Due to their unique physical and chemical properties, hydrogels have attracted significant attention in several medical fields, specifically, drug delivery applications in which gel-based nanocarriers deliver drug molecules to the region of interest in biological organs. For different drug delivery applications, hydrogel systems can be manipulated to provide passive and/or active delivery. Thus, several drug targeting, loading, and releasing mechanisms have been devised and reported in the literature. This chapter discusses these mechanisms and their efficacy with respect to different drug delivery applications. Furthermore, the drug dosage is dependent on the design and shape of the hydrogel systems, which in turn depend on the route of the drug administration. This chapter covers the types of hydrogel-based products applied via different routes of drug administration. Lastly, this chapter addresses different classifications of delivered drugs including small molecular weight drugs; therapeutic proteins and peptides; and vaccines.
Purpose
Tether breakage was reported as the most common complication of vertebral body tethering. However, as the literature suggests the physiological loads do not have the potential to cause the failure of the tether. Currently, the biomechanical reason behind the tether breakage is unknown. The current study aims to elucidate the effects of the tension forces on the failure mechanisms of the VBT and provide mechanical justification for how it can be identified radiographically.
Methods
Tensile tests (20%/min strain rate) were performed on single-unit VBT samples. Failure modes and mechanical characteristics were reported.
Results
The failure took place prematurely due to the slippage of the tether at the screw–tether junction where the tether is damaged significantly by the locking cap. Slippage was initiated at 10–13% tensile strain level where the tensile stress and tension force were 50.4 ± 1.5 MPa and 582.2 ± 30.8 N, respectively.
Conclusion
The failure occurs because of high-stress concentrations generated within the locking region which damages the tether surface and leads to the slippage of the tether. We observed that the loads leading to failure are within the physiological limits and may indicate the high likelihood of the tether breakage. The failure mode observed in our study is shown to be the dominant failure mode, and a design improvement on the gripping mechanism is suggested to avoid failure at the screw–tether junction. We observed that the tether elongates 10–13% prior to the breakage, which can be employed as a diagnostic criterion to screen for tether breakages radiographically.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.