Meniscal replacement in dogs. Tissue regeneration in two different materials with similar properties

A gel microparticle-based self-thickening strategy for 3D printing high-modulus hydrogels skeleton cushioned with PNAGA hydrogel mimicking anisotropic mechanics of meniscus

Developing a meniscus substitute mimicking the anisotropic mechanics (higher circumferential tensile modulus and lower compressive modulus) of native tissue remains a great challenge. In this work, based on the pendant group structure-dependent H-bonding strengthening mechanism, two kinds of amide-based H-bonding crosslinked hydrogels with distinct mechanical behaviors, that is, the flexible poly(N-acryloyl glycinamide) (PNAGA) and the ultra-stiff poly(N-acryloylsemicarbazide) (PNASC) hydrogels are employed to construct the biomimetic meniscus substitute. To this end, a gel microparticle-based self-thickening strategy is first proposed to fabricate PNASC (GMP-PNASC) high-modulus hydrogels skeleton by extrusion printing technology in mimicking the collagen fibers in native meniscus to resist the circumferential tensile stress. Then, the PNAGA hydrogel is infused into the PNASC skeleton to replicate the proteoglycan, providing a lower compressive modulus. By regulating the structural features at the interior and peripheral regions, the GMP-PNASC/PNAGA hydrogel meniscus scaffold with the higher tensile modulus (87.28 ± 6.06 MPa) and lower compressive modulus (2.11 ± 0.28 MPa) can be constructed. In vivo outcome at 12 weeks post-implantation of rabbit's medial meniscectomy model confirms the effects of GMP-PNASC/PNAGA meniscus scaffold on alleviating the wear of articular cartilage and ameliorating the development of osteoarthritis (OA).

Controllable Damping Magnetorheological Elastomer Meniscus

The human healthy meniscus fulfills key biomechanical functions in the tibiofemoral (knee) joint. Meniscal injury leads to an increased risk for symptomatic osteoarthritis. In order to prevent osteoarthritis, many researchers have put efforts into developing new-type meniscal substitute materials. In this study, MRI data of the human knee joint is obtained by CT scanning, and a three-dimensional finite element model of the meniscus is established. Compressive forces of 400 N, 600 N, 800 N, and 1000 N are selected to complete the meniscus modeling and finite element simulation analysis of the meniscus by ANSYS; at the same time, the compressive force and compressive displacement of the magnetorheological elastomer are controlled by changing the current size. The results show that the compressive force and compressive displacement of the magnetorheological elastomer can be controlled by an electric current, so as to adapt to the required mechanical properties of the meniscus under external complex loads and provide a theoretical and experimental basis for clinical meniscus replacement.

Comparison of Clinical Results and Pathological Examinations Between Locally Synthesized Bone-derived Hydroxyapatite and Medpor® Orbital Implants in Animal Models

We aimed to compare clinical and pathological reactions towards locally synthesized bovine bone derived from hydroxyapatite (bone docosahexaenoic acid (dHA)) and commercially available porous polyethylene (Medpor®, Porex Surgical Incorporation, Georgia, USA) orbital implants in animal models. An experimental study was performed on 14 New Zealand white rabbits. Group A (n=7) was implanted with bovine bone dHA and group B (n=7) was implanted with Medpor®. Clinical examinations were performed on Days 1, 7, 14, 28, and 42 post-implantation. The implanted eyes were enucleated on Day 42 and were sent for pathological evaluation. Serial clinical examinations included urine color and odor; feeding and physical activity demonstrated normal wellbeing in all the subjects. Localized minimal infection was observed in both groups during the first two weeks following implantation, and the subjects responded well to topical moxifloxacin. Both groups exhibited evidence of wound breakdown. No signs of implant migration or extrusion were observed in either group. The histopathological examination revealed no statistically significant difference in inflammatory cell reactions and fibrovascular tissue maturation between both types of implants. However, all (100%) of the bovine bone dHA implants displayed complete fibrovascular ingrowth compared to Medpor® implants (57.1%) at six weeks post-implantation (p=0.001). In conclusion, bovine bone dHA and Medpor® orbital implants were well-tolerated clinically and displayed similar inflammatory reactions and fibrovascular tissue maturation. Locally synthesized bovine bone dHA orbital implants displayed significantly greater complete fibrovascular ingrowth in comparison with Medpor® implants.

The challenge of implant integration in partial meniscal replacement: an experimental study on a silk fibroin scaffold in sheep

PURPOSE

To restore meniscal function after excessive tissue damage, a silk fibroin implant for partial meniscal replacement was developed and investigated in an earlier sheep model. After 6 months implantation, it showed promising results in terms of chondroprotection and biocompatibility. To improve surgical fixation, the material was subjected to optimisation and a fibre mesh was integrated into the porous matrix. The aim of the study was the evaluation of this second generation of silk fibroin implants in a sheep model.

