The invention provides tissue engineering compositions and methods wherein three-dimensional matrices for growing cells are prepared for in vitro and in vivo use. The matrices comprise biodegradable polymer fibers capable of the controlled delivery of therapeutic agents. The spatial and temporal distribution of released therapeutic agents is controlled by use of defined nonhomogeneous patterns of therapeutic agents in the matrices.

Description of the Invention

SUMMARY OF THE INVENTION

The present invention provides tissue engineering compositions and methods wherein three-dimensional matrices for growing cells are prepared for in vitro and in vivo use. The matrices comprise biodegradable polymer fibers capable of the controlled delivery of therapeutic agents. The spatial and temporal distribution of released therapeutic agents is controlled by the use of predefined nonhomogeneous patterns of polymer fibers, which are capable of releasing one or more therapeutic agents as a function of time. The terms "scaffold," "scaffold matrix" and "fiber-scaffold" are also used herein to describe the three dimensional matrices of the invention. "Defined nonhomogeneous pattern" in the context of the current application means the incorporation of specific fibers into a scaffold matrix such that a desired three-dimensional distribution of one or more therapeutic agents within the scaffold matrix is achieved. The distribution of therapeutic agents within the matrix fibers controls the subsequent spatial distribution within the interstitial medium of the matrix following release of the agents from the polymer fibers. In this way, the spatial contours of desired concentration gradients can be created within the three dimensional matrix structure and in the immediate surroundings of the matrix. Temporal distribution is controlled by the polymer composition of the fiber and by the use of coaxial layers within a fiber.

One aspect of the present invention is a biocompatible implant composition comprising a scaffold of biodegradable polymer fibers. In various embodiments of the present invention, the distance between the fibers may be about 50 microns, about 70 microns, about 90 microns, about 100 microns, about 120 microns, about 140 microns, about 160 microns, about 180 microns, about 200 microns, about 220 microns, about 240 microns, about 260 microns, about 280 microns, about 300 microns, about 320 microns, about 340 microns, about 360 microns, about 380 microns, about 400 microns, about 450 microns or about 500 microns. In various embodiments the distance between the fibers may be less than 50 microns or greater than 500 microns.

Additionally, it is envisioned that in various embodiments of the invention, the fibers will have a diameter of about 20 microns, about 40 microns, about 60 microns, about 80 microns, about 100 microns, about 120 microns, about 140 microns, about 160 microns, about 180 microns, about 200 microns, about 220 microns, about 240 microns, about 260 microns, about 280 microns, about 300 microns, about 320 microns, about 340 microns, about 360 microns, about 380 microns, about 400 microns, about 450 microns or about 500 microns (including intermediate lengths). In various embodiments the diameter of the fibers may be less than about 20 microns or greater than about 500 microns. Preferably, the diameter of the fibers will be from about 60 microns to about 80 microns.

"About", in this one context is intended to mean a range of from 1-10 microns, which includes the intermediate lengths within the range. It will be readily understood that "intermediate lengths", in this context, means any length between the quoted ranges, such as 21, 22, 23, 24, 25, 26, 27, 28, 29 etc.; 30, 31, 32, etc.; 50, 51, 52, 53, etc.; 100, 101, 102, 103, etc.; 150, 151, 152, 153, etc.; including all integers through the 200-500 range.

The inventors also contemplate that the matrix may be woven, non-woven, braided, knitted, or a combination of two or more such preparations. For example, potential applications such as artificial arteries may well use a combination of woven, non-woven and knitted preparations or a combination of all four preparations. In certain embodiments of the invention, braided compositions may find particular utility for use with tendons and ligaments. Such braiding may, for example, provide superior strength.

In certain embodiments of the invention, the fibers containing one or more therapeutic agents are distributed within the scaffold matrix in a defined nonhomogeneous pattern. In one embodiment, the fibers may comprise two or more subsets of fibers that differ in biodegradable polymer content. The fibers or subsets of fibers may comprise a plurality of co-axial biodegradable polymer layers.

