Extracting structural features of rat sciatic nerve using polarization-sensitive spectral domain optical coherence tomography

We present spectral domain polarization-sensitive optical coherence tomography (SD PS-OCT) imaging of peripheral nerves. Structural and polarization-sensitive OCT imaging of uninjured rat sciatic nerves was evaluated both qualitatively and quantitatively. OCT and its functional extension, PS-OCT, were used to image sciatic nerve structure with clear delineation of the nerve boundaries to muscle and adipose tissues. A long-known optical effect, bands of Fontana, was also observed. Postprocessing analysis of these images provided significant quantitative information, such as epineurium thickness, estimates of extinction coefficient and birefringence of nerve and muscle tissue, frequency of bands of Fontana at different stretch levels of nerve, and change in average birefringence of nerve under stretched condition. We demonstrate that PS-OCT combined with regular-intensity OCT (compared with OCT alone) allows for a clearer determination of the inner and outer boundaries of the epineurium and distinction of nerve and muscle based on their birefringence pattern. PS-OCT measurements on normal nerves show that the technique is promising for studies on peripheral nerve injury.

The tissue-engineered auricle: past, present, and future

The reconstruction, repair, and regeneration of the external auricular framework continue to be one of the greatest challenges in the field of tissue engineering. To replace like with like, we should emulate the native structure and composition of auricular cartilage by combining a suitable chondrogenic cell source with an appropriate scaffold under optimal in vitro and in vivo conditions. Due to the fact that a suitable and reliable substitute for auricular cartilage has yet to be engineered, hand-carved autologous costal cartilage grafts and ear-shaped porous polyethylene implants are the current treatment modalities for auricular reconstruction. However, over the last decade, significant advances have been made in the field of regenerative medicine and tissue engineering. A variety of scaffolds and innovative approaches have been investigated as alternatives to using autologous carved costal cartilage or porous polyethylene implants. A review of recent developments and the current state of the art and science is presented, focusing on scaffolds, cell sources, seeding densities, and mechanical characteristics of tissue-engineered auricular cartilage.

In vivo evaluation of demyelination and remyelination in a nerve crush injury model

Nerves of the peripheral nervous system have, to some extent, the ability to regenerate after injury, particularly in instances of crush or contusion injuries. After a controlled crush injury of the rat sciatic nerve, demyelination and remyelination are followed with functional assessments and imaged both ex vivo and in vivo over the course of 4 weeks with video-rate coherent anti-Stokes Raman scattering (CARS) microscopy. A new procedure compatible with live animal imaging is developed for performing histomorphometry of myelinated axons. This allows quantification of demyelination proximal and remyelination distal to the crush site ex vivo and in vivo respectively.

Implant-assisted meniscal repair in vivo using a chondrocyte-seeded flexible PLGA scaffold

A cell-based engineered construct can be used for healing of intractable meniscal lesions. Our aims were to assess the culture conditions (static versus dynamic oscillation) and the healing capacity of the chondrocyte-seeded flexible implants in a heterotopic mouse model. Swine articular chondrocytes were labeled with PKH 26 or DiI dye and seeded onto a flexible PLGA scaffold using dynamic oscillating conditions for 24 h. Half of cell-seeded scaffolds were cultured in the same dynamic conditions, while the remaining scaffolds were cultured statically. After 7 days, scaffolds were placed between swine meniscal discs and were implanted subcutaneously in nude mice for 6 weeks. Additional constructs for assessing in vivo cell tracking were implanted for 12 weeks. Live/dead assays demonstrated labeled chondrocytes attached throughout the scaffold in both culture conditions. DNA measurements showed no significant difference between the culture conditions. A continuous fibro-cartilaginous healing tissue was observed between meniscal discs in all 12 dynamically cultured constructs and 9 of 11 statically cultured ones. There was no evidence of meniscal healing using acellular scaffold as well as in meniscal constructs lacking an implant. Both PKH 26- and DiI-labeled cells were identified along the healing interface. We conclude the chondrocyte-seeded flexible PLGA implants induce healing of meniscal discs in nude mice. Culture conditions after seeding have no apparent effects on healing.

