Patent Publication Number: US-2023142433-A1

Title: Fluid drainage devices, systems, and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 63/276,170, filed Nov. 5, 2021, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates generally to apparatuses, systems, and methods for draining fluid and diverting the fluid to be reabsorbed elsewhere in the body. More specifically, the disclosure relates to apparatuses, systems, and methods for draining aqueous humor from the anterior chamber of a patient&#39;s eye such that it may be reabsorbed by the body. 
     BACKGROUND 
     Various medical interventions involve evacuating excess fluid such as biological fluid from one portion of the body and redirecting it to another location of the body where it can be reabsorbed. In certain instances, this evacuation is achieved via minimally invasive procedures such as endoscopic third ventriculostomy (ETV) and choroid plexus cauterization procedure (CPC). In other instances, this evacuation is performed post-operatively via implantable medical devices, such as a shunt. Proven useful in various medical procedures, shunts of different forms have been employed as treatment for numerous diseases, such as hydrocephalus and glaucoma. 
     Without treatment, excessive biological fluid can lead to unhealthy pressure build ups. For instance, glaucoma is a progressive eye disease characterized by elevated intraocular pressure. Aqueous humor is a fluid that fills the anterior chamber of the eye and contributes to intraocular pressure or intraocular fluid pressure. This increase in intraocular pressure is usually caused by an insufficient amount of aqueous humor absorbed by the body. In some cases, the aqueous humor is not absorbed quickly enough or even not absorbed at all, while in other cases, the aqueous humor is additionally or alternatively produced too quickly. Elevated intraocular pressure is associated with gradual and sometimes permanent loss of vision in the affected eye. 
     Many attempts have been made to treat glaucoma. However, some conventional devices are relatively bulky and lack flexibility, compliance, and device/tissue attachment required to avoid relative motion between the device and the surrounding tissue. Such movement can result in continued stimulation of the surrounding tissue, causing irritation at the implantation site. Irritation, in turn, can lead to increased chronic inflammatory tissue response, excessive scarring at the device site, and increased risk of device erosion through conjunctival and endophthalmitis. Scar tissue effectively prevents resorption of aqueous humor without erosion. These complications may prevent the device from functioning properly. The result is a gradual rise in intraocular pressure and progression of glaucoma. 
     SUMMARY 
     According to one example (“Example 1”), a glaucoma shunt for draining a fluid from an eye to a tissue surrounding the eye is disclosed herein. The glaucoma shunt is implantable within tissue of the eye and includes: a shunt body that is formed from a microporous material that is arranged so as to form a reservoir within the shunt body; and a conduit in fluid communication with the reservoir, the conduit being insertable into the eye such that the fluid at a distal end of the conduit is allowed to flow through the conduit and accumulate within the reservoir. The microporous material transitions from a hydrophobic state to a hydrophilic state within 30 days as the fluid that is accumulated in the reservoir diffuses to the tissue surrounding the eye through the microporous material so as to provide a variable flow resistance as the microporous material transitions from the hydrophobic state to the hydrophilic state. 
     According to another example (“Example 2”) further to Example 1, a first portion of the microporous material transitions from the hydrophobic state to the hydrophilic state within 3 days. 
     According to another example (“Example 3”) further to Example 2, a second portion of the microporous material different from the first portion transitions from the hydrophobic state to the hydrophilic state within 7 days. 
     According to another example (“Example 4”) further to any preceding Example, an entirety of the microporous material transitions from the hydrophobic state to the hydrophilic state within 30 days. 
     According to another example (“Example 5”) further to any preceding Example, in the hydrophobic state, the microporous material is opaque. 
     According to another example (“Example 6”) further to any preceding Example, in the hydrophilic state, the microporous material is transparent. 
     According to another example (“Example 7”) further to any preceding Example, the shunt body has a maximum thickness of no greater than 500 μm. 
     According to another example (“Example 8”) further to any preceding Example, in the hydrophobic state, a drop of water placed on a surface of the microporous material forms a contact angle of greater than 90 degrees with respect to the surface, and in the hydrophilic state, a drop of water placed on a surface of the microporous material forms the contact angle of less than 90 degrees with respect to the surface. The transition from the hydrophobic state to the hydrophilic state constitutes a decrease in the contact angle by at least 10 degrees. 
     According to another example (“Example 9”) further to any preceding Example, the variable flow resistance is greater in the hydrophobic state than in the hydrophilic state. 
     According to another example (“Example 10”) further to any preceding Example, the microporous material is more translucent in the hydrophilic state than in the hydrophobic state. 
     According to another example (“Example 11”) further to any preceding Example, the shunt body has a continuous wall that defines the reservoir and a reservoir opening in the continuous wall communicating with the internal reservoir and through which the conduit is engagingly receive. At least a portion of the continuous wall has a wall portion composed of the microporous material. The wall portion has an internal side facing the internal reservoir and an opposing external side facing the exterior region of the human eye. The wall portion internal side has a low porosity surface extending an entirety of the wall portion internal side. The wall portion external side has an alternating surface including the low porosity surface disposed between high porosity surfaces. 
     According to another example (“Example 12”) further to any preceding Example, the microporous material comprises a first layer having a first microporous membrane integrated with a second microporous membrane and a second layer having a third microporous membrane integrated with a fourth microporous membrane. 
     According to another example (“Example 13”) further to Example 12, the microporous material comprises expanded polytetrafluoroethylene (ePTFE). 
     According to another example (“Example 14”) further to Example 13, a first microporous membrane permeability of the first microporous membrane is greater than a second microporous membrane permeability of the second microporous membrane. A fourth microporous membrane permeability of the fourth microporous membrane is greater than a third microporous membrane permeability of the third microporous membrane. 
     According to another example (“Example 15”) further to Example 14, the first layer and the second layer are in a stacked configuration such that the first microporous membrane and the fourth microporous membrane are outermost membranes of the shunt body and the second microporous membrane and third microporous membrane are innermost membranes of the shunt body defining the reservoir. 
     According to another example (“Example 16”) further to Example 12, the first microporous membrane has a first microporous membrane permeability, the second microporous membrane has a second microporous membrane permeability, the third microporous membrane has a third microporous membrane permeability, and the fourth microporous membrane has a fourth microporous membrane permeability. The second microporous membrane permeability is about the same as the third microporous membrane permeability, and the first microporous membrane permeability is about the same as the fourth microporous membrane permeability. Each of the second microporous membrane permeability and the third microporous membrane permeability are different from the first microporous membrane permeability and the fourth microporous membrane permeability. 
     According to another example (“Example 17”) further to Example 12, the second and third microporous membranes are bonded to each other along peripheral edges of the first and second layers to define the reservoir and to dispose the reservoir between the second and third microporous membranes. The second and third microporous membranes are configured to resist tissue ingrowth. The second and third microporous membranes have an expanded state that is maintained adjacent to the peripheral edges of the first and second layers. 
     According to another example (“Example 18”) further to Example 12, the reservoir is configured to move between a collapsed state in which the second and third microporous membranes resist fluid flow therebetween and an expanded state in which fluid is allowed to flow between the second and third microporous membranes. 
     According to another example (“Example 19”) further to Example 18, fluid flow into the reservoir is directed from the distal end of the conduit toward a periphery of chamber. 
     According to another example (“Example 20”) further to Example 18, the reservoir has a reservoir proximal section that is adjacent the distal end of the conduit and a reservoir distal section that is positioned opposite of the reservoir proximal section. During drainage of the fluid, the reservoir proximal section is configured to inflate before the reservoir distal section. 
     According to another example (“Example 21”) further to any preceding Example, the variable flow resistance corresponds to a rate of change in pressure with respect to flow rate over time. 
     According to another example (“Example 22”) further to Example 21, the microporous material transitions from the hydrophobic state having a first flow resistance to a partially hydrophilic state having a second flow resistance and then to the hydrophilic state having a third flow resistance. The first flow resistance is greater than both the second flow resistance and the third flow resistance, and the second flow resistance is greater than the third flow resistance. 
     According to another example (“Example 23”) further to any preceding Example, the microporous material is configured to transition from the hydrophobic state to the hydrophilic state based on a wetting of the microporous material with the fluid. The microporous material is configured such that wetting of an outer portion of the shunt body occurs before wetting of the reservoir. 
     According to another example (“Example 24”), an aqueous humor diffusion device is disclosed herein. The device includes a device body that is formed from a microporous material that is arranged so as to form a reservoir within the device body, the reservoir being configured to receive and accumulate fluid. The microporous material transitions from a hydrophobic state to a hydrophilic state within 30 days as fluid that is accumulated in the reservoir diffuses to tissue surrounding the device through the microporous material so as to provide a variable flow resistance as the microporous material transitions from the hydrophobic state to the hydrophilic state. 
     According to another example (“Example 25”) further to Example 24, a first portion of the microporous material transitions from the hydrophobic state to the hydrophilic state within 3 days. 
     According to another example (“Example 26”) further to Example 25, a second portion of the microporous material different from the first portion transitions from the hydrophobic state to the hydrophilic state within 7 days. 
     According to another example (“Example 27”) further to any one of Examples 24-26, an entirety of the microporous material transitions from the hydrophobic state to the hydrophilic state within 30 days. 
     According to another example (“Example 28”) further to any one of Examples 24-27, in the hydrophobic state, the microporous material is opaque. 
     According to another example (“Example 29”) further to any one of Examples 24-28, in the hydrophilic state, the microporous material is transparent. 
     According to another example (“Example 30”) further to any one of Examples 24-29, the shunt body has a maximum thickness of no greater than 500 μm. 
     According to another example (“Example 31”) further to any one of Examples 24-30, in the hydrophobic state, a drop of water placed on a surface of the microporous material forms a contact angle of greater than 90 degrees with respect to the surface, and in the hydrophilic state, a drop of water placed on a surface of the microporous material forms the contact angle of less than 90 degrees with respect to the surface. The transition from the hydrophobic state to the hydrophilic state constitutes a decrease in the contact angle by at least 10 degrees. 
     According to another example (“Example 32”) further to any one of Examples 24-31, the variable flow resistance is greater in the hydrophobic state than in the hydrophilic state. 
     According to another example (“Example 33”) further to any one of Examples 24-32, the microporous material is more translucent in the hydrophilic state than in the hydrophobic state. 
     According to another example (“Example 34”) further to any one of Examples 24-33, the microporous material comprises a first layer having a first microporous membrane bonded to a second microporous membrane and a second layer comprising a third microporous membrane bonded to a fourth microporous membrane. 
     According to another example (“Example 35”) further to Example 34, the microporous material comprises expanded polytetrafluoroethylene (ePTFE). 
     According to another example (“Example 36”) further to Example 35, a first microporous membrane permeability of the first microporous membrane is greater than a second microporous membrane permeability of the second microporous membrane. A fourth microporous membrane permeability of the fourth microporous membrane is greater than a third microporous membrane permeability of the third microporous membrane. 
     According to another example (“Example 37”) further to Example 36, the first layer and the second layer are in a stacked configuration such that the first microporous membrane and the fourth microporous membrane are outermost membranes of the device body and the second microporous membrane and third microporous membrane are innermost membranes of the device body defining the reservoir. 
