Personalized Fiber-Reinforcement Networks for Meniscus Reconstruction.

The menisci are fibrocartilaginous tissues that are crucial to the load-sharing and stability of the knee, and when injured, these properties are compromised. Meniscus replacement scaffolds have utilized the circumferential alignment of fibers to recapitulate the microstructure of the native meniscus; however, specific consideration of size, shape, and morphology has been largely overlooked. The purpose of this study was to personalize the fiber-reinforcement network of a meniscus reconstruction scaffold. Human cadaveric menisci were measured for a host of tissue (length, width) and subtissue (regional widths, root locations) properties, which all showed considerable variability between donors. Next, the asymmetrical fiber network was optimized to minimize the error between the dimensions of measured menisci and predicted fiber networks, providing a 51.0% decrease (p = 0.0091) in root-mean-square (RMS) error. Finally, a separate set of human cadaveric knees was obtained, and donor-specific fiber-reinforced scaffolds were fabricated. Under cyclic loading for load-distribution analysis, in situ implantation of personalized scaffolds following total meniscectomy restored contact area (253.0 mm2 to 488.9 mm2, p = 0.0060) and decreased contact stress (1.96 MPa to 1.03 MPa, p = 0.0025) to near-native values (597.4 mm2 and 0.83 MPa). Clinical use of personalized meniscus devices that restore physiologic contact stress distributions may prevent the development of post-traumatic osteoarthritis following meniscal injury.

Achieving molecular orientation in thermally extruded 3D printed objects.

Three-dimensional (3D) printing is used to fabricate tissue scaffolds. Polymer chains in these objects are typically unoriented. The mechanical properties of these scaffolds can be significantly enhanced by proper alignment of polymer chains. However, post-processing routes to increase orientation can be limited by the geometry of the printed object. Here, we show that it is possible to orient polymer chains during printing by optimizing printing parameters to take advantage of the flow characteristics of the polymer. This is demonstrated by printing a polymeric scaffold for meniscus regeneration using poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate), poly(DTD DD). Alignment of polymer chains was achieved by translating the printhead at sufficiently high speeds when the polymer was still in a semi-solid state as it cooled from the fluid state at the tip of the nozzle using a critical combination of nozzle diameter, extrusion pressure, and temperature. The degree of orientation as evaluated by x-ray diffraction and thermal shrinkage, was greater than that of drawn fibers. Significant orientation and defect-free printing was achieved even for scaffolds with complex geometries. The ability to orient polymers during 3D printing has the potential to combine the advantages of 3D printing with the superior mechanical performance of more conventional polymer processing methods, such as drawing.

Biomechanical characterization of a novel collagen-hyaluronan infused 3D-printed polymeric device for partial meniscus replacement.

The menisci transmit load by increasing the contact area and decreasing peak contact stresses on the articular surfaces. Meniscal lesions are among the most common orthopedic injuries, and resulting meniscectomies are associated with adverse polycaprolactone contact mechanics changes and, ultimately, an increased likelihood of osteoarthritis. Meniscus scaffolds were fabricated by 3D-printing a network of circumferential and radial filaments of resorbable polymer (poly(desaminotyrosyl-tyrosine dodecyl ester dodecanoate)) and infused with collagen-hyaluronan. The scaffold demonstrated an instantaneous compressive modulus (1.66 ± 0.44 MPa) comparable to native meniscus (1.52 ± 0.59 MPa). The scaffold aggregate modulus (1.33 ± 0.51 MPa) was within 2% of the native value (1.31 ± 0.36 MPa). In tension, the scaffold displayed a comparable stiffness to native tissue (127.6-97.1 N/mm) and an ultimate load of 33% of the native value. Suture pull-out load of scaffolds (83.1 ± 10.0 N) was within 10% of native values (91.5 ± 15.4 N). Contact stress analysis demonstrated the scaffold reduced peak contact stress by 60-67% and increased contact area by 38%, relative to partial meniscectomy. This is the first meniscal scaffold to match both the axial compressive properties and the circumferential tensile stiffness of the native meniscus. The improvement of joint contact mechanics, relative to partial meniscectomy alone, motivates further investigation using a large animal model. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2457-2465, 2019.

