Analysis of the Ability of Different Allografts to Act as Carrier Grafts for Local Drug Delivery

Abstract

Bone defects and infections pose significant challenges for treatment, requiring a comprehensive approach for prevention and treatment. Thus, this study sought to evaluate the efficacy of various bone allografts in the absorption and release of antibiotics. A specially designed high-absorbency, high-surface-area carrier graft composed of human demineralized cortical fibers and granulated cancellous bone (fibrous graft) was compared to different human bone allograft types. The groups tested here were three fibrous grafts with rehydration rates of 2.7, 4, and 8 mL/g (F(2.7), F(4), and F(8)); demineralized bone matrix (DBM); cortical granules; mineralized cancellous bone; and demineralized cancellous bone. The absorption capacity of the bone grafts was assessed after rehydration, the duration of absorption varied from 5 to 30 min, and the elution kinetics of gentamicin were determined over 21 days. Furthermore, antimicrobial activity was assessed using a zone of inhibition (ZOI) test with S. aureus. The fibrous grafts exhibited the greatest tissue matrix absorption capacity, while the mineralized cancellous bone revealed the lowest matrix-bound absorption capacity. For F(2.7) and F(4), a greater elution of gentamicin was observed from 4 h and continuously over the first 3 days when compared to the other grafts. Release kinetics were only marginally affected by the varied incubation times. The enhanced absorption capacity of the fibrous grafts resulted in a prolonged antibiotic release and activity. Therefore, fibrous grafts can serve as suitable carrier grafts, as they are able to retain fluids such as antibiotics at their intended destinations, are easy to handle, and allow for a prolonged antibiotic release. Application of these fibrous grafts can enable surgeons to provide longer courses of antibiotic administration for septic orthopedic indications, thus minimizing infections.

Keywords: allograft; antibiotics; bone; grafting material; infection.

Figure 1

Schematic of the gentamicin elution experimental setup. Abbreviation: Abx, antibiotics.

Figure 2

Compact letter display (CLD) graphs portraying pairwise differences between allografts for (A) total fluid absorbed into the matrix and (B) interstitial spaces. Data represented as mean ± SD n = 4–8: 8 for low-density cancellous bone, 4 for high-density cancellous bone and demineralized cancellous bone, and 6 for the other groups. Statistical analysis (Supplementary Table S3) was performed using the ordinary one-way ANOVA with Tukey’s multiple comparisons test (p ≤ 0.05). Significances are displayed using the compact letter display. Groups that do not share the same letter differed significantly from each other. F(2.7) and F(4): fibrous allograft with rehydration ratio of 2.7/4 mL/g; DBM: demineralized bone matrix granules; Cor: cortical granules; Min. Canc: mineralized cancellous bone (low-, med-, high-den = density); Demin. Canc: demineralized cancellous bone.

Figure 3

(A) Gentamicin uptake in different allografts calculated via the mass differences. (B) Quantitative determination of gentamicin after elution from different grafts in μg/mL (n = 3). (C) Inhibition zones of the respective grafts (n = 3). (D) Images of the ZOI tests of the respective grafts at 1 h. Significant differences of F(2.7) and F(4) to Min. Canc are shown by * and to DBM by #. The statistical significances for the other groups are presented in Supplementary Tables S4 and S5. Data are represented as mean ± SD. Statistical analysis was performed using the two-way ANOVA with Tukey’s multiple comparisons test (p ≤ 0.05).

Figure 4

Gentamicin elution from the respective grafts with different incubation times and ZOI test results. (A) Elution of F(2.7) and (B) ZOI test results for F(2.7) with different incubation times. (C) Elution of F(8) and (D) ZOI test results for F(8) with different incubation times. (E) Elution of mineralized cancellous bone and (F) ZOI test results for mineralized cancellous bone with different incubation times (n = 3). Significant differences for the 5 min incubation time group compared to the 30 min group are shown with *. Data are represented as mean ± SD. Statistical analysis was performed using the two-way ANOVA with Tukey’s multiple comparisons test (p ≤ 0.05).