As filed with the Securities and Exchange Commission on January 12, 2024. Registration No. 333-275361 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Amendment No. 5 to FORM S-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 FibroBiologics, Inc. (Exact name of registrant as specified in its charter) (State or other jurisdiction of (Primary Standard Industrial Delaware 2834 86-3329066 (I.R.S. Employer Identification Number) 455 E. Medical Center Blvd. Suite 300 Houston, Texas ...