METHODS

Nine adult merino sheep received subtotal meniscal replacement using the silk fibroin scaffold. In nine additional animals, the defect was left untreated. Sham surgery was performed in another group of nine animals. After 6 months of implantation macroscopic, biomechanical and histological evaluations of the scaffold, meniscus, and articular cartilage were conducted.

RESULTS

Macroscopic evaluation revealed no signs of inflammation of the operated knee joint and most implants were located in the defect. However, there was no solid connection to the remaining peripheral meniscal rim and three devices showed a radial rupture at the middle zone. The equilibrium modulus of the scaffold increased after 6 months implantation time as identified by biomechanical testing (before implantation 0.6 ± 0.3 MPa; after implantation: 0.8 ± 0.3 MPa). Macroscopically and histologically visible softening and fibrillation of the articular cartilage in the meniscectomy- and implant group were confirmed biomechanically by indentation testing of the tibial cartilage.

CONCLUSIONS

In the current study, biocompatibility of the silk fibroin scaffold was reconfirmed. The initial mechanical properties of the silk fibroin implant resembled native meniscal tissue. However, stiffness of the scaffold increased considerably after implantation. This might have prevented integration of the device and chondroprotection of the underlying cartilage. Furthermore, the increased stiffness of the material is likely responsible for the partial destruction of some implants. Clinically, we learn that an inappropriate replacement device might lead to similar cartilage damage as seen after meniscectomy. Given the poor acceptance of the clinically available partial meniscal replacement devices, it can be speculated that development of a total meniscal replacement device might be the less challenging option.

Suitability of developed composite materials for meniscal replacement: Mechanical, friction and wear evaluation

The meniscus is a complex and frequently damaged tissue which requires a substitute capable of reproducing similar biomechanical functions. This study aims to develop a synthetic meniscal substitute that can mimic the function of the native meniscus. Medical grade silicones reinforced with nylon were fabricated using compression moulding and evaluated for mechanical and tribological properties. The optimal properties were obtained with tensile modulus increased considerably from 10.7 ± 2.9 MPa to 114.6 ± 20.9 MPa while compressive modulus was found to reduce from 2.5 ± 0.6 MPa to 0.7 ± 0.3 MPa. Using a tribometer, the coefficient of friction of 0.08 ± 0.02 was measured at the end of the 100,000 cycles. The developed composite could be an auspicious substitute for the native meniscus and the knowledge gained from this study is useful as it enhances the understanding of a potentially suitable material for meniscal implants.

Biomechanical, structural and biological characterisation of a new silk fibroin scaffold for meniscal repair

Meniscal injury is typically treated surgically via partial meniscectomy, which has been shown to cause cartilage degeneration in the long-term. Consequently, research has focused on meniscal prevention and replacement. However, none of the materials or implants developed for meniscal replacement have yet achieved widespread acceptance or demonstrated conclusive chondroprotective efficacy.

A redesigned silk fibroin scaffold, which already displayed promising results regarding biocompatibility and cartilage protection in a previous study, was characterised in terms of its biomechanical, structural and biological functionality to serve as a potential material for permanent partial meniscal replacement. Therefore, different quasi-static but also dynamic compression tests were performed. However, the determined compressive stiffness (0.56 ± 0.31 MPa and 0.30 ± 0.12 MPa in relaxation and creep configuration, respectively) was higher in comparison to the native meniscal tissue, which could potentially disturb permanent integration into the host tissue. Nevertheless, µ-CT analysis met the postulated requirements for partial meniscal replacement materials in terms of the microstructural parameters, like mean pore size (215.6 ± 10.9 µm) and total porosity (80.1 ± 4.3%). Additionally, the biocompatibility was reconfirmed during cell culture experiments. The current study provides comprehensive mechanical and biological data for the characterisation of this potential replacement material. Although some further optimisation of the silk fibroin scaffold may be advantageous, the silk fibroin scaffold showed sufficient biomechanical competence to support loads already in the early postoperative phase.

