for the following defined terms , these definitions shall be applied , unless a different definition is given in the claims or elsewhere in this specification . all numeric values are herein assumed to be modified by the term “ about ”, whether or not explicitly indicated . the term “ about ” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value , i . e ., having the same function or result . in many instances , the term “ about ” may include numbers that are rounded to the nearest significant figure . the recitation of numerical ranges by endpoints includes all numbers within that range . for example , a range of 1 to 5 includes 1 , 1 . 5 , 2 , 2 . 75 , 3 , 3 . 80 , 4 and 5 . as used in this specification and in the appended claims , the singular forms “ a ”, “ an ”, and “ the ” include plural referents unless the content clearly dictates otherwise . as used in this specification and in the appended claims , the term “ or ” is generally employed in its sense including “ and / or ” unless the content clearly dictates otherwise . the following description should be read with reference to the drawings , in which like elements in different drawings are numbered in like fashion . the drawings , which are not necessarily to scale , depict selected embodiments and are not intended to limit the scope of the invention . although examples of construction , dimensions , and materials are illustrated for the various elements , those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized . a hydrophilic polymer is a polymer that attracts or binds water molecules when the polymer is placed in contact with an aqueous system . examples of aqueous systems that can provide water molecules that can bind to a hydrophilic polymer include blood and other bodily fluids . when a hydrophilic polymer comes into contact with such a system , water molecules can bind to the polymer via mechanisms such as hydrogen bonding between the water molecules and substituents or functional groups present within or on the polymer . in some instances , a hydrophilic polymer can bind at least 2 times its own weight in water and in particular instances some hydrophilic polymers can bind up to about 20 times their own weight in water . one class of polymers that can be considered as hydrophilic includes certain nonionic polymers such as hydrophilic polyurethanes . examples of suitable materials include nonionic polyether polyurethanes available commercially under the hydroslip ® name . another suitable material includes nonionic aliphatic polyether polyurethanes available commercially under the tecogel ® name . examples of other suitable nonionic polymers include polymers such as poly ( hydroxy methacrylate ), poly ( vinyl alcohol ), poly ( ethylene oxide ), poly ( n - vinyl - 2 - pyrolidone ), poly ( acrylamide ) and other similar materials . another class of polymers that can be considered as hydrophilic includes ionomer polymers . an ionomer polymer is a polymer that has includes charged functional groups . the charged functional groups can be positively charged , in which case the polymer can be referred to be a cationomer , or the functional groups can be negatively charged , in which case the polymer can be referred to as an anionomer . an ionomeric polymer can be formed using a variety of negatively charged functional groups . the negatively charged functional group can be added to a previously formed polymer , or the negatively charged functional groups can be part of one or more of the monomers used to form the ionomeric polymer . examples of suitable negatively charged functional groups include sulfonates and carboxylates . the ionomeric polymer can , in particular , include sulfonate functional groups . these groups are negatively charged and can readily hydrogen bond sufficient amounts of water when brought into contact with a source of water such as an aqueous system . additional examples of ionomeric polymers include poly ( acrylic acid ), poly ( methacrylic acid ), hydroluronic acid , collagen , and other similar materials . turning now to the figures , fig1 is a perspective view of an example intravascular filter 10 , which includes a filter membrane 12 . the filter membrane 12 can be formed from any suitable material or combination of materials as will be discussed in greater detail hereinafter . the filter membrane 12 can be porous , having pores 14 that are configured to permit blood flow while retaining embolic material of a desired size . the filter membrane 12 can have a mouth 16 and a closed end 18 and is capable of moving between an open state and a closed state . the mouth 16 can be sized to occlude the lumen of the body vessel in which the filter may be installed , thereby directing all fluid and any emboli into the filter with emboli retained therein . a support hoop 20 can be attached to the filter membrane 12 at or proximate to the mouth 16 . the support hoop 20 can be attached to the filter membrane 12 through melt bonding or other suitable means . in some embodiments , as discussed in greater detail hereinafter , the support loop 20 can be integrally molded within the filter membrane 12 . the support hoop 20 has an expanded state and a compressed state . the expanded state of the support hoop 20 is configured to urge the mouth 16 to its full size , while the compressed state permits insertion into a small lumen . the support hoop 20 can be made from a flexible metal such as spring steel , from a super - elastic elastic material such as a suitable nickel - titanium alloy , or from other suitable material . the support hoop 20 can be a closed hoop made from a wire of uniform diameter , it can be a closed hoop made from a wire having a portion with a smaller diameter , it can be an open hoop having a gap , or it can have another suitable configuration . a strut 22 can be fixedly or slideably attached to and extend from the support hoop 20 . an elongate member 24 can be attached to and extend