Does paying a small business debt with personal funds open you to liability?

I am running a small start-up business , and we are currently struggling. I have paid the majority of business expenses so far on a personal credit card or from my personal bank accounts.
A friend recently told me that his college professor advised that a personal account should NEVER be used to cover business debt because by doing so it opens the person to liability. the theory being something like, you have now mingled your personal assets with the business assets and now if someone ever went after the business legally or financially for whatever reason your personal assets would be at risk of loss.
Does anybody know if this is true, and if so what would a person do to correct the situation , after all of the pymts were already made with a personal card.

It depends on lots of factors.

Why not just play it safe.

Put the money into the company as owner's equity, then have the business pay the debt.

Write the company a bill for the money paid already on the credit card, and have them pay you back. You can always put it back into the company as owners equity.

The risk is, that if the business goes under, and is in a lot of debt, the creditors might say, "hey, it is his company, not a seperate entity, we can collect from him.

There is not much risk, you are actually paying the company's debts, you are thinking like the creditors. In the future don't do that. Let the company pay the bills via the company, otherwise if the company goes under, and has huge debts, they might sue you for everything to pay the debts.

Make sure that once this creditor is paid off, you don't use them again. They already have you compromised. It might be too late anyway.

correct you should never have to use your own funds or as you see it could send you and company into bankrupt.

If ur business is a family business then it is ok. If u have a prtnership business or company business then it si better to keep expenses seperately, donot mix.

If you are incorporated, it won't be a problem. If you're an
entrepreneur or a partnership then maybe. It may be worth a
consultation fee with a business lawyer or accountant to
know for sure. If you can't afford that, try using a zero-balance
credit card for business debt and record it as an investment.
The idea being to avoid mixing personal and business debt
on the same account. The problem as you presented it does
sound like it sets you up as an entrepreneur (proprietor) which
does consolidate your liability.

Yes, this opens you to personal liability. The credit card is personally guaranteed by you, not the business. Does the business have a line of credit at the bank you have your account with? If so, try getting funds from there. Also, check with an accountant to see how to legally have the funds you put into the business converted over as a legal low interest loans. Moving money between personal and business accounts is called comingling of funds and can cause problems with the IRS in the long run.