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  <xs:element id="sttk_KayakAgreementMember" abstract="true" name="KayakAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_KayakAgreementContingentMilestonesMember" abstract="true" name="KayakAgreementContingentMilestonesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_SubleaseAgreementConsideration" abstract="false" name="SubleaseAgreementConsideration" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sttk_UnderwrittenPublicOfferingMember" abstract="true" name="UnderwrittenPublicOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_AtTheMarketOfferingMember" abstract="true" name="AtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_PublicOfferingMember" abstract="true" name="PublicOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_BeneficialOwnersMember" abstract="true" name="BeneficialOwnersMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_CommonStockNumberOfVotesPerCommonShare" abstract="false" name="CommonStockNumberOfVotesPerCommonShare" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="sttk_ClassOfWarrantOrRightPriceOfPreFundedWarrants" abstract="false" name="ClassOfWarrantOrRightPriceOfPreFundedWarrants" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="sttk_ClassOfWarrantOrRightPreFundedWarrantsOwnershipLimitationPostExercise" abstract="false" name="ClassOfWarrantOrRightPreFundedWarrantsOwnershipLimitationPostExercise" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="sttk_SaleOfStockMaximumAggregateSalesPrice" abstract="false" name="SaleOfStockMaximumAggregateSalesPrice" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sttk_SaleOfStockCommissionPercentage" abstract="false" name="SaleOfStockCommissionPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="sttk_ClassOfWarrantOrRightWarrantsExercised" abstract="false" name="ClassOfWarrantOrRightWarrantsExercised" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="sttk_A2023FinancingMember" abstract="true" name="A2023FinancingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_A2025FinancingMember" abstract="true" name="A2025FinancingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_A2026FinancingMember" abstract="true" name="A2026FinancingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_A2020StockIncentivePlanMember" abstract="true" name="A2020StockIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_A2020EmployeeStockPurchasePlanMember" abstract="true" name="A2020EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAuthorizedAnnualIncreasePercentage" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAuthorizedAnnualIncreasePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="sttk_CommonStockAdditionalCapitalSharesReservedForFutureIssuance" abstract="false" name="CommonStockAdditionalCapitalSharesReservedForFutureIssuance" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="sttk_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumSharesPerEmployeeValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumSharesPerEmployeeValue" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sttk_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInNumberOfSharesAuthorizedTerm" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInNumberOfSharesAuthorizedTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="sttk_BlackScholesOptionPricingModelMember" abstract="true" name="BlackScholesOptionPricingModelMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_ReportableSegmentMember" abstract="true" name="ReportableSegmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_SL325Member" abstract="true" name="SL325Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_SL846Member" abstract="true" name="SL846Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_OtherResearchAndDevelopmentMember" abstract="true" name="OtherResearchAndDevelopmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sttk_ResearchAndDevelopmentNonEquityCompensation" abstract="false" name="ResearchAndDevelopmentNonEquityCompensation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sttk_ResearchAndDevelopmentEquityCompensation" abstract="false" name="ResearchAndDevelopmentEquityCompensation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sttk_GeneralAndAdministrativeNonEquityCompensation" abstract="false" name="GeneralAndAdministrativeNonEquityCompensation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sttk_GeneralAndAdministrativeEquityCompensation" abstract="false" name="GeneralAndAdministrativeEquityCompensation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sttk_OtherResearchAndDevelopmentExpenseTechnicalOperations" abstract="false" name="OtherResearchAndDevelopmentExpenseTechnicalOperations" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sttk_NeilGibsonMember" abstract="true" name="NeilGibsonMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
</xs:schema>
