Patent Description:
The present disclosure is generally related to a blood oxygenator configured for use in extracorporeal membrane oxygenation procedures. More specifically, the disclosure relates to a blood oxygenator having a stacked fiber membrane. Background art in this technical field includes documents <CIT>, <CIT>, <CIT>, <CIT>.

Blood oxygenators are commonly used to accomplish the gas exchange functions normally performed by the lungs. Conventional blood oxygenators contain a gas exchange medium, such as a filter membrane made from hollow fibers, across which blood is flowed. The filter membrane is connected to an oxygen supply such that oxygen is diffused from the filter membrane into the blood and carbon dioxide is removed from the blood into the filter membrane.

Conventional oxygenators are commonly used in medical situations when a patient's lungs are temporarily disabled and/or incapable of performing their normal function. In some medical situations, blood oxygenators are used as a temporary gas exchange member to substitute or supplement the lung function during, for example, open heart surgery. During such procedures, vital functions of the circulatory system are assumed by an extracorporeal bypass circuit in which a pump sends the patient's blood through a blood oxygenator to deliver oxygen to the patient. In other medical situations, a patient may have an indwelling catheter connected to a pump to deliver blood to a blood oxygenator. In these applications, the oxygenator can be used for an indefinite term.

Membrane blood oxygenators transfer oxygen into the blood as the blood flows over a bundle of hollow fibers having oxygen flowing therethrough. Within the prior art, the bundle of hollow fibers may be formed by rolling a fiber mat around a core to form a spirally-wound bundle or by stacking a plurality of individual fiber layers. In blood oxygenators with stacked fiber layers, gas exchange efficiency can be increased by orienting the fibers between adjacent layers at an angle, such as up to <NUM> degrees relative to each other. Blood oxygenators having such fiber arrangement have a square outer shape in order to minimize the amount of potting that must be used to isolate the gas path from the blood path. The square shape increases the physical size of the oxygenator. There is a need in the art for an improved blood oxygenator having an increased gas exchange efficiency and a smaller size compared to conventional blood oxygenators having a stacked fiber membrane.

In some examples or aspects of the present disclosure, an improved blood oxygenator has an increased gas exchange efficiency and a small size. The blood oxygenator may have a housing having a first end opposite a second end with a sidewall extending between the first end and the second end along a longitudinal axis. The housing may define an interior chamber having a liquid inlet at the first end and a liquid outlet at the second end. The oxygenator further may include a gas exchange assembly positioned within the interior chamber. The gas exchange assembly may include a retainer having an upper cap spaced apart from a lower cap by one or more spacers, and a gas exchange medium disposed between the upper cap and the lower cap. The gas exchange medium may have a plurality of subunits stacked on top of each other, with each subunit having a plurality of layers of hollow fiber mats.

In some examples or aspects, the liquid inlet may be formed on a liquid inlet cap enclosing the first end of the housing. The liquid outlet may be formed on a liquid outlet cap enclosing the second end of the housing. The housing may have a circular cross-sectional shape, taken transverse to the longitudinal axis. The upper cap and the lower cap each may have a plurality of openings. The one or more spacers may be a pair of spacers positioned diametrically opposite to each other. The upper cap may be removable from the one or more spacers.

In some examples or aspects, the plurality of subunits may be identical to each other in at least one characteristic. In other examples or aspects, at least one of the plurality of subunits may differ from other subunits in at least one characteristic. The at least one characteristic may be a size of the subunit, a shape of the subunit, a thickness of the subunit, a number of layers of hollow fiber mats, and an angle of orientation of layers of hollow fiber mats.

The illustrations generally show preferred and non-limiting examples or aspects of the apparatus and methods of the present disclosure. While the description presents various aspects of the apparatus, it should not be interpreted in any way as limiting the disclosure. Furthermore, modifications, concepts, and applications of the disclosure's aspects are to be interpreted by those skilled in the art as being encompassed, but not limited to, the illustrations and descriptions herein.

The following description is provided to enable those skilled in the art to make and use the described examples contemplated for carrying out the disclosure.

