FORM 4
[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         	UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
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                      	Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	                      	

1. Name and Address of Reporting Person *

Haines Timothy	2. Issuer Name and Ticker or Trading Symbol

Sientra, Inc. [ SIEN ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable)

__ X __ Director                      _____ 10% Owner
_____ Officer (give title below)      __ X __ Other (specify below)
Former 10% Holder	
(Last)          (First)          (Middle)

C/O 420 SOUTH FAIRVIEW, SUITE 200	3. Date of Earliest Transaction (MM/DD/YYYY)

5/7/2018		
(Street)

SANTA BARBARA, CA 93117
(City)        (State)        (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)

 	6. Individual or Joint/Group Filing (Check Applicable Line)

_ X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person	

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned	
1.Title of Security
(Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. Code
(Instr. 8)	4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)	5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)	
			Code	V	Amount	(A) or (D)	Price				
Common Stock  	5/7/2018  	 	P	  	281482  	A	$13.50  	2480494  	I  	See Notes   (1) (2) (3)	
Common Stock  	 	 	 	  	 	 	 	31546  	D  	 	

Table II - Derivative Securities Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities)	
1. Title of Derivate Security
(Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. Code
(Instr. 8)	5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)	6. Date Exercisable and Expiration Date	7. Title and Amount of Securities Underlying Derivative Security
(Instr. 3 and 4)	8. Price of Derivative Security
(Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)	
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares					

Explanation of Responses:	
(1) 	Consists of (i) 1,240,247 shares held of record by Abingworth Bioventures V LP ("ABV V"), and (ii) 1,240,247 shares held of record by Abingworth Bioventures V Co-Invest Growth Equity Fund LP ("AGE"). ABV V and AGE are collectively referred to as the "Abingworth Funds." The investment manager of the Abingworth Funds is Abingworth LLP ("Abingworth"). Abingworth Bioventures V GP LP ("Abingworth GP"), a Scottish limited partnership, serves as the general partner of each of the Abingworth Funds. Abingworth General Partner V LLP, a Scottish limited liability partnership, serves as the general partner of Abingworth GP. Abingworth GP (acting by its general partner Abingworth General Partner V LLP) has delegated to Abingworth all investment and dispositive power over the shares held by the Abingworth Funds. The reporting person holds the reported securities indirectly through Abingworth.	
(2) 	The reporting person is part of an investment committee of Abingworth, which approves investment and voting decisions by a majority vote, and no individual member has the sole control or voting power over the shares held by the Abingworth Funds. From time to time, the investment committee may delegate investment and voting authority over certain securities held by the Abingworth Funds to employees of Abingworth subject to the supervision and oversight of the investment committee, including any limits on such authority imposed by the investment committee in its discretion and the right of the investment committee to revoke such authority at any time.	
(3) 	The reporting person disclaims beneficial ownership of all shares held of record by the Abingworth Funds. This report shall not be deemed an admission that the reporting person, Abingworth or any other person is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose.	

Reporting Owners	
Reporting Owner Name / Address	Relationships	
	Director	10% Owner	Officer	Other	
Haines Timothy
C/O 420 SOUTH FAIRVIEW, SUITE 200
SANTA BARBARA, CA 93117	X			Former 10% Holder	

Signatures		
/s/ Timothy Haines		5/9/2018	
** Signature of Reporting Person		Date

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.	
*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).	
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).	
Note:	File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.	
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.