In another embodiment of the present invention, the fibers or a subset of fibers, contain one or more therapeutic agents such that the concentration of the therapeutic agent or agents varies along the longitudinal axis of the fibers or subset of fibers. The concentration of the active agent or agents may vary linearly, exponentially or in any desired fashion, as a function of distance along the longitudinal axis of a fiber. The variation may be monodirectional, that is, the content of one or more therapeutic agents decreases from the first end of the fibers or subset of the fibers to the second end of the fibers or subset of the fibers. The content may also vary in a bidirection fashion, that is, the content of the therapeutic agent or agents increases from the first ends of the fibers or subset of the fibers to a maximum and then decreases towards the second ends of the fibers or subset of the fibers.

In certain embodiments of the present invention, a subset of fibers comprising the scaffold may contain no therapeutic agent. For fibers that contain one or more therapeutic agents, the agent or agents may include a growth factor, an immunodulator, a compound that promotes angiogenesis, a compound that inhibits angiogenesis, an anti-inflammatory compound, an antibiotic, a cytokine, an anti-coagulation agent, a procoagulation agent, a chemotactic agent, an agents that promotes apoptosis, an agent that inhibits apoptosis, a mitogenic agent, a radioactive agent, a contrast agent for imaging studies, a viral vector, a polynucleotide, therapeutic genes, DNA, RNA, a polypeptide, a glycosaminoglycan, a carbohydrate, a glycoprotein. The therapeutic agents may also include those drugs that are to be administered for long-term maintenance to patients such as cardiovascular drugs, including blood pressure, pacing, anti-arrhythmia, beta-blocking drugs, and calcium channel based drugs. Therapeutic agents of the present invention also include anti-tremor and other drugs for epilepsy or other movement disorders. These agents may also include long term medications such as contraceptives and fertility drugs. They could comprise neurologic agents such as dopamine and related drugs as well as psychological or other behavioral drugs. The therapeutic agents may also include chemical scavengers such as chelators, and antioxidants. Wherein the therapeutic agent promotes angiogenesis, that agent may be vascular endothelial growth factor. The therapeutic agents may be synthetic or natural drugs, proteins, DNA, RNA, or cells (genetically altered or not). As used in the specification and claims, following long-standing patent law practice, the terms "a" and "an," when used in conjunction with the word "comprising" or "including" means one or more.

In general, the present invention contemplates the use of any drug incorporated in the biodegradable polymer fibers of the invention. The word "drug" as used herein is defined as a chemical capable of administration to an organism, which modifies or alters the organism's physiology. More preferably the word "drug" as used herein is defined as any substance intended for use in the treatment or prevention of disease. Drug includes synthetic and naturally occurring toxins and bioaffecting substances as well as recognized pharmaceuticals, such as those listed in "The Physicians Desk Reference," 471st edition, pages 101-321; "Goodman and Gilman's The Pharmacological Basis of Therapeutics" 8th Edition (1990), pages 84-1614 and 1655-1715; and "The United States Pharmacopeia, The National Formulary", USP XXII NF XVII (1990), the compounds of these references being herein incorporated by reference. The term "drug" also includes compounds that have the indicated properties that are not yet discovered or available in the U.S. The term "drug" includes pro-active, activated, and metabolized forms of drugs.

The biodegradable polymer may be a single polymer or a co-polymer or blend of polymers and may comprise poly(L-lactic acid), poly(DL-lactic acid), polycaprolactone, poly(glycolic acid), polyanhydride, chitosan, or sulfonated chitosan, or natural polymers or polypeptides, such as reconstituted collagen or spider silk.

One aspect of the present invention is a drug-delivery fiber composition comprising a biodegradable polymer fiber containing one or more therapeutic agents. In one embodiment, the content of the one or more therapeutic agents within the fiber varies along the longitudinal axis of the fiber such that the content of the therapeutic agent or agents decreases from the first end of the fiber to the second end of the fiber. In another embodiment, the fiber comprises a plurality of co-axial layers of biodegradable polymers. The drug delivery fiber composition may be implanted into many sites in the body including dermal tissues, cardiac tissue, soft tissues, nerves, bones, and the eye. Ocular implantation has particular use for treatment of cataracts, diabetically induced proliferative retinopathy and non-proliferative retinopathy, glaucoma, macular degeneration, and pigmentosa XXXX.

