Exhibit 10.44


                      STOCK PURCHASE AND VESTING AGREEMENT
                      ------------------------------------



           THIS STOCK  PURCHASE AND VESTING  AGREEMENT is made this 21st day of
March,  2002,  by and between  Spine Wave,  Inc., a Delaware  corporation  (the
"Company"),  and Protein  Polymer  Technologies,  Inc., a Delaware  corporation
("Purchaser").

           NOW THEREFORE, IT IS HEREBY AGREED:

           1. Sale of Stock. Subject to the terms hereof, the Company shall sell
to Purchaser and Purchaser shall purchase from the Company Four Hundred Thousand
(400,000)  shares of common  stock of the Company  (the  "Stock").  The sale and
purchase  shall  occur at the offices of the Company on the date set forth above
or at such other place and time as the parties may agree (the "Closing").

           2.  Consideration.  In exchange for and as full consideration for the
Stock,  the Purchaser  shall (i) enter into that certain  Amendment No. 1 to the
Supply and Services  Agreement dated April 12, 2001 attached hereto as Exhibit A
(the  "Amendment"),  (ii) have  entered  into and  delivered to the Company that
certain  Certificate of Acknowledgement of Termination by and among the Company,
Purchaser and Windamere  Venture  Partners,  LLC terminating that certain Voting
Agreement dated April 12, 2001,  attached hereto as Exhibit B (the  "Certificate
of  Termination"),  (iii) have  entered  into and  delivered to the Company that
certain Letter Agreement  attached hereto as Exhibit C (the "Letter  Agreement")
and (iv) have previously voted all of the shares of the Company's  capital stock
beneficially  held by Purchaser in favor of (A) the Company's merger with VERTx,
Inc. (the  "Merger")  and (B) the  Company's  sale and issuance of shares of the
Company's  Series A  Preferred  Stock  (the  "Series A  Financing")  to  certain
investors  immediately  thereafter  and (C) any matter that could  reasonably be
expected to facilitate the Merger and Series A Financing as well as delivered to
the  Company or its  representatives  written  evidence  thereof.  In  addition,
Purchaser  shall deliver two (2) duly executed blank  Assignments  Separate from
Certificate in the form attached hereto as Exhibit D, which Assignments Separate
from  Certificate  shall only be used in  connection  with the  exercise  of the
Company's Repurchase Option as set forth in Section 5 below. The Company and the
Purchaser agree that the fair market value of each share of Stock as of the date
of this Agreement equals $0.05 per share (the "Purchase Price").

           3.  Issuance  of  Stock.  Upon  the  execution  and  delivery  of the
Amendment,  Certificate of Termination and Letter Agreement by the Purchaser and
contingent upon the Company's  verification of Purchaser's  vote in favor of the
approval of the Merger and the Series A  Financing,  the  Company  shall issue a
duly  executed  certificate  evidencing  the Stock in the name of Purchaser  and
provide  Purchaser  with a copy  of  such  certificate.  The  original  of  such
certificate  shall be held in escrow by the Company until the  expiration of the
Repurchase  Option  (as  defined  below);  provided  however,  upon  Purchaser's
request,  Company  shall release to Purchaser a  certificate  representing  that
number  of shares of the Stock  which,  as of the date of such  request,  are no
longer subject to the Repurchase Option.

           4. Repurchase  Option. The Stock shall be subject to a right (but not
an  obligation)  of repurchase  by the Company (the  "Repurchase  Option").  The
Company shall have the


<PAGE>


right to purchase  Unvested  Shares (as defined below) from the Purchaser at the
Purchase Price as follows.

              a.  All of the  Stock  shall  initially  be  considered  "Unvested
Shares" subject to the Repurchase Option.

              b. The Repurchase  Option shall lapse with respect to such portion
of the  Stock  upon  the  attainment  by  Purchaser  of each of the  performance
milestones as set forth on Exhibit E attached hereto (the "Milestones").

