An apparatus (100, 200) comprising: a needle; a positioning device configured to position said needle at a first vertical position in response to control signals; a sealing member having a passage with a first opening at a first end for receiving a tip of said needle, wherein positioning said needle at said first vertical position causes: contact between inner sidewalls of the first opening of said sealing member with surfaces of said tip of said needle, and application of a force against said inner sidewalls of said first opening of said sealing member by surfaces of said tip of said needle causing vertical downward movement of said sealing member toward a spring engaged with said sealing member which, responsive to application of said force, is compressed a distance proportional to said force; a force sensor coupled to the spring, said force sensor measuring said force; and a computing device electrically connected to said force sensor and said positioning device, said computing device configured to receive a signal from said force sensor indicating said force measured by the force sensor, to determine an adjustment to said first vertical position of said needle in accordance with whether said force measured by said force sensor is at a desired force setting, and configured to send control signals to said positioning device causing said positioning device to vertically position said needle in accordance with said adjustment. a needle; a positioning device configured to position said needle at a first vertical position in response to control signals; a sealing member having a passage with a first opening at a first end for receiving a tip of said needle, wherein positioning said needle at said first vertical position causes: contact between inner sidewalls of the first opening of said sealing member with surfaces of said tip of said needle, and application of a force against said inner sidewalls of said first opening of said sealing member by surfaces of said tip of said needle causing vertical downward movement of said sealing member toward a spring engaged with said sealing member which, responsive to application of said force, is compressed a distance proportional to said force; contact between inner sidewalls of the first opening of said sealing member with surfaces of said tip of said needle, and application of a force against said inner sidewalls of said first opening of said sealing member by surfaces of said tip of said needle causing vertical downward movement of said sealing member toward a spring engaged with said sealing member which, responsive to application of said force, is compressed a distance proportional to said force; a force sensor coupled to the spring, said force sensor measuring said force; and a computing device electrically connected to said force sensor and said positioning device, said computing device configured to receive a signal from said force sensor indicating said force measured by the force sensor, to determine an adjustment to said first vertical position of said needle in accordance with whether said force measured by said force sensor is at a desired force setting, and configured to send control signals to said positioning device causing said positioning device to vertically position said needle in accordance with said adjustment.