Biomedical subjects

Molly S Shoichet

Publications and source records attributed to Molly S Shoichet.

At least 19 recordsLinked to original sources

PubMed2006

Synthesis of cell-adhesive dextran hydrogels and macroporous scaffolds.

Dextran hydrogels have been previously investigated as drug delivery vehicles and more recently as macroporous scaffolds; however, the non-cell-adhesive nature of dextran has limited its utility for tissue engineering. To overcome this limitation, macroporous scaffolds of methacrylated dextran (Dex-MA) copolymerized with aminoethyl methacrylate (AEMA) were synthesized, thereby introducing primary amine groups for covalent immobilization of extracellular-matrix-derived peptides. The amino group density for hydrogels copolymerized with 0.5 wt% AEMA was found to be 36.1+/-0.4 micromol/cm(3) by elemental analysis. To further enhance cellular interaction, poly(Dex-MA-co-AEMA) hydrogels were modified with either CRGDS or a mixture of CDPGYIGSR and CQAASIKVAV (1:1, v/v) using sulfo-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC). The immobilized peptide concentration was determined using amino acid analysis at: 2.6+/-0.9 micromol/cm(3) for CRGDS-derived hydrogels and 2.2+/-0.3 micromol/cm(3) plus 1.9+/-0.2 micromol/cm(3) for CDPGYIGSR plus CQAASIKVAV-derived hydrogels, respectively. Cellular interactions of primary embryonic chick dorsal root ganglia (DRGs) were compared on the hydrogels. Cell adhesion and neurite outgrowth on poly(Dex-MA) increased with copolymerization of AEMA and further improved with peptide modification and significantly for CDPGYIGSR/CQAASIKVAV-derived poly(Dex-MA-co-AEMA) hydrogels. Moreover, DRGs penetrated within the first 600 microm of the scaffolds, thereby demonstrating the potential of this scaffold for guided cell and axonal regeneration in vivo.

Adhesives↗

PubMed2006

Complete spinal cord transection treated by implantation of a reinforced synthetic hydrogel channel results in syringomyelia and caudal migration of the rostral stump.

OBJECTIVE: Previously, we reported that synthetic poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) channels promoted regeneration of a small number of axons from brainstem motor nuclei yet provided limited functional recovery after complete spinal cord transection at T8 in rats. However, we found that these modulus channels partially collapsed over time. Therefore, we synthesized coil-reinforced PHEMA or PHEMA-MMA channels with greater elastic moduli and introduced a new spinal fixation technique to prevent collapse. We also assessed axonal regeneration within the new channels containing a cocktail of autologous peripheral nerve grafts, fibrin matrix, and acidic fibroblast growth factor. METHODS: After spinal cord transection, rats were divided into six groups: Groups 1 and 2 had either a PHEMA or PHEMA-MMA reinforced channel implanted between the stumps of the transected spinal cord with the cocktail; Groups 3 and 4 had either an unfilled reinforced PHEMA or PHEMA-MMA channel similarly implanted; Group 5 had an spinal cord transection without channel implanted, and Group 6 underwent the identical procedure to Group 1, but rats were sacrificed by 8 weeks for early histological assessment. Groups 1 to 5 were sacrificed at 18 weeks. RESULTS: There was no channel collapse at any time. However, there was no improvement in axonal regeneration or functional recovery among Groups 1 to 4 because of the unexpected development of syringomyelia and caudal migration of the rostral stump. Functional recovery was better in Groups 1 to 4 compared with Group 5 (P < 0.05). CONCLUSION: The use of channels to enhance regeneration of axons is promising; however, improvement of the design of the channels is required.

Animals↗

PubMed2005

Incorporation of protein-eluting microspheres into biodegradable nerve guidance channels for controlled release.

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.

Algorithms↗

PubMed2005

Fast-gelling injectable blend of hyaluronan and methylcellulose for intrathecal, localized delivery to the injured spinal cord.

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.

Animals↗

PubMed2005

Nerve guidance channels as drug delivery vehicles.

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.

Capsules↗

PubMed2005

Coil-reinforced hydrogel tubes promote nerve regeneration equivalent to that of nerve autografts.

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.

Action Potentials↗

PubMed2005

Matrix inclusion within synthetic hydrogel guidance channels improves specific supraspinal and local axonal regeneration after complete spinal cord transection.

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.

Animals↗

PubMed2005

Controlling cell adhesion and degradation of chitosan films by N-acetylation.

