Apparatus for transferring a viscous material

Abstract

An apparatus for transferring a viscous material comprising: a) a first container capable of containing a viscous material; b) a transfer piston insertable in the first container so that the piston forms a circumferential seal with respect to the container, the transfer piston including a hole; and c) a mechanism for attaching an aperture of a second container to the hole in the transfer piston wherein insertion of the transfer piston into the first container causes the viscous material to pass through the aperture into the second container.

Claims

1. An apparatus for transferring a viscous material, the apparatus comprising: a) a first container capable of containing a viscous material; b) a transfer piston insertable into the first container so that the piston forms a circumferential seal with respect to the container, the transfer piston including an aperture; and c) a second container connected to the aperture in the transfer piston; wherein insertion of the transfer piston into the first container causes the viscous material to pass through the aperture and into the second container; the apparatus further comprising a mechanism between the first container and the transfer piston for applying a force to the insertion of the transfer piston into the first container.

2. Apparatus according to claim 1, adapted to provide sufficient force to cause a viscous material characterized by a viscosity of at least 500 Pascal/second to flow through the aperture of the transfer piston.

3. Apparatus according to claim 2, configured so that manual manipulation of the first container and the transfer piston produces the sufficient force.

4. Apparatus according to claim 1, wherein the transfer piston is adapted to remove at least a portion of the viscous material from a mixing element as the mixing element is removed from the first container.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary non-limiting embodiments of the invention described ill the following description, read with reference to the figures attached hereto. In the figures, identical and similar structures, elements or parts thereof that appear in more than one figure are generally labeled with the same or similar references in the figures in which they appear. Dimensions of components and features shown in the figures are chosen primarily for convenience and clarity of presentation and are not necessarily to scale. The attached figures are:

(2) FIG. 1 is a simplified flow diagram illustrating an exemplary sequence of events associated with use of a mixing apparatus according to exemplary embodiments of the invention;

(3) FIG. 2 is a perspective view of an exemplary mixing apparatus with the mixing elements removed from the mixing well;

(4) FIG. 3 partial cut away view of assembled mixer showing portion of an exemplary drive mechanism;

(5) FIGS. 4A and 4B are a schematic representation and an engineering projection showing rotation direction and distances for an exemplary drive mechanism respectively;

(6) FIG. 5 is a diagram illustrating shear stress gradients between a planetary mixing element and a central mixing element according to exemplary embodiments of the invention;

(7) FIGS. 6, 7 and 8 illustrate an exemplary wiping element adapted for use with an exemplary mixing apparatus; and

(8) FIGS. 9 and 10 illustrate a transfer module adapted for use with exemplary mixing apparatus.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

(9) Overview

(10) U.S. applications 60/738,556; U.S. 60/762,789; U.S. 60/765,484; and Ser. No. 11/360,251 (hereinafter the inventor's previous applications), the disclosures of which are each fully incorporated herein by reference, disclose polymeric bone cement formulations which are characterized by a rapid transition to a high viscosity state. According to exemplary cement formulations disclosed in these applications, mixture of monomer and polymer components produces a mixture characterized by a viscosity in the range of 400 to 500 Pascal/second substantially as soon as the polymer is wetted by the monomer. In practice, this can take as little as 30 seconds.

(11) Previously available bone cement formulations were characterized by a relatively long liquid phase and a short working window during which the cement was suitable for injection. A new class of cement formulations, disclosed in the inventor's previous applications is characterized by a rapid transition to a high viscosity without a persistent liquid phase followed by a relatively long working window before the cement sets to solidity. The almost immediate transition to high viscosity of the new class of cement formulations disclosed in the inventor's previous applications means that high shear forces are desirable in order to assure complete mixing. For this new class of cement formulations, it is not feasible to mix components when the mixture is still in the liquid state because there is essentially no liquid state.

(12) Because bone cement is typically prepared in small batches (e.g. 5, 10, 20, 30, 40, 50 ml or lesser or greater or intermediate volumes), these new cement formulations of the inventor's previous applications impose new constraints on bone cement mixing apparatus.

(13) Exemplary mixing apparatus according to the present invention may also be employed with conventional bone cement formulations. Optionally, exemplary mixing apparatus according to the present invention may be employed after the polymerization reaction has progressed past the liquid phase and achieved a viscosity of 400, optionally 500 Pascal/second or lesser or greater or intermediate viscosity. Optionally, exemplary mixing apparatus according to the present invention may be employed to mix a liquid mixture by adjusting a distance between the mixing elements. Optionally, exemplary mixing apparatus according to the present invention may be employed to mix a cement prepared according to a previously known formulation after the mixture reaches viscosity of at least 100 Pascal/second.

