Establishment of an in vivo rat model for chronic musculoskeletal implant infection

The Effect of 3-Dimensional-Printed Sequential Dual Drug-Releasing Patch on the Capsule Formation Around the Silicone Implant in a Rat Model

BACKGROUND

Implant-based breast reconstruction is associated with increased risk of early infection and late-stage capsular contracture.

OBJECTIVES

We evaluated the feasibility of a dual drug-releasing patch that enabled the controlled delivery of antibiotics and immunosuppressants in a temporally and spatially appropriate manner to the implant site.

METHODS

The efficacy of a dual drug-releasing patch, which was 3-dimensional-printed (3D-printed) with tissue-derived biomaterial ink, was evaluated in rats with silicone implants. The groups included implant only (n = 10); implant plus bacterial inoculation (n = 14); implant, bacterial inoculation, and patch loaded with gentamycin placed on the ventral side of the implant (n = 10), and implant, bacterial inoculation, and patch loaded with gentamycin and triamcinolone acetonide (n = 9). Histologic and immunohistochemical analyses were performed 8 weeks after implantation.

RESULTS

The 2 drugs were sequentially released from the dual drug-releasing patch and exhibited different release profiles. Compared to the animals with bacterial inoculation, those with the antibiotic-only and the dual drug-releasing patch exhibited thinner capsules and lower myofibroblast activity and inflammation, indicating better tissue integration and less foreign body response. These effects were more pronounced with the dual drug-releasing patch than with the antibiotic-only patch.

CONCLUSIONS

The 3D-printed dual drug-releasing patch effectively reduced inflammation and capsule formation in a rat model of silicone breast reconstruction. The beneficial effect of the dual drug-releasing patch was better than that of the antibiotic-only patch, indicating its therapeutic potential as a novel approach to preventing capsular contracture while reducing concerns of systemic side effects.

Novel Peptides Targeting the β-Clamp Rapidly Kill Planktonic and Biofilm Staphylococcus epidermidis Both in vitro and in vivo

Antimicrobial resistance is an increasing threat to global health and challenges the way we treat infections. Peptides containing the PCNA interacting motif APIM (APIM-peptides) were recently shown to bind to the bacterial PCNA homolog, the beta (β)-clamp, and to have both antibacterial and anti-mutagenic activities. In this study we explore the antibacterial effects of these peptides on Staphylococcus epidermidis, a bacterial species commonly found in prosthetic joint infections (PJI). Drug-resistant bacterial isolates from PJIs often lead to difficult-to-treat chronic infections. We show that APIM-peptides have a rapid bactericidal effect which when used at sublethal levels also increase the efficacy of gentamicin. In addition, APIM-peptides reduce development and eliminate already existing S. epidermidis biofilm. To study the potential use of APIM-peptides to prevent PJI, we used an in vivo bone graft model in rats where APIM-peptide, gentamicin, or a combination of the two was added to cement. The bone grafts containing cement with the combination was more effective than cement containing only gentamicin, which is the current standard of care. In summary, these results suggest that APIM-peptides can be a promising new drug candidate for anti-infective implant materials to use in the fight against resistant bacteria and chronic PJI.

A new sequential animal model for infection-related non-unions with segmental bone defect

BACKGROUND

The treatment of fracture-related infections (FRI) is still a challenge for orthopedic surgeons. The prevalence of FRI is particularly high in open fractures with extensive soft-tissue damage. This study aimed to develop a new two-step animal model for non-unions with segmental bone defects, which could be used to evaluate new innovative bone substitutes to improve the therapeutic options in humans with FRI and bone defects.

METHODS

After randomization to infected or non-infected groups, 30 Sprague-Dawley rats underwent a transverse osteotomy of the mid-shaft femur with a 5 mm defect. Additionally, the periosteum at the fracture zone was cauterized at both sides. After intramedullary inoculation with 10³ CFU Staphylococcus aureus (infected group) or PBS (non-infected group), a fracture stabilization was done by intramedullary K-wires. After 5 weeks, the bone healing process was evaluated, and revision surgery was performed in order to obtain increased bone healing. The initial K-wires were removed, and debridement of the osteotomy-gap was done followed by a more stable re-osteosynthesis with an angle-stable plate. After further 8 weeks all rats were euthanized and the bone consolidation was tested biomechanically and the callus formation quantitatively by micro-CT analysis.

RESULTS

We developed and presented a new two-stage non-union animal model through a targeted S. aureus infection. After 5 weeks, all animals showed a non-union irrespective of assignment to the infected and non-infected group. Lane and Sandhu score showed a higher callus formation in the infected group. In all infected animals, the inoculated S. aureus strain was detected in the revision surgery. The second surgery did not improve bone healing, as shown by the Lane Sandhu score and in the μ-CT analysis. Similarly, biomechanical testing showed in both groups a significantly lower maximum torque as compared to the contralateral side (p < 0.0001).

CONCLUSIONS

We were able to successfully develop a new two-stage non-union animal model, which reflects a genuine clinical situation of an infection-related non-union model with segmental bone defects. This model could be used to evaluate various therapeutic anti-infectious and osteoinductive strategies in FRIs.