Partial Meniscus Replacement with a Collagen-Hyaluronan Infused Three-Dimensional Printed Polymeric Scaffold.

IMPACT STATEMENT: The only FDA-approved partial meniscus scaffold, the Collagen Meniscus Implant (CMI), is not approved for reimbursement by government and only reimbursable by certain private insurers. Scaffolds with improved mechanical properties and greater efficacy are needed. A previous study (Ghodbane, et al. DOI: 10.1002/jbm.b.34331) demonstrated the ability of our novel acellular, off-the shelf scaffold to restore knee biomechanics following partial meniscectomy, which could potentially decrease the risk of osteoarthritis following partial meniscectomy, providing the motivation for this study. This article presents a first-in-animal feasibility study.

Tissue-Engineered Total Meniscus Replacement With a Fiber-Reinforced Scaffold in a 2-Year Ovine Model.

BACKGROUND: Meniscus injuries and associated meniscectomies cause patients long-term pain and discomfort and can lead to joint deterioration. PURPOSE: To evaluate a collagen-hyaluronan sponge reinforced with synthetic resorbable polymer fiber for total meniscus reconstruction in a long-term ovine model. STUDY DESIGN: Controlled laboratory study. METHODS: Eleven skeletally mature sheep were implanted with the total meniscus scaffold. At 2 years, explants were evaluated biologically (radial/circumferential histology, immunofluorescence) and mechanically (compression, tension), and articular surfaces were examined for damage. RESULTS: The fiber-reinforced scaffold induced formation of functional neomeniscus tissue that was intact in 8 of 11 animals. The implant was remodeled into organized circumferentially aligned collagen bundles to resist meniscus hoop stresses. Moreover, type II collagen and proteoglycan deposition near the inner margin suggested a direct response to compressive stresses and confirmed fibrocartilage formation. Cartilage damage was observed, but end-stage (severe) joint deterioration associated with meniscectomy was avoided, even with limitations regarding the ovine surgical procedure and postoperative care. CONCLUSION: A fiber-reinforced total meniscus replacement device induces formation of functional neomeniscus tissue that has the potential to prevent catastrophic joint deterioration associated with meniscectomy. CLINICAL RELEVANCE: An off-the-shelf meniscus device that can be remodeled into functional tissue and thus prevent or delay the onset of osteoarthritis could address a widespread clinical need after meniscus injury.

Interference Screw Versus Suture Endobutton Fixation of a Fiber-Reinforced Meniscus Replacement Device in a Human Cadaveric Knee Model.

BACKGROUND: Meniscal lesions represent one of the most common intra-articular knee injuries. Meniscus replacement devices are needed to restore load distribution and knee stability after meniscectomy. Fixation of these devices is crucial to the generation of hoop stresses and the distribution of loads in the joint. PURPOSE: To evaluate 2 different fixation techniques (suture endobutton and interference screw) for implantation of a novel meniscus device. STUDY DESIGN: Controlled laboratory study. METHODS: In 7 human cadaveric knees (aged 17-61 years), 1 anterior and 2 potential posterior tunnel locations were investigated, and both fixation techniques were tested in each tunnel. The native meniscus roots, devices fixed with a suture endobutton, and devices fixed with an interference screw were gripped with cryoclamps, and tibias were drilled and loaded into a custom jig. Samples were preloaded, preconditioned, loaded for 500 cycles (50-150 N), and tested in tension until failure. RESULTS: For all 3 tunnels, suture fixation resulted in greater elongation (54.1%-150.7% greater; P < .05) during cyclic loading than interference screw fixation, which approximated the native roots. Both fixation techniques displayed ultimate tensile loads in the same range as native roots. However, stiffness of the suture fixation groups (36.5-41.6 N/mm) was only 28% to 37% of that of the interference screw fixation groups (98.7-131.6 N/mm), which had values approaching those of the native roots (anterior: 175.4 ± 24.2 N/mm; posterior: 157.6 ± 22.9 N/mm). CONCLUSION: Interference screw fixation was found to be superior to suture fixation with regard to elongation and stiffness, a finding that should be considered in the design and implantation of novel meniscus replacement devices. CLINICAL RELEVANCE: With the emergence of various devices for total meniscus replacement, the establishment of fixation strategies is crucial for the generation of tensile hoop stresses and the efficacy of these approaches.

