Biodegradable coronary artery stents are soughtafter alternatives to permanent stents. These devices are designed to degrade after the blood vessel heals, leaving behind a regenerated artery. The original generation of clinically available biodegradable stents required significantly thicker struts (∼150 μm) than nondegradable ones to ensure sufficient mechanical strength. However, these thicker struts proved to be a key contributor to the clinical failure of the stents. A current challenge lies in the fabrication of stents that possess both thin struts and adequate mechanical strength. In this contribution, we describe a method for the bottom-up, additive manufacturing of biodegradable composite stents with ultrathin fibers and superior mechanical properties compared to the base polymer. Specifically, we illustrate that melt electrowriting (MEW) can be used to 3D print composite structures with thin struts (60−80 μm) and a high degree of geometric complexity required for stenting applications. Additionally, this technology allows additive manufacture of personalized stents that are customized to a patient's unique anatomy and disease state. Furthermore, we illustrate that polycaprolactone-reduced graphene oxide nanocomposites have superior mechanical properties compared to original polycaprolactone without detriment to the material's cytocompatibility and that customizable stent-like structures can be fabricated from these materials with struts as thin as 60 μm, well below the target value for clinical use of 80 μm.
The delivery of hydrophilic drugs from hydrophobic polymers is a long-standing challenge in the biomaterials field due to the limited solubility of the therapeutic agent within the polymer matrix. In this work, we develop a drug delivery mechanism that enables the impregnation and subsequent elution of hydrophilic drugs from a hydrophobic polymer material. This was achieved by synthesizing core cross-linked star polymer amphiphiles with hydrophilic cores and hydrophobic coronas. While significant work has been done to create nanocarriers for hydrophilic drugs, this work is distinct from previous work in that it designs amphiphilic and core cross-linked particles for controlled release from hydrophobic matrices. Ultraviolet-mediated atom transfer radical polymerization was used to synthesize the poly(ethylene glycol) (PEG)-based hydrophilic cores of the star polymers, and hydrophobic coronas of poly(caprolactone) (PCL) were then built onto the stars using ring-opening polymerization. We illustrated the cytocompatibility of PCL loaded with these star polymers through human endothelial cell adhesion and proliferation for up to 7 days, with star loadings of up to 40 wt %. We demonstrated successful loading of the hydrophilic drug heparin into the star polymer core, achieving a loading efficiency and content of 50 and 5%, respectively. Finally, the heparin-loaded star polymers were incorporated into a PCL matrix and sustained release of heparin was illustrated for over 40 days. These results support the use of core cross-linked star polymer amphiphiles for the delivery of hydrophilic drugs from hydrophobic polymer matrices. These materials were developed for application as drug-eluting and biodegradable coronary artery stents, but this flexible drug delivery platform could have impact in a broad range of medical applications.
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