GB2150935A - Enteral feeding tubes or boluses made from elastomeric polymeric composition - Google Patents

Abstract

Enteral feeding tubes are formed from the polymeric composition of, by wt, (a) 10 to 20% of a thermoplastic elastomeric block copolymer (e.g. of monovinyl arene and conjugated diene blocks) and (b) 0.1 to 12% of a linear polysiloxane (e.g. a silicone oil) of kinematic viscosity 20-10<6> cst., which mixture is known to be used for medical tubing, and (c) 80 to 90% of tungsten powder, and optionally a polypropylene binder. The stem of the tube may be formed without the tungsten (c),which must be present in the bolus at the distal end of the tube; the bolus (48) and a female connector (44) preferably being insert moulded onto the stem (42). The bolus may have a plurality of holes to the exterior each connected to a central bore. <IMAGE>

Description

SPECIFICATION Enteral feeding tubes or boluses made from elastomeric polymeric composition The present invention relates to enteral feeding tubes. More specifically, this invention relates to enteral feeding tubes formed of a polymeric composition comprising a block copolymer and a polysiloxane, and a weighted bolus for use therewith and to a novel weighted polymeric composition.

Enteral feeding (stomach and intestinal feeding) is commonly used to nourish patients who, for a variety of reasons, cannot consume food normally. Compared with intravenous (parenteral) feeding, enteral feeding is a more natural way to supply the patient with nutrition while helping to reduce possible infection and vein damage.

Conventional enteral feeding tubes are made of polyvinylchloride, elastomeric silicone or polyurethane.

These materials have been found to be unsatisfactory for the following reasons. For polyvinylchloride, stomach acids can leach out the plasticizer from the polyvinylchloride. If the tube is left in the stomach for an extended period of time, the leached tube hardens and becomes brittle and distorted. As is apparent, this causes discomfort to the patient and can make removal of the tube difficult and painful. On the other hand, elastomeric silicone tubing is much softer and resists hardening. However, because of its limpness, an elastomeric silicone tubing is extremely difficult to insert and position in the stomach. Although polyurethane tubes have intermediate flexibility and are easier to insert than silicone, they are still difficult to insert and position.

In general, an enteral feeding tube comprises an elongated stem (tube body) having two ends, namely a distal end which ultimately is positioned within the stomach or intestines of a patient and a proximal end which remains out of the patient and preferably is equipped with a connector for attachment to a nutritional support system. The distal end may be joined to a weighted terminal (bolus) and the proximal end may have a female connector with an integrally formed closure plug. The connector and bolus usually are connected to the stem by bonding agents or adhesives. But by the use of these bonding agents, the bond may not be secure and additional foreign substances are introduced into the body of the patient.

The weighted bolus normally comprises a pouch containing therein a heavy material. Mercury has been most often used as the weighted material. However, inasmuch as mercury is a highly toxic material and can cause much harm to the patient should the pouch burst, a substitute therefor should be used.

In order to administer nutrients to the patient through the enteral feeding tubes, tubes now used have openings formed in the wall of the tube body proximally of the weighted bolus. These openings create weakened areas in the tube body which may cause the tubes to kink and, thus, to occlude the tube and obstruct the flow of nutrient. Because of the use of mercury or other such materials in the bolus, it heretofore has been impossible or impractical to provide the openings in the bolus itself where the likelihood of kinking would be greatly reduced or totally eliminated.

Thus there is a need for an enteral feeding tube formed of a material which is easy to handle because of the desired degree of flexibility, can withstand the action of stomach acid and have a smooth surface which will not irritate the patient's tissues. Moreover, there is a need to eliminate the hazards associated with the use of mercury and other unbonded substances in the weighted bolus and also to eliminate or greatly reduce the possibility of kinking and its associated problems. The present invention was made with the objective of overcoming the known shortcomings of conventional enteral feeding tubes.

Specification No. GB 2108971A described and claims thermoplastic elastomeric compositions comprising a mixture of (i) an elastomeric thermoplastic hydrocarbon block copolymer, e.g. of A-B-A configuration in which A is a monovinyl arene polymer block and B is an optionally hydrogenated conjugated diene polymer block; and (ii) an essentially linear polysiloxane (silicone oil), having a kinematic viscosity of 20 to 106 centistokes at room temperature (20-25 C) preferably in an amount of 0.1 to 12% by weight of the composition.

A mineral oil and/or polypropylene may optionally be included, as may BaSO4 orTiO2 pigments.

The polysiloxane coats pellets of the block copolymer prior to melting and molding the pellets and allows the composition to be extruded to form a smooth tubing useful for a medical tubing such as an endotracheal tube.

