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  <xsd:element id="astm_ClassofWarrantorRightNumberofHolders" name="ClassofWarrantorRightNumberofHolders" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element id="astm_ClassofWarrantorRightWarrantsIssued" name="ClassofWarrantorRightWarrantsIssued" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_CommonStockRemainingCapacity" name="CommonStockRemainingCapacity" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="astm_CovenantPeriodAxis" name="CovenantPeriodAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_CovenantPeriodDomain" name="CovenantPeriodDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_CowenandCompanyLLCMember" name="CowenandCompanyLLCMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_DebtFinancingAgreementMaximumBorrowingCapacity" name="DebtFinancingAgreementMaximumBorrowingCapacity" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="astm_DebtFinancingAgreementMember" name="DebtFinancingAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_DebtInstrumentNumberofInstallments" name="DebtInstrumentNumberofInstallments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="astm_December312017Member" name="December312017Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_DepreciationDepletionandAmortizationExcludingIntangibleAssets" name="DepreciationDepletionandAmortizationExcludingIntangibleAssets" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="astm_DistributionAgreementAdditionalTerm" name="DistributionAgreementAdditionalTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_DistributionAgreementNumberOfAdditionalTerms" name="DistributionAgreementNumberOfAdditionalTerms" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="astm_DocumentAndEntityInformationAbstract" name="DocumentAndEntityInformationAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_IncreaseDecreaseInTenantImprovementReimbursement" name="IncreaseDecreaseInTenantImprovementReimbursement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_InnovativeCellularTherapeuticsMember" name="InnovativeCellularTherapeuticsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_LargestCustomerMember" name="LargestCustomerMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_LicenseAgreementContingentConsiderationAsset" name="LicenseAgreementContingentConsiderationAsset" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="astm_LicenseAgreementContingentConsiderationLiability" name="LicenseAgreementContingentConsiderationLiability" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="astm_LicenseAgreementDaysWithinEffectiveDateOfAgreementInitialPaymentDue" name="LicenseAgreementDaysWithinEffectiveDateOfAgreementInitialPaymentDue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_LicenseAgreementInitialPayment" name="LicenseAgreementInitialPayment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="astm_LineofCreditFacilityMinimumRevenueCovenant" name="LineofCreditFacilityMinimumRevenueCovenant" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="astm_LineofCreditandTermLoanCreditAgreementCurrentNetofDeferredCosts" name="LineofCreditandTermLoanCreditAgreementCurrentNetofDeferredCosts" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="astm_NumberOfPatentsAndPatentApplicationsAcquired" name="NumberOfPatentsAndPatentApplicationsAcquired" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="astm_OperatingLeasesLeasedOfficeSpaceFutureMinimumPaymentsDueAbstract" name="OperatingLeasesLeasedOfficeSpaceFutureMinimumPaymentsDueAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_OperatingLeasesSalesForceLeasedAutoFleetFutureMinimumPaymentsDueAbstract" name="OperatingLeasesSalesForceLeasedAutoFleetFutureMinimumPaymentsDueAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDue" name="OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="astm_OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueCurrent" name="OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueCurrent" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="astm_OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueInFourYears" name="OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueInFourYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="astm_OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueInThreeYears" name="OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueInThreeYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="astm_OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueInTwoYears" name="OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueInTwoYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="astm_OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueThereafter" name="OperatingandCapitalLeasesandPurchaseCommitmentsFutureMinimumPaymentsDueThereafter" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="astm_OrganizationConsolidationAndPresentationOfFinancialStatementsLineItems" name="OrganizationConsolidationAndPresentationOfFinancialStatementsLineItems" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_OrganizationConsolidationAndPresentationOfFinancialStatementsTable" name="OrganizationConsolidationAndPresentationOfFinancialStatementsTable" nillable="true" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_OrsiniPharmaceuticalservicesInc.Member" name="OrsiniPharmaceuticalservicesInc.Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_PercentageOfGrossProceedsPayableAsCommission" name="PercentageOfGrossProceedsPayableAsCommission" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_PreferredClassAAndClassBMember" name="PreferredClassAAndClassBMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_ScheduleOfChangeInEstimatedFairValueOfWarrantLiabilitiesTableTextBlock" name="ScheduleOfChangeInEstimatedFairValueOfWarrantLiabilitiesTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_ScheduleOfClassOfWarrantOrRightValuationAssumptionsTableTextBlock" name="ScheduleOfClassOfWarrantOrRightValuationAssumptionsTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_SecondLargestCustomerMember" name="SecondLargestCustomerMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceAbstract" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_SiliconValleyBankMember" name="SiliconValleyBankMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_TermLoanMember" name="TermLoanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_ValuationAllowancesAndReservesPeriodAxis" name="ValuationAllowancesAndReservesPeriodAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_ValuationAllowancesAndReservesPeriodDomain" name="ValuationAllowancesAndReservesPeriodDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_ValuationAllowancesAndReservesPeriodRelatedTo2016Member" name="ValuationAllowancesAndReservesPeriodRelatedTo2016Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_ValuationAllowancesAndReservesPeriodRelatedTo2017Member" name="ValuationAllowancesAndReservesPeriodRelatedTo2017Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="astm_WarrantsAndRightsNoteDisclosureTextBlock" name="WarrantsAndRightsNoteDisclosureTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_WarrantsAndRightsRollForward" name="WarrantsAndRightsRollForward" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_WarrantsIssuedInAugust2013Member" name="WarrantsIssuedInAugust2013Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="astm_WarrantsIssuedInSeptember2016Member" name="WarrantsIssuedInSeptember2016Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
</xsd:schema>