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Title:  Nitric oxide-producing hydrogel materials
United States Patent: 
October 9, 2007

West; Jennifer L. (Houston, TX), Bohl; Kristyn Simcha (Houston, TX)
Rice University (Houston, TX)
Appl. No.: 
September 1, 2000


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Hydrogels releasing or producing NO, most preferably photopolymerizable biodegradable hydrogels capable of releasing physiological amounts of NO for prolonged periods of time, are applied to sites on or in a patient in need of treatment thereof for disorders such as restenosis, thrombosis, asthma, wound healing, arthritis, penile erectile dysfunction or other conditions where NO plays a significant role. The hydrogels are typically formed of macromers, which preferably include biodegradable regions, and have bound thereto groups that are released in situ to elevate or otherwise modulate NO levels at the site where treatment is needed. The macromers can form a homo or hetero-dispersion or solution, which is polymerized to form a hydrogel material, that in the latter case can be a semi-interpenetrating network or interpenetrating network. Compounds to be released can be physically entrapped, covalently or ionically bound to macromer, or actually form a part of the polymeric material. The hydrogel can be formed by ionic and/or covalent crosslinking. Other active agents, including therapeutic, prophylactic, or diagnostic agents, can also be included within the polymeric material.


Biocompatible polymeric materials releasing or producing physiological amounts of NO for prolonged periods of time, are applied to sites on or in a patient in need of treatment thereof for disorders such as restenosis, thrombosis, asthma, wound healing, arthritis, penile erectile dysfunction or other conditions where NO plays a significant role. The polymeric materials can also be formed into films, coatings, or microparticles. The polymers are typically formed of macromers, which may include biodegradable regions, and have bound thereto groups that are released in situ to elevate or otherwise modulate levels at the site where treatment is needed. The macromers can form a homo or hetero-dispersion or solution, which is polymerized to form a polymeric material, that in the latter case can be a semi-interpenetrating network or interpenetrating network. Compounds to be released can be physically entrapped, covalently or ionically bound to macromer, or actually form a part of the polymeric material. Hydrogels can be formed by ionic and/or covalent crosslinking. Other active agents, including therapeutic, prophylactic, or diagnostic agents, can also be included within the polymeric material.


I. Polymeric Materials for Release of NO

The polymeric materials are biocompatible and release or produce NO. In various preferred embodiments, the polymers are also biodegradable, form hydrogels, polymerize in situ and are tissue adherent. These properties are conferred by the selection of the macromer components as well as addition of various groups to the components.

The term "polymerizable" means that the regions have the capacity to form additional covalent bonds resulting in macromer interlinking, for example, carbon-carbon double bond of acrylate-type molecules. Such polymerization is characteristically initiated by free-radical formation resulting from photon absorption of certain dyes and chemical compounds to ultimately produce free-radicals, although it can be obtained using other methods and reagents known to those skilled in the art.

A. Polymeric Materials

The polymeric materials must be biocompatible, i.e., not eliciting a significant or unacceptable toxic or immunogenic response following administration to or implantation into an individual.

A number of polymeric materials are known which are biocompatible, including both natural and synthetic polymers. Examples include proteins (of the same origin as the recipient), polysaccharides such as chondroitin sulfate and hyaluronic acid, polyurethanes, polyesters, polyamides, and acrylates. Polymers can be degradable or non-degradable.

Most polymeric materials will be selected based on a combination of properties conferred by the various components, which may include water soluble regions such as PEG or PVA, biodegradable regions such as regions that degrade hydrolytically, and groups that can be used to polymerize the macromers in situ.

Water-Soluble and/or Tissue Adhesive Regions

There are a variety of water soluble materials that can be incorporated into the polymers. The term "at least substantially water soluble" is indicative that the solubility should be at least about 5 g/100 ml of aqueous solution. In preferred embodiments, the core water soluble region can consist of poly(ethylene glycol), poly(ethylene oxide), poly(vinyl acetate), poly(vinyl alcohol), poly(vinylpyrrolidone), poly(ethyloxazoline), poly(ethylene oxide)-co-poly(propyleneoxide) block copolymers, polysaccharides or carbohydrates such as hyaluronic acid, dextran, heparin sulfate, chondroitin sulfate, heparin, or alginate, or proteins such as gelatin, collagen, albumin, or ovalbumin.