We have now found that such compositions are also very useful for enteral feeding tubes; and also that the inclusion of tungsten powder forms a novel weighted composition which is useful for making weighted portions of such tubes.

The present invention provides an enteral feeding tube formed of a polymeric composition comprising a thermoplastic elastomeric hydrocarbon block copolymer and a polysiloxane. The block copolymer may comprise blocks of styrene-ethylene-butylene-styrene wherein the styrene blocks have a molecular weight of 5,000 to 40,000 and the ethylene-butylene block, 20,000 to 500,000. The polysiloxane has a kinematic viscosity of 20 to 1 o6 centistokes at room temperature.

In one embodiment of the invention, the distal end of the enteral feeding tube is provided with a weighted bolus formed from a unique formulation of a polymeric composition and tungsten. Tungsten is a heavy material that, when compounded with the polymeric composition, may be molded into a variety of configurations and, preferably, it may be insert molded directly onto the distal end of the tube body. This eliminates the necessity of using bonding agents to secure the bolus to the tube.

Also, the novel compounded bolus formulation may be molded or otherwise formed into a hollow configuration which permits the formation of openings directly in the bolus, thus, avoiding the requirement of having the openings in the tube body where kinking may occur.

As a further advantage of the present invention, because of the compatibility of materials utilized in the construction of the tubing stem and the connector, these components also may be firmly secured together during the insert molding of the connector directly onto the proximal end of the tubing without the use of bonding agents.

The present invention provides enteral feeding tubing formed of a composition comprising a substantially uniform mixture of at least one elastomeric thermoplastic hydrocarbon block copolymer and said polysiloxane.

This composition possesses physical and surface properties which avoid all of the above-described problems found in conventional enteral feeding tubes.

In its simplest form, the composition comprises from about 0.1 to 12 per cent, by weight, of the polysiloxane, the remainder being the block copolymer. This represents an unusual result primarily because of the dissimilar nature of the polysiloxane molecule compared to the hydrocarbon backbone of the elastomeric macromolecule.

The polysiloxane content of the composition becomes even more unusual where the latter includes an appreciable amount of mineral oil. In fact, the mineral oil may even represent 60 per cent of the composition's total weight. Nonetheless, the composition appears able to take up an appreciable amount of polysiloxane and achieve the beneficial results.

The composition may include other additives such as polypropylene, generally in an amount less than 45 per cent of the total weight of the composition. In addition, antioxidants and radiopaque materials may be included in the composition.

The block copolymer which preferably comprises from about 23 to 73 per cent by weight of the total weight of the composition may have an A - B, preferably A - B - A, configuration in which A takes the form of a monovinyl arene (aromatic hydrocarbon) polymer block. To provide the elastomeric properties, B may be a hydrogenated or nonhydrogenated conjugated diene polymer block. The copolymer may contain more than two or three blocks suggested above. It may have several interspersed A and B blocks linearly interconnected as A - B - A - B - A - B. Alternatively or additionally, the block copolymer may have blocks with a branched connection to the main chain such as

In the following description the A - B - A structure will be used to encompass all of these variations in polymer block structure.

The styrene-ethylene-butylene-styrene macromolecule represents a prime example of this type of block copolymer, wherein the styrene blocks typically constitute about 20 to 50 per cent of the copolymer's weight while the ethylene-butylene block provides the remaining 50 to 80 per cent. The styrene blocks themselves normally have a molecular weight in the range of 5,000 to 40,000. The ethylene-butylene block has a molecular weight greatly exceeding that of the styrene blocks and falling within the approximate range of 20,000 to 500,000. The total molecular weight of the copolymer typically ranges from 50,000 to 600,000. By molecular weight is mean either the weight average or number average molecular weight, since for the block copolymers useful in the present invention there is little difference between these molecular weights.

When more than one block copolymer is used to prepare the polymeric composition, the block copolymers have different contents of terminal A blocks and middle B blocks.

Examples of such block copolymers are described in a series of U.S. patents issued to the Shell Chemical Company, namely: 3,485,787; 3,830,767; 4,006,116; 4,039,629 and 3,041,103.

Typically, the middle or B, block of the A - B - A elastomeric hydrocarbon block copolymer provides the molecule with its elastomeric properties; the B blocks themselves possess the rubber qualities. Polymers formed from conjugated dienes are preferred in this role. Butadiene and isoprene represent monomers which, after polymerization provide the middle, elastomeric block.

The resulting block copolymertypically has its mechanical properties determined primarily by the eleastomeric B block. Accordingly, the middle block should provide at least a majority of the block copolymer's total molecular weight. In fact, it usually constitutes 50 to 80 per cent of the molecular weight of the copolymer. The molecular weight of the middle B block usually falls within the range of 20,000 to 500,000 and typically comes within the narrower range of 20,000 to 200,000.

