101
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Moore K, MacSween M, Shoichet M. Immobilized concentration gradients of neurotrophic factors guide neurite outgrowth of primary neurons in macroporous scaffolds. ACTA ACUST UNITED AC 2006; 12:267-78. [PMID: 16548685 DOI: 10.1089/ten.2006.12.267] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Neurotrophic factors present as concentration gradients are neurotropic cues that direct axonal growth toward their targets. Multiple factors work together in vivo to ensure axons reach the proper targets, likely interacting with one another via intracellular signalling pathways. Nerve growth factor (NGF) and neurotrophin-3 (NT-3) are neurotrophins known to guide axons as well as promote axonal growth following injury to both the spinal cord and peripheral nerve. These molecules interact with neurons through different tyrosine kinase receptors. In this study, the receptors for these growth factors were shown to be co-localized on E10 chick dorsal root ganglion (DRG) cells, providing an opportunity for synergism. Well-defined concentration gradients of NGF and NT-3 were immobilized for the first time in a cell-penetrable, cell-adhesive scaffold of poly(2-hydroxyethylmethacrylate) and poly(L-lysine). An NGF concentration gradient of 310 ng/mL/mm was required to guide chick DRG neurites. A lower concentration gradient of 200 ng/mL/mm of NGF was shown to elicit guidance when an NT-3 concentration gradient of 200 ng/mL/mm was also present, indicating a synergistic response in the DRG neurons. These gradient scaffolds may be useful for guided regeneration following injury to the spinal cord or peripheral nerve and may also elucidate the mechanism for intracellular signaling of neurotrophic factors.
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Affiliation(s)
- Kathryn Moore
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Ontario, Canada
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102
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Abstract
This article reviews bioengineered strategies for spinal cord repair using tissue engineered scaffolds and drug delivery systems. The pathophysiology of spinal cord injury (SCI) is multifactorial and multiphasic, and therefore, it is likely that effective treatments will require combinations of strategies such as neuroprotection to counteract secondary injury, provision of scaffolds to replace lost tissue, and methods to enhance axonal regrowth, synaptic plasticity, and inhibition of astrocytosis. Biomaterials have major advantages for spinal cord repair because of their structural and chemical versatility. To date, various degradable or non-degradable biomaterial polymers have been tested as guidance channels or delivery systems for cellular and non-cellular neuroprotective or neuroregenerative agents in experimental SCI. There is promise that bioengineering technology utilizing cellular treatment strategies, including Schwann cells, olfactory ensheathing glia, or neural stem cells, can promote repair of the injured spinal cord. This review is divided into three parts: (1) degradable and non-degradable biomaterials; (2) device design; and (3) combination strategies with scaffolds. We will show that bioengineering combinations of cellular and non-cellular strategies have enhanced the potential for experimental SCI repair, although further pre-clinical work is required before this technology can be translated to humans.
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Affiliation(s)
- Hiroshi Nomura
- Toronto Western Research Institute, Toronto Western Hospital and University of Toronto, Toronto, Ontario, Canada
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103
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Steward O, Sharp K, Selvan G, Hadden A, Hofstadter M, Au E, Roskams J. A re-assessment of the consequences of delayed transplantation of olfactory lamina propria following complete spinal cord transection in rats. Exp Neurol 2006; 198:483-99. [PMID: 16494866 DOI: 10.1016/j.expneurol.2005.12.034] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Revised: 11/30/2005] [Accepted: 12/19/2005] [Indexed: 11/17/2022]
Abstract
This study is part of the NIH "Facilities of Research-Spinal Cord Injury" contract to support independent replication of published studies. We repeated a study reporting that delayed transplantation of olfactory lamina propria (OLP) into the site of a complete spinal cord transection led to significant improvement in hindlimb motor function and induced axon regeneration. Adult female rats received complete spinal cord transections at T10. Thirty days post-injury, pieces of OLP, which contains olfactory ensheathing cells (OECs), or respiratory lamina propria (RLP), which should not contain OECs, were placed into the transection site. Hindlimb motor function was tested using the BBB scale from day 1 post-injury through 10 weeks following transplantation. To assess axonal regeneration across the transection site, Fluorogold was injected into the distal segment, and the distribution of 5HT-containing axons was assessed using immunostaining. BBB analyses revealed no significant recovery after OLP transplantation and no significant differences between OLP vs. RLP transplant groups. Fluorogold injections into caudal segments did not lead to retrograde labeling in any animals. Immunostaining for 5HT revealed that a few 5HT-labeled axons extended into both RLP and OLP transplants and a few 5HT-labeled axons were present in sections caudal to the injury in 2 animals that received OLP transplants and 1 animal that received RLP transplants. Our results indicate that, although OLP transplants may stimulate regeneration under some circumstances, the effect is not so robust as to reliably overcome the hostile setting created by a complete transection paradigm.
