Multifunctional implants Prevention is better than cure

Millions of people around the globe receive orthopedic implants every year. These implants help people to regain their mobility and contribute tremendously to improve the quality of life. However, a significant number of patients suffer from complications, such as implant associated infections (IAI) and aseptic loosening. The number of orthopedic implants is expected to increase due to an aging and increasingly obese population. As a result, the number of complications will rise too. In addition, the treatment of IAI is complicated by the development of antibiotic resistant bacteria. The focus of researchers has, therefore, shifted more and more towards the prevention of complications. In the words of Desiderius Erasmus: “Prevention is better than cure.”Biomaterials & Tissue Biomechanic

Antibacterial Titanium Implants Biofunctionalized by Plasma Electrolytic Oxidation with Silver, Zinc, and Copper: A Systematic Review

Patients receiving orthopedic implants are at risk of implant-associated infections (IAI). A growing number of antibiotic-resistant bacteria threaten to hamper the treatment of IAI. The focus has, therefore, shifted towards the development of implants with intrinsic antibacterial activity to prevent the occurrence of infection. The use of Ag, Cu, and Zn has gained momentum as these elements display strong antibacterial behavior and target a wide spectrum of bacteria. In order to incorporate these elements into the surface of titanium-based bone implants, plasma electrolytic oxidation (PEO) has been widely investigated as a single-step process that can biofunctionalize these (highly porous) implant surfaces. Here, we present a systematic review of the studies published between 2009 until 2020 on the biomaterial properties, antibacterial behavior, and biocompatibility of titanium implants biofunctionalized by PEO using Ag, Cu, and Zn. We observed that 100% of surfaces bearing Ag (Ag-surfaces), 93% of surfaces bearing Cu (Cu-surfaces), 73% of surfaces bearing Zn (Zn-surfaces), and 100% of surfaces combining Ag, Cu, and Zn resulted in a significant (i.e., >50%) reduction of bacterial load, while 13% of Ag-surfaces, 10% of Cu-surfaces, and none of Zn or combined Ag, Cu, and Zn surfaces reported cytotoxicity against osteoblasts, stem cells, and immune cells. A majority of the studies investigated the antibacterial activity against S. aureus. Important areas for future research include the biofunctionalization of additively manufactured porous implants and surfaces combining Ag, Cu, and Zn. Furthermore, the antibacterial activity of such implants should be determined in assays focused on prevention, rather than the treatment of IAIs. These implants should be tested using appropriate in vivo bone infection models capable of assessing whether titanium implants biofunctionalized by PEO with Ag, Cu, and Zn can contribute to protect patients against IAI.Biomaterials & Tissue Biomechanic

Inorganic Agents for Enhanced Angiogenesis of Orthopedic Biomaterials

Aseptic loosening of a permanent prosthesis remains one of the most common reasons for bone implant failure. To improve the fixation between implant and bone tissue as well as enhance blood vessel formation, bioactive agents are incorporated into the surface of the biomaterial. This study reviews and compares five bioactive elements (copper, magnesium, silicon, strontium, and zinc) with respect to their effect on the angiogenic behavior of endothelial cells (ECs) when incorporated on the surface of biomaterials. Moreover, it provides an overview of the state-of-the-art methodologies used for the in vitro assessment of the angiogenic properties of these elements. Two databases are searched using keywords containing ECs and copper, magnesium, silicon, strontium, and zinc. After applying the defined inclusion and exclusion criteria, 59 articles are retained for the final assessment. An overview of the angiogenic properties of five bioactive elements and the methods used for assessment of their in vitro angiogenic potential is presented. The findings show that silicon and strontium can effectively enhance osseointegration through the simultaneous promotion of both angiogenesis and osteogenesis. Therefore, their integration onto the surface of biomaterials can ultimately decrease the incidence of implant failure due to aseptic loosening.Biomaterials & Tissue Biomechanic