The terminal, or A, blocks of the copolymer provide the cohesiveness between the individual macromolecules in the thermoplastic rubber. These terminal blocks themselves behave as a thermoplastic.

They do not usually display any elastomeric quality. However, representing a majority of the weight of the final elastomer, they do not impart their own mechanical properties to the product.

The thermoplastic adherence between molecules of the A blocks replaces the vulcanization of the natural, latex, or silicone rubbers. In vulcanization, actual chemical bonds develop between the macromolecules constituting the rubber. These crosslinking reactions generally occur at elevated temperatures and thus impart the name "thermoset" to the materials. These rubbers generally require extensive peiods of time to cure": or undergo the required crosslinking. The crosslinking does not represent a reversable process. As a consequence, the nonthermoplastic rubbers, once cured to a particular form, cannot melt to adopt a different form. At elevated temperatures they only oxidize or, in more extreme cases, burn.

The terminal A blocks of the block copolymer adhere to each other through physical attraction bonds characteristic of all thermoplastics. Thus, when in the solid form, the terminal blocks of several molecules adhere to each other to provide the required cohesiveness throughout the material. These particles serve to bind the sundry macromolecules in the mass into an integral whole.

At elevated temperatures, these "particles" of physically bonded terminal blocks of different macromolecules actually melt. The entire mass of material then assumes the liquid or molten state and can undergo the usual processing techniques such as injection molding. When cooled, the terminal blocks of different macromolecules again physically bond to each other and form particles. The material then generally retains the shape it possessed when the particles formed by the terminal A blocks coalesced into the solid state.

The monovinyl arenes monomers provide suitable thermoplastic terminal A blocks for these polymers.

Examples of the monomers which can polymerize into the terminal blocks include isoprene and alphamethyl isoprene. The former of these two has generally received greater use.

The terminal A blocks generally have a molecular weight within the range of 5,000 to 40,000, and most fall within the range of 8,000 to 20,000. The terminal blocks constitute about 20 to 50 per cent of the total weight of the macromolecule.

As discussed above, the elastomeric block copolymer molecule may include more than two or three blocks of the A - B - Aformula. The macromolecule may contain additional blocks arranged in either the linear or branched fashion. In such copolymers the thermoplastic A block may not actually represent the terminal blocks at all ends of the molecule. In any event, the macromolecule generally has a total molecular weight falling within the range of 50,000 to 600,000.

As mentioned previously, one or more of the block copolymers may be used in forming the composition.

When more than one block copolymer is used, the block copolymers differ from each other with respect to the amounts of terminal A blocks and middle B blocks present therein. For instance, a mixture of a first block copolymer containing about 28 per cent by weight styrene block A (e.g., Shell Kraton G 1650) and a second block copolymer containing about 33 per cent by weight styrene block A (e.g., Shell Kraton G 1651) can be used. The weight ratio of the first: second block copolymer can vary from 15:85 to 50:50.

The polysiloxane may have the following repeating stucture: where R1, R2 = H, CH3, or

(CH3 being preferred) and n is a positive integer between 10 and 20,000. The readily available silicone oils generally employ the methyl group for both of the radicals R1 and R2. The polysiloxane is essentially linear as shown in the above formula. A preferred example of the polysiloxane is silicone oil.

The viscosity of the polysiloxane should permit it to easily coat and mix with the crumbs or pellets of the elastomer. This results in a general requirement that the kinematic viscosity be within the range of 20 to 1,000,000 centistokes at room temperature. (20-25"C). At the lower end of the above range, the polysiloxane encounters some difficulty in coating the polymer pellets. As a preferred embodiment, silicone oil having a kinematic viscosity of 200 to 13,000 centistokes works well without complication.

In the present invention, a medical grade polysiloxane should be employed. Furthermore, devolatilizing the polysiloxane prior to its introduction to the block copolymer removes very low molecular weight elements that could leach and irritate the patient's tissues and so this is preferred.

The polysiloxane generally constitutes 0.1 to 12 per cent of the total weight of the elastomeric composition, preferably from 1 to 7 per cent. The ability of the block copolymer to take up this amount of the polysiloxane is surprising; the hydrocarbon backbone of the polymer has a very different nature as compared to the silicone structure of the polysiloxane.

The surprise becomes even greater for polymeric compositions that already include substantial amounts of mineral oil as a lubricant. Mineral oil, if present, may constitute up to 60 per cent of the total weight of the composition. Typically, the mineral oil constituted from 25 to 50 per cent of the composition's total weight.