(14) FIG. 1 is a simplified flow diagram illustrating sequence of acts associated with performance of a method 100 according to exemplary embodiments of the invention.

(15) At 110 components are placed into a mixing well or mixing well of a mixing apparatus. Optionally this operation may be performed as part of a manufacturing procedure of apparatus 200.

(16) Optionally, one or more wiping elements are deployed 120. Deployment may be in the mixing well or on a cover and/or on mixing elements of the mixing apparatus and may occur before or after components are placed 110 in the mixing well

(17) At 130 mixing elements are inserted into the mixing well so that they are at least partially submerged in components of the mixture. If a wiping element has been deployed 120, the components of the mixture are generally below the wiping element at this stage.

(18) A drive mechanism is operated to mix 140 the components. As described hereinabove, according to exemplary embodiments of the invention, mixing 140 will cause the components to form a high viscosity mixture in a relatively short period of time, optionally in a few seconds. In an exemplary embodiment of the invention, satisfactory preparation of bone cement is achieved by continuing mixing 140 after the high viscosity mixture has been formed. Optionally, operation of the drive mechanism is manual and/or driven by a motor or by compressed air or by any other external source of force known in the art.

(19) After mixing 140 is complete, mixing elements 150 are removed. If a wiping element has been deployed 120, automatic wiping 152 of the mixing elements occurs at this stage. Optionally, the wiping element remains in the mixing well during and/or after withdrawal 150.

(20) Optionally, cement is transferred 160 from the mixing well to an injection reservoir directly. Optionally, transfer 160 is accomplished using transfer apparatus which comprises an exemplary embodiment of the invention.

(21) Exemplary Apparatus

(22) FIGS. 2, 3, 6, 7 and 8 depict an exemplary embodiment of a mixing apparatus 200 according to the present invention.

(23) FIG. 2 shows an exemplary apparatus 200 with a cover 220 removed from a base 250. Cover 220 is depicted with an optional locking ring 224 which mates to a set of threads 256 on base 250.

(24) In some exemplary embodiments of the invention, components are placed 110 in a mixing well 252 at this stage.

(25) In other embodiments of the invention, components are placed 110 in mixing well 252 as part of a manufacturing and assembly process. Optionally, apparatus 200 is supplied assembled as depicted in FIG. 3. When apparatus 200 is supplied assembled with mixture components inside, undesired premature mixing of monomer liquid and polymer powder may be prevented by a variety of methods. Exemplary methods of preventing undesired premature mixing are described below.

(26) Cover 220 includes portions of a drive mechanism. The drive mechanism is optionally a manual mechanism operable by a handle 210. In the pictured embodiment, cover 220 includes a downward facing protrusion 222 (FIG. 6) configured to engage a wiping element 260 by means of engagement arms 262.

(27) In the pictured exemplary embodiment, engagement arms 262 B function primarily to engage protrusion 222.

(28) In another exemplary embodiment, engagement arms 262 A function to engage protrusion 222 and to engage a groove 264 in base 250. A relationship between engagement arms 262 A and groove 264 in base 250 is described below.

(29) A central mixing element 230 and a planetary mixing element 240 are visible protruding downwards from cover 220. Optionally, two or more planetary mixing elements 240 are provided. A portion of a planetary drive gear 270 is also visible in this view.

(30) Base 250 includes an inner mixing well 252 and a series of inward facing teeth which function as a stationary circumferential gear 254. Stationary circumferential gear 254 is a part of the drive mechanism and is configured to engage planetary drive gear 270 when cover 220 is assembled with base 250.

(31) FIG. 3 is a partial cut-away view of assembled apparatus 200 illustrating the drive mechanism in greater detail. Mixing elements 230 and 240 are inserted 130 in this view and optional wiping element 120 has been deployed in the pictured embodiment. Planetary drive gear 270 is positioned above a center axis of planetary mixing element 240 and connected thereto so that mixing element 240 travels and/or rotates together with gear 270. Gear 270 is coupled to cover 220 by drive shaft 272 seated in drive shaft receptacle 274 of cover 220. Teeth of planetary gear 270 engage complementary teeth of stationary circumferential gear 254 in mixing well 252 of base 250. Planetary mixing element 240 is coupled to central mixing element 230 by drive element 232. Wiping element 260 concurrently engages an inner surface of mixing well 252 and mixing elements 230 and 240.

