ANTIBIOTIC-LOADED HYALURONIC ACID-TYRAMINE HYDROGEL FOR ANNULUS FIBROSUS REPAIR IN MICRODISCECTOMY WITH INFECTED HERNIATED DISCS

Intradiscal Cutibacterium acnes is a risk factor for Modic type 1 changes (MC1) after microdiscectomy. 1 Oral antibiotics (amoxicillin-clavulanate) have shown significant clinical benefits in MC1 patients. 1 Microdiscectomy may enable intradiscal antibiotic application to prevent bacteria-induced disc degeneration and MC1. Our goal is to deliver antibiotics via a hydrogel while improving disc biomechanics and preventing re-herniation. We combine an antibiotic-loaded hyaluronic acid-tyramine hydrogel (HA-Tyr) with annulus fibrosus repair using a mechanically interlocking patch (iPatch). We previously confirmed that HA-Tyr (|G*|=0.76 kPa) did not herniate and improved disc biomechanics (under review). This study tests (i) the effect of antibiotic loading into HA-Tyr on rheological properties and (ii) antibacterial activity against Gram-positive and Gram-negative bacteria. HA-Tyr with previously identified viscosity was loaded with amoxicillin/clavulanate, clindamycin, or doxycycline at a concentration of 0.1, 1.0, and 10.0 mg/ml. These antibiotics were selected for their established use in chronic low back pain, effective disc penetration, and broad-spectrum activity. Rheological properties were evaluated through amplitude sweep tests (n=3/group). Antibacterial activity against Staphylococcus aureus , Escherichia coli , and C. acnes was evaluated using a zone of inhibition test. C. acnes , isolated from symptomatic human discs, was included due to its prevalence in herniated discs, 1 while S. aureus ATCC25923 and E. coli MG1655 represent bacteria with differing antibiotic susceptibility. Loaded hydrogels (n=5/group) were placed on bacteria-inoculated agar plates, and inhibition zone diameters were measured. Group differences were analyzed using ANOVA, with α=0.05. Amoxicillin/clavulanate reduced HA-Tyr storage modulus at 10.0 mg/ml (–77.7%; p=0.013) but not at lower concentrations. Doxycycline reduced storage modulus at 10.0 mg/ml (–98.4%, p=0.001) and 1.0 mg/ml (–71.4%, p=0.006). For clindamycin, structural integrity was maintained across all concentrations (Fig.1). For Gram-positive bacteria ( S. aures and C. acnes ), clindamycin had the largest inhibition zones at all concentrations (Fig.2), while doxycycline was the least effective. For Gram-negative E. coli , amoxicillin/clavulanate and doxycycline were superior to clindamycin. Clindamycin did not alter HA-Tyr viscoelastic properties up to 10 mg/ml, thereby proving the antibiotic better maintaining HA-Tyr hydrogel characteristics. Clindamycin was also the most effective in killing C. acnes and S. aureus , two known disc pathogens. Treating microdiscectomy patients with clindamycin-loaded HA-Tyr combined with iPatch repair may prevent bacteria-caused disc degeneration and MC1, while preventing re-herniation and improving disc biomechanics. Further translational research is both required and ongoing. For any figures or tables, please contact the authors directly.