Patent Description:
Exosomes are cell-derived vesicles that can carry nucleic acids, lipids, or proteins from one cell to another. Exosomes play an important role in communication between cells, and are necessary for the proper functioning of the human body. In addition to their role in the regular physiology of humans, exosomes are also connected with certain diseases. There has been growing interest in exosome research due to their role as intercellular messengers and their potential in both the diagnosis and treatment of disease. For example, because exosomes have different secretory components under physiological and pathological conditions, they have been studied as a therapeutic target, a drug or gene delivery vector, and a cancer marker.

Exosomes are a type of extracellular vesicle secreted from most cell types, and typically have diameters of between <NUM> and <NUM>. Exosomes are normally secreted along with other types of extracellular vesicles, such as apoptotic bodies having diameters of <NUM>-<NUM>, and ectosomes having diameters of <NUM>-<NUM>. Exosomes may be separated from these other types of extracellular vesicles using centrifugation. However, because these additional extracellular vesicles often have similar physical properties as exosomes (e.g., similar sizes and densities), isolating exosomes from other cellular secretions commonly found in biological suspensions can require extremely high g-forces.

The amount of g-force that can be generated by a centrifuge depends at least in part on the physical properties of the rotor. Minor imperfections such as uneven distributions in mass or minor structural defects that would not be an issue in conventional centrifuges can cause vibrations or failures at the rotational speeds desired to efficiently separate exosomes.

Thus, there is a need for improved rotors that can be used in ultracentrifugation applications for separating exosomes and other materials having similar physical properties. A centrifuge rotor is known for example from <CIT>.

The present invention overcomes the foregoing and other shortcomings and drawbacks of centrifuge rotors heretofore known for use in ultra-high-speed centrifugation.

In an advantageous embodiment of the present invention, each of the first cross-sectional shape and the second cross-sectional shape may be rectangular.

In an advantageous embodiment of the present invention, the rotor body may include an upper bore opening in communication with the elongated bore, and the elongated bore may be cylindrical in cross-section transverse to the axis of rotation between the lower bore opening and the upper bore opening.

In an advantageous embodiment of the present invention, the rotor further includes a lid having a central wall portion, a conical wall portion extending upwardly and outwardly from the central wall portion, and an annular wall portion extending radially outward from the conical wall portion remote from the central wall portion such that the annular wall portion is radially and axially offset from the central wall portion.

In an advantageous embodiment of the present invention, the conical wall portion of the lid may be configured to engage each sample container placed into a respective cavity when the lid is operatively coupled to the rotor.

In an advantageous embodiment of the present invention, the upper surface of the rotor body may define an upper recess, and the central and conical wall portions of the lid may be received in the upper recess.

In an advantageous embodiment of the present invention, the lid may include a lid-lifting handle that projects axially upward from the central wall portion of the lid.

In an advantageous embodiment of the present invention, the lid-lifting handle may include a cylindrical wall and a handle flange that projects radially outward from a free end of the cylindrical wall remote from the central wall portion of the lid.

According to the present invention, the drive hub includes a cylindrical shaft that projects upwardly through the elongated bore from the drive portion of the drive hub.

Further according to the present invention, an upper portion of the cylindrical shaft includes a threaded outer surface.

Further according to the present invention, the rotor further includes a lid screw having a lower bore with a threaded inner surface and a lid screw flange that extends radially outward from a lower end of the lid screw. The threaded outer surface of the drive hub is configured to threadedly engage the threaded inner surface of the lower bore of the lid screw, and the lid screw flange has a lower surface configured to urge the lid into contact with the rotor body in response to threaded engagement of the lid screw and the drive hub.

In an advantageous embodiment of the present invention, the cylindrical wall of the lid-lifting handle may be configured to receive the lid screw flange and position the lid screw concentrically with the lid-lifting handle.

In an advantageous embodiment of the present invention, the lower surface of the lid screw flange may include an annular groove, and the rotor may further include an elastic member positioned within the annular groove that is compressed against an upper surface of the central wall portion of the lid in response to threaded engagement of the lid screw with the drive hub.

