Elsevier

Biomaterials

Volume 223, December 2019, 119479
Biomaterials

Remote eradication of biofilm on titanium implant via near-infrared light triggered photothermal/photodynamic therapy strategy

https://doi.org/10.1016/j.biomaterials.2019.119479Get rights and content

Abstract

Biofilm formation is a main challenge in treatment of bone-implant-associated infections, resulting in tolerance to immune system and antibiotics. However, smart non-surgical or non-invasive treatment methods of combating established biofilm on an implant have been less reported. Herein, a therapeutic system consisting of mesoporous polydopamine nanoparticles (MPDA) to combat biofilm is reported for the first time. We develop a synergistic photothermal/photodynamic therapy (PTT/PDT) strategy aiming for biofilms eradication on titanium (Ti) implant, which is integrated with MPDA loading with photosensitizer Indocyanine Green (ICG) by π-π stacking. Specifically, MPDA is functionalized with RGD peptide to endow the modified Ti sample (Ti-M/I/RGD) with good cytocompatibility. More importantly, Ti-M/I/RGD implant remarkably kills Staphylococcus aureus (S. aureus) biofilm with an efficiency of 95.4% in vivo upon near infrared (NIR). After biofilm eradication, implant still displays great performance regarding osteogenesis and osseointegration. Overall, this study provides a PTT/PDT strtategy for the development of antibacterial Ti implants for potential orthpediac application.

Introduction

Clinically, a foreign implant is vulnerable for bacteria infection. Despite treating with peri-operative antibiotics, very few bacteria may lead to implants-associated infection. The activation of neutrophils on the implant surfaces would result in the release of human neutrophil peptides deactivating granulocytes [1,2]. Staphylococcus aureus (S. aureus) is a typical gram-positive microorganism contributing to life-threatening infections worldwide. The S. aureus tend to organize themselves into sticky and multicellular community known as biofilm, which could withstand host immune system, antibiotics and environmental stress [3,4]. In clinic, bone-implant-associated infections are mostly related to bacteria in biofilm, rather than suspending bacteria. Once biofilm forms, second replacement surgery is inevitable [5,6]. So far, many strategies have been dedicated to prevent or destroy biofilm formation on an implant, including anti-adhesive surface [7], incorporation of antibacterial substances [8,9], noble metal nanoparticles [10,11], antimicrobial peptides [12], ZnO nanorods [13], DNAase I and DNase biomimetics [14,15]. During the survival of implants, once above-mentioned antibacterial surface become invalid, bacterial infection may still emerge in some cases. Thus, it is urgent to develop new remotely controllable noninvasive therapies for combating the biofilms that have been established on an implant.

In recent years, the potential application of PTT based on NIR irradiation has gained increasing attention in nanomedicine field, due to its minimal invasiveness, deep tissue penetration and high selectivity [16]. Moreover, PTT has been recognized as a promising antibacterial strategy through local hyperthermia to destroy bacteria integrity or biofilm structure [[17], [18], [19], [20], [21], [22], [23]]. As for antibacterial application of PTT, graphene [18,19], gold nanoparticles [20,21], CuS nanodots [22] and molybdenum disulfide nanosheets [23,24] were developed. Strikingly, mussel-inspired polydopamine (PDA) is emerging as a competitive photothermal agent, owing to its good biocompatibility, high NIR photothermal conversion efficiency and facile functionalization [[25], [26], [27], [28]]. To the best of our knowledge, few attempts of directly utilizing PDA nanoparticles as antibacterial photothermal agent to destroy biofilm in bone-implant-associated infection were reported so far.

