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                                                                EXHIBIT 10.13(b)

                                CO-SALE AGREEMENT


                  THIS CO-SALE AGREEMENT (the "Co-Sale Agreement") is entered
into as of November __, 2000, by and among Advanced Material Sciences, Inc., a
Delaware corporation (the "Company"), CombiMatrix Corporation, a Delaware
corporation ("CombiMatrix") and Acacia Research Corporation, a Delaware
corporation ("Acacia"; together with CombiMatrix, the "Investors" each of which
is herein referred to as an "Investor".)

                                    RECITALS

                  WHEREAS, the Company and the Investors are acquiring the
Common Stock of the Company (the "Common Stock");

                  WHEREAS, the rights and obligations granted in this Co-Sale
Agreement are a condition to the effectiveness of the acquisition of such Common
Stock;

                  NOW, THEREFORE, the parties agree as follows:

         1. Definitions. For purposes of this Co-Sale Agreement, the following
terms shall have the following meanings.

                  1.1 "Act" means the Securities Act of 1933, as amended.

                  1.2 "Common Stock" means the common stock, par value $.001 per
share, of the Company.

                  1.3 "Common Stock Equivalents" means and includes all shares
of Common Stock issued and outstanding at the relevant time plus (i) all shares
of Common Stock that may be issued upon exercise of any options, warrants and
other rights of any kind that are then exercisable, and (ii) all shares of
Common Stock that may be issued upon conversion or exchange of any convertible
securities which are by their terms then convertible into or exchangeable for
Common Stock, including without limitation, preferred stock.

         2. Investors' Right of First Offer. Before any Common Stock owned by
any Investor may be Transferred (as defined hereinafter), the other Investor
shall have a right of first offer with respect to such Common Stock, all on the
terms and conditions set forth in this Section 2.

                  Each time an Investor proposes to sell, transfer or otherwise
dispose of Common Stock other than to any wholly owned subsidiary or parent of,
or to any corporation that is, within the meaning of the Act, controlling,
controlled by or under common control with, any such investor, in the case of a
limited liability company, to its members, or gift transfers to its family
members or one or more trusts for the benefit of the foregoing (in each case a
"Transfer"), that Investor (the "Transferring Investor") shall first make an
offering of Common Stock to the other Investor (the "Other Investor") in
accordance with the following provisions:
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                  (a) The Transferring Investor shall provide notice (an
"Investor Transfer Notice") to the Other Investor stating (i) its bona fide
intention to Transfer such Common Stock, (ii) the number of such Common Stock
shares proposed to be Transferred (the "Offered Stock"), (iii) the name of each
proposed transferee, and (iv) the cash price or other consideration (including
the cash equivalent value of any non-cash consideration) per share for which the
Transferring Investor proposes to transfer the Offered Stock (the "Offered
Price").

                  (b) By written notification received by the Other Investor
within ten (10) calendar days of the mailing of the Investor Transfer Notice,
the Other Investor may elect to purchase or obtain, at the price and on the
terms specified in the Investor Transfer Notice, all of the Offered Stock.

                  (c) If all Offered Stock which the Other Investor is entitled
to obtain pursuant to subsection 2(b) is not elected to be obtained, the
Transferring Investor may, during the sixty (60) day period following the
expiration of the period provided in subsection 2(b) hereof, offer the Offered
Stock to any person or persons, subject to Section 3 hereof, at a price not less
than, and upon terms no more favorable to the offeree than those specified in
the Investor Transfer Notice. If the Transferring Investor does not enter into
an agreement for the sale of the Common Stock within such period, or if such
agreement is not consummated within ninety (90) days of the execution thereof,
the right provided hereunder shall be deemed to be revived and such Offered
Stock shall not be transferred unless first reoffered to the Other Investor in
accordance herewith.

                  (d) The right of first offer set forth in this Section 2 shall
terminate upon the completion of an underwritten public offering of shares of
Common Stock of the Company (a "Qualified Public Offering").

                  (e) Any attempt by an Investor to transfer Common Stock in
violation of Section 2 hereof shall be void and the Company agrees it will not
effect such a transfer nor will it treat any alleged transferee as the holder of
such shares without the written consent of a majority in interest of the
Investors.

         3. Rights of Co-Sale

                  3.1 Investors' Rights. If the Other Investor does not fully
exercise its right of first offer pursuant to Section 2(b) hereof, such Other
Investor shall have a right of co-sale with respect to the sale of any Common
Stock owned by the Transferring Investor, all on the terms and conditions set
forth in this Section 3.