Physiologically Distributed Loading Patterns Drive the Formation of Zonally Organized Collagen Structures in Tissue-Engineered Meniscus

The meniscus is a dense fibrocartilage tissue that withstands the complex loads of the knee via a unique organization of collagen fibers. Attempts to condition engineered menisci with compression or tensile loading alone have failed to reproduce complex structure on the microscale or anatomic scale. Here we show that axial loading of anatomically shaped tissue-engineered meniscus constructs produced spatial distributions of local strain similar to those seen in the meniscus when the knee is loaded at full extension. Such loading drove formation of tissue with large organized collagen fibers, levels of mechanical anisotropy, and compressive moduli that match native tissue. Loading accelerated the development of native-sized and aligned circumferential and radial collagen fibers. These loading patterns contained both tensile and compressive components that enhanced the major biochemical and functional properties of the meniscus, with loading significantly improved glycosaminoglycan (GAG) accumulation 200-250%, collagen accumulation 40-55%, equilibrium modulus 1000-1800%, and tensile moduli 500-1200% (radial and circumferential). Furthermore, this study demonstrates local changes in mechanical environment drive heterogeneous tissue development and organization within individual constructs, highlighting the importance of recapitulating native loading environments. Loaded menisci developed cartilage-like tissue with rounded cells, a dense collagen matrix, and increased GAG accumulation in the more compressively loaded horns, and fibrous collagen-rich tissue in the more tensile loaded outer 2/3, similar to native menisci. Loaded constructs reached a level of organization not seen in any previous engineered menisci and demonstrate great promise as meniscal replacements.

Clinical Application of Scaffolds for Partial Meniscus Replacement

Meniscal tears are common injuries often treated by partial meniscectomy. This may result in altered joint contact mechanics which in turn may lead to worsening symptoms and an increased risk of osteoarthritis. Meniscal scaffolds have been proposed as a treatment option aimed at reducing symptoms while also potentially reducing progression of degenerative change. There are 2 scaffolds available for clinical use at the present time; Collagen Meniscus Implant and Actifit. Medium-term to long-term data (4.9 to 11.3 y) demonstrate efficacy of partial meniscus replacement. The patients who seem to benefit most are chronic postmeniscectomy rather than acute meniscal injuries. Herein we report on available clinical data for Collagen Meniscus Implant and Actifit while describing our preferred surgical technique and postoperative rehabilitation program.

Meniscal Scaffolds - Preclinical Evidence to Support their Use: A Systematic Review

Arthroscopic meniscal treatment is the most common procedure performed in the orthopedic practice. Current management of meniscal pathology relies on different therapeutic options, ranging from selective meniscectomy, suturing, and to meniscal replacement by using either allografts or scaffolds. The progresses made in the field of regenerative medicine and biomaterials allowed to develop several meniscal substitutes, some of those currently used in the clinical practice. Before reaching the clinical application, these devices necessarily undergo accurate testing in the animal model: the aim of the present manuscript is to systematically review the scientific evidence derived by animal model results for the use of meniscal scaffolds, in order to understand the current state of research in this particular field and to identify the trends at preclinical level that may influence in the near future the clinical practice. Thirty-four papers were included in the present analysis. In 12 cases the meniscal scaffolds were used with cells to further stimulate tissue regeneration. With the exception of some negative reports regarding dacron-based scaffolds, the majority of the trials highlighted that biomaterials and bio-engineered scaffolds are safe and could play a beneficial role in stimulating meniscal healing and in chondral protection. With regard to the benefits of cell augmentation, the evidence is limited to a small number of studies and no conclusive evidence is available. However, preclinical evidence seems to suggest that cells could enhance tissue regeneration with respect to the use of biomaterials alone, and further research should confirm the translational potential of cell-based approach.

Development and evaluation of elastomeric hollow fiber membranes as small diameter vascular graft substitutes

Engineering of small diameter (<6mm) vascular grafts (SDVGs) for clinical use remains a significant challenge. Here, elastomeric polyester urethane (PEU)-based hollow fiber membranes (HFMs) are presented as an SDVG candidate to target the limitations of current technologies and improve tissue engineering designs. HFMs are fabricated by a simple phase inversion method. HFM dimensions are tailored through adjustments to fabrication parameters. The walls of HFMs are highly porous. The HFMs are very elastic, with moduli ranging from 1-4MPa, strengths from 1-5MPa, and max strains from 300-500%. Permeability of the HFMs varies from 0.5-3.5×10(-6)cm/s, while burst pressure varies from 25 to 35psi. The suture retention forces of HFMs are in the range of 0.8 to 1.2N. These properties match those of blood vessels. A slow degradation profile is observed for all HFMs, with 71 to 78% of the original mass remaining after 8weeks, providing a suitable profile for potential cellular incorporation and tissue replacement. Both human endothelial cells and human mesenchymal stem cells proliferate well in the presence of HFMs up to 7days. These results demonstrate a promising customizable PEU HFMs for small diameter vascular repair and tissue engineering applications.

In vivo performance of a novel silk fibroin scaffold for partial meniscal replacement in a sheep model

PURPOSE

Due to the negative effects of meniscectomy, there is a need for an adequate material to replace damaged meniscal tissue. To date, no material tested has been able to replace the meniscus sufficiently. Therefore, a new silk fibroin scaffold was investigated in an in vivo sheep model.

