FIELD OF THE INVENTION
This application is based on and claims priority of U.S. Provisional Application No. 60/238,971, filed Oct. 10, 2000.
- BACKGROUND OF THE INVENTION
This invention relates to fabrics preferably comprising a plurality of different materials, wherein filaments within the fabric are fused or otherwise joined together to control various physical properties of the fabric.
The physical characteristics of fabrics, such as stiffness (also known as “hand”), porosity, density, elasticity, resilience, tensile strength, resistance to abrasion, are largely controlled by the size and type of yarns or filaments which are interlaced together, the material from which the yarns or filaments are made and the manner in which they are interlaced, for example, by weaving, knitting or braiding.
There is generally a limit on the degree of stiffness which can be attained in a fabric. This is due, in part, to the inherent flexibility of the long, slender filamentary members comprising the fabric and the fact that they are generally free to move relatively to one another to some degree within the fabric.
It is sometimes desirable to have a fabric formed of relatively thin filamentary members of a relatively flexible material but having a stiffness which is relatively greater than would normally be achieved when the filamentary members are interlaced. Such fabrics are expected to find use as human implants to reinforce soft tissue for the treatment of conditions, such as sleep apnea and snoring. It would also be beneficial if the stiffness of the fabric could be designed to change over time to become less stiff in relation to the formation of scar tissue resulting from the implant, which tends to stiffen the tissue. If the fabric can be made to become less stiff over time, the total stiffness of the affected area will remain relatively constant over time for optimum treatment of the disorder.
It may also be desired to maintain or augment a particular porosity or interstice size in the fabric which is otherwise incompatible with the desired stiffness of the fabric. If relatively large interstices are desired in the fabric, for example, to allow flow of fluid therethrough or promote ingrowth of tissue into the fabric, this is achieved by interlacing relatively small diameter filamentary members in a relatively open mesh. This will yield a fabric of relatively low stiffness, especially if polymers such as polyester, nylon or polypropylene are used which are themselves relatively soft, pliant filaments.
- SUMMARY OF THE INVENTION
If the stiffness of fabrics could be controlled and relatively high stiffness could be achieved in conjunction with other fabric properties which are presently considered incompatible or inconsistent with the higher stiffness, then woven, knitted and braided fabrics may find a wider spectrum of applications, especially, but not only, in the treatment of human diseases and disorders.
The invention concerns a stiffened fabric comprising a plurality of filamentary members interlaced together, for example, by weaving, knitting or braiding. The filamentary members engage one another at mutual points of contact where, at selected ones of the mutual points of contact, they are substantially rigidly joined together to substantially inhibit relative motion between the filamentary members and thereby impart a predetermined stiffness to the fabric. The selected ones of the mutual points of contact joined together may comprise a portion of the total number of the mutual points of contact or substantially all of the mutual points of contact between the filamentary members as required to obtain a desired stiffness. The filamentary members are free to move relatively to one another between the selected ones of the mutual points of contact at which they are attached, thus providing for a degree of flexibility in the fabric.
In one embodiment, the plurality of filamentary members comprises a first group of filamentary members having a relatively low melting point interlaced with a second group of filamentary members having a relatively high melting point. The filamentary members of the first group are joined to filamentary members of the second group by heating the fabric to a temperature higher than the melting point of the first group of filamentary members and lower than the melting point of the second group of filamentary members thereby causing filamentary members of the first group to fuse with filamentary members of the second group at the mutual points of contact between the filamentary members of the first and the second groups. In another embodiment of the stiffened fabric according to the invention, an adhesive, positioned at the selected ones of the mutual points of contact, is used to join the filamentary members together, thereby stiffening the fabric.
The invention also contemplates a stiffened fabric wherein the plurality of filamentary members includes a first group of filamentary members comprising a material which is absorbable when implanted in living tissue. Filamentary members comprising such bio-absorbable material are interlaced with a second group of filamentary members, preferably comprising non bio-absorbable material. The bio-absorbable filamentary members of the first group are initially joined to filamentary members of the second group at the mutual points of contact to provide a relatively high stiffness to the fabric. The filamentary members of the first group are absorbed upon implantation of the fabric in living tissue and, over time, provide a relatively lower stiffness to the fabric as the filamentary members of the first group are absorbed. The purpose of this embodiment is to construct an implant formed by braiding the filamentary members into an elongated rod which is implanted in soft tissue to provide stiffness. Over time, as the bio-absorbable filaments are absorbed the rod becomes less stiff, thereby compensating for the increased stiffness of the surrounding tissue due to the formation of scar tissue to keep the overall stiffness of the tissue near the implant a constant.
