Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-06-22
2004-05-04
Sellers, II, Robert E. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S357000, C528S370000, C528S409000, C528S421000
Reexamination Certificate
active
06730772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the synthesis of degradable polymers. More particularly, the present invention relates to degradable polymers having increased functionality.
2. Related Art
Interest in the synthesis of new degradable polymers has expanded in recent years. This increased interest stems in part from the concern that the extensive and continuing use of polymers in today's society will result in environmental damage. The concern is that many polymers used in commercial applications are inert and thus able to withstand natural processes that cause other non-inert materials to disintegrate and decompose. As a result of this inertness, polymers have accumulated in landfills and thereby have contributed to the shortage of landfill space generally. This problem will only be exacerbated as polymers are used in more and more commercial products and services. Thus, there is a need for developing polymers for commercial applications that have an enhanced ability to degrade.
The increased interest in the synthesis of new degradable polymers also stems in part from the use of synthetic polymers in medical applications. In medical applications, not only must the polymer be able to degrade, but the degradation products also must be compatible with the human body, i.e., be nontoxic. In this situation, the polymers are termed biodegradable, indicating their ability to degrade due to biological processes occurring inside the human body. As early as the 1960s, synthetic polymers were used in the field of surgical medicine as suture material. The polymeric suture material was both biodegradable and absorbable, that is, the polymers decomposed after a period of time after implantation in the human body, and those decomposition products were absorbed by the human body without any adverse or toxic effects. The advantage of biodegradable polymer-based suture materials is the ability to fabricate fibers with varying absorption rates to match the healing profiles of the tissues they help to repair. Another advantage of such polymer-based sutures over traditional silk and gut sutures is enhanced versatility and low tissue reactivity.
In addition to use as suture material, degradable polymers have been used in other biomedical applications, such as polymer-based drug delivery systems. In such a system, degradable polymers are used as a matrix for the controlled or sustained delivery or release of biologically active agents, such as, drugs, to the human body. In addition, the development of endoscopic surgical techniques has resulted in the need for developing such degradable drug delivery systems wherein the placement of the drug delivery device is targeted for specific anatomical locations. Examples of such polymer-based drug delivery systems are described in the following U.S. patents: U.S. Pat. No. 6,183,781, entitled “Method for Fabricating Polymer-based Controlled-release Devices”; U.S. Pat. No. 6,110,503, entitled “Preparation of Biodegradable, Biocompatible Microparticles Containing a Biologically Active Agent”; U.S. Pat. No. 5,989,463, entitled “Methods for Fabricating Polymer-based Controlled-release Devices”; U.S. Pat. No. 5,916,598, entitled “Preparation of Biodegradable, Biocompatible Microparticles Containing a Biologically Active Agent”; U.S. Pat. No. 5,817,343, entitled “Method for Fabricating Polymer-based Controlled-release Devices”; U.S. Pat. No. 5,650,173, entitled “Preparation of Biodegradable, Biocompatible Microparticles Containing a Biologically Active Agent.” Other examples of polymer-based drug delivery systems are described in U.S. Pat. No. 5,922,253, entitled “Production Scale Method of Forming Microparticles” and U.S. Pat. No. 5,019,400, entitled “Very Low Temperature Casting of Controlled Release Microspheres,” the technology described therein also known as Prolease®. All of the above-identified patent applications are assigned to Alkermes Controlled Therapeutics, Inc. of Cambridge, Mass., and are incorporated herein by reference.
Degradable polymers have also been used in other biomedical applications, including use as polymer scaffolds for tissue engineering. In this biomedical application, porous polymer scaffolds are shaped into articles for tissue engineering and tissue guided regeneration and repair applications, including reconstructive surgery. Scaffold applications include the regeneration of tissues such as nervous, musculoskeletal, cartilaginous, tendenous, hepatic, pancreatic, ocular, integumentary, arteriovenous, urinary or any other tissue forming solid or hollow organs. Scaffolds have been used as materials for vascular grafts, ligament reconstruction, adhesion prevention and organ regeneration. In one embodiment, the polymer scaffold provides physical support and an adhesive substrate for isolated cells during in vitro culturing and subsequent in vivo implantation in the human body. An alternate use of degradable polymer scaffolds is to implant the scaffold directly into the body without prior culturing of cells onto the scaffold in vivo. Once implanted, cells from the surrounding living tissue attach to the scaffold and migrate into it, forming functional tissue within the interior of the scaffold. Regardless of whether the scaffold is populated with cells before or after implantation, the scaffold is designed so that as the need for physical support of the cells and tissue diminishes over time, the scaffold will degrade. Degradable polymer scaffolds are described, for example, in U.S. Pat. No. 6,103,255, entitled “Porous polymer scaffolds for tissue engineering,” and is incorporated herein by reference.
Additional biomedical applications for synthetic biodegradable polymers include use with fracture fixation, for example, as absorbable orthopedic fixation devices. In particular, such biodegradable polymers permit treatment of bone fractures through fixation, providing good tissue/material compatibility, and facile molding (into potentially complex shapes) for easy placement. Controlled degradation of the polymers permits optimum bone function upon healing. The materials can reestablish the mechanical integrity of the bone and subsequently degrade to allow new bone formation to bear load and remodel. These biodegradable polymers maintain mechanical integrity while undergoing a gradual degradation and loss in size permitting bone ingrowth. In contrast to the traditional use of steel fixation devices, the degradable polymer-based device is advantageous in those situations where the device is not needed permanently or would require removal at a later point in time. Also, metallic orthopedic devices shield stress during healing and can lead to bone atrophy. Polymers for use in such orthopedic applications are described in U.S. Pat. No. 5,902,599, entitled “Biodegradable Polymer Networks for Use in Orthopedic and Dental Applications,” and U.S. Pat. No. 5,837,752, entitled “Semi-Interpenetrating Polymer Networks,” both of which are incorporated herein by reference. U.S. Pat. No. 5,902,599 also describes synthetic biodegradable polymers for use in dental applications.
The wide variety of commercial and biomedical applications just described for synthetic degradable polymers demonstrates the need for the development of multiple types of polymers with varying degradability profiles.
Synthetic polymers for use in commercial applications are legion. For example, polyethylene, polypropylene, and polystyrene are commercially produced polymers wherein monomer units of ethylene, propylene, and styrene, respectively, are sequentially added to a growing polymer chain by a process known as addition polymerization. The incorporation of monomer units into the polymer continues until the polymerization process is terminated by the addition of a compound that reacts with the end of the polymer chain and which itself is incapable of polymerization, thus quenching the polymerization.
Dacron is a commercial polyester synthesized by the condensation polymerization reaction of dimethyl terephthalate and ethylene
Covington & Burling
Reister Andrea G.
Ruschke David P.
Sellers II Robert E.
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