     According to another example (“Example 38”) further to Example 34, the first microporous membrane has a first microporous membrane permeability, the second microporous membrane has a second microporous membrane permeability, the third microporous membrane has a third microporous membrane permeability, and the fourth microporous membrane has a fourth microporous membrane permeability. The second microporous membrane permeability is about the same as the third microporous membrane permeability, and the first microporous membrane permeability is about the same as the fourth microporous membrane permeability. Each of the second microporous membrane permeability and the third microporous membrane permeability are different from the first microporous membrane permeability and the fourth microporous membrane permeability. 
     According to another example (“Example 39”) further to Example 34, the second and third microporous membranes are bonded to each other along peripheral edges of the first and second layers to define the reservoir and to dispose the reservoir between the second and third microporous membranes. The second and third microporous membranes are configured to resist tissue ingrowth. The first and fourth microporous membranes are configured to permit tissue ingrowth. The second and third microporous membranes have an expanded state that is maintained adjacent to the peripheral edges of the first and second layers. 
     According to another example (“Example 40”) further to Example 34, the reservoir is configured to move between a collapsed state in which the second and third microporous membranes resist fluid flow therebetween and an expanded state in which fluid is allowed to flow between the second and third microporous membranes. 
     According to another example (“Example 41”) further to Example 40, fluid flow into the reservoir is directed from a proximal portion of the reservoir toward a periphery of chamber. 
     According to another example (“Example 42”) further to Example 40, the reservoir has a reservoir proximal section that is configured to be positioned adjacent a reservoir port through which the fluid is received and a reservoir distal section that is positioned opposite of the reservoir proximal section. During drainage of the fluid, the reservoir proximal section is configured to inflate before the reservoir distal section. 
     According to another example (“Example 43”) further to any one of Examples 24-42, the variable flow resistance corresponds to a rate of change in pressure with respect to flow rate over time. 
     According to another example (“Example 44”) further to Example 43, the microporous material transitions from the hydrophobic state having a first flow resistance to a partially hydrophilic state having a second flow resistance and then to the hydrophilic state having a third flow resistance. The first flow resistance is greater than both the second flow resistance and the third flow resistance, and the second flow resistance is greater than the third flow resistance. 
     According to another example (“Example 45”) further to any one of Examples 24-44, the microporous material is configured to transition from the hydrophobic state to the hydrophilic state based on a wetting of the microporous material with the fluid. The microporous material is configured such that wetting of an outer portion of the device body occurs before wetting of the reservoir. 
     According to another example (“Example 46”), methods are disclosed for forming glaucoma drainage device that is implantable. The method includes: arranging a microporous material so as to form a device body with a reservoir defined therein, the reservoir being configured to receive and accumulate fluid; and securing portions of the microporous material that forms the reservoir such that as fluid is accumulated in the reservoir the microporous material transitions from a hydrophobic state to a hydrophilic state within 30 days as the fluid diffuses to tissue surrounding the device through the microporous material so as to provide a variable flow resistance as the microporous material transitions from the hydrophobic state to the hydrophilic state. 
     According to another example (“Example 47”) further to Example 46, a first portion of the microporous material transitions from the hydrophobic state to the hydrophilic state within 3 days. 
     According to another example (“Example 48”) further to Example 47, a second portion of the microporous material different from the first portion transitions from the hydrophobic state to the hydrophilic state within 7 days. 
     According to another example (“Example 49”) further to any one of Examples 46-48, an entirety of the microporous material transitions from the hydrophobic state to the hydrophilic state within 30 days. 
     According to another example (“Example 50”) further to any one of Examples 46-49, in the hydrophobic state, the microporous material is opaque. 
     According to another example (“Example 51”) further to any one of Examples 46-50, in the hydrophilic state, the microporous material is transparent. 
     According to another example (“Example 52”) further to any one of Examples 46-51, the shunt body has a maximum thickness of no greater than 500 μm. 
     According to another example (“Example 53”) further to any one of Examples 46-52, in the hydrophobic state, a drop of water placed on a surface of the microporous material forms a contact angle of greater than 90 degrees with respect to the surface, and in the hydrophilic state, a drop of water placed on a surface of the microporous material forms the contact angle of less than 90 degrees with respect to the surface. The transition from the hydrophobic state to the hydrophilic state constitutes a decrease in the contact angle by at least 10 degrees. 
     According to another example (“Example 54”) further to any one of Examples 46-53, the variable flow resistance is greater in the hydrophobic state than in the hydrophilic state. 
     According to another example (“Example 55”) further to any one of Examples 46-54, the microporous material is more translucent in the hydrophilic state than in the hydrophobic state. 
     According to another example (“Example 56”) further to any one of Examples 46-55, the reservoir receives the fluid through a port in the device body. The method further comprises securing an intake conduit to the device body at the port, the intake conduit being configured to receive the drainage. 
     According to another example (“Example 57”) further to any one of Examples 46-56, the one or more microporous materials comprise a first layer having a first microporous membrane bonded to a second microporous membrane and a second layer comprising a third microporous membrane bonded to a fourth microporous membrane. Securing portions of the one or more microporous materials comprises bonding the second microporous membrane to the third microporous membrane. 
     According to another example (“Example 58”) further to Example 57, the second and third microporous membranes are bonded to each other along peripheral edges of the first and second layers to define the reservoir and to dispose the reservoir between the second and third microporous membranes. The second and third microporous membranes are configured to resist tissue ingrowth. The first and fourth microporous membranes are configured to permit tissue ingrowth. The second and third microporous membranes have an expanded state that is maintained adjacent to the peripheral edges of the first and second layers. 
     According to another example (“Example 59”) further to Example 57, securing portions of the microporous material comprises refraining from bonding the first microporous membrane to the fourth microporous membrane. 
     According to another example (“Example 60”) further to Example 57, securing portions of the one or more microporous materials comprises arranging the first layer and the second layer in a stacked configuration such that the first microporous membrane and the fourth microporous membrane are outermost membranes of the device body and the second microporous membrane and third microporous membrane are innermost membranes of the device body. 
     According to another example (“Example 61”), a glaucoma drainage device for draining a fluid from an interior region of a human eye to an exterior region of the human eye is disclosed herein. The device includes a body having a continuous wall defining an internal reservoir within the body and a reservoir opening in the wall communicating with the internal reservoir, and a conduit extending from the body by a conduit length. The conduit has opposing first and second ends defining a passage through the conduit extending between the opposing first and second ends, the conduit first end engaging the reservoir opening to provide a fluidic connection between the conduit second end and the reservoir, the conduit length being sufficient to dispose the conduit first end at the exterior region of the human eye and to dispose the conduit second end at the interior region of the human eye. At least a portion of the continuous wall has a wall portion composed of a microporous material. The wall portion has an internal side facing the reservoir and an opposing external side facing the exterior region of the human eye, the wall portion internal side low porosity surface extending an entirety of the wall portion internal side. The wall portion external side has an alternating surface comprising the low porosity surface disposed between high porosity surfaces. The wall portion has an initial hydrophobic state that transitions to a final hydrophilic state within 30 days when the fluid engages the wall portion. 
     According to another example (“Example 62”) further to Example 61, a first portion of the microporous material transitions from the hydrophobic state to the hydrophilic state within 3 days. 
     According to another example (“Example 63”) further to Example 62, a second portion of the microporous material different from the first portion transitions from the hydrophobic state to the hydrophilic state within 7 days. 
     According to another example (“Example 64”) further to any one of Examples 61-63, an entirety of the microporous material transitions from the hydrophobic state to the hydrophilic state within 30 days. 
     According to another example (“Example 65”) further to any one of Examples 61-64, in the hydrophobic state, the microporous material is opaque. 
     According to another example (“Example 66”) further to any one of Examples 61-65, in the hydrophilic state, the microporous material is transparent. 
     According to another example (“Example 67”) further to any one of Examples 61-66, the shunt body has a maximum thickness of no greater than 500 μm. 
     According to another example (“Example 68”) further to any one of Examples 61-67, in the hydrophobic state, a drop of water placed on a surface of the microporous material forms a contact angle of greater than 90 degrees with respect to the surface, and in the hydrophilic state, a drop of water placed on a surface of the microporous material forms the contact angle of less than 90 degrees with respect to the surface. The transition from the hydrophobic state to the hydrophilic state constitutes a decrease in the contact angle by at least 10 degrees. 
     According to another example (“Example 69”) further to any one of Examples 61-68, the variable flow resistance is greater in the hydrophobic state than in the hydrophilic state. 
     According to another example (“Example 70”) further to any one of Examples 61-69, the microporous material is more translucent in the hydrophilic state than in the hydrophobic state. 
     According to another example (“Example 71”) further to any one of Examples 61-70, the wall portion defines a wall portion thickness extending between the internal side and the external side. The wall portion thickness defines an internal region of the wall portion having a transition porosity that is between a porosity of the low porosity surface of the internal side and a porosity of the high porosity surface of the external side. 
     According to another example (“Example 72”) further to any one of Examples 61-70, the wall portion defines a wall portion thickness extending between the internal side and the external side. The wall portion thickness defines an internal region of the wall portion extending between the low porosity surface of the internal side and the low porosity surface of the external side. The internal region has an internal region porosity that is equal to porosities of the low porosity surfaces of the internal side and the external side. 
     According to another example (“Example 73”) further to any one of Examples 61-70, the wall portion defines a wall portion thickness extending between the internal side and the external side. The wall portion thickness defines an internal region of the wall portion extending between the low porosity surface of the internal side and the high porosity surface of the external side. The internal region has an internal region porosity that is equal to a porosity of the low porosity surface of the internal side. 
     According to another example (“Example 74”) further to any one of Examples 61-70, the wall portion defines a wall portion thickness extending between the internal side and the external side. The wall portion thickness defines an internal region of the wall portion extending between the low porosity surface of the internal side and the high porosity surface of the external side. The internal region has an internal region porosity that is equal to a porosity of the high porosity surface of the external side. 
     According to another example (“Example 75”) further to any one of Examples 61-74, the fluidic connection between the conduit second end and the reservoir further extends from the reservoir through the microporous material to provide a fluidic communication from the reservoir to the exterior region of the human eye. 
     According to another example (“Example 76”) further to Example 75, the fluidic communication defines a flow path through the microporous material. 
     According to another example (“Example 77”) further to Example 76, the flow path through the microporous material is in a direction that is directed away from the reservoir. 
     According to another example (“Example 78”) further to Example 76, the flow path through the microporous material proceeds from a microporous region having a low porosity to a microporous region having a high porosity. 
     According to another example (“Example 79”), a method is disclosed for controlling a flow of a fluid from an eye to a tissue surrounding the eye. The method includes: inflating a reservoir with the fluid disposed to engage a hydrophobic material defining the reservoir, the hydrophobic material providing a first flow resistance; transitioning the hydrophobic material into a hydrophilic material within 30 days after engaging the fluid, the transitioning defining a variable flow resistance of the material that decreases from the first flow resistance to a second flow resistance that is lower than the first flow resistance; and draining the reservoir by directing the fluid out through the hydrophilic material to the tissue surrounding the eye to relieve a fluidic pressure of the eye. 