In another embodiment of the stiffened fabric according to the invention, the filamentary members are interlaced by weaving to provide a plurality of interstices in the fabric having a predetermined size and resulting in the fabric having a first predetermined porosity. The fabric further comprises a plurality of absorbable filamentary members again formed of a material which is absorbable when implanted in living tissue. The absorbable filamentary members are interwoven in the fabric in overlying relation with the interstices thereby reducing the size of the interstices and resulting in the fabric having a second predetermined porosity smaller than the first predetermined porosity. The absorbable filamentary members are absorbed when the fabric is implanted in living tissue causing the porosity of the fabric to change from the second predetermined porosity to the first (larger) predetermined porosity.
It is an object of the invention to provide a fabric wherein the stiffness or “hand” may be controlled.
It is another object of the invention to provide a fabric wherein the stiffness may be varied.
It is another object of the invention to provide a fabric wherein the porosity of the fabric may be varied.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and advantages of the invention may be discerned upon consideration of the following drawings and detailed description of the preferred embodiments.
FIG. 1 shows a side view of a braided fabric rod according to the invention;
FIG. 2 shows a perspective view of a knitted fabric tube according to the invention;
FIG. 3 shows a perspective view of a woven fabric sleeve according to the invention; and
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 4 shows a perspective view of a wound rod according to the invention.
The invention comprises a fabric of interlaced filamentary members wherein the members, once interlaced, are joined together at points of contact with one another to prevent relative motion between them and thereby stiffen the fabric. The filamentary members are not otherwise constrained between the points of contact at which they are joined and may, thus, move relatively to one another between the joined contact points to provide some flexibility to the fabric. Joining together of the filamentary members is preferably accomplished by including throughout the fabric filamentary members having a relatively low melting point with filamentary members having a relatively higher melting point and subjecting the fabric to a temperature somewhere between the melting points of the two members. The lower melting point members fuse with the higher melting point members, locking all of the members in place and substantially increasing the stiffness of the fabric while maintaining other fabric characteristics such as porosity, interstice size, which would otherwise only be associated with a fabric having relatively less stiffness.
A stiffened fabric according to the invention may find use as a human implant in the area of the soft palate and air passageways of the body to stiffen the palate and passageways in the treatment of excessive snoring and obstructive sleep apnea (OSA). OSA, while not life threatening, is nevertheless a serious disorder which interrupts sleep and is recognized as a leading cause of excessive daytime sleepiness which increases the risk factors in automobile and industrial accidents.
OSA results from an occlusion of the upper airway at the level of the oropharynx. The occlusion occurs because the tissue defining the airway is insufficiently stiff and collapses when the airway is subjected to sub-atmospheric pressure during inspiration. The resulting apnea leads to progressive asphyxia until there is a brief arousal from sleep and the airway dilator and abductor muscles reopen the airway and airflow to the lungs resumes. The person then returns to sleep. The sequence repeats itself throughout sleep as many as 400 to 500 times per night. The compliant tissue is also naturally prone to vibrate at relatively low frequencies resulting in snoring. currently, severe OSA is treated by a tracheotomy which bypasses the occluded passageways.
By way of example, a stiffened fabric rod 500, shown in FIG. 1, having a of length 30 mm, a diameter of 3 mm, an elastic modulus of 80,000 psi and a porosity of 60% was made according to the invention to serve as an implant to stiffen the soft palate.
To achieve the above specified properties, 24 polyester yarns 510 of 150 denier were braided at a +/−45° braid angle with 12 axially oriented yarns 512 of 100 denier, also of polyester. A further 12 axial filamentary members 514 were also braided into rod 500, members 514 comprising monofilament polypropylene of 6 mil diameter. A further 22 polypropylene monofilaments 516 were braided axially into the rod to form a core.
The rod was then heated to a temperature of 163° C., the melting point of the polypropylene (the melting point of the polyester was 250° C.) to fuse the polypropylene and polyester together and form a stiffened rod of braided fabric. The ratio of polyester and polypropylene was chosen to achieve the required elastic modulus of 80,000 psi. The axially oriented core monofilaments 516 help stabilize the rod when subjected to bending forces and prevent the rod from kinking when bent. When implanted in the soft palate, the rod stiffens the palate and increases its natural frequency to reduce snoring and any effects of sleep apnea caused by the compliance of the upper palate.
Rather than using heat to fuse the filamentary members to form the stiffened fabric rod 500, adhesive bonding of the filamentary members may be employed. Selected points of contact such as 511 between filamentary members 510 are bonded together with an adhesive 513. Adhesive 513 is preferably substantially inelastic and effectively prevents relative sliding motion as well as relative rotation of the filamentary members 510 to provide increased stiffness to the stiffened fabric rod 500. The stiffness of the rod is proportional to the number of mutual points of contact which are adhered to one another. The adhesive may be a permanent adhesive, activated by heat, chemicals or water, as well as a solvent which chemically fuses the filamentary members together at the cross-over points. The adhesive may also be water soluble, yielding a rod with one stiffness when dry, and a second, lower stiffness when wetted to dissolve the adhesive bonds thereby allowing the filamentary members to move relatively to one another.