In an advantageous embodiment of the present invention, the lower bore opening may include one or more sidewalls, the drive portion of the drive hub may have one or more faces each engaging a respective sidewall of the lower bore opening, and the application of torque to the rotor body may be by the one or more faces engaging the respective sidewalls.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with the general description of the present invention given above, and the detailed description given below, serve to explain the present invention.

Embodiments of the present invention are directed to a rotor suitable for use in ultracentrifugation.

Ultracentrifugation uses differences in the sedimentation rate of particles, which may be affected by the size, density, and shape of the particles, to separate sample components suspended in a liquid. Centrifugal forces may be applied in steps to separate sample components sequentially according to their physical properties. Because sedimentation rates are dependent at least in part on the size of the particles, smaller particles may be isolated from larger particles using a series of sequentially increasing centrifugation speeds. By way of example, relatively low g-forces (e.g., <NUM>-<NUM>,<NUM>×g) may be applied to remove cells, cell debris, and other large particles from a sample of the suspension. The remaining supernatant may then be aspirated and subjected to subsequent rounds of centrifugation at increasing g-forces, with each round separating out progressively smaller particles. Ultracentrifugation producing high g-forces (e.g., up to <NUM>,<NUM>,<NUM>×g) may be used in later rounds of centrifugation to obtain a pellet of the desired material. Density gradient separation using ultracentrifugation may also be used to isolate or purify sample components.

Embodiments of the present invention include rotors that provide improved uniformity in the distribution of mass with respect to their respective axes of rotation, increased strength, and reduced overall mass as compared to conventional rotors. The low levels of vibration and high g-forces (e.g., <NUM>,<NUM>×g at <NUM>,<NUM> to <NUM>,<NUM> RPM) enabled by these rotors may allow improved isolation and purification processes for materials suspended in biological fluids, such as cells, exosomes, mitochondria, and other organelles.

<FIG> depict a rotor <NUM> in accordance with an exemplary embodiment of the present invention. As best shown by <FIG>, the rotor <NUM> includes a rotor body <NUM>, a reinforcement <NUM>, a balance ring <NUM>, a lid <NUM>, a drive hub <NUM>, and a lid screw <NUM>. The rotor <NUM> has an axis of rotation <NUM> about which the rotor <NUM> is configured to rotate when used in a centrifuge, and about which the components of the rotor <NUM> are concentrically arranged.

As best shown by <FIG> and <FIG>, the rotor body <NUM> may be made from a carbon fiber composite or other suitable lightweight, rigid material, and includes an upper surface <NUM>, a lower surface <NUM>, a circumferential sidewall <NUM>, and an elongated bore <NUM> that passes through the upper and lower surfaces <NUM>, <NUM>. The elongated bore <NUM> may be axially aligned with the axis of rotation <NUM>, and intersects an upper recess <NUM> in the upper surface <NUM> and a lower bore opening <NUM> in the lower surface <NUM> of rotor body <NUM>. As described in more detail below, the lower bore opening <NUM> may have a horizontal cross sectional shape that is keyed to the drive hub <NUM> to prevent rotation of the rotor body <NUM> relative to the drive hub <NUM>.

The upper surface <NUM> of rotor body <NUM> may include an annular surface <NUM>, a central surface <NUM> that is recessed axially downward relative to the annular surface <NUM>, and an annular groove <NUM>. The annular groove <NUM> may define an outer perimeter <NUM> of the annular surface <NUM> and an upper edge <NUM> of the circumferential sidewall <NUM>. The annular groove <NUM> may be defined by an upper rabbet <NUM> and a lower rabbet <NUM> that overlap to define a shoulder <NUM>. The central surface <NUM> may be connected to the annular surface <NUM> by a connecting surface <NUM>. The connecting surface <NUM> may extend axially upward and radially outward from an outer perimeter of the central surface <NUM> to an inner perimeter of the annular surface <NUM>. The connecting surface <NUM> may be oriented such that it faces axially upward and radially inward, and may include a lower portion <NUM> and an upper portion <NUM>. The upper portion <NUM> of connecting surface <NUM> may be elevated above the lower portion <NUM> in a direction normal to the connecting surface <NUM>.