                  3.2 Notice of Proposed Transfer. Before a Transferring
Investor may transfer its shares of Common Stock and after the Other Investor
has elected not to fully exercise its right of first offer pursuant to Section
2, such Transferring Investor shall provide notice (a "Transferring Investor
Notice") to the Other Investor stating (i) its bona fide intention to Transfer
such Common Stock, (ii) the number of shares of Offered Stock, (iii) the name of
each proposed transferee, and (iv) the Offered Price.




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                  3.3 Right of Co-Sale.

                  (a) Exercise of Right of Co-Sale. The Other Investor shall
have the right to participate in the Transferring Investor's transfer of the
Offered Stock to the proposed transferee pursuant to the specified terms and
conditions of the Transfer as set forth in the Transferring Investor Notice and
in accordance with the terms and conditions of the Transfer as set forth in this
Section 3.3 (the "Right of Co-Sale"). For purposes of the preceding sentence,
the participation of the Other Investor shall be on the same terms as the
Transferring Investor. To the extent the Other Investor exercises his, her or
its Right of Co-Sale, the number of shares of Offered Stock that the
Transferring Investor may transfer pursuant to the Transferring Investor Notice
shall be correspondingly reduced. The Other Investor shall be responsible for
its pro rata share of the reasonable fees and expenses of the Transferring
Investor relating to the negotiation of the transaction. The Right of Co-Sale of
the Other Investor shall be subject to the following terms and conditions:

                           (i) The Other Investor may transfer all or any part
of such Investor's Common Stock that is not in excess of the number obtained by
multiplying the aggregate number of shares of Common Stock constituting the
Offered Stock by a fraction (A) the numerator of which is the number of shares
of such Investor's Common Stock, and (B) the denominator of which is the total
number of Common Stock Equivalents then owned by the Investors and investors, if
any, who are parties to any other co-sale agreement with the Company and the
Investors which is in existence at the time of the Transfer.

                           (ii) By written notice received by the Company within
fifteen (15) calendar days of the mailing of the Transferring Investor Notice by
the Transferring Investor to the Company, the Other Investor may effect its
election to participate in the transfer subject to this Section 3.3. Such
written notice shall contain the Other Investor's election to participate in the
Transfer of the Offered Stock setting forth the number and type of shares that
the Other Investor elects to include in the Transfer, accompanied by one or more
certificates or other documentation, properly endorsed for transfer,
representing those shares (if the Other Investor so elects, then such Other
Investor shall be referred to in this Co-Sale Agreement as a "Participant"). The
Company shall keep the Transferring Investor promptly informed at all times as
to the Other Investor's election to participate.

                  (b) Delivery of Stock Certificates and Proceeds. Upon the
closing of the Transfer subject to this Section 3.3, the stock certificate(s) or
other documentation representing the Common Stock to be transferred shall be
transferred and delivered to the investor or transferee pursuant to the terms
and conditions specified in the Transferring Investor Notice, and there shall be
promptly thereafter remitted to the Participant that portion of the proceeds
from the Transfer to which it is entitled by reason of participating in the
Transfer.

                  3.4 Offering Investor's Right to Transfer. The Transferring
Investor may transfer that portion of the Offered Stock permitted to be
transferred by the Transferring Investor, after application of the Right of
Co-Sale contained in Section 3.3 hereof, to any person named as an investor or
other transferee in the Transferring Investor Notice, at the Offered Price,
provided that the transfer (i) is consummated within ninety (90) days after the
date of the



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Transferring Investor Notice and (ii) is in accordance with all the terms of
this Co-Sale Agreement. If the Offered Stock is transferred in accordance with
the terms and conditions of this Co-Sale Agreement, then the transferee(s) of
the Offered Stock shall thereafter hold the Offered Stock free of this Co-Sale
Agreement and the Right of Co-Sale set forth herein. If the Offered Stock is not
so transferred during such ninety (90) day period, then the Transferring
Investor shall not transfer any of the Offered Stock without complying again in
full with the provisions of this Co-Sale Agreement.