METHODS

Partial meniscectomy was carried out to the medial meniscus of 28 sheep, and a scaffold was implanted in 19 menisci (3-month scaffold group, n = 9; 6-month scaffold group, n = 10). In 9 sheep, the defect remained empty (partial meniscectomy group). Sham operation was performed in 9 animals.

RESULTS

The silk scaffold was able to withstand the loads experienced during the implantation period. It caused no inflammatory reaction in the joint 6 months postoperatively, and there were no significant differences in cartilage degeneration between the scaffold and sham groups. The compressive properties of the scaffold approached those of meniscal tissue. However, the scaffolds were not always stably fixed in the defect, leading to gapping between implant and host tissue or to total loss of the implant in 3 of 9 cases in each scaffold group. Hence, the fixation technique needs to be improved to achieve a better integration into the host tissue, and the long-term performance of the scaffolds should be further investigated.

CONCLUSION

These first in vivo results on a new silk fibroin scaffold provide the basis for further meniscal implant development. Whilst more data are required, there is preliminary evidence of chondroprotective properties, and the compressive properties and biocompatibility are promising.

Scaffolds drive meniscus tissue engineering

The review focuses on the recent research trend on scaffold types and biomedical applications, and perspectives in meniscus tissue engineering.

Fibrochondrogenic potential of synoviocytes from osteoarthritic and normal joints cultured as tensioned bioscaffolds for meniscal tissue engineering in dogs

Meniscal tears are a common cause of stifle lameness in dogs. Use of autologous synoviocytes from the affected stifle is an attractive cell source for tissue engineering replacement fibrocartilage. However, the diseased state of these cells may impede in vitro fibrocartilage formation. Synoviocytes from 12 osteoarthritic (“oaTSB”) and 6 normal joints (“nTSB”) were cultured as tensioned bioscaffolds and compared for their ability to synthesize fibrocartilage sheets. Gene expression of collagens type I and II were higher and expression of interleukin-6 was lower in oaTSB versus nTSB. Compared with nTSB, oaTSB had more glycosaminoglycan and alpha smooth muscle staining and less collagen I and II staining on histologic analysis, whereas collagen and glycosaminoglycan quantities were similar. In conclusion, osteoarthritic joint—origin synoviocytes can produce extracellular matrix components of meniscal fibrocartilage at similar levels to normal joint—origin synoviocytes, which makes them a potential cell source for canine meniscal tissue engineering.

Hemocompatibility evaluation of small elastomeric hollow fiber membranes as vascular substitutes

One of the main challenges for clinical implementation of small diameter vascular grafts (SDVGs) is their limited hemocompatibility. Important design specifications for such grafts include features that minimize the long-term risks of restenosis, fouling, and thrombus formation. In our lab, we have developed elastomeric hollow fiber membranes (HFMs), using a phase inversion method, as candidates for SDVGs. Here, we present our results for in vitro hemocompatibility testing of our HFM under flow and static conditions. Our results showed that the polymer-based HFMs do not damage the integrity of human red blood cells (RBCs) as shown by their low hemolytic extent (less than 2%). When analyzed for blood cell lysis using lactate dehydrogenase (LDH) activity as an indicator, no significant differences were observed between blood exposed to our HFMs and uncoagulated blood. Analysis of protein adsorption showed a low concentration of proteins deposited on the surfaces of HFM after 24 h. Platelet adhesion profiles using human platelet-rich plasma (PRP) showed that a low level of platelets adhered to the HFMs after 24 h, indicating minimal thrombotic potential. Under the majority of conditions, no significant differences were observed between medical-grade polymers and our HFMs. Eventual optimization of hemocompatible elastomeric HFM vessel grafts could lead to improved tissue vascularization as well as vascularized, tissue-engineered scaffolds for organ repair.

Comparison of meniscal fibrochondrocyte and synoviocyte bioscaffolds toward meniscal tissue engineering in the dog

Tissue engineering is a promising field of study toward curing the meniscal deficient stifle; however the ideal cell type for this task is not known. We describe here the extraction of synoviocytes and meniscal fibrochondrocytes from arthroscopic debris from six dogs, which were cultured as tensioned bioscaffolds to synthesize meniscal-like fibrocartilage sheets. Despite the diseased status of the original tissues, synoviocytes and meniscal fibrochondrocytes had high viability at the time of removal from the joint. Glycosaminoglycan and collagen content of bioscaffolds did not differ. Meniscal fibrochondrocyte bioscaffolds contained more type II collagen, but collagen deposition was disorganized, with only 30-40% of cells viable. The collagen of synoviocyte bioscaffolds was organized into sheets and bands and 80-90% of cells were viable. Autologous, diseased meniscal fibrochondrocytes and synoviocytes are plausible cell sources for future meniscal tissue engineering research, however cell viability of meniscal fibrochondrocytes in the tensioned bioscaffolds was low.