Another aspect of the present invention is a method of controlling the spatial and temporal concentration of one or more therapeutic agents within a fiber-scaffold implant, comprising implanting a fiber-scaffold into a host. The spatial concentrations may be provided across multiple fibers, or alternatively along a single fiber by imposing a concentration gradient along the length of a fiber. The fiber-scaffold typically comprises biodegradable polymer fibers containing one or more therapeutic agents, wherein the therapeutic agent or agents are distributed in the fiber-scaffold in a defined nonhomogeneous pattern. The host will typically be an animal, preferably a mammal and more preferably a human.

Yet another aspect of the present invention is a method of producing a fiber-scaffold for preparing an implant capable of controlling the spatial and temporal concentration of one or more therapeutic agents. This method generally comprises forming biodegradable polymer fibers into a three dimensional fiber-scaffold. The biodegradable polymer fibers contain one or more therapeutic agents. The therapeutic agent or agents are distributed in the fiber-scaffold in a defined nonhomogeneous pattern.

It is further envisioned that the scaffold of the invention may be used to direct and/or organize tissue structure, cell migration and matrix deposition and participate in or promote general wound healing.

In another embodiment of the invention, a method is provided for creating a drug releasing fiber from chitosan comprising use of hydrochloric acid as a solvent and Tris base as a coagulating bath. The hydrochloric acid concentration may be, for example, from about 0.25% to about 5%, or from about 1% to about 2%, including all concentrations within such ranges. In the method, the tris base concentration may be, for example, from about 2% to about 25%, from about 4% to about 17%, or from about 5% to about 15%, including all concentrations within such ranges. The method may, in one embodiment of the invention, comprise a heterogeneous mixture comprising chitosans with different degrees of deacetylation. The method may also comprise creating a drug releasing fiber comprising segments of chitosan with different degrees of deacetylation.

A drug releasing fiber in accordance with the invention may be created, for example, from chitosan and extracellular matrix. In creating a drug releasing fiber in accordance with the invention, the chitosan concentration may be, for example, from about 0.5 wt. % to about 10 wt. %, from about 1 wt. % to about 7 wt. %, from about 2 wt. % to about 5 wt. %, from about 3 wt. % to about 4 wt. %, or about 3.5 wt. %. In one embodiment of the invention, the Matrigel. The extracellular matrix concentration may be from about 1 vol. % to about 20 vol. %, from about 2 vol. % to about 15 vol. %, from about 3 vol. % to about 10 vol. %, or from about 4 vol. % to about 6 vol. %, including about 5 vol. %. In the method, the fiber may be coated with said extracellular matrix.

Chitosan used in accordance with the invention may be sulfated or unsulfated. In one embodiment of the invention, when sulfated chitosan is used the concentration may be from about 0.025 wt. % to about 2 wt. %, from about 0.05 wt. % to about 1 wt. %, from about 0.1 wt. % to about 0.5 wt. %, or from about 0.15 wt. % to about 0.3 wt. %, including about 0.2 wt. %. In the method, chitosan and sulfated chitosan may be extruded into a fiber.

In still another embodiment of the invention, a method is provided of creating a drug releasing fiber, the method comprising adding poly(L-lactic acid) microspheres to chitosan in acid and a coagulation bath. In the method, the acid may be, for example, acetic acid or hydrochloric acid. Where the acid is hydrochloric acid, the concentration may be, for example, from about 0.25% to about 5%, or from about 1% to about 2%, including 1.2 vol. % and all other concentrations within such ranges. The chitosan concentration may be, for example, from about 0.5 wt. % to about 10 wt. %, from about 1 wt. % to about 7 wt. %, from about 2 wt. % to about 5 wt. %, from about 3 wt. % to about 4 wt. %, or about 3.5 wt. %. The coagulation bath may comprise sodium hydroxide, for example, in a concentration of about 1 vol. % to about 20 vol. %, 2 vol. % to about 15 vol. %, 3 vol. % to about 10 vol. %, 4 vol. % to about 7 vol. %, or about 4 vol. % to about 6 vol. %, including about 5 vol. %. In one embodiment of the invention, the method comprises adding poly(L-lactic acid) microspheres to a solution of about 3.5 wt. % chitosan in from about 1 vol. % hydrochloric acid to about 2 vol. % hydrochloric acid and using a coagulation bath comprising from about 5 vol. % tris base to about 15 vol. % tris base. The method may further comprise adding a surfactant to the solution, including albumin, for example, from about 1 wt. % to about 5 wt. % of said albumin, including about 3 wt. %. In yet another embodiment of the invention, a composition of chitosan fibers is provided comprising microspheres of a second polymer, said microspheres comprising one or more biological molecules. The composition may comprise a surfactant that is a biological molecule.

