Methods and devices are provided for enhancing mass transport through any fibrous tissue capsule that may form around an implanted medical device following implantation. Methods and devices are also provided to enhance vascularization around the implanted device, which also will aid in mass transport to/from the device. The device preferably comprises multiple reservoirs containing (i) a drug formulation for short- or long-term, controlled drug delivery, (ii) sensors for sensing an analyte in the patient, or (iii) a combination thereof.