The rotor body <NUM> may further include a plurality of cavities <NUM> each extending axially downward and radially outward from the lower portion <NUM> of connecting surface <NUM> and into the rotor body <NUM>. Each cavity <NUM> may have a central axis that is normal to the connecting surface <NUM>, and be suitably sized and shaped receive a sample container <NUM>. Each cavity <NUM> may be configured to hold its respective sample container <NUM> in a suitable position and orientation for centrifugation, e.g., at a <NUM> degree angle relative to the axis of rotation <NUM>. Each sample container <NUM> may be configured to hold an amount of a sample suspension (e.g., <NUM>) and include a cap <NUM> that seals the sample container <NUM> when pressed into a closed position. The cap <NUM> may include a tab <NUM> configured to facilitate opening of the sample container <NUM>. The cavity <NUM>, sample container <NUM>, and cap <NUM> may be configured so that when the sample container <NUM> is fully inserted into its respective cavity <NUM>, the tab <NUM> is supported by the upper portion <NUM> of connecting surface <NUM>. Advantageously, the upper portion <NUM> of connecting surface <NUM> may prevent high g-forces generated by centrifugation from causing deflection of the cap <NUM>, which could potentially break the seal between the cap <NUM> and the body of the sample container <NUM> or damage the sample container <NUM>.

As best shown by <FIG>, the reinforcement <NUM> may include one or more helical windings that extend around and above the circumferential sidewall <NUM> of rotor body <NUM>. An inner surface <NUM> of reinforcement <NUM> may operate cooperatively with the annular groove <NUM> of rotor body <NUM> to define a channel <NUM> in which the balance ring <NUM> is positioned. The reinforcement <NUM> may be formed by a filament winding process followed by a compression molding process using a suitable material, such as an epoxy-coated carbon fiber. For example, the reinforcement <NUM> may be compression molded onto the rotor body <NUM> and balance ring <NUM> after placing layers of resin-coated carbon fiber laminate material, or winding one or more strands of carbon fiber, onto the outwardly-facing surface of circumferential sidewall <NUM>.

To prevent the reinforcement <NUM> from moving axially, the circumferential sidewall <NUM> may include an inward taper that defines a circumferential recess <NUM> in the circumferential sidewall <NUM>. The inner surface <NUM> of reinforcement <NUM> may conform to the circumferential recess <NUM> so that reinforcement <NUM> resists axial movement relative to the rotor body <NUM>. The reinforcement <NUM> may be configured to bear the majority of the centrifugal forces placed on the rotor <NUM>. Methods of forming reinforcements for centrifugal rotors using a filament winding process are described in detail by <CIT>.

As best shown by <FIG>, the balance ring <NUM> may include a body <NUM> having a rectangular cross section and a flange <NUM>. The flange <NUM> may project radially inward from a top portion of the body <NUM> of balance ring <NUM>, and may be configured to engage the shoulder <NUM> of rotor body <NUM>. The balance ring <NUM> may be heated so that it expands before placing it on the annular groove <NUM>, and allowed to cool in place so that it is held to the rotor body <NUM> by a shrink-fit. The balance ring <NUM> may be placed in the annular groove <NUM> of rotor body <NUM> prior to forming the configured to engage the shoulder <NUM> of rotor body <NUM>. The balance ring <NUM> may be heated so that it expands before placing it on the annular groove <NUM>, and allowed to cool in place so that it is held to the rotor body <NUM> by a shrink-fit. The balance ring <NUM> may be placed in the annular groove <NUM> of rotor body <NUM> prior to forming the reinforcement <NUM> so that the reinforcement <NUM> holds the balance ring <NUM> in place. An adhesive may also be used to operatively couple the balance ring <NUM> to the surface of the annular groove <NUM>. The adhesive may be used alone or in combination with the shrink fit.

The balance ring <NUM> may include a plurality of apertures <NUM> each configured to receive a weight <NUM>. One or more weights <NUM> may be selectively positioned in one or more of the apertures <NUM> of balance ring <NUM> in order to balance the rotor <NUM>. Each weight <NUM> may include a threaded shaft <NUM> and a head <NUM>. Each aperture <NUM> may include a threaded bore <NUM> configured to receive the threaded shaft <NUM> of weight <NUM>, and a receptacle <NUM> (e.g., a countersink, counterbore, or the like) configured to receive the head <NUM> of weight <NUM>. The receptacle <NUM> may thereby allow the top of the weight <NUM> to be flush with or recessed below an upper surface <NUM> of the balance ring <NUM> when the weight <NUM> is fully inserted into the aperture <NUM>.