     According to another example (“Example 80”) further to Example 79, the hydrophobic material and the hydrophilic material are a microporous material. 
     According to another example (“Example 81”) further to Example 80, the hydrophobic material is the microporous material in a hydrophobic state. 
     According to another example (“Example 82”) further to Example 80, he hydrophilic material is the microporous material in a hydrophilic state. 
     According to another example (“Example 83”) further to Example 80, the microporous material is initially in a hydrophobic state and the transitioning of the hydrophobic material into the hydrophilic material changes the microporous material from the hydrophobic state to the hydrophobic state. 
     According to another example (“Example 84”) further to Example 83, a first portion of the microporous material transitions from the hydrophobic state to the hydrophilic state within 3 days. 
     According to another example (“Example 85”) further to Example 84, a second portion of the microporous material different from the first portion transitions from the hydrophobic state to the hydrophilic state within 7 days. 
     According to another example (“Example 86”) further to Example 83, an entirety of the microporous material transitions from the hydrophobic state to the hydrophilic state within 30 days. 
     According to another example (“Example 87”) further to Example 83, in the hydrophobic state, the microporous material is opaque. 
     According to another example (“Example 88”) further to Example 83, in the hydrophilic state, the microporous material is transparent. 
     According to another example (“Example 89”) further to Example 79, the hydrophobic material has a maximum thickness of no greater than 500 μm. 
     According to another example (“Example 90”) further to Example 83, in the hydrophobic state, a drop of water placed on a surface of the microporous material forms a contact angle of greater than 90 degrees with respect to the surface, and in the hydrophilic state, a drop of water placed on a surface of the microporous material forms the contact angle of less than 90 degrees with respect to the surface. The transition from the hydrophobic state to the hydrophilic state constitutes a decrease in the contact angle by at least 10 degrees. 
     According to another example (“Example 91”) further to Example 83, the variable flow resistance is greater in the hydrophobic state than in the hydrophilic state. 
     According to another example (“Example 92”) further to Example 83, the microporous material is more translucent in the hydrophilic state than in the hydrophobic state. 
     According to another example (“Example 93”) further to Example 80, the method includes providing a continuous wall that defines the reservoir and a reservoir opening in the continuous wall communicating with the reservoir and through which the conduit is engagingly received. At least a portion of the continuous wall has a wall portion composed of the microporous material. The wall portion has an internal side facing the reservoir and an opposing external side facing the exterior region of the eye. The wall portion internal side has a low porosity surface extending an entirety of the wall portion internal side. The wall portion external side has alternating low porosity and high porosity surfaces. 
     According to another example (“Example 94”) further to Example 80, the microporous material comprises a first layer having a first microporous membrane integrated with a second microporous membrane and a second layer having a third microporous membrane integrated with a fourth microporous membrane. 
     According to another example (“Example 95”) further to Example 94, the microporous material comprises expanded polytetrafluoroethylene (ePTFE). 
     According to another example (“Example 96”) further to Example 95, a first microporous membrane permeability of the first microporous membrane is greater than a second microporous membrane permeability of the second microporous membrane. A fourth microporous membrane permeability of the fourth microporous membrane is greater than a third microporous membrane permeability of the third microporous membrane. 
     According to another example (“Example 97”) further to Example 96, the first layer and the second layer are in a stacked configuration such that the first microporous membrane and the fourth microporous membrane are outermost membranes of the shunt body and the second microporous membrane and third microporous membrane are innermost membranes of the shunt body defining the reservoir. 
     According to another example (“Example 98”) further to Example 94, the first microporous membrane has a first microporous membrane permeability, the second microporous membrane has a second microporous membrane permeability, the third microporous membrane has a third microporous membrane permeability, and the fourth microporous membrane has a fourth microporous membrane permeability. The second microporous membrane permeability is about the same as the third microporous membrane permeability, and the first microporous membrane permeability is about the same as the fourth microporous membrane permeability. Each of the second microporous membrane permeability and the third microporous membrane permeability are different from the first microporous membrane permeability and the fourth microporous membrane permeability. 
     According to another example (“Example 99”) further to Example 94, the second and third microporous membranes are bonded to each other along peripheral edges of the first and second layers to define the reservoir and to dispose the reservoir between the second and third microporous membranes. The second and third microporous membranes are configured to resist tissue ingrowth. The first and fourth microporous membranes are configured to permit tissue ingrowth. The second and third microporous membranes have an expanded state that is maintained adjacent to the peripheral edges of the first and second layers. 
     According to another example (“Example 100”) further to Example 94, the reservoir is configured to move between a deflated state in which the second and third microporous membranes resist fluid flow therebetween and an inflated state in which fluid is allowed to flow between the second and third microporous membranes. 
     According to another example (“Example 101”) further to Example 100, fluid flow into the reservoir is directed from the distal end of the conduit toward a periphery of chamber. 
     According to another example (“Example 102”) further to Example 100, the reservoir has a reservoir proximal section that is adjacent the distal end of the conduit and a reservoir distal section that is positioned opposite of the reservoir proximal section. During drainage of the fluid, the reservoir proximal section is configured to inflate before the reservoir distal section. 
     According to another example (“Example 103”) further to Example 83, the variable flow resistance corresponds to a rate of change in pressure with respect to flow rate over time. 
     According to another example (“Example 104”) further to Example 103, the microporous material transitions from the hydrophobic state having a first flow resistance to a partially hydrophilic state having a second flow resistance and then to the hydrophilic state having a third flow resistance. The first flow resistance is greater than both the second flow resistance and the third flow resistance, and the second flow resistance is greater than the third flow resistance. 
     According to another example (“Example 105”) further to Example 83, the microporous material is configured to transition from the hydrophobic state to the hydrophilic state based on a wetting of the microporous material with the fluid. The microporous material is configured such that wetting of an outer portion of the shunt body occurs before wetting of the reservoir. 
     According to another example (“Example 106”), a method is disclosed for managing a fluidic pressure of the eye. The method includes: identifying an undesirable fluidic pressure of the eye relating to an ocular fluid disposed in the eye; inflating a reservoir proximate to the eye with a conduit fluidically engaging the ocular fluid to deliver the ocular fluid to the reservoir and engage a reservoir wall comprising a material that transitions from an initial hydrophobic state to a hydrophilic state within 30 days after the reservoir wall engages the ocular fluid, the transition from the hydrophobic state to the hydrophilic state defining a variable flow resistance of the material that decreases from an initial first flow resistance to a second flow resistance that is lower than the first flow resistance; and draining the reservoir by directing the ocular fluid through the material to the tissue surrounding the eye to improve the undesirable fluidic pressure of the eye. 
     According to another example (“Example 107”) further to Example 106, the variable flow resistance provides sufficient flow resistance to maintain a minimal fluidic pressure to mitigate the creation of a short-term post-operative hypotony condition. 
     According to another example (“Example 108”) further to Example 106 or 107, the material is a microporous material. 
     According to another example (“Example 109”) further to Example 108, a first portion of the microporous material transitions from the hydrophobic state to the hydrophilic state within 3 days. 
     According to another example (“Example 110”) further to Example 109, a second portion of the microporous material different from the first portion transitions from the hydrophobic state to the hydrophilic state within 7 days. 
     According to another example (“Example 111”) further to Example 108, an entirety of the microporous material transitions from the hydrophobic state to the hydrophilic state within 30 days. 
     According to another example (“Example 112”) further to Example 108, in the hydrophobic state, the microporous material is opaque. 
     According to another example (“Example 113”) further to Example 108, in the hydrophilic state, the microporous material is transparent. 
     According to another example (“Example 114”) further to Example 108, the microporous material in the hydrophobic state has a maximum thickness of no greater than 500 μm. 
     According to another example (“Example 115”) further to Example 108, in the hydrophobic state, a drop of water placed on a surface of the microporous material forms a contact angle of greater than 90 degrees with respect to the surface, and in the hydrophilic state, a drop of water placed on a surface of the microporous material forms the contact angle of less than 90 degrees with respect to the surface. The transition from the hydrophobic state to the hydrophilic state constitutes a decrease in the contact angle by at least 10 degrees. 
     According to another example (“Example 116”) further to Example 106, the variable flow resistance is greater in the hydrophobic state than in the hydrophilic state. 
     According to another example (“Example 117”) further to Example 108, the microporous material is more translucent in the hydrophilic state than in the hydrophobic state. 
     According to another example (“Example 118”) further to Example 108, the reservoir wall defines a reservoir opening communicating with the reservoir and through which the conduit is engagingly received. At least a portion of the reservoir wall has a wall portion composed of the microporous material. The wall portion has an internal side facing the reservoir and an opposing external side facing the exterior region of the eye. The wall portion internal side has a low porosity surface extending an entirety of the wall portion internal side. The wall portion external side has alternating low porosity and high porosity surfaces. 
     According to another example (“Example 119”) further to Example 108, the microporous material comprises a first layer having a first microporous membrane integrated with a second microporous membrane and a second layer having a third microporous membrane integrated with a fourth microporous membrane. 
     According to another example (“Example 120”) further to Example 108, the microporous material comprises expanded polytetrafluoroethylene (ePTFE). 
     According to another example (“Example 121”) further to Example 120, a first microporous membrane permeability of the first microporous membrane is greater than a second microporous membrane permeability of the second microporous membrane, and wherein a fourth microporous membrane permeability of the fourth microporous membrane is greater than a third microporous membrane permeability of the third microporous membrane. 
     According to another example (“Example 122”) further to Example 121, the first layer and the second layer are in a stacked configuration such that the first microporous membrane and the fourth microporous membrane are outermost membranes of the shunt body and the second microporous membrane and third microporous membrane are innermost membranes of the shunt body defining the reservoir. 
     According to another example (“Example 123”) further to Example 119, the first microporous membrane has a first microporous membrane permeability, the second microporous membrane has a second microporous membrane permeability, the third microporous membrane has a third microporous membrane permeability, and the fourth microporous membrane has a fourth microporous membrane permeability. The second microporous membrane permeability is about the same as the third microporous membrane permeability, and the first microporous membrane permeability is about the same as the fourth microporous membrane permeability. Each of the second microporous membrane permeability and the third microporous membrane permeability are different from the first microporous membrane permeability and the fourth microporous membrane permeability. 
     According to another example (“Example 124”) further to Example 119, the second and third microporous membranes are bonded to each other along peripheral edges of the first and second layers to define the reservoir and to dispose the reservoir between the second and third microporous membranes. The second and third microporous membranes are configured to resist tissue ingrowth. The first and fourth microporous membranes are configured to permit tissue ingrowth. The second and third microporous membranes have an expanded state that is maintained adjacent to the peripheral edges of the first and second layers. 
     According to another example (“Example 125”) further to Example 119, the reservoir is configured to move between a deflated state in which the second and third microporous membranes resist fluid flow therebetween and an inflated state in which fluid is allowed to flow between the second and third microporous membranes. 
     According to another example (“Example 126”) further to Example 125, fluid flow into the reservoir is directed from the distal end of the conduit toward a periphery of chamber. 
     According to another example (“Example 127”) further to Example 125, the reservoir has a reservoir proximal section that is adjacent the distal end of the conduit and a reservoir distal section that is positioned opposite of the reservoir proximal section. During drainage of the fluid, the reservoir proximal section is configured to inflate before the reservoir distal section. 
