Current in vivo models for testing biomaterials are time and labor intensive as well as expensive. This article describes a new approach for testing biomaterials in vivo using the chorioallantoic membrane (CAM) of the developing chicken embryo, as an alternative to the traditional mammalian models. Fertilized chicken eggs were incubated for 4 days, at which time a small window was cut in the shell of the egg. After 1 week of incubation, the CAM received several test materials, including the endotoxin LPS, a cotton thread and a Silastic tubing. One day and 1 week later, the tissue response to the test materials was assessed using gross, histological, and scanning electron microscope evaluations. The inflammatory response of the chorioallantoic membrane to biomaterials was fully characterized and found to be similar to that of the mammalian response and was also seen to vary according to test materials. We also found that the structure and geometry of the test materials greatly influenced the incorporation of the samples in the CAM. The similarity of the tissue response of the CAM with the mammalian models, plus the low cost, simplicity, and possibility to continuously visualize the test site through the shell window make this animal model particularly attractive for the rapid in vivo screening of biomaterials.

Nafion™ is the membrane material preferred for in situ glucose sensors. Unfortunately, surface properties of Nafion promote random protein adsorption and eventual foreign body encapsulation thus leading to loss if glucose signal over time. Here we detail surface modifications made by RF plasma deposition to Nafion with the intent to prevent random protein adsorption while providing enough functional sites (hydroxyl groups) to bind a biologically active peptide known to induce cellular adhesion (YRGDS). Nafion surfaces were modified by RF plasma polymerizing five different combinations of (1) tetraethylene glycol dimethyl ether (tetraglyme) and (2) 2-hydroxyethyl methacrylate (HEMA): pure tetraglyme, 2.5% HEMA/97.5% tetraglyme; 5% HEMA/95% tetraglyme, 10% HEMA/90% tetraglyme; and pure HEMA. Resultant surfaces were characterized by XPS (low and high resolution), dynamic contact angle, and atomic force microscopy. Protein adsorption and retention was determined and correlated to surface layer composition. The ability to bind a cell adhesion peptide was also determined and correlated well with surface layer composition.

The presence of glucose in vitro and in vivo led to the production of H2O2, suggesting this to be the main agent responsible for enzyme degradation. The use of a Nafion coating did not provide any additional protection.

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A major problem with implantable sensors is their short in vivo lifetime, due to strong tissue reactions (i.e., inflammation and fibrosis) caused by the implant and the failure of sensor components. The tissue reactions to the sensor, the biocompatibility of components, and the function of the sensor must be evaluated by using in vivo models. Current methods of in vivo biosensor testing are time- and labor- intensive and expensive. In addition, the results often vary on the basis of the surgical skills of the investigator. The in ova chorioallantoic membrane (CAM) of the developing chicken embryo was previously developed in our laboratory as a novel in vivo system to test biomaterials. In this new article, we describe a novel approach for testing biosensors in vivo using the ex ova CAM model as an alternative to the traditional mammalian models. Fertilized chicken eggs were incubated for 3 days in ova and then transferred into a petri dish (ex ova) for further incubation at 37 degrees C and 80% humidity. After 1 week of incubation, acetaminophen biosensors, used as model sensors, were placed on top of the CAM and allowed to incorporate for 1 week. Biosensors were then tested for their sensitivity to acetaminophen. CAM venules were injected with 0.2 mL of a 3.6 mM acetaminophen solution. The current produced by the sensor reflected the change in blood acetaminophen levels. Sensors were also assessed by using gross and histological evaluations. We previously reported on the similarity of the tissue response of the CAM with the mammalian models. The low cost, simplicity, and possibility to continuously visualize the sensor test site through a cell culture dish make this animal model particularly attractive for the rapid in vivo screening of biosensors.