                  3.5 Effect of Prohibited Transfer. In the event an Investor
should sell any Common Stock in contravention of the co-sale rights of the other
Investor under this Co-Sale Agreement (such an investor a "Violating Investor";
such a transaction a "Prohibited Transfer"), the other Investor, in addition to
all other remedies available at law, in equity or hereunder, shall have the put
option provided below, and the Violating Investor shall be bound by the
applicable provisions of that option. Any attempt by a Violating Investor to
transfer Common Stock in violation of Section 3 hereof shall be void and the
Company agrees it will not effect such a transfer nor will it treat any alleged
transferee as the holder of such shares without the written consent of a
majority in interest of the Investors.

                  3.6 Put Option. Notwithstanding Section 3.5 hereof, in the
event of a Prohibited Transfer, the other Investor shall have the right to sell
to the Violating Investor the type and number of shares of Common Stock equal to
the number of shares such Investor would have been entitled to sell to the
Violating Investor or transferee under Section 3.3 hereof had the Prohibited
Transfer been effected pursuant to and in compliance with the terms hereof. This
sale shall be made on the following terms and conditions:

                  (a) The price per share at which the Common Stock is to be
sold to the Violating Investor shall be equal to the price per share (on an
as-converted basis) paid by the transferee to the Violating Investor in the
Prohibited Transfer. The Violating Investor shall also reimburse the other
Investor for any and all fees and expenses, including legal fees and expenses,
incurred pursuant to the exercise or the attempted exercise of the Investor's
rights under Section 3.

                  (b) Within ninety (90) days after the later of the dates on
which the other Investor (A) receives notice of the Prohibited Transfer or (B)
otherwise becomes aware of the Prohibited Transfer, the other Investor, if
exercising the option created hereby, shall deliver to the Violating Investor
the certificate or certificates representing shares to be sold, each certificate
to be properly endorsed for transfer.

                  (c) The Violating Investor shall, upon receipt of the
certificate or certificates for the shares to be sold by the Investor pursuant
to this Section 3.6, pay the aggregate purchase price therefor and the amount of
reimbursable fees and expenses, as specified in Section 3.6(a), in cash or by
other means acceptable to the other Investor.




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         4. Exceptions, Termination.

                  4.1 Exceptions. Notwithstanding anything in this Co-Sale
Agreement to the contrary, the Right of Co-Sale set forth in this Co-Sale
Agreement shall not apply to any Transfer or series of Transfers of Common Stock
by an Investor (i) pursuant to a reorganization or merger of the Company with or
into any other corporation or entity, or a sale of all or substantially all of
the assets of the Company, in which the Investors in the aggregate own
immediately after such transaction less than 50% of the voting equity securities
of the surviving entity, (ii) pursuant to the winding up and dissolution of the
Company or (iii) in connection with a Qualified Public Offering.

                  4.2 Termination of Rights. The Right of Co-Sale set forth
herein shall terminate upon the earlier to occur of (i) the closing of a
Qualified Public Offering, or (ii) the date on which this Co-Sale Agreement is
terminated by a written agreement to such effect executed by the Company and
holders of at least seventy five percent (75%) of the shares of Common Stock
then held by the Investors.

         5. Restrictive Legend and Stop-Transfer Orders.

                  5.1 Legend. The Investors understand and agree that the
Company shall cause the legend set forth below, or a legend substantially
equivalent thereto, to be placed upon any certificate(s) evidencing ownership of
the Common Stock:

                  THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO
                  CERTAIN RESTRICTIONS ON TRANSFER SET FORTH IN A CO-SALE
                  AGREEMENT ENTERED INTO BY THE ORIGINAL HOLDER OF THESE SHARES,
                  THE COMPANY AND OTHER PERSONS, A COPY OF WHICH IS ON FILE AT
                  THE PRINCIPAL OFFICE OF THE COMPANY. SUCH RESTRICTIONS ARE
                  BINDING ON TRANSFEREES OF THESE SHARES UNDER SOME
                  CIRCUMSTANCES.

                  5.2 Stop Transfer Instructions. The Investors agree, to ensure
compliance with the restrictions referred to herein, that the Company may issue
appropriate "stop transfer" certificates or instructions with respect to the
Common Stock and that, the Company may make appropriate notations to the same
effect in its records.