Hydrophilic (i.e., water soluble) regions will generally be tissue adhesive. Both hydrophobic and hydrophilic polymers which include a large number of exposed carboxylic groups will be tissue adhesive or bioadhesive. Ligands such as RGD peptides and lectins which bind to carbohydrate molecules on cells can also be bound to the polymer to increase tissue adhesiveness.

Degradable Regions

Polyesters (Holland et al., 1986 Controlled Release, 4:155-180) of .alpha.-hydroxy acids (viz., lactic acid, glycolic acid), are the most widely used biodegradable materials for applications ranging from closure devices (sutures and staples) to drug delivery systems (U.S. Pat. No. 4,741,337 to Smith et al.; Spilizewski et al., 1985 J. Control. Rel. 2:197-203). In addition to the poly(hydroxy acids), several other polymers are known to biodegrade, including polyanhydrides and polyorthoesters, which take advantage of labile backbone linkages, as reported by Domb et al., 1989 Macromolecules, 22:3200; Heller et al., 1990 Biodegradable Polymers as Drug Delivery Systems, Chasin, M. and Langer, R., Eds., Dekker, New York, 121-161. Polyaminoacids have also been synthesized since it is desirable to have polymers that degrade into naturally occurring materials, as reported by Miyake et al., 1974, for in vivo use.

The time required for a polymer to degrade can be tailored by selecting appropriate monomers. Differences in crystallinity also alter degradation rates. Due to the relatively hydrophobic nature of these polymers, actual mass loss only begins when the oligomeric fragments are small enough to be water soluble. Hence, initial polymer molecular weight influences the degradation rate.

The biodegradable region is preferably hydrolyzable under in vivo conditions. Hydrolyzable groups may be polymers and oligomers of glycolide, lactide, .epsilon.-caprolactone, other .alpha.-hydroxy acids, and other biologically degradable polymers that yield materials that are non-toxic or present as normal metabolites in the body. Preferred poly(.alpha.-hydroxy acid)s are poly(glycolic acid), poly(DL-lactic acid) and poly(L-lactic acid). Other useful materials include poly(amino acids), poly(anhydrides), poly(orthoesters), and poly(phosphoesters). Polylactones such as poly(.epsilon.-caprolactone), poly(.epsilon.-caprolactone), poly(.delta.-valerolactone) and poly(gamma-butyrolactone), for example, are also useful.

Biodegradable regions can also be constructed from polymers or monomers using linkages susceptible to biodegradation by enzymes, such as ester, peptide, anhydride, orthoester, and phosphoester bonds. Degradable materials of biological origin are well known, for example, crosslinked gelatin. Hyaluronic acid has been crosslinked and used as a degradable swelling polymer for biomedical applications (U.S. Pat. No. 4,987,744 to della Valle et al., U.S. Pat. No. 4,957,744 to Della Valle et al. (1991) Polym. Mater. Sci. Eng., 62:731-735]).

Biodegradable Hydrogels

A number of polymers have been described which include both water soluble regions and biodegradable regions. Sawhney et al., (1990) J. Biomed. Mater. Res. 24:1397-1411, copolymerized lactide, glycolide and .epsilon.-caprolactone with PEG to increase its hydrophilicity and degradation rate. U.S. Pat. No. 4,716,203 to Casey et al. (1987) synthesized a PGA-PEG-PGA block copolymer, with PEG content ranging from 5-25% by mass. U.S. Pat. No. 4,716,203 to Casey et al. (1987) also reports synthesis of PGA-PEG diblock copolymers, again with PEG ranging from 5-25%. U.S. Pat. No. 4,526,938 to Churchill et al. (1985) described noncrosslinked materials with MW in excess of 5,000, based on similar compositions with PEG; although these materials are not water soluble. Cohn et al. (1988) J. Biomed. Mater. Res. 22:993-1009 described PLA-PEG copolymers that swell in water up to 60%; these polymers also are not soluble in water, and are not crosslinked. The features that are common to these materials are that they use both water-soluble polymers and degradable polymers, and that they are insoluble in water, collectively swelling up to about 60%.