Engineering ear constructs with a composite scaffold to maintain dimensions

Engineered cartilage composed of a patient's own cells can become a feasible option for auricular reconstruction. However, distortion and shrinkage of ear-shaped constructs during scaffold degradation and neocartilage maturation in vivo have hindered the field. Scaffolds made of synthetic polymers often generate degradation products that cause an inflammatory reaction and negatively affect neocartilage formation in vivo. Porous collagen, a natural material, is a promising candidate; however, it cannot withstand the contractile forces exerted by skin and surrounding tissue during normal wound healing. We hypothesised that a permanent support in the form of a coiled wire embedded into a porous collagen scaffold will maintain the construct's size and ear-specific shape. Half-sized human adult ear-shaped fibrous collagen scaffolds with and without embedded coiled titanium wire were seeded with sheep auricular chondrocytes, cultured in vitro for up to 2 weeks, and implanted subcutaneously on the backs of nude mice. After 6 weeks, the dimensional changes in all implants with wire support were minimal (2.0% in length and 4.1% in width), whereas significant reduction in size occurred in the constructs without embedded wire (14.4% in length and 16.5% in width). No gross distortion occurred over the in vivo study period. There were no adverse effects on neocartilage formation from the embedded wire. Histologically, mature neocartilage extracellular matrix was observed throughout all implants. The amount of DNA, glycosaminoglycan, and hydroxyproline in the engineered cartilage were similar to that of native sheep ear cartilage. The embedded wire support was essential for avoiding shrinkage of the ear-shaped porous collagen constructs.

Injectable and photopolymerizable tissue-engineered auricular cartilage using poly(ethylene glycol) dimethacrylate copolymer hydrogels

In this study we investigated the histological, biochemical, and integrative features of the neocartilage using swine auricular chondrocytes photoencapsulated into two poly(ethylene glycol) dimethacrylate (PEGDM) copolymer hydrogels of a different degradation profile: degradable (PEG-4,5LA-DM) and nondegradable (PEGDM) macromers in molar ratios of 60:40 and 70:30. Integration of the engineered tissue with existing native cartilage was examined using an articular cartilaginous ring model. Experimental group samples (total n=96) were implanted subcutaneously into nude mice and harvested at 6, 12, and 18 weeks. Nonimplanted constructs (total n=16) were used as controls for quantification of DNA, glycosaminoglycan, and hydroxyproline. Histologically, neocartilage resembled both the cellular population and composition of the extracellular matrix of the native swine auricular cartilage. DNA content demonstrated that the photoencapsulated chondrocytes were capable of survival and proliferation over time. Both glycosaminoglycan and hydroxyproline contents appeared higher in the neotissue, which was supported by less degradable PEGDM hydrogel. Integration of neocartilage with surrounding native cartilage improved with time, resulting in the development of tight integration interface. PEGDM copolymer hydrogels can support in vivo chondrogenesis by photoencapsulating auricular chondrocytes.

Porous poly(vinyl alcohol)-alginate gel hybrid construct for neocartilage formation using human nasoseptal cells

BACKGROUND

Limited options exist for the restoration of craniofacial cartilage. Autologous tissue or porous polyethylene is currently used for nasal and auricular reconstruction. Both options are associated with drawbacks, including donor site morbidity and implant extrusion. Poly(vinyl alcohol) (PVA) is a non-degradable flexible biocompatible polymer than can be engineered to mimic the properties of cartilage. The goal of this study was to engineer a biosynthetic hybrid construct using a combination of PVA-alginate hydrogels and human nasal septum chondrocytes.

MATERIALS AND METHODS

Chondrocytes isolated from human nasal septum cartilage were expanded and mixed with 2% sodium alginate hydrogel. The chondrocyte-alginate mix was injected into a non-degradable porous PVA hydrogel, creating biosynthetic constructs. A group of these constructs were implanted into the subcutaneous environment of nude mice, while the other group was cultured in a spinner flask bioreactor system for 10 d and then implanted. After 6 wk in vivo, the histologic, biochemical, and biomechanical properties were examined.