Release of growth factors from a reinforced collagen GAG matrix supplemented with platelet rich plasma: Influence on cultured human meniscal cells

Damage to meniscal cartilage has been strongly linked to accelerated articular wear and consequently to osteoarthritis. Damage might be ameliorated by delivery of growth factors from platelet rich plasma (PRP) via a fiber reinforced collagen matrix designed for meniscal repair. PRP composition, release of growth factors, and influence on meniscal cell growth and gene expression were investigated. PRP was prepared using Harvest Smartprep (HS-PRP), Cascade Fibrinet (CF-PRP), and a simple centrifuge protocol (DC-PRP) from four donors each. CF-PRP had the highest ratio of platelets, with very few other blood cell types. HS-PRP had the highest total number of platelets but also contained high levels of red and white blood cells. Absorbed to collagen matrices HS-PRP released the highest levels of TGF-β1 and PDGF-AB with DC-PRP the most IGF-1. Cumulative release from collagen matrix was 48 ng/cm(3) IGF-1, 96 ng/cm(3) TGF-β1, and 9.6 ng/cm(3) PDGF-AB. Collagen matrix with PRP was able to increase meniscal cell number above peripheral whole blood and up-regulated gene expression of Aggrecan, Collagen type I (α1), and Elastin (3.3 ± 0.8-fold, 2.9 ± 0.6-fold, 4.0 ± 1.4-fold, respectively). Demonstrating that PRP combined with fiber reinforced collagen matrix could influence meniscal cells and might be of use for treating meniscal defects.

Growth factor treated tensioned synoviocyte neotissues: towards meniscal bioscaffold tissue engineering

Meniscal injury is a common cause of osteoarthritis, pain, and disability in dogs and humans, but tissue-engineered bioscaffolds could be a treatment option for meniscal deficiency. The objective of this study was to compare meniscus-like matrix histology, composition, and biomechanical properties of autologous tensioned synoviocyte neotissues (TSN) treated with fetal bovine serum (TSNfbs) or three chondrogenic growth factors (TSNgf). Fourth passage canine synoviocytes from 10 dogs were grown in hyperconfluent monolayer culture, formed into TSN, and then cultured for 3 weeks with 17.7% FBS or three human recombinant TSNgf (bFGF, TGF-β1, and IGF-1). Cell viability was determined with laser microscopy. Histological architecture and the composition of fibrocartilage matrix were evaluated in TSN by staining tissues for glycosaminoglycan (GAG), α-smooth muscle actin, and collagen 1 and 2; quantifying the content of GAG, DNA, and hydroxyproline; and measuring the gene expression of collagens type 1α and 2α, the GAG aggrecan, and transcription factor Sry-type Homeobox Protein-9 (SOX9). Biomechanical properties were determined by materials testing force-deformation curves. The TSN contained components and histological features of mensical fibrocartilage extracellular matrix. Growth factor-treated TSN had higher DNA content but lower cell viability than TSNfbs. TSNgf had greater fibrocartilage-like matrix content (collagen 2 and GAG content with increased collagen 2α and SOX9 gene expression). Additionally, TSNgf collagen was more organized histologically and so had greater tensile biomechanical properties. The results indicate the potential of TSN when cultured with growth factors as implantable bioscaffolds for the treatment of canine meniscal deficiency.

The collagen meniscus implant

Lesions in the meniscus occur particularly in young, active patients in the nonvascularized area which, consequently have a bad intrinsic healing capacity. This has a large impact on the mobility and function of the knee joint. Lesions, and partial lesions, lead to the progression of osteoarthritis over time in a large proportion of patients. The only clinical treatment for severe cases so far is an allograft donor meniscus, which is used mostly in patients with severe osteoarthritis with a completely destroyed meniscus. However, this technique still has to be considered as experimental and, thus, is not yet used on a routine basis. Various technical solutions have been advocated to repair meniscus lesions. One solution is to perform a partial meniscectomy and insert a collagen meniscus implant (CMI) at the site of the lesion. However, the initial mechanical properties of the collagen scaffold are inferior to the native meniscus. Therefore, it is only possible to perform a CMI implantation if the peripheral rim of the meniscus is still intact. Histology of preclinical and clinical biopsies of the implanted CMI demonstrated a repopulation of the scaffold by fibrous tissue and in time a remodeling of the fibrous tissue into fibrocartilaginous-like tissue. Based on histology, the ingrowth of new tissue into the CMI might occur by a process of synovial overgrowth, but other mechanisms of revitalization are also possible. Although some clinical studies demonstrated improvement in outcome scores, the number of patients was small in all studies and the positive effect on the prevention of progression of osteoarthritis was not compared with control groups.

