You can channel arcane energy into your melee weapon, unarmed strike, or natural weapons. As a free action, you can expend one of your prepared spells (or an open spell slot) for the day of 1st-level or higher, and you gain a bonus equal to the level of the spell or spell slot expended to all of your melee attack rolls, as well as bonus damage equal to 1d4 x the level of the spell or spell slot expended for this round. 

You cannot use this feat more than once per round.