Sec. 18. Indebtedness, a bond, or an obligation incurred or created under the authority of this chapter may not be or become a lien, charge, or liability against:
(1) the state of Indiana;
(2) the state educational institution issuing the bonds; or
(3) the property or funds of the state or the state educational institution issuing the bonds, except to the extent of the property or income authorized to be pledged or mortgaged.