Biodegradable polyurethane meniscal scaffold for isolated partial lesions or as combined procedure for knees with multiple comorbidities: clinical results at 2 years

PURPOSE

The aim of this study is to evaluate the safety and clinical efficacy of this novel polyurethane meniscal scaffold to treat partial meniscal loss.

METHODS

Eighteen patients (11 men and 7 women, mean age: 45 years) affected by irreparable acute meniscal tears requiring partial meniscectomy or chronic prior loss of meniscal tissue were enrolled in the study. They underwent arthroscopic polyurethane meniscal scaffold implantation (13 medial and 5 lateral) and, in case of presence of other comorbidities, concurrent procedures were also performed. Patients were prospectively evaluated up to 2 years of follow-up through IKDC objective, IKDC subjective, and Tegner scores. Furthermore, MRI evaluation of the meniscal scaffold was performed.

RESULTS

No major adverse events were observed. A statistically significant increase in all the clinical parameters considered was found. The IKDC objective score increased from 61 % of normal or nearly normal knees at basal evaluation to 94 % at 2 years of follow-up (p = 0.01). There was also a significant increase in the IKDC subjective score both at 6-12 months of follow-up (p = 0.03 and p < 0.005), which was confirmed at 24 months. The Tegner score also showed a significant increase from the pre-operative level (median value 2, range 1-5) to final evaluation (median value 3, range 2-5; p = 0.005), albeit not reaching the pre-injury sports activity level.

CONCLUSIONS

The implantation of this novel polyurethane scaffold proved to be a safe and potentially effective procedure to treat partial meniscal loss with encouraging results at short-term follow-up. Further high-quality studies with larger numbers of patients and longer evaluation times are needed to confirm these preliminary data.

In vitro synthesis of tensioned synoviocyte bioscaffolds for meniscal fibrocartilage tissue engineering

Background

Meniscal injury is a common cause of lameness in the dog. Tissue engineered bioscaffolds may be a treatment option for meniscal incompetency, and ideally would possess meniscus- like extracellular matrix (ECM) and withstand meniscal tensile hoop strains. Synovium may be a useful cell source for meniscal tissue engineering because of its natural role in meniscal deficiency and its in vitro chondrogenic potential. The objective of this study is to compare meniscal -like extracellular matrix content of hyperconfluent synoviocyte cell sheets (“HCS”) and hyperconfluent synoviocyte sheets which have been tensioned over wire hoops (tensioned synoviocyte bioscaffolds, “TSB”) and cultured for 1 month.

Results

Long term culture with tension resulted in higher GAG concentration, higher chondrogenic index, higher collagen concentration, and type II collagen immunoreactivity in TSB versus HCS. Both HCS and TSB were immunoreactive for type I collagen, however, HCS had mild, patchy intracellular immunoreactivity while TSB had diffuse moderate immunoreactivity over the entire bisocaffold. The tissue architecture was markedly different between TSB and HCS, with TSB containing collagen organized in bands and sheets. Both HCS and TSB expressed alpha smooth muscle actin and displayed active contractile behavior. Double stranded DNA content was not different between TSB and HCS, while cell viability decreased in TSB.

Conclusions

Long term culture of synoviocytes with tension improved meniscal- like extra cellular matrix components, specifically, the total collagen content, including type I and II collagen, and increased GAG content relative to HCS. Future research is warranted to investigate the potential of TSB for meniscal tissue engineering.

Culture of canine synoviocytes on porcine intestinal submucosa scaffolds as a strategy for meniscal tissue engineering for treatment of meniscal injury in dogs

Meniscal injury is a common cause of canine lameness. Tissue engineered bioscaffolds may be a treatment option for dogs suffering from meniscal damage. The aim of this study was to compare in vitro meniscal-like matrix formation and biomechanical properties of porcine intestinal submucosa sheets (SIS), used in canine meniscal regenerative medicine, to synoviocyte-seeded SIS bioscaffold (SSB), cultured with fetal bovine serum (SSBfbs) or chondrogenic growth factors (SSBgf). Synoviocytes from nine dogs were seeded on SIS and cultured for 30days with 17.7% fetal bovine serum or recombinant chondrogenic growth factors (IGF-1, TGFβ1 and bFGF). The effect on fibrochondrogenesis was determined by comparing mRNA expression of collagen types Iα and IIα, aggrecan, and Sry-type homeobox protein-9 (SOX9) as well as protein expression of collagens I and II, glycosaminoglycan (GAG), and hydroxyproline. The effect of synoviocyte seeding and culture conditions on biochemical properties was determined by measuring peak load, tensile stiffness, resilience, and toughness of bioscaffolds. Pre-culture SIS contained 13.6% collagen and 2.9% double-stranded DNA. Chondrogenic growth factor treatment significantly increased SOX9, collagens I and IIα, aggrecan gene expression (P<0.05), and histological deposition of fibrocartilage extracellular matrix (GAG and collagen II). Culture with synoviocytes increased SIS tensile peak load at failure, resilience, and toughness of bioscaffolds (P<0.05). In conclusion, culturing SIS with synoviocytes prior to implantation might provide biomechanical benefits, and chondrogenic growth factor treatment of cultured synoviocytes improves in vitro axial meniscal matrix formation.