U.S. Pat. No. 5,410,016 issued on Apr. 25, 1995 to Hubbell, et al., describes materials which are based on polyethylene glycol (PEG), because of its high biocompatible and thromboresistant nature, with short polylactide extensions to impart biodegradation and acrylate termini to allow rapid photopolymerization without observable heat production. These materials are readily modified to produce hydrogels which release or produce NO.

The polymerizable regions are separated by at least one degradable region to facilitate uniform degradation in vivo. There are several variations of these polymers. For example, the polymerizable regions can be attached directly to degradable extensions or indirectly via water soluble nondegradable sections so long as the polymerizable regions are separated by a degradable section. For example, if the macromer composition contains a simple water soluble region coupled to a degradable region, one polymerizable region may be attached to the water soluble region and the other attached to the degradable extension or region. In another embodiment, the water soluble region forms the central core of the macromer composition and has at least two degradable regions attached to the core. At least two polymerizable regions are attached to the degradable regions so that, upon degradation, the polymerizable regions, particularly in the polymerized gel form, are separated. Conversely, if the central core of the macromer composition is formed by a degradable region, at least two water soluble regions can be attached to the core and polymerizable regions can be attached to each water soluble region. The net result will be the same after gel formation and exposure to in vivo degradation conditions.

In another embodiment, the macromer composition has a water soluble backbone region and a degradable region affixed to the macromer backbone. At least two polymerizable regions are attached to the degradable regions, so that they are separated upon degradation, resulting in gel product dissolution. In a further embodiment, the macromer backbone is formed of a nondegradable backbone having water soluble regions as branches or grafts attached to the degradable backbone. Two or more polymerizable regions are attached to the water soluble branches or grafts. In another variation, the backbone may be star shaped, which may include a water soluble region, a biodegradable region or a water soluble region which is also biodegradable. In this general embodiment, the star region contains either water soluble or biodegradable branches or grafts with polymerizable regions attached thereto. Again, the polymerizable regions must be separated at some point by a degradable region.

Polymerizable Groups

The polymerizable regions may be polymerizable by photoinitiation by free radical generation, most preferably in the visible or long wavelength ultraviolet radiation. The preferred polymerizable regions are acrylates, diacrylates, oligoacrylates, dimethacrylates, oligomethoacrylates, or other biologically acceptable photopolymerizable groups. A preferred tertiary amine is triethanol amine.

Useful photoinitiators are those which can be used to initiate by free radical generation polymerization of the macromers without cytotoxicity and within a short time frame, minutes at most and most preferably seconds. Preferred dyes as initiators of choice for LWUV initiation are ethyl eosin, 2,2-dimethoxy-2-phenyl acetophenone, other acetophenone derivatives, and camphorquinone. In all cases, crosslinking and polymerization are initiated among copolymers by a light-activated free-radical polymerization initiator such as 2,2-dimethoxy-2-phenylacetophenone or a combination of ethyl eosin (10.sup.-4-10.sup.-2 milliM) and triethanolamine (0.001 to 0.1 M), for example.

The choice of the photoinitiator is largely dependent on the photopolymerizable regions. For example, when the macromer includes at least one carbon-carbon double bond, light absorption by the dye causes the dye to assume a triplet state, the triplet state subsequently reacting with the amine to form a free radical which initiates polymerization. Preferred dyes for use with these materials include eosin dye and initiators such as 2,2-dimethyl-2-phenylacetophenone, 2-methoxy-2-phenylacetophenone, and camphorquinone. Using such initiators, copolymers may be polymerized in situ by long wavelength ultraviolet light or by laser light of about 514 nm, for example.

Initiation of polymerization is accomplished by irradiation with light at a wavelength of between about 200-700 nm, most preferably in the long wavelength ultraviolet range or visible range, 320 nm or higher, most preferably about 514 nm or 365 nm.

There are several photooxidizable and photoreducible dyes that may be used to initiate polymerization. These include acridine dyes, for example, acriblarine; thiazine dyes, for example, thionine; xanthine dyes, for example, rose bengal; and phenazine dyes, for example, methylene blue. These are used with cocatalysts such as amines, for example, triethanolamine; sulphur compounds, for example, RSO.sub.2R.sub.1; heterocycles, for example, imidazole; enolates; organometallics; and other compounds, such as N-phenyl glycine. Other initiators include camphorquinones and acetophenone derivatives.