     According to another example (“Example 128”) further to Example 108, the variable flow resistance corresponds to a rate of change in pressure with respect to flow rate over time. 
     According to another example (“Example 129”) further to Example 128, the microporous material transitions from the hydrophobic state having a first flow resistance to a partially hydrophilic state having a second flow resistance and then to the hydrophilic state having a third flow resistance. The first flow resistance is greater than both the second flow resistance and the third flow resistance, and the second flow resistance is greater than the third flow resistance. 
     According to another example (“Example 130”) further to Example 108, the microporous material is configured to transition from the hydrophobic state to the hydrophilic state based on a wetting of the microporous material with the fluid. The microporous material is configured such that wetting of an outer portion of the shunt body occurs before wetting of the reservoir. 
     The foregoing Examples are just that, and should not be read to limit or otherwise narrow the scope of any of the inventive concepts otherwise provided by the instant disclosure. While multiple examples are disclosed, still other embodiments will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative examples. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature rather than restrictive in nature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       The accompanying drawings are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments, and together with the description serve to explain the principles of the disclosure. 
         FIG.  1 A  is an illustration of an eye with a drainage system implanted therein consistent with various aspects of the present disclosure; 
         FIG.  1 B  is an illustration of a cross section of Detail A 1  from  FIG.  1 A ; 
         FIG.  1 C  is a schematic representation of the implanted drainage device at Detail A 2  in  FIG.  1 B ; 
         FIG.  2 A  is a side-view illustration of a drainage system in the form of a glaucoma shunt consistent with various aspects of the present disclosure; 
         FIG.  2 B  is a bottom-view illustration of the drainage system of  FIG.  2 A ; 
         FIG.  2 C  is a cross-sectional view of the drainage system of  FIG.  2 A  taken at section B-B with the drainage system in a deflated state and having a conjunctival tab; 
         FIG.  2 D  is a cross-sectional view of the drainage system  100  of  FIG.  2 A  taken at section C-C with the drainage system in the deflated state and having first and second layers with different microstructure and thickness; 
         FIG.  2 E  is a perspective view of an alternative, miniature embodiment of the drainage system  100  of  FIG.  2 A ; 
         FIG.  3 A  is a schematic view of wall of the drainage device in a deflated state; 
         FIG.  3 B  is a schematic view of the wall of the drainage device in an inflated state; 
         FIG.  3 C  is an SEM image of a portion of the microstructure schematically illustrated in the drainage system of  FIGS.  3 A and  3 B , with the SEM image scaled as shown; 
         FIG.  4 A  is a flowchart of a method of manufacture consistent with various aspects of the present disclosure; 
         FIG.  4 B  is a flowchart of a method of use consistent with various aspects of the present disclosure; 
         FIGS.  5 A and  5 B  (prior art) are schematic top and side views, respectively, of a prior-art Ahmed glaucoma valve device for glaucoma drainage; 
         FIG.  6 A  (prior art) is a photograph of a top view of a prior-art Ahmed glaucoma valve modified with a polyethylene shell and implementing solid plates as known in the art; 
         FIG.  6 B  (prior art) is a photograph of a side view of the prior-art glaucoma valve of  FIG.  6 A  when a portion of the solid plates are removed to show the reservoir located therein; and 
         FIG.  6 C  (prior art) is an SEM image of a portion of a surface of the solid plate used in the prior-art glaucoma valve of  FIG.  6 A ; 
         FIGS.  7 A and  7 B  are schematic side views of a sessile drop method test performed on a surface; 
         FIGS.  8 A through  8 E  are backlit microscope images of a drainage device in various states of transitioning from a hydrophobic state to a hydrophilic state consistent with various aspects of the present disclosure; 
         FIGS.  9 A through  9 C  are microscope images of a drainage device in various states of transitioning from a hydrophobic state to a hydrophilic state consistent with various aspects of the present disclosure; 
         FIG.  10    is a graph comparing flowrate vs pressure over three different periods of time during the wetting; 
         FIG.  11 A  is a graph comparing a percentage of device flow resistance over the course of wetting; and 
         FIG.  11 B  is a graph comparing a percentage of the area of the device that is wetted over the course of wetting. 
     
    
    
     DETAILED DESCRIPTION 
     Definitions and Terminology 
     This disclosure is not meant to be read in a restrictive manner. For example, the terminology used in the application should be read broadly in the context of the meaning those in the field would attribute such terminology. 
     With respect to terminology of inexactitude, the terms “about” and “approximately” may be used, interchangeably, to refer to a measurement that includes the stated measurement and that also includes any measurements that are reasonably close to the stated measurement. Measurements that are reasonably close to the stated measurement deviate from the stated measurement by a reasonably small amount as understood and readily ascertained by individuals having ordinary skill in the relevant arts. Such deviations may be attributable to measurement error, differences in measurement and/or manufacturing equipment calibration, human error in reading and/or setting measurements, minor adjustments made to optimize performance and/or structural parameters in view of differences in measurements associated with other components, particular implementation scenarios, imprecise adjustment and/or manipulation of objects by a person or machine, and/or the like, for example. In the event it is determined that individuals having ordinary skill in the relevant arts would not readily ascertain values for such reasonably small differences, the terms “about” and “approximately” can be understood to mean plus or minus 10% of the stated value. 
     DESCRIPTION OF VARIOUS EMBODIMENTS 
     Persons skilled in the art will readily appreciate that various aspects of the present disclosure can be realized by any number of methods and apparatuses configured to perform the intended functions. It should also be noted that the accompanying drawing figures referred to herein are not necessarily drawn to scale, but may be exaggerated to illustrate various aspects of the present disclosure, and in that regard, the drawing figures should not be construed as limiting. 
     The device shown in  FIGS.  5 A and  5 B  is an Ahmed Glaucoma Value model FP7 (New World Medical, Inc., Rancho Cucamonga, Calif.) with a silicone plate, a silicone drainage tube, a silicone valve membrane, and a polypropylene (PP) valve casing, with a maximum thickness of 2.1 mm. The Ahmed device includes a plate body (“Body”) which defines a surface over which the drained fluid (aqueous humor) is directed to flow, and a drainage tube (“Tube”) which directs the fluid (aqueous humor) to flow over the surface of the plate body. The plate body has a maximum thickness (“Thickness”) and is made of medical-grade silicone which is rigid and lacks flexibility to conform to the curvature of the eye when implanted. As such, the plate body has a curvature (defined by the broken line C-C) which is preformed (that is, formed before implantation) to approximate the curvature of the surface of the eye. The curvature C-C is fixed and is the same for all similarly designed Ahmed glaucoma drainage devices and thus, in some cases, may fail to accommodate the unique curvature of each patient&#39;s eye. Additionally, in order to regulate fluidic pressures, the device requires the inclusion of a mechanical valve structure (“Valve”) that is non-dissolvable and nonbiodegradable in order to control a fluid pressure within the device over a long period of time (e.g., for years). The valve, in certain examples known in the art, is capable of closing when the pressure exceeds above a threshold, such as 7 mmHg, in order to decrease the risk of postoperative hypotony-related complications. The valve, as shown, has a certain thickness and rigidity which defines the thickness of the device, thereby causing the device to lack the flexibility to conform to the curvature of the eye when implanted, as well as increasing the thickness of the plate body. 
     It is understood that the Ahmed Glaucoma Valves are designed such that flow resistance remains the same for years, but as the flow rate decreases over a prolonged period of time, the devices&#39; functionality and performance as a valve may vary, according to articles such as: Choudhari et al. “Is Ahmed Glaucoma Valve Consistent in Performance?” Translational Vision Science &amp; Technology. 2018 June 22; 7(3):19. doi: 10.1167/tvst.7.3.19. PMID: 29946493; PMCID: PMC6016431; Moss et al. “Assessment of closing pressure in silicone Ahmed FP7 glaucoma valves.” Journal of Glaucoma. 2008 September; 17(6):489-93. doi: 10.1097/IJG.0b013e3181622532. PMID: 18794686; and Bochmann et al. “Intraoperative testing of opening and closing pressure predicts risk of low intraocular pressure after Ahmed glaucoma valve implantation.” Eye (Lond). 2014 October; 28(10):1184-9. doi: 10.1038/eye.2014.168. Epub 2014 Jul. 25. PMID: 25060848; PMCID: PMC4194337. 
       FIGS.  6 A through  6 C  show another example of a glaucoma drainage device as known in the art. The device as shown includes two solid plates, such as those made from silicone as shown in  FIGS.  5 A and  5 B , forming two layers (“L1” and “L2”) to receive fluid from the anterior chamber (AC) of the eye and store it inside an internal chamber formed between the plates. The device shown in  FIGS.  6 A and  6 B  is an Ahmed Glaucoma Value model M4 (New World Medical, Inc., Rancho Cucamonga, Calif.) with a polyethylene shell to reduce the fibrotic reaction around the drainage plate compared with the S2 and FP7 models in patients with glaucoma, as previously disclosed in Kim et al. “Clinical experience with a novel glaucoma drainage implant.” Journal of Glaucoma. 2014 February; 23(2):e91-7. DOI: 10.1097/ijg.0b013e3182955d73. PMID: 23689073. The prior-art device is made of a tube (“Tube”) installed between the two layers L1 and L2 of solid material such as porous polyethylene shells (e.g., Medpor) that follow the curvature of the eye, and between the layers L1 and L2 is defined a reservoir (“R”) into which the tube directs the fluid from the eye. As shown in the prior-art device of  FIG.  6 C , which is scaled such that the black bar on the bottom of the figure represents 500 μm, the surface of the layers L1 and L2 include pores to improve tissue integration, such that the adjacent tissue can be integrated into the polyethylene shell surrounding the drainage device, as well as to ensure that fluid stored inside the reservoir R can be released back to the surrounding environment in order to prevent the shell from applying undue stress on the surrounding tissue. 
     However, in contrast to various embodiments described herein, implanting a solid or rigid piece of material, such as those shown in  FIGS.  6 A to  6 C , (that is, a material lacking in flexibility and thinness) inside the eye increases the stress applied on the eye, especially within the conjunctival tissue of the eye, when subjected to pressure from the anterior chamber of the eye, which may not only lead to discomfort but also other complications that may arise from extended pressure increase within such a sensitive area of the eye. 
     Various features of devices, systems, and methods disclosed herein can be seen in  FIGS.  1 A- 1 C . Aspects of the present disclosure relate to drainage devices, systems, and methods for biological fluids. More particularly, the present disclosure relates to devices, systems, and methods for draining aqueous humor from the anterior chamber ‘AC’ of an eye  10  of a patient so that the aqueous humor may be resorbed by the body elsewhere. To that end,  FIG.  1 A  is an illustration of an eye  10  with a subconjunctival space  11  between a conjunctiva  13  and a sclera  15  of the eye  10 . Implanted within the eye  10  is a drainage system  100  in accordance with principles of the present disclosure.  FIG.  1 B  shows a cross section of detail A 1  from  FIG.  1 A .  FIG.  1 C  shows a schematic representation of the implanted drainage device  110  at Detail A 2  in  FIG.  1 B . In an aspect of the present disclosure, a mechanism is provided for reabsorption of aqueous humor that has been expelled from the anterior chamber ‘AC’ of the eye  10  to reduce or otherwise stabilize intraocular pressure. One skilled in the art, however, will appreciate that aspects of the present disclosure are useful in other applications where drainage of biological fluid to be redirected in the body is desired. 