              c. The  Repurchase  Option  shall also  terminate  and cease to be
exercisable  with respect to any and all Unvested Shares in the event of (i) the
consummation  of a merger or  consolidation  of the Company  ("Merger") with and
into another corporation where the Company's  stockholders of record immediately
prior to such merger or consolidation  hold less than fifty percent (50%) of the
outstanding voting stock of the successor  corporation,  (ii) a sale or transfer
of greater  than fifty  percent  (50%) of the  outstanding  voting  stock of the
Company (other than as a result of a transaction or series of  transactions  the
primary  purpose of which is the raising of equity  capital) (a "Sale") or (iii)
the completion of a sale of all or substantially all of the Company's assets.

              d. The  Repurchase  Option shall be  exercised  by written  notice
signed by the President or Treasurer of the Company and delivered as provided in
subparagraph  9(b) hereof.  The Company shall pay for the shares of Stock it has
elected to  repurchase  by delivery of a cashier's  check or by wire transfer of
immediately  available funds in an aggregate  amount equal to the Purchase Price
multiplied by the number of shares of Stock being repurchased.


              e.  Adjustments to Stock. If, from time to time during the term of
the Repurchase Option,  there is any change affecting the Company's  outstanding
common stock as a class that is effected without the receipt of consideration by
the Company (through  merger,  consolidation,  reorganization,  reincorporation,
stock dividend,  dividend in property other than cash, stock split, liquidating,
dividend,  combination  of  shares,  change in  corporation  structure  or other
transaction not involving the receipt of consideration by the Company), then any
and all new,  substituted  or additional  securities or other  property to which
Purchaser  is  entitled  by reason of  Purchaser's  ownership  of Stock shall be
immediately subject to the Repurchase Option and be included in the word "Stock"
for all purposes of the Repurchase  Option with the same force and effect as the
shares of the Stock presently subject to the Repurchase  Option, but only to the
extent the Stock is, at the time, covered by such Repurchase  Option.  While the
aggregate  Purchase  Price  shall  remain the same after  each such  event,  the
Purchase Price per share of Stock upon exercise of the  Repurchase  Option shall
be appropriately adjusted.

           5. Exercise of Repurchase Option. The Company shall have the right to
exercise its Repurchase Option as follows:

              a. The  Company  shall have the right to exercise  its  Repurchase
Option to repurchase any Unvested  Shares covered by the First Milestone and the
Second


                                       2
<PAGE>


Milestone  (each as defined  and set forth on Exhibit E) from  Purchaser  at the
Purchase Price at any time on or after **.

              b. The  Company  shall have the right to exercise  its  Repurchase
Option to  repurchase  any Unvested  Shares  covered by the Third  Milestone (as
defined and set forth on Exhibit E) from  Purchaser at the Purchase Price at any
time on or after **.

           6. Right of First Refusal. Stock subject to the Repurchase Option may
not  be  transferred,  except  for  transfers  by  operation  of  law  or  other
involuntary  transfer.  Before  any  shares of Stock  registered  in the name of
Purchaser,  not subject to the Repurchase Option and not otherwise restricted by
applicable  federal  and  state  securities  laws  may be  sold  or  transferred
(excluding  transfer by operation  of law or other  involuntary  transfer)  such
shares shall first be offered to the Company in the following manner:

              a. The Purchaser or its transferee shall deliver a notice pursuant
to subparagraph 10(b) ("Notice") to the principal business office of the Company
stating (i) the bona fide  intention to sell or transfer  such shares,  (ii) the
number of such  shares of Stock to be sold or  transferred,  (iii) the price and
other terms, if any, for which  Purchaser or its transferee  proposes to sell or
transfer  such shares of Stock,  and (iv) the name and  address of the  proposed
purchaser  or  transferee,  if  any,  and  that  such  identified  purchaser  or
transferee  is  committed  to acquire the stated  number of shares on the stated
price and terms.

