In order to restore bone function after musculoskeletal disorders, different types of biomaterials have been studied for the production of implantable devices. Among them, titanium and titanium alloys are considered the most significant biomaterials due to their excellent biocompatibility, corrosion resistance and wear resistance. Possible applications in the orthopedic field include joint prostheses that can restore the functionality of the damaged tissue. However, prosthetic implants present complications associated with the mobilization of the prosthesis at the implant site and the risk of bacterial infection, which today represent the main causes of failure of interventions. Dealing with acute infections, implant revision or replacement surgery have to be carried out, with obvious implications for health and social costs for the long-term hospital stay (a single episode of explanted and replaced prosthesis cost an average of $ 50,000). In the last decades, therefore, the scientific research has been focused on the develop of strategies to prevent bacterial adhesion. In particular, biomaterial surface modifications were investigated by regulating the chemical-physical properties of the surface, thanks to the ability to embed antibiotic agents. However, such treatments have shown criticalities dealing with ongoing infections and, furthermore, the progressive increase in antibiotics resistance by bacteria has required the development of more innovative and effective strategies to prevent bacterial adhesion. In particular, the use of metal agents with antibacterial properties has demonstrated high potential. Among them, the antimicrobial effect of silver has been extensively studied in literature. Ag+ ions are electrostatically bound to the bacteria phospholipid membrane, preventing the microorganism from moving. As a result, the bacteria membrane undergoes its break and thus it dies. In recent years, however, gallium (Ga3+) has been studied as an antibacterial: it competes with Iron ions because of their structural similarity, thus interrupting many biochemical processes necessary for the development of bacteria. In order to embed these ions into the surface of the material, the Anodic Spark Deposition (ASD) process is considered the most promising and versatile surface modification solution. In particular, ASD is an electrochemical technique that allows to modify the titanium oxide composition in order to obtain homogeneous, stable surfaces and characterized by a microporous and nanorough morphology. At the same time, the ASD technique allows to incorporate into the coating some chemical species present in the electrolytic solution. These characteristics can be tailored by controlling electrical process parameters (current density and final voltage) and the electrolyte solution composition. Thus, the oxide obtained through ASD treatment has the advantage of providing chemical-physical properties able to encourage the formation of a new mineralized bone tissue and in addition it provides antibacterial properties. Several studies have evaluated the effectiveness of post-treatments that can increase surface bioactivity. In particular, chemical treatment in alkaline environment is known to enrich the surface with hydroxides, thus increasing surface energy. According to scientific reviews, it is assumed that such modification may affect bacterial and cell adhesion. The aim of this present study is to provide surface treatments on Ti6Al7Nb and Ti6Al4V alloys capable of conferring antibacterial properties without inducing cytotoxic effects for eukaryotic cells.
Nel tentativo di ripristinare la funzionalità ossea in seguito a patologie a carico del sistema muscolo-scheletrico, diverse tipologie di biomateriali sono state studiate per la realizzazione di dispositivi impiantabili. Tra questi, il titanio e leghe di titanio sono considerati alcuni dei biomateriali più idonei, grazie alla loro ottima biocompatibilità, alla resistenza a corrosione e a usura. Le possibili applicazioni in campo ortopedico includono protesi articolari in grado ripristinare la funzionalità del tessuto danneggiato. Tuttavia, agli interventi di impianto protesico sono associate complicazioni relative alla mobilizzazione della protesi nel sito di impianto e al rischio di infezione batterica, che rappresentano oggi le principali cause di fallimento degli interventi. In caso di infezione acuta, è necessario eseguire interventi di revisione e di sostituzione dell’impianto, con ovvie implicazioni in termini di costi sanitari e sociali per la prolungata degenza ospedaliera che comportano (un singolo episodio di protesi infetta da espiantare e sostituire costa in media $ 50.000). Negli ultimi decenni, dunque, l’attenzione della ricerca scientifica si è rivolto verso lo sviluppo di strategie per ostacolare l’adesione batterica. In particolare, sono stati proposti trattamenti di modifica della superficie del biomateriale attraverso variazioni delle proprietà chimico-fisiche della superficie sfruttando la capacità di incorporare agenti antibiotici. Tuttavia, tali trattamenti hanno mostrato criticità verso infezioni già in corso e inoltre il progressivo aumento della resistenza agli antibiotici da parte dei batteri ha reso necessario sviluppare strategie più innovative ed efficaci per ostacolarne l'adesione. In particolare l’utilizzo di agenti metallici con proprietà antibatteriche ha dimostrato elevate potenzialità. Tra questi, l’effetto antimicrobico dell’argento è stato ampiamente studiato in letteratura. Gli ioni Ag+ si legano elettrostaticamente alla membrana fosfolipidica dei batteri, impedendo il movimento del microorganismo