For purposes of the description hereinafter, the terms "upper", "lower", "right", "left", "vertical", "horizontal", "top", "bottom", "lateral", "longitudinal", and derivatives thereof shall relate to the disclosure as it is oriented in the drawing figures.

As used herein, the terms "parallel" or "substantially parallel" mean a relative angle as between two objects (if extended to theoretical intersection), such as elongated objects and including reference lines, that is from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, inclusive of the recited values.

As used herein, the term "perpendicular" or "substantially perpendicular" mean a relative angle as between two objects (if extended to theoretical intersection), such as elongated objects and including reference lines, that is from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, or from <NUM>° to <NUM>°, inclusive of the recited values.

It is to be understood, however, that the disclosure may assume alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary aspects of the disclosure. Hence, specific dimensions and other physical characteristics related to the examples disclosed herein are not to be considered as limiting.

It should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein.

In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of "or" means "and/or" unless specifically stated otherwise, even though "and/or" may be explicitly used in certain instances. Further, in this application, the use of "a" or "an" means "at least one" unless specifically stated otherwise.

Referring to <FIG>, a blood oxygenator <NUM> is shown in accordance with one example or aspect of the present disclosure. The blood oxygenator <NUM> may be suitable for use in an extracorporeal membrane oxygenation (ECMO) system. The blood oxygenator <NUM> has a housing <NUM> having a liquid inlet <NUM>, a liquid outlet <NUM>, a gas inlet <NUM>, and a gas outlet <NUM> (shown in <FIG>). The housing <NUM> has a first end <NUM> opposite a second end <NUM> extending along a longitudinal axis <NUM>. A liquid inlet cap <NUM> is provided at the first end <NUM> of the housing <NUM>, with the liquid inlet <NUM> extending through the liquid inlet cap <NUM>. A liquid outlet cap <NUM> is provided at the second end <NUM> of the housing <NUM>, with the liquid outlet <NUM> extending through the liquid outlet cap <NUM>. The liquid inlet cap <NUM> and the liquid outlet cap <NUM> may be shaped to prevent velocity change of the blood as the blood enters or exits the oxygenator <NUM>. For example, the liquid inlet cap <NUM> and the liquid outlet cap <NUM> may have a radial draft to prevent eddy flow and recirculation of blood.

In some examples or aspects, the liquid inlet <NUM> and/or the liquid outlet <NUM> may be coaxially arranged with the longitudinal axis <NUM>. In other examples or aspects, the liquid inlet <NUM> and/or the liquid outlet <NUM> may be offset relative to the longitudinal axis <NUM>, extending parallel to the longitudinal axis <NUM> or at an angle relative to the longitudinal axis <NUM>. The liquid inlet <NUM> and the liquid outlet <NUM> may have a barbed fitting for facilitating connection of a liquid inlet cannula and a liquid outlet cannula, respectively. In some examples or aspects, the liquid inlet cannula may be connected to an outlet of a blood pump for delivering blood withdrawn from the patient's body to the oxygenator <NUM> via the blood pump. The liquid outlet cannula may be configured to deliver oxygenated blood to the patient's body after the blood has been oxygenated by passing through the oxygenator <NUM>.

With reference to <FIG>, the housing <NUM> has at least one gas cap <NUM> between the liquid inlet cap <NUM> and the liquid outlet cap <NUM>. The at least one gas cap <NUM> defines the sidewall of the housing between the liquid inlet cap <NUM> and the liquid outlet cap <NUM>. In some examples or aspects, such as shown in <FIG>, the at least one gas cap <NUM> can be a pair of gas caps 30a, 30b that are configured to connect to each other along their longitudinal length in a liquid-tight sealing manner. Upper and lower portions of the at least one gas cap <NUM> are configured to connect to the liquid inlet cap <NUM> and the liquid outlet cap <NUM>, respectively, in a liquid-tight sealing manner. For example, as shown in <FIG>, the liquid inlet cap <NUM> and the liquid outlet cap <NUM> may have grooves <NUM> configured to receive a projection <NUM> on upper and lower ends of the at least one gas cap <NUM>.