         6. Miscellaneous Provisions.

                  6.1 Notices. All notices, requests, demands and other
communications which are required to be or may be given under this Co-Sale
Agreement to any party by any of the other parties shall be in writing and shall
be deemed to have been duly given when (a) delivered in person, (b) the day
following dispatch by a nationally recognized overnight courier service (such as
Federal Express or UPS, etc.) for next day delivery, (c) five (5) days after
dispatch by certified or registered first class mail, postage prepaid, return
receipt requested, to the party to whom the same is so given or made or (d) in
the case of notice sent by telecopy, on the date of dispatch, provided that the
report generated by the sender's telecopy machine shows that all pages of such



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notice or other communication were properly transmitted to each recipient's
telecopy number. Any notice or other communication given hereunder shall be
addressed to the Company, at its principal offices as set forth below or to the
Investors at their addresses indicated on the signature page hereto.

                  6.2 Binding on Successors and Assigns. This Co-Sale Agreement,
and the rights and obligations of the parties hereunder, shall inure to the
benefit of, and be binding upon, their respective successors, assigns and legal
representatives.

                  6.3 Severability. If one or more of the provisions of this
Co-Sale Agreement should, for any reason, be held to be invalid, illegal or
unenforceable in any respect, such invalidity, illegality or unenforceability
shall not affect any other provisions of this Co-Sale Agreement, and such
invalid, illegal or unenforceable provision shall be enforced to the extent
permissible.

                  6.4 Amendment. Any amendment, modification or waiver of this
Co-Sale Agreement shall be effective only with the written consent of (i)
Investors holding more than seventy five percent (75%) of the then outstanding
Common Stock, and (ii) the Company; provided, however, that any person may
waive, reduce or release (in whole or in part) any of its rights hereunder
without the consent of any other parties hereto. Any waiver by a party of its
rights hereunder shall be effective only if evidenced by a written instrument
executed by a duly authorized representative of such party.

                  6.5 Governing Law. This Co-Sale Agreement shall be governed by
and construed in accordance with the internal laws (and not the laws pertaining
to choice of conflict of laws) of the State of Delaware. The parties hereby
agree that any dispute which may arise between them arising out of or in
connection with this Co-Sale Agreement shall be adjudicated before a court
located in Wilmington, Delaware and they hereby submit to the exclusive
jurisdiction of the courts of the State of Delaware located in Wilmington,
Delaware and of the federal courts in the State of Delaware with respect to any
action or legal proceeding commenced by any party, and irrevocably waive any
objection they now or hereafter may have respecting the venue of any such action
or proceeding brought in such a court or respecting the fact that such court is
an inconvenient forum, relating to or arising out of this Co-Sale Agreement or
any acts or omissions relating to the sale of the securities hereunder, and
consent to the service of process in any such action or legal proceeding by
means of registered or certified mail, return receipt requested, in care of the
address set forth in Section 6.1 or such other address as each party shall
furnish in writing to the other parties.

                  6.6 Obligations of Company. The Company agrees to use its best
efforts to enforce and abide by the terms of this Co-Sale Agreement, to inform
the Investors of any breach hereof (to the extent the company has knowledge
thereof) and to assist the Investors in the exercise of their rights hereunder.

                  6.7 Expenses. If any action at law or in equity is necessary
to enforce or interpret the terms of this Co-Sale Agreement, the prevailing
party shall be entitled to reasonable



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attorneys' fees, costs and necessary disbursements in addition to any other
relief to which such party may be entitled.

                  6.8 Counterparts. This Co-Sale Agreement may be executed in
any number of counterparts, each of which shall be deemed an original and all of
which together shall constitute one and the same instrument.

                  6.9 Facsimile Signatures. Any signature page delivered by a
fax machine or telecopy machine shall be binding to the same extent as an
original signature page, with regard to any agreement subject to the terms
hereof or any amendment thereto. Any party who delivers such a signature page
agrees to later deliver an original counterpart to any party which requests it.

                  6.10 Entire Agreement. This Co-Sale Agreement, together with
the exhibit hereto, constitutes the entire understanding and agreement of the
parties with respect to the subject matter hereof and supersedes all prior
understandings and agreements with respect to such subject matter.



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                  IN WITNESS WHEREOF, the parties hereto have executed this
Co-Sale Agreement as of the date first written above.

                                   ADVANCED MATERIAL SCIENCES, INC.,
                                   a Delaware corporation


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


                                   Address:



                                   INVESTORS:

                                   ACACIA RESEARCH CORPORATION, a
                                   Delaware corporation


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

                                   Address:



                                   COMBIMATRIX CORPORATION, a Delaware
                                   corporation


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

                                   Address:





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