Furthermore, the mineral oil and the polysiloxane also have distinctly different chemical properties. The former has a hydrocarbon composition as compared to the silicone of the polysiloxane. Moreover, the mineral oil fills the spaces that would presumably accomodate the polysiloxane. Yet, a composition having 50 per cent of mineral oil can still assimilate several per cent of the polysiloxane to produce a drastically different elastomer.

The addition of the polysiloxane, preferably silicone oil, to the one or more thermoplastic hydrocarbon block copolymers accomplishes several distinct and desirable results. Initially, the composition displays a substantial improvement in its processability. This has particular importance when the material is formed into thin webs. Without the polysiloxane, the copolymer appears to have flow and surface properties which cause the molten plastic to form globules, and thus a rough surface.

The surface effects produced by the polysiloxane appear to derive from a slightly increased concentration of silicone molecules at the composition's surface. The processing techniques discussed below should typically result in a uniform dispersement of the polysiloxane throughout the composition. However, a slight migration of the silicone molecules to the material's surface may occur. As a result, the material's surface, to a depth of about 5 to 20 nm, appears to have a concentration of silicone molecules approximately twice that of the bulk of the material. The thiness of this layer, of course, prevents the greater concentration there from affecting the bulk concentration of the polysiloxanethroughoutthe material. Consequently, on a macroscopic scale, the material has a substantially uniform dispersement of the polysiloxane.This gives the surface substantially different properties than the hydrocarbon block copolymer without the polysiloxane.

Adding polypropylene as a binder to the present elastomeric composition produces a stiffening effect upon the elastomeric composition. The polypropylene also reduces its elasticity slightly. The amount of added polypropylene generally remains less than 45 per cent of the composition's total weight. It more usually falls within the range of 2 to 20 per cent or in the narrower range of 5 to 10 per cent. The addition of bismuth oxychloride or barium sulfate provides the polymeric composition with an opacity to X-rays.

Titanium dioxide pigment can also be added to affect the polymer's visual appearance.

The following represents a summary of the weight percentages of the components in the present polymeric composition: Component Weight % Broad Preferred Polysiloxane 0.1-12 1-7 Polypropylene 0-45 1-30 Mineral Oil 0-60 25-50 Block copolymer balance 20 - 73 The block copolymer is, by nature, a hydrophobic composition and its surface remains unwetted. Water absorption by the copolymer is low as indicated by ASTM-D-570. Scanning electron micrographs of the surface of the copolymer show a smooth, closed surface, free of surface interruptions or defects. Qualitative observation of the copolymer surface when wet with water indicates that the surface tends to have a slick and lubricious feel. No coating is used to obtain this surface characteristic which is believed to be inherent in the silicone nature of the surface.

Both the surface smoothness and concentration of polysiloxane favour a blood and tissue compatibility of the material. Both factors reduce the likelihood of the attachment and clotting of blood components to the polymer.

Preparing the elastomeric composition with the dispersed polysiloxane begins with the hydrocarbon block copolymer. The techniques for preparing the elastomeric thermoplastics appear in many publications including the patents referenced above. The inclusion of the usual additives is also described in these publications.

Mixing the crumbs or pellets of one or more of the elastomeric copolymers, having different amounts of the constituent blocks, with the polysiloxane should result in a coating of the former with the latter. To do so, the pellets or crumbs and the polysiloxane may be mixed in a tumbler. Any additional ingredients, such as polypropylene, polystyrene, and/or stabilizer may also be added to the mixture at this point.

The coated elastomer pellets or crumbs next receive sufficient heat to induce their melting. Applying a shearing pressure to the melted coated crumbs or pellets appears to induce a substantially uniform dispersement of the polysiloxane in the mixture. The heat required to effect the melting depends, of course, upon the individual elastomer. Typically, the melting point is from 160"C to 225"C.

After melting the block copolymer by heating, the mixture comprising the block copolymer, the polysiloxane and other suitable ingredients described above may be optionally fed through a plurality of calender rolls to form sheets of the mixture. Thereafter, the sheets are subjected to shearing pressure by feeding the cut strips of sheets to an extruder or a compression molding machine for better dispersement of the polysiloxane.

To ensure adequate dispersement of the polysiloxane, the composition is subjected to an appropriate amount of pressure, usually about 1,500 p.s.i. (105 Kg/cm2). However, it has been found that by increasing the pressure, further improved properties of the product are obtained. Thus, the molten mixture may be subjected to pressures of 2,500 p.s.i., 3,000 p.s.i., (175,210 Kg/cm2) or higher.