from the strut 22 . the elongate member 24 can be attached to the strut 22 at an angle or the strut 22 can have a small bend , either at a point or over a region . the strut 22 can be attached to the support hoop 20 at a slight angle such that when the elongate member 24 , the strut 22 , and the support hoop 20 are in an unconstrained position , the elongate member 24 can generally extend perpendicular to the support hoop 20 . in the unconstrained position , the elongate member 24 can also lie along an axis which passes through the center of the region created by the support hoop 20 . this may help position the support hoop 20 in contact with the wall of a vascular lumen or it may help in enhancing predictability or reliability during deployment . in some embodiments , the elongate member 24 can terminate at the strut 22 . in other embodiments , the elongate member 24 can extend through the filter membrane 12 , as shown . whether or not the elongate member 24 extends through the filter membrane 12 , it may be fixedly or slideably / rotatably attached to the filter membrane 12 . the filter membrane 12 can include a waist 26 at a closed end 28 . in some embodiments , the waist 26 can be integrally formed with the filter membrane 12 . in other embodiments , the filter membrane 12 can be further processed to form the waist 26 . in some embodiments , integrally forming the waist 26 with the filter membrane 12 can reduce the outer diameter of the filter device when in a compressed state , increase the reliability and uniformity of the bond between the filter membrane and the elongate member , and reduce the number of steps or components needed to form the filter device . the waist 26 is a region largely incapable of moving between two states and having a lumen of substantially constant diameter therethrough . the elongate member 24 can extend through and be bonded to the waist 26 . this bonding can be heat bonding such as laser bonding , or may be an adhesive or other suitable means . fig3 through 5 illustrate exemplary methods of forming the filter membrane 12 in accordance with the invention . fig3 shows a filter forming mandrel 28 and a spray apparatus 30 . the filter forming mandrel 28 can be dimensioned as appropriate for any particular filter size and configuration and can be formed of any suitable metallic or polymeric material . in some instances , the filter forming mandrel 28 can have a release coating applied thereto in order to facilitate removal of a finished filter membrane 12 . the spray apparatus 30 can generically represent any suitable spraying apparatus that can be configured to provide appropriately sized particles of whichever polymeric material is being applied . in some instances , the spray apparatus 30 can provide particle sizes in the range of about 5 μm to about 100 μm and more particularly about 15 μm to about 60 μm when spraying suitable materials such as polyurethanes . in fig4 , a first layer 32 has been sprayed onto the filter forming mandrel 28 . in some instances , the first layer 32 can be a base layer while in other cases the first layer 32 can be a hydrophilic layer . a second layer 34 can subsequently be applied , as shown schematically in fig5 . if the first layer 32 is a base layer , the second layer 34 can be a hydrophilic layer . conversely , if the first layer is a hydrophilic layer , then the second layer 34 can be a base layer . while not expressly illustrated , additional layers can also be applied . for example , in some cases it can be useful to have a hydrophilic layer on an inside surface of the base layer as well as on the outside surface of the base layer . fig6 is a perspective view of the finished filter membrane 12 . fig7 is a cross - section illustrating the multi - layer construction of the filter membrane 12 . fig7 shows first layer 32 and second layer 34 , although additional layers are permissible as discussed above . merely for illustrative purposes , the first layer 32 can be considered to represent a base layer while the second layer 34 can be considered as representing a hydrophilic layer . the first layer 32 has an inner surface 36 and an outer surface 38 . as illustrated , the second layer 34 ( representing the hydrophilic layer ) is disposed on the outer surface 38 of the first layer 32 ( representing the base layer ). in some embodiments , the base layer can be applied to have a thickness that is in the range of about 5 μm to about 50 μm . in particular embodiments , the base layer can have a thickness that is in the range of about 10 μm to about 50 μm . the hydrophilic layer can have a thickness that is in the range of about 0 . 5 μm to about 8 μm . in particular embodiments , the hydrophilic layer can have a thickness that is in the range of about 0 . 5 μm to about 5 μm . in other embodiments , the hydrophilic layer can be disposed on the inner surface 36 of the first layer 32 . in some instances , a first hydrophilic layer can be disposed on the inner surface 36 of the first layer 32 while a second hydrophilic layer can be disposed on the outer surface 38 of the first layer 32 , assuming of course that the first layer 32 represents a base layer . the base layer can be formed of any suitable polymeric materials , such as polyether block amide , polybutylene terephthalate / polybutylene oxide copolymers sold under the hytrel ® and arnitel ® trademarks , nylon 11 , nylon 12 , polyurethane , polyethylene terephthalate , polyvinyl chloride , polyethylene naphthalene dicarboxylate , olefin / ionomer copolymers , polybutylene terephthalate , polyethylene naphthalate , ethylene terephthalate , butylene terephthalate , ethylene naphthalate copolymers , polyamide / polyether / polyester , polyamides , aromatic polyamides , polyurethanes , aromatic polyisocyanates , polyamide / polyether , and polyester / polyether block copolymers , among others . in some embodiments , the base layer can be formed of a polyurethane that absorbs