In yet another embodiment of the invention, a composition is provided comprising a fiber containing chitosan and an extracellular matrix. The chitosan may be sulfated or non-sulfated.

In yet another embodiment of the invention, a composition is provided comprising a three-dimensional scaffold, said scaffold comprising fibers that are woven, non-woven, or knitted, wherein said fibers comprise any of the compositions described herein above. A composition in accordance with the invention may, in one embodiment, comprise fibers containing chitosan, extracellular matrix and a biological molecule. The chitosan may sulfated non-sulfated.

In yet another embodiment of the invention, a composition is provided comprising a heterogeneous scaffold of fibers a biological molecule as described above, wherein the biological molecule not the same for all fibers of the scaffold. In the composition, the degree of deacetylation may vary as a function of distance along the fiber. The composition may an extracellular matrix. The composition may also, in certain embodiments of the invention, comprise sulfated or non-sulfated chitosan.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention provides compositions and methods to create a heterogeneous, woven, knitted, or non-woven or braided three-dimensional matrix for growing cells in tissue engineering applications. These scaffolds can be used in vitro and in vivo, and due to their heterogeneity can create both spatial and temporal distributions of therapeutic agents. In this invention, therapeutic agents may include drugs, proteins, peptides, mono- and di-saccharides, polysaccharides, glycoproteins, DNA, RNA, viruses, or other biological molecules of interest. The term therapeutic agent in this invention also includes radioactive materials used to help destroy harmful tissues such as tumors in the local area, or to inhibit growth of healthy tissues, such as in current stent applications; or markers to be used in imaging studies.

A. Three Dimensional Fiber Matrix

To create the heterogeneous scaffolds of the present invention, the therapeutic agents are encapsulated into individual fibers of the matrix by methods to be described herein. The therapeutic agents are released from each individual fiber slowly, and in a controlled manner. The fiber format has many advantages as a drug delivery platform over other slow drug-releasing agents known to those familiar in the art such as microspheres, porous plugs or patches. The primary advantage of fibers is that they can provide complex three-dimensional woven (FIG. 1 (see Original Patent)), or non-woven (FIG. 2 (see Original Patent)) scaffolding, with or without patterning, to allow cells to attach, spread, differentiate, and mature into appropriately functioning cells. Because they can form patterns, a "smart fabric" can be woven to induce cells of specific types to migrate to specific regions of the scaffold due to specific chemotactic factors being released. This scaffold mimics the function of the extracellular matrix material both during embryological development and in post-embryological tissues. Additionally, filaments could be formed into a unique scaffold that provides a growth substrate for tissue repair or reconstruction that is not reminiscent of a natural like structure.

Because of the ability to weave patterns to induce appropriate cell types into specific regions, it is possible to incorporate strands that will induce the formation of blood vessels into the fabric. This may be accomplished by providing fibers that release growth factors such as vascular endothelial growth factor (VEGF). By appropriate spacing of VEGF containing-fibers into the weave pattern, large tissues may be engineered, and the cells in such tissues can be provided with a sufficient blood supply and thereby receive oxygen and nutrients and enable the removal of waste products.

Fibers also have the advantage of providing the body with short term mechanical support in such applications as stents (FIGS. 3A and 3B (see Original Patent)), wherein the polymer fiber can maintain the lumen of any tubular body, such as arteries, veins, ducts (e.g. bile duct, ureter, urethra, trachea, etc.), organs of the digestive track such as esophagus, intestine, colon, and connective tissue such as tendons, ligaments, muscle and bone. The fibers provide a useful structure to support mechanical strength or tension during the healing process. Fibers may also be useful to promote neural regeneration or reconstruction of nerves or spinal cord.

