A kit comprising: a) a substrate attached to a binding unit configured to bind a surface of a target cell, wherein all or a portion of the substrate liquefies upon decreased availability of a crosslinking agent wherein the substrate comprises hydrogel microbeads, and the hydrogel comprises a cross-linkable polymer, wherein the cross-linkable polymer is a hydrogel comprising an alginic acid-polyethylene glycol copolymer, wherein the crosslinking agent is a cation, wherein the microbeads have a diameter of 1-200 μm, wherein the PEG is a branched PEG; and b) a strainer through which cells can pass but the substrate cannot, optionally wherein the binding unit: (i) comprises an antibody or antigen-binding fragment thereof, biotin, or a biotin binding protein, optionally wherein the antibody or antigen binding fragment thereof is a monoclonal antibody or antigen-binding fragment thereof, a Fab, a humanized antibody or antigen-binding fragment thereof, a bispecific antibody or antigen-binding fragment thereof, a monovalent antibody or antigen-binding fragment thereof, a chimeric antibody or antigen-binding fragment thereof, a single-chain Fv molecule, a bispecific single chain Fv ((scFv')2) molecule, a domain antibody, a diabody, a triabody, an affibody, a domain antibody, a SMIP, a nanobody, a Fv fragment, a Fab fragment, a F(ab')2 molecule, or a tandem scFv (taFv) fragment; or (ii) binds one or more cell surface molecules selected from the group consisting of T cell receptor, CD3, CD4, CD8, CD11 a, CD11 b, CD11 c, CD14, CD15, CD16, CD19, CD25, CD33, CD34, CD45RO, CD56, major histocompatibility complex, and chimeric antigen receptor. a) a substrate attached to a binding unit configured to bind a surface of a target cell, wherein all or a portion of the substrate liquefies upon decreased availability of a crosslinking agent wherein the substrate comprises hydrogel microbeads, and the hydrogel comprises a cross-linkable polymer, wherein the cross-linkable polymer is a hydrogel comprising an alginic acid-polyethylene glycol copolymer, wherein the crosslinking agent is a cation, wherein the microbeads have a diameter of 1-200 μm, wherein the PEG is a branched PEG; and b) a strainer through which cells can pass but the substrate cannot, optionally wherein the binding unit: (i) comprises an antibody or antigen-binding fragment thereof, biotin, or a biotin binding protein, optionally wherein the antibody or antigen binding fragment thereof is a monoclonal antibody or antigen-binding fragment thereof, a Fab, a humanized antibody or antigen-binding fragment thereof, a bispecific antibody or antigen-binding fragment thereof, a monovalent antibody or antigen-binding fragment thereof, a chimeric antibody or antigen-binding fragment thereof, a single-chain Fv molecule, a bispecific single chain Fv ((scFv')2) molecule, a domain antibody, a diabody, a triabody, an affibody, a domain antibody, a SMIP, a nanobody, a Fv fragment, a Fab fragment, a F(ab')2 molecule, or a tandem scFv (taFv) fragment; or (ii) binds one or more cell surface molecules selected from the group consisting of T cell receptor, CD3, CD4, CD8, CD11 a, CD11 b, CD11 c, CD14, CD15, CD16, CD19, CD25, CD33, CD34, CD45RO, CD56, major histocompatibility complex, and chimeric antigen receptor. (i) comprises an antibody or antigen-binding fragment thereof, biotin, or a biotin binding protein, optionally wherein the antibody or antigen binding fragment thereof is a monoclonal antibody or antigen-binding fragment thereof, a Fab, a humanized antibody or antigen-binding fragment thereof, a bispecific antibody or antigen-binding fragment thereof, a monovalent antibody or antigen-binding fragment thereof, a chimeric antibody or antigen-binding fragment thereof, a single-chain Fv molecule, a bispecific single chain Fv ((scFv')2) molecule, a domain antibody, a diabody, a triabody, an affibody, a domain antibody, a SMIP, a nanobody, a Fv fragment, a Fab fragment, a F(ab')2 molecule, or a tandem scFv (taFv) fragment; or (ii) binds one or more cell surface molecules selected from the group consisting of T cell receptor, CD3, CD4, CD8, CD11 a, CD11 b, CD11 c, CD14, CD15, CD16, CD19, CD25, CD33, CD34, CD45RO, CD56, major histocompatibility complex, and chimeric antigen receptor.