Controlled drug delivery systems have been utilized to enhance the therapeutic effects of many current drugs by effectively delivering drugs in a time-dependent and repeatable manner. The ability to control the delivery of drugs, whether through sequential, instantaneous, sustained, delayed and/or enhanced release has the potential to provide effective dosing regimens with enhanced therapeutic effects for a plethora of diseases and injuries. For instance, such systems can enhance anti-tumoral responses or, alternatively, promoting tissue regeneration. The current need for organ and tissue replacement, repair and regeneration for patients is continually growing such that supply is not meeting the high demand primarily due to a paucity of donors as well as biocompatibility issues that lead to immune rejection of the transplant. To overcome this problem, scientists working in the field of tissue engineering and regenerative medicine have investigated the use of scaffolds as an alternative to transplantation. These scaffolds are designed to mimic the extracellular matrix (ECM) by providing structural support as well as promoting attachment, proliferation, and differentiation with the goal of yielding functional tissues or organs.
Continued advancement and hybrid approaches using different material combinations and printing methodologies will further advance the progress of 3D printing technologies toward developing scaffolds, and other implantable drug delivery devices, capable of being utilized in the clinic. Such advancements will not only make inroads into improving structural integrity of implantable devices but will also provide platforms for controlled drug delivery from such devices. The primary focus of this thesis will be on controlled drug delivery as well as the integration of controlled drug delivery into 3D printed devices aimed at promoting tissue regeneration.
We initially assessed the efficacy of a controlled drug delivery system for the treatment of cancer using on-demand, and sustained, release of an anticancer drug, doxorubicin (DOX), for the treatment of melanoma in a murine model. Using a melanoma model, we investigated the antitumor potential of combining ultrasound (US) with poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with DOX. An in vitro release assay demonstrated an ability of US to affect the release kinetics of DOX from DOX-loaded PLGA microspheres by inducing a 12% increase in rate of release where this treatment resulted in synergistic tumor cell (B16-F10 melanoma cells) killing. Melanoma-bearing mice treated intratumorally with DOX (8 µg)-loaded microspheres and subjected to US treatment at the tumor site were shown to significantly extended survival compared to untreated mice or mice subjected to either treatment alone. The synergistic increase in survival of melanoma-challenged mice treated with the combination of US and DOX-loaded microspheres implicates a promising additional tool for combatting an otherwise currently incurable cancer.
We then further investigated other novel control drug delivery systems which included a 3D printed device (tube) for the purposes of sequential drug delivery. 3D printed hollow alginate tubes were fabricated through co-axial bioprinting and then injected with PLGA to provide sequential release of distinct fluorescent dyes (model drugs), where fluorescein was initially released from alginate followed by the delayed release (up to 55 h) of rhodamine B in PLGA. With an alginate shell and a PLGA core, the fabricated tubes showed no cytotoxicity when incubated with the human embryonic kidney (HEK293) cell line or bone marrow stromal stem cells (BMSC). Microscale printing through two-photon polymerization (2PP) was then investigated for controlled drug delivery potential. Poly(ethylene glycol) dimethacrylate (PEGDMA) devices were fabricated using a Photonic Professional GT two-photon polymerization system while rhodamine B was homogenously entrapped inside the polymer matrix during photopolymerization. These devices were printed with varying porosity and morphology and using varying printing parameters such as slicing and hatching distance. Overall, tuning the hatching distance, slicing distance, and pore size of the fabricated devices provided control of rhodamine B release due to resulting changes in the motility of the small molecule and its access to structure edges. In general, increased spacing provided higher drug release while smaller spacing resulted in some occlusion, preventing media infiltration and thus resulting in reduced drug release. 2PP was further explored for its ability to tailor topographical cues in addition to controlled drug release. These physical cues, similar to those of the ECM, have been seen to promote differentiation. With 2PP, we explored microscale topographies with nanoscale precision, where different star size topographies were fabricated. It was observed that the smallest star size topographies differentiated human iPSCs towards the endoderm and mesoderm germ layer.
Integrating the facility for controlled drug release into 3D printed devices provides a demand for constructs that not only need to fulfill their purpose of temporarily substituting for the missing tissue at the site of injury, but also providing the necessary cues to promote appropriate tissue regeneration. With 3D printing technology, novel drug delivery constructs were fabricated and tested to appraise functionality such as the ability to control drug delivery and the ability to function as a non-toxic medium for cellular attachment, proliferation, and forced differentiation.