An aspect of the invention is the creation of a structure whose stiffness and/or porosity changes over time. For example, filamentary members 514 may be bio-absorbable filaments made from materials such as polylactic acid or polyglycolic acid instead of polypropylene. The bio-absorbable filaments are interbraided with the polyester yarns 510 forming the stiffened rod and joined with them at the mutual points of contact. Once implanted, the bio-absorbable filaments 514 degrade over time and are absorbed into and eliminated from the tissue, leaving only the polyester yarns and/or polypropylene filaments in the implant. Stiffness of the rod is reduced over time as a result of the elimination of some of the filaments which would normally contribute some stiffness to the rod. This is useful, for example, to maintain the stiffness of the tissue constant as scar tissue, which is stiffer than regular tissue, forms as the tissue heals after the operation. The degrading components compensate for the development of the stiffer scar tissue by reducing the stiffness provided by the rod.
Porosity of the fabric may also be increased by interlacing the bio-absorbable filaments to coincide with interstices 515 formed by the non-biodegradable filamentary members 510 of the stiffened fabric rod as shown in FIG. 1. As the bio-absorbable filaments degrade, they no longer block the interstices 515 between the other filamentary members 510, resulting in increased porosity over time. This is of interest to promote the ingrowth of living cells into the implant to secure it in position and prevent migration.
The composite stiffened fabric according to the invention is not limited to the above described application, and several examples of additional applications are provided below.
In the construction of a Bowden cable, used for the remote mechanical actuation of a device, a flexible yet relatively stiff outer sleeve houses a coaxial wire core which is movable longitudinally through the sleeve to place a tension or compression force on a mechanism connected to one end of the wire core, such as the trunk release of an automobile, to actuate it and allow the trunk to be opened remotely, for example, from within the passenger compartment. Such a Bowden cable 518, a portion of which is shown in FIG. 2, may have an outer sleeve formed from a warp knitted tube 520 comprising polyester yarns 522 having a relatively low melting point and PTFE yarns or filaments 524, which has a relatively higher melting point. Tube 520 is knitted by techniques well known in the art so that the polyester yarns comprise the outer surface 526 of the tube, and the PTFE filaments comprise the inner surface 528 of the tube. When the tube is heated, the polyester yarns fuse to each other and the PTFE filaments provide the required stiffness to the tube. The PTFE provides for a non-stick inner surface 528 allowing the wire core 530 to slide within the tube substantially without friction, thus, providing an excellent bearing surface on the inside of the tube.
By way of a further example, in the construction of a flexible sheath 532 (see FIG. 3) for covering electrical wiring harnesses to protect the wires 534 against abrasion, a woven tube 536 may be manufactured from a combination of two different filamentary materials 538 and 540 having different melting points, such as polypropylene and polyester respectively. If the two materials are interwoven to form a substantially homogeneous fabric, then when the heat is applied to fuse the lower melting point material (the polypropylene 538) a continuously stiffened tube will be formed. However, if the polypropylene 538 is interwoven with the polyester 540 at selected points intermittently along the length of the tube, for example, at regular intervals, this will form an intermittently stiffened tube having stiffened segments 542 alternating with unstiffened segments 544. The length of tube having the alternating section will be more flexible than the continuously stiffened tube and will bend more easily to follow a curved path.
In another example, shown in FIG. 4, a filament wound rod 546 may be formed by the stiffened composite fabric according to the invention. Starting with a core 548 of polyester filaments, polypropylene filaments 550 may be wrapped, either alone or in combination with other filaments or yarns 552, around the polyester core 548. Upon fusing of the lower melting polypropylene filaments 550, a stiffened rod is produced. If bio-absorbable filaments such as polyglycolic or polylactic are used for filaments 552, then the rod will be capable of changing stiffness as the bio-absorbable filaments are absorbed over time. The filament-wound embodiment may also be used to stiffen living tissue similar to the braided embodiment.
The composite stiffened fabric according to the invention may also be used to create flat fabric and stiffen the flat fabric into a desired three dimensional shape. Materials having different melting points, such as polyester and polypropylene, are woven, knitted or braided together. The fabric may be shaped in a mold or on a mandrel having the desired shape, and when heated to the melting temperature of the lower melting point material and then cooled, the fabric will be fixed into the desired shape by the fusing of the yarns or filaments together.
In all the examples provided above, the relative stiffness of the end product may be tailored to a desired value by the choice of materials and the ratio of lower melting to higher melting temperature materials used, with greater stiffness being achieved if more lower melting temperature material is used. In addition to joining the various yarns and/or filaments together by heat fusing, adhesives may also be used. Selected ones or all of the filamentary members comprising the fabric may be coated with adhesive which causes the filamentary members to bond together at points of contact.