     The drainage system  100  illustrated in  FIGS.  1 A- 1 C  includes a drainage device  110  for treating glaucoma. As illustrated here, this glaucoma drainage device  110  has a wall  112  (best seen in  FIGS.  1 B and  1 C ) that has a first side  114  and a second side  116 . Although discussed below in connection with an intake conduit  120 , it should be understood that the drainage device  110  can be a standalone product so long as some portion thereof is configured to receive fluid (e.g., directly from an incision, from the fluid conduit  120 , etc.) and as such should not be considered outside the scope of this disclosure. Fluidly coupled to the drainage device  110  can be an intake conduit  120 . When implanted, the intake conduit  120  extends from the anterior chamber CAC′ of the eye  10  to the drainage device  110 . The aqueous humor at the anterior chamber CAC′ then flows through intake conduit  120  and into the drainage device  110 . 
     Material selection of the drainage device  110  can contribute to its functionality and relatively low profile in comparison to other devices known in the art. The drainage device  110  can comprise biocompatible materials, including microporous materials such as expanded polytetrafluoroethylene (ePTFE) as discussed below. The intake conduit  120  can include biocompatible materials that are flexible and suitable for use in constructing elongate members. Some such suitable materials can include silicone, polytetrafluoroethylene, polypropylene, polymethyl methacrylate, acrylic, polyurethane, silastic, and metal. Such construction of the drainage system  100  is particularly useful for surgical implantation. 
     In general, surgical implantation of drainage devices, such as the drainage system  100 , involve risk of abnormal pressures within the eye  10 . For instance, when drainage devices are surgically implanted, such as in surgeries that require the creation of a bleb (as indicated by the dashed lines around the device  110 ) under the exterior surface tissue of the eye  10  (i.e., the conjunctiva  13 ), surrounding tissues fresh from the insult of the surgery do not provide appreciable flow resistance to aqueous flow until sufficient wound healing occurs. During this early post-operation period, the patient is at risk of hypotony of the eye  10  (e.g., too low eye pressure). To avoid hypotony, measures are taken to manage flow through the drainage device  110  for a period of time. For example, surgeons traditionally ‘tie-off’ a portion of the intake conduit  120  near its proximal end fora period of time and release the tie after surgical wound healing has sufficiently progressed such that the surrounding tissue will provide the necessary flow resistance. In certain commercial glaucoma shunt devices, a restrictive flow ‘valve’ is added distal of the intake conduit  120  where a plate section is located. These devices, however, are relatively stiff and bulky and still can result in hypotony. To the contrary, advantageously, drainage devices, systems, and methods according to principles of the present disclosure include low profile devices without the presence of a valve that generate appreciable flow resistance in the early post-operation period (a.k.a. a post-surgical wound healing period which may last for about 30 days after the operation), e.g., to avoid hypotony, by changing the flow resistance over a period of time from a state of high resistance with hydrophobic properties to a state of low resistance with hydrophilic properties over time, for example 30 days. 
     With reference to  FIGS.  1 B and  1 C , a non-limiting example implantation of the drainage system  100  is shown. In this example, the drainage system  100  is shown disposed in a subconjunctival space  11  between the conjunctiva  13  and the sclera  15  of the eye  10 . The drainage system  100  is shown oriented such that the first layer  114  extends along the sclera  15  and such that the second layer  116  extends along the conjunctiva  13 . It will be appreciated that the portion of the second layer  116  that interfaces with the conjunctiva  13  may be configured to promote or permit tissue ingrowth, as discussed below. It will also be appreciated that the portion of the first layer  114  that interfaces with the sclera  15  may additionally or alternatively be configured to promote or permit tissue ingrowth, as discussed below. Such configurations help minimize relative movement between the drainage device  110  and the surrounding tissue. 
     Moreover, the intake conduit  120  is shown in  FIGS.  1 B and  1 C  as extending from the drainage device  110 , and extending through a scleral access, perforation, or hole CH′ (e.g., made by a physician during the implantation procedure according to known methods) such that a first end  122  (e.g., a proximal end) accesses the anterior chamber CAC′ and places a port  271  in communication therewith. In some embodiments, when implanted, aqueous humor enters the first end  122  of the intake conduit  120  and travels to a second end  124  (e.g., a distal end) of the intake conduit  120  in fluid communication with the drainage device  110 . Together, the wall  112  and the intake conduit  120  can define a flow passage  140  along which the drainage flows through the drainage device  110 . In some embodiments the second end  124  is positioned within the drainage device  110  such that the evacuated aqueous humor enters a reservoir  130  defined within the drainage device  110  and penetrates through the various diffusion membranes of the drainage device  110 , where the aqueous humor is then absorbable by the surrounding and/or ingrown tissue. 
     Turning to  FIGS.  2 A- 2 E , various aspects of an example drainage system  100  in the form of a glaucoma shunt  110  are shown.  FIG.  2 A  shows a side-view illustration of a drainage system  100 .  FIG.  2 B  shows a bottom-view illustration of the drainage system  100  of  FIG.  2 A .  FIG.  2 C  shows a cross-sectional view of the drainage system  100  of  FIG.  2 A  taken at section B-B with the drainage system  100  in a deflated state, a collapsed state, or a drained state in which the drainage system  100  (or more particularly the reservoir  130 ) is drained of its inner fluid such as a biological fluid. This drainage system  100  illustrates a conjunctival tab to prevent erosion of the conjunctiva  13  by the conduit  120 , a neck where the conduit  120  is bonded (e.g., via adhesive at “b”) to the wall  112 , and a reservoir  130  at a distal end of the conduit  120 .  FIG.  2 D  shows a cross-sectional view of the drainage system  100  of  FIG.  2 A  taken at section C-C with the drainage system  100  in the deflated state or the collapsed state.  FIG.  2 E  shows a perspective view of an alternative, miniature embodiment of the drainage system  100  of  FIG.  2 A . As is also the case in  FIGS.  1 A- 1 C , here, the drainage system  100  relates to draining biological fluid from one portion of a patient&#39;s body to another. Notably, the conduit  120  can be inserted into the reservoir  130  at variable depth such as at a shallow depth as shown in  FIG.  2 C  or a major depth in as shown in  FIG.  2 D  so long as fluid is allowed to escape the distal end  124  of the conduit  120  to fill the reservoir  130 . Such devices can have a low profile with appreciable fluid flow resistance in the early post-operation period to avoid hypotony. 
     Being a glaucoma shunt  110 , the drainage system  100  shown in these figures is useful for draining a biological fluid from the eye. This drainage can proceed from an internal portion (e.g., the anterior chamber) of the eye to a surrounding tissue external to an eye. The drainage device  110  can include a wall  112  that defines a reservoir  130  disposed within the wall  112 . The reservoir  130  can be configured to be in fluid communication with the eye to receive the drainage from the internal portion of the eye into the reservoir  130 . The wall  112  may be integrated into or altogether form a body of the drainage device  110 . In this regard, the body can have a wall  112  defining an internal reservoir  130  within the body and an internal reservoir opening (e.g., at or around adhesive ‘b’ in  FIG.  2 C ) that is arranged in the wall  112  so as to communicate with the internal reservoir  130 . As often described herein, this wall  112  is continuous (e.g., a continuous wall  112 ) but other types of walls  112  with sealed discontinuities are also contemplated. 
     According to some examples, a user may identify an undesirable fluidic pressure of the eye relating to an ocular fluid disposed in the eye. The user may inflate the reservoir  130  proximate to the eye with the conduit  120  fluidically engaging the ocular fluid to deliver the ocular fluid to the reservoir  130  and engage the reservoir wall  112  comprising a material that transitions from an initial hydrophobic state to a hydrophilic state within 30 days after the wall  112  engages the ocular fluid. The transition from the hydrophobic state to the hydrophilic state defines a variable flow resistance of the material that decreases from an initial first flow resistance to a second flow resistance that is lower than the first flow resistance. Subsequently, the reservoir  130  may be drained by directing the ocular fluid through the hydrophilic material to the tissue surrounding the eye to improve the undesirable fluidic pressure of the eye. The hydrophilic material may be the wall  112  in the hydrophilic state as explained herein. 
     The wall  112  can include a microporous material that transitions from a hydrophobic state to a hydrophilic state. In examples, the wall  112  is configured to provide a variable flow resistance as the wall  112  transitions from the hydrophobic state to the hydrophilic state. The drainage device  110  can include a flow passage  140  that is configured to facilitate the drainage of a biological fluid from the internal portion of the eye to a surrounding tissue that is external to the eye. Notably, the flow passage  140  can include a variable flow resistance to the drainage that passes through the flow passage  140 . The flow passage  140  can have a first flow resistance portion with a first flow resistance and a second flow resistance portion with a second flow resistance. Optionally, as explained in more detail below, the first flow resistance can be different from the second flow resistance. 
     The wall  112  can be a multi-layered structure comprising one or more microstructures. The wall  112  can also be a continuous single-layer structure comprising multiple sub-layers within the continuous single-layer structure or that can define opposing sides of the continuous single-layer structure that present one porosity on a first side and a second porosity on a second side of the single-layer structure. In this regard, examples of the wall  112  can include a first layer  114  having a first microporous membrane  241  engaging a second microporous membrane  242  and a second layer  116  comprising a third microporous membrane  243  engaging a fourth microporous membrane  244 . In many instances, this engaging between the first and second microporous membranes  241 ,  242  and the third and fourth microporous membranes  243 ,  244  is such that the first and second microporous membranes  241 ,  242  and the third and fourth microporous membranes  243 ,  244  respectively are integrally formed with each other. In certain instances, the first and second layers  114 ,  116  can comprise more or less microporous membranes, some such configurations are discussed in U.S. application Ser. No. 15/922,692 entitled “Integrated aqueous shunt for glaucoma treatment” and filed on Mar. 15, 2018, the full contents of which are incorporated herein by reference. 
     The presentation of varying microporous materials within the continuous single-layer structure can facilitate operation of the reservoir  130 . As fluid flows into the reservoir  130 , the fluid can engage the microporous material of the wall  112 . Under certain circumstances, the second and third microporous membranes  242 ,  243  are engaging each other along peripheral edges  247  of the drainage device  110 . For instance, the second and third microporous membranes  242 ,  243  can engage at the periphery of the first and second layers  114 ,  116  to define a reservoir  130  disposed between the second and third microporous membranes  242 ,  243 . This engagement can be a bond that is a hermitically sealing bond to ensure structural integrity of the reservoir  130 . In certain instances, the second and third microporous membranes  242 ,  243  may initially contact or be in close proximity to one another such that, to initially inflate the reservoir  130 , the fluid can engage the interface between the second and third microporous membranes  242 ,  243 . In this regard, initially and thereafter, the reservoir  130  can be configured to move between a deflated state (or, alternatively, a collapsed state, a draining state, or a drained state) in which the second and third microporous membranes  242 ,  243  resist fluid flow therebetween and an inflated state (or, alternatively, an expanded state) in which fluid is allowed to flow between the second and third microporous membranes  242 ,  243 . In certain instances, the first and fourth microporous membranes  241 ,  244  can remain unbonded to each other while in other instances it may be useful to engage them to one another (e.g., similarly to the engagement of the second and third microporous membranes  242 ,  243 ). 