With continued reference to <FIG>, a first gas cap 30a may have the gas inlet <NUM> extending therethrough, while the second gas cap 30b may have the gas outlet <NUM> extending therethrough. The gas inlet <NUM> and the gas outlet <NUM> may have a barbed fitting for facilitating connection of a gas inlet hose and a gas outlet hose, respectively. The gas inlet <NUM> may be in fluid communication with a gas source, such as a tank of medical-grade oxygen gas.

With continued reference to <FIG>, the housing <NUM> may have a circular or oval cross-sectional shape and may be made from a rigid material, such as a biocompatible plastic. The plastic may be transparent, translucent, or opaque.

With reference to <FIG>, the liquid inlet cap <NUM>, the liquid outlet cap <NUM>, and the gas cap <NUM> together enclose an interior chamber <NUM> that provides the space in which gas exchange functions are performed via a gas exchange assembly <NUM>, as described herein. The gas inlet <NUM> and the gas outlet <NUM> are in fluid communication with each other via a gas flow path through a plurality of fibers of the gas exchange assembly <NUM>. The liquid inlet <NUM> and the liquid outlet <NUM> are in fluid communication with each other via a blood flow path extending between the fibers of the gas exchange assembly <NUM>.

With reference to <FIG>, the gas exchange assembly <NUM> is shown separate from the oxygenator <NUM> and prior to being potted with a potting material. The gas exchange assembly <NUM> includes a retainer <NUM> configured to hold a gas exchange medium <NUM>. The retainer <NUM> holds the gas exchange medium <NUM> and maintains the spacing between individual subunits of the gas exchange medium <NUM> prior to potting, as described herein. As shown in <FIG>, the retainer has an upper cap <NUM> spaced apart from a lower cap <NUM> by one or more spacers <NUM>. The upper cap <NUM> is shaped to be received within the interior chamber <NUM> of the housing <NUM> (shown in <FIG>) such that the upper cap <NUM> is positioned proximate to the liquid inlet cap <NUM>. Similarly, the lower cap <NUM> is shaped to be received within the interior chamber <NUM> of the housing <NUM> such that the lower cap <NUM> is positioned proximate to the liquid outlet cap <NUM>. In some examples or aspects, the upper cap <NUM> and the lower cap <NUM> have a substantially circular shape that corresponds to a circular shape of the interior chamber <NUM> of the housing <NUM>.

With continued reference to <FIG>, the upper cap <NUM> and the lower cap <NUM> each have a plurality of openings <NUM> configured to allow liquid to flow from one side of the upper cap <NUM> and the lower cap <NUM> to the opposing side of the upper cap <NUM> and the lower cap <NUM>. In this manner, blood entering the oxygenator <NUM> through the liquid inlet <NUM> (shown in <FIG>) passes through the openings <NUM> on the upper cap <NUM> to get to the gas exchange medium <NUM>. After becoming oxygenated via diffusion of oxygen flowing through the fibers of the gas exchange medium <NUM> into the blood, the blood passes through the openings <NUM> on the lower cap <NUM> before exiting the oxygenator <NUM> through the liquid outlet <NUM> (shown in <FIG>). The size, shape, and arrangement of openings <NUM> is selected to minimize pressure loss between the liquid inlet <NUM> and the liquid outlet <NUM>.

With continued reference to <FIG>, the one or more spacers <NUM> of the retainer <NUM> may be a pair of spacers <NUM> positioned diametrically opposite to each other. The spacers <NUM> may be positioned at an outer edge of the upper cap <NUM> and the lower cap <NUM> and are configured to maintain the upper cap <NUM> and the lower cap <NUM> spaced apart from each other by a predetermined distance D. The spacers <NUM> may extend substantially parallel with the longitudinal axis <NUM> of the oxygenator <NUM> (shown in <FIG>). In some examples or aspects, each of the one or more spacers <NUM> has a first end <NUM> that is connected to the upper cap <NUM> and an opposing second end <NUM> that is connected to the lower cap <NUM>. The one or more spacers <NUM> may be removably or non-removably connected to the upper cap <NUM> and the lower cap <NUM>. In some examples or aspects, such as shown in <FIG>, the one or more spacers <NUM> may be removably connected to the upper cap <NUM> and monolithically formed with the lower cap <NUM>. The first end <NUM> of each spacer <NUM> may have a first connector <NUM> that is configured to be removably connected to a corresponding second connector <NUM> on the upper cap <NUM>. In some examples or aspects, the first and second connectors <NUM>, <NUM> may be tongue and groove connectors.

