AM Open Cell porous Ti Structures were investigated for compressive strength, morphology (i.e. pore size, struts size and porosity), and wear resistance with the aim to improve design capability at support of implant manufacturing.

Specimens were manufactured in Ti6Al4V using a SLM machine. Struts sizes had nominal diameters of 200µm or 100µm, pores had nominal diameters of 700µm, 1000µm or 1500µm. These dimensions were applied to three different open-cell geometrical configurations: one with unit-cells based on a regular cubic arrangement (Regular), one with a deformed cubic arrangement (Irregular), and one based on a fully random arrangement (Fully Random).

Morphological analysis was performed by image analysis applied onto optical and SEM acquired pictures. The analyses estimated the maximum and minimum Feret pores diameter, and the latter was used as one of the key parameters to describe the interconnected network of pores intended for bone colonization.

Outcome revealed the systematic oversizing of the actual struts diameter Vs designed diameter; by opposite min. Feret diameters of the pores resulted significantly smaller than nominal pore diameters, thus better fitting within the range of pores dimension acknowledged to favor the osseointegration. Consequently, the actual total porosity is also reduced.

Many technologic factors are responsible for the morphologic differences design vs actual, among these the influence of melting pool dimension, the struts orientation during building and the layer thickness have a significant impact.

Mechanical compression was performed on porous cylinder samples. Test revealed the Yield Strength and Stiffness are highly sensitive to the actual porosity. Deformation behavior follows densification phenomenon at lower porosity, whereas at higher porosity the Gibson-Ashby model fits for most of the structure tested. The relationship among load direction, struts alignment and the collapse behavior of the unit cell geometries are discussed. Stiffness of the porous structure is evaluated in both quasistatic and cyclic compression.

Wear was investigated according to Taber test method. The abrasion resistance is measured by scratching a ceramic wheel against the different AM porous structures along a circular path. Metal debris eventually loss were quantified by gravimetric analysis at different number of cycles. Correlation among AM porous structure geometry, porosity and wear loss is discussed. All the tested structures showed a debris loss within the limit suggested by FDA for the porous coating in contact with the bone tissue.

The actual AM porous Titanium unit cell geometry and features are a key design input. In combination with all the other design factors of a device they may result helpful in address the stress shielding and prevent metal debris release issues. The study underlines the importance of the research activity in AM to support Design for Additive Manufacturing (DFAM) capability.

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Aims: A serious problem in orthopedic surgery is the development of infections. The realization of antibacterial and biocompatible/bioactive surfaces represents a challenge. In this study antibacterial behavior has been conferred to surfaces of glasses and glass-caramics, with different degrees of bioactivity, by the introduction of silver through ion exchange.

Methods: Materials have been studied both in bulk form, and as coatings. All samples have been analyzed by means of XRD, SEM and EDS before and after the treatment. Coatings’ roughness, porosity and adhesion resistance have been also analyzed. In vitro reactivity and silver release were carried out soaking samples in SBF. Samples have been analyzed by means of SEM/ EDS and XRD; silver has been quantified in solution by GFAAS. Cellular tests have been performed in order to evaluate materials biocompatibility before and after the treatment. Antibacterial behavior has been tested against S.Aureus.

Results: Characterization analyses show that glassy or crystalline structure and morphology are maintained after the ion-exchange. As well the coating adhesion resistance is higher then the limit provided by ISO standard for hydroxyapatite coatings. GFAAS analysis determined that silver is gradually released in solution. Cellular tests demonstrate that biocompatibility is generally maintained after treatment but it is closely connected to the amount of silver released. Microbiological tests show antibacterial behavior for silver-doped samples.

Conclusions: Ion-exchange technique permits the introduction of controlled silver amount without modifying materials’ structural and morphological properties. Comparing cellular and microbiological tests it is possible to design process parameters to confer, antibacterial properties but not cytotoxic behavior.

Introduction: A novel device for two-stage septic revision of TKA was checked to evaluate for mechanical and pharmacological properties. Methods: The articulated knee spacer is a temporary device made entirely of gentamicin bone cement industrially preformed and available in 3 sizes. It maintains joint space and motion, allowing partial weight-bearing. It provides an in situ release of antibiotic. Static and dynamic mechanical testing was performed according to ISO/DIN 14243-1. Surface rugosity was assessed according to DIN 4768. Pharmacological behaviour was evaluated according to the European Pharmacopoeia. Results: Static mechanical testing: the device resists a load > 10000N (physiological load peak = 2500N). Dynamic mechanical testing: no breakage after 500.000 cycles at 1300N (half load for physiological knee joint). Wear produced by the PMMA-PMMA coupling is not much higher than wear produced by PE-metal coupling. Surface rugosity (polishing effect) decreases of an order of magnitude after 8 weeks of implantation, and no difference is found between 8 weeks and 5 months of implantation. The in vitro gentamicin release in 7 days is around 2% of the initial amount of antibiotic and ranges from 15 mg (small) and 35 mg (large). Conclusions: The articulated knee spacer has excellent mechanical properties comparable to standard prostheses, which guarantee safety of use for the time of implantation foreseen (up to 6 months). As an ancillary property it delivers locally a high concentration of gentamicin.