Carbodiimide cross-linking counteracts the detrimental effects of gamma irradiation on the physical properties of collagen-hyaluronan sponges.

Collagen-based scaffolds are extensively used in biomaterials and tissue engineering applications. These scaffolds have shown great biocompatibility and versatility, but their relatively low mechanical properties may limit use in orthopaedic load-bearing applications. Moreover, terminal sterilization with gamma irradiation, as is commonly performed with commercial devices, presents concerns over structural integrity and enzymatic stability. Therefore, the goal of this study was to test the hypothesis that EDC/NHS cross-linking (10 mM/5 mM) can protect collagen-hyaluronan sponges from the damaging effects of gamma irradiation. Specifically, we evaluated compressive and tensile mechanical properties, enzymatic stability, porosity and pore size, and swelling ratio. Ultimate tensile strength and elastic modulus exhibited increases (168.5 and 245.8%, respectively) following irradiation, and exhibited over tenfold increases (1049.2 and 1270.6%, respectively) following cross-linking. Irradiation affected pore size (38.4% decrease), but cross-linking prior to irradiation resulted in only a 17.8% decrease. Cross-linking also showed an offsetting effect on the equilibrium modulus, enzymatic stability, and swelling ratio of sponges. These results suggest that carbodiimide cross-linking of collagen-hyaluronan sponges can mitigate the structural damage typically experienced during gamma irradiation, warranting their use in tissue engineering applications.

* The Ovine Model for Meniscus Tissue Engineering: Considerations of Anatomy, Function, Implantation, and Evaluation.

Meniscus injuries represent one of the most-common intra-articular knee injuries. The current treatment options include meniscectomy and allograft transplantation, both with poor long-term outcomes. Therefore, there is a need for regenerative techniques to restore meniscal function. To preclinically test scaffolds for meniscus replacement, large animal models need to be established and standardized. This review establishes the anatomical and compositional similarities between human and sheep menisci and provides guidance for implantation and evaluation of such devices. The ovine meniscus represents a scaled-down version of the human meniscus, with only slight structural differences that can be addressed during device fabrication. Implantation protocols in sheep remain a challenge, as the meniscus cannot be visualized with the arthroscopic-assisted procedures commonly performed in human patients. Thus, we recommend the appropriate implantation protocols for meniscus visualization, ligamentous restoration, and surgical fixation of both total and partial meniscus replacement devices. Last, due to the lack of standardization in evaluation techniques, we recommend a comprehensive battery of tests to evaluate the efficacy of meniscus replacement implants. We recommend other investigators utilize these surgical and testing techniques to establish the ovine model as the gold standard for preclinical evaluation of meniscus replacement devices.

Negative Outcomes of Poly(l-Lactic Acid) Fiber-Reinforced Scaffolds in an Ovine Total Meniscus Replacement Model.

Our objective was to test the efficacy of collagen-hyaluronan scaffolds reinforced with poly(l-lactic acid) (PLLA) fibers in an ovine total meniscus replacement model. Scaffolds were implanted into 9 sheep (n = 1 at 8 weeks, n = 2 at 16 weeks, n = 3 at both 24, 32 weeks) following total medial meniscectomy. From 16 weeks on, explants were characterized by confined compression creep, histological, and biochemical analyses. Articular surfaces were observed macroscopically and damage was ranked histologically using the Mankin score. At sacrifice, three of the nine PLLA scaffolds had completely ruptured, and the intact scaffolds experienced progressive shape changes and severe narrowing in the body region at 16, 24, and 32 weeks. Aggregate compressive modulus and permeability did not improve with time. Histological and biochemical analyses showed significantly less extracellular matrix and less matrix organization compared to native tissue. Osteophytes, bone erosion, and cartilage damage were observed, increasing with time postimplantation. A buildup of lactic acid and/or the rapid loss of scaffold mechanical integrity due to PLLA degradation are probable causes for the joint abnormalities observed in this study. These results are in sharp contrast to those of our previous successful total meniscus replacement studies using polyarylate [p(DTD DD)] fiber-reinforced scaffolds. This suggests that PLLA fiber as produced in this study cannot be used as reinforcement for a meniscus replacement scaffold.