With reference to <FIG>, the gas exchange medium <NUM> is disposed within the space between the upper cap <NUM> and the lower cap <NUM>. The gas exchange medium <NUM> is configured for diffusing a gas flowing therethrough into the liquid flowing around the gas exchange medium <NUM>. In some examples or aspects, the gas exchange medium <NUM> has a plurality of subunits <NUM> that are stacked on top each other between the upper cap <NUM> and the lower cap <NUM>. Each subunit <NUM> is made up of a plurality of layers of fiber mats, with each fiber mat having a plurality of individual hollow fibers. The fibers are configured to carry a gas, such as oxygen, in such a manner that allows the gas to be taken up by a liquid, such as blood, flowing around the fibers, and to absorb any other gas given off by the liquid, such as carbon dioxide. The gas exchange medium <NUM> provides the required surface area for the gas exchange to occur.

In some examples or aspects, the plurality of subunits <NUM> may be identical to each other in at least one characteristic, such as size, shape, thickness, number of layers of fibers mats, type of fiber mats, and orientation of layers of fiber mats relative to each other. In other examples or aspects, at least one of the plurality of subunits <NUM> may differ from other subunits in at least one characteristic, such as size, shape, thickness, number of layers of fibers mats, type of fiber mats, and orientation of layers of fiber mats relative to each other. For example, the number of layers of fiber mats in each subunit <NUM> may vary such that a thickness of the subunits <NUM> varies. The thickness of the subunits <NUM> may be varied progressively along the length of the gas exchange medium <NUM> between the upper cap <NUM> and the lower cap <NUM> of the retainer <NUM>.

With continued reference to <FIG>, each subunit <NUM> of the gas exchange medium <NUM> may have a substantially circular shape that corresponds to the circular shape of the upper cap <NUM> and the lower cap <NUM> of the retainer <NUM>. Each subunit <NUM> may have one or more notches <NUM> configured to receive at least a portion of the corresponding one or more spacers <NUM>. In this manner, rotation of the subunits <NUM> about the longitudinal axis of the gas exchange medium <NUM> can be prevented in order to maintain a desired orientation of the hollow fibers between adjacent subunits <NUM>.

With reference to <FIG>, each subunit <NUM> is made by stacking a plurality of individual fiber mats <NUM> on top of each other. The individual fiber mats <NUM> may be arranged such that they are angled relative to one another, such as by <NUM> to <NUM> degrees between adjacent layers of fiber mats <NUM>, or by <NUM> to <NUM> degrees between adjacent layers of fiber mats <NUM>, or by <NUM> to <NUM> degrees between adjacent layers of fiber mats <NUM>, or by <NUM> to <NUM> degrees between adjacent layers of fiber mats <NUM>, or by <NUM> to <NUM> degrees between adjacent layers of fiber mats <NUM>, or by about <NUM> degrees between adjacent layers of fiber mats <NUM>. As shown in <FIG>, the stack of fiber mats <NUM> is then cut into a shape of the subunit <NUM> using a die <NUM>. In some examples or aspects, cutting of the stack of fiber mats <NUM> into the shape of the subunit <NUM> (<FIG>) may seal the outside edge of the fiber mats <NUM> together such that the fiber mats <NUM> are not separable from each other after cutting. A plurality of subunits <NUM> may then be stacked in the retainer <NUM>. After stacking the plurality of subunits <NUM> into the retainer <NUM>, upper cap <NUM> is connected to the spacers <NUM> to enclose the plurality of subunits <NUM> between the upper cap <NUM> and the lower cap <NUM>, thereby completing a stacked gas exchange assembly <NUM>.