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Affiliation(s)
- Oswald Steward
- Reeve-Irvine Research Center, University of California at Irvine School of Medicine, Department of Anatomy and Neurobiology, 1105 Gillespie Neuroscience Research Facility, Irvine, CA 92697-4292, USA.
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104
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Moss JA, Stokols S, Hixon M, Ashley F, Chang JY, Janda KD. Solid-phase synthesis and kinetic characterization of fluorogenic enzyme-degradable hydrogel cross-linkers. Biomacromolecules 2006; 7:1011-6. [PMID: 16602715 PMCID: PMC2546486 DOI: 10.1021/bm051001s] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Of critical importance in drug delivery and tissue engineering applications is the degradability of implanted polymeric materials. The use of peptide-derived cross-linkers in hydrogel design is a valuable approach by which polymeric carriers can be endowed with enzymatic degradability in a predictable, "programmable" fashion. The solid-phase synthesis strategy described herein allows for an expeditious, flexible synthesis of bis-acrylamide-derivatized peptides with complex modifications, as exemplified by the incorporation of fluorophore and quencher moieties into a matrix metalloprotease (MMP)-degradable cross-linker. The crude synthetic product was obtained in high yield and purity and purified by standard methods; it was then used directly for polymerization without the need for tedious and often nonchemoselective solution-phase modifications. Functional appendages incorporated for detection provided a direct, quantitative link between enzymatic activity and hydrogel degradation using routine methods for identification of optimal enzyme-specific degradability.
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Affiliation(s)
| | - Shula Stokols
- Department of Chemistry and The Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037
| | - Mark Hixon
- Department of Chemistry and The Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037
| | - Fawn Ashley
- Department of Chemistry and The Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037
| | - Jason Y. Chang
- Department of Chemistry and The Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037
| | - Kim D. Janda
- Department of Chemistry and The Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037
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105
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Piotrowicz A, Shoichet MS. Nerve guidance channels as drug delivery vehicles. Biomaterials 2006; 27:2018-27. [PMID: 16239029 DOI: 10.1016/j.biomaterials.2005.09.042] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2005] [Accepted: 09/26/2005] [Indexed: 11/18/2022]
Abstract
Nerve guidance channels (NGCs) have been shown to facilitate regeneration after transection injury to the peripheral nerve or spinal cord. Various therapeutic molecules, including neurotrophic factors, have improved regeneration and functional recovery after injury when combined with NGCs; however, their impact has not been maximized partly due to the lack of an appropriate drug delivery system. To address this limitation, nerve growth factor (NGF) was incorporated into NGCs of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate), P(HEMA-co-MMA). The NGCs were synthesized by a liquid-liquid centrifugal casting process and three different methods of protein incorporation were compared in terms of protein distribution and NGF release profile: (1) NGF was encapsulated (with BSA) in biodegradable poly(d,l-lactide-co-glycolide) 85/15 microspheres, which were combined with a PHEMA polymerization formulation and coated on the inside of pre-formed NGCs by a second liquid-liquid centrifugal casting technique; (2) pre-formed NGCs were imbibed with a solution of NGF/BSA and (3) NGF/BSA alone was combined with a PHEMA formulation and coated on the inside of pre-formed NGCs by a second liquid-liquid centrifugal casting technique. Using a fluorescently labelled model protein, the distribution of proteins in NGCs prepared with a coating of either protein-loaded microspheres or protein alone was found to be confined to the inner PHEMA layer. Sustained release of NGF was achieved from NGCs with either NGF-loaded microspheres or NGF alone incorporated into the inner layer, but not from channels imbibed with NGF. By day 28, NGCs with microspheres released a total of 220 pg NGF/cm of channel whereas those NGCs imbibed with NGF released 1040 pg/cm and those NGCs with NGF incorporated directly in a PHEMA layer released 8624 pg/cm. The release of NGF from NGCs with microspheres was limited by a slow-degrading microsphere formulation and by the maximum amount of microspheres that could be incorporated into the NGCs structure. Notwithstanding, the liquid-liquid centrifugal casting process is promising for localized and controlled release of multiple factors that are key to tissue regeneration.
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Affiliation(s)
- Alexandra Piotrowicz
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College St., Toronto, Ont., Canada
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106
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Katayama Y, Montenegro R, Freier T, Midha R, Belkas JS, Shoichet MS. Coil-reinforced hydrogel tubes promote nerve regeneration equivalent to that of nerve autografts. Biomaterials 2006; 27:505-18. [PMID: 16125771 DOI: 10.1016/j.biomaterials.2005.07.016] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2005] [Accepted: 07/11/2005] [Indexed: 10/25/2022]
Abstract
Despite spontaneous sprouting of peripheral axons after transection injury, peripheral regeneration is incomplete and limited to short gaps, even with the use of autograft tissue, which is considered to be the "gold" standard. In an attempt to obviate some of the problems associated with autografts, including limited donor tissue and donor site morbidity, we aimed to synthesize a synthetic nerve guidance channel that would perform as well as the nerve autograft. Given that the patency of the nerve guidance channel is critical for repair, we investigated a series of nerve guidance channel designs where patency and the resulting regenerative capacity were compared in a transected rat sciatic nerve injury model. Three tube designs were compared to autograft tissue: plain, corrugated and coil-reinforced tubes of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate). Of the three designs, the coil-reinforced tubes demonstrated superior performance in terms of patency. By electrophysiology and histomorphometry, the coil-reinforced tubes demonstrated outcomes that were comparable to autografts after both 8 and 16 weeks of implantation. The nerve action potential (NAP) velocity and muscle action potential (MAP) velocity for the coil-reinforced PHEMA-MMA tube was 54.6+/-10.1 and 10.9+/-1.3 m/s, respectively at 16 weeks, which was statistically equivalent to those of the autograft at 37.5+/-7.9 and 11.3+/-2.0 m/s. The axon density in the coil-reinforced tube was 2.16+/-0.61x10(4) axons/mm2, which was statistically similar to that of the autograft of 2.41+/-0.62x10(4) axons/mm2 at 16 weeks. These coil-reinforced tubes demonstrated equivalence to autografts for nerve regeneration, demonstrating the importance of channel design to regenerative capacity and more specifically the impact of patency to regeneration.
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Affiliation(s)
- Yusuke Katayama
- matREGEN Corporation, 200 College Street, Suite 28, Toronto, Ont., Canada M5S 3E5
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107
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Tsai EC, Dalton PD, Shoichet MS, Tator CH. Matrix inclusion within synthetic hydrogel guidance channels improves specific supraspinal and local axonal regeneration after complete spinal cord transection. Biomaterials 2006; 27:519-33. [PMID: 16099035 DOI: 10.1016/j.biomaterials.2005.07.025] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2005] [Accepted: 07/12/2005] [Indexed: 01/28/2023]
Abstract
We have previously shown that a novel synthetic hydrogel channel composed of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (pHEMA-MMA) is biocompatible and supports axonal regeneration after spinal cord injury. Our goal was to improve the number and type of regenerated axons within the spinal cord through the addition of different matrices and growth factors incorporated within the lumen of the channel. After complete spinal cord transection at T8, pHEMA-MMA channels, having an elastic modulus of 263+/-13 kPa were implanted into adult Sprague Dawley rats. The channels were then filled with one of the following matrices: collagen, fibrin, Matrigel, methylcellulose, or smaller pHEMA-MMA tubes placed within a larger pHEMA-MMA channel (called tubes within channels, TWC). We also supplemented selected matrices (collagen and fibrin) with neurotrophic factors, fibroblast growth factor-1 (FGF-1) and neurotrophin-3 (NT-3). After channel implantation, fibrin glue was applied to the cord-channel interface, and a duraplasty was performed with an expanded polytetrafluoroethylene (ePTFE) membrane. Controls included animals that had either complete spinal cord transection and implantation of unfilled pHEMA-MMA channels or complete spinal cord transection. Regeneration was assessed by retrograde axonal tracing with Fluoro-Gold, and immunohistochemistry with NF-200 (for total axon counts) and calcitonin gene related peptide (CGRP, for sensory axon counts) after 8 weeks survival. Fibrin, Matrigel, methylcellulose, collagen with FGF-1, collagen with NT-3, fibrin with FGF-1, and fibrin with NT-3 increased the total axon density within the channel (ANOVA, p<0.05) compared to unfilled channel controls. Only fibrin with FGF-1 decreased the sensory axon density compared to unfilled channel controls (ANOVA, p<0.05). Fibrin promoted the greatest axonal regeneration from reticular neurons, and methylcellulose promoted the greatest regeneration from vestibular and red nucleus neurons. With Matrigel, there was no axonal regeneration from brainstem motor neurons. The addition of FGF-1 increased the axonal regeneration of vestibular neurons, and the addition of NT-3 decreased the total number of axons regenerating from brainstem neurons. The fibrin and TWC showed a consistent improvement in locomotor function at both 7 and 8 weeks. Thus, the present study shows that the presence and type of matrix contained within synthetic hydrogel guidance channels affects the quantity and origin of axons that regenerate after complete spinal cord transection, and can improve functional recovery. Determining the optimum matrices and growth factors for insertion into these guidance channels will improve regeneration of the injured spinal cord.
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Affiliation(s)
- Eve C Tsai
- Toronto Western Hospital Research Institute and Krembil Neuroscience Centre, University of Toronto, Toronto, Ontario, Canada M5T 2S8
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108
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Goraltchouk A, Scanga V, Morshead CM, Shoichet MS. Incorporation of protein-eluting microspheres into biodegradable nerve guidance channels for controlled release. J Control Release 2006; 110:400-407. [PMID: 16325953 DOI: 10.1016/j.jconrel.2005.10.019] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2005] [Revised: 10/18/2005] [Accepted: 10/25/2005] [Indexed: 11/27/2022]
Abstract
Nerve guidance channels (NGCs) promote axonal regeneration after transection injury of the peripheral nerve or spinal cord, yet this regeneration is limited. To enhance regeneration further, we hypothesize that localized delivery of therapeutic molecules combined with the NGC is required. In an attempt to achieve such an NGC, we designed and synthesized a novel NGC in which protein-encapsulated microspheres were stably incorporated into the tube wall. Specifically, poly(lactide-co-glycolide) (PLGA 50/50) microspheres were physically entrapped in the annulus between two concentric tubes, consisting of a chitosan inner tube and a chitin outer tube. Taking advantage of the extensive shrinking that the outer chitin tube undergoes with drying, >15 mg of microspheres were loaded within the tube walls. Using BSA-encapsulated microspheres as the model drug delivery system, BSA was released from microsphere loaded tubes (MLTs) for 84 days, and from freely suspended PLGA microspheres for 70 days. An initial burst release was observed for both MLTs and free microspheres, followed by a degradation-controlled release profile that resulted in a higher release rate from MLTs initially, which was then attenuated likely due to the buffering effect of chitin and chitosan tubes. Epidermal growth factor (EGF), co-encapsulated with BSA in PLGA 50/50 microspheres in MLTs, was released for 56 days with a similar profile to that of BSA. Released EGF was found to be bioactive for at least 14 days as assessed by a neurosphere forming bioassay.
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Affiliation(s)
- Alex Goraltchouk
- Department of Chemical Engineering and Applied Chemistry, University of Toronto 200 College Street, Toronto, ON, Canada M5S 3E5; Institute of Biomaterials and Biomedical Engineering, University of Toronto 4 Taddle Creek Road, Room 407, Toronto, ON, Canada M5S 3G9
| | - Vanessa Scanga
- Department of Surgery, University of Toronto, 1 King's College Circle-1182, Toronto, ON, Canada M5S 1A8
| | - Cindi M Morshead
- Department of Surgery, University of Toronto, 1 King's College Circle-1182, Toronto, ON, Canada M5S 1A8
| | - Molly S Shoichet
- Department of Chemical Engineering and Applied Chemistry, University of Toronto 200 College Street, Toronto, ON, Canada M5S 3E5; Department of Chemistry, 80 St. George St., Toronto, ON, Canada M5S 1AH; Institute of Biomaterials and Biomedical Engineering, University of Toronto 4 Taddle Creek Road, Room 407, Toronto, ON, Canada M5S 3G9.
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109
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Abstract
Biomaterials research in Canada began in the 1960s. Over the past four decades significant contributions have been made across a broad spectrum covering dental, orthopaedic, cardiovascular, neuro, and ocular biomaterials. Canadians have also been active in the derivative area of tissue engineering. Biomaterials laboratories are now established in universities and research institutes from coast to coast, supported mainly by funding from the Federal and Provincial Governments. The Canadian Biomaterials Society was formed in 1971 and has played an important role in the development of the field. The Society played host to the 5th World Biomaterials Congress in Toronto in 1996. The work of Canadian researchers over the past four decades is summarized briefly. It is concluded that biomaterials and tissue engineering is a mature, strong area of research in Canada and appears set to continue as such into the future.
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Affiliation(s)
- John L Brash
- School of Biomedical Engineering and Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L7.
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110
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Gupta D, Tator CH, Shoichet MS. Fast-gelling injectable blend of hyaluronan and methylcellulose for intrathecal, localized delivery to the injured spinal cord. Biomaterials 2005; 27:2370-9. [PMID: 16325904 DOI: 10.1016/j.biomaterials.2005.11.015] [Citation(s) in RCA: 412] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2005] [Accepted: 11/09/2005] [Indexed: 10/25/2022]
Abstract
Strategies for spinal cord injury repair are limited, in part, by poor drug delivery techniques. A novel drug delivery system (DDS) is being developed in our laboratory that can provide localized release of growth factors from an injectable gel. The gel must be fast-gelling, non-cell adhesive, degradable, and biocompatible as an injectable intrathecal DDS. A gel that meets these design criteria is a blend of hyaluronan and methylcellulose (HAMC). Unlike other injectable gels, HAMC is already at the gelation point prior to injection. It is injectable due to its shear-thinning property, and its gel strength increases with temperature. In vivo rat studies show that HAMC is biocompatible within the intrathecal space for 1 month, and may provide therapeutic benefit, in terms of behavior, as measured by the Basso, Beattie and Bresnahan (BBB) locomotor scale, and inflammation. These data suggest that HAMC is a promising gel for localized delivery of therapeutic agents to the injured spinal cord.
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Affiliation(s)
- Dimpy Gupta
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ont., Canada
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111
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Yang Y, De Laporte L, Rives CB, Jang JH, Lin WC, Shull KR, Shea LD. Neurotrophin releasing single and multiple lumen nerve conduits. J Control Release 2005; 104:433-46. [PMID: 15911044 PMCID: PMC2648409 DOI: 10.1016/j.jconrel.2005.02.022] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Revised: 02/20/2005] [Accepted: 02/25/2005] [Indexed: 01/06/2023]
Abstract
Tissue engineering strategies for nerve repair employ polymer conduits termed guidance channels and bridges to promote regeneration for peripheral nerve injury and spinal cord injury, respectively. An approach for fabrication of nerve conduits with single and multiple lumens capable of controlled release of neurotrophic factors was developed. These conduits were fabricated from a mixture of poly(lactide-co-glycolide) (PLG) microspheres and porogen (NaCl) that was loaded into a mold and processed by gas foaming. The porosity and mechanical properties of the constructs were regulated by the ratio of porogen to polymer microsphere. The neurotrophin, nerve growth factor (NGF), was incorporated into the conduit by either mixing the protein with microspheres or encapsulating the protein within microspheres prior to gas foaming. A sustained release was observed for at least 42 days, with the release rate controlled by method of incorporation and polymer molecular weight. Released NGF retained its bioactivity, as demonstrated by its ability to stimulate neurite outgrowth from primary dorsal root ganglion (DRG). In vivo results indicate that conduits retain their original architecture, and allow for cellular infiltration into the channels. Polymer conduits with controllable lumen diameters and protein release may enhance nerve regeneration by guiding and stimulating neurite outgrowth.
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Affiliation(s)
- Yang Yang
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States
| | - Laura De Laporte
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States
| | - Christopher B. Rives
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States
| | - Jae-Hyung Jang
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States
| | - Wei-Chun Lin
- Department of Materials Science, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States
| | - Kenneth R. Shull
- Department of Materials Science, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States
| | - Lonnie D. Shea
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States
- Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States
- Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, IL 60611, United States
- Corresponding author. Department of Chemical Engineering, Northwestern University, 2145 Sheridan Rd E156, Evanston, IL 60208-3120, United States. Tel.: +1 847 491 7043; fax: +1 847 491 3728. E-mail address: (L.D. Shea)
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112
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Stokols S, Tuszynski MH. Freeze-dried agarose scaffolds with uniaxial channels stimulate and guide linear axonal growth following spinal cord injury. Biomaterials 2005; 27:443-51. [PMID: 16099032 DOI: 10.1016/j.biomaterials.2005.06.039] [Citation(s) in RCA: 199] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2005] [Accepted: 06/30/2005] [Indexed: 10/25/2022]
Abstract
Although several approaches to stimulate axonal regeneration after spinal cord injury have succeeded in stimulating robust growth of axons into a lesion site, the growth is generally highly disorganized, losing the distinct arrangement of axonal tracts within the spinal cord. Previously described freeze-dried agarose scaffolds, composed of individual, uniaxial channels extending through their entire length, were prepared with and without recombinant Brain-Derived Neurotrophic Factor (BDNF) protein and tested in an adult rat model of spinal cord injury to determine whether regenerating axons could be guided across a site of injury in an organized fashion. After 1 month, both the cellular and axonal responses within and around scaffolds were evaluated. Scaffolds were found to be well integrated with host tissue, individual channels were penetrated by cells, and axons grew through scaffolds in a strikingly linear fashion. Furthermore, the regeneration was significantly augmented by the incorporation of BDNF protein into the walls and lumen of the scaffold. These findings clearly demonstrate that axonal regeneration can be organized and guided across a site of injury.
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Affiliation(s)
- Shula Stokols
- Department of Bioengineering, University of California-San Diego, La Jolla, CA 92093, USA
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113
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Yu TT, Shoichet MS. Guided cell adhesion and outgrowth in peptide-modified channels for neural tissue engineering. Biomaterials 2005; 26:1507-14. [PMID: 15522752 DOI: 10.1016/j.biomaterials.2004.05.012] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2004] [Accepted: 05/26/2004] [Indexed: 11/19/2022]
Abstract
A hydrogel scaffold of well-defined geometry was created and modified with laminin-derived peptides in an aqueous solution, thereby maintaining the geometry of the scaffold while introducing bioactive peptides that enhance cell adhesion and neurite outgrowth. By combining a fiber templating technique to create longitudinal channels with peptide modification, we were able to synthesize a scaffold that guided cell adhesion and neurite outgrowth of primary neurons. Scaffolds were designed to have numerous longitudinally oriented channels with an average channel diameter of 196 +/- 6 microm to ultimately promote fasciculation of regenerating cables and a compressive modulus of 192 +/- 8 kPa to match the modulus of the soft nerve tissue. Copolymerization of 2-hydroxylethyl methacrylate (HEMA) with 2-aminoethyl methacrylate (AEMA) scaffolds, provided primary amine groups to which two sulfhydryl terminated, laminin-derived oligopeptides, CDPGYIGSR and CQAASIKVAV, were covalently bound using the sulfo-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC) crosslinking agent. The concentration of peptides on the scaffolds was measured at 106 +/- 4 micromol/cm(2) using the ninhydrin method and 92 +/- 9 micromol/cm(2) using the BCA protein assay. The peptide modified P(HEMA-co-AEMA) scaffolds were easily fabricated in aqueous conditions, highly reproducible, well-defined, and enhanced neural cell adhesion and guided neurite outgrowth of primary chick dorsal root ganglia neurons relative to non-peptide-modified controls. The copolymerization of AEMA with HEMA can be extended to other radically polymerized monomers and is advantageous as it facilitates scaffold modification in aqueous solutions thereby obviating the use of organic solvents which can be cytotoxic and often disrupt scaffold geometry. The combination of well-defined chemical and physical stimuli described herein provides a means for guided regeneration both in vitro and in vivo.
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Affiliation(s)
- T Tina Yu
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
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114
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Ramer LM, Ramer MS, Steeves JD. Setting the stage for functional repair of spinal cord injuries: a cast of thousands. Spinal Cord 2005; 43:134-61. [PMID: 15672094 DOI: 10.1038/sj.sc.3101715] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Here we review mechanisms and molecules that necessitate protection and oppose axonal growth in the injured spinal cord, representing not only a cast of villains but also a company of therapeutic targets, many of which have yet to be fully exploited. We next discuss recent progress in the fields of bridging, overcoming conduction block and rehabilitation after spinal cord injury (SCI), where several treatments in each category have entered the spotlight, and some are being tested clinically. Finally, studies that combine treatments targeting different aspects of SCI are reviewed. Although experiments applying some treatments in combination have been completed, auditions for each part in the much-sought combination therapy are ongoing, and performers must demonstrate robust anatomical regeneration and/or significant return of function in animal models before being considered for a lead role.
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Affiliation(s)
- L M Ramer
- ICORD (International Collaboration on Repair Discoveries), The University of British Columbia, Vancouver, BC, Canada
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115
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Zhang N, Yan H, Wen X. Tissue-engineering approaches for axonal guidance. ACTA ACUST UNITED AC 2005; 49:48-64. [PMID: 15960986 DOI: 10.1016/j.brainresrev.2004.11.002] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2004] [Revised: 09/29/2004] [Accepted: 11/29/2004] [Indexed: 02/04/2023]
Abstract
Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.
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Affiliation(s)
- Ning Zhang
- Department of Bioengineering, Clemson University, BSB# 303, 173 Ashley Avenue, Charleston, SC 29425, USA
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