              b. The  Company  shall have the right at any time  within ten (10)
days of receipt of the Notice to purchase  all of the shares to which the Notice
refers at the price per share  specified  in the  Notice.  Said  right  shall be
exercised by written notice signed by the President or any Vice President of the
Company and delivered as provided in  subparagraph  10(b)  hereof,  which notice
shall specify the time, place and date for settlement of such purchase.

              c. In the event the Company does not, for any reason, exercise its
right pursuant  hereto,  the Company may assign such right,  provided such right
shall not extend  beyond such ten (10) day period.  If exercised by the assignee
pursuant  hereto,  the right to purchase  shall be exercised  by written  notice
signed by the  exercising  assignee and  delivered  as provided in  subparagraph
10(b) hereof, which notice shall specify the time, place and date for settlement
of such  purchase.  Purchaser  shall  sell the  shares  to the  Company  or such
assignees within thirty (30) days after the date of the Notice.

              d.  If all of the  shares  to  which  the  Notice  refers  are not
purchased,  as provided in  subparagraphs  6(b) or 6(c) above, the Purchaser may
sell  such  shares  to the  person  named in the  Notice  at the price and terms
specified  in the Notice,  provided  that such sale or  transfer is  consummated
within  seventy  five (75) days of the date of the  Notice to the  Company,  and
provided  further  that any such  sale is in  accordance  with all the terms and
conditions  hereof. If Purchaser does not consummate the sale or transfer within
such seventy five (75) day period,  the right provided hereby shall be deemed to
be revived with respect to such shares and no sale or transfer shall be effected
without first offering the shares in accordance herewith.


**   Material is confidential and has been omitted and filed separately with the
Securities and Exchange Commission.


                                       3
<PAGE>


              e.   Notwithstanding  the  above,  neither  the  Company  nor  the
assignees  of the  Company  shall  have any right of first  refusal  under  this
Section 6 at any time  subsequent  to the  following:  (i) the closing of a bona
fide,  firm commitment  underwritten  public offering of the common stock of the
Company pursuant to a Registration  Statement  declared effective under the Act,
(ii) the  first  date on which  the  Stock is held of  record  by more than five
hundred  (500)  persons  (ii) a Merger or Sale,  other  than a Merger or Sale in
which the consideration  includes capital stock that is not registered under the
Securities  Act of  1933,  as  amended,  and/or  is  not  listed  on a  national
securities exchange, unless the issuer is subject to a contractual obligation to
register  and list such  stock  within  six  months of such  Merger or Sale.  In
addition,  the  Company's  right of first refusal under this Section 6 shall not
apply to the proposed  sale or transfer by  Purchaser  of stock  subject to this
Agreement as part of the sale of all or substantially all of Purchaser's  assets
("Sale of  Assets")  except in the event  that the Sale of Assets is to a direct
competitor  of the Company or to such other entity which  directly or indirectly
controls  a  direct  competitor  of  the  Company  and  provided  that  in  such
circumstance,  the time period set forth in subparagraph 6(d) above shall be 180
days.

           7. "Market Stand-Off"  Agreement.  If requested by the Company and an
underwriter  of Common Stock (or other  securities)  of the  Company,  Purchaser
shall not sell or  otherwise  transfer or dispose of any Common  Stock (or other
securities) of the Company held by such Holder (other than those included in the
registration) for no more than (i) 180 days from the effective date of the first
registration of the Company's securities, including securities to be sold on its
behalf to the public in an  underwritten  offering and (ii) 90 days for the next
two  subsequent  registration  statement of the Company after the initial public
offering;  provided,  however,  that all executive  officers,  directors and two
percent  (2%) or greater  stockholders  of the Company  must enter into  similar
lock-up agreements as well.

           In order to enforce the  foregoing  covenant,  the Company may impose
stop-transfer  instructions with respect to common stock held by Purchaser until
the end of such period.