The effects of plasma electrolytically oxidized layers containing Sr and Ca on the osteogenic behavior of selective laser melted Ti6Al4V porous implants

Surface biofunctionalization is frequently applied to enhance the functionality and longevity of orthopedic implants. Here, we investigated the osteogenic effects of additively manufactured porous Ti6Al4V implants whose surfaces were biofunctionalized using plasma electrolytic oxidation (PEO) in Ca/P-based electrolytes with or without strontium. Various levels of Sr and Ca were incorporated in the oxide layers by using different current densities and oxidation times. Increasing the current density and oxidation time resulted in thicker titanium oxide layers and enhanced the release of Ca2+ and Sr2+. Biofunctionalization with strontium resulted in enhanced pore density, a thinner TiO2 layer, four-fold reduced release of Ca2+, and mainly anatase phases as compared to implants biofunctionalized in electrolytes containing solely Ca/P species under otherwise similar conditions. Different current densities and oxidation times significantly increased the osteogenic differentiation of MC3T3-E1 cells on implants biofunctionalized with strontium, when the PEO treatment was performed with a current density of 20 A/dm2 for 5 and 10 min as well as for a current density of 40 A/dm2 for 5 min. Therefore, addition of Sr in the PEO electrolyte and control of the PEO processing parameters represent a promising way to optimize the surface morphology and osteogenic activity of future porous AM implants.Biomaterials & Tissue Biomechanic

Self-defending additively manufactured bone implants bearing silver and copper nanoparticles

Effective preventive measures against implant-associated infection (IAI) are desperately needed. Therefore, the development of self-defending implants with intrinsic antibacterial properties has gained significant momentum. Biomaterials biofunctionalized with silver (Ag) have resulted in effective antibacterial biomaterials, yet regularly induce cytotoxicity. In this study, the use of both Ag and copper (Cu) nanoparticles (NPs) on TiO2 surfaces was investigated to generate antibacterial and osteoconductive biomaterials. Hence, additively manufactured Ti-6Al-4V volume-porous implants were biofunctionalized with plasma electrolytic oxidation (PEO) through the incorporation of varying ratios of Ag and/or Cu NPs in the TiO2 layer covering the implant surface. For all experimental groups, the surface morphology, chemical composition, ion release profile, generation of reactive ion species, antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) in vitro and ex vivo, as well as the response of pre-osteoblastic MC3T3-E1 cells in metabolic activity and differentiation assays were determined. PEO biofunctionalization resulted in rough and highly porous surfaces that released Ag and Cu ions for 28 days and generated hydroxyl as well as methyl radicals. A strong synergistic bactericidal behavior between Ag and Cu ions was detected, which allowed to decrease the concentration of Ag ions by 10-fold, while maintaining the same level of antibacterial activity. Antibacterial agar diffusion and quantitative assays indicated strong antibacterial activity in vitro for the implants containing Ag and Ag/Cu, while no antibacterial activity was observed for implants bearing only Cu NPs. Moreover, the biofunctionalized implants with ratios of up to 75% Ag and 25% Cu NP totally eradicated all bacteria in an ex vivo model using murine femora. Meanwhile, the biofunctionalized implants did not show any signs of cytotoxicity, while implants bearing only Cu NPs improved the metabolic activity after 7 and 11 days. The biomaterials developed here, therefore, exploit the synergistic behavior of Ag and Cu to simultaneously offer strong antibacterial behavior while fully mitigating the cytotoxicity of Ag against mammalian cells.Biomaterials & Tissue Biomechanic

Biofunctionalization of selective laser melted porous titanium using silver and zinc nanoparticles to prevent infections by antibiotic-resistant bacteria