Current strategies in meniscal regeneration

The meniscus plays an important role in the biomechanics and tribology of the knee joint. Damage to or disease of the meniscus is now recognized to predispose to the development of osteoarthritis. Treatment of meniscal injury through arthroscopic surgery has become one of the most common orthopedic surgical procedures, and in the United States this can represent 10 to 20% of procedures related to the knee. The meniscus has a limited healing capacity constrained to the vascularized periphery and therefore, surgical repair of the avascular regions is not always feasible. Replacement and repair of the meniscus to treat injuries is being investigated using tissue engineering strategies. Promising as these approaches may be, there are, however, major barriers to overcome before translation to the clinic.

High density type I collagen gels for tissue engineering of whole menisci

This study investigates the potential of high density type I collagen gels as an injectable scaffold for tissue engineering of whole menisci, and compares these results with previous strategies using alginate as an injectable scaffold. Bovine meniscal fibrochondrocytes were mixed with collagen and injected into micro-computed tomography-based molds to create 10 and 20mgml(-1) menisci that were cultured for up to 4weeks and compared with cultured alginate menisci. Contraction, histological, confocal microscopy, biochemical and mechanical analysis were performed to determine tissue development. After 4weeks culture, collagen menisci had preserved their shape and significantly improved their biochemical and mechanical properties. Both 10 and 20mgml(-1) menisci maintained their DNA content while significantly improving the glycosaminoglycan and collagen content, at values significantly higher than the alginate controls. Collagen menisci matched the alginate control in terms of the equilibrium modulus, and developed a 3- to 6-fold higher tensile modulus than alginate by 4weeks. Further fibrochondrocytes were able to reorganize the collagen gels into a more fibrous appearance similar to native menisci.

PLDLA/PCL-T Scaffold for Meniscus Tissue Engineering

The inability of the avascular region of the meniscus to regenerate has led to the use of tissue engineering to treat meniscal injuries. The aim of this study was to evaluate the ability of fibrochondrocytes preseeded on PLDLA/PCL-T [poly(L-co-D,L-lactic acid)/poly(caprolactone-triol)] scaffolds to stimulate regeneration of the whole meniscus. Porous PLDLA/PCL-T (90/10) scaffolds were obtained by solvent casting and particulate leaching. Compressive modulus of 9.5±1.0 MPa and maximum stress of 4.7±0.9 MPa were evaluated. Fibrochondrocytes from rabbit menisci were isolated, seeded directly on the scaffolds, and cultured for 21 days. New Zealand rabbits underwent total meniscectomy, after which implants consisting of cell-free scaffolds or cell-seeded scaffolds were introduced into the medial knee meniscus; the negative control group consisted of rabbits that received no implant. Macroscopic and histological evaluations of the neomeniscus were performed 12 and 24 weeks after implantation. The polymer scaffold implants adapted well to surrounding tissues, without apparent rejection, infection, or chronic inflammatory response. Fibrocartilaginous tissue with mature collagen fibers was observed predominantly in implants with seeded scaffolds compared to cell-free implants after 24 weeks. Similar results were not observed in the control group. Articular cartilage was preserved in the polymeric implants and showed higher chondrocyte cell number than the control group. These findings show that the PLDLA/PCL-T 90/10 scaffold has potential for orthopedic applications since this material allowed the formation of fibrocartilaginous tissue, a structure of crucial importance for repairing injuries to joints, including replacement of the meniscus and the protection of articular cartilage from degeneration.