The gas exchange assembly <NUM> is then placed into a potting cup and a potting material poured into the cup while the cup is rotated about its longitudinal axis. Due to a centrifugal force, the potting material accumulates and solidifies at an outer edge of the gas exchange assembly <NUM>. After potting, the gas exchange assembly <NUM> is taken out of the potting cup and is trimmed by cutting away the potting material to expose the openings to the individual hollow fibers of the fiber mats. The potting material that surrounds the openings of the individual hollow fibers seals the hollow fibers of the gas exchange medium <NUM> in order to prevent direct mixing of the gas flowing through the hollow fibers with the liquid flowing around the hollow fibers.

In some examples or aspects, the gas exchange assembly <NUM> may be trimmed to have a uniform outer diameter along its longitudinal length. In this manner, the length of the gas path of individual fibers is constant along the length of the gas exchange medium <NUM>. In other examples or aspects, the gas exchange assembly <NUM> may be trimmed to have a non-uniform outer diameter along its longitudinal length. For example, the gas exchange assembly <NUM> may be sloped such that its diameter increases or decreases along its longitudinal length. In this manner, the length of the gas path of individual fibers is a function of the slope of the gas exchange assembly <NUM>. Regions with thicker potting have a reduced cross-sectional flow area compared to regions with thinner potting, which allows for increased blood velocity and decrease in boundary layer thickness to aid in gas exchange rate in such regions. After trimming, the gas exchange assembly <NUM> is inserted into the interior chamber <NUM> of the housing <NUM> and the liquid inlet and outlet caps <NUM>, <NUM> are sealed with the gas caps <NUM> to define a finished oxygenator <NUM>.

With reference to <FIG>, a schematic diagram shows a minimum potting thickness for the gas exchange medium <NUM> as a function of an overlap angle between layers of stacked fiber mats <NUM>. In this exemplary diagram, each fiber mat <NUM> has a circular shape with a radius ri and a center E. Given an angle α between adjacent layers of fiber mats <NUM>, a first flow path through the first layer of fiber mats <NUM> is defined in a direction between points A and C, and a second flow path through the second layer of fiber mats <NUM> is defined in a direction between points B and D. A quadrilateral that connects points A, B, C, and D has tangential points W, X, Y, and Z with the outer surface <NUM> of the fiber mats <NUM>. A distance between point A and the outer surface <NUM> of the fiber mats <NUM> represents a minimum thickness tmin of the potting material that must be used in order to isolate the gas path extending through the hollow fibers of the gas exchange medium <NUM> from the blood path extending around the hollow fibers of the gas exchange medium <NUM>. In other words, the minimum thickness tmin of the potting material can be expressed as a difference between an outer radius ro defined by point A and the inner radius ri defined by the outer surface <NUM> of the fiber mats <NUM>. The minimum thickness tmin may be calculated using the following formula: <MAT>.

With reference to <FIG>, an alternative blood oxygenator <NUM> is shown in accordance with another example or aspect of the present disclosure. Unless specifically stated otherwise, the blood oxygenator <NUM> includes all elements of the blood oxygenator <NUM> described above. The blood oxygenator <NUM> differs from the blood oxygenator <NUM> in the shape of the housing <NUM> and gas exchange medium <NUM>, but the two blood oxygenators <NUM>, <NUM> function in the same manner.

The blood oxygenator <NUM> has a housing <NUM> having a liquid inlet <NUM>, a liquid outlet <NUM>, a gas inlet <NUM>, and a gas outlet <NUM> (shown in <FIG>). The housing <NUM> has a first end <NUM> opposite a second end <NUM> extending along a longitudinal axis <NUM>. A liquid inlet cap <NUM> is provided at the first end <NUM> of the housing <NUM>, with the liquid inlet <NUM> extending through the liquid inlet cap <NUM>. A liquid outlet cap <NUM> is provided at the second end <NUM> of the housing <NUM>, with the liquid outlet <NUM> extending through the liquid outlet cap <NUM>.