An extruder provides the most convenient means of achieving the temperatures and pressures required to disperse the polysiloxane within the composition. An extrudertypically has several temperature zones and thus can pass the crumbs or pellets of the polymer through the temperature stages required for melting.

The accompanying drawings illustrate the feeding tubes of the invention and their production.

Figure 1 shows an extruder screw useful in forming an enteral feeding tube; Figure la shows in enlarged scale flights in the material section and in the feed section of the screw of Figure 1; Figure 2 is a side view of an enteral feeding tube of this invention wherein openings are provided in the weighted bolus; Figure 3 shows in detail the distal end of the enteral feeding tube of Figure 2; Figure 4 illustrates the distal end of an embodiment of the enteral feeding tube of the invention wherein an opening is provided at the distal end of the weighted bolus; and Figure 5 shows the distal end of an enteral feeding tube having no weighted bolus.

Figure 1 shows an extruder screw generally indicated as 20, modified to apply a greater shearing pressure to the composition.

The screw 20 has the four zones characteristic of most extruder screws. The first section 21, known as the feed zone, initiates the melting of the polymer pellets and moves them along to the compression or transition zone 22. In zone 22, the polymer generally completely melts and undergoes a sufficient shearing stress to cause thorough mixing of the ingredients. The metering section 23 provides the melted resin to the die at a known rate and pressure. Working section 30 allows mixing of the polymer melt.

The screw shown in Figure 1 has a length-to-diameter ("L/D") ratio of 24:1. In this type of screw, the metering section 23 typically has about 20 to 25 per cent of the total flights, or pitch lengths, of the entire screw. On the modified screw 20 shown in Figure 1, the metering section 23 has ten flights 24 of the screw's total of 24.62 flights; the feed section 21 has 6.62 flights 27, and the transition section 22 has eight flights.

Thus, for the screw 20, the metering section 23 has 40 per cent of the total flights. This large fraction of the flights increases the length of time that the resin remains in the metering section 23 and the amount of pressure applied to it.

Furthermore, as shown in Figure 1 a, the flights 24 of the metering section 23 have a much smaller cross-sectional area than the flights 27 of the feed section 21. In fact, the depth 28 of the feed-section flight 27 amounts to four times the depth 29 of the metering-section flight 24. This high compression ratio of 4:1 drastically increases the pressure applied to the material in the metering section 23. To increase the pressure even further, the compression ratio of the feed section flights 21 to those in the metering section 23 may even go to 5:1 or higher. As this ratio increases, the material becomes squeezed into the smaller flights 24 and, thus experiences a greater shearing pressure.

Naturally, the pressure experienced by the polymer in the flights 24 also depends upon the size of the orifice through which it passes when leaving the extruder. At the small orifice sizes of .015, .010, or even .005 inch (.38, .25 or .13 mm) only a small amount of polymer leave the extruder over a period of time. The remainder backs up against the orifice opening and maintains the pressure upon the polymer in the pump section 23.

Larger orifices, of course, allow the pressure in the metering section 23 to dissipate. However, placing a screen, called a breaker plate, adjacent to the screw's working section 30 can retain a sufficient back pressure on the metering section 23. This screen can have a mesh of 100 or finer.

Placing additional obstacles in the path of the molten polymer beyond the breaker plate can also increase the pressure experienced in the metering section 23. Furthermore, a longer land, which is the distance along which the bore of the extruder narrows down to the orifice size, can also retain the desired pressure in the flights 24. A pressure blender and a mixing head can also give increased pressure. An extruder with the appropriate modification can deliver the resin to its die under a pressure of 3,000 p.s.i. (210 Kg/cm2) at the breaker plate.

Once produced, the material, as a thermoplastic, will submit to the usual product-forming techniques.

Thus, it can undergo further extrusion to a particular shape, if not achieved in the original extrusion.

Moreover, its thermoplastic nature allows the reuse of scraps of material and of rejected parts.

Figure 2 illustrates one embodiment ofthe present invention. Enteral feeding tube, generally designated by the numeral 40, comprises a stem 42 having one end (proximal end) connected to female connector 44 integrally formed with plug 46 and the other end (distal end) connected to weighted bolus 48. Both the connector 44 and weighted bolus 48 are attached to the stem 42 by insert molding to be described below.

In Figures 3 - 5, only the distal end of the enteral feeding tube is shown. It is understood that the proximal end of the tube is connected to a female connector with plug as shown in Figure 2.