Antibiotic-resistant bacteria are frequently involved in implant-associated infections (IAIs), making the treatment of these infections even more challenging. Therefore, multifunctional implant surfaces that simultaneously possess antibacterial activity and induce osseointegration are highly desired in order to prevent IAIs. The incorporation of multiple inorganic antibacterial agents onto the implant surface may aid in generating synergistic antibacterial behavior against a wide microbial spectrum while reducing the occurrence of bacterial resistance. In this study, porous titanium implants synthesized by selective laser melting (SLM) were biofunctionalized with plasma electrolytic oxidation (PEO) using electrolytes based on Ca/P species as well as silver and zinc nanoparticles in ratios from 0 to 100% that were tightly embedded into the growing titanium oxide layer. After the surface bio-functionalization process, silver and zinc ions were released from the implant surfaces for at least 28 days resulting in antibacterial leaching activity against methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, the biofunctionalized implants generated reactive oxygen species, thereby contributing to antibacterial contact-killing. While implant surfaces containing up to 75% silver and 25% zinc nanoparticles fully eradicated both adherent and planktonic bacteria in vitro as well as in an ex vivo experiment performed using murine femora, solely zinc-bearing surfaces did not. The minimum inhibitory and bactericidal concentrations determined for different combinations of both types of ions confirmed the presence of a strong synergistic antibacterial behavior, which could be exploited to reduce the amount of required silver ions by two orders of magnitude (i.e., 120 folds). At the same time, the zinc bearing surfaces enhanced the metabolic activity of pre-osteoblasts after 3, 7, and 11 days. Altogether, implant biofunctionalization by PEO with silver and zinc nanoparticles is a fruitful strategy for the synthesis of multifunctional surfaces on orthopedic implants and the prevention of IAIs caused by antibiotic-resistant bacteria. Statement of Significance: Implant-associated infections are becoming increasingly challenging to treat due to growing antibiotic resistance against antibiotics. Here, we propose an alternative approach where silver and zinc nanoparticles are simultaneously used for the biofunctionalization of rationally designed additively manufactured porous titanium. This combination of porous design and tailored surface treatment allows us to reduce the amount of required silver nanoparticles by two orders of magnitude, fully eradicate antibiotic-resistant bacteria, and enhance the osteogenic behavior of pre-osteoblasts. We demonstrate that the resulting implants display antibacterial activity in vitro and ex vivo against methicillin-resistant Staphylococcus aureus.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Biomaterials & Tissue Biomechanic

Data on the surface morphology of additively manufactured Ti-6Al-4V implants during processing by plasma electrolytic oxidation

Additively manufactured Ti-6Al-4V implants were biofunctionalized using plasma electrolytic oxidation. At various time points during this process scanning electron microscopy imaging was performed to analyze the surface morphology (van Hengel et al., 2017) [1]. This data shows the changes in surface morphology during plasma electrolytic oxidation. Data presented in this article are related to the research article “Selective laser melting porous metallic implants with immobilized silver nanoparticles kill and prevent biofilm formation by methicillin-resistant Staphylococcus aureus” (van Hengel et al., 2017) [1].Biomaterials & Tissue Biomechanic

Functionality-packed additively manufactured porous titanium implants

The holy grail of orthopedic implant design is to ward off both aseptic and septic loosening for long enough that the implant outlives the patient. Questing this holy grail is feasible only if orthopedic biomaterials possess a long list of functionalities that enable them to discharge the onerous task of permanently replacing the native bone tissue. Here, we present a rationally designed and additive manufacturing (AM) topologically ordered porous metallic biomaterial that is made from Ti-6Al-4V using selective laser melting and packs most (if not all) of the required functionalities into a single implant. In addition to presenting a fully interconnected porous structure and form-freedom that enables realization of patient-specific implants, the biomaterials developed here were biofunctionalized using plasma electrolytic oxidation to locally release both osteogenic (i.e. strontium) and antibacterial (i.e. silver ions) agents. The same single-step biofunctionalization process also incorporated hydroxyapatite into the surface of the implants. Our measurements verified the continued release of both types of active agents up to 28 days. Assessment of the antibacterial activity in vitro and in an ex vivo murine model demonstrated extraordinarily high levels of bactericidal effects against a highly virulent and multidrug-resistant Staphylococcus aureus strain (i.e. USA300) with total eradication of both planktonic and adherent bacteria. This strong antibacterial behavior was combined with a significantly enhanced osteogenic behavior, as evidenced by significantly higher levels of alkaline phosphatase (ALP) activity compared with non-biofunctionalized implants. Finally, we discovered synergistic antibacterial behavior between strontium and silver ions, meaning that 4–32 folds lower concentrations of silver ions were required to achieve growth inhibition and total killing of bacteria. The functionality-packed biomaterial presented here demonstrates a unique combination of functionalities that make it an advanced prototype of future orthopedic biomaterials where implants will outlive patients.Biomaterials & Tissue BiomechanicsMechanical, Maritime and Materials Engineerin