The housing <NUM> of the oxygenator <NUM> is angled relative to the longitudinal axis <NUM>, as shown in <FIG>. The angle Θ is measured between the longitudinal axis <NUM> extending through the liquid inlet <NUM> and the liquid outlet <NUM>, and the plane that the base of the liquid outlet cap <NUM> lies in. The plane that the base of the liquid inlet cap <NUM> lies in may also be at the angle Θ from the longitudinal axis <NUM>. The housing <NUM> may be at an angle Θ between <NUM> and <NUM> degrees relative to the longitudinal axis. In other words, the rim of the liquid inlet cap <NUM> may lie in a plane at an angle Θ relative to the longitudinal axis <NUM> and/or the rim of the liquid outlet cap <NUM> may lie in a plane at an angle Θ relative to the longitudinal axis <NUM>. The housing <NUM> of the oxygenator <NUM> shown in <FIG> is at an angle Θ of <NUM> degrees relative to the longitudinal axis <NUM>. In other examples, the housing may be skewed at an acute angle of less than <NUM> degrees, such as between <NUM> degrees and <NUM> degrees, between <NUM> degrees and <NUM> degrees, between <NUM> degrees and <NUM> degrees, between <NUM> degrees and <NUM> degrees, <NUM> degrees, <NUM> degrees, or <NUM> degrees. In the example shown in <FIG>, the housing <NUM> is skewed at an acute angle Θ of <NUM> degrees relative to the longitudinal axis <NUM>. In addition to being skewed relative to the longitudinal axis, the shape of the liquid inlet cap <NUM> and the liquid outlet cap <NUM> may be an ellipse, as shown in <FIG>. Furthermore, the shape of the cross-section of the housing <NUM> between liquid inlet cap <NUM> and the liquid outlet cap <NUM> taken in a plane perpendicular to the longitudinal axis <NUM> may also be elliptical. The housing <NUM> may be made from a rigid material, such as a biocompatible plastic. The plastic may be transparent, translucent, or opaque.

With reference to <FIG>, the housing <NUM> has at least one gas cap <NUM> defining the sidewall of the housing <NUM> between the liquid inlet cap <NUM> and the liquid outlet cap <NUM>. In some examples or aspects, such as shown in <FIG>, the at least one gas cap <NUM> can be a pair of gas caps 130a, 130b that are configured to connect to each other along their longitudinal length in a liquid-tight sealing manner. Upper and lower portions of the at least one gas cap <NUM> are configured to connect to the liquid inlet cap <NUM> and the liquid outlet cap <NUM>, respectively, in a liquid-tight sealing manner.

With continued reference to <FIG>, a first gas cap 130a may have the gas inlet <NUM> extending therethrough, while the second gas cap 130b may have the gas outlet <NUM> extending therethrough. The gas inlet <NUM> and the gas outlet <NUM> may have a barbed fitting for facilitating connection of a gas inlet hose and a gas outlet hose, respectively. The gas inlet <NUM> may be in fluid communication with a gas source, such as a tank of medical-grade oxygen gas.

With reference to <FIG>, the liquid inlet <NUM> and the liquid outlet <NUM> are in fluid communication with each other via a blood flow path extending between the fibers of the gas exchange medium <NUM> in the gas exchange assembly <NUM>. The gas inlet <NUM> and the gas outlet <NUM> are in fluid communication with each other via a gas flow path through a plurality of fibers of the gas exchange assembly <NUM>.

With reference to <FIG>, the elements of the oxygenator <NUM> are shown in an exploded view, with the gas exchange medium removed. The gas exchange assembly includes a retainer <NUM> configured to hold a gas exchange medium (not shown). The retainer <NUM> holds the gas exchange medium and maintains the spacing between individual subunits of the gas exchange medium prior to potting, as described above. As shown in <FIG>, the retainer <NUM> has an upper cap <NUM> spaced apart from a lower cap <NUM> by one or more spacers <NUM>. The upper cap <NUM> is shaped to be received within the interior chamber of the housing <NUM> such that the upper cap <NUM> is positioned proximate to the liquid inlet cap <NUM>. Similarly, the lower cap <NUM> is shaped to be received within the interior chamber of the housing <NUM> such that the lower cap <NUM> is positioned proximate to the liquid outlet cap <NUM>. In some examples or aspects, the upper cap <NUM> and the lower cap <NUM> have a substantially elliptical shape that corresponds to an elliptical shape of the interior chamber of the housing <NUM> defined by the pair of gas caps 130a, 130b.

