Plastic and nonmetallic article shaping or treating: processes – With severing – removing material from preform mechanically,... – Forming continuous work followed by cutting
Reexamination Certificate
1999-12-21
2002-07-16
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With severing, removing material from preform mechanically,...
Forming continuous work followed by cutting
C264S210500, C264S210800, C264S211170, C264S235600
Reexamination Certificate
active
06419866
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to synthetic, absorbable monofilament fibers of glycolide-based polymers, especially poly(lactide-co-glycolide) copolymers, that are useful in the fabrication of brachytherapy seed spacers in brachytherapy seed delivery systems.
BACKGROUND OF THE INVENTION
Prostatic cancer has been estimated to affect as many as one in three men. In the U.S. alone, this implies an estimated fifty-million patients who are candidates for treatment of prostatic cancer. Prior methods of treatment include surgical intervention, external radiotherapy, and other brachytherapy (interstitial radiation) techniques. A general discussion of the localized use of radiation therapy is found in Bagshaw, M. A., Kaplan, I. D. and Cox, R. C., Radiation Therapy for Localized Disease, CANCER 71: 939-952, 1993. Disadvantages associated with surgical intervention include impotence and incontinence. External radiotherapy may have deleterious effects on surrounding normal tissues (e.g., the bladder, the rectum, and the urethra). In contrast, brachytherapy diminishes complications such as impotence and incontinence, and allows a higher and more concentrated radiation dose to be delivered to the prostate gland as compared to external radiotherapy. An additional advantage of brachytherapy is that treatment can be accomplished within a matter of days as compared to weeks, greatly reducing radiation exposure of the adjacent organs.
Prostate brachytherapy can be divided into two categories, based upon the radiation level used. The first category is temporary implantation, which uses high activity sources, and the second category is permanent implantation, which uses lower activity sources. These two techniques are described in Porter, A. T. and Forman, J. D., Prostate Brachytherapy, CANCER 71: 953-958, 1993. The predominant radioactive sources used in prostate brachytherapy include iodine-125, palladium-103, gold-198, ytterbium-169, and iridium-192. Prostate brachytherapy can also be categorized based upon the method by which the radioactive material is introduced into the prostate. For example, an open or closed procedure can be performed via a suprapubic or a perineal retropubic approach.
Prostate cancer is a common cancer for men. While there are various therapies to treat this condition, one of the more successful approaches is to expose the prostate gland to radiation by implanting radioactive seeds. The seeds are implanted in rows and are carefully spaced to match the specific geometry of the patient's prostate gland and to assure adequate radiation dosages to the tissue. Current techniques to implant these seeds include loading them one at a time into the cannula of a needle-like insertion device, which may be referred to as a brachytherapy needle. Between each seed may be placed a spacer. In this procedure, a separate brachytherapy needle is loaded for each row of seeds to be implanted.
Although seed spacers may be made from a variety of materials, both absorbable and non- absorbable, there are advantages if the material is absorbable. These advantages include minimizing or eliminating any effects due to the long-term presence of the material in the body. Absorbable materials include catgut, collagen, and synthetic absorbable polymers. Catgut and collagen usually degrade by an enzymatic mechanism, as opposed to a chemical mechanism such as reaction with water, that is, hydrolysis. The preferred method of sterilization for brachytherapy seeds and spacers is steam sterilization (autoclaving). When catgut is used as a seed spacer material, the autoclaving process utilized may make the spacer soft, presumably by the plastisizing effects of the water which these materials uptake during exposure. Besides not retaining physical characteristics, catgut seed spacers also can change shape when exposed to autoclaving. Present-day synthetic absorbable materials do not uptake as much water as catgut or collagen. They do, however, degrade by a hydrolysis mechanism. It is well known that these hydrolysis reactions occur at faster rates at higher temperatures. As the preferred sterilization method for brachytherapy seeds and spacers is steam sterilization (autoclaving), it is surprising that synthetic materials known to date can effectively function in these applications. Indeed, based on the knowledge that synthetic absorbable polymers generally degrade by chemical hydrolysis, most would not even consider them for use as medical devices that would be sterilized by autoclaving.
One approach to minimizing the effects of steam sterilization on the premature degradation of seed spacers made from synthetic absorbable polymers would be to consider those synthetic absorbable polymers that are much more resistant to hydrolysis. Such a material is polylactide. This material has a much higher probability of maintaining mechanical properties required for use in brachytherapy seed delivery devices after it has been exposed to autoclaving, compared to, for instance, polyglycolide. Yet, because polylactide takes so much longer to absorb in the body, it is not generally a material of choice. The high-lactide polymer, 95/5 poly(lactide-co-glycolide), used in the production of certain long-term commercial suture materials useful in certain orthopedic surgical procedures, also takes too long to absorb in the brachytherapy procedures.
Other problems exist with certain synthetic absorbable polymers. For instance, the synthetic absorbable polymer poly(p-dioxanone), although known to retain its strength for much longer time periods than polyglycolide, is too low melting to be suitable for sterilization by autoclaving. As such, proper selection of material is an important criterion in the manufacture of monofilament fibers having properties suitable for use as brachytherapy seed spacers.
In addition to material selection, we have found that the process of manufacture is an important factor. Although injection molding appears to be an entirely suitable manufacturing process to make seed spacers, if injection molding most synthetic absorbable polymers is utilized as the manufacturing process, the spacers so produced tend to break down excessively during the sterilization process, retaining very little strength. We have found a process of making brachytherapy seed spacers from glycolide-rich synthetic absorbable polymers entailing a preferred extrusion, drawing, and annealing process to provide monofilament fibers with suitable properties which can be cut to length.
Monofilament fiber, for use in many applications, needs to be particularly straight, devoid of curves or bows, to allow proper functioning. One such application is brachytherapy seed spacers. If the seeds are curved or bowed, they may jam the applier during application of the seed/seed spacer assembly. Additionally, undesirable dimensional spacing variation may result if the seeds are curved initially, or worse yet, curve or bow irreproducibily once in the assembly, as this may initially go undetected. Since the function of brachytherapy seed spacers is to help position radioactive seeds to provide radioactivity in spatially suitable pattern, the seeds must be sufficiently dimensionally accurate and stable. Fibers made by some spinning processes are not straight after extrusion and drawing. They tend to retain some coil memory. Even after rack annealing, fibers made by some processes still can be curved due to residual coil memory.
Other various process conditions may adversely affect the properties required of the fibers for use as brachytherapy seed spacers. Upon sterilization by autoclaving, too much undesirable shrinkage in length may occur or the parts may undergo warping or bending.
Besides the “brooming” that may be experienced upon cutting fibers to length, some fabricated devices, i.e. seed spacers, also may “broom” or split during surgery under mechanical loading. Too much undesirable shrinkage in length, warping or bending upon autoclaving sterilization, or “brooming” or collapse during loading are failures that are particula
Andjelić Sa{haeck over (s)}a
Jamiolkowski Dennis D.
Karl John J.
Keilman Kenneth Michael
Popadiuk Nicholas
Ethicon Inc.
Tentoni Leo B.
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