Acoustic Parameters for Optimal Ultrasound-Triggered Release from Novel Spinal Hardware Devices

Ultrasound-triggered release of vancomycin from a novel spinal device: Antibiotic release and efficacy in vivo

Post-surgical spinal infection occurs in up to 20 % of patients, despite aggressive peri-operative antibiotic treatments. To improve prophylaxis, we have designed and evaluated an ultrasound-activated prophylactic antibiotic release system to combat post-surgical bacterial survival. Polylactic acid (PLA) clips (1 cm3) were 3D-printed with an interior reservoir (0.8 cm3) for carrying drug payload, specifically vancomycin (VAN). Under IACUC approval, clips were surgically implanted into the spines of sheep (n = 9) and swine (n = 2) by removing the spinous process at several levels of the lumbar spine. In the sheep, clips were insonated and the interstitial wound fluid was collected to quantify the ultrasound-triggered VAN release. Uninsonated control sheep exhibited an average VAN concentration of 6.32 ± 5.99 µg/mL after 72 h, while ultrasound-triggered clips released significantly higher VAN concentrations at 72 h (22.98 ± 11.22 µg/mL, p = 0.033). In the swine, device efficacy against Staphylococcus aureus was evaluated. Insonated sites saw significant reduction in colony forming units (CFU) to 4.3 ± 3.2 CFU in the activated clips, compared to uninsonated controls where bacterial colonization was higher (2898 ± 1214 CFU, p = 0.017). Overall, these results demonstrate the ability to non-invasively release VAN from an implanted reservoir in vivo, and that this VAN release is effective in mitigating invading microbes in the wound site.

In Vitro and In Vivo Evaluation of Ultrasound-Triggered Release From Novel Spinal Device

OBJECTIVES

Bacterial infection following spinal fusion is a major clinical concern with up to 20% incidence. An ultrasound-triggered bulk-release system to combat postsurgical bacterial survival was designed and evaluated.

METHODS

Polylactic acid (PLA) clips were loaded with vancomycin (VAN) and microbubbles (Sonazoid, GE HealthCare) in vitro. Stability was determined over 14 days. VAN-loaded clips were submerged in water and insonated using a Logiq E10 scanner (GE HealthCare) with a curvilinear C6 probe. Doppler-induced VAN release was quantified using spectrophotometry. For in vivo testing, clips were loaded with methylene blue (MeB) solution and Sonazoid. These clips were implanted into a rabbit along the spine at L2 and L5, as well as a pig at L1 and L3, then insonated in Doppler mode using the C6 probe.

RESULTS

Sonazoid microbubbles were better preserved when incubated in VAN compared with distilled water at 4°C, 25°C, and 37°C incubation temperatures (P = .0131). Contrast enhancement was observed from both solutions when incubated at 4°C storage conditions. Insonated clips achieved average cumulative VAN release of 101.8 ± 2.8% (81.4 ± 2.8 mg) after 72 hours. Uninsonated clips had only 0.3 ± 0.1% (0.3 ± 0.1 mg) average cumulative VAN release (P < .0001). Clips retrieved from the rabbit did not rupture with insonation nor produce MeB staining of surrounding tissues. In the pig, the PLA film was visibly ruptured and MeB tissue was observed following insonation, whereas the uninsonated clip was intact.

CONCLUSION

These results demonstrate ultrasound-triggered release of an encapsulated prophylactic solution and provide an important proof-of-concept for continuing large animal evaluations for translational merit.

Making waves: how ultrasound-targeted drug delivery is changing pharmaceutical approaches

Administration of drugs through oral and intravenous routes is a mainstay of modern medicine, but this approach suffers from limitations associated with off-target side effects and narrow therapeutic windows. It is often apparent that a controlled delivery of drugs, either localized to a specific site or during a specific time, can increase efficacy and bypass problems with systemic toxicity and insufficient local availability. To overcome some of these issues, local delivery systems have been devised, but most are still restricted in terms of elution kinetics, duration, and temporal control. Ultrasound-targeted drug delivery offers a powerful approach to increase delivery, therapeutic efficacy, and temporal release of drugs ranging from chemotherapeutics to antibiotics. The use of ultrasound can focus on increasing tissue sensitivity to the drug or actually be a critical component of the drug delivery. The high spatial and temporal resolution of ultrasound enables precise location, targeting, and timing of drug delivery and tissue sensitization. Thus, this noninvasive, non-ionizing, and relatively inexpensive modality makes the implementation of ultrasound-mediated drug delivery a powerful method that can be readily translated into the clinical arena. This review covers key concepts and areas applied in the design of different ultrasound-mediated drug delivery systems across a variety of clinical applications.

Accelerated Neutral Atom Beam (ANAB) Modified Poly-Ether-Ether-Ketone for Increasing In Vitro Bone Cell Functions and Reducing Bacteria Colonization Without Drugs or Antibiotics

Poly-ether-ether-ketone (PEEK) has become the spinal implant material of choice due to its radiolucency, low elastic modulus, manufacturability, and mechanical durability. However, studies have highlighted less that optimal cytocompatibility properties of conventional PEEK leading to decreased bone growth and/or extensive bacteria infection. In order to improve the surface properties of PEEK for orthopedic applications, here, Accelerated Neutral Atom Beam (ANAB) technology was used to modify PEEK and such samples were tested In Vitro for osteoblast (bone-forming cell) functions and bacterial colonization. Results showed significantly improved osteoblast responses (such as deposition of calcium containing mineral as well as alkaline phosphatase, osteocalcin, osteopontin, and osteonectin synthesis) on ANAB modified PEEK compared to controls due to optimized surface energy from nanostructured features and greater exposure of PEEK chemistry. ANAB treatment enhanced protein absorption (specifically, mucin, casein, and lubricin) to the PEEK surface and consequently significantly reduced bacterial (including methicillin resistant Staph. aureus (or MRSA), E. coli, and Staph. epidermidis) colonization. Collectively, this study introduces ANAB treated PEEK as a novel material that should be further studied for a wide range of improved orthopedic applications.

Structure, properties, and bioactivity of 3D printed PAEKs for implant applications: A systematic review

Additive manufacturing (AM) of high temperature polymers, specifically polyaryletherketones (PAEK), is gaining significant attention for medical implant applications. As 3D printing systems evolve toward point of care manufacturing, research on this topic continues to expand. Specific regulatory guidance is being developed for the safe management of 3D printing systems in a hospital environment. PAEK implants can benefit from many advantages of AM such as design freedom, material and antibacterial drug incorporation, and enhanced bioactivity provided by cancellous bone-like porous designs. In addition to AM PAEK bioactivity, the biomechanical strength of 3D printed implants is crucial to their performance and thus widely studied. In this review, we discuss the printing conditions that have been investigated so far for additively manufactured PAEK implant applications. The effect of processing parameters on the biomechanical strength of implants is summarized, and the bioactivity of PAEKs, along with material and drug incorporation, is also covered in detail. Finally, the therapeutic areas in which 3D printed PAEK implants are investigated and utilized are reviewed.