RESULTS

Histological analysis demonstrated sulfated glycosaminoglycans and deposition of collagen type II in constructs from both groups. Constructs cultured in the bioreactor system prior in vivo implantation demonstrated higher levels of DNA, glycosaminoglycans, and hydroxyproline. An increase of 22% in the compressive strength of the engineered constructs exposed to the bioreactor was also observed.

CONCLUSION

A novel porous PVA-alginate gel hybrid was used to successfully engineer human cartilage in vivo. A 10-d period of bioreactor culturing increased levels of DNA, glycosaminoglycans, hydroxyproline, and the compressive modulus of the constructs.

In vivo observations of cell trafficking in allotransplanted vascularized skin flaps and conventional skin grafts

The problem of allogeneic skin rejection is a major limitation to more widespread application of clinical composite tissue allotransplantation (CTA). Previous research examining skin rejection has mainly studied rejection of conventional skin grafts (CSG) using standard histological techniques. The aim of this study was to objectively assess if there were differences in the immune response to CSG and primarily vascularized skin in composite tissue allotransplants (SCTT) using in vivo techniques in order to gain new insights in to the immune response to skin allotransplants. CSG and SCTT were transplanted from standard Lewis (LEW) ad Wistar Furth (WF) to recipient transgenic green fluorescent Lewis rats (LEW-GFP). In vivo confocal microscopy was used to observe cell trafficking within skin of the transplants. In addition, immunohistochemical staining was performed on skin biopsies to reveal possible expression of class II major histocompatibility antigens. A difference was observed in the immune response to SCTT compared to CSG. SCTT had a greater density cellular infiltrate than CSG (p<0.03) that was focused more at the center of the transplant (p<0.05) than at the edges, likely due to the immediate vascularization of the skin. Recipient dendritic cells were only observed in rejecting SCTT, not CSG. Furthermore, dermal endothelial class II MHC expression was only observed in allogeneic SCTT. The immune response in both SCTT and CSG was focused on targets in the dermis, with infiltrating cells clustering around hair follicles (CSG and SCTT; p<0.01) and blood vessels (SCTT; p<0.01) in allogeneic transplants. This study suggests that there are significant differences between rejection of SCTT and CSG that may limit the relevance of much of the historical data on skin graft rejection when applied to composite tissue allotransplantation. Furthermore, the use of novel in vivo techniques identified characteristics of the immune response to allograft skin not previously described, which may be useful in directing future approaches to overcoming allograft skin rejection.

Sequential limb ischemia demonstrates remote postconditioning protection of murine skeletal muscle

BACKGROUND

Ischemic postconditioning, the process of exposing tissues to brief cycles of ischemia-reperfusion after critical ischemia, can mitigate local ischemia-reperfusion injury. Remote protection of skeletal muscle has never been demonstrated in postconditioning models of ischemia-reperfusion injury.

METHODS

Mice were subjected to 2 hours of ipsilateral hind limb ischemia followed by reperfusion. Contralateral limb ischemia was subsequently induced for 2 hours after either 0 (n = 6), 20 (n = 6), or 120 (n = 5) minutes of ipsilateral limb reperfusion. These groups were compared with animals subjected to bilateral simultaneous injury (n = 8) and sham animals that did not undergo ischemia (n = 6). The gastrocnemius muscles were harvested for histologic evaluation, and injury was recorded as the percentage of injured fibers.

RESULTS

The first limbs undergoing injury in the 20-minute interval group had a 59 percent injury reduction compared with contralateral limbs (16.0 +/- 2.4 percent versus 39.5 +/- 6.5 percent) after 24 hours of reperfusion and 62 percent reduction after 48 hours (24.4 +/- 3.0 percent versus 63.6 +/- 5.5 percent). In animals with no interval or a 120-minute interval between the onset of limb ischemia, there was no significant difference in injury between hind limbs. The injury in these groups was similar to that in hind limbs subjected to simultaneous bilateral ischemia.

