Category: Formulation and Quality
Purpose: Total Joint Replacement (TJR) is predicted to become the number one elective surgery in the USA by 2030, with about 5 million people opting for TJR each year to relieve pain . Infection remains the major cause of revision surgery accounting for up to 25% of all revisions. Many of these infections are related to bacterial biofilm and are caused by Staphylococcus aureus . According to Center for Disease Control (CDC) 99% of pathogenic bacteria may harbor in biofilms. Treating these infections are difficult due to the complex nature of TJR, local long bone environment and presence of biofilm. Biofilm on prostheses may necessitate replacement of the prostheses in several stages of surgery if not treated effectively. Current standard treatment options include high dose systemic antibiotic (4-6 weeks), non-biodegradable antibiotic-releasing PMMA based bone cements and pellets, and surgical debridement etc. Long term systemic antibiotic can cause toxicity and antibacterial resistance. Unfortunately, the local delivery of antibiotic from bone cements do not contain antibiotic active against biofilm. Rifampicin is a good antibiofilm antibiotic, but it is not compatible with bone cement due to its oxidation potential that hinders polymerization of PMMA . Although vancomycin works well against S. aureus, only vancomycin is not effective against S. aureus in biofilms. So, a local implantable Bone Void Filler (BVF) which is putty-like easily press-fitting, biodegradable, provides dual antibiotic delivery may prove to be a better option. It is also important that the BVF provides osseointegration and supports bone growth. Here, we report a biodegradable, osseointegrating, combination antibiotic releasing ABVF putty to treat bacterial biofilm infections after orthopedic surgery.
Methods: ABVF putty was formulated using polymers (PLGA, PEG, PCL), a tri-calcium phosphate and hyaluronic acid substrate (Pro-osteon). Rifampicin and vancomycin were the antibiotics used. The polymers were mixed by hot melt mixing method followed by solid dispersion of antibiotics and substrate in the polymer matrix. After homogeneous mixing the putty was cast in to a 3D printed mold to get desired cylindrical size and shape. To assess the usability of the ABVF putty, the putty was press-fitted into a defect in 3D printed bone. For drug release and dissolution study, the ABVF putty was submerged into 2 mL of Phosphate Buffered Saline (PBS). Samples were collected at different time points until 6 weeks. Zone of Inhibition (ZOI) study was done using Staphylococcus aureus (107 CFU/mL) to assess in vitro antibacterial activity of the released drug. An antibofilm assay was done using the release drug. Biofilm was formed on kirschner wire (k-wire) by using S. aureus. The biofilm containing k-wire was then incubated with released drug. Bacterial colony count was done to assess the antibiofilm activity. A k-wire biofilm infection rodent model was used to assess in vivo efficacy of ABVF. Micro computed tomography (µ-CT), colony count and histology (H&E staining) were done to assess the in vivo experiment outcome.
Results: The ABVF could be easily put into defect in a 3D printed bone and stayed in place. Drug released from ABVF for 6 weeks. The ZOI study showed excellent antibacterial activity (ZOI of 40.35±0.75 mm at day one and 21.71±1.23 mm at week 6) against S. aureus. In the antibiofilm assay, complete eradication of bacterial biofilm was seen. In vitro data correlated with in vivo findings. In vivo study showed complete eradication of bacterial biofilm and infection cure in the treatment group, compared to high bacterial load and infection in control group as was evident by bacterial colony count. µ-CT also confirmed the finding where healed bone was seen in treatment group as opposed to infected and unhealed bone in control group. H&E staining also shown healed bone in treatment group.
Conclusion: ABVF putty was easily moldable and could be press fitted in bone. The released antibiotic shoed efficient antibacterial and antibiofilm property. In vivo study backed up the findings of in vitro study. ABVF was biodegradable and showed osseointegration. Our finding suggests that ABVF putty can be a promising alternative and effective treatment after revision TJR surgery to treat infection and may lead to the possibility of salvaging the implant reducing the number of surgeries leading to better patient outcome and reducing the cost of treatment significantly.