As part of our ongoing effort to develop a biodegradable nerve guidance channel based on chitin/chitosan, we conducted a systematic in vitro study on the biodegradation and neural cell compatibility of chitosan and N-acetylated chitosan. The in vitro degradation (pH 7.4, 37 degrees C) in the presence of 1.5 microg/ml lysozyme showed a progressive mass loss to greater than 50% within 4 weeks for films with 30-70% acetylation. In contrast, the degradation of samples with very low or high acetylation was minimal over the 4-week period. Neural cell compatibility of chitosan and N-acetylated chitosan was tested using primary chick dorsal root ganglion (DRG) neurons. All chitosan-based films showed DRG cell adhesion after 2 days of culture. However, cell viability decreased with increasing acetylation. Chitosan that was 0.5% acetylated had the greatest cell viability, which was approximately 8 times higher than that of chitosan that was 11% acetylated. Chitosan with 0.5% and 11% acetylation showed more and longer neurites than the other samples studied. Thus chitosan amine content can be tuned for optimal biodegradation and cell compatibility, which are important for tissue engineering in the nervous system.

Acetylation↗

PubMed2005

Chitin-based tubes for tissue engineering in the nervous system.

The purpose of this study was to investigate chitin and chitosan as potential materials for biodegradable nerve guides. Transparent chitin hydrogel tubes were synthesized, for the first time, from chitosan solutions using acylation chemistry and mold casting techniques. Alkaline hydrolysis of chitin tubes resulted in chitosan tubes, with the extent of hydrolysis controlling the resulting amine content. This, in turn, impacted compressive strength and cell adhesion. Chitosan tubes were mechanically stronger than their chitin origins, as measured by the transverse compressive test, where tubes having degrees of acetylation of 1%, 3%, 18% (i.e. chitosan) and 94% (i.e. chitin) supported loads at a 30% displacement of 40.6 +/- 4.3, 25.3 +/- 4.5, 10.6 +/- 0.8, and 8.7 +/- 0.4 g, respectively. However, the chitin processing methodology could be optimized for compressive strength, by either incorporating reinforcing coils in the tube wall, or air-drying the hydrogel tubes. Chitin and chitosan supported adhesion and differentiation of primary chick dorsal root ganglion neurons in vitro. Chitosan films showed significantly enhanced neurite outgrowth relative to chitin films, reflecting the dependence of nerve cell affinity on the amine content in the polysaccharide: neurites extended 1794.7 +/- 392.0 microm/mm(2) on chitosan films vs. 140.5 +/- 41.6 microm/mm(2) on chitin films after 2 days of culture. This implies that cell adhesion and neurite extension can be adjusted by amine content, which is important for tissue engineering in the nervous system. The methods for easy processing and modification of chitin and chitosan described herein, allow the mechanical properties and cyto-compatibility to be controlled and provide a means for a broader investigation into their use in biomedical applications.

Animals↗

PubMed2005

Guided cell adhesion and outgrowth in peptide-modified channels for neural tissue engineering.

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.

Adsorption↗

PubMed2005

Long-term in vivo biomechanical properties and biocompatibility of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) nerve conduits.

Artificial grafts are promising alternatives to nerve grafts for peripheral nerve repair because they obviate the complications and disadvantages associated with autografting such as donor site morbidity and limited tissue availability. We have synthesized poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) porous tubes and studied their efficacy in vivo. Specifically, we studied the short- and long-term stability and biocompatibility of 12 mm long tubes for the repair of surgically created 10 mm nerve gaps in rat sciatic nerves. Prior to implantation, tubes were analyzed in vitro using a micro-mechanical tester to measure displacement achieved with load applied. These results served as a calibration curve, y = 6.8105 x -0.0073 (R2 = 0.9750, n = 28), for in vivo morphometric tube compression measurements. In vivo, most of the PHEMA-MMA conduits maintained their structural integrity up to 8 weeks, but 29% (4/14) of them collapsed by 16 weeks. Interestingly, the tube wall area of collapsed 16-week tubes was significantly lower than those of patent tubes. Tubes were largely biocompatible; however, a small subset of 16-week tubes displayed signs of chronic inflammation characterized by "finger-like" tissue extensions invading the inner tube aspect, inflammatory cells (some of which were ED1+macrophages) and giant cells. Tubes also demonstrated signs of calcification, which increased from 8 to 16 weeks. To overcome these issues, future nerve conduits will be re-designed to be more robust and biocompatible.

Animals↗

PubMed2005

Synthesis of degradable poly(L-lactide-co-ethylene glycol) porous tubes by liquid-liquid centrifugal casting for use as nerve guidance channels.