CONCLUSIONS

A 20-minute reperfusion interval between hind limb ischemia significantly protects against injury in the initially ischemic limb, while similar injury is observed with simultaneous ischemia or an interval of 120 minutes. This study demonstrates remote postconditioning of skeletal muscle and may lead to the development of post hoc therapies.

Engineering cartilage in a photochemically crosslinked collagen gel

This study's purpose was to investigate whether photochemically crosslinking collagen gel to encapsulate chondrocytes (articular, auricular, costal) would permit new cartilage formation in vivo, and to determine whether this neocartilage had the ability to integrate with existing native cartilage. Chondrocytes from swine were embedded in collagen gel that was photochemically crosslinked using riboflavin and visible light. Controls were collagen gels containing cells that were not crosslinked. Cylindrical implants (0.1 cc) were placed in athymic mice for 4 and 8 weeks. To study integration, the constructs were crosslinked within articular cartilage rings and implanted in the mice. Samples were analyzed in terms of macroscopic, microscopic, and biochemical aspects. Photocrosslinking did not affect the amount of glycosaminoglycan and type II collagen produced by the cells. We found that photochemical crosslinking collagen gel enhances the physical parameters of the gel and permits new cartilage formation that can integrate with existing native cartilage.

Ischemic preconditioning of skeletal muscle mitigates remote injury and mortality

BACKGROUND

Ischemic preconditioning (IPC) mitigates ischemia-reperfusion (I/R) injury in experimental models. However, the clinical significance of this protection has been unclear and a mortality reduction has not been previously reported in noncardiac models. This study examined the local and remote protection afforded by skeletal muscle IPC and sought to determine the significance of this protection on mortality.

METHODS

Mice subjected to 2 h hindlimb ischemia/24 h reperfusion (standard I/R injury) were compared with those undergoing a regimen of two 20-min cycles of IPC followed by standard I/R injury. Local injury was assessed via gastrocnemius histology, and remote injury was evaluated via intestinal histology and pulmonary neutrophil infiltration (n = 7). Mortality was compared in parallel groups for 1 week (n = 6). Groups were analyzed using an unpaired Student's t-test for gastrocnemius and pulmonary injury, and a Mann-Whitney rank sum test for intestinal injury. Mortality differences were interpreted through a hazard ratio.

RESULTS

Significant protection was observed in preconditioned animals. There was a 35% local injury reduction in skeletal muscle (71.2% versus 46.0%, P < 0.01), a 50% reduction in remote intestinal injury (2.3 versus 1.1, P < 0.01), and a 43% reduction in remote pulmonary injury (14.9 versus 8.5, P < 0.01) compared with standard injury controls. Preconditioned animals were also significantly protected from mortality, demonstrating a 66.7% survival at 1 wk compared with 0% survival after standard injury alone (hazard ratio 0.20, 95% CI: 0.02-0.59).

CONCLUSIONS

We have developed a murine model of IPC that demonstrates local and remote protection against I/R injury, and exhibits significant mortality reduction. This model demonstrates the powerful effect of IPC on local and remote tissues and will facilitate further study of potential mechanisms and therapies.

Photochemical sealing improves outcome following peripheral neurorrhaphy

INTRODUCTION

Peripheral nerve transection initiates a complex molecular response in the severed nerve endings, resulting in the release of neurotrophic and neurotropic factors that are central to axonal survival and regeneration. In this study we tested the hypothesis that sealing the neurorrhaphy site from the surrounding environment using a photochemically bonded nerve wrap would optimize the endoneural environment and enhance regeneration and nerve function recovery.

MATERIALS AND METHODS

Adult rats underwent unilateral sciatic nerve transection and standard epineural nerve repair. The repair site was wrapped with amniotic membrane or autologous vein and then was either sealed using photochemical tissue bonding (PTB) or secured with sutures. Photochemical sealing without a wrap was also carried out. Functional recovery was assessed at 2-wk intervals using walking track analysis and nerve histomorphometry was assessed at 12 wk.

