LbL-assembled gentamicin delivery system for PMMA bone cements to prolong antimicrobial activity

Abstract

Introduction: Antibiotic-loaded poly(methyl methacrylate) bone cements (ALBCs) are widely used in total joint replacement (TJR), for local delivery of antibiotics to provide prophylaxis against prosthetic joint infections (PJI). One of the shortcomings of the current generation of ALBCs is that the antibiotic release profile is characterized by a burst over the first few hours followed by a sharp decrease in rate for the following several days (often below minimum inhibitory concentration (MIC)), and, finally, exhaustion (after, typically, ~ 20 d). This profile means that the ALBCs provide only short-term antimicrobial action against bacterial strains involved PJI.

Rationale: The purpose of the present study was to develop an improved antibiotic delivery system for an ALBC. This system involved using a layer-by-layer technique to load the antibiotic (gentamicin sulphate) (GEN) on silica nanoparticles, which are then blended with the powder of the cement. Then, the powder was mixed with the liquid of the cement (NP-GEN cement). For controls, two GEN-loaded brands were used (Cemex Genta and Palacos R+G). Gentamicin release and a host of other relevant properties were determined for all the cements studied.

Results: Compared to control cement specimens, improved GEN release, longer antimicrobial activity (against clinically-relevant bacterial strains), and comparable setting time, cytocompatibility, compressive strength (both prior to and after aging in PBS at 37 oC for 30 d), 4-point bend strength and modulus, fracture toughness, and PBS uptake.

Conclusions: NP-GEN cement may have a role in preventing or treating PJI.

Fig 1

Sample rheological test results for Palacos R+G (a), Palacos-NP-GEN (b), Cemex Genta (c) and Cemex-NP-GEN (d).

Fig 2. Summary of the gentamicin release results (n=6±SD).

Fig 3

Summary of the antimicrobial test results (n=6±SD) (a) and expected versus observed antimicrobial activity (b).

Fig 4. Summary of mitochondrial activity of osteoblasts exposed to bone cements assessed through MTT (n=6±SD).

Fig 5. Summary of cytocompatibility test results, assessed through LDH assay: (n=6±SD).

Fig 6. Summary of the cytocompatibility test results, assessed through Alizarin Red assay (n=6±SD).

Fig 7. Summary of the images of the live cells (green color), dead cells (red color), and cell nuclei (blue color).

(Top panels: 100 μm bar, bottom panels: 20 μm bar).

Fig 8. Summary of the images of the actin/dapi filaments (red color) and the cell nuclei (blue color).

(Top panel: 100 μm bar, bottom panel: 20 μm bar).

Fig 9. Summary of compressive strength bone cement bone cements before (grey column) and after aging in PBS, at 37 ºC, for 3 mo (black columns) (n=5±SD).

Fig 10. Summary of the PBS uptake test results for different types of gentamicin containing bone cements after incubation in PBS buffer, pH 7.4 (n=3±SD).