Is it permissible to take a portion of the trust fund's money for medical treatment with the ability to return it later?

Your job requires you to be entrusted by your employer with the money under your hand, and you must safeguard this trust (amanah); as Allah Almighty says: "Indeed, Allah commands you to render trusts to whom they are due," and He Almighty says: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]." Your taking anything from the till is considered a betrayal, even if you intend to return it, unless with permission from the authorized official. If you wish, seek permission from the official; if he grants you permission, then all is well, otherwise refrain from doing so, and safeguard the trust with which you have been entrusted.