RESULTS

Treating nerves with PTB-sealed amnion significantly improved functional recovery and increased distal axon and fiber diameters and myelin thickness compared to nerves treated with standard neurorrhaphy alone. Direct PTB sealing of the repair site also improved function. Neither amnion secured with sutures nor vein wraps exhibited improved functional or histological recovery compared to standard neurorrhaphy.

CONCLUSIONS

These results suggest that sealing the peripheral nerve repair site with amnion using a photochemical technique may lead to earlier restoration of neural homeostasis and consequent enhanced repair of nerve injury.

Microvascular anastomosis using a photochemical tissue bonding technique

BACKGROUND AND OBJECTIVES

Photochemical tissue bonding (PTB) combines photoactive dyes with visible light to create fluid-tight seals between tissue surfaces without causing collateral thermal damage. The potential of PTB to improve outcomes over standard of care microsurgical reanastomoses of blood vessels in ex vivo and in vivo models was evaluated.

STUDY DESIGN

The mechanical strength and integrity of PTB and standard microsurgical suture repairs in ex vivo porcine brachial arteries (n = 10) were compared using hydrostatic testing of leak point pressure (LPP). Femoral artery repair in vivo was measured in Sprague-Dawley rats using either standard microvascular sutures (n = 20) or PTB (n = 20). Patency was evaluated at 6 hours (n = 10) and 8 weeks post-repair (n = 10) for each group.

RESULTS

PTB produced significantly higher LPPs (1,100+/- 150 mmHg) than suture repair (350+/-40 mmHg, P<0.001) in an ex vivo study. In an in vivo study all femoral arteries in both suture and PTB repair groups were patent at 6 hours post-repair. At 8 weeks post-repair the patency rate was 80% for both groups. No evidence of aneurysm formation was seen in either group and bleeding was absent from the repair site in the PTB-treated vessels, in contrast to the suture repair group.

CONCLUSION

PTB is a feasible microvascular repair technique that results in an immediate, mechanically robust bond with short- and long-term patency rates equal to those for standard suture repair.

Photochemical Tissue Bonding: A Promising Technique for Peripheral Nerve Repair

BACKGROUND

Photochemical tissue bonding (PTB) is a novel tissue repair technique that uses visible light and a photosensitizing dye to crosslink proteins on tissue surfaces. This technique has been successfully demonstrated in a number of tissue repair models. An ideal nerve repair technique would be atraumatic and avoid placement of foreign bodies at the repair site. The epineurium is suited to photochemical repair as it is thin, translucent and has a relatively high collagen content. This study was designed to determine if PTB could be successfully applied in a peripheral nerve repair model.

MATERIAL AND METHODS

Forty Sprague Dawley rats underwent transection of the sciatic nerve. Animals were then randomized to four treatment groups; epineurial suture repair, epineurial cuff with PTB, epineurial cuff alone, and no repair. Functional recovery was assessed at 10 day intervals using walking track analysis and sciatic function index calculations. At 90 days postoperatively animals were sacrificed and sciatic nerves harvested for histology and histomorphometry.

RESULTS

Functional recovery in the suture repair and epineural cuff with PTB groups were not significantly different (-70.6 +/- 17.8 versus -76.9 +/- 10.3, P = 0.64) at 90 days postrepair. Histology showed good axonal regeneration with all repair techniques. Histomorphometric analysis found no significant difference between the repair groups.

CONCLUSIONS

This study illustrates that peripheral nerves can be successfully repaired using a photochemical tissue bonding technique with results similar to those achieved with the current gold standard. With further development and refinement PTB may prove a useful tool in peripheral nerve repair.