(32) Operation of the drive mechanism, for example by rotation of handle 210, causes cover 220 to rotate with respect to base 250. This causes planetary drive shaft 272 to advance on a circular path concentric to an inner wall of mixing well 252. Planetary gear 270 engages stationary circumferential gear 254 so that planetary gear 270 rotates planetary mixing element 240 as planetary drive shaft 272 and planetary mixing element 240 advance along their circular path. In an exemplary embodiment of the invention, drive element 232 is coupled to both planetary mixing element 240 and central mixing element 230. Optionally, drive element 232 causes central mixing element 230 to rotate as planetary mixing element 240 advances. In other embodiments of the invention, central mixing element 230 does not rotate. As mixing element 240 advances, mixing 140 occurs.

(33) FIG. 4A is a schematic representation of an exemplary drive mechanism viewed from above base 250. The physical relationship between planetary gear 270, planetary drive shaft 272, central mixing element 230, stationary circumferential gear 254 and drive element 232 (pictured here as a lever) is more clearly visible in this view than in the preceding figure. Engineering considerations of the drive mechanism are discussed below. In an exemplary embodiment of the invention, stationary circumferential gear 254 has 3 times as many teeth as planetary drive gear 270.

(34) Mixing elements 230 and 240 are optionally roughened, serrated or striated to insure formation of a boundary layer in the material being mixed in proximity to a surface of the mixing elements during mixing. Optionally, an inner surface of well 252 is similarly roughened, serrated or striated to insure formation of a boundary layer in proximity to a surface of the well

(35) In an exemplary embodiment of the invention, serrations in the form of vertical slits that extend along the full height of mixing elements 230 and/or 240. Optionally, the longitudinal slits contribute to easy introduction and removal of mixing elements 230 and/or 240 through wiping apertures in wiping element 260. Optionally, vertical slits are characterized by a depth of 0.1, 0.5 or 1 mm or lesser or greater or intermediate depths.

(36) Exemplary Drive Mechanism Engineering Considerations

(37) FIG. 4B is an engineering projection showing rotation directions and distances for an exemplary drive mechanism respectively. The view is looking down on base 250 as for FIG. 4A.

(38) During operation point A on an outer surface of central mixing element 230 will move counterclockwise (arrow) with a radial velocity V(A):
V(A)=1*R1
where 1 is a rotational speed of mixing element 230 in radians/sec and R1 is the radius of mixing element 230.
During operation point B on a surface of planetary mixing element 240 will have a radial velocity V(B) comprising the sum of velocity due to planetary mixing element 240 rotation relative to the axis of central mixing element 230 and velocity due to planetary mixing element 240 rotation on its own axis:
V(B)=1*R(B)+2*R2 where 2=i*1 where i is the ratio between the number of teeth of the stationary circumferential gear 254 and the number of teeth on planetary gear 270; and 1 is a rotational speed of mixing element 230; R(B) is a distance from a center of mixing element 230 to a closest point (B) on mixing element 240; and R2 is the radius of mixing element 240
During operation point C on an opposite surface of planetary mixing element 240 will have a radial velocity V(C) comprising the difference between velocity due to planetary mixing element 240 rotation relative to the axis of central mixing element 230 and velocity due to planetary mixing element 240 rotation on its own axis:
V(C)=1*R(C)i*1*R2

(39) where R(C) is a distance from a center of mixing element 230 to a farthest point (C) on mixing element 240; and

(40) the remaining terms are as defined above.

(41) Point D on stationary circumferential gear 254 will have a velocity of zero.

(42) The shear stresses on a mixture flowing between pints A and B, or between points C and D, can be calculated by the subtraction of radial velocities between opposing points (velocity gradients):

(43) The shear stresses between the fixed position and planetary mixing elements correlate to:
V(B)V(A)=1*(R(B)R1+iR2)
The shear stresses between the planetary mixing element and to stationary mixing chamber inner surface correlate to V(C)V(D)=1*(R(C)i R2).
In an exemplary embodiment of the invention, apparatus 200 is operated manually, so 1 is set by the operator. Optionally, 1 can be 10, 15, 22, or 30 RPM or lesser or greater or intermediate values.
In an exemplary embodiment of the invention, R1, R2, R(B), R(C) and i, are selected to meet both geometry considerations and relatively similar velocity gradients that are sufficient to produce adequate shear stresses in consideration of a selected viscosity, such as, for example, 500 Pascal/second.