In Vivo Prevention of Implant-Associated Infections Caused by Antibiotic-Resistant Bacteria through Biofunctionalization of Additively Manufactured Porous Titanium

Additively manufactured (AM) porous titanium implants may have an increased risk of implant-associated infection (IAI) due to their huge internal surfaces. However, the same surface, when biofunctionalized, can be used to prevent IAI. Here, we used a rat implant infection model to evaluate the biocompatibility and infection prevention performance of AM porous titanium against bioluminescent methicillin-resistant Staphylococcus aureus (MRSA). The specimens were biofunctionalized with Ag nanoparticles (NPs) using plasma electrolytic oxidation (PEO). Infection was initiated using either intramedullary injection in vivo or with in vitro inoculation of the implant prior to implantation. Nontreated (NT) implants were compared with PEO-treated implants with Ag NPs (PT-Ag), without Ag NPs (PT) and infection without an implant. After 7 days, the bacterial load and bone morphological changes were evaluated. When infection was initiated through in vivo injection, the presence of the implant did not enhance the infection, indicating that this technique may not assess the prevention but rather the treatment of IAIs. Following in vitro inoculation, the bacterial load on the implant and in the peri-implant bony tissue was reduced by over 90% for the PT-Ag implants compared to the PT and NT implants. All infected groups had enhanced osteomyelitis scores compared to the noninfected controls.Biomaterials & Tissue Biomechanic

Fighting Antibiotic-Resistant Bacterial Infections by Surface Biofunctionalization of 3D-Printed Porous Titanium Implants with Reduced Graphene Oxide and Silver Nanoparticles

Nanoparticles (NPs) have high multifunctional potential to simultaneously enhance implant osseointegration and prevent infections caused by antibiotic-resistant bacteria. Here, we present the first report on using plasma electrolytic oxidation (PEO) to incorporate different combinations of reduced graphene oxide (rGO) and silver (Ag) NPs on additively manufactured geometrically ordered volume-porous titanium implants. The rGO nanosheets were mainly embedded parallel with the PEO surfaces. However, the formation of ‘nano-knife’ structures (particles embedded perpendicularly to the implant surfaces) was also found around the pores of the PEO layers. Enhanced in vitro antibacterial activity against methicillin-resistant Staphylococcus aureus was observed for the rGO+Ag-containing surfaces compared to the PEO surfaces prepared only with AgNPs. This was caused by a significant improvement in the generation of reactive oxygen species, higher levels of Ag+ release, and the presence of rGO ‘nano-knife’ structures. In addition, the implants developed in this study stimulated the metabolic activity and osteogenic differentiation of MC3T3-E1 preosteoblast cells compared to the PEO surfaces without nanoparticles. Therefore, the PEO titanium surfaces incorporating controlled levels of rGO+Ag nanoparticles have high clinical potential as multifunctional surfaces for 3D-printed orthopaedic implants.Biomaterials & Tissue BiomechanicsTeam Yaiza Gonzalez GarciaBT/Biocatalysi