Thermal polymerization initiator systems may also be used. Such systems that are unstable at C. and would initiate free radical polymerization at physiological temperatures include, for example, potassium persulfate, with or without tetramethyl ethylenediamine; benzoylperoxide, with or without triethanolamine; and ammonium persulfate with sodium bisulfite.

Other initiation chemistries may be used besides photoinitiation. These include, for example, water and amine initiation schemes with isocyanate or isothiocyanate containing macromers used as the polymerizable regions.

Preferred Embodiments

In a preferred embodiment, the polymeric materials are a biodegradable, polymerizable and at least substantially water soluble macromer composition. The first macromer includes at least one water soluble region, at least one NO carrying region and at least one free radical-polymerizable region. The second macromer includes at least one water soluble region and at least two free radical polymerizable regions. The regions can, in some embodiments, be both water soluble and biodegradable. The macromer composition is polymerized by exposure of the polymerizable regions to free radicals generated, for example, by photosensitive chemicals and dyes.

Examples of these macromers are PVA or PEG-oligoglycolyl-acrylates. The choice of appropriate end caps permits rapid polymerization and gelation. Acrylates are preferred because they can be polymerized using several initiating systems, e.g., an eosin dye, by brief exposure to ultraviolet or visible light. A poly(ethyleneglycol) or PEG central structural unit (core) is preferred on the basis of its high hydrophilicity and water solubility, accompanied by excellent biocompatibility. A short oligo or poly(.alpha.-hydroxy acid), such as polyglycolic acid, is selected as a preferred chain extension because it rapidly degrades by hydrolysis of the ester linkage into glycolic acid, a harmless metabolite. Although highly crystalline polyglycolic acid is insoluble in water and most common organic solvents, the entire macromer composition is water-soluble and can be rapidly gelled into a biodegradable network while in contact with aqueous tissue fluids. Such networks can be used to entrap and homogeneously disperse water-soluble drugs and enzymes and to deliver them at a controlled rate. Further, they may be used to entrap particulate suspensions of water-insoluble drugs. Other preferred chain extensions are polylactic acid, polycaprolactone, polyorthoesters, and polyanhydrides. Polypeptides may also be used. Such "polymeric" blocks should be understood to include timeric, dimeric, and oligomeric blocks.

PVA contains many pendant hydroxyl groups. These hydroxyl groups are easily reacted to form side chains such as various crosslinking agents and nitric oxide donors. PVA is water soluble and has excellent biocompatibility. Modification of PVA to attach methacrylate groups via a diacetal bond with the pendant hydroxyl groups and addition of an appropriate photoinitiator enables the PVA to be photopolymerized to form hydrogels under long wavelength UV light. In another preferred embodiment, the hydrogel is formed from modified polyvinyl alcohol (PVA) macromers, such as those described in U.S. Pat. Nos. 5,508,317, 5,665,840, 5,849,841, 5,932,674, 6,011,077, 5,939,489, and 5,807,927. The macromers disclosed in U.S. Pat. No. 5,508,317, for example, are PVA prepolymers modified with pendant crosslinkable groups, such as acrylamide groups containing crosslinkable olefinically unsaturated groups. These macromers can be polymerized by photopolymerization or redox free radical polymerization, for example. The starting polymers are, in particular, derivatives of polyvinyl alcohol or copolymers of vinyl alcohol that contain, for example, a 1,3-diol skeleton. The crosslinkable group or the further modifier can be bonded to the starting polymer skeleton in various ways, for example through a certain percentage of the 1,3-diol units being modified to give a 1,3-dioxane, which contains a crosslinkable radical, or a further modifier in the 2-position. Another possibility is for a certain percentage of hydroxyl groups in the starting polymer to be esterified by means of an unsaturated organic acid, these ester-bonded radicals containing a crosslinkable group. The hydrophobicity of these macromers can be increased by substituting some of the pendant hydroxyl groups with more hydrophobic substituents. The properties of the macromers, such as hydrophobicity, can also be modified by incorporating a comonomer in the macromer backbone. The macromers can also be formed having pendant groups crosslinkable by other means.