Further, fibers can be coated, forming co-axial fibers as shown in FIG. 4 (see Original Patent).  Each coating can be of a different polymer material, or combination of polymers, and each layer can release a different therapeutic agent or combination of therapeutic agents. The coating can also be physically divided into multiple sections, meaning that if desired, different therapeutic agents can be released in various directions. For example, as depicted in FIG. 4, a fiber may have a two component coating, with each component loaded with different therapeutic agents. Therefore, not only is spatial distribution of various therapeutic agents possible, as described above, but these agents may have different release kinetics, thus yielding temporal distribution of therapeutic agents. The release kinetics of such a coated fiber is characterized in FIG. 5 (see Original Patent). For example, if a fiber has two coatings over the core polymer, then three different therapeutic agents or combinations of therapeutic agents can be released. The outside coating will release its therapeutic agents followed by the inner coating material and finally from the core fiber. Therefore, each polymer system has its own release kinetics profile that can be adjusted by polymer type and processing conditions for that particular coating layer. Each coating can consist of different polymers as well as being loaded with different molecules. This provides the ability to control release kinetics at each layer. The ability to release different agents at different times is particularly important in tissue engineering, because cells that are rapidly dividing often do not display the specialized functions of non-dividing cells of the same type of class. With the present invention, it is possible, by release of the appropriate therapeutic agents, to induce cells to first migrate to a specific location, then enter a rapid division phase to fill the tissue space, and then differentiate into a functional form.

Additionally, cells are known to follow concentration gradients. It is the change in concentration of a particular factor that appears to be important for directed cell migration. Therefore, the present invention provides a method of achieving gradients of therapeutic agents along the length of the fibers. A linear gradient is depicted in FIGS. 6A and 6B (see Original Patent). By methods disclosed in this invention, this concentration gradient can be linear, exponential, or any other shape as a function of distance along the length of the fiber. It can also be bidirectional, meaning that it can be low at both ends and reach a maximum in the middle for example. This induces the cells to migrate and grow in specific directions along the fibers. By extension, by methods disclosed in this invention, a banded fiber can also be produced, as shown in FIG. 7 (see Original Patent). The distribution and frequency of these bands can be changed as desired. Therefore, the therapeutic agents delivery aspect of this invention goes far beyond simple drug-delivery microspheres or plugs, and the fiber based "smart scaffold" exceeds typical fiber based matrices into orchestrating the development of viable tissue, providing a three-dimensional biological architecture as well as mechanical support.

B. Biodegradable Polymers

Preferred polymers for use in the present invention include single polymer, co-polymer or a blend of polymers of poly(L-lactic acid), poly(DL-lactic acid), polycaprolactone, poly(glycolic acid), polyanhydride, chitosan, or sulfonated chitosan. Naturally occurring polymers may also be used such as reconstituted collagen or natural silks. Those of skill in the art will understand that these polymers are just examples of a class of biodegradable polymer matrices that may be used in this invention. Further biodegradable matrices include polyanhydrides, polyorthoesters, and poly(amino acids) (Peppas and Langer, 1994). Any such matrix may be utilized to fabricate a biodegradable polymer matrix with controlled properties for use in this invention. Further biodegradable polymers that produce non-toxic degradation products are listed in Table 1 (see Original Patent).

C. Agents that Promote Angiogenesis

One class of therapeutic agents to be encapsulated by the polymer fibers of the present invention are therapeutic agents that promote angiogenesis. The successful engineering of new tissue requires the establishment of a vascular network. The induction of angiogenesis is mediated by a variety of factors, any of which may be used in conjunction with the present invention (FoLkman and Klagsbrun, 1987, and references cited therein, each incorporated herein in their entirety by reference). Examples of angiogenic factors includes, but is not limited to: vascular endothelial growth factor (VEGF) or vascular permeability factor (VPF); members of the fibroblast growth factor family, including acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF); interleukin-8 (IL-8); epidermal growth factor (EGF); platelet-derived growth factor (PDGF) or platelet-derived endothelial cell growth factor (PD-ECGF); transforming growth factors alpha and beta (TGF-.alpha., TGF-.beta.); tumor necrosis factor alpha (TNF-.alpha.); hepatocyte growth factor (HGF); granulocyte-macrophage colony stimulating factor (GM-CSF); insulin growth factor-1 (IGF-1); angiogenin; angiotropin; fibrin and nicotinamide (Folkman, 1986, 1995; Auerbach and Auerbach, 1994; Fidler and Ellis, 1994; Folkman and Klagsbrun, 1987; Nagy et al., 1995)

D. Cytokines

In certain embodiments the use of particular cytokines incorporated in the polymer fibers of the present invention is contemplated. Table 2 (see Original Patent) is an exemplary, but not limiting, list of cytokines and related factors contemplated for use in the present invention.