less than about 5 percent of its own weight in water . in some cases , the base layer can be formed from a polycarbonate urethane such as that available commercially under the bionate ® name . the hydrophilic layer ( or layers ) can as discussed above be formed of hydrophilic materials that can absorb from about 2 to about 20 times their own weight in water . the hydrophilic material can be a nonionic material such as the hydroslip ® and tecogel ® materials discussed above . in some embodiments , these materials can be particularly useful , as they are readily dissolvable in water / alcohol mixtures to form low viscosity solutions that are easily sprayable . these materials are compatible with materials used to form the base layer and exhibit good adhesion to the base layer . the hydrophilic material can be an anionic material such as a sulfonated polyurethane or a carboxylated polyurethane . a polyurethane can be formed from monomers , chain extenders or oligomers that include a desired functional group that can provide a polymer with desired anionomer character . in some embodiments , a diamine disulfonic acid can be used as a chain extender in synthesizing a sulfonated polyurethane . in particular , a sulfonated polyurethane can be produced using 4 , 4 ′- diamino - 2 , 2 ′- biphenyl disulfonic acid as a chain extender . alternatively , a polyurethane can be formed , and desired functional groups such as sulfonate groups can subsequently be added via a grafting reaction . an illustrative but non - limiting method of forming a sulfonated polyurethane is described herein . a polyurethane can be formed by first reacting a diisocyanate with an active hydrogen source to create a polyurethane backbone , and subsequently substituting a desired functional group . for example , a desirable functional group includes a sulfonate functional group . a sulfonate functional group can be added to a polyurethane backbone by reacting the polyurethane with a molecule bearing the desired substituent . an example of a desired substituent is a pendent propyl sulfonate group . one way of adding this functional group is to react the polyurethane backbone with propane sulftone , which is also known as 1 , 2 - oxathiolane - 2 , 2 - dione and has the following structure : polyurethanes suitable for use in the present invention can also include copolymers formed by reacting a diisocyanate , a diol and an ether . in particular , a suitable polyurethane can be formed by reacting methylene bis -( p - phenyl isocyanate ) ( mdi ), n - methyldiethanolamine ( mdea ) and poly ( tetra - methylene oxide ) ( ptmo ). alternatively , 1 , 4 - butanediol can be used as a chain extender in place of the mdea . a carboxylated polyurethane can be formed in a variety of ways . an illustrative but non - limiting method is described herein . a polyurethane bearing pendent carboxyl groups can be formed by reacting an aliphatic diisocyanate , a diol component and a carboxylic acid . in particular , a carboxylated polyurethane polymer can be produced as a reaction product of a diol component , an aliphatic diisocyanate , water and a 2 , 2 - di -( hydroxymethyl ) alkanoic acid . alternatively , an amount of amine , such as diglycolamine can be used for at least a portion of the water in the reaction to form the reaction product . the diol component can include a polyoxyalkylene diol , such as polyoxyethylene diol having a molecular weight of from about 400 to about 20 , 000 , polyoxypropylene diol having a number average molecular weight of about 200 to about 2 , 500 , block copolymers of ethylene oxide and propylene oxide having a molecular weight of about 1 , 000 to about 9 , 000 and polyoxytetramethylene diol having a number average molecular weight of about 200 to about 4 , 000 . the polyurethane can include a low molecular weight alkylene glycol such as ethylene glycol , propylene glycol , 2 - ethyl - 1 - 1 , 3 - hexanediol , tripropylene glycol , triethylene glycol , 2 ,- 4 - pentane diol , 2 - methyl - 1 , 3 - propanediol , 2 ,- methyl - 1 , 3 - pentanediol , cyclohexanediol , cyclohexanedimethanol , dipropylene glycol , diethylene glycol , and mixtures thereof . an amine can be used in the reaction for at least a portion of the water in the reaction mixture . the amine can be diglycolamine , although other amines such as ethylene diamine , propylene diamine , monoethanolamine , diglycolamine , and propylene diamine can also be used . the diisocyanate used can include both aliphatic and aromatic types and mixtures thereof . an example of a suitable isocyanate is methylene bis ( cyclohexyl - 4 - isocyanate ). other examples of diisocyanates are trimethyl hexamethylene diisocyanate and isophorone diisocyanate . representative examples of aliphatic diisocyanates include tetramethylene diisocyanate , hexamethylene diisocyanate , trimethylene diisocyanate , trimethylene hexamethylene diisocyanate , cyclohexyl 1 , 2 - diisocyanate , cyclohexylene 1 , 4 - diisocyanate , and aromatic diisocyanates such as 2 , 4 - toluene diisocyanates and 2 , 6 - toluene diisocyanates . the invention should not be considered limited to the particular examples described above , but rather should be understood to cover all aspects of the invention as set out in the attached claims . various modifications , equivalent processes , as well as numerous structures to which the invention can be applicable will be readily apparent to those of skill in the art upon review of the instant specification .
intravascular filters can include a filter membrane having a hydrophilic polymer coating on the filter membrane . the hydrophilic polymer coating can be on an inner surface , an outer surface or both an inner surface and an outer surface of the filter membrane . intravascular filters including a hydrophilic polymer coating may be considered as providing increased hemocompatibility , decreased risk of filter - induced thrombosis and reduced sheathing forces .