Exhibit 10.43

PROMISSORY NOTE

|$6,521,111 | December 31, 2007
|---------- | -----------------

Osiris Therapeutics, Inc., a corporation organized under the laws of the State of Delaware (the "Borrower"), for value received,
hereby promises to pay to Boston Scientific Corporation, or its registered assigns (the "Holder"), the principal sum of Six Million Five Hundred Twenty One Thousand One Hundred Eleven Dollars
($6,521,111) ("Principal Sum"), together with any unpaid accrued interest hereon as set forth below from the date of this Note, upon the terms and conditions specified below.

1.Interest; Payment Terms.Interest shall accrue on any unpaid balance of the Principal Sum from the date of
the execution hereof at the simple interest rate of eight percent (8%) per annum, based upon a 360 day year. The Principal Sum shall be due and payable in four equal installments paid on
January 2, 2008, April 1, 2008, July 1, 2008, and October 1, 2008. Each installment payment shall include accrued interest on the Principal Sum balance then outstanding.
Upon final payment of all amounts due under this Note, Holder agrees to immediately return the Note to Borrower so that it may be marked "canceled."

2.Events of Default.If any of the events specified in this Section 2 shall occur (herein individually
referred to as an "Event of Default"), the Holder of the Note may, so long as such condition exists, declare the
entire principal, and unpaid accrued interest hereon, immediately due and payable, by notice in writing to the Borrower:



3.Prepayment.The Borrower may at any time prepay in whole or in part the Principal Sum, plus accrued interest
to the date of payment, of this Note, without penalty.

4.Assignment.The rights and obligations of the Borrower shall not be assignable without the consent of Holder.
Holder may not assign this Note without the consent of the Borrower. If this Note is assigned pursuant to this Section 4, this Note shall be binding upon and benefit the successors, assigns,
heirs, administrators and transferees of the parties.

5.Presentment, Failure to Act.Presentment for payment, demand, protest and notice of demand, protest and
nonpayment and all other notices, except as specifically required herein, are hereby waived by Borrower. No failure to accelerate the debt evidenced hereby by reason of default hereunder, acceptance
of a past due amount, or indulgences granted from time to time shall be construed (i) as a novation of this Note or as a waiver of the right of Holder thereafter to insist upon strict
compliance with the terms of this Note, or (ii) to prevent the exercise of such right of acceleration or any other right granted hereunder or by the laws of the State of Delaware; and Borrower
hereby expressly waives the benefit of any statute or rule of law or equity now provided, or which may hereafter be provided, which would produce a result contrary to or in conflict with the
foregoing. No extension of the time for the payment of this Note or any installment due hereunder, made by agreement with any person now or hereafter liable for the payment of this Note shall operate
to release, discharge, modify, change or

---



affect
the original liability of Borrower under this Note, either in whole or in part unless Holder agrees otherwise in writing.

6.Amendment.This Note may be amended, waived or modified only upon the written consent of the Borrower and the
Holder.

7.Notices.Any notice, request or other communication required or permitted hereunder shall be in writing and
shall be deemed to have been duly given if personally delivered or if telegraphed or mailed by registered or certified mail, postage prepaid, at the respective addresses of the parties. Any party
hereto may by notice so given change its address for future notice hereunder. Notice shall conclusively be deemed to have been given when personally delivered or when deposited in the mail or
telegraphed in the manner set forth above and shall be deemed to have been received when delivered.

8.Governing Law.This Note shall be governed by and construed in accordance with the laws of the State of
Delaware, excluding that body of law relating to conflict of laws.

9.Heading; References.All headings used herein are used for convenience only and shall not be used to construe
or interpret this Note. Except where otherwise indicated, all references herein to Sections refer to Sections hereof.

IN WITNESS WHEREOF,the Borrower has caused this Note to be issued this 31st day of December, 2007.

| | BORROWER                                                                           
| | -----------------------------------------------------------------------------------
| | OSIRIS THERAPEUTICS, INC.                                                          
| | By: /s/ C. Randal MillsC. Randal Mills, Ph.D.
President and Chief Executive Officer

---



QuickLinks