E. Polynucelotides

The polynucleotides to be incorporated within the polymer fibers of the present invention, extend to the full variety of nucleic acid molecules. The nucleic acids thus include genomic DNA, cDNAs, single stranded DNA, double stranded DNA, triple stranded DNA, oligonucleotides, Z-DNA, mRNA, tRNA and other RNAs. DNA molecules are generally preferred, even where the DNA is used to express a therapeutic RNA, such as a ribozyme or antisense RNA.

A "gene" or DNA segment encoding a selected protein or RNA, generally refers to a DNA segment that contains sequences encoding the selected protein or RNA, but is isolated away from, or purified free from, total genomic DNA of the species from which the DNA is obtained. Included within the terms "gene" and "DNA segment", are DNA segments and smaller fragments of such segments, and also recombinant vectors, including, for example, plasmids, cosmids, phage, retroviruses, adenoviruses, and the like.

The term "gene" is used for simplicity to refer to a functional protein or peptide encoding unit. As will be understood by those in the art, this functional term includes both genomic sequences and cDNA sequences. "Isolated substantially away from other coding sequences" means that the gene of interest forms the significant part of the coding region of the DNA segment, and that the DNA segment does not contain large portions of naturally-occurring coding DNA, such as large chromosomal fragments or other functional genes or cDNA coding regions. Of course, this refers to the DNA segment as originally isolated, and does not exclude genes or coding regions, such as sequences encoding leader peptides or targeting sequences, later added to the segment by the hand of man.

The present invention does not require that highly purified DNA or vectors be used, so long as any coding segment employed encodes a selected protein or RNA and does not include any coding or regulatory sequences that would have a significant adverse effect on the target cells. Therefore, it will also be understood that useful nucleic acid sequences may include additional residues, such as additional non-coding sequences flanking either of the 5' or 3' portions of the coding region or may include various internal sequences, i.e., introns, that are known to occur within genes.

Many suitable DNA segments may be obtained from existing, including commercial sources. One may also obtain a new DNA segment encoding a protein of interest using any one or more of a variety of molecular biological techniques generally known to those skilled in the art. For example, cDNA or genomic libraries may be screened using primers or probes with designed sequences. Polymerase chain reaction (PCR) may also be used to generate a DNA fragment encoding a protein of interest.

After identifying an appropriate selected gene or DNA molecule, it may be inserted into any one of the many vectors currently known in the art, so that it will direct the expression and production of the selected protein when incorporated into a target cell. In a recombinant expression vector, the coding portion of the DNA segment is positioned under the control of a promoter/enhancer element. The promoter may be in the, form of the promoter that is naturally associated with a selected gene, as may be obtained by isolating the 5' non-coding sequences located upstream of the coding segment or exon, for example, using recombinant cloning and/or PCR technology.

In other embodiments, it is contemplated that certain advantages will be gained by positioning the coding DNA segment under the control of a recombinant, or heterologous, promoter. As used herein, a recombinant or heterologous promoter is intended to refer to a promoter that is not normally associated with a selected gene in its natural environment. Such promoters may include those normally associated with other selected genes, and/or promoters isolated from any other bacterial, viral, eukaryotic, or mammalian cell. Naturally, it will be important to employ a promoter that effectively directs the expression of the DNA segment in the chosen target cells.

The use of recombinant promoters to achieve protein expression is generally known to those of skill in the art of molecular biology, for example, see Sambrook et al. (1989; incorporated herein by reference). The promoters employed may be constitutive, or inducible, and can be used under the appropriate conditions to direct high level or regulated expression of the introduced DNA segment. Expression of genes under the control of constitutive promoters does not require the presence of a specific substrate to induce gene expression and will occur under all conditions of cell growth. In contrast, expression of genes controlled by inducible promoters is responsive to the presence or absence of an inducing agent.

Promoters isolated from the genome of viruses that grow in mammalian cells, e.g., RSV, vaccinia virus 7.5K, SV40, HSV, adenoviruses MLP, MMTV LTR and CMV promoters, may be used herewith, as well as promoters produced by recombinant DNA or synthetic techniques. Currently preferred promoters are those such as CMV, RSV LTR, the SV40 promoter alone, and the SV40 promoter in combination with the SV40 enhancer.

