Abstract: A kit for a bioreactor includes a bioreactor bag, a connector, an impeller assembly, and a clamp. The connector defines an aperture. The connector also includes a welding surface extending between a first end and a second end, with the second end including an outwardly extending flange. The welding surface can be heat-sealable to the bioreactor bag. The impeller assembly includes a shaft and a blade configured to pass through the aperture. The impeller assembly includes an impeller flange configured to contact the flange of the connector when the impeller shaft is received in the aperture. The impeller assembly also includes a bearing supporting the impeller shaft. The clamp is configured to secure the connector flange to the impeller assembly. Preparing a bioreactor includes welding the connector to the neck of the bioreactor bag and then inserting the shaft and blade through the aperture into the bioreactor bag.