(44) FIG. 5 illustrates a theoretic gradient of the shear stress applied to a mixture 500 flowing between a two elements (e.g. planetary mixing element 240 and central mixing element 230 or planetary mixing element 240 and an inner wall of mixing well 252). As the viscosity of mixture 500 increases, the shear stress necessary for mixing also increases.

(45) In an exemplary embodiment of the invention, sufficient shear force to mix a mixture 500 characterized by a viscosity of 500 Pascal/second is provided by adjusting distance between the two mixing elements (A to B in FIG. 4B) or between planetary mixing element 240 and an inner wall of mixing well 252 (C to D in FIG. 4B) to 1 to 5 mm, optionally about 2 mm. Alternatively or additionally, shear force may be adjusted by varying the surface area of mixing elements 230 and/or 240 and/or an inner surface of well 252 which contacts the mixture.

(46) Wiping Element

(47) FIGS. 6, 7 and 8 illustrate placement and function of optional wiping element 260 according to an exemplary embodiment of the invention.

(48) FIG. 6 illustrates wiping element 260 engaging downward facing protrusion 222 by means of engagement arms 262 A and 262 B. Circumferential groove 264 of mixing well 252 is empty at this stage. Mixing elements 230 and 240 protrude through wiping apertures in wiping element 260.

(49) FIG. 7 illustrates cover 220 assembled on base 250 so that mixing elements 230 and 240 are in close proximity to floor 258 of mixing well 252. Engagement arms 262A of wiping element 260 are seated in groove 264 of mixing well 252 (magnified in inset for clarity). Each of engagement arms 262A slides circumferentially around mixing well 252 in groove 264 as planetary mixing element 240 travels around mixing well 252.

(50) FIG. 8 illustrates removal 150 of mixing elements 230 and 240 from mixing well 252. Engagement arms 262A are retained by groove 264 so that wiping element is locked into position. Removal of elements 230 and 240 results in automatic wiping 152 by the edges of the wiping apertures.

(51) Transfer Mechanism:

(52) FIGS. 9 and 10 illustrate a transfer mechanism according to exemplary embodiments of the invention as previously disclosed in prior related U.S. Pat. No. 8,415,407, the disclosure of which is fully incorporated herein by reference. FIG. 9 is a cross-sectional view and FIG. 10 is a partial cut-away view in perspective.

(53) FIGS. 9 and 10 illustrate an exemplary transfer element 900 including a transfer piston cup 950 inserted in mixing well 252. In the pictured embodiment, threads 956 of piston cup 950 engage threads 256 of base 250. As transfer piston cup 950 is screwed onto base 250, floor 958 of transfer piston cup 950 is forced downwards and towards floor 258 of mixing well 252. This action applies downward pressure on wiping element 260. The downward pressure causes engagement arms 262 to be released from groove 264. Once engagement arms 262 are released, wiping element 260 is free to travel downwards towards floor 258 of mixing well 252. Optionally, wiping element 260 also serves also as a piston which pushes the mixture into injection reservoir 910.

(54) In the pictured embodiment transfer piston cup 950 is fitted with a second set of threads 952 which engage matching threads 930 on injection reservoir 910. In operation injection reservoir 910 is attached to transfer piston cup 950 by threads 930 and 952 before transfer piston cup 950 is inserted into mixing well 252. As transfer piston cup 950 descends into mixing well 252, contents of mixing well 252 (e.g. high viscosity bone cement) are forced upwards into injection reservoir 910. Injection nozzle 920 serves to release air from injection reservoir 910 so that no resistive pressure accumulates. The mixed material has been transferred STEP 160 to the injection reservoir 910 at this stage. Optionally, an operator of the apparatus knows that reservoir 910 is full when bone cement exits injection nozzle 920.

(55) Exemplary Dimensions:

(56) According to various exemplary embodiments of the invention, an inner volume of the mixing well 252 is 5, optionally 10, optionally 20, optionally 40, optionally 60, optionally 80, optionally 100 ml or lesser or greater or intermediate volumes. In an exemplary embodiment of the invention, the mixing well volume is 50 to 60 ml, optionally about 66 ml, and 10 to 20 ml of mixture, optionally about 15 ml of mixture is placed in the chamber for mixing. In an exemplary embodiment of the invention, a portion of the inner volume of well 252 is occupied by mixing elements 230 and 240.