Influence of gel properties on neocartilage formation by auricular chondrocytes photoencapsulated in hyaluronic acid networks

The objective of this study was to determine how changes in the network structure and properties of hyaluronic acid (HA) hydrogels, due to variations in the macromer molecular weight (50-1,100 kDa) and macromer concentration (2-20 wt %), affect neocartilage formation by encapsulated auricular chondrocytes. To investigate tissue formation, swine auricular chondrocytes were photoencapsulated in the various networks, implanted subcutaneously in the dorsum of nude mice, and explanted after 6 and 12 weeks for biochemical and histological analysis. After 12 weeks, the various constructs were 81-93% water, contained between 0.1 x 10(6) and 0.6 x 10(6) chondrocytes per sample, and consisted of 0-0.049 microg chondroitin sulfate/mug wet weight (glycosaminoglycan (GAG) content) and 0.002-0.060 microg collagen/microg wet weight. Histological staining showed an even distribution of chondrocytes and GAGs in addition to minimal type I collagen staining and intense and uniform type II collagen staining in the constructs with greatest neocartilage production. Hydrogels fabricated from 2 wt % of the 50 kDa HA macromer most resembled the properties of native cartilage and show the greatest promise for continued development for cartilage regeneration.

Skin tolerance: in search of the Holy Grail

In 1943, Gibson and Medawar opened the modern era of transplantation research with a paper on the problem of skin allograft rejection. Ten years later Billingham, Brent and Medawar demonstrated that it was possible to induce selective immune acceptance of skin grafts in mice, a state of tolerance. After over six decades, however, the precise mechanism of skin allograft rejection remains still ill-defined. Furthermore, it has not been possible to achieve reliably clinical tolerance allowing the widespread application of skin allotransplantation techniques. The first successful applications of skin allotransplantation have included the hand and face. However, complications from the chronic immunosuppression regimens limit the application of these techniques. Induction of tolerance to skin (and the other tissues in the allograft) would be the most effective way to overcome all these difficulties, but this is yet to be achieved reliably, stimulating some to look for other ways to surmount the current limitations. This paper summarizes alternatives to enlarge the scope of skin allotransplantation techniques, current understanding of mechanisms of skin rejection, and the utility and limitations of animal models used to study skin rejection and tolerance induction. Finally, manipulation strategies to achieve skin tolerance are outlined.

Photochemically Cross-Linked Collagen Gels as Three-Dimensional Scaffolds for Tissue Engineering

Collagen gels have many favorable attributes for tissue engineering, but the gels undergo dramatic contraction when cells are added because of the weak noncovalent bonds that form during spontaneous gelation. We hypothesized that photochemically cross-linking collagen gels would make suitable scaffolds for tissue engineering with favorable cell viability and minimal gel contraction. Rose Bengal and riboflavin were chosen as candidate photo-initiators for gel cross-linking using 532- and 458-nm-light wavelengths, respectively. Chondrocyte viability was measured after initial gelation for several concentrations of initiators. Cell viability and gel contraction were then measured using chondrocytes and fibroblasts over 7 days of culture. Rose Bengal used at concentrations necessary for gelation resulted in little or no cell viability. Short-term viability results showed that 0.25- or 0.5-mM concentrations of riboflavin, and 40 s of illumination permitted more than 90% cell viability. Using riboflavin concentrations of 0.25 or 0.5 mM, long-term chondrocyte viability was 113.1 +/- 11.6% and 25.4 +/- 2.7%, respectively, at day 7. Although non-cross-linked chondrocyte constructs contracted to 59.9 +/- 11.8% of their original diameter and fibroblasts contracted to 24.9 +/- 5.0% of their original diameter by day 7, the cross-linked constructs retained 88.8 +/- 7.4% and 85.5 +/- 5.0% of the original diameter, respectively. In conclusion, by photochemically cross-linking collagen gels using riboflavin and visible light, stable gel scaffolds with favorable cell survival can be produced.

Embryonic stem cell-derived motor neurons preserve muscle after peripheral nerve injury

BACKGROUND

The potential of motor neuron progenitor cell transplants to preserve muscle tissue after denervation was studied in in vivo and in vitro adult mammalian model of peripheral nerve injury.