Previous studies confirmed that PTT alone to kill bacteria required relatively high local temperature [29,30]. Consequently, hyperthermia would cause tremendous negative effects on surrounding healthy tissues when killing already-formed biofilms. Although healthy tissues could withstand above 50 °C for a long time, the antibacterial efficiency is limited at such temperature [31]. Thus, the combination PTT (moderate temperature around 50 °C) with other antibacterial strategies is essentially urgent to be developed, leading to remarkable effect for combating bacterial infection or established biofilm [19,28,30]. Thus, the combination PTT (moderate temperature around 50 °C) with other antibacterial strategies is essentially urgent to be developed, leading to remarkable effect for combating bacterial infection or established biofilm. Recent study reported that CuS nanodots irradiated by NIR laser exhibited strong lethal effect for drug-resistant pathogens via a combination treatment of PTT with Cu2+ ions [22]. Additionally, antibacterial PDT is another promising modality. Antibacterial PDT is another promising modality. Nanomaterials or photosensitizers are irradiated with NIR or visible light to motivate reactive oxygen species (ROS), which would destroy the integrity of bacteria membranes and cause bacteria death [32,33]. Destruction of membrane integrity of bacteria is an important step to achieve the final bactericidal effect. A previous study confirmed that bacteria-adhesive antibacterial nanoparticles with the intrinsic function of membrane-disruption combined with antibiotics delivery could effectively combat severe bacterial infection [34]. We envisage that, if the cell membrane permeability of S. aureus bacteria in biofilm increased when exposing to ROS, the biofilm scavenging efficiency would remarkably increase at relatively bio-safe temperature (around 50 °C) from PTT. Moreover, except for antibacterial or anti-biofilm, efficient osseointegration for bone implant is also essentially important. Recently, polydopamine (PDA) served as an important bridge to fabricate biofunctional interface on an implant, exhibiting desirable adhesion and biocompatibility [13,30]. Additionally, surface modification of an implant with osteogenic peptides (e.g. RGD) is an effective approach for facilitating specific cell responses (adhesion, proliferation and differentiation) and final osseointegration in vivo [35,36].

Herein, for the first time, we develop a multifunctional hybrid coating on Ti surface that was capable of combating established biofilm by remotely controllable way and improving osteointegration of the Ti implants. MPDA nanoparticles were immobilized onto amino-modified Ti surface to simultaneously act as photothermal material and photosensitizer carrier. Abundant aromatic rings and mesoporous structure in PDA would facilitate substantial loading of Indocyanine Green (ICG) via π-π stacking interaction. Importantly, sufficient dihydroxyindole/indolequinone groups on MPDA surface further facilitate the conjugation of biocompatible RGD peptide via Michael addition reaction or Schiff base reaction. The final sample was named as Ti-M/I/RGD. Scheme 1 presents the elimination process of Ti-M/I/RGD implant for already-established S. aureus biofilm in vivo through PDT/PTT synergistic effect. The hyperthermia firstly improves the ICG diffusion into biofilm. The PDT generated ROS would destroy the bacteria membranes to make them sensitive for moderate hyperthermia. The NIR triggered hyperthermia further accelerates the bacteria death. Thus, we hypothesized that our strategy would effectively eradicate already-formed biofilms and simultaneously improve osseointegration in vivo.

Section snippets

Materials

Commercial pure Ti foils (0.25 mm thick, 99.5% purity) were purchased from Alfa Awsar Co. (Tianjin, China) and Ti rods (1.2 mm of diameter, 10 mm of length) were purchased from Northwest Institute for Non-ferrous Metal Research (Shaanxi, China). 1,3,5-trimethylbenzene (TMB, 97%), tris(hydroxymethyl)aminomethane (TRIS, 99.9%), indocyanine green (ICG), (3-Aminopropyl) trimethoxysilane (APTES) and dopamine hydrochloride were bought from Aladdin Industrial Co. (Shanghai, China). The RGDC peptide

Characterization of MPDA nanoparticles

Firstly, MPDA nanoparticles were prepared by a facile one-pot synthesis method, with stable and high drug loading capacity under physiological environment [25,26,35]. As shown in Fig. 1A, Pluronic F127 and TMB were employed as organic templates in water/ethanol solution. The primary PDA would self-assemble at water/TMB interface via π-π stacking [27,39]. After removal of templates, MPDA nanoparticles were obtained with good dispersity in water. Dopamine monomer in water solution is colorless

Conclusions

In summary, we developed an original strategy for surface modification of Ti implants based on MPDA nanoparticles with RGD peptide immobilization and photosensitizer (ICG) loading. The anti-biofilm ability based on synergistic PDT/PTT effect of Ti-M/I/RGD samples was systematically evaluated with NIR laser irradiation both in vitro and in vivo. Specifically, due to ROS generation from ICG induced the bacterial membrane destruction, S. aureus in biofilm became was sensitive to moderate

Conflicts of interest

The authors declare no competing interests.

Acknowledgements

This work was financially supported by State Key Project of Research and Development (2016YFC1100300 & 2017YFB0702603), National Natural Science Foundation of China (51825302, 21734002 & 51673032), Fundamental Research Funds for the Central Universities (2018CDYJSY0055, 2019CDXYSG0004 & 2018CDXYSW0023), Chongqing Research Program of Technological Innovation and Application Demonstration (cstc2018jscx-msybX0299), Innovation Team in University of Chongqing Municipal Government (CXTDX201601002).

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