     The wall portion has an initial hydrophobic state that transitions to a final hydrophilic state when the biological fluid engages the wall portion. In an embodiment, a first sub-layer within the wall portion has a first initial hydrophobic state that transitions to a first final hydrophilic state at a transition rate that is greater than another second sub-layer within the wall portion that transitions from a second initial hydrophobic state to a second final hydrophilic state. In some examples, the draining or emptying of the reservoir may occur when the wall portion is in the hydrophilic state. For instance, upon initial filling, the first and second layers may be gradually separated by inflowing drainage filling the reservoir formed between the first and second layers. As fluid from the drainage encounters the wall portion internal side  251 , due to its low porosity, the microporous material at this side can take an extended time wetting out but may wet out fully at a reservoir proximal portion before wetting out fully at a reservoir distal portion. At the same time, tissue ingrowth is penetrating through the microstructure at the wall portion external side  253  until it reaches an area of low porosity such as at the wall portion internal side  251 . Because the wall portion external side  253  has a higher porosity than that of the wall portion internal side  251 , fluid from surrounding tissue may begin to wet out the wall portion external side  253  more quickly than the drainage within the reservoir. This action creates a gradient across the thickness of the microstructure where certain portions (e.g., high porosity portions) of the microporous material wet out and transition from hydrophobic to hydrophilic more quickly than other portions. On average, this gradient will be such that the wall portion internal side  251  makes this transition later (and thus provides a greater flow resistance that is variable) than the wall portion external side  253 . Eventually, this gradient will disperse as both the wall portion internal side  251  and wall portion external side  253  become hydrophilic to a point where drainage through the microporous material is fairly constant in some examples. 
     Arrangement of the microporous material to form the wall  112  can be such that wetting of the microporous material is promoted at an external side  253  of the wall  112  before an internal side  251  of the wall  112 . In this regard, the internal side  251  of the wall  112  can form the reservoir  130 . In examples, the first layer  114  and the second layer  116  are in a stacked configuration such that the first microporous membrane  241  and the fourth microporous membrane  244  are the outermost membranes of the wall  112  and the second microporous membrane  242  and third microporous membrane  243  are the innermost membranes of the wall  112 . 
     In examples, the microporous material can comprise ePTFE. In this regard, the microporous material can be configured to transition from the hydrophobic state to the hydrophilic state based on a wetting of the microporous material with the biological fluid, and wherein the microporous material is configured such that wetting of an outer portion of the wall  112  occurs before wetting of the surfaces defining the reservoir  130 . In examples, the hydrophilic state promotes tissue ingrowth. In some such examples, the hydrophilic state can define a first side of the microporous material, and the hydrophobic state can define a second side of the microporous material. Furthermore, other materials similar to ePTFE are contemplated. Those other materials can include polymers, such as, but not limited, to polyethylene, polyurethane, polysulfone, polyvinylidene fluorine (PVDF), polyhexafluoropropylene (PHFP), perfluoroalkoxy polymer (PFA), polyolefin, fluorinated ethylene propylene (FEP), acrylic copolymers and other suitable fluoro-copolym ers. 
     Drainage from the internal portion of the eye can flow through the drainage device  110  via a flow passage  140  as exemplified in  FIGS.  1 C and  2 D  but also as presented in other figures defining a reservoir and/or a tube to allow a fluid to pass into the device. The flow passage  140  can include portions (e.g., some or all) of the wall  112  and, optionally, an intake conduit  120  as discussed in further detail below. In this regard, in an example, fluid can flow into the reservoir  130  via the flow passage  140  after being received at the wall  112  via an intake conduit  120  or directly and then out of the reservoir  130 . For instance, upon a first instance of the reservoir  130  filling with biological fluid, the reservoir  130  can gradually move from the deflated state (collapsed state) toward the inflated state (expanded state). Biological fluid can then remain in the reservoir  130  until portions of the wall  112  transition from the hydrophobic state to the hydrophilic state. In such instances, the biologic fluid can penetrate through the wall  112  (e.g., from the internal side  251  of the wall  112  to either the external side  253  or peripheral edge of the wall  112 ) to be diverted into surrounding portions of the body at the wall  112 . 
     In an embodiment that may in part or in whole use bonding to secure membranes together, the bonding of the microporous material can occur at the peripheral edges  261 ,  262 ,  263 ,  264  of the microporous membranes  241 ,  242 ,  243 ,  244  in the drainage device  110 . In particular, the first microporous membrane  241  is shown with a first peripheral edge  261 , the second microporous membrane  242  is shown with a second peripheral edge  262 , the third microporous membrane  243  is shown with a third peripheral edge  263 , and the fourth microporous membrane  244  is shown with a fourth peripheral edge  264 . As alluded to above, any combination of these microporous membranes  241 ,  242 ,  243 ,  244  can be bonded at their respective peripheral edges  261 ,  262 ,  263 ,  264 . In examples, the second and third microporous membranes  242 ,  243  are bonded at their peripheral edges  262 ,  263  to form the reservoir  130  therebetween the second and third microporous membranes  242 ,  243 . In some such examples, the first and fourth microporous membranes  241 ,  244  are unbonded from the second and third peripheral edges  262 ,  263  of the second and third microporous membranes  242 ,  243  respectively. In some such examples, the first and fourth microporous membranes  241 ,  244  are unbonded from each other in part or entirely. In any of these instances, the bonding at peripheral edges  261 ,  262 ,  263 ,  264  of the microporous membranes  241 ,  242 ,  243 ,  244  can be a sealing bond and can optionally accommodate and sealingly bond additional structures, such as the intake conduit  120 , to the drainage device  110 . In an alternative embodiment similar to the embodiment described above, the bonding can be applied as described except between the first and second membranes  241  and  242  which can be replaced with a single unified layer with sub-layers having the properties of the first and second membranes, and except between the third and fourth membranes  243  and  244  which can likewise be replaced with a single unified layer with sub-layers having the properties of the third and fourth membranes. 
     Notably, at least a portion of the continuous wall  112  can have a wall portion (e.g., some or all of the wall  112 ) composed of a microporous material. The wall portion can have a wall portion internal side  251  facing the internal reservoir  130  and a wall portion external side  253  that opposes the wall portion internal side  251  and faces the exterior region of the human eye. The wall portion internal side  251  can have a low porosity surface extending an entirety of the wall portion internal side  251 . The wall portion external side  253  can have an alternating surface comprising the low porosity surface disposed between high porosity surfaces. 
     The conduit  120  can be arranged so as to be extending from the body by a conduit length. The conduit  120  can have opposing first and second conduit ends  122 ,  124  defining a passage through the conduit  120  such that the passage extends between the opposing first and second conduit ends  122 ,  124 . The first conduit end  122  can be engaging the internal reservoir opening to provide a fluidic connection between the second conduit end  124  and the internal reservoir  130 . The conduit length can be sufficient enough to dispose the first conduit end  122  at the exterior region of the human eye and to dispose the second conduit end  124  at the interior region of the human eye. In examples, the fluidic connection between the second conduit end  124  and the internal reservoir  130  further extends from the internal reservoir  130  through the microporous material to provide a fluidic communication from the internal reservoir  130  to the exterior region of the human eye. This fluidic communication can define a flow path through the microporous material. As further described below, the flow path through the microporous material can be in a direction that is directed away from the internal reservoir  130  and/or proceeds from a low porosity microporous region to a high porosity microporous region. 
     Various features of another example of a drainage system  100  consistent with various aspects of the present disclosure is shown in  FIG.  2 E . In particular, like other drainage devices discussed elsewhere herein,  FIG.  2 E  shows a drainage system  100  having a wall  112  with a reservoir  130  defined therein and an intake conduit  120  that is in fluid communication with the reservoir  130 . As is also the case in  FIGS.  1 A- 1 C and  2 A- 2 D , here, the drainage system  100  relates to draining biological fluid from one portion of a patient&#39;s body to another. Such devices can have a low profile with appreciable fluid flow resistance in the early post-operation period to avoid hypotony. This device  110  may be smaller in size (e.g., in one or multiple dimensions, including length, width, and thickness) and therefore more suitable for smaller patients than the device  110  in  FIGS.  2 A- 2 D . In some examples, thickness of the device  110  (that is, a maximum thickness of the shunt or shunt body  110 ) may range from about 25 μm to about 30 μm, about 30 μm to about 40 μm, about 40 μm to about 50 μm, about 50 μm to about 60 μm, from about 60 μm to about 70 μm, from about 70 μm to about 80 μm, from about 80 μm to about 90 μm, from about 90 μm to about 100 μm, from about 10 μm to about 150 μm, from about 150 μm to about 200 μm, from about 200 μm to about 250 μm, from about 250 μm to about 300 μm, from about 300 μm to about 350 μm, from about 350 μm to about 400 μm, from about 400 μm to about 450 μm, from about 450 μm to about 500 μm, or any other suitable value or range therebetween and/or combination of ranges thereof. 
     The drainage system  100  shown here is similar in many respects to the drainage systems discussed above. For instance, the drainage system  100  shown here can include first and second layers as discussed with respect to  FIGS.  2 A- 2 D . These layers are bonded (e.g., at second and third microporous membranes) around an intake conduit  120  similar to that discussed with respect to  FIGS.  1 A- 1 C . Although shown extending to a particular location, the distal end of the intake conduit  120  can be positioned (e.g., more proximally or distally than illustrated, suspended between or positioned along the internal side of the reservoir  130 , etc.) such that it is in communication with the reservoir  130 . Other variations will be apparent to those skilled in the art. 
     As discussed above, drainage from the internal portion of the eye into the reservoir  130  can be facilitate by creating a flow passage therebetween. An example medium for creating such a fluid passage is via an intake conduit  120 . The intake conduit  120  can be a hollow member that is optionally elongate and flexible, such as a shunt. The intake conduit  120  can be arranged to be in fluid communication with the reservoir  130  and optionally in sealing engagement therewith. In this regard, the intake conduit  120  can have the second end thereof communicating with the reservoir  130  and the opposing first defining a port. As such, the first end can be a proximal end of the intake conduit  120 , and the second end can be a distal end of the intake conduit  120 . The intake conduit  120  can be configured for placement within the eye to facilitate a drainage from the internal portion of the eye, through the port, and to the reservoir  130 . 
     Additional configurations of flow passages with variable resistance are discussed in detail in U.S. Provisional Application No. 63/276,183 (attorney docket number: 450385.003251 2400US01), entitled “BIOLOGICAL FLUID DRAINAGE DEVICES, SYSTEMS, AND METHODS,” filed on Nov. 5, 2021, the entire disclosure of which is herein incorporated by reference in its entirety. 