Exemplary tissue specific promoter/enhancer elements and transcriptional control regions that exhibit tissue specificity include, but are not limited to: the elastase I gene control region that is active in pancreatic acinar cells; the insulin gene control region that is active in pancreatic cells; the immunoglobulin gene control region that is active in lymphoid cells; the albumin, 1-antitrypsin and -fetoprotein gene control regions that are active in liver; the -globin gene control region that is active in myeloid cells; the myelin basic protein gene control region that is active in oligodendrocyte cells in the brain; the myosin light chain-2 gene control region that is active in skeletal muscle; and the gonadotropic releasing hormone gene control region that is active in the hypothalamus. U.S. application Ser. No. 08/631,334, filed Apr. 12, 1996 and PCT Application Serial No. PCT/US97/07301, filed Apr. 11, 1997, are both incorporated herein by reference for the purposes of incorporating references even further describing the foregoing elements.

Specific initiation signals may also be required for sufficient translation of inserted protein coding sequences. These signals include the ATG initiation codon and adjacent sequences. In cases where the entire coding sequence, including the initiation codon and adjacent sequences are inserted into the appropriate expression vectors, no additional translational control signals may be needed. However, in cases where only a portion of the coding sequence is inserted, exogenous translational control signals, including the ATG initiation codon should be provided. The initiation codon must be in phase with the reading frame of the protein coding sequences to ensure translation of the entire insert. These exogenous translational control signals and initiation codons can be of a variety of origins, both natural and synthetic. The efficiency and control of expression may be enhanced by the inclusion of transcription attenuation sequences, enhancer elements, etc.

A variety of vectors may be used including, but not limited to, those derived from recombinant bacteriophage DNA, plasmid DNA or cosmid DNA. For example, plasmid vectors such as pBR322, pUC 19/18, pUC 118, 119 and the M13 mp series of vectors may be used. Bacteriophage vectors may include gt10, gt11, gt18-23, ZAP/R and the EMBL series of bacteriophage vectors. Cosmid vectors that may be utilized include, but are not limited to, pJB8, pCV 103, pCV 107, pCV 108, pTM, pMCS, pNNL, pHSG274, COS202, COS203, pWE15, pWE16 and the charomid 9 series of vectors. Vectors that allow for the in vitro transcription of RNA, such as SP6 vectors, may also be used to produce large quantities of RNA that may be incorporated into matrices.

The selected genes and DNA segments may also be in the form of a DNA insert located within the genome of a recombinant virus, such as, for example a recombinant herpes virus, retroviruses, vaccinia viruses, adenoviruses, adeno-associated viruses or bovine papilloma virus. While integrating vectors may be used, non-integrating systems, which do not transmit the gene product to daughter cells for many generations will often be preferred. In this way, the gene product is expressed during a defined biological process, e.g., a wound healing process, and as the gene is diluted out in progeny generations, the amount of expressed gene product is diminished.

In such embodiments, to place the gene in contact with a target cell, one would prepare the recombinant viral particles, the genome of which includes the gene insert, and contact the target cells or tissues via release from the polymer fiber of the present invention, whereby the virus infects the cells and transfers the genetic material. The following U.S. patents are each incorporated herein by reference for even further exemplification of viral gene therapy: U.S. Pat. No. 5,747,469, concerning adenovirus, retrovirus, adeno-associated virus, herpes virus and cytomegalovirus gene therapy; U.S. Pat. No. 5,631,236, concerning adenovirus gene therapy; and U.S. Pat. No. 5,672,344, concerning herpesvirus gene therapy.

Genes with sequences that vary from those described in the literature are also contemplated for use in the invention, so long as the altered or modified gene still encodes a protein that functions to effect the target cells in the desired (direct or indirect) manner. These sequences include those caused by point mutations, those due to the degeneracies of the genetic code or naturally occurring allelic variants, and further modifications that have been introduced by genetic engineering, i.e., by the hand of man.

Techniques for introducing changes in nucleotide sequences that are designed to alter the functional properties of the encoded proteins or polypeptides are well known in the art, e.g., U.S. Pat. No. 4,518,584, incorporated herein by reference, which techniques are also described in further detail herein. Such modifications include the deletion, insertion or substitution of bases, and thus, changes in the amino acid sequence. Changes may be made to increase the activity of a protein, to increase its biological stability or half-life, to change its glycosylation pattern, confer temperature sensitivity or to alter the expression pattern of the protein, and the like. All such modifications to the nucleotide sequences are encompassed by this invention.