METHODS

Embryonic stem cells were differentiated to induce cholinergic motor neuron progenitors. Flourescent-labeled progenitor cells were injected into the gastrocnemius muscle of Sprague-Dawley rats (n = 10) after denervation by ipilateral sciatic nerve transection. Control rats received injections of either a phosphate-buffered saline solution only (n = 12), murine embryonic fibroblast (STO) cells (n= 6), or undifferentiated embryonic stem cells (n= 6). Muscles were weighed and analyzed at 7 and 21 days using histology, histomorphometry, and immunostaining.

RESULTS

Seven days after progenitor cell transplant, both muscle mass and myocyte cross-sectional area were preserved, compared with control muscles, which demonstrated muscle mass reduction to 70 percent and reduction of cross-sectional area to 72 percent of normal. Fluorescent microscopy of transplanted muscles confirmed the presence of motor neuron progenitors. Presynaptic neuronal staining of the transplants overlapped with alpha-bungarotoxin-labeled muscle fibers, revealing the presence of new neuromuscular junctions. By 21 days, muscle atrophy in the experimental muscles was equal to that of controls and no transplanted cells were observed. Co-culture of the motor neuron progenitor cells and myocytes also demonstrated new neuromuscular junctions by immunofluorescence.

CONCLUSIONS

Transplanted motor neuron progenitors prevent muscle atrophy after denervation for a brief time. These progenitor cell transplants appear to form new neuromuscular junctions with denervated muscle fibers in vivo and with myocytes in vitro.

An allogenic cell-based implant for meniscal lesions

BACKGROUND

Meniscal tears in the avascular zones do not heal. Although tissue-engineering approaches using cells seeded onto scaffolds could expand the indication for meniscal repair, harvesting autologous cells could cause additional trauma to the patient. Allogenic cells, however, could provide an unlimited amount of cells.

HYPOTHESIS

Allogenic cells from 2 anatomical sources can repair lesions in the avascular region of the meniscus.

STUDY DESIGN

Controlled laboratory study.

METHODS

Both autologous and allogenic chondrocytes were seeded onto a Vicryl mesh scaffold and sutured into a bucket-handle lesion created in the medial menisci of 17 swine. Controls consisted of 3 swine knees treated with unseeded implants and controls from a previous experiment in which 4 swine were treated with suture only and 4 with no treatment. Menisci were harvested after 12 weeks and evaluated histologically for new tissue and percentage of interface healing surface; they were also evaluated statistically.

RESULTS

The lesions were closed in 15 of 17 menisci. None of the control samples demonstrated healing. Histologic analysis of sequential cuts through the lesion showed formation of new scar-like tissue in all experimental samples. One of 8 menisci was completely healed in the allogenic group and 2 of 9 in the autologous group; the remaining samples were partially healed in both groups. No statistically significant differences in the percentage of healing were observed between the autologous and allogenic cell-based implants.

CONCLUSION

Use of autologous and allogenic chondrocytes delivered via a biodegradable mesh enhanced healing of avascular meniscal lesions.

CLINICAL RELEVANCE

This study demonstrates the potential of a tissue-engineered cellular repair of the meniscus using autologous and allogenic chondrocytes.

Healing potential of transplanted allogeneic chondrocytes of three different sources in lesions of the avascular zone of the meniscus: a pilot study

Successful treatment of tears to the avascular region of the meniscus remains a challenge. Current repair techniques, such as sutures and anchors, are effective in stabilizing the peripheral, vascularized regions of the meniscus, but are not adequate for promoting healing in the avascular region. The purpose of this study was to demonstrate the healing ability of a tissue-engineered repair technique using allogenic chondrocytes from three different sources for the avascular zone of the meniscus.

MATERIAL AND METHODS

Articular, auricular, and costal chondrocytes were harvested from 3-month-old Yorkshire swine. A 1-cm bucket-handle lesion was created in the avascular zone of each three swine. A cell-scaffold construct, composed of a single chondrocyte cell type and Vicryl mesh, was implanted into the lesion and secured with two vertical mattress sutures. Controls consisted of each three sutured unseeded mesh implants, suture only, and untreated lesions. The swine were allowed immediate post-operative full weight bearing. Menisci and controls were harvested after 12 weeks.

