A method for three-dimensional printing, comprising: applying a powder onto a build platform or a previously formed layer of a final 3D object, wherein the powder comprises a polymeric build material selected from crystalline polymer particles and semi-crystalline polymer particles or a polymeric composite build material selected from composite particles comprising a polymer and a ceramic; negatively patterning some of the polymeric or polymeric composite build material to define a removable build material portion and a remaining build material portion, the negatively patterning including: selectively applying a polymer solution including a polymer having a pendant reactive functional group onto build material that will become part of the removable build material portion, wherein the pendant reactive functional group is selected from a maleic anhydride functionality, a maleimide functionality, an alcohol functionality, an epoxide functionality, or a combination thereof; and selectively applying a crosslinker solution including a multifunctional crosslinker onto build material that will become part of the removable build material portion, wherein the multifunctional crosslinker is selected from the group consisting of a diamine, a dithiol, a di-acid chloride, a tetraborate, a di-nucleophile, and a combination thereof; wherein the pendant reactive functional group and the multifunctional crosslinker react to form an insoluble gel network among the polymeric or polymeric composite build material in the removable build material portion, wherein the insoluble gel network is insoluble in water, organic solvents and any co-solvents used in the polymer solution and/or the crosslinker solution; based on a 3D object model, forming a layer of the final 3D object from at least some of the remaining build material portion outside the insoluble gel network, wherein the insoluble gel network prevents the build material in the removable build material portion from fusing or semi-fusing with build material in the remaining build material portion by forming a physical barrier between build material in the removable build material portion and the layer. applying a powder onto a build platform or a previously formed layer of a final 3D object, wherein the powder comprises a polymeric build material selected from crystalline polymer particles and semi-crystalline polymer particles or a polymeric composite build material selected from composite particles comprising a polymer and a ceramic; negatively patterning some of the polymeric or polymeric composite build material to define a removable build material portion and a remaining build material portion, the negatively patterning including: selectively applying a polymer solution including a polymer having a pendant reactive functional group onto build material that will become part of the removable build material portion, wherein the pendant reactive functional group is selected from a maleic anhydride functionality, a maleimide functionality, an alcohol functionality, an epoxide functionality, or a combination thereof; and selectively applying a crosslinker solution including a multifunctional crosslinker onto build material that will become part of the removable build material portion, wherein the multifunctional crosslinker is selected from the group consisting of a diamine, a dithiol, a di-acid chloride, a tetraborate, a di-nucleophile, and a combination thereof; wherein the pendant reactive functional group and the multifunctional crosslinker react to form an insoluble gel network among the polymeric or polymeric composite build material in the removable build material portion, wherein the insoluble gel network is insoluble in water, organic solvents and any co-solvents used in the polymer solution and/or the crosslinker solution; selectively applying a polymer solution including a polymer having a pendant reactive functional group onto build material that will become part of the removable build material portion, wherein the pendant reactive functional group is selected from a maleic anhydride functionality, a maleimide functionality, an alcohol functionality, an epoxide functionality, or a combination thereof; and selectively applying a crosslinker solution including a multifunctional crosslinker onto build material that will become part of the removable build material portion, wherein the multifunctional crosslinker is selected from the group consisting of a diamine, a dithiol, a di-acid chloride, a tetraborate, a di-nucleophile, and a combination thereof; wherein the pendant reactive functional group and the multifunctional crosslinker react to form an insoluble gel network among the polymeric or polymeric composite build material in the removable build material portion, wherein the insoluble gel network is insoluble in water, organic solvents and any co-solvents used in the polymer solution and/or the crosslinker solution; based on a 3D object model, forming a layer of the final 3D object from at least some of the remaining build material portion outside the insoluble gel network, wherein the insoluble gel network prevents the build material in the removable build material portion from fusing or semi-fusing with build material in the remaining build material portion by forming a physical barrier between build material in the removable build material portion and the layer.