Biodegradable nerve guidance channels are advantageous, obviating the need for their removal after regeneration; however, most channels lack the appropriate mechanical properties for soft tissue implantation and/or degrade too quickly, resulting in reduced regeneration and necessitating the need for the design of polymers with tunable degradation profiles and mechanical properties. We designed a series of biodegradable polymeric hydrogel tubes consisting of L-lactide (LLA) and polyethylene glycol (PEG) where both the ratio of LLA to PEG and PEG molar mass were varied. By adjusting the PEG:LLA ratio and the molecular weight of the PEG oligomer we were able to control degradation and mechanical properties of our polymers. By incorporating methacrylate (MA) groups on both termini of the linear oligomers, porous tubes were synthesized by a redox-initiated free radical mechanism during a liquid-liquid centrifugal casting process. The tube wall had a bead-like morphology, as determined by SEM, which was reminiscent of previous porous hydrogel tubes synthesized by the same method. Tubes swelled with degradation to 160 vol%, or 640 wt%, and an increased radius calculated at 1.26 times. Those tubes with greater PEG content and PEG molar mass degraded faster than those with greater LLA content, as was expected. Interestingly, the wall morphology changed with degradation to a fiber-like structure and the mechanical properties decreased with degradation. By correlating the accelerated degradation study to a physiologic one, these porous hydrogel tubes were stable for an equivalent of 1.5 months, after which the mechanical properties began to deteriorate. This study demonstrates how porous hydrogel tubes can be designed to meet tissue regeneration criteria by tuning the formulation chemistry and specifically how the ratio of hydrophobic/crystalline LLA and hydrophilic/amorphous PEG impact tube properties.

Absorbable Implants↗

PubMed2005

Macroporous interconnected dextran scaffolds of controlled porosity for tissue-engineering applications.

Dextran hydrogels have been studied as drug delivery vehicles but not as scaffolds for tissue-engineering likely because previously synthesized dextran hydrogels had pores too small for cell penetration. Our goal was to create macroporous, interconnected dextran scaffolds. To this end, we took advantage of the liquid-liquid immiscibility of poly(ethylene glycol) and methacrylated dextran during radical crosslinking of the methacrylated moieties. By controlling the degree of methacrylate substitution on dextran, dextran molar mass and PEG concentration, macroporous hydrogels were created. The presence of PEG in solution had a significant effect on the final morphology of the dextran hydrogel leading to the formation of different types of structures, from microporous gel to macroporous gel-wall to a macroporous interconnected-beaded structure. A series of formulation diagrams were prepared which allowed us to determine which conditions led to the formation of macroporous interconnected-beaded scaffolds. Dextran macroporous interconnected-beaded gels had a high water content, between 89% and 94%, a homogeneous morphology, determined by scanning electron microscopy, with interconnected macroporous pores, as determined by protein diffusivity where the effective diffusion coefficients of BSA were calculated to be 3.1 x 10(-7)cm2/s for Dex-MA 40 kDa DS 5 and 1 x 10(-7)cm2/s for Dex-MA 6 kDa DS10, which are similar to that of BSA in water, 5.9 x 10(-7)cm2/s. Mercury intrusion porosimetry showed that the macroporous interconnected-beaded scaffolds had a bimodal distribution of macropores, with a median diameter of 41 microm, interconnected by throats, which had a median diameter of 11 microm. Together, these data suggest that the dextran scaffolds will be advantageous in applications that require an interconnected macroporous geometry, such as those of tissue engineering where cell penetration and nutrient diffusion are necessary for tissue regeneration.

Acrylates↗

PubMed2005

Thrombin mediated migration of osteogenic cells.

Given that thrombin is ubiquitously expressed at sites of vascular injury, and that osteogenic cells express receptors for thrombin, we questioned whether thrombin could attract osteogenic cells to a bony wound. Using a scratch wound assay, thrombin stimulated a significant increase in migration of osteogenic cultures of primary marrow cells. This effect was dependent on thrombin proteolytic activity; however, thrombin was unable to stimulate the migration of a more differentiated marrow-derived osteogenic cell line. To better understand the role of thrombin in osteoprogenitor migration, we developed an osteoprogenitor migration assay that combines a modified Boyden chamber with a bone nodule assay. Primary cells that migrated through the transwell filter in the presence of thrombin formed significantly more bone nodules compared to the condition without thrombin. This was not due to proliferation or differentiation effects of thrombin. In contrast, thrombin was unable to stimulate an increase in the number of nodules for the more differentiated osteogenic cell line. Thus, our results suggest that thrombin exhibits differential motogenic effects on osteogenic cells depending on their differentiation state. The cell migration/bone nodule assay described here is the first assay that can be specifically used to examine the effects of factors on the migration of osteoprogenitor cells, particularly those derived from primary populations.

Actins↗

PubMed2005

Injectable intrathecal delivery system for localized administration of EGF and FGF-2 to the injured rat spinal cord.