           8. Representations and Warranties of Purchaser.

              a. Due Authorization.  Purchaser hereby represents and warrants to
Company that it is duly  authorized and empowered to enter into and perform this
Agreement; and the execution and performance of this Agreement by Purchaser does
not and will not conflict  with or violate any contract,  agreement,  indenture,
mortgage,  instrument,  writ,  judgment,  or  order  of any  court,  arbiter  or
governmental  or  quasi-governmental  body to which  Purchaser  is a party or by
which Purchaser is bound.

              b.  Investment  Intent.  This  Agreement is made with Purchaser in
reliance upon its representation to the Company, which by Purchaser's acceptance
hereof  confirms,  that the Stock has been acquired by Purchaser for  investment
for an indefinite period for Purchaser's own account, not as a nominee or agent,
and not with a view to the sale or  distribution  of any part thereof,  and that
Purchaser has no present  intention of selling,  granting  participation  in, or
otherwise distributing the same. By executing this Agreement,  Purchaser further
represents that Purchaser does not have any contract, undertaking,  agreement or
arrangement with any person to sell, transfer, or grant participations,  to such
person or to any third person, with respect to any of the Stock.


                                       4
<PAGE>


              c. Restricted Securities. Purchaser understands that the Stock has
not been  registered  under the Act, on the ground that the sale provided for in
this Agreement is exempt from the registration requirements of the Act, and that
the  Company's   reliance  on  such   exemption  is  predicated  on  Purchaser's
representations set forth herein.

           Purchaser  understands that if the Company does not register with the
Securities  and  Exchange  Commission  pursuant  to  Section  12 or  15  of  the
Securities  Exchange Act of 1934,  as amended,  or if a  registration  statement
covering  the Stock (or a filing  pursuant to the  exemption  from  registration
under  Regulation  A of the Act) under the Act is not in effect  when  Purchaser
desires to sell the Stock,  Purchaser  may be  required to hold the Stock for an
indeterminate period. The Purchaser also acknowledges that Purchaser understands
that any sale of the Stock that might be made by Purchaser in reliance upon Rule
144 under the Act may be made only in  limited  amounts in  accordance  with the
terms and conditions of that rule and that Purchaser may not be able to sell the
Stock at the time or in the amount  Purchaser so desires.  Purchaser is familiar
with Rule 144 and understands that the Stock constitutes "restricted securities"
within the meaning of that Rule.

              d.  Investment  Experience.  In  connection  with  the  investment
representations  made herein  Purchaser  represents  that Purchaser is either an
"Accredited  Investor",  as that term is  defined  in Rule 501 of  Regulation  D
promulgated  under the Act,  or is able to fend for  itself in the  transactions
contemplated by this  Agreement,  has such knowledge and experience in financial
and business  matters as to be capable of evaluating the merits and risks of its
investment, has the ability to bear the economic risks of its investment and has
been  furnished  with and has had access to such  information  as Purchaser  has
requested and deems appropriate to its investment decision.

              e.  Limitations on Disposition.  Purchaser agrees that in no event
will  Purchaser  make a  disposition  of any of the Stock,  unless and until (i)
Purchaser shall have notified the Company of the proposed disposition,  and (ii)
Purchaser   shall  have  furnished  the  Company  with  an  opinion  of  counsel
satisfactory to the Company to the effect that such disposition will not require
registration of such Stock under the Act or that  appropriate  action  necessary
for  compliance  with the Act has been taken,  or (iii) the  Company  shall have
waived,  expressly and in writing, its rights under clauses (i) and (ii) of this
subparagraph.  In addition,  prior to any  disposition of any of the Stock,  the
Company  shall  require  the  transferee  or  assignee  to  provide  in  writing
investment  representations and such transferee's or assignee's  agreement to be
bound by the market  stand-off  provisions  hereof in a form  acceptable  to the
Company.