Blood entering the oxygenator <NUM> through the liquid inlet <NUM> passes through openings the upper cap <NUM> to get to the gas exchange medium <NUM> (shown in <FIG>). After becoming oxygenated via diffusion of oxygen flowing through the fibers of the gas exchange medium <NUM> into the blood, the blood passes through the lower cap <NUM> before exiting the oxygenator <NUM> through the liquid outlet <NUM>.

With continued reference to <FIG>, the one or more spacers <NUM> of the retainer <NUM> may be a pair of spacers <NUM> positioned diametrically opposite to each other. The spacers <NUM> may be positioned at an outer edge of the upper cap <NUM> and the lower cap <NUM> and are configured to maintain the upper cap <NUM> and the lower cap <NUM> spaced apart from each other by a predetermined distance. The spacers <NUM> may extend substantially parallel with the longitudinal axis <NUM> of the oxygenator <NUM> (shown in <FIG>) and be positioned equidistantly on opposite sides of the longitudinal axis <NUM>. The spacers <NUM> may be positioned at the maximum radial dimension of the elliptical shape (measured from the longitudinal axis <NUM>) of the upper cap <NUM> and the lower cap <NUM>, for example. The one or more spacers <NUM> may be removably or non-removably connected to the upper cap <NUM> and the lower cap <NUM>. In some examples or aspects, the one or more spacers <NUM> may be removably connected to the upper cap <NUM> and monolithically formed with the lower cap <NUM>.

The gas exchange medium <NUM> is disposed within the space between the upper cap <NUM> and the lower cap <NUM>. The gas exchange medium <NUM> is configured for diffusing a gas flowing therethrough into the liquid flowing around the gas exchange medium <NUM>. In some examples or aspects, the gas exchange medium <NUM> includes a plurality of subunits <NUM>, shown in <FIG>, that are stacked on top each other between the upper cap <NUM> and the lower cap <NUM>. Each subunit <NUM> is made up of a plurality of layers of fiber mats, with each fiber mat having a plurality of individual hollow fibers. The fibers are configured to carry a gas, such as oxygen, in such a manner that allows the gas to be taken up by a liquid, such as blood, flowing around the fibers, and to absorb any other gas given off by the liquid, such as carbon dioxide. The gas exchange medium <NUM> provides the required surface area for the gas exchange to occur.

With continued reference to <FIG>, each subunit <NUM> of the gas exchange medium <NUM> may have a substantially elliptical shape that corresponds to the elliptical shape of the upper cap <NUM> and the lower cap <NUM> of the retainer <NUM>. The centroid of the elliptical shape of each subunit <NUM> may be centered on the longitudinal axis <NUM> of the housing <NUM> when positioned within the housing <NUM>. Each subunit <NUM> may have one or more notches <NUM> configured to receive at least a portion of the corresponding one or more spacers <NUM>. For example, each subunit <NUM> may have opposing notches <NUM> positioned at the maximum radial dimension of the elliptical shape (measured from the longitudinal axis <NUM>) that mate with and receive the spacers <NUM>. In this manner, rotation of the subunits <NUM> about the longitudinal axis of the gas exchange medium <NUM> can be prevented in order to maintain a desired orientation of the hollow fibers between adjacent subunits <NUM>.