As best shown by <FIG>, the balance ring <NUM> may be angularly positioned about the axis of rotation <NUM> with respect to the rotor body <NUM> such that the apertures <NUM> of balance ring <NUM> are symmetrically positioned relative to the cavities. This symmetry may result in each of the two apertures <NUM> closest to a respective cavity <NUM> of rotor body <NUM> being an equal distance from, and on opposite sides of, a line extending radially outward from the axis of rotation <NUM> and passing thorough the central axis of the cavity <NUM>. This angular positioning of the balance ring <NUM> may provide the ring with an orientation such that each cavity <NUM> of rotor body <NUM> is angularly centered between the two apertures <NUM> of balance ring <NUM> closest to the cavity <NUM>, and ensure positional symmetry between the cavities <NUM> of rotor body <NUM> and the apertures <NUM> of balance ring <NUM>.

As best shown by <FIG>, the lid <NUM> of rotor <NUM> may include an annular wall portion <NUM>, a central wall portion <NUM>, and a conical wall portion <NUM>, and may be made of a carbon fiber composite, aluminum, or any other suitable rigid low-mass material. The conical wall portion <NUM> of lid <NUM> may connect an inner edge <NUM> of the annular wall portion <NUM> to an outer edge <NUM> of the central wall portion <NUM>. The conical wall portion <NUM> may be joined to each of the annular wall portion <NUM> and the shape of the lid <NUM> may generally conform to that of the upper surface <NUM> of rotor body <NUM>.

Referring again to <FIG>, and with continued reference to <FIG>, the annular wall portion <NUM> of lid <NUM> may include a lower surface <NUM> having an annular groove <NUM> that is configured to receive an elastic member <NUM>, e.g., an O-ring. The elastic member <NUM> may be made of any suitable material (e.g., silicone), and may be configured to engage the upper surface <NUM> of balance ring <NUM> when the lid <NUM> is operatively coupled to the rotor <NUM>.

The central wall portion <NUM> of lid <NUM> may include an upper surface <NUM>, a central bore <NUM>, and a lid-lifting handle <NUM> that projects axially upward from the upper surface <NUM>. The central bore <NUM> may have the same diameter as the elongated bore <NUM> of rotor body <NUM> so that the bores are axially aligned by the drive hub <NUM>. The lid-lifting handle <NUM> may include a cylindrical wall <NUM> having an inner surface <NUM>, and a flange <NUM>. The cylindrical wall <NUM> may be joined to the lid <NUM> at a lower end thereof. The flange <NUM> may project radially outward from an upper portion of the lid-lifting handle <NUM> at a free end of the cylindrical wall <NUM> remote from the central wall portion <NUM> of lid <NUM> to provide a grip for grasping the rotor <NUM>. This grip may improve the ergonomics of installing of the rotor <NUM> in, and removing the rotor <NUM> from, a centrifuge as compared to rotors lacking this feature. The inner surface <NUM> of cylindrical wall <NUM> may include a neck <NUM> proximate or adjacent to the upper surface <NUM>. The neck <NUM> may have a diameter d<NUM> which is less than the diameter d<NUM> of the main portion of inner surface <NUM>. The main portion of inner surface <NUM> may be joined to the neck <NUM> by a bevel <NUM>.

As best shown by <FIG>, the drive hub <NUM> may include a shaft <NUM>, a flange <NUM> that projects radially outward from a bottom portion of the shaft <NUM>, and a center bore <NUM> which extends axially into a bottom end of the shaft <NUM>. The center bore <NUM> of drive hub <NUM> may be axially aligned with the axis of rotation <NUM> of rotor <NUM>, include a bottom surface <NUM>, and be configured to receive a spindle of the centrifuge (not shown). An upper portion <NUM> of shaft <NUM> may be configured to receive the lid screw <NUM>. To this end, the upper portion <NUM> of shaft <NUM> may include a threaded outer surface <NUM> configured to threadedly engage the lid screw <NUM>.

