Evaluation of silver-titanium implants activated by low intensity direct current for orthopedic infection control: Anin vitroandin vivostudy

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.

Functionalization of 3D-printed titanium alloy orthopedic implants: a literature review

Titanium alloy orthopedic implants produced by 3D printing combine the dual advantages of having a complex structure that cannot be manufactured by traditional techniques and the excellent physical and chemical properties of titanium and its alloys; they have been widely used in the field of orthopedics in recent years. The inherent porous structure of 3D-printed implants and the original modification processes for titanium alloys provide conditions for the functionalization of implants. To meet the needs of orthopedic surgeons and patients, functionalized implants with long-term stability and anti-infection or anti-tumor properties have been developed. The various methods of functionalization deserve to be summarized, compared and analyzed. Therefore, in this review, we will collect and discuss existing knowledge on the functionalization of 3D-printed titanium alloy orthopedic implants.

Different activation of monocyte-derived macrophages by antimicrobial peptides at a titanium tibial implantation in rabbits

The aim of our study was to assess the functional and morphological features of monocyte derived Mfs from rabbits with titanium (Ti) tibial implants, their ability to polarize towards M1 or M2 and their reactivity after stimulation with neutrophil antimicrobial peptides extract (AMP). The study was conducted on six White New Zealand rabbits with tibial implants of pure titanium Grade 2. Blood was taken before implantation and 14days after biomaterial implantation. Then, blood-derived Mfs were cultured and their function was assessed on the basis of morphological changes, generation of nitric oxide (NO), superoxide, and proteases release after treatment with LPS or dexamethasone (Dex). As a result of polarization we specified two subpopulations of Mfs with features characteristic of each subtype. M1 stimulated with LPS exhibited an increased NO and superoxide level, and M2 stimulated with Dex which showed higher arginase and lower free radical generation. Addition of AMP evoked further changes in Mfs morphology and function. After 24h stimulation with AMP an increase of NO was observed in all cultures, whereas after 48h it decreased. Production of superoxide lowered, especially after 48h, when M1 generated 6.00±0.2nM and M1/AMP culture generated 5.2±0.1nM of superoxide. Our study revealed that activated Mfs stimulated with AMP demonstrated both pro- and anti-inflammatory features. Moreover, we did not detect significant differences between the response of Mfs cultured from blood derived monocytes before and after implantation of Ti implants.

Evaluation of calcium dihydroxide- and silver-coated implants in the rat tibia

BACKGROUND

Silver ions (Ag+) have strong antibacterial effects, and silver-coated materials are in widespread clinical use. However, the application of silver-coated medical devices is not without concerns: its use with direct bone contact is not established, and systemic toxic side effects of released Ag+ have been described. Therefore, alternative bactericidal coatings with a more localized way of acting - e.g., calcium dihydroxide, Ca(OH)2 (CH) - would be advantageous.

METHODS

A new rat model of the animal's tibial metaphysis was developed. In the left proximal tibiae of 36 male Wistar rats, titanium screws were implanted. The screws were coated with hydroxyapatite (HA; 12 animals: group I), low-dosed HA silver (HA-Ag; 12 animals: group II) and CH (12 animals: group III). After 6 weeks, all rats were sacrificed. The implants were evaluated for morphological changes on their surfaces, by light microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy; for osteointegration, by measurement of resistance to removal; and for bacterial colonization, by quantitative culture analysis. Additionally, the tibial bone was investigated histologically for signs of osteomyelitis and sonicated to detect bacterial loads.

RESULTS

(i) No microbiological or histological signs of infection could be determined on any of the screws or the surrounding bone. (ii) The bone-implant interface analysis revealed extensive bone formation and direct bone-implant contact on all HA, HA-Ag and HA-CH coated screws. (iii) HA and HA-Ag were partially, and CH was fully, degraded on the screw coating, allowing host bone to osteointegrate.

A new model of implant-related osteomyelitis in the metaphysis of rat tibiae

Background

Animal models serve as an important tool to understand peri-implant infection. Most of the models use high bacterial loads (>10⁴ colony forming units, CFU) to provide high infection rates. Therefore these animals evolve rather similarly, making comparison between groups and statistical analysis possible. On the other hand, to mimic clinical constellation of surgery-related infections the use of low amounts of bacteria would be more advantageous.

Methods

We developed a metaphyseal rat model of peri-implant bone infection with low amount of bacterial loads (10² and 10³ CFU of Staphylococcus aureus) and investigated osseointegration of the implants coated with hydroxyapatite (HA) and low-dosed HA-silver (HA-Ag). Non-infected implants served as controls. After 6 weeks rats were sacrificed and implants evaluated for osseointegration and infection.

Results

Infection of implanted devices was reliably induced, independently whether 10² or 10³ CFU of S. aureus were inoculated and HA or HA-Ag coated implants were used. No systemic infection was present in any of the animals at the time of sacrifice, and no animal developed acute infection requiring premature sacrifice. All CFU counts of the implant and the bone at sacrifice were significantly higher than the inoculated load (p < .05). All sterilely inserted implants showed excellent osseointegration and no infection.

Conclusions

Our present study of a rat tibia model reliably induced osteomyelitis in the metaphysis with low-doses of bacteria. The addition of low-dosed Ag to the implant coating was not able to reduce the infection rates. The results demonstrate that it is possible to develop a model of implant-related osteomyelitis in rats with low amounts of bacteria to better mimic clinical constellations. No other promoters of infection besides insertion of the screw implant were used in this model.