Physical and mechanical properties of cross-linked type I collagen scaffolds derived from bovine, porcine, and ovine tendons.

Collagen scaffolds are often utilized in tissue engineering applications where their performance depends on physical and mechanical properties. This study investigated the effects of collagen source (bovine, porcine, and ovine tendon) on properties of collagen sponge scaffolds cross-linked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS). Scaffolds were tested for tensile and compressive properties, stability (resistance to enzymatic degradation), pore size, and swelling ratio. No significant differences in tensile modulus were observed, but ovine scaffolds had significantly greater ultimate strain, stress, and toughness relative to bovine and porcine scaffolds. No significant differences in compressive properties, pore size, or swelling ratio were observed as a function of collagen source. Ovine scaffolds were more resistant to collagenase degradation compared to bovine samples, which were more resistant than porcine scaffolds. In comparison to bovine scaffolds, ovine scaffolds performed equivalently or superiorly in all evaluations, and porcine scaffolds were equivalent in all properties except enzymatic stability. These results suggest that collagen sponges derived from bovine, porcine, and ovine tendon have similar physical and mechanical properties, and are all potentially suitable materials for various tissue engineering applications. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2685-2692, 2016.

One-Year Outcomes of Total Meniscus Reconstruction Using a Novel Fiber-Reinforced Scaffold in an Ovine Model.

BACKGROUND: Meniscus injuries and resulting meniscectomies lead to joint deterioration, causing pain, discomfort, and instability. Tissue-engineered devices to replace the meniscus have not shown consistent success with regard to function, mechanical integrity, or protection of cartilage. PURPOSE: To evaluate a novel resorbable polymer fiber-reinforced meniscus reconstruction scaffold in an ovine model for 52 weeks and assess its integrity, tensile and compressive mechanics, cell phenotypes, matrix organization and content, and protection of the articular cartilage surfaces. STUDY DESIGN: Controlled laboratory study. METHODS: Eight skeletally mature ewes were implanted with the fiber-reinforced scaffold after total meniscectomy, and 2 additional animals had untreated total meniscectomies. Animals were sacrificed at 52 weeks, and the explants and articular surfaces were analyzed macroscopically. Explants were characterized by ultimate tensile testing, confined compression creep testing, and biochemical, histological, and immunohistochemical analyses. Cartilage damage was characterized using the Mankin score on histologic slides from both the femur and tibia. RESULTS: One sheep was removed from the study because of a torn extensor tendon; the remaining 7 explants remained fully intact and incorporated into the bone tunnels. All explants exhibited functional tensile loads, tensile stiffnesses, and compressive moduli. Fibrocartilagenous repair with both types 1 and 2 collagen were observed, with areas of matrix organization and biochemical content similar to native tissue. Narrowing in the body region was observed in 5 of 7 explants. Mankin scores showed less cartilage damage in the explant group (femoral condyle: 3.43 ± 0.79, tibial plateau: 3.50 ± 1.63) than in the meniscectomy group (femoral condyle: 8.50 ± 3.54, tibial plateau: 6.75 ± 2.47) and were comparable with Mankin scores at the previously reported 16- and 32-week time points. CONCLUSION: A resorbable fiber-reinforced meniscus scaffold supports formation of functional neomeniscus tissue, with the potential to prevent joint degeneration that typically occurs after total meniscectomy. Further studies with improvements to the initial mechanics of the scaffold and testing for longer time periods are warranted. CLINICAL RELEVANCE: Meniscectomy is an extremely common orthopaedic procedure, and few options currently exist for the treatment of significant loss of meniscus tissue. Successful development of a tissue-engineered meniscus scaffold could substantially reduce the incidence of postmeniscectomy joint degeneration and the subsequent procedures used for its treatment.

Successful Total Meniscus Reconstruction Using a Novel Fiber-Reinforced Scaffold: A 16- and 32-Week Study in an Ovine Model.

