Since direct exposure of the perfusate to the heating elements could result in the compromise of the said substances due to uneven heating, it is not recommended. Therefore an indirect method must be determined to prevent the possible seperate the perfusate. This involves conducting the heating element's heat through a secondary substance before it can be transferred to the perfusate. For this there are two methods:

Flowing Water
-Reservoir with water jacket: http://www.harvardapparatus.com/webapp/wcs/stores/servlet/product_11051_10001_39621_-1_HAI_ProductDetail___
-Water Circulator: http://www.quorumtech.com/products/water-circulating-heaters-and-chillers/e3500-thermocirculator.html

Flowing Medium
-Water jacket is placed around glass tubing through which medium is flowing at some point along its closed circuit, thus utilizing the already existing medium pump to safely distribute the heat produced by the heating element.

An existing heating system used in an example heart bioreactor relies on a perfusate flowing through a bath of hot water in coiled glass. The team's best option, at this point, is to recreate such a device, using a water circulator to maintain the intermediate's temperature, and then having the perfusate flow through the intermediate substance using a Graham Condenser. Although having a heating element in the coil would be the most efficient option, it would require modification to the existing glassware. Out of ease of use and reliability, a water circulator with built in temperature control will accomplish the same task in a simpler fashion.

Our possible configuration-
Graham Condenser-http://www.sciencelab.com/page/S/PVAR/10568/10-302-13
Water Circulator-http://www.quorumtech.com/products/water-circulating-heaters-and-chillers/e3500-thermocirculator.html