A portion of the shaft <NUM> adjacent to and below the threaded outer surface <NUM> may have a reduce radius (e.g., an undercut) to provide thread relief. This thread relief may ensure a lower surface <NUM> of a flange <NUM> of lid screw <NUM> engages the upper surface <NUM> of the central wall portion <NUM> of lid <NUM> without interference from the shaft <NUM> when the lid screw <NUM> is threadedly engaged with the drive hub <NUM>. The upper portion <NUM> of shaft <NUM> may include a protruding end <NUM> at the top thereof. The protruding end <NUM> may have a diameter about the same as the minor diameter of the threaded outer surface <NUM>, and extend a distance of <NUM> to <NUM> thread widths beyond the threads of the threaded outer surface <NUM>. The drive hub <NUM> may be manufactured from a solid billet of metal using computer numerical control (CNC) machining, for example, or using any other suitable process.

Referring again to <FIG>, and with continued reference to <FIG>, to prevent the drive hub <NUM> from rotating relative to the spindle, one or more drive-pins <NUM> may extend axially downward from the bottom surface <NUM> of center bore <NUM>. Each drive-pin <NUM> may be configured to engage a respective receptacle in the spindle of the centrifuge. Each drive-pin <NUM> may comprise a rod <NUM> inserted into a respective bore <NUM> that extends axially into the bottom surface <NUM> of center bore <NUM>. Each bore <NUM> may be offset radially from the center axis of center bore <NUM>. This offset may cause the drive-pins <NUM> to be subjected to a shearing force in response to the spindle applying torque to the rotor <NUM> that would be sufficient to, absent the drive-pins <NUM>, cause slippage between the spindle and drive hub <NUM>.

A drive portion <NUM> of hub <NUM> may extend axially upward from the flange <NUM> and radially outward from the shaft <NUM>. The drive portion <NUM> of hub <NUM> may have a horizontal cross sectional shape that is keyed, or is otherwise complementary, to the horizontal cross sectional shape of the lower bore opening <NUM> of rotor body <NUM>. Keying the drive portion <NUM> to the lower bore opening <NUM> may prevent the angular position of the rotor body <NUM> from shifting relative to the drive hub <NUM> under angular acceleration. To this end, the cross sectional shape of the drive portion <NUM> may be the same as that of the lower bore opening <NUM>, a different shape that fits within the lower bore opening <NUM> and has one or more faces <NUM> that engage corresponding faces <NUM> in a sidewall of the lower bore opening <NUM>, or that is otherwise keyed to the cross sectional shape of the lower bore opening <NUM>.

For example, the cross sectional shape of the drive portion <NUM> may be a polygon (e.g., a square) having the same number of faces <NUM>, or more faces <NUM>, than the shape of the lower bore opening <NUM>. By way of example, for a lower bore opening <NUM> having a square-shaped horizontal cross-section, the drive portion <NUM> may have a square-shaped, an octagonal-shaped, or other cross-sectional shape having one or more faces <NUM> complementary to the faces <NUM> of lower bore opening <NUM>. The lower bore opening <NUM> may also include one or more axially-aligned channels <NUM> positioned where the vertexes of the faces <NUM> would otherwise be to facilitate insertion of the drive portion <NUM> of drive hub <NUM> into the lower bore opening <NUM>.

As best shown by <FIG>, the lid screw <NUM> may be made from any suitable material (e.g., aluminum), and comprises a cylindrical body having an outer surface <NUM>, an upper bore <NUM>, a lower bore <NUM>, and the flange <NUM> that projects radially outward from a lower end of the cylindrical body. The flange <NUM> may have an outer diameter the same as or slightly less than the diameter d<NUM> of neck <NUM>. The bevel <NUM> may guide the flange <NUM> into the neck <NUM> as the flange <NUM> is inserted into the lid-lifting handle <NUM> and the lid screw <NUM> screwed onto the drive hub <NUM>. The neck <NUM> and bevel <NUM> may thereby work cooperatively with the flange <NUM> to position the lid screw <NUM> concentrically with the lid <NUM> and drive hub <NUM>, thereby aligning the lid <NUM> with the axis of rotation <NUM> of rotor <NUM> during engagement of the lid screw <NUM> with the drive hub <NUM>. The final alignment between the lid <NUM> and the axis of rotation <NUM> of rotor <NUM> may be defined by the engagement of the shaft <NUM> of drive hub <NUM> and the central bore <NUM> of lid <NUM>.