Figure 3 illustrates in further detail the bolus and stem. Bolus 50 is generally cylindrically shaped, having end 50a connected to stem 52 and the other end 50b being rounded or devoid of sharp edges to avoid injuring the patient. Disposed within bolus 50 is a central bore 54 which extends longitudinally from end 50a through almost the entire length of bolus 50. Bore 54 terminates at a distance from end 50b so as to define a closed end. A plurality of openings 56 connect bore 54 with the exterior of bolus 50. Although four openings are shown in Figure 3, this number is not critical as long as one or more openings are used. End 50a is joined to stem 52 which is in the form of a tube. Thus, liquid nutrient can be fed to a patient through the enteral feeding tube afterthe bolus has been inserted into the patient's stomach or intestines.Conversely, stomach fluids can be drained from the patient's stomach by using the enteral feeding tube.

Figure 4 shows another embodiment of the present invention. The construction of the bolus 60 is similar to that shown in Figure 3, with the exception that central bore 62 extends through the entire length of the bolus.

Thus, bolus 60 is provided with end opening 64 and side openings 66.

Figure 5 illustrates a further embodiment of the present invention As shown in Figure 5, enteral feeding tube 70 comprises only stem 72, no bolus being connected thereto. The distal end of stem 72 is provided with a plurality of openings 74 including end opening 76.

In the above described embodiments, the stem is formed of the polymeric composition described hereinabove. More specifically, the formulation shown in Table I is most preferred. As shown in Table I, two block copolymers having different amounts of terminal A blocks and middle B blocks are used in forming the stem.

TABLE I Material Components Weight % KraftonG-1651 15 - 20 Shell Oil Co.

Kraton G-1650 3 - 6 Shell Oil Co.

Polypropylene No.5520 1 - 5 Shell Oil Co.

Polypropylene No. 5820 20 - 25 Shell Oil Co.

Polypropylene No. 467DP 1 - 3 Eastman Corp.

Silicone Oil, No. 360 3 - 5 Dow Corning Mineral Oil 40 - 50 Witco Chem Co.

Stabilizer 0.01 - 0.1 Irganox No. 1010 Ciba Geigy Corp.

In forming the stem, it may be desirable to add to the formulation a radiopaque material such as bismuth oxychloride or barium sulfate. In such an event, the amount of radiopaque material added usually constitutes 5% to 50% by weight of the resulting mixture. Generally, when bismuth oxychloride is used, this compound together with the polymeric composition are added to the extruder to form an extrudate containing about 5 to 20 weight per cent bismuth oxychloride. Alternatively, barium sulfate may be co-extruded as a stripe in the stem. In such an event, the amount of barium sulfate used constitutes about 10 to 50 weight per cent of the resulting product. Such stripes are shown as 43 and 73 in Figures 2 and 5.

With reference to the weighted bolus, this is formed by mixing the polymeric composition with a heavy material such as tungsten particles. Since tungsten is non-toxic, its presence in the bolus does not adversely affect the health of the patient. The polymeric composition may comprise one or more of the thermoplastic elastomeric block copolymers having different amounts of terminal A blocks and middle B blocks. Other ingredients which may be present in the composition include polypropylene and mineral oil. The tungsten particles typically have an average particle diameter of about 2 to 6 microns. The material for the bolus comprises from about 10 to 20 weight per cent of the thermoplastic elastomeric hydrocarbon block copolymer and from about 80 to 90 weight per cent of the tungsten powder.

Atypical formulation for the bolus is shown in Table il.

TABLE II Material Components Weight % Tungsten powder, 2-6 microns dia 85 - 90 Kraton G-1651 4 - 6 Shell Oil Co.

KratonG-1650 1 - 2 Shell Oil Co.

Polypropylene 467DP 0.3 - 0.5 Eastman Corp.

Polypropylene 5520 0.1 - 0.2 Shell Oil Co.

Polypropylene 5820 0.2 - 0.6 Shell Oil Co.

Silicone Oil 360 0.3 - 0.7 Dow Corning Mineral Oil 4 - 6 Witco Chem Co.

Stabilizer, Irganox 1010 0.006 Ciba-Geigy Corp.

As to the integrally formed female connector and plug, these are made of the above-described thermoplastic elastomeric hydrocarbon block copolymer. For easy identification, the connector and plug are usually colored. Thus, a typical formulation for the connector and plug is shown in Table Ill.

Both the female connector with plug and weighted bolus are directly connected to the stem by insert molding. Since all of the parts are made of the same general polymeric composition, a very firm bond is obtained.

It has been found that the stem can be most conveniently formed by extrusion. The female connector with plug and weighted bolus are then formed onto the stem by injection molding.

TABLE III Material Components Weight% Kraton G-2705 97.00 Shell Oil Co.