(57) Optionally, an inner diameter of the mixing well is 20, optionally 40, optionally 60, optionally 80, optionally 100 mm or lesser or greater or intermediate sizes. In an exemplary embodiment of the invention, the inner diameter of the mixing well is 40 to 50 mm, optionally about 46 mm.

(58) Optionally, a height of the mixing well is 20, although it can be 40, 60, 80, or 100 mm or lesser or greater or intermediate sizes. In an exemplary embodiment of the invention, the height of the mixing well is 35 to 45 mm, optionally about 40 mm.

(59) Optionally, an aspect ratio (diameter/height) of the mixing well is 0.7, 0.9, 1.1, or 1.3, or lesser or greater or intermediate values. In an exemplary embodiment of the invention, aspect ratio (diameter/height) of the mixing well is 1.1 to 1.2, optionally about 1.15.

(60) In an exemplary embodiment of the invention, a distance (d.sub.1) between the central mixing element and the planetary mixing element (indicated by A to B in FIG. 4A) and/or a distance (d.sub.2) between the planetary mixing element and an inner wall of the mixing well (indicated by C to D in FIG. 4A) is 1, 2, 3, 4, or 5 mm or lesser or greater or intermediate distances. In an exemplary embodiment of the invention, d 1 is substantially equivalent to d.sub.2.

(61) In typical vertebrae treatment procedures, a volume of approximately 5 ml is injected in a single vertebra. It is common to prepare a batch of approximately 8 ml of cement if a single vertebra is to be injected, approximately 15 ml of cement if two vertebrae are to be injected and progressively larger volumes if three or more vertebrae are to be injected. Combination of powdered polymer component and liquid monomer component leads to a reduction in total mixture volume as the polymer is wetted by the monomer. For example, 40 to 50 ml of polymer powder may be mixed 112 with 7 to 9 ml of monomer liquid to produce 18 ml of polymerized cement. In an exemplary embodiment of the invention, a volume of well 252 is selected to accommodate the large initial column of monomer powder, even when a significantly smaller batch of cement is being prepared.

(62) In an exemplary embodiment of the invention, a dead volume of cement remaining in well 242 after transfer to injection reservoir 910 by transfer element 900 is less than 2, 1, or 0.5 ml or lesser or intermediate values.

(63) In an exemplary embodiment of the invention, a diameter of central mixing element 230 and a diameter of injection reservoir 910 are both equivalent to a diameter of an aperture in wiping element 260. Optionally, this conformity of diameters reduces a dead volume of cement left in well 252 after operation of transfer apparatus 900. Optionally the diameters are all approximately 18 mm.

(64) In other embodiments of the invention (not shown), mixing well 252 of base 250 is transferred to an injection apparatus and cement is injected into a subject directly from well 252. Optionally, this occurs after removal of mixing elements 230 and 240.

(65) Exemplary Materials

(66) In an exemplary embodiment of the invention, component parts of the mixing apparatus are constructed of Polyamides (e.g., Nylon) and/or Polypropylene.

(67) Optionally, some portions of the apparatus are constructed of a metal, for example stainless steel. In an exemplary embodiment of the invention, metal is employed to construct parts which are subject to large forces, such as friction or torque. Optionally, one or more of handle 210, gears (e.g. 270), teeth (e.g. 254), drive arms (e.g. 232) and mixing elements (e.g. 230 and/or 240) are constructed of metal.

(68) Exemplary Methods of Use

(69) In an exemplary embodiment of the invention, apparatus 200 is provided with instructions for use. In an exemplary embodiment of the invention, the instructions indicate a procedure for achieving complete mixing of a mixture placed in well 252.

(70) Optionally, these instructions indicate an amount of time recommended to insure complete mixing. In an exemplary embodiment of the invention, the time is 30 to 90 seconds, optionally 30 to 60 seconds, optionally about 45 seconds or lesser or greater or intermediate amounts of time.

(71) Optionally, these instructions indicate a number of turns recommended to insure complete mixing. In an exemplary embodiment of the invention, the number of turns is 20 to 100, optionally 40 to 60, optionally about 50 or a lesser or greater or intermediate number.

(72) Optionally, these instructions indicate a signal which will be presented to the user when mixing is complete. The signal may be a visual signal (e.g. indicator light) or an audible signal (e.g. buzzer or bell) or a tactile signal (e.g. gear 270 slips on teeth 254 when a desired viscosity is reached). In an exemplary embodiment of the invention, the signal is triggered by a closed feedback loop. The loop may rely upon, for example, an indirect measure of viscosity (e.g. torque), centripetal force, time, number of revolutions of a portion of apparatus 200 (e.g. handle 210, gear 270 or mixing element 230 and/or 240) or mixture volume.