RESULTS

In all experimental samples, lesion closure was observed. Gross mechanical testing with two Adson forceps demonstrated bonding of the lesion. Histological analysis showed formation of new tissue in all three experimental samples. None of the control samples demonstrated closure and formation of new matrix.

CONCLUSION

We present preliminary data that demonstrates the potential of a tissue-engineered, allogenic cellular repair to provide successful healing of lesions in the avascular zone in a large animal model.

Effects of auricular chondrocyte expansion on neocartilage formation in photocrosslinked hyaluronic acid networks

The overall objective of this study was to examine the effects of in vitro expansion on neocartilage formation by auricular chondrocytes photoencapsulated in a hyaluronic acid (HA) hydrogel as a next step toward the clinical application of tissue engineering therapies for treatment of damaged cartilage. Swine auricular chondrocytes were encapsulated either directly after isolation (p = 0), or after further in vitro expansion ( p = 1 and p = 2) in a 2 wt%, 50-kDa HA hydrogel and implanted subcutaneously in the dorsum of nude mice. After 12 weeks, constructs were explanted for mechanical testing and biochemical and immunohistochemical analysis and compared to controls of HA gels alone and native cartilage. The compressive equilibrium moduli of the p = 0 and p = 1 constructs (51.2 +/- 8.0 and 72.5 +/- 35.2 kPa, respectively) were greater than the p = 2 constructs (26.8 +/- 14.9 kPa) and the control HA gel alone (12.3 +/- 1.3 kPa) and comparable to auricular cartilage (35.1 +/- 12.2 kPa). Biochemical analysis showed a general decrease in glycosaminoglycan (GAG), collagen, and elastin content with chondrocyte passage, though no significant differences were found between the p = 0 and p = 1 constructs for any of the analyses. Histological staining showed intense and uniform staining for aggrecan, as well as greater type II collagen versus type I collagen staining in all constructs. Overall, this study illustrates that constructs with the p = 0 and p = 1 auricular chondrocytes produced neocartilage tissue that resembled native auricular cartilage after 12 weeks in vivo. However, these results indicate that further expansion of the chondrocytes (p = 2) can lead to compromised tissue properties.

Isolated Perfusion of a Tubed Superficial Epigastric Flap in a Rodent Model

BACKGROUND

Isolated perfusion models can yield important data regarding metabolism of the skin. An effective model must remain stable during perfusion but respond appropriately to metabolic and vascular stimuli. We describe the design and characterization of a tubed superficial epigastric isolated perfusion flap.

MATERIALS AND METHODS

Tubed superficial epigastric flaps were created in 20 male Sprague Dawley rats. Forty-eight hours later the femoral vessels were cannulated and the flaps were perfused using a Krebs-Heinseleit buffer containing albumin for a period of 2 h. In five of the flaps norepinephrine and acetylcholine were added sequentially to the perfusate to determine vascular reactivity. In a further four flaps insulin (20 U/liter) and iodoacetate (5 mM) were added to the perfusate to confirm that the flap was metabolically active and reactive. Venous outflow was collected at regular intervals and analyzed for electrolytes, lactate, and glucose content. Vascularity and skin perfusion were characterized using barium microangiography and methylene blue dye injection.

RESULTS

This flap model was found to be stable in terms of arterial pressure, electrolyte levels, and lactate production over the perfusion period. Norepinephrine caused a sharp increase in vascular resistance, which was reversed by administration of acetylcholine. Lactate production increased appropriately with the addition of insulin to the perfusate with a rapid decline following addition of the glycolysis inhibitor iodoacetate. There was no leakage of perfusate or significant swelling of the flap during the perfusion.

CONCLUSIONS

The tubed superficial epigastric artery flap makes an effective model for isolated perfusion studies of the skin with a wide range of experimental applications.