The flange <NUM> may include the lower surface <NUM>, and the lower surface <NUM> may have an annular groove <NUM> configured to receive an elastic member <NUM>. The elastic member <NUM> may be an O-ring or other type of gasket made of a suitable material, such as silicone. The elastic member <NUM> may be compressed against the upper surface <NUM> of the central wall portion <NUM> of lid <NUM> in response to tightening the lid screw <NUM> against the drive hub <NUM>. The elastic member <NUM> may thereby urge the lid <NUM> into operable engagement with the rotor <NUM>.

The lid screw <NUM> may further include one or more pairs of radially-aligned holes <NUM> on opposing sides of the upper bore <NUM>. The radially-aligned holes <NUM> may be configured to receive a rod or other tool for applying torque to the lid screw <NUM>. The radially-aligned holes <NUM> may thereby facilitate tightening the lid screw <NUM> to the drive hub <NUM>, and loosening the lid screw <NUM> from the drive hub <NUM>.

The lower bore <NUM> of lid screw <NUM> may include a threaded inner surface <NUM> configured to threadedly engage the threaded outer surface <NUM> of drive hub <NUM>. The protruding end <NUM> of shaft <NUM> may facilitate this threaded engagement <NUM>. The radially-aligned holes <NUM> may thereby facilitate tightening the lid screw <NUM> to the drive hub <NUM>, and loosening the lid screw <NUM> from the drive hub <NUM>.

The lower bore <NUM> of lid screw <NUM> may include a threaded inner surface <NUM> configured to threadedly engage the threaded outer surface <NUM> of drive hub <NUM>. The protruding end <NUM> of shaft <NUM> may facilitate this threaded engagement between the drive hub <NUM> and lid screw <NUM> by providing a clean start to engagement between the threaded outer surface <NUM> of shaft <NUM> and the threaded inner surface <NUM> of lower bore <NUM>. Threadedly engaging the lid screw <NUM> with the drive hub <NUM> may urge the lid <NUM> against at least a portion of the upper surface <NUM> of rotor body <NUM>. The lid screw <NUM> may also urge the lid <NUM> against the caps <NUM> of sample containers <NUM>, thereby maintaining the caps <NUM> fully seated on the sample containers <NUM>. In this way, the lid <NUM> may also hold the sample containers <NUM> in a fully seated position within their respective cavities <NUM> by applying a nominal force to the surface of each cap <NUM>.

<FIG> and <FIG> depict top views of the rotor <NUM> without the lid <NUM>, and <FIG> and <FIG> depict cross-sectional views of a balance ring <NUM>. The balance ring <NUM> may include a body <NUM> having a rectangular cross section, a flange <NUM>, and a plurality of apertures <NUM> each configured to receive a weight <NUM>,. Each weight <NUM> may include a threaded shaft <NUM> and a head <NUM> configured to receive a tool, e.g., a hex key. Each aperture <NUM> may include a threaded bore <NUM> configured to receive the weight <NUM>. The threaded bore <NUM> may have a length greater than the length of the weight <NUM>, thereby allowing the position of the weight <NUM> within the threaded bore <NUM> to be selectively adjusted by rotating the weight <NUM> in one of a clockwise or counter-clockwise direction. This ability to adjust the position of each weight <NUM> in an axial direction relative to an upper surface <NUM> of the balance ring <NUM> may facilitate achieving dynamic balance of the rotor <NUM>. The head <NUM> of weight <NUM> may be configured so that the head <NUM> can be positioned below the upper surface <NUM> of balance ring <NUM>. This may allow the weight <NUM> to be positioned anywhere within the threaded bore <NUM>. The weights <NUM> may comprise, for example, set screws made from a suitable material, such <NUM> stainless steel. Different length set screws may be used to provide weights <NUM> having different masses. By way of example, metric SST-<NUM> set screws sized M4 X <NUM> come in variety of lengths, and provide excellent maps for balancing.