Silicone Oil 360 1.98 Dow Corning Colorant .991 Since the weighted bolus does not contain liquid mercury as weight, it can contain the exterior openings, as shown in Figures 2 to 5, without weakening the stem by the presence of openings. Thus the invention also comprises an enteral feeding tube comprising a stem and a weighted bolus connected to one end of the stem, the bolus having a central bore extending over a portion of the length of the bolus, the distal end of the bolus being closed, and the central bore being in communication with the exterior of the bolus through at least one opening.

The present invention is further illustrated in the following illustrative examples.

Example 7 This example illustrates the formation of the stem portion of an enteral feeding tube of the invention.

9071 grams of a polymer composition having the following formulation is mixed with 907 g of barium sulfate and fed to the hopper of a 1 inch (2.54 cm) Killion extruder.

Material Components Weight % Kraton G-1651 18.4 Shell Oil Co.

Kraton G-1650 4.6 Shell Oil Co.

Polypropylene 5520 3.0 Shell Oil Co.

Polypropylene 5820 23.0 Shell Oil Co.

Polypropylene 467DP 2.0 Eastman Corp.

Silicone Oil 360 4.0 Dow Corning Mineral Oil 45.0 Witco Chem Co.

Stabilizer, Irganox 1010 0.05 Ciba Geigy Corp.

Total 100.05 The mixture is extruded into a tubing under the conditions set forth below.

Feed Zone temperature 300"F (149"C) Transition Zone temperature 350"F (177 C) Metering Zone temperature 355"F (1 80"C) Working Zone (die) temperature 360"F (182"C) Extruder speed 701 cm/min The three screen packs had meshes of respectively 40, 60 and 80 wires per inch, i.e. 15.7, 23.6 and 31.5 wires per centimetre, respectively of diameters 0.01, 0.0075 and 0.0055 inches, i.e. .25.19 and .14 millimetre diameters.

The tubing is cut to 35 inch (90.17 cm) length and marked at 19.7 inch (50.04cm) from one end.

Example 2 This example shows the preparation of the polymeric composition used for forming the weighted bolus.

31.3 grams of a block copolymer A-30 and 25.4 g of a block copolymer A-50, the formulations for both A-30 and A-50 being shown below, are prepared.

Block copolymer A-30 Material Components Weight % Kraton G-1651 32.2 Shell Oil Co.

Kraton G-1650 13.8 Shell Oil Co.

Polypropylene 467DP 5.0 Eastman Corp.

Silicone Oil 360 4.0 Mineral Oil 45.0 Stabilizer, Irganox 1010 0.05 Ciba Geigy Corp.

Total 100.05 Block copolymer A-50 Material Components Weight % Kraton G-1651 30.4 Shell Oil Co.

Kraton G-1650 7.6 Shell Oil Co.

Polypropylene 5520 3.0 Shell Oil Co.

Polypropylene 5820 8.0 Shell Oil Co.

Polypropylene 467DP 2.0 Eastman Corp.

Silicone Oil 360 4.0 Dow Corning Mineral Oil 45.0 Witco Chem Co.

Stabilizer, Irganox 1010 0.05 Ciba Geigy Total 100.05 397 grams of tungsten powder, having an average particle diameter of 2 to 6 microns, is divided into three approximately equal portions.

The copolymers which are in pellet form are fed to a Banbury mixer operating at 50 rpm, Sterlco Banbury temperature (0F) of 400/300 (204/149C), drop temperature (0F) of 320/340, (160/1710C)with atotal mixing time of 25-35 minutes. The copolymers are mixed for about 6-9 minutes. The first portion of the tungsten powder is added, with the mixture being mixed for about 4-6 minutes. Thereafter, the second portion of tungsten powder is added and mixed for about 7-9 minutes. The last portion of the tungsten powder is then added and mixed for about 10 to 12 minutes.

The mixture is removed from the Banbury mixer, placed on a two-roll mill and rolled irito a sheet having a thickness of about 0.075 to 0.250 inch (.019 to .064 mm). The formed sheet is permitted to cool at room temperature for about 10 to 30 minutes, after which it is granulated.

Although it is shown in this Example that two separate block copolymer formulations A-30 and A-50 are mixed, it is understood that a singie formation having the identical composition as the combined formulations can be used. Since there is no reaction among the ingredients forming the block copolymer, the sequence of mixing of the ingredients is immaterial.

Example 3 This example illustrates the formation of a colored female connector and plug which are joined to the stem of Example 1.

449 grams of block copolymer A-50M described below is mixed with 4.53 g of orange colorant.

Material Components Weight% Kraton G-2705 98 Shell Oil Co.

