Implanted sensors ideally should measure glucose in an extracellular fluid that closely reflects changing concentrations of glucose in plasma; yet fibroblasts, fibrocytes, collagen, and giant cells provide adherent, impermeable, avascular barriers when they encapsulate irregularly-surfaced implants. Thus, sensor design should seek to provide a surface configuration that is without anchoring points for encapsulating cells, a consideration not unlike those posed in developing a nonthrombogenic surface. Examples of well-characterized host responses to various surface configurations are provided to illustrate how surface design features can avoid evoking a barrier of collagen as the host response to the sensor.