BACKGROUND: Meniscus injuries in the United States result in an estimated 850,000 surgical procedures each year. Although meniscectomies are the most commonly performed orthopaedic surgery, little advancement has been made in meniscus replacement and regeneration, and there is currently no total meniscus replacement device approved by the Food and Drug Administration. HYPOTHESIS: A novel fiber-reinforced meniscus scaffold can be used as a functional total meniscus replacement. STUDY DESIGN: Controlled laboratory study. METHODS: A tyrosine-derived, polymer fiber-reinforced collagen sponge meniscus scaffold was evaluated mechanically (tensile and compressive testing) and histologically after 16 and 32 weeks of implantation in an ovine total meniscectomy model (N = 20; 16 implants plus 4 meniscectomies, divided equally over the 2 time periods). The extent of cartilage damage was also measured on tibial plateaus by use of toluidine blue surface staining and on femoral condyles by use of Mankin scores on histological slides. RESULTS: Scaffolds induced formation of neomeniscus tissue that remained intact and functional, with breaking loads approximating 250 N at both 16 and 32 weeks compared with 552 N for native menisci. Tensile stiffness values (99 and 74 N/mm at 16 and 32 weeks, respectively) were also comparable with those of the native meniscus (147 N/mm). The compressive modulus of the neomeniscus tissue (0.33 MPa at both 16 and 32 weeks) was significantly increased compared with unimplanted (time 0) scaffolds (0.15 MPa). There was histological evidence of extensive tissue ingrowth and extracellular matrix deposition, with immunohistochemical evidence of types I and II collagen. Based on significantly decreased surface damage scores as well as Mankin scores, the scaffold implants provided greater protection of articular cartilage compared with the untreated total meniscectomy. CONCLUSION: This novel fiber-reinforced meniscus scaffold can act as a functional meniscus replacement, with mechanical properties similar to those of the native meniscus, while protecting the articular cartilage of the knee from the extensive damage after a total meniscectomy. CLINICAL RELEVANCE: This meniscus replacement scaffold has the potential to improve surgical treatment and provide better long-term outcomes for those suffering from severe meniscus damage.

Fetal and neonatal exposure to the endocrine disruptor, methoxychlor, reduces lean body mass and bone mineral density and increases cortical porosity.

Endogenous estrogen has beneficial effects on mature bone and negatively affects the developing skeleton, whereas the effect of environmental estrogens is not known. Methoxychlor (MXC) is a synthetic estrogen known as a persistent organochlorine and used as a pesticide. Methoxychlor and its metabolites display estrogenic, anti-estrogenic and anti-androgenic activity and may therefore influence bone. Fifty-eight male fetal and neonatal rats were exposed to either: a negative control (DMSO), 0.020, 100 mg/kg MXC, or 1 mg/kg ß-estradiol-3-benzoate (EB; positive control). Rats were treated daily for 11 days, from embryonic day 19 to postnatal day (PND) 7 or for 4 days during the postnatal period (PND 0-7). All rats were analyzed at PND-84. Total body, femur, spine, and tibia areal bone mineral density (BMD) and content (BMC), lean body mass (LBM) and fat were measured by dual energy X-ray absorptiometry. Bone geometry and volumetric (v) BMD were measured using micro-computed tomography and biomechanical properties using three-point bending were assessed. Rats exposed to EB or MXC (at either the high and/or low dose), independent of exposure interval showed lower body weight, LBM, tibia and femur BMD and length, and total body BMD and BMC than DMSO control group (p ≤ 0.05). Methoxychlor and EB exposure increased cortical porosity compared to DMSO controls. Trabecular vBMD, number and separation, and cortical polar moment of inertia and cross-sectional area were lower due to EB exposure compared to control (p < 0.05). Early MXC exposure compromises cortical porosity and bone size at maturity, and could ultimately increase the risk of fracture with aging.

Development of a silk and collagen fiber scaffold for anterior cruciate ligament reconstruction.