     Details of the microporous material will now be discussed with reference to  FIGS.  3 A- 3 C . For clarity, these figures omit showing the conduit but it is understood that the conduit can be placed in fluid communication with the reservoir  130  as discussed elsewhere herein. In particular,  FIGS.  3 A and  3 B  show cross-sectional views of the wall  112  in the drainage system with a reservoir  130  disposed therein taken along a midsection of a width of the drainage system. More specifically,  FIG.  3 A  shows the drainage device in a deflated or drained state (where little to no fluid is in the reservoir  130 ); and  FIG.  3 B  shows the drainage device in an inflated state (where fluid has collected in the reservoir  130  so as to cause the reservoir  130  to inflate). In some examples, the inflated state may be when the wall  112  of the reservoir  130  is in the hydrophobic state, and the drained state may be when the wall  112  of the reservoir  130  is in the hydrophobic state, such that the draining of the fluid inside the reservoir  130  may occur in the hydrophilic state or as when the wall  112  transitions from the hydrophobic state to the hydrophilic state as explained herein.  FIG.  3 C  is a close-up view of a microstructure in the drainage system of  FIGS.  3 A and  3 B . Displayed at the bottom of  FIG.  3 C  is: “5.00 kV 4.2 mm x500 SE Jan. 23, 2018,” and the distance between two consecutive lines as shown at the bottom right hand corner represents 10 μm. 
     With reference to  FIGS.  3 A and  3 B , a microstructure, through which biological fluid penetrates, can be included within a portion (e.g., some or all) of the microporous material. The microstructure can comprise multiple deposits of microporous membranes therein such that the microporous material is a multi-membrane material. Grouped or coupled deposits of microporous membranes can form a layer of the microporous material, which can be overlapped, folded, or similarly arranged. Under these circumstances, a reservoir  130  can be formed with a reservoir proximal section  231  and a reservoir distal section  232  and can diffuse collected fluid into surrounding tissue outside of the wall  112 . 
     Inflation of the reservoir  130  can occur at the unbonded portions of the wall  112 . As noted above, the second and third microporous membranes  242 ,  243  can be bonded at their peripheries such that interior portions thereof are unbonded. As these portions are unbonded, they are free to separate from each other (or one from the other) to allow the reservoir  130  to fill with fluid. The reservoir  130  can have a reservoir proximal section  231 , which can be positioned adjacent the distal end of the intake conduit as further discussed below, and a reservoir distal section  232  that is positioned opposite of the reservoir proximal section  231 . Fluid flow into (or within) the reservoir  130  can be directed from the distal end of the intake conduit toward a periphery of chamber. In this regard, the reservoir proximal section  231  can be configured to inflate before the reservoir distal section  232 . 
     Engagement of the fluid with the microporous material can impart a flow resistance, which can result in pressure within the reservoir  130 . For instance, second and third microporous membranes  242 ,  243  of the wall  112  can be situated adjacent to each other and can optionally be in contact with each other. As the reservoir  130  fills, the second and third microporous membranes  242 ,  243  can be gradually forced apart by fluid flowing into the reservoir  130 . For instance, because the interior surface of the reservoir  130  can initially be hydrophobic, flow into the reservoir  130  can build pressure thereby forcing inflation of the reservoir  130  (e.g., second and third chambers being forced away from each other). As the wall  112  transitions from the hydrophobic state to the hydrophilic state and the fluid flow engages the reservoir  130 , a variable flow resistance can be imparted to the fluid flow. The variable flow resistance can correspond to a rate of change in pressure with respect to flow rate over time. In examples, the wall  112  transitions from the hydrophobic state having a first flow resistance, to a partially hydrophilic state having a second flow resistance, to the hydrophilic state having a third flow resistance; and wherein the first flow resistance is greater than both the second flow resistance and the third flow resistance, and the second flow resistance is greater than the third flow resistance. 
     Diffusion rates of biological fluid from the reservoir  130  through the wall  112  can be influenced by the flow rate, which increases with decreasing flow resistance. As the reservoir  130  is inflated and the microporous material transitions from the hydrophobic state to the hydrophilic state, this diffusion can occur in many directions (e.g., radially outward from the reservoir  130 , through unbonded portions of the peripheral edge, etc.). When flow into the reservoir  130  is less than flow out of the reservoir  130 , the reservoir  130  can move from the inflated state toward the deflated state. On the other hand, when flow into the reservoir  130  is more than flow out of the reservoir  130 , the reservoir  130  can move from the deflated state toward the inflated state. Assuming continuous flow into the reservoir  130 , the reservoir  130  can remain in the inflated state, in an intermediate state between the inflated and deflated states. In any of these instances, there is a pressure associated with the amount of flow and/or a fill level of the reservoir  130 . After collection of the fluid in the reservoir  130 , fluid can be diffuse via penetration through the wall  112  at various rates depending on the state of transition of the microporous material. 
     Permeabilities of each layer of the microporous material can vary across dimensions (e.g., the thickness or length) of the microstructure therein. Under these circumstances, in certain instances, a first microporous membrane  241  permeability of the first microporous membrane  241  can be higher than a second microporous membrane  242  permeability of the second microporous membrane  242 . Similarly, a fourth microporous membrane  244  permeability of the fourth microporous membrane  244  can be higher than a third microporous membrane  243  permeability of the third microporous membrane  243 . In examples, the second microporous membrane  242  permeability can be about the same as the third microporous membrane  243  permeability. In examples, the first microporous membrane  241  permeability can be about the same as the fourth microporous membrane  244  permeability. In some such examples, each of the second microporous membrane  242  permeability and the third microporous membrane  243  permeability are different from the first microporous membrane  241  permeability and the fourth microporous membrane  244  permeability. 
     Porosities of membranes within the microporous material can be arranged to influence tissue ingrowth capabilities at portions thereof. It may be desired that tissue ingrowth occurs at portions of the wall  112  (e.g., at an external side  253  of the wall  112 ) and resisted at other portions of the wall  112  (e.g., at the reservoir  130 ). Tissue ingrowth at the external side  253  of the wall  112  can fix the device at an implanted location, and resisting ingrowth at the reservoir  130  can inhibit the reservoir  130  from being uninflatable due to tissue growth across the reservoir  130 . For this function to be achieved, porosity at one side of the microporous material can be greater than that of another opposing side of the microporous material. In this regard, the microporous material can have a tight side (e.g., where the porosity is greater) and an open side (e.g., where the porosity is lesser). In examples, the second and third microporous membranes  242 ,  243  can be configured to resist tissue ingrowth. In some examples, the first and fourth microporous membranes  241 ,  244  are configured to permit tissue ingrowth, and wherein the second and third microporous membranes  242 ,  243  have an expanded state that is maintained adjacent to the bonded peripheral edges of the first and second layers  114 ,  116 . 
     Penetrations in the microstructure can permit penetration of fluid into the microporous material. These penetrations can vary in size, e.g., based on the function of a given microporous membrane. In examples, either or both of the first and fourth microporous membranes  241 ,  244  can include penetrations that range in size (or average size) to permit ingrowth of vessels and other tissues. In further examples, either or both of the second and third microporous membranes  242 ,  243  are configured or selected such that the penetrations therein are generally sized to minimize, resist, or prevent the ingrowth and attachment of tissue, while maintaining aqueous humor permeability. 
     Internal portions of the microporous material can have varying porosities as can be seen in  FIG.  3 C . The internal portions can extend between the wall internal side  251  and the wall external side  253 . At any of these portions of the wall, the porosity can comparatively range in degree from low porosity (LP), medium-low porosity (MLP), medium porosity (MP), medium-high porosity (MHP), and high porosity (HP). Assuming for discussion purposes here that drainage travels along a relatively straight path through a microporous material so as to sequentially engage porosities of the wall portion internal side  251 , a uniform internal portion, and the wall portion external side  253 , the combined flow resistance can be represented by likewise concatenating their respective porosities. For instance, the wall portion internal side  251  typically has a low porosity throughout (e.g., to resist tissue ingrowth into the reservoir  130 ), and portions of the interior portions and wall portion external side  253  can have any of the aforementioned degrees of porosity. Under these circumstances when the internal portion has a medium porosity and, for example, the internal portions have a medium porosity and the wall portion external side  253  has a high porosity, the flow passage through the microporous material from the reservoir  130  to tissue surrounding the device can be represented as LP-MP-HP. More examples are discussed here below. 
     Various flow paths can be present within the microporous material. Relatively linear flow paths may comprise regions LP1-LP4-LP5, for example or LP3-MHP1-MP1-MLP1. Under some conditions, e.g., where there is high pressure in the reservoir  130 , at least some flow may proceed through the most direct path through the microporous material, such as LP1-LP4-LP5 or LP2-HP1-HP2. Although some flow paths may be relatively straight, there are also flow paths that are nonlinear. For instance, under certain conditions, at least some flow may proceed to flow through areas of increasingly less resistance such as LP1-HP1-HP2 or LP3-MHP1-HP1-HP2. As will be appreciated, the microstructure of the microporous materials may undergo modification processes to obtain certain types of flow through the microstructure. For instance, the microstructure may have relatively uniform layers across layered within the microstructure, or as shown here, have variable portions throughout the thickness of the microporous material. 
     In examples, the wall portion defines a wall portion thickness extending between the wall portion internal side  251  and the wall portion external side  253 . The wall portion thickness can define an internal region of the wall portion having a transition porosity that is between a porosity of the low porosity surface of the wall portion internal side  251  and a porosity of the high porosity surface of the wall portion external side  253 . In addition, or in alternative, the internal region can have an internal region porosity that is equal to porosities of the low porosity surfaces of the internal side and the external side. In addition, or in alternative, the internal region can have an internal region porosity that is equal to a porosity of the low porosity surface of the internal side. In addition, or in alternative, the internal region can have an internal region porosity that is equal to a porosity of the high porosity surface of the external side. 
       FIG.  4 A  shows a flowchart of a method  400  consistent with aspects of the present disclosure. As shown, the method  400  can be useful for forming glaucoma drainage device is disclosed herein and can include drainage systems disclosed elsewhere herein, including the drainage system  100 . At step  401 , the method  400  can include arranging a first portion of a first microporous material over a second portion of a second microporous material. Each of the first microporous material and the second microporous material that transitions from a hydrophobic state that to a hydrophilic state. At step  403 , the method  400  can include securing the first portion to the second portion so as to form a wall that has a reservoir therebetween. The reservoir can be configured to be in fluid communication within the eye to receive a drainage from an internal portion of the eye into the reservoir. The wall can define a variable flow resistance as the wall transitions from the hydrophobic state to the hydrophilic state. In examples, at step  405 , the method  400  can include securing an intake conduit between the first portion and the second portion. The intake conduit can be configured to receive the drainage. 
     A user may take care when constructing the drainage system, particular as it pertains to bonding portions thereof. In examples, securing the first portion to the second portion can include refraining from bonding the first microporous membrane to the fourth microporous membrane. In examples, securing the first portion to the second portion can include arranging the first layer and the second layer in a stacked configuration such that the first microporous membrane and the fourth microporous membrane are the outermost membranes of the wall and the second microporous membrane and third microporous membrane are the innermost membranes of the wall. 
