The airplane collided with a berm following a loss of directional control while landing on Runway 13 at the Eastern Iowa Airport, in Cedar Rapids, Iowa, at 1315 Central time. No one among the ATP-rated captain, Commercial-rated co-pilot, or two medical crew members was injured. The aeromedical positioning flight was being conducted in VMC; an IFR flight plan had been filed with an intended destination of McAllen, Texas. Both pilots later reported what they thought were rough spots on the runway during the takeoff roll. After raising the landing gear the crew noticed an unsafe gear indication for the nose gear. The flight leveled off at 5000 feet and recycled the landing gear at least four times to no avail. The crew then requested a landing back at the departure airport and observed a down-and-locked indication for all three landing gear during the visual approach. After the nose wheel touched down, the airplane made a sharp left turn off the side of the runway and contacted a four-foot high berm. Post-accident inspection revealed a nose-gear strut seal had blown, preventing the nose gear from centering.