              The Company shall not be required (i) to transfer on its books any
shares of Stock of the  Company  which  shall have been sold or  transferred  in
violation of any of the provisions set forth in this Agreement, or (ii) to treat
as owner of such  shares or to accord  the right to vote as such owner or to pay
dividends to any transferee to whom such shares shall have been so  transferred.
Purchaser  shall,  during the term of this  Agreement,  exercise  all rights and
privileges of a  stockholder  of the Company with respect to the Stock after the
issuance, and prior to the repurchase, thereof.


                                       5
<PAGE>


              f. Legends.  All certificates  representing any shares of Stock of
the Company  subject to the  provisions  of this  Agreement  shall have endorsed
thereon the following legends:

              (i) "THE SECURITIES  REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
REGISTERED  UNDER THE  SECURITIES  ACT OF 1933,  AS AMENDED (THE  "ACT").  THESE
SECURITIES HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO DISTRIBUTION
OR RESALE,  AND THEY MAY NOT BE  TRANSFERRED  WITHOUT AN EFFECTIVE  REGISTRATION
STATEMENT FOR SUCH SHARES UNDER THE ACT OR PURSUANT TO RULE 144 UNDER THE ACT OR
AN OPINION OF COUNSEL  SATISFACTORY  TO THE  COMPANY  THAT  REGISTRATION  IS NOT
REQUIRED UNDER THE ACT."

              (ii) "THE SECURITIES  REPRESENTED BY THIS  CERTIFICATE ARE SUBJECT
TO THE TERMS AND  CONDITIONS OF A CERTAIN STOCK  PURCHASE AND VESTING  AGREEMENT
BETWEEN THE  COMPANY AND THE HOLDER  HEREOF  WHICH  INCLUDES A MARKET  STAND-OFF
AGREEMENT, A RIGHT OF REPURCHASE AND A RIGHT OF FIRST REFUSAL ON THE SALE OF THE
SECURITIES. THESE SECURITIES MAY NOT BE SOLD, ASSIGNED, TRANSFERRED, ENCUMBERED,
OR IN ANY  MANNER  DISPOSED  OF  EXCEPT  IN  CONFORMITY  WITH THE  TERMS OF SUCH
AGREEMENT.  COPIES OF THE AGREEMENT MAY BE OBTAINED UPON WRITTEN  REQUEST TO THE
SECRETARY OF THE COMPANY."

              (iii) Any legend required to be placed thereon by applicable state
laws.

           9. Representations and Warranties of Company.

              a. Company hereby  represents and warrants to Purchaser that it is
duly authorized and empowered to enter into and perform this Agreement;  and the
execution and performance of this Agreement by the Company does not and will not
conflict  with  or  violate  any  contract,  agreement,   indenture,   mortgage,
instrument,  writ,  judgment,  or order of any court, arbiter or governmental or
quasi  governmental body to which the Company is a party or by which the Company
is bound.

              b. To the  best  of its  knowledge,  all  business  and  financial
information  that the  Company  has  provided  to  Purchaser  is accurate in all
material  respects;  provided,  however,  that Purchaser  acknowledges  that the
business and financial information provided by the Company to Purchaser includes
certain statements and estimates provided by the Company and its representatives
with respect to the  historical,  pro forma and  anticipated  performance of the
Company or that of potential strategic  partners.  Such statements and estimates
reflect  various  assumptions  by the Company,  which may or may not prove to be
accurate,  as well as the exercise of a  substantial  degree of judgement by the
Company as to the scope and presentation of such information.