It is an advantage of the present invention that one or more than one selected gene may be used in the gene transfer methods and compositions. The nucleic acid delivery methods may thus entail the administration of one, two, three, or more, selected genes. The maximum number of genes that may be applied is limited only by practical considerations, such as the effort involved in simultaneously preparing a large number of gene constructs or even the possibility of eliciting an adverse cytotoxic effect. The particular combination of genes may be chosen to alter the same, or different, biochemical pathways. For example, a growth factor gene may be combined with a hormone gene; or a first hormone and/or growth factor gene may be combined with a gene encoding a cell surface receptor capable of interacting with the polypeptide product of the first gene.

In using multiple genes, they may be combined on a single genetic construct under control of one or more promoters, or they may be prepared as separate constructs of the same of different types. Thus, an almost endless combination of different genes and genetic constructs may be employed. Certain gene combinations may be designed to, or their use may otherwise result in, achieving synergistic effects on cell stimulation and tissue growth, any and all such combinations are intended to fall within the scope of the present invention. Indeed, many synergistic effects have been described in the scientific literature, so that one of ordinary skill in the art would readily be able to identify likely synergistic gene combinations, or even gene-protein combinations.

It will also be understood that, if desired, the nucleic segment or gene could be administered in combination with further agents, such as, e.g. proteins or polypeptides or various pharmaceutically active agents. So long as genetic material forms part of the composition, there is virtually no limit to other components which may also be included, given that the additional agents do not cause a significant adverse effect upon contact with the target cells or tissues. The nucleic acids may thus be delivered along with various other agents, for example, in certain embodiments one may wish to administer an angiogenic factor as disclosed in U.S. Pat. No. 5,270,300 and incorporated herein by reference.

As the chemical nature of genes, i.e., as a string of nucleotides, is essentially invariant, and as the process of gene transfer and expression are fundamentally the same, it will be understood that the type of genes transferred by the fiber matrices of the present invention is virtually limitless. This extends from the transfer of a mixture of genetic material expressing antigenic or immunogenic fragments for use in DNA vaccination; to the stimulation of cell function, as in wound-healing; to aspects of cell killing, such as in transferring tumor suppressor genes, antisense oncogenes or apoptosis-inducing genes to cancer cells.

By way of example only, genes to be supplied by the invention include, but are not limited to, those encoding and expressing: hormones, growth factors, growth factor receptors, interferons, interleukins, chemokines, cytokines, colony stimulating factors and chemotactic factors; transcription and elongation factors, cell cycle control proteins, including kinases and phosphatases, DNA repair proteins, apoptosis-inducing genes; apoptosis-inhibiting genes, oncogenes, antisense oncogenes, tumor suppressor genes; angiogenic and anti-angiogenic proteins; immune response stimulating and modulating proteins; cell surface receptors, accessory signaling molecules and transport proteins; enzymes; and anti-bacterial and anti-viral proteins.

F. Kits

All the essential materials and reagents required for the various aspects of the present invention may be assembled together in a kit. The kits of the present invention also will typically include a means for containing the vials comprising the desired components in close confinement for commercial sale such as, e.g., injection or blow-molded plastic containers into which the desired vials are retained. Irrespective of the number or type of containers, the kits of the invention are typically packaged with instructions for use of the kit components.
 

Claim 1 of 10 Claims

1. A method of fabricating fibers with a linear gradient of biomolecules, said method comprising: a) obtaining a first polymer solution comprising a first biodegradable polymer at a concentration between 5 to 30 wt % and a first solvent, and a second polymer solution comprising a second biodegradable polymer; and b) mixing said first polymer solution and said second polymer solution in a continuously changing ratio to obtain a mixture of said first and second polymer solutions, while extruding said mixture into a coagulating bath, wherein the coagulating bath comprises a second solvent that is miscible with the first solvent and is a non-solvent for the first and second polymers, and wherein at least one of said first polymer solution and said second polymer solution is a surfactant stabilized water-in-oil type emulsion of an aqueous phase comprising a biomolecule of interest.

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