e causandone la rottura e dunque la morte del batterio. Negli ultimi anni invece è stato studiato l’utilizzo del gallio (Ga3+): esso infatti compete con gli ioni Ferro in virtù della loro somiglianza strutturale, interrompendo quindi molti processi biochimici necessari allo sviluppo dei batteri. Allo scopo di incorporare tali ioni nella superficie del materiale, la tecnica di Anodic Spark Deposition (ASD) risulta la soluzione più promettente e versatile di modifica superficiale. In particolare, l’ASD è una tecnica elettrochimica che permette di modificare la composizione di ossido di titanio al fine di ottenere superfici omogenee, stabili e caratterizzate da una morfologia microporosa e nanorugosa. Al contempo il processo ASD consente di incorporare nel rivestimento le specie chimiche presenti nella soluzione elettrolitica. Tali caratteristiche possono essere regolate attraverso il controllo dei parametri elettrici di processo (densità di corrente e voltaggio finale) e della composizione della soluzione elettrolitica. L’ossido di titanio così progettato ha dunque il vantaggio di possedere caratteristiche chimico-fisiche favorevoli alla formazione di un nuovo tessuto osseo mineralizzato, con l’aggiunta di possedere proprietà antibatteriche. Inoltre, diversi studi hanno valutato l’efficacia di post-trattamenti in grado di aumentare la bioattività della superficie. In particolare il trattamento chimico in ambiente alcalino è noto per arricchire la superficie con ossidrili aumentando così l’energia superficiale. Sulla base di studi di letteratura, si suppone che tale modifica possa influenzare l’adesione batterica e cellulare. Il presente lavoro si propone dunque di realizzare trattamenti superficiali su leghe di titanio (Ti6Al7Nb e Ti6Al4V) in grado di conferire proprietà antibatteriche, senza indurre effetti citotossici per le cellule eucariote.
Trattamenti elettrochimici antibatterici su lega di titanio per impianti ortopedici
AZZI, MARIAVITTORIA
2016/2017
Abstract
In order to restore bone function after musculoskeletal disorders, different types of biomaterials have been studied for the production of implantable devices. Among them, titanium and titanium alloys are considered the most significant biomaterials due to their excellent biocompatibility, corrosion resistance and wear resistance. Possible applications in the orthopedic field include joint prostheses that can restore the functionality of the damaged tissue. However, prosthetic implants present complications associated with the mobilization of the prosthesis at the implant site and the risk of bacterial infection, which today represent the main causes of failure of interventions. Dealing with acute infections, implant revision or replacement surgery have to be carried out, with obvious implications for health and social costs for the long-term hospital stay (a single episode of explanted and replaced prosthesis cost an average of $ 50,000). In the last decades, therefore, the scientific research has been focused on the develop of strategies to prevent bacterial adhesion. In particular, biomaterial surface modifications were investigated by regulating the chemical-physical properties of the surface, thanks to the ability to embed antibiotic agents. However, such treatments have shown criticalities dealing with ongoing infections and, furthermore, the progressive increase in antibiotics resistance by bacteria has required the development of more innovative and effective strategies to prevent bacterial adhesion. In particular, the use of metal agents with antibacterial properties has demonstrated high potential. Among them, the antimicrobial effect of silver has been extensively studied in literature. Ag+ ions are electrostatically bound to the bacteria phospholipid membrane, preventing the microorganism from moving. As a result, the bacteria membrane undergoes its break and thus it dies. In recent years, however, gallium (Ga3+) has been studied as an antibacterial: it competes with Iron ions because of their structural similarity, thus interrupting many biochemical processes necessary for the development of bacteria. In order to embed these ions into the surface of the material, the Anodic Spark Deposition (ASD) process is considered the most promising and versatile surface modification solution. In particular, ASD is an electrochemical technique that allows to modify the titanium oxide composition in order to obtain homogeneous, stable surfaces and characterized by a microporous and nanorough morphology. At the same time, the ASD technique allows to incorporate into the coating some chemical species present in the electrolytic solution. These characteristics can be tailored by controlling electrical process parameters (current density and final voltage) and the electrolyte solution composition. Thus, the oxide obtained through ASD treatment has the advantage of providing chemical-physical properties able to encourage the formation of a new mineralized bone tissue and in addition it provides antibacterial properties. Several studies have evaluated the effectiveness of post-treatments that can increase surface bioactivity. In particular, chemical treatment in alkaline environment is known to enrich the surface with hydroxides, thus increasing surface energy. According to scientific reviews, it is assumed that such modification may affect bacterial and cell adhesion. The aim of this present study is to provide surface treatments on Ti6Al7Nb and Ti6Al4V alloys capable of conferring antibacterial properties without inducing cytotoxic effects for eukaryotic cells.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/138767