Exhibit 10.6

    

    

    THIS PROMISSORY NOTE (“NOTE”) HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”). THIS NOTE HAS BEEN ACQUIRED FOR INVESTMENT ONLY
      AND MAY NOT BE SOLD, TRANSFERRED OR ASSIGNED IN THE ABSENCE OF REGISTRATION OF THE RESALE THEREOF UNDER THE SECURITIES ACT OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY IN FORM, SCOPE AND SUBSTANCE TO THE COMPANY THAT SUCH REGISTRATION IS NOT
      REQUIRED.

    

    

    PROMISSORY NOTE

     

    

    	
            Principal Amount: up to $300,000

          	
            Dated as of March 2, 2020

          


    (as set forth on the Schedule of Borrowings attached hereto)

    

    

    ARYA Sciences Acquisition Corp II, a Cayman Islands exempted company and blank check company (the “Maker”),
      promises to pay to the order of ARYA Sciences Holdings II, a Cayman Islands limited company, or its registered assigns or successors in interest (the “Payee”), or order, the principal sum of up to three hundred
      thousand U.S. dollars ($300,000) (as set forth on the Schedule of Borrowings attached hereto) in lawful money of the United States of America, on the terms and conditions described below. All payments on this Note shall be made by check or wire
      transfer of immediately available funds or as otherwise determined by the Maker to such account as the Payee may from time to time designate by written notice in accordance with the provisions of this Note.

    

    

    Principal. The principal balance of this Note shall be payable by the Maker on the earlier of: (i) December 31,
      2020 or (ii) the date on which Maker consummates an initial public offering of its securities (the “IPO”). The principal balance may be prepaid at any time. Under no circumstances shall any individual, including but not limited to any officer,
      director, employee or shareholder of the Maker, be obligated personally for any obligations or liabilities of the Maker hereunder.

    

    

    Interest. No interest shall accrue on the unpaid principal balance of this Note.

    

    

    Drawdown Requests. Maker and Payee agree that Maker may request up to Three Hundred Thousand Dollars ($300,000)
      for costs reasonably related to Maker’s initial public offering of its securities. The principal of this Note may be drawn down from time to time prior to the earlier of: (i) December 31, 2020 or (ii) the date on which Maker consummates an initial
      public offering of its securities, upon written request from Maker to Payee (each, a “Drawdown Request”). Each Drawdown Request must state the amount to be drawn down, and must not be an amount less than One
      Thousand Dollars ($1,000) unless agreed upon by Maker and Payee. Payee shall fund each Drawdown Request no later than one (1) business day after receipt of a Drawdown Request; provided, however, that the maximum amount of drawdowns collectively under
      this Note is Three Hundred Thousand Dollars ($300,000). No fees, payments or other amounts shall be due to Payee in connection with, or as a result of, any Drawdown Request by Maker.

    

    

    Application of Payments. All payments shall be applied first to payment in full of any costs incurred in the
      collection of any sum due under this Note, including (without limitation) reasonable attorney’s fees, then to the payment in full of any late charges and finally to the reduction of the unpaid principal balance of this Note.

    

    

    Events of Default. The following shall constitute an event of default (“Event of Default”):

    

    

    (a)          Failure to Make Required Payments. Failure by Maker
        to pay the principal amount due pursuant to this Note within five (5) business days of the date specified above.

    

    

    (b)          Voluntary Bankruptcy, Etc. The commencement by Maker
        of a voluntary case under any applicable bankruptcy, insolvency, reorganization, rehabilitation or other similar law, or the consent by it to the appointment of or taking possession by a receiver, liquidator, assignee, trustee, custodian,
        sequestrator (or other similar official) of Maker or for any substantial part of its property, or the making by it of any assignment for the benefit of creditors, or the failure of Maker generally to pay its debts as such debts become due, or the
        taking of corporate action by Maker in furtherance of any of the foregoing.

    
      
        

        

      

      
        


    

    (c)          Involuntary Bankruptcy, Etc. The entry of a decree
        or order for relief by a court having jurisdiction in the premises in respect of Maker in an involuntary case under any applicable bankruptcy, insolvency or other similar law, or appointing a receiver, liquidator, assignee, custodian, trustee,
        sequestrator (or similar official) of Maker or for any substantial part of its property, or ordering the winding-up or liquidation of its affairs, and the continuance of any such decree or order unstayed and in effect for a period of 60 consecutive
        days.

    

    

    Remedies.

    

    

    (a)          Upon the occurrence of an Event of Default specified in
        Section 5(a) hereof, Payee may, by written notice to Maker, declare this Note to be due immediately and payable, whereupon the unpaid principal amount of this Note, and all other amounts payable thereunder, shall become immediately due and payable
        without presentment, demand, protest or other notice of any kind, all of which are hereby expressly waived, anything contained herein or in the documents evidencing the same to the contrary notwithstanding.

