Elsevier

Biomaterials

Volume 25, Issue 18, August 2004, Pages 4383-4391
Biomaterials

An in vitro assessment of the antibacterial properties and cytotoxicity of nanoparticulate silver bone cement

Abstract

Infections with multiresistant bacteria have become a serious problem in joint arthroplasty. This study reports about in vitro antibacterial activity against multiresistant bacteria and in vitro cytotoxicity of polymethylmetacrylate bone cement loaded with metallic silver particles with a size of 5–50 nm called NanoSilver.

In vitro antibacterial activity against S. epidermidis, methicillin-resistant S. epidermidis (MRSE), and methicillin-resistant S. aureus (MRSA) was studied by microplate proliferation tests. Quantitative elution testing and qualitative ongrowth of human osteoblasts was done to study in vitro cytotoxicity.

Only NanoSilver cement showed high-antibacterial activity against all strains, including MRSE and MRSA. Gentamicin cement was not effective against MRSA and MRSE due to the high-level gentamicin resistance of the tested strains. Plain cement did not inhibit proliferation of any strains. There was no significant difference regarding in vitro cytotoxicty between NanoSilver and the non-toxic control.

Cytotoxicity of cement loaded with silver salts made this kind of silver unsuitable for all day clinical use in the past. This new form of silver called NanoSilver was free of in vitro cytotoxicity and showed high effectiveness against multiresistant bacteria. If the results can be confirmed in vivo NanoSilver may have a high interest in joint arthroplasty.

Introduction

Bone cement based on polymethylmetacrylate (PMMA) is golden standard for the anchoring of artificial joints [1]. Like all biomaterials PMMA has an elevated risk of infection when implanted into the human body compared to autogenous vital tissue [2]. Therefore, the loading of PMMA with antibiotics to reduce infection rate has been postulated in the literature [3], [4], [5], [6]. Despite of strict antiseptic operative procedure including systemic antibiotic prophylaxis and special enclosure using laminar flow the infection rates range from 1% to 3% in total joint procedures [7], [8].

Buchholz and Engelbrecht [3] were the first to load bone cement with antibiotics to reduce infection rates in arthroplasty. The first significant reduction of infection rate by the use of gentamicin loaded bone cement compared to plain PMMA cement was reported by Thierse [5]. Wannske and Tscherne [6] confirmed significant difference in antimicrobial activity between antibiotic-loaded and plain PMMA cement in a prospective study. Josefsson et al. [9] and Espehaug et al. [10] contradicted these observations due to the results in their own studies. However, antibiotic loaded bone cements are widely used nowadays [11]. The increasing number and percentage of total joint infections with multiresistant bacteria [12] makes an adequate prophylaxis against these organisms necessary which cannot be achieved by standard antibiotic bone cements.

The broad antimicrobial effect of silver is well known and it has been used in different fields in medicine since years, e.g. as Credé's prophylaxis for ophthalmia neonatorum [13], in wound healing [14], [15], [16], [17] or in biomaterials [18], [19], [20]. Relevant clinical cytotoxicity of silver has also been reported [21], [22], [23], [24], [25], [26], [27], [28], [29].

The purpose of this study was to evaluate bone cement loaded with a new form of silver consisting of metallic silver particles with a size of 5–50 nm called NanoSilver. Antibacterial activity against S. epidermidis, MRSE and MRSA of bone cement loaded with NanoSilver was studied in vitro.

Furthermore, in vitro cytotoxicity of NanoSilver bone cement was assessed by both quantitative and qualitative methods.

Section snippets

Nanosilver

The term “NanoSilver” refers to the nanoparticulate size of the silver particles of 5–50 nm (Fig. 1). The active surface of NanoSilver is 4 m2/g compared to 1–2 m2/g of commercial silver powder. The NanoSilver particles form aggregates of 2–5 μm. The porosity of NanoSilver is 85–95% compared to 0% in commercial silver powder.

Bone cement

Plain polymethylmetacrylate (PMMA) bone cement (Coripharm, Dieburg, Germany) was loaded with 0.1%, 0.5% or 1.0% of NanoSilver. The concentration of silver refers to the weight

S. epidermidis EDCC 5245 (Fig. 3)

Plain PMMA cement could not inhibit proliferation of S. epidermidis EDCC 5245, whereas gentamicin-loaded bone cement led to complete inhibition of bacterial proliferation. There was a dose dependent-effect of NanoSilver bone cement. The higher the concentration of NanoSilver, the higher was the antibacterial effect of the NanoSilver bone cement. Cement with a concentration of 1% of NanoSilver completely inhibited the proliferation of S. epidermidis EDCC 5245 and showed the same result as

Discussion

Antibacterial materials for loading of bone cements have to fulfil several major preconditions. Firstly, they have to be effective in reducing infection rates in total joint arthroplasty. Secondly, biomaterials must not have intolerable cytotoxic effects in the human body. Furthermore, facing increasing problems with multiresistant nosocomial infections, any antimicrobial bone cement should try to minimize the risk of resistance spreading. The following discussion will focus on these major

Conclusion

NanoSilver bone cement completely inhibited the proliferation of S. epidermidis EDCC 5245, MRSE EDCC 5130, and MRSA EDCC 5246 in the absence of in vitro cytotoxicity. If these results can be confirmed in vivo NanoSilver may have a high interest in total joint arthroplasty particularly due to its effect against multiresistant bacteria that cannot be achieved by gentamicin-loaded bone cement.

Acknowledgements

In vitro cytotoxicity testing was done in cooperation with Dr. Scheddin, CYTOX, 91052 Erlangen, Germany.

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