The apertures <NUM> may be located a fixed radial distance from the axis of rotation <NUM> of rotor <NUM>, and may be arranged in aperture groups <NUM>. By way of example, the balance ring <NUM> may include <NUM> apertures <NUM> arranged in <NUM> aperture groups <NUM>, with each aperture group <NUM> having three apertures <NUM>. Each aperture <NUM> may be a fixed angular distance θ<NUM> (e.g., <NUM> degrees) from angularly adjacent apertures <NUM> within the same aperture group <NUM>. Each aperture group <NUM> may be a fixed angular distance θ<NUM> (e.g., <NUM> degrees) from angularly adjacent aperture groups <NUM>. Each aperture group <NUM> may provide a plurality (e.g., three) balancing locations, and may be located between two adjacent cavities <NUM>. A marker <NUM> may be located between each aperture group <NUM>, and may include numerals other indicia that uniquely identifies each cavity <NUM> in the rotor.

The balance ring <NUM> may be angularly positioned about the axis of rotation <NUM> with respect to the rotor body <NUM> such that the apertures <NUM> of balance ring <NUM> are symmetrically positioned relative to the cavities <NUM>. This symmetry may result in each aperture group <NUM> closest to a respective cavity <NUM> of rotor body <NUM> being an equal distance from, and on opposite sides of, a line extending radially outward from the axis of rotation <NUM> and passing thorough the central axis of the cavity <NUM>. This angular positioning of the balance ring <NUM> may provide the ring with an orientation such that each cavity <NUM> of rotor body <NUM> is angularly centered between the two aperture groups <NUM> closest to the cavity <NUM>, and ensure positional symmetry between the cavities <NUM> of rotor body <NUM> and the apertures <NUM> of balance ring <NUM>.

Balance rings <NUM>, <NUM> may be made from aluminum or any other suitable lightweight rigid material. One or more weights <NUM>, <NUM> may be selectively placed into respective apertures <NUM>, <NUM> to offset imbalances in the rotor <NUM>. For example, weights <NUM>, <NUM> may be added to align the center of mass of the rotor <NUM> with the axis of rotation <NUM> (i.e., to achieve static balance), to align a principal axis of the rotor's moment of inertia with the axis of rotation <NUM> (i.e., dynamic balance), or so that the rotor <NUM> is both statically and dynamically balanced.

Claim 1:
A rotor (<NUM>) for use in a centrifuge, comprising:
a rotor body (<NUM>) including an axis of rotation (<NUM>), an upper surface (<NUM>), a lower surface (<NUM>) opposite the upper surface, and an elongated bore (<NUM>) extending along the axis of rotation between the upper surface and the lower surface, the upper surface of the rotor body including a plurality cavities (<NUM>) extending from the upper surface and into the rotor body, each of the plurality of cavities being configured to receive a sample container (<NUM>), and the lower surface of the rotor body including a lower bore opening (<NUM>) in communication with the elongated bore and having a first cross-sectional shape transverse to the axis of rotation; and
a drive hub (<NUM>) mounted within the elongated bore and including a drive portion (<NUM>) having a second cross-sectional shape transverse to the axis of rotation that is complementary to the first cross-sectional shape such that the drive portion of the drive hub applies torque to the rotor body via engagement of the drive portion with the lower bore opening of the rotor body, further comprising:
a lid (<NUM>),
characterized in that, the drive hub includes a cylindrical shaft (<NUM>) that projects upwardly through the elongated bore from the drive portion of the drive hub,
wherein an upper portion (<NUM>) of the cylindrical shaft includes a threaded outer surface (<NUM>) having threads with a major diameter and a minor diameter, further comprising:
a lid screw (<NUM>) including a lower bore (<NUM>) having a threaded inner surface (<NUM>), and a lid screw flange (<NUM>) that extends radially outward from a lower end of the lid screw, wherein the threaded outer surface of the drive hub is configured to threadedly engage the threaded inner surface of the lower bore of the lid screw, and the lid screw flange has a lower surface (<NUM>) configured to urge the lid into contact with the rotor body in response to threaded engagement of the lid screw and the drive hub.