The effect of IGF-I on anatomically shaped tissue-engineered menisci

This study investigates the effect of insulin-like growth factor (IGF)-I on the development of anatomically-shaped alginate menisci seeded with meniscal fibrochondrocytes. To accomplish this, bovine meniscal fibrochondrocytes were seeded into 2% w/v alginate, crosslinked with calcium sulfate, and injected into anatomical molds derived from microcomputed tomography scans. The meniscal constructs were then cultured for up to 4 weeks with or without 100 ng/mL IGF-I supplemented in the media. Histological, immunohistological, biochemical, and mechanical analyses were performed to characterize tissue development, accumulation and localization of extracellular matrix, and mechanical properties. After 4 weeks of culture, IGF-I treatment significantly improved mechanical and biochemical properties, while maintaining DNA content, with a 26-fold increase in glycosaminoglycan (GAG) content and 10-fold increase in collagen content compared to 0-week controls, and a 3-fold increase in the equilibrium modulus at 2 weeks compared to controls. IGF-I-treated menisci had ∼60% of the GAG content of native tissue and the compressive equilibrium modulus matched native properties by 2 weeks of culture. Further, IGF-I-treated menisci developed a distinct surface layer similar to native tissue with elongated cells and collagen fibers aligned parallel to the surface, the presence of types I and II collagen, and accumulation of lubricin. This study demonstrates that IGF-I treatment can greatly increase the mechanical and biochemical properties of engineered tissues and aid in the development of a distinct surface zone similar to the superficial zone of native menisci.

Meniscus reconstruction: today's achievements and premises for the future

Injuries of the meniscus remain a burden for the development of premature cartilage degeneration and osteoarthritis. This review surveys all treatment options and focuses on the recent development of tissue engineering. Tissue engineering of the meniscus means a successful combination of cells, scaffolds and specific stimuli. Each element of the combination can be subject to variation. Studies investigating the optimum meniscus implant and previous steps in producing these implants are presented in this article. A comprehensive search of the English and German literature was performed in PubMed to retrieve appropriate manuscripts for review. Based on the literatures, autografts and allografts can delay the progress of osteoarthritis for a restricted time period, but several concerns persist. The biomechanical properties of the native meniscus are not copied entirely by the current existing autografts. Congruence, fixation, biocompatibility and potential infection will always remain as limitations for the users of allografts. Long-term results are still not available for meniscus prosthesis and even though it permits fast recovery, several aspects are questionable: bioincompatibility and a lack of cellular adhesion are likely to compromise their long-term fate. Currently, there is no ideal implant generated by means of tissue engineering. However, meniscus tissue engineering is a fast developing field, which promises to develop an implant that mimics histological and biomechanical properties of the native meniscus. At present several cell sources and scaffolds have been used successfully to grow 3-dimensional constructs. In future, optimal implants have to be developed using growth factors, modified scaffolds and stimuli that support cellular proliferation and differentiation to regenerate the native meniscus more closely.

Synthetic meniscus replacement: a review

The number of meniscus-related operations continues to rise due to the ageing and more active population. Irreparable meniscal lesions generally require (partial) meniscectomy. Although a majority of the patients benefit from pain relief and functional improvement post-meniscectomy, some remain symptomatic. As an alternative to a meniscal allograft, which is only indicated for the severely damaged meniscus, most patients can nowadays be treated by implantation of a synthetic meniscal substitute. Currently three of these implants, two partial and one total replacement, are clinically available and several others are in the stage of preclinical testing. Grossly, two types of meniscal substitutes can be distinguished: porous, resorbable implants that stimulate tissue regeneration and solid, non-resorbable implants that permanently replace the whole meniscus. Although the implantation of a porous meniscus replacement generally seems promising and improves clinical outcome measures to some degree, their superiority to partial meniscectomy still needs to be proven. The evaluation of new prostheses being developed requires a wider focus than has been adopted so far. Upon selection of the appropriate materials, preclinical evaluation of such implants should comprise a combination of (in vitro) biomechanical and (in vivo) biological tests, while up to now the focus has mainly been on biological aspects. Obviously, well-defined randomised controlled trials are necessary to support clinical performance of new implants. Since the use of a meniscus replacement requires an additional costly implant and surgery compared to meniscectomy only, the clinical outcome of new products should be proven to surpass the results of the conventional therapies available.

Biological enhancement of meniscus repair and replacement

When a meniscus injury occurs, it is generally accepted that preserving the meniscus is important for life-long joint preservation. Traditional suture repair of the meniscus has good results; however, the healing potential of meniscus tissue remains as a biological challenge because it is not a completely vascularized structure. For this reason, investigators have continued to search for adjuncts to improve clinical results. Mechanical adjuncts, local factor enhancement, scaffolds, gene therapy, and cell therapy have all been examined as options for improvement of biology and structure. This study reviews the basic science and clinical application of these modalities and provides an assessment of techniques on the horizon.

Meniscus transplantation using treated xenogeneic meniscal tissue: viability and chondroprotection study in rabbits

PURPOSE

This was a preliminary study performed in vivo to evaluate the viability and the chondroprotective effects of irradiated deep-frozen xenogeneic meