Antibiotic Refilling, Antimicrobial Activity, and Mechanical Strength of PMMA Bone Cement Composites Critically Depend on the Processing Technique

Antibiotic-laden poly(methyl methacrylate) (PMMA) bone cement is used in a variety of applications including temporary spacers for load-bearing arthroplasties and non-load bearing orthopedic revision procedures and antibiotic beads to treat infections. Depending upon the surgical preparation technique, properties of PMMA can widely vary. The primary objective of this work was to perform an in-depth structure-function analysis regarding how processing of PMMA impacted material and structural properties (i.e., porosity) and downstream functional properties (i.e., drug refilling and strength). PMMA with cyclodextrin (CD) microparticles was generated via hand- or vacuum-mixing and characterized for material and structural properties including porosity and internal morphology and functional properties of drug refilling, compressive strength, and antimicrobial activity. CD microparticles were incorporated into PMMA to enable functional refilling properties and to determine new information on drug distribution and distance or depth of PMMA which the refilled drug was able to penetrate. Vacuum-mixing of PMMA resulted in improved mechanical strength and allowed for incorporation of greater amounts of CD microparticles but less homogeneity relative to hand-mixing. Refilling studies showed shallow penetration of the drug into PMMA samples without CD. However, PMMA with CD microparticles showed increased depth of drug penetration, indicating that the drug could be delivered deeper within the device, resulting in more drug being available for delivery and more opportunity for later antibiotic refilling on a patient-specific basis. Knowledge of structure-function relationships can assist and provide valuable information in design and optimization of PMMA-CD for specific loadbearing or non-load-bearing applications.