The objective of this study was to determine a silk-collagen fiber ratio for an anterior cruciate ligament (ACL) reconstruction composite scaffold device. Composite fiber scaffolds with silk volumes ≥14 % and collagen volume <86 % demonstrated comparable or greater initial ultimate tensile stress relative to the human ACL. Silk scaffolds implanted subcutaneously and intraarticularly in rabbits demonstrated an 84 and 92 % reduction in strength with a 26 and 22 % reduction in volume after 8 weeks, respectively. The mechanical degradation findings of this preliminary study suggest that a composite scaffold with an initial UTS value of at least 129 MPa, or roughly a 48:52 silk to collagen volume ratio meets the minimal mechanical requirements necessary to proceed to a functional ACL reconstruction study in vivo.

Sterilization of tendon allografts: a method to improve strength and stability after exposure to 50 kGy gamma radiation.

Terminal sterilization of tendon allografts with high dose gamma irradiation has deleterious effects on tendon mechanical properties and stability after implantation. Our goal is to minimize these effects with radio protective methods. We previously showed that radio protection via combined crosslinking and free radical scavenging maintained initial mechanical properties of tendon allografts after irradiation at 50 kGy. This study further evaluates the tissue response and simulated mechanical degradation of tendons processed with radio protective treatment, which involves crosslinking in 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide followed by soaking in an ascorbate/riboflavin-5-phosphate solution. Control untreated and treated tendons were irradiated at 50 kGy and implanted in New Zealand White rabbit knees within the joint capsule for four and 8 weeks. Tendons were also exposed to cyclic loading to 20 N at one cycle per 12 s in a collagenase solution for 150 cycles, followed by tension to failure. Control irradiated tendons displayed increased degradation in vivo, and failed prematurely during cyclic processing at an average of 25 cycles. In contrast, radio protected irradiated tendons displayed greater stability following implantation over 8 weeks, and possessed strength at 59 % of native tendons and modulus equivalent to that of native tendons after cyclic loading in collagenase. These results suggest that radio protective treatment improves the strength and the stability of tendon allografts.

Design and mechanical evaluation of a novel fiber-reinforced scaffold for meniscus replacement.

A fiber-reinforced degradable scaffold for replacement of meniscal tissue was designed, fabricated, and mechanically evaluated. The hypotheses were that (1) the fiber network design would share a portion of compressive loads via the generation of circumferential tensile loads, and (2) the scaffold tensile properties would be similar to those of the meniscus. Two meniscus scaffold designs varying in fiber content (1000 or 500 fibers: MS1000, MS500) underwent cyclic compressive loading up to 100 and 250N, with resultant tensile loads measured at the anterior and posterior anchors. Standard tensile testing was also performed on each device and ovine menisci. Both scaffolds generated tensile loads directly proportional to the applied compressive loads, with MS1000 scaffolds generating approximately twice the tensile loads of MS500 scaffolds. The tensile strength of MS1000 scaffolds was significantly higher than that of the medial and lateral ovine menisci, and approximately twice that of the MS500 scaffolds. The stiffness of MS1000 scaffolds was lower than that of the lateral meniscus, but not statistically different from that of the medial meniscus. These results support our hypotheses that this novel fiber-reinforced scaffold can mimic the tensile and hoop stress behavior of normal meniscal tissue under compressive loading. The circumferential tensile strength and stiffness are appropriate for a meniscus replacement device.

Exogrip: assisted hand strength glove - biomed 2011.

A large number of American troops fighting in Afghanistan and Iraq have received wounds in their upper extremities leading to significant nerve damage and loss of strength. These injuries impair their ability to perform day-to-day tasks such as lifting a cup of coffee or opening a door. Although the cause of some injuries in service-people is often unique to their employment, civilian employees in other industries are also plagued with similar physical damage due to other kinds of injuries. Our goal is to develop a device to augment the strength of injured troops and civilian workers so they can perform everyday tasks despite their physical limitations. The ExoGrip is a glove designed to provide this necessary strength augmentation. The ExoGrip consists primarily of pressure sensors, linear actuators, and a microcontroller to provide a force multiplier based on a person’s strength. The goal of the first phase of the project was to conduct research and also produce a working prototype of one finger. This goal was achieved by a group of classmates who started the project a year before. Their research and feasibility analysis ended in the mechanical movement of a single finger when the sensors were activated. The next phase of this project is to design and integrate a working prototype that manipulates all four fingers, while keeping the thumb in a fixed position. This paper describes the integration of new microcontrollers, linear actuators utilizing pulse width modulation technology, and improved pressure sensors needed to manipulate the fingers, as well as laying the foundation for future testing and development of a final product.