Silicone Oil 360 2 Dow Corning The mixture is then added to a Banbury mixer which is operated under the following conditions: Drop temperature, 310 F (154 C) Sterico Banburytemperature, 41 0/320"F (21 0/1 60"C) Screw speed 50 rpm Mixing time 15 minutes Thereafter, the mixture is placed on a two-roll mill at a speed setting of 15 ft./min (4.57 m/mm) and formed into a sheet which is then granulated.

To form the female connector onto the stem of Example 1, a 15-ton (15240 Kg) Boy press is used and operated under the following conditions: Mold temperature, both halves, 120"F (49"C) Nozzle heat on Variac set at 60 Front zone temperature, 450"F (232 C) Rear zone temperature, 430"F (221 C) Injection speed full open Screw RPM 200 Mold open time 1 sec.

Injection time 3.5 sec.

Cool time 15 sec.

Shot size setting 13 Cushion 1/8 inch (.3175 cm) The mold is opened and the tubing is placed on to the core pin; care is exercised to ensure placement of the tubing into the tubing channel. The core pin is placed into the mold. The mold is closed and the copolymer/colorant mixture is injected to form the connector. When the mold opens, the formed product is removed from the core pin and inspected for major molding flaws such as sinks and short-shot.

The weighted bolus is then insert molded onto the marked other end of the stem using a 15 ton Boy press under the same conditions. The polymeric material injected is that shown in Example 2.

Claims (21)

1. A polymeric composition which comprises, by weight: (a) 10 to 20% of a thermoplastic elastomeric hydrocarbon block copolymer; (b) 0.1 to 12% of a polysiloxane having a kinematic viscosity of 20 to 1 o6 centistokes at 20 to 25 C and (c) 80 to 90% of tungsten powder.

2. A composition as claimed in Claim 1, wherein the block copolymer has an A - B - A configuration where A is a monovinyl arene polymer block and B is a hydrogenated or non-hydrogenated conjugated diene polymer block.

3. A composition as claimed in Claim 1 or 2, wherein A comprises a styrene block and has a molecular weight of 5,000 to 40,000 and B comprises an ethylene-butylene block and has a molecular weight of 20,000 to 50,000.

4. A composition as claimed in Claim 2 or 3, wherein the block copolymer comprises a mixture of thermoplastic elastomeric hydrocarbon block copolymers, each having different amounts of A and B blocks.

5. A composition as claimed in any of Claims 1 to 4, wherein the total molecular weight of the polymeric composition is from 50,000 to 600,000.

6. A composition as claimed in any preceding claim, wherein the polysiloxane has the repeating structure:

wherein R1, R2 = H, CH3 or

and n is a positive integer of from 10 to 20,000.

7. A composition as claimed in any preceding claim, wherein said tungsten powder has an average particle size of 2 to 6 microns.

8. A composition as claimed in any preceding claim, wherein the polymeric composition also contains up to 60% by weight, based on the composition, of mineral oil.

9. A composition as claimed in any preceding claim, wherein the polymeric composition also contains up to 40% by weight, based on the composition, of polypropylene.

10. A composition as claimed in any preceding claim, wherein the composition also contains a radio-opaque material in an amount of 5 to 50% by weight

11. A composition as claimed in Claim 10, wherein said amount of material is 10% by weight

12. A polymeric composition as claimed in Claim 1, substantially as hereinbefore described with reference to any of the Examples.

13. A weighted bolus for medical tubing formed from a composition as claimed in any of Claims 1 to 12.

14. An enteral feeding tube without any weighted bolus, the stem of the tube being formed of a polymeric composition as claimed in any of Claims 1 to 12 but modified by the absence of the tungsten particles.

15. An enteral feeding tube comprising a stem and a weighted bolus connected to one end of the stem, the bolus having a central bore extending over a portion of the length of the bolus, the distal end of the bolus being closed, and the central bore being in communication with the exterior of the bolus through at least one opening.

16. A tube as claimed in Claim 15, wherein the stem is formed of a polymeric composition as claimed in any of Claims 1 to 12.

17. A tube as claimed in Claim 15 or 16, wherein the central bore in the bolus extends along the entire length of the bolus.

18. A tube as claimed in Claim 15, 16 or 17, wherein the central bore is in communication with the exterior of the bolus through a plurality of openings.

19. A weighted bolus for medical tubing, formed from a composition comprising tungsten particles bonded together by a biocompatible material.

20. An enteral feeding tube, substantially as hereinbefore described with reference to Figure 2 and 3, Figure 4 or Figure 5 of the accompanying drawings.

21. A method of feeding a patient, comprising inserting into the patient's gastrointestinal tract an enteral feeding tube as claimed in Claim 14, 15, 16,17,18 or 20.