           10. Miscellaneous.


                                       6
<PAGE>


              a. Further  Instruments and Actions.  The parties agree to execute
such further  instruments  and to take such further  action as may reasonably be
necessary to carry out the intent of this Agreement.

              b. Notices.  All notices required or permitted  hereunder shall be
in writing and shall be deemed  effectively given: (i) upon personal delivery to
the party to be notified,  (ii) when sent by confirmed facsimile transmission if
sent during normal  business  hours of the  recipient;  if not, then on the next
business day, or (iii) for domestic addresses one (1) business day after deposit
with a nationally  recognized  overnight courier,  specifying next day delivery,
with written  verification of receipt and for international  addresses three (3)
business  days after  deposit with a nationally  recognized  overnight  courier,
specifying  next  day  delivery,  with  written  verification  of  receipt.  All
communications  shall be sent to the party to be  notified at the address as set
forth on the  signature  pages hereof or at such other address as such party may
designate by ten (10) days advance written notice to the other parties hereto.

              c. Governing Law,  Assignment and  Enforcement.  This Agreement is
governed by the internal law of California and shall inure to the benefit of the
successors  and  assigns of the  Company  and,  subject to the  restrictions  on
transfer  herein set forth,  be  binding  upon  Purchaser,  its  successors  and
assigns.  The prevailing  party in any action to enforce this Agreement shall be
entitled to attorneys' fees and costs. The parties agree that damages are not an
adequate  remedy for breach hereof and each party shall  accordingly be entitled
to specific performance of this Agreement.

              d. Entire  Agreement;  Amendments and Waivers.  This Agreement and
the related  Amendment,  Certificate of Termination and Letter Agreement,  among
Purchaser  and  Company,  and all of even  date  herewith  (and any  agreements,
exhibits or schedules referenced  therein),  constitute the entire agreement and
understanding  between the parties with respect to the subject matter  contained
herein, and there are no promises,  representations,  conditions,  provisions or
terms related  thereto other than as set forth in this Agreement and the related
Amendment, Certificate of Termination and Letter Agreement between the Purchaser
and Company all of even date  herewith.  This Agreement may only be amended with
the written consent of the parties hereto,  or their successors or assigns,  and
no  oral  waiver  or  amendment  shall  be  effective  under  any  circumstances
whatsoever.

              e. Cooperation.  Purchaser agrees to cooperate  affirmatively with
the Company,  to the extent  reasonably  requested  by the  Company,  to enforce
rights and obligations pursuant to this Agreement.

           11.  California  Commissioner  of  Corporations.   THE  SALE  OF  THE
SECURITIES  WHICH ARE THE SUBJECT OF THIS  AGREEMENT HAS NOT BEEN QUALIFIED WITH
THE COMMISSIONER OF CORPORATIONS OF THE STATE OF CALIFORNIA, AND THE ISSUANCE OF
SUCH  SECURITIES  OR THE  PAYMENT OR  RECEIPT  OF ANY PART OF THE  CONSIDERATION
THEREFOR PRIOR TO SUCH  QUALIFICATION  IS UNLAWFUL UNLESS THE SALE OF SECURITIES
IS EXEMPT FROM  QUALIFICATION BY SECTION 25100, 25102 OR 25105 OF THE CALIFORNIA
CORPORATIONS  CODE.  THE RIGHTS OF ALL PARTIES TO THIS  AGREEMENT  ARE EXPRESSLY
CONDITIONED UNLESS THE SALE IS SO EXEMPT.


                                       7
<PAGE>


           IN WITNESS  WHEREOF,  the parties hereto have executed this Agreement
as of the day and year first above written.

                               SPINE WAVE, INC.


                               By:  /s/ Mark LoGuidice
                                    --------------------------------------------
                                    Mark LoGuidice,
                                    President and Chief Executive Officer

                    Address:   12230 El Camino Real, Suite 300
                               San Diego, California 92130



                               PURCHASER

                               Protein Polymer Technologies, Inc.


