Abstract
Tissue regeneration-promoting and drug-eluting biomaterials are commonly implanted into animals as a part of late-stage testing before committing to human trials required by the government. Because the trials are very expensive (e.g., they can cost over a billion U.S. dollars), it is critical for companies to have the best possible characterization of the materials' safety and efficacy before it goes into a human. However, the conventional approaches to biomaterial evaluation necessitate sacrificial analysis (i.e., euthanizing a different animal for measuring each time point and retrieving the implant for histological analysis), due to the inability to monitor how the host tissues respond to the presence of the material in situ. This is expensive, inaccurate, discontinuous, and unethical. In contrast, our manuscript presents a novel microfluidic platform potentially capable of performing non-disruptive fluid manipulations within the spatial constraints of an 8 mm diameter critical calvarial defect-a "gold standard" model for testing engineered bone tissue scaffolds in living animals. In particular, here, addressable microfluidic plumbing is specifically adapted for the in vivo implantation into a simulated rat's skull, and is integrated with a combinatorial multiplexer for a better scaling of many time points and/or biological signal measurements. The collected samples (modeled as food dyes for proof of concept) are then transported, stored, and analyzed ex vivo, which adds previously-unavailable ease and flexibility. Furthermore, care is taken to maintain a fluid equilibrium in the simulated animal's head during the sampling to avoid damage to the host and to the implant. Ultimately, future implantation protocols and technology improvements are envisioned toward the end of the manuscript. Although the bone tissue engineering application was chosen as a proof of concept, with further work, the technology is potentially versatile enough for other in vivo sampling applications. Hence, the successful outcomes of its advancement should benefit companies developing, testing, and producing vaccines and drugs by accelerating the translation of advanced cell culturing tech to the clinical market. Moreover, the nondestructive monitoring of the in vivo environment can lower animal experiment costs and provide data-gathering continuity superior to the conventional destructive analysis. Lastly, the reduction of sacrifices stemming from the use of this technology would make future animal experiments more ethical.