Which of the following is a method for manual closure without mechanical assistance?

The method for manual closure without mechanical assistance among the given options is the use of a thrombogenic patch. This technique involves placing a specialized patch over the puncture site. The patch stimulates the body's natural coagulation processes, promoting the formation of a clot at the site of vascular access. This enables successful closure of the puncture without the use of mechanical devices or techniques.

In contrast, the other options involve some form of mechanical assistance or technology. A Femo-stop is a mechanical device designed to apply pressure to the access site to achieve hemostasis. The C-Clamp applies direct mechanical pressure to the puncture site, and thrombin injection involves injecting a clotting agent into the access site to facilitate closure. While these methods can also be effective, they do not qualify as manual closure techniques that rely solely on biological mechanisms or passive interactions without mechanical devices.