B. NO groups or Modulating Compounds

A number of molecules that produce NO under physiological conditions (NO donors) have been identified and evaluated both in vitro and in vivo, including S-nitrosothiols, organic nitrates, and complexes of NO with nucleophiles. L-arginine is a NO donor, since L-arginine is a substrate for NO synthase, and thus administration of L-arginine increases endogenous NO production and elicits responses similar to those caused by NO donors in most cases. Other NO donors include molsidomine, CAS754, SPM-5185, and SIN-1. Other compounds capable of producing and/or donating NO may also be used. These include organic nitrates, nitrosylating compounds, nitrosoesters, and L-arginine.

The molecules which produce NO, or release or generate NO, are preferably attached to regions containing nucleophiles and/or thiols such as S-nitrosothiols capable of forming a complex with NO.

C. Prophylactic, Therapeutic and Diagnostic Agents

The polymeric materials can also be used for drug delivery, preferably localized release of prophylactic, therapeutic or diagnostic agents at the site where the materials are needed, although the polymeric materials can be loaded with agent to be released systemically. These agents include proteins or peptides, polysaccharides, nucleic acid molecules, and simple organic molecules, both natural and synthetic. Representative materials include antibiotics, antivirals, and antifungal drugs, anti-inflammatories (steroidal or non-steroidal), hormones, growth factors, cytokines, neuroactive agents, vasoconstrictors and other molecules involved in the cardiovascular responses, enzymes, antineoplastic agents, local anesthetics, antiangiogenic agents, antibodies, drugs affecting reproductive organs, and oligonucleotides such as antisense oligonucleotides. Diagnostic materials may be radioactive, bound to or cleave a chromogenic substrate, or detectable by ultrasound, x-ray, MRI, or other standard imaging means.

These agents can be mixed with macromer prior to polymerization, applied into or onto the polymer, or bound to the macromer prior to or at the time of polymerization, either covalently or ionically, so that the agent is released by degradation (enzymatic or hydrolytic) or diffusion at the site where the polymer is applied.

II. Method of Use

A. Coatings; Films; Microparticles

Although described primarily with respect to in vivo treatment, it is apparent that the polymeric materials described herein can be used in cell culture, on cell culture substrates, or as coatings on medical implants or devices such as stents or catheters, or formed using standard techniques into microparticles or other types of formulations which may be used in or administered to a patient.

B. Therapeutic Applications

Polymeric materials capable of releasing physiological amounts of NO for prolonged periods of time can be applied to sites on or in a patient in need of treatment thereof. Representative disorders or conditions that can be treated with NO include restenosis, thrombosis, asthma, would healing, arthritis, and penile or female erectile dysfunction. The material is typically applied as a macromer solution and polymerized in situ, although polymerization can be initiated prior to application.

Wound Healing

The formulations are particularly useful for treatment of all types of wounds, including burns, surgical wounds, and open leg and foot wounds. There are generally three types of open leg wounds, termed ulcers: venous stasis ulcers, generally seen in sedentary elderly people when blood flow to the leg becomes sluggish; decubitus ulcers, also termed pressure sores or bed sores, which occurs most often in people who are bedridden and are unable to frequently change position; and diabetic foot ulcers, caused by poor blood circulation to the feet. Due to the aging of the population, there will likely be a greater demand for effective and user friendly wound treatments in the near future.

The term "wound" as used herein refers to all types of tissue injuries, including those inflicted by surgery and trauma, including burns, as well as injuries from chronic or acute medical conditions, such as atherosclerosis or diabetes.

Treatment of Restenosis

A preferred application is a method of reducing the effects of restenosis on post-surgical patients. The method includes coating the surface within an artery with an aqueous solution of light-sensitive free radical polymerizable initiator and a number of macromers. The coated artery is subjected to a Xenon arc laser inducing polymerization of the macromers. As the newly polymerized macromer composition is formed, the physiological conditions within the artery will induce the release of NO. This release will be strictly localized for prolonged periods of time.

Prevention of Surgical Adhesions

A preferred application is a method of reducing formation of adhesions after a surgical procedure in a patient. In one embodiment the method includes coating damaged tissue surfaces in a patient with an aqueous solution of a light-sensitive free-radical polymerization initiator and a macromer solution as described above. The coated tissue surfaces are exposed to light sufficient to polymerize the macromer. The light-sensitive free-radical polymerization initiator may be a single compound (e.g., 2,2-dimethoxy-2-phenyl acetophenone) or a combination of a dye and a cocatalyst (e.g., ethyl eosin and triethanol amine).

