Antibiotics are commonly added to poly(methyl methacrylate) (PMMA) by surgeons to locally treat infections such as in bone cement for joint replacement surgeries, but also as implantable antimicrobial "beads". However, this strategy is of limited value in high risk patients where infections can be recurrent or chronic and otherwise hard to treat. Also when only one drug is incorporated and applied toward poly-microbial infections (multiple bacterial species), there is a high risk that bacteria can develop antibiotic resistance. To combat these limitations, we developed a combination-antibiotic PMMA composite system comprised of rifampicin-filled β cyclodextrin (β-CD) microparticles added into PMMA filled with a second drug. Different formulations were evaluated through Zone-of-Inhibition, drug activity, antibiotic release and refilling, as well as mechanical studies. Our combination-antibiotic PMMA composite system achieved up to an eight-fold increase in duration of antimicrobial activity in comparison to clinically used antibiotic-filled PMMA. Inclusion of CD microparticles also allowed for refilling of additional antibiotics after simulated implantation, resulting in additional windows of therapeutic efficacy. Mechanical testing showed that our tested formulations did have a small, but significant decrease in mechanical properties when compared to unmodified controls. While further studies are needed to determine whether the tested formulations are still suitable for loadbearing applications (e.g. bone cement), our composites are certainly amenable for a variety of non-load bearing applications (e.g. antimicrobial "beads" and temporary spacer in two-stage arthroscopic revisions).

Standard chemotherapy for primary and secondary bone tumors typically involves systemic administration of chemotherapeutic drugs, such as doxorubicin (DOX). However, non-targeted delivery increases dose requirements, and results in off-target toxicity and suboptimal chemotherapeutic efficacy. When chemotherapy is ineffective, substantial resection of tissue and/or total amputation become necessary – a debilitating outcome for any patient. In this work, we developed a proof-of-concept, non-biodegradable, mechanically robust, and refillable composite system for chemotherapeutic (i.e. DOX) delivery comprised of poly(methyl methacrylate) (PMMA) bone cement and insoluble polymeric γ-cyclodextrin (γ-CD) microparticles. The porosity and compressive strength of DOX-filled PMMA composites were characterized. DOX filling capacity, elution kinetics, cytotoxicity against primary osteosarcoma and lung cancer cells, and refilling capacity of composites were evaluated. PMMA composites containing up to 15wt% γ-CD microparticles provided consistent, therapeutically-relevant release of DOX with ~100% of the initial DOX released after 100 days. Over the same period, only ~6% of DOX was liberated from PMMA with free DOX. Following prolonged curing, PMMA composites with up to 15wt% γ-CD surpassed compressive strength requirements outlined by international standards for acrylic bone cements. Compared to DOX-filled PMMA, DOX-filled PMMA/γ-CD composites provided long-term release with decreased burst effect, correlating to long-term cytotoxicity against cancer cells. Refillable properties demonstrated by the PMMA composite system may find utility for treating local recurrences, limiting chemoresistance, and altering drug combinations to provide customized treatment regimens. Overall, findings suggest that PMMA composites have the potential to serve as a platform for the delivery of combinatorial chemotherapeutics to treat bone tumors.