With reference to <FIG> and <FIG>, the gas exchange assembly <NUM> is shown separate from the oxygenator <NUM> and prior to being potted with a potting material. The gas exchange assembly <NUM> includes a retainer <NUM> configured to hold the gas exchange medium <NUM>. The retainer <NUM> holds the gas exchange medium <NUM> and maintains the spacing between individual subunits of the gas exchange medium <NUM> prior to potting, as described herein. The retainer <NUM> has an upper cap <NUM> spaced apart from a lower cap <NUM> by one or more spacers <NUM>. The upper cap <NUM> is shaped to be received within the interior chamber of the housing <NUM> such that the upper cap <NUM> is positioned proximate to the liquid inlet cap <NUM>. Similarly, the lower cap <NUM> is shaped to be received within the interior chamber of the housing <NUM> such that the lower cap <NUM> is positioned proximate to the liquid outlet cap <NUM>. In some examples or aspects, the upper cap <NUM> and the lower cap <NUM> have a substantially elliptical shape that corresponds to an elliptical shape of the interior chamber of the housing <NUM>.

With reference to <FIG>, the ellipse configuration of the oxygenator <NUM> is achieved by stacking the individual subunits <NUM> that make up the gas exchange medium <NUM>. The individual subunits <NUM> may lie in a plane parallel to adjacent subunits <NUM>. Thus, the subunits <NUM> may be stacked such that an axis extending through the centroid of each subunit <NUM> is at an acute angle to a plane that the upper surface and/or lower surface of each subunit <NUM> lies in. The axis extending through the centroids may be coaxially or otherwise parallel to the longitudinal axis <NUM> of the housing <NUM>. Accordingly, adjacent subunits <NUM> may be stacked with the outer periphery offset from adjacent subunits <NUM> and at an angle relative to one another rather than flat on top of each other as is seen in the oxygenator <NUM> shown in <FIG>. Each subunit <NUM> is in the shape of an ellipse, and in the centroid of adjacent subunits <NUM> are skewed at a desired angle, such as the <NUM> degree angle shown in <FIG>. Each subunit <NUM> is laid offset to the adjacent subunit <NUM> such that the stack is tilted away from the vertical axis at the desired angle. In other words, the stack of the plurality of subunits <NUM> forming the gas exchange medium <NUM> is tilted at the acute angle Θ relative to the longitudinal axis <NUM>. This allows the cross section taken transverse to the longitudinal axis to be mostly circular (this is the cross section the blood "sees" visualizable by looking down the long axis), as shown in <FIG>. The subunits <NUM> themselves are wider than the equivalent surface area circular cross section bundle which allows fewer subunits <NUM> to be used to get a desired surface area. This may allow for lower pressure drop as well as manufacturing and material efficiency. Angled fiber layers like this may promote mixing as well which may enhance gas exchange. This configuration allows a wider bundle without significantly altering the aspect ratio of the final device. A wider bundle device may be made without making it look like a pancake.

Claim 1:
A blood oxygenator (<NUM>, <NUM>) comprising:
a housing (<NUM>, <NUM>) having a first end (<NUM>, <NUM>) opposite a second end (<NUM>, <NUM>) with a sidewall extending between the first end and the second end along a longitudinal axis (<NUM>, <NUM>), the housing (<NUM>, <NUM>) defining an interior chamber (<NUM>) having a liquid inlet (<NUM>, <NUM>) at the first end (<NUM>, <NUM>) and a liquid outlet (<NUM>, <NUM>) at the second end (<NUM>, <NUM>); and
a gas exchange assembly (<NUM>, <NUM>) positioned within the interior chamber (<NUM>), the gas exchange assembly (<NUM>, <NUM>) comprising:
a retainer (<NUM>, <NUM>) having an upper cap (<NUM>, <NUM>) spaced apart from a lower cap (<NUM>, <NUM>) by one or more spacers (<NUM>, <NUM>); and
a gas exchange medium (<NUM>, <NUM>) disposed between the upper cap (<NUM>, <NUM>) and the lower cap (<NUM>, <NUM>),
wherein the gas exchange medium (<NUM>, <NUM>) comprises a plurality of subunits (<NUM>, <NUM>) stacked on top of each other, each subunit comprising a plurality of layers of hollow fiber mats;
characterized in that
the plurality of subunits (<NUM>, <NUM>) are stacked offset from one another such that an axis extending through the centroid of each of the subunits is at an acute angle relative to the longitudinal axis (<NUM>, <NUM>) of the housing (<NUM>, <NUM>).