Tissue Adhesives

Another use of the polymers is in a method for adhering tissue surfaces in a patient. In one embodiment the macromer is mixed with a photoinitiator or photoinitiator/cocatalyst mixture to form an aqueous mixture and the mixture is applied to a tissue surface to which tissue adhesion is desired. The tissue surface is contacted with the tissue with which adhesion is desired, forming a tissue junction. The tissue junction is then irradiated until the macromers are polymerized.

Tissue Coatings

In a particularly preferred application of these macromers, an ultrathin coating is applied to the surface of a tissue, most preferably the lumen of a tissue such as a blood vessel. One use of such a coating is in the treatment or prevention of restenosis, abrupt reclosure, or vasospasm after vascular intervention. An initiator is applied to the surface of the tissue, allowed to react, adsorb or bond to tissue, the unbound initiator is removed by dilution or rising, and the macromer solution is applied and polymerized. This method is capable of creating uniform polymeric coating of between one and 500 microns in thickness, most preferably about twenty microns, which does not evoke thrombosis or localized inflammation.

Tissue Supports

The polymeric materials can also be used to create tissue supports by forming shaped articles within the body to serve a mechanical function. Such supports include, for example, sealants for bleeding organs, sealants for bone defects and space-fillers for vascular aneurisms. Further, such supports can include strictures to hold organs, vessels or tubes in a particular position for a controlled period of time.

Controlled Drug Delivery

As noted above, the polymeric materials can be use as carriers for biologically active materials such as therapeutic, prophylactic or diagnostic agents, including hormones, enzymes, antibiotics, antineoplastic agents, and cell suspensions. The polymeric material may be used to temporarily preserve functional properties of an agent to be released, as well as provide prolonged, controlled release of the agent into local tissues or systemic circulation.

In a variation of the method for controlled drug deliver in which an agent is mixed with the macromer solution then polymerized in situ, the macromers are polymerized with the biologically active materials to form microspheres or nanoparticles containing the biologically active material. The macromer, photoinitiator, and agent to be encapsulated are mixed in an aqueous mixture. Particles of the mixture are formed using standard techniques, for example, by mixing in oil to form an emulsion, forming droplets in oil using a nozzle, or forming droplets in air using a nozzle. The suspension or droplets are irradiated with a light suitable for photopolymerization of the macromer.

These materials are particularly useful for controlled drug delivery of hydrophilic materials, since the water soluble regions of the polymer enable access of water to the materials entrapped within the polymer. Moreover, it is possible to polymerize the macromer composition containing the material to be entrapped without exposing the material to organic solvents. Release may occur by diffusion of the material from the polymer prior to degradation and/or by diffusion of the material from the polymer as it degrades, depending upon the characteristic pore sizes within the polymer, which is controlled by the molecular weight between crosslinks and the crosslink density. Deactivation of the entrapped material is reduced due to the immobilizing and protective effect of the gel and catastrophic burst effects associated with other controlled-release systems are avoided. When the entrapped material is an enzyme, the enzyme can be exposed to substrate while the enzyme is entrapped, provided the gel proportions are chosen to allow the substrate to permeate the gel. Degradation of the polymer facilitates eventual controlled release of free macromolecules in vivo by gradual hydrolysis of the terminal ester linkages.

Claim 1 of 18 Claims

1. A method for controlled release of NO or an NO donor comprising administering to tissue a biocompatible, polymerizable, macromer composition comprising at least one NO carrying region or the NO donor, wherein NO or the NO donor is complexed to the macromer composition, and wherein the NO or the NO donor is released from the macromer composition following polymerization in situ, under physiological conditions, wherein the macromer composition comprises one or more region selected from the group consisting of water soluble regions, tissue adhesive regions, and polymerizable end group regions and one or more therapeutic or diagnostic agents selected from the group consisting of proteins, carbohydrates, nucleic acids, organic molecules, inorganic molecules, biologically active molecules, cells, tissue, and tissue aggregates.


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