The administration of growth factors (GFs) for treatment of experimental spinal cord injury (SCI) has shown limited benefits. One reason may be the mode of delivery to the injury site. We have developed a minimally invasive and safe drug delivery system (DDS) consisting of a highly concentrated collagen solution that can be injected intrathecally at the site of injury providing localized delivery of GFs. Using the injectable DDS, epidermal growth factor (EGF) and basic fibroblast growth factor (FGF-2) were co-delivered in the subarachnoid space of Sprague-Dawley rats. The in vivo distribution of EGF and FGF-2 in both injured and uninjured animals was monitored by immunohistochemistry. Although significant differences in the distribution of EGF and FGF-2 in the spinal cord were evident, localized delivery of the GFs resulted in significantly less cavitation at the lesion epicenter and for at least 720 mum caudal to it compared to control animals without the DDS. There was also significantly more white matter sparing at the lesion epicenter in animals receiving the GFs compared to control animals. Moreover, at 14 days post-injection, delivery of the GFs resulted in significantly greater ependymal cell proliferation in the central canal immediately rostral and caudal to the lesion edge compared to controls. These results demonstrate that the injectable DDS provides a new paradigm for localized delivery of bioactive therapeutic agents to the injured spinal cord.

Animals↗

PubMed2005

Peripheral nerve regeneration through a synthetic hydrogel nerve tube.

PURPOSE: As alternatives to nerve grafts for peripheral nerve repair, we have synthesized 12 mm long poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) porous tubes and studied their regenerative capacity for the repair of surgically-created 10 mm rat sciatic nerve gaps. We compared the in vivo regenerative efficacy of these artificial tubes with the gold standard, the nerve autograft. METHODS: Tubes were assessed in vivo for their ability to support nerve regeneration at 4, 8, and 16 weeks post-implantation by histology, electrophysiology, histomorphometry, and reinnervated lateral gastrocnemius (LG) dry muscle mass. RESULTS: Axonal regeneration within the tubes was observed by 8 weeks, with outcome parameters comparable to autografts. This finding was further supported by the electrophysiological and histomorphometric results. The 16 week tube group had a bimodal response, with 60% of the tubes having a similar response to autografts and the other 40% having significantly lower (p < 0.05) outcome measures in several parameters. CONCLUSIONS: Axonal regeneration in artificial tubes was similar to that in autografts at 8 and 16 weeks, however, a bimodal distribution of regeneration was observed in 16 week tubes.

Action Potentials↗

PubMed2004

Fibrin-filled scaffolds for bone-tissue engineering: An in vivo study.

Recently, fibrin sealants that typically contain supra physiological concentrations of fibrinogen and thrombin have been investigated as matrices to facilitate the delivery of cells within biodegradable scaffolds for tissue engineering applications. It is well known from in vitro experiments that the thrombin concentration present during fibrin polymerization influences the structural properties of fibrin, and these can affect cell invasion. This study was conducted to determine whether the structural properties of fibrin can affect bony wound healing in vivo. Drill hole defects were created in the distal femurs of 20 rats. Four experimental groups were used: nontreated defects, scaffolds alone, and scaffolds filled with fibrin polymerized with either a low thrombin concentration [fibrin(low T)] or a high thrombin concentration [fibrin(high T)]. The area of bone formed at 2, 5, and 11 days after implantation was determined histomorphometrically. After 5 days, scaffolds filled with fibrin(high T) were infiltrated with less bone than empty scaffolds (p < 0.05), but no statistical difference was found between the empty scaffolds and the scaffolds filled with fibrin(low T). After 11 days, both fibrin-filled scaffolds significantly delayed bony wound healing (p < 0.004). Reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of the two fibrin formulations showed no difference in gamma-gamma crosslink formation. This work demonstrates that fibrin sealants in their present state are not ideal for enhancing bone-tissue invasion into scaffolds, and that the structural properties of fibrin matrices may be an important design parameter for maximizing host tissue invasion during wound healing.

Animals↗

PubMed2004

A photolabile hydrogel for guided three-dimensional cell growth and migration.

Tissue engineering aims to replace, repair or regenerate tissue/organ function, by delivering signalling molecules and cells on a three-dimensional (3D) biomaterials scaffold that supports cell infiltration and tissue organization. To control cell behaviour and ultimately induce structural and functional tissue formation on surfaces, planar substrates have been patterned with adhesion signals that mimic the spatial cues to guide cell attachment and function. The objective of this study is to create biochemical channels in 3D hydrogel matrices for guided axonal growth. An agarose hydrogel modified with a cysteine compound containing a sulphydryl protecting group provides a photolabile substrate that can be patterned with biochemical cues. In this transparent hydrogel we immobilized the adhesive fibronectin peptide fragment, glycine-arginine-glycine-aspartic acid-serine (GRGDS), in selected volumes of the matrix using a focused laser. We verified in vitro the guidance effects of GRGDS oligopeptide-modified channels on the 3D cell migration and neurite outgrowth. This method for immobilizing biomolecules in 3D matrices can generally be applied to any optically clear hydrogel, offering a solution to construct scaffolds with programmed spatial features for tissue engineering applications.

Animals↗