    

    

    (b)          Upon the occurrence of an Event of Default specified in
        Sections 5(b) and 5(c), the unpaid principal balance of this Note, and all other sums payable with regard to this Note, shall automatically and immediately become due and payable, in all cases without any action on the part of Payee.

    

    

    Waivers. Maker and all endorsers and guarantors of, and sureties for, this Note waive presentment for payment,
      demand, notice of dishonor, protest, and notice of protest with regard to the Note, all errors, defects and imperfections in any proceedings instituted by Payee under the terms of this Note, and all benefits that might accrue to Maker by virtue of
      any present or future laws exempting any property, real or personal, or any part of the proceeds arising from any sale of any such property, from attachment, levy or sale under execution, or providing for any stay of execution, exemption from civil
      process, or extension of time for payment; and Maker agrees that any real estate that may be levied upon pursuant to a judgment obtained by virtue hereof, on any writ of execution issued hereon, may be sold upon any such writ in whole or in part in
      any order desired by Payee.

    

    

    Unconditional Liability. Maker hereby waives all notices in connection with the delivery, acceptance,
      performance, default, or enforcement of the payment of this Note, and agrees that its liability shall be unconditional, without regard to the liability of any other party, and shall not be affected in any manner by any indulgence, extension of time,
      renewal, waiver or modification granted or consented to by Payee, and consents to any and all extensions of time, renewals, waivers, or modifications that may be granted by Payee with respect to the payment or other provisions of this Note, and
      agrees that additional makers, endorsers, guarantors, or sureties may become parties hereto without notice to Maker or affecting Maker’s liability hereunder.

    

    

    Notices. All notices, statements or other documents which are required or contemplated by this Agreement shall
      be: (i) in writing and delivered personally or sent by first class registered or certified mail, overnight courier service or facsimile or electronic transmission to the address designated in writing, (ii) by facsimile to the number most recently
      provided to such party or such other address or fax number as may be designated in writing by such party and (iii) by electronic mail, to the electronic mail address most recently provided to such party or such other electronic mail address as may be
      designated in writing by such party. Any notice or other communication so transmitted shall be deemed to have been given on the day of delivery, if delivered personally, on the business day following receipt of written confirmation, if sent by
      facsimile or electronic transmission, one (1) business day after delivery to an overnight courier service or five (5) days after mailing if sent by mail.

    

    

    Construction. THIS NOTE SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH THE LAWS OF NEW YORK, WITHOUT REGARD
      TO CONFLICT OF LAW PROVISIONS THEREOF.

    

    

    Severability. Any provision contained in this Note which is prohibited or unenforceable in any jurisdiction
      shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof, and any such prohibition or unenforceability in any jurisdiction shall not invalidate or render
      unenforceable such provision in any other jurisdiction.

    

    

    Trust Waiver. Notwithstanding anything herein to the contrary, the Payee hereby waives any and all right, title,
      interest or claim of any kind (“Claim”) in or to any distribution of or from the trust account to be established in which the proceeds of the IPO conducted by the Maker (including the deferred underwriters discounts and commissions) and certain of
      the proceeds of the sale of the units issued in a private placement to occur in connection with the consummation of the IPO are to be deposited, as described in greater detail in the registration statement and prospectus to be filed with the
      Securities and Exchange Commission in connection with the IPO, and hereby agrees not to seek recourse, reimbursement, payment or satisfaction for any Claim against the trust account for any reason whatsoever.

    

    

    Amendment; Waiver. Any amendment hereto or waiver of any provision hereof may be made with, and only with, the
      written consent of the Maker and the Payee.

    

    

    Assignment. No assignment or transfer of this Note or any rights or obligations hereunder may be made by any
      party hereto (by operation of law or otherwise) without the prior written consent of the other party hereto and any attempted assignment without the required consent shall be void.

    

    

    [Signature page follows]

    
      
        

        

      

      
        


    

    IN WITNESS WHEREOF, Maker, intending to be legally bound hereby, has caused this Note to be duly executed by the undersigned as of the
      day and year first above written.

    

    

    

    

    	 	
            ARYA SCIENCES ACQUISITION CORP II

          
	 	
            a Cayman Islands exempted company

          
	 	
            By:

          	
            /s/ Samuel Cohn

          
	 	 	
            Name:

          	
            Samuel Cohn

          
	 	 	
            Title:

          	
            Secretary

          


    

    

    [Signature Page to Promissory Note]

    
      
        

        

      

      
        


    

    SCHEDULE OF BORROWINGS

    

    

    The following increases or decreases in this Promissory Note have been made:

    

    

    	
            
              Date of Increase or 

              Decrease

            

          	
            
              Amount of decrease in 

              Principal Amount of this 

              Promissory Note

            

          	
            
              Amount of increase in 

              Principal Amount of this

                Promissory Note

            

          	
            
              Principal Amount of this 

              Promissory Note following 

              such decrease or increase