesta tesi se centra en la funcionalització de la superfície de Ti. En primer lloc, la superfície d'andamiatges de Ti es va funcionalitzar amb un fragment recombinant fibronectina d'adhesió cel·lular per optimitzar l’adhesió cel·lular. A més, també es va estudiar un recobriment multifuncional basat en l'ús de recobriments de fosfat de calci com a portadors per a l'alliberament de medicaments per aconseguir un equilibri entre la adhesió cel·lular i la reducció de l'adhesió bacteriana. Les estructures poroses de Ti s'han recobert amb èxit amb un procés d'electrodeposició polsada d'un pas, aconseguint una capa uniforme de fosfat de calci tant a la superfície interna com exterior de les estructures, amb resistències d’adhesió superiors a 22 MPa. La co-deposició d'un agent antibacterià amb una electrodeposició polsada i polsada inversa es va aconseguir tant a les superfícies de Ti d'estructura oberta coma les llises. La velocitat de l'agent antibacterià es pot modular en un terminí d'hores o dies ajustant les condicions de recobriment i sense alterar el potencial antimicrobià del propi agent antibacterià carregat. Els recobriments biofuncionalitzats van mostrar una notable activitat antibacteriana in vitro contra les soques de bacteris S. aureus i E. coli, amb una disminució significativa de bacteris adherits viables a les superfícies tractades. Les proves de cultiu cel·lular també van demostrar que les estructures de Ti carregades de l'agent antimicrobià presentaven una millor adhesió cel·lular en comparació amb la Ti no tractat. Per tant. les estratègies proposades poden millorar els implants ortopèdics de manera eficient en termes de millora de la biointegració la resistència a l'adherència microbiana.Postprint (published version

Synthesis, Characterisation and 3D Printing of a Light-Curable Degradable Polymer for Craniofacial Bone Regeneration

A surgeon’s options for correcting congenital deformities, removing oral tumours and reconstructing the head and neck region are typically restricted by the equipment available to restore bone function and appearance for the patient. New production techniques and implants with improved osseointegration performance are urgently needed to meet the growing demand for effective implants at a reasonable price. Non-degradable materials are used widely for bone repair; however, they will stay in the body indefinitely until removed surgically. Metals, such as titanium, can be used for three-dimensional (3D) printing of scaffolds. 3D printing has the potential to enhance the creation of anatomically fitting patient-specific devices with highly effective delivery in a cost-effective manner. However, metal implants have the disadvantage that they can release traces of material over time and induce immunological responses. Non-degradable polymers, such as poly (methyl methacrylate), have the disadvantages that they undergo highly exothermic polymerisation, are prone to infection and lack osseointegration. Ceramics, such as calcium phosphates, have also been studied for use in craniofacial bone regeneration, however, they have poor fracture toughness, brittleness and excessive stiffness. In view of the disadvantages associated with several of the known 3D printable materials, this thesis takes you through the development of an improved material that addresses some of the disadvantages discussed above. In this study, the synthesis of the new material referred to as “CSMA-2” is investigated along with its mechanical properties and the effects of the addition of different ratios of calcium phosphate fillers to the isosorbide-based, light-curable, degradable polymer. A comparison between two different photoinitiator systems is carried out throughout this study to ultimately find the most suited formulation for the 3D printing of the resin. Mechanical tests showed the modulus values to be between 1.7-3 kN/mm2 in CSMA-2 and its composites dependant on the photoinitiator system used. In vitro cell culture studies, using human bone osteosarcoma cells and human adipose-derived stem cells confirmed cytocompatibility of the material. Finally, Digital Light Processing 3D printing, allowed a direct photo-polymerisation of the resin to form bone- like scaffolds ready to be implanted in vivo