                               /s/J. Thomas Parmeter
                                    --------------------------------------------
                                    J. Thomas Parmeter
                                    President and Chief Executive Officer

                    Address:   10655 Sorrento Valley Road
                               San Diego, California 92121


                  [SIGNATURE PAGE TO STOCK PURCHASE AGREEMENT]


<PAGE>


                                    EXHIBIT A
                                    ---------

                                   [AMENDMENT]


<PAGE>


                                    EXHIBIT B
                                    ---------

                  CERTIFICATE OF ACKNOWLEDGEMENT OF TERMINATION
                               OF VOTING AGREEMENT

               The undersigned parties to that certain Voting Agreement dated as
of April 12, 2001, as amended through the date hereof (the "Voting Agreement"),
by and among Spine Wave, Inc., Protein Polymer Technologies, Inc. and Windamere
Venture Partners, LLC, hereby acknowledge and consent to the following:

                      Pursuant to Sections 5 and 7 of the Voting Agreement,
        effective as of the effective date of this Certificate of
        Acknowledgement of Termination of Voting Agreement, the Voting Agreement
        is hereby terminated in its entirety for all time, is of no further
        force and effect and no party thereto shall have any remaining rights or
        obligations thereunder.

               This Certificate of Acknowledgement of Termination of Voting
Agreement has been executed and is effective as of March __, 2002 and may be
executed in more than one counterpart, each of which shall be deemed an
original, but all of which shall constitute one and the same instrument.

                                            SPINE WAVE, INC.



                                            By:
                                               ---------------------------------
                                                   Mark LoGuidice,
                                                   President and Chief Executive
                                                   Officer



                                            PROTEIN POLYMER TECHNOLOGIES, INC.



                                            By:
                                               ---------------------------------
                                                   J. Thomas Parmeter,
                                                   President and Chief Executive
                                                   Officer



                                            WINDAMERE VENTURE PARTNERS, LLC



                                            By:
                                               ---------------------------------

                                            Its:
                                               ---------------------------------



<PAGE>


                                    EXHIBIT C
                                    ---------

                                LETTER AGREEMENT



                                 March 21, 2002




Protein Polymer Technologies, Inc.
10655 Sorrento Valley Road
San Diego, CA  92121
Attn:  J. Thomas Parmeter, President and Chief Executive Officer

        Re:    License Agreement.

Dear Mr. Parmeter:

        This letter agreement (the "Letter Agreement") sets forth our
understanding regarding the treatment of a certain termination provision under
that certain License Agreement dated as of April 12, 2001, as amended, by and
between Spine Wave, Inc. ("Spine Wave") and Protein Polymer Technologies, Inc.
("PPTI"). This Letter Agreement is being entered into in connection with and as
consideration under the Stock Purchase and Vesting Agreement of even date
herewith between Spine Wave and PPTI.

        1. Termination of License Agreement. Notwithstanding the provisions of
Section 9.2(b) of the License Agreement, and subject to the limitation set forth
in the following sentence, Spine Wave and PPTI hereby agree that if Spine Wave
has not closed its currently contemplated Series A Preferred Stock Financing on
or before April 12, 2002, PPTI shall not, at any time prior to May 12, 2002,
exercise its right to terminate the License Agreement pursuant to Section 9.2(b)
thereof if and provided that Spine Wave has paid to PPTI all payments due and
payable as of April 1, 2002 under that certain Supply and Services Agreement
dated as of April 12, 2001, as amended through the date hereof.

        2. License Agreement. Except as otherwise modified in this Letter
Agreement, the License Agreement and the terms and conditions therein remain
unchanged and in full force and effect.

        3. Amendments and Waivers. Any term of this Letter Agreement may be
amended and the observance of any term of this Letter Agreement may be waived
only with the written consent of Spine Wave and PPTI.

        4. Counterparts. This Letter Agreement may be executed in two
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.



<PAGE>



        5. Governing Law. This Letter Agreement shall be construed and the
rights of the parties shall be determined in accordance with the substantive
laws of the State of California, without regard to its conflict of laws
principles.



                                Very truly yours,

                                SPINE WAVE, INC.