A comparison of degradable synthetic polymer fibers for anterior cruciate ligament reconstruction.

We compared mechanical properties, degradation rates, and cellular compatibilities of two synthetic polymer fibers potentially useful as ACL reconstruction scaffolds: poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate)(12,10), p(DTD DD) and poly(L-lactic acid), PLLA. The yield stress of ethylene oxide (ETO) sterilized wet fibers was 150 +/- 22 MPa and 87 +/- 12 MPa for p(DTD DD) and PLLA, respectively, with moduli of 1.7 +/- 0.1 MPa and 4.4 +/- 0.43 MPa. Strength and molecular weight retention were determined after incubation under physiological conditions at varying times. After 64 weeks strength decreased to 20 and 37% of the initial sterile fiber values and MW decreased to 41% and 36% of the initial values for p(DTD DD) and PLLA, respectively. ETO sterilization had no significant effect on mechanical properties. Differences in mechanical behavior may be due to the semicrystalline nature of PLLA and the small degree of crystallinity induced by mesogenic ordering in p(DTD DD) suggested by DSC analysis. Fibroblast growth was similar on 50-fiber scaffolds of both polymers through 16 days in vitro. These data suggest that p(DTD DD) fibers, with higher strength, lower stiffness, favorable degradation rate and cellular compatibility, may be a superior alternative to PLLA fibers for development of ACL reconstruction scaffolds.

Improved tendon radioprotection by combined cross-linking and free radical scavenging.

Allograft safety is a great concern owing to the risk of disease transmission from nonsterile tissues. Radiation sterilization is not used routinely because of deleterious effects on the mechanical integrity and stability of allograft collagen. We previously reported several individual cross-linking or free radical scavenging treatments provided some radioprotective effects for tendons. We therefore asked whether a combination of treatments would provide an improved protective effect after radiation exposure regarding mechanical properties and enzyme resistance. To address this question we treated 90 rabbit Achilles tendons with a combination of cross-linking (1-ethyl-3-[3-dimethyl aminopropyl] carbodiimide [EDC]) and one of three scavenging regimens (mannitol, ascorbate, or riboflavin). Tendons then were exposed to one of three radiation conditions (gamma or electron beam irradiation at 50 kGy or unsterilized). Combination-treated tendons (10 per group) had increases in mechanical properties and higher resistance to collagenase digestion compared with EDC-only and untreated tendons. Irradiated tendons treated with EDC-mannitol, -ascorbate, and -riboflavin combinations had comparable strength to native tendon and had averages of 26%, 39%, and 37% greater, respectively, than those treated with EDC-only. Optimization of a cross-linking protocol and free radical scavenging cocktail is ongoing with the goal of ensuring sterile allografts through irradiation while maintaining their structure and mechanical properties.

Radioprotection of tendon tissue via crosslinking and free radical scavenging.

Ionizing radiation could supplement tissue bank screening to further reduce the probability of diseases transmitted by allografts if denaturation effects can be minimized. It is important, however, such sterilization procedures be nondetrimental to tissues. We compared crosslinking and free radical scavenging potential methods to accomplish this task in tendon tissue. In addition, two forms of ionizing irradiation, gamma and electron beam (e-beam), were also compared. Crosslinkers included 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and glucose, which were used to add exogenous crosslinks to collagen. Free radical scavengers included mannitol, ascorbate, and riboflavin. Radioprotective effects were assessed through tensile testing and collagenase resistance testing after irradiation at 25 kGy and 50 kGy. Gamma and e-beam irradiation produced similar degenerative effects. Crosslinkers had the highest strength at 50 kGy, EDC treated tendons had 54% and 49% higher strength than untreated, for gamma and e-beam irradiation respectively. Free radical scavengers showed protective effects up to 25 kGy, especially for ascorbate and riboflavin. Crosslinked samples had higher resistance to collagenase and over a wider dose range than scavenger-treated. Of the options studied, the data suggest EDC precrosslinking or glucose treatment provides the best maintenance of native tendon properties after exposure to ionizing irradiation.