(73) Optionally, the apparatus combines a mechanism that allow turning of handle only during a preset window of time and/or number of rotations.

(74) Shear Force Considerations

(75) Shear force on a mixture within well 252 is affected primarily by surface properties, distance between surfaces, and differences in velocities between surfaces.

(76) Surface properties of mixing elements 230, 240 and an inner surface of well 252 all affect applied shear forces on mixture 500 (FIG. 5). Increasing roughness (e.g. by serration or striation) prevents mixture 500 from slipping against these surfaces by increasing the force of friction. When the surfaces are sufficiently roughened, a boundary layer will have a relative velocity of zero with respect to the surface. Optionally, this zero relative velocity contributes to increased shear force.

(77) Distances between surfaces are inversely related to shear forces acting on a mixture 500 moving between the surfaces. In an exemplary embodiment of the invention, as distances defined by lines A-B and/or C-D (FIG. 4B) increase, an applied shear force to a portion of mixture 500 crossing those lines decreases.

(78) Differences in relative velocities between portions of mixer 200 also affect shear forces on mixture 200. As the difference in relative velocities increases, the applied shear force to a portion of mixture 500 flowing between the elements increases. The relative velocities are optionally influenced by angular velocities and/or radial velocities and/or radius of the elements involved as discussed in more detail above. In an exemplary embodiment of the invention, differences in relative velocity are amplified by imparting angular velocities with different directions to mixing elements 240 and 230.

(79) General

(80) Because some components of a bone cement mixture may have an unpleasant odor and/or be toxic if inhaled, some exemplary embodiments of the invention include safety features to reduce exposure to undesired vapors.

(81) In an exemplary embodiment of the invention, locking ring 224 is equipped with an air-tight seal (e.g. rubber or silicon) which prevents vapors from escaping from well 252.

(82) Alternatively or additionally, apparatus 200 may be provided with an evacuation port (not shown) connectable to a vacuum source. In an exemplary embodiment of the invention, the vacuum source is a standard wall suction unit in a hospital operating room and the undesired vapors are from an MMA component of a bone cement mixture.

(83) In cases where apparatus 200 is supplied with components to be mixed inside well 252, a method for preventing undesired premature mixing may be implemented.

(84) One exemplary method of preventing undesired premature mixing of monomer liquid and polymer powder is to provide the monomer liquid in a sealed bag or capsule which is burst when apparatus 200 is operated. The capsule may be burst when it is drawn across line A-B or C-D by the flow of mixture 500. In an exemplary embodiment of the invention, the capsule is designed so that it is characterized by a smallest dimension which exceeds the length of A-B and/or C-D. In an exemplary embodiment of the invention, the bag or capsule is constructed of a biocompatible material which may be injected together with the bone cement.

(85) Another exemplary method of preventing undesired premature mixing of monomer liquid and polymer powder is to provide the monomer liquid inside central mixing element 230. Optionally, partial removal of cover 220 from base 250 permits the monomer liquid to exit mixing element 230 into well 252. Optionally, tightening of locking ring 224 breaks a seal in mixing element 230. Breaking the seal releases the liquid monomer onto the powder component.

(86) Another exemplary method of preventing undesired premature mixing of monomer liquid and polymer powder is to provide the monomer liquid in a cavity inside a wall of mixing well 252. Optionally, contents of the cavity are dumped into well 252 manually or automatically when mixing commences.

(87) The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to necessarily limit the scope of the invention. In particular, numerical values may be higher or lower than ranges of numbers set forth above and still be within the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention.

(88) Some embodiments of the invention utilize only some of the features or possible combinations of the features. Alternatively or additionally, portions of the invention described/depicted as a single unit may reside in two or more separate physical entities which act in concert to perform the described/depicted function. Alternatively or additionally, portions of the invention described/depicted as two or more separate physical entities may be integrated into a single physical entity to perform the described/depicted function. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments can be combined in all possible combinations including, but not limited to use of features described in the context of one embodiment in the context of any other embodiment. The scope of the invention is limited only by the following claims. In the description and claims of the present application, each of the verbs comprise, include and have as well as any conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb. All publications and/or patents and/or product descriptions cited in this document are fully incorporated herein by reference to the same extent as if each had been individually incorporated herein by reference.