                                By:
                                     -------------------------------------------
                                     Mark LoGuidice,
                                     President and Chief Executive Officer


AGREED AND ACCEPTED:

PROTEIN POLYMER TECHNOLOGIES, INC.


By:
    -------------------------------------
    J. Thomas Parmeter,
    President and Chief Executive Officer



<PAGE>


                                    EXHIBIT D
                                    ---------

                      ASSIGNMENT SEPARATE FROM CERTIFICATE



           FOR VALUE RECEIVED, Protein Polymer Technologies,  Inc. hereby sells,

assigns and transfers unto _____________________________, ______________________

(__) shares of the Common Stock of Spine Wave, Inc., standing in its name on the

books of said  corporation  represented  by  Certificate  No.  herewith and does

hereby  irrevocably  constitute  and  appoint  __________________   attorney  to

transfer said stock on the books of the within-named corporation with full power

of substitution in the premises.

Dated: _________________, _____.


                               Protein Polymer Technologies, Inc.



                               _________________________________________________
                               By:
                               Its:

           This Assignment Separate from Certificate was executed in conjunction

with the terms of a Stock  Purchase  Agreement  between the above  assignor  and

Spine Wave, Inc. dated March__, 2002.


<PAGE>



                                    EXHIBIT E
                                    ---------

                                   MILESTONES **



**   Material is confidential and has been omitted and filed separately with the
Securities and Exchange Commission.

<PAGE>

                                   APPENDIX A
                                   ----------

1. Completion of all Acute Toxicity testing and reports (see Pre-clinical Tests
   below)
2. Completion of all Chronic Testing with ninety (90) day report (see
   Pre-clinical Tests below)
3. Characterization of the Master Cell Bank for the protein selected for the IDN
4. Characterization of the protein selected for the IDN
5. Characterization of the specified IDN material
6. Qualification of the protein manufacturing process for submission of an
   investigational device exemption application for a pilot clinical study of
   the IDN with the FDA
7. Successful results, in the Company's reasonable judgment, from the mechanical
   testing

                               Preclinical Tests*

Acute Tests

--------------------------------------------------------------------------------
Test                Article Form       Animal Model       Follow up
--------------------------------------------------------------------------------
Cytotoxicity        MEM extract        In-vitro L929      48 hours
--------------------------------------------------------------------------------
Sensitization       Saline/CSO         Guinea pig         22 days
                    extracts
--------------------------------------------------------------------------------
Intracutaneous      Saline/CSO         Rabbit             7 days
reactivity          extracts
--------------------------------------------------------------------------------
Systemic            Saline/CSO         Mouse              72 hours
toxicity            extracts
--------------------------------------------------------------------------------
Pyrogenicity        Saline extract     In vitro           N/A
LAL Endotoxin
--------------------------------------------------------------------------------
Irritation          In-situ cured      Rabbit (muscle)    5 days
                    implant
--------------------------------------------------------------------------------
Genotoxicity -      Saline/DMSO        In vitro           N/A
Bacterial           extracts
reverse mutation
--------------------------------------------------------------------------------
Genotoxicity        Saline/DMSO        In vitro           N/A
Chromosome          extracts
aberration
--------------------------------------------------------------------------------
Genotoxicity        Saline/DMSO        In vitro           N/A
Micronucleus        extracts
test
--------------------------------------------------------------------------------


Chronic Tests

--------------------------------------------------------------------------------
Test                Article Form       Animal Model       Follow up
--------------------------------------------------------------------------------
Subchronic          In-situ cured      Rabbit (peri-      30 days
Neural toxicity     implant            sciatic nerve
                                       injection)
--------------------------------------------------------------------------------
Implantation        In-situ cured      Sheep              90 day interim
                    implant            intradiscal        1 year total
                                       injection
--------------------------------------------------------------------------------
Chronic toxicity    In-situ cured      Rabbit             7 days
                    implant
--------------------------------------------------------------------------------

* The tests required are subject to change based on feedback from the FDA.