The 助動詞（じょどうし） (auxiliary verbs) せる and させる will be modified in 関西弁（かんさいべん）, creating a new form that interacts with the 未然形（みぜんけい） (indeterminate form) of verbs. In the case of う - Verbs, this is the form that interacts with ない, not the form that interacts with う. In standard Japanese, the せる and させる forms are referred to as ‘causative’ (someone/thing is made to perform an action). This meaning stays the same in the Kansai dialect.
The kansai form of せる will be す (with う - Verbs), while させる will become さす (with る - Verbs, する, and くる).
I make the baby eat baby food.
If you make my son go shopping alone, he spends money frivolously.
When I get tired, I make my wife drive.
You're going to make them pick us up? Isn't it faster to walk home?
These short forms of せる and させる are ‘preferred’ in the Kansai dialect, but are not a requirement. The standard forms may still occasionally be heard.