     Another method  450  is shown in  FIG.  4 B . This method a method of use for drainage devices disclosed elsewhere herein, including the drainage device  110 . At step  451 , the method  450  can include directing a drainage from an internal portion of the human to flow toward a reservoir in a drainage device. At step  453 , the method  450  can include collecting drainage in the reservoir until microporous material transitions from a hydrophobic state to a partially hydrophilic state. At step  455 , the method  450  can include directing the drainage to flow from the reservoir to a portion of the body external to the eye via compliant wall. 
     The system shown in  FIGS.  1 A- 1 C  is provided as an example of the various features of the system and, although the combination of those illustrated features is clearly within the scope of invention, that example and its illustration are not meant to suggest the inventive concepts provided herein are limited from fewer features, additional features, or alternative features to one or more of those features shown in  FIGS.  1 A- 1 C . For example, in various embodiments, the components and/or characteristics of the system shown in  FIG.  1 A- 1 C  may include the components and characteristics described with reference to any other figure, such as  FIGS.  2 A- 2 E,  3 A- 3 C, and  4 A and  4 B . It should also be understood that the reverse is true as well. One or more of the components depicted in  FIGS.  1 A- 1 C  can be employed in addition to, or as an alternative to components depicted in  FIGS.  2 A- 2 E,  3 A- 3 C, and  4 A and  4 B . This goes for any figure and the components and characteristics shown therein and discussed with reference thereto herein. 
       FIGS.  7 A and  7 B  show an example of how to test whether a surface is hydrophobic or hydrophilic, also referred to as a “sessile drop method”. Such a test is typically performed with an optical tensiometer which ranges from manual instruments to completely automated systems. In both of these examples, a drop of liquid or fluid (“Liquid”) is placed on a surface that is to be tested, which in this case is the wall  112  (represented by the horizontal arrow) of the glaucoma drainage device  110 . Subsequently, a static contact angle (Θ) of the liquid is measured from the surface, i.e. the wall  112 , by taking an image of the drop using a high-resolution camera, from which the contact angle may be automatically determined using any suitable software. In  FIG.  7 A , the contact angle is an obtuse angle, i.e. greater than 90 degrees, which indicates that the surface of the wall  112  is hydrophobic. In  FIG.  7 B , the contact angle is an acute angle, i.e. less than 90 degrees, which indicates that the surface of the wall  112  is hydrophilic. In some examples, the transition from the hydrophobic state to the hydrophilic state constitutes a decrease in the contact angle by at least 10 degrees, at least 15 degrees, at least 20 degrees, at least 25 degrees, at least 30 degrees, at least 35 degrees, at least 40 degrees, at least 45 degrees, at least 50 degrees, at least 55 degrees, at least 60 degrees, at least 65 degrees, at least 70 degrees, at least 75 degrees, at least 80 degrees, at least 85 degrees, at least 90 degrees, or any other suitable value or range therebetween. As previously explained, the wall  112 , or more specifically a microporous material thereof, may transition from a hydrophobic state to a hydrophilic state, and the speed or rate of this transition can be measured using this method. 
       FIGS.  8 A through  8 E  show different stages of the wall  112  during its transition from one state to another, as shown in five different backlit microscope images. The measurements may be taken using a process defined by the following steps: (1) a device  110  with a reservoir  130  is fluidly connected to any suitable micropump apparatus that has a pressure sensor in line; (2) the pump flow rate is arbitrarily set to 50 μL/m in and the micropump apparatus is activated to apply the predetermined pressure by injecting a fluid (liquid) into the reservoir  130 ; (3) the pressure is measured with respect to the reservoir  130  can be recorded over time; and (4) a change in the measured pressure is detected/recorded over a period of time, such as 3 days, 7 days, 14 days, and 30 days, as suitable. Thereafter the device  110  may be placed on a backlit stage for observation, as done to produce  FIGS.  8 A through  8 E  in an example. 
       FIG.  8 A  is the image taken on Day 0,  FIG.  8 B  is the image taken on Day 3,  FIG.  8 C  is the image taken on Day 7,  FIG.  8 D  is the image taken on Day 14, and  FIG.  8 E  is the image taken on Day 30 after the reservoir  130  is filled with a fluid. In  FIG.  8 A , the outline of the reservoir  130  is shown in a broken white line for reference. The wall  112  is shown to include comparatively darker regions  800  and comparatively lighter regions  802 . The lighter regions  802  indicate areas of the wall  112  that are more translucent than the darker regions  800 , with the translucency representing the amount of wetness, transparency, and/or hydrophilicity of the wall  112  as it transitions from one state to another. As such, in the hydrophobic state, the microporous material is opaque or less translucent, and in the hydrophilic state, the microporous material is transparent or more translucent. Hereinafter, the term “opaque” may be used when an object has less than 20% optical transmission, less than 15% optical transmission, less than 10% optical transmission, or less than 5% optical transmission, for example. The term “translucent” may be used when an object has optical transmission greater than “opaque” and less than “transparent”, such as from 20% to 80% optical transmission, for example. The term “transparent” may be used when an object has greater than 80% transmission, greater than 85% transmission, greater than 90% transmission, or greater than 95% transmission, for example. In some examples, the microporous material may be transparent when it is possible to observe an object through the material. 
     As shown in  FIG.  8 A , on Day 0, substantially the entire surface of the wall  112  shows darker regions  800  which are opaque. As shown in  FIG.  8 B , on Day 3, a region of translucency (lighter region  802 ) appears in a section of the wall  112 . In  FIG.  8 C , on Day 7, the region of translucency (lighter region  802 ) spreads to cover a greater section of the wall  112  than in  FIG.  8 B , and the spreading continues in  FIG.  8 D , on Day 14. In  FIG.  8 E , on Day 30, substantially the entire surface of the wall  112  shows lighter regions  802  which are transparent. As such, of the course of 30 days, the wall  112  transitions from an opaque, hydrophobic state to a translucent, hydrophilic state. 
       FIGS.  9 A through  9 C  show different stages of the wall  112  during its transition from one state to another, as shown in three different microscope images. In these figures, the white portions are unwetted regions  900  which correspond to the darker regions  800  of  FIGS.  8 A through  8 E , and the shaded portions are wetted regions  902  which correspond to the lighter regions  802  of  FIGS.  8 A through  8 E . The walls  112  of the device  110  as shown are in scale, as shown by the ruler indicating centimeters (in  FIG.  9 A ) and millimeters (in  FIG.  9 C ). As such, in  FIG.  9 A , which is the image taken on Day 3, most of the surface of the wall  112  is unwetted and therefore show hydrophobic properties with regions of wetted regions  902  dispersed throughout, whereas in  FIG.  9 B , which is the image taken on Day 7, a portion of the wall  112  are wetted in vivo, and in  FIG.  9 C , which is the image taken on Day 30 (with a dotted line showing a periphery of the wall  112 ), substantially the entire surface of the wall  112  are wetted and therefore show hydrophilic properties. Therefore, over the course of 30 days, the entirety of the microporous material of the wall  112  transitions from the hydrophobic state to the hydrophilic state. In some examples, a first portion of the microporous material transitions from the hydrophobic state to the hydrophilic state within 3 days. In some examples, a second portion of the microporous material different from the first portion transitions from the hydrophobic state to the hydrophilic state within 7 days. The first portion and the second portion may be the lighter regions  802  shown in  FIG.  8 B  or the shaded regions  902  shown in  FIG.  9 A , where these figures show the wall  112  after 3 days of including fluid in the reservoir  130  or wetting, respectively. Alternatively, the first portion and the second portion may be the lighter regions  802  shown in  FIG.  8 C  or the shaded regions  902  shown in  FIG.  9 B , where these figures show the wall  112  after 7 days of including fluid in the reservoir  130  or wetting, respectively. In some examples, less than 10%, less than 7%, less than 5%, less than 3%, less than 1%, or any other suitable value or range therebetween, of the surface of the wall  112  may be the first portion that has transitioned from hydrophobic state to hydrophilic state within 3 days. Furthermore, in some examples, from 10% to 20%, from 7% to 15%, from 5% to 10%, from 3% to 5%, or any other suitable value or range therebetween may be the sum of the first portion and the second portion that have transitioned from hydrophobic state to hydrophilic state within 7 days. 
       FIG.  10    shows a graph  1000  with flowrate on the x-axis and pressure on the y-axis, showing the difference in the properties of the device  110  over time using three different lines as the device  110  undergoes wetting in vivo. A solid line  1002  (represented by a square) shows an initial state of the device  110  at the beginning of a wet-out, i.e. being placed in an environment with fluid/liquid to facilitate the wetting of the device  110 . The initial state may be at day 0 of being disposed in the fluid/liquid environment. A dotted line  1004  (represented by a circle) shows a state of partial wet-out, which may be between day 0 and day 30, for example at day 3, day 7, day 14, or any other suitable number of days therebetween but excluding day 0 and day 30. Another dotted line  1006  (represented by a triangle) shows a state of full or complete wet-out, which may be at day 30. The graph  1000  compares the slopes of the lines  1002 ,  1004 , and  1006 , which represent flow resistance. It is to be understood that the flow resistance is calculated as: Flow Resistance=Pressure/Flowrate. Therefore, because the slope decreases from line  1002  to line  1006 , the flow resistance also decreases from the initial (day 0) state to the final (day 30) state of wetting. 
       FIG.  11 A  shows a graph  1100  with time after implant on the x-axis and percentage change in flow resistance of the device  110  on the y-axis. The flow resistance is shown to decrease over time from 100% at day 3 to near 0% at day 30. The change over time of the flow resistance is shown as asymptotic, although in some examples the change over time may be more linear. In some examples, a portion of the flow resistance does not change, which is represented by a “latent flow resistance” of the device. The portion of the flow resistance that does change is the flow resistance of the portion of the structure which is affected by the wetting of the device as the device transitions from the hydrophobic state to the hydrophilic state, by which time the device only has the latent flow resistance. For example, in the example shown, the 0% flow resistance represents that the changeable flow resistance of the device has reached 0%, whereas the latent flow resistance of the device remains due to the fact that any physical device cannot realistically be completely free of all flow resistance unless the device disintegrates or melts, leaving no structure behind. Because the device  110  does not disintegrate over time but rather wets out to transition to its hydrophilic state, as explained above, the device would retain the latent flow resistance even after the wetting is complete, for example after the 30-day mark. 
       FIG.  11 B  shows a graph  1102  with time after implant on the x-axis and percentage area of the device  110  which has completed the wetting on the y-axis. The graph  1102  shows an increase in the percentage area of the device that is wetted as time progresses from day 0 (beginning of the wetting) to day 30 by which point 100% of the area of the device is completely wetted. In some examples, such as the one shown in the graph, the percentage increase is substantially linear over time, but in some examples, the change may be nonlinear. In some examples, a “substantially linear” percentage increase may be defined as a set of percentage datapoints having a coefficient of determination (a.k.a. the R 2  value) of at least 0.90, at least 0.91, at least 0.92, at least 0.93, at least 0.94, at least 0.95, or any other suitable value or range therebetween, for example, but no greater than 1, with respect to a linear regression model which is calculated based on the datapoints. 
     The invention of this application has been described above both generically and with regard to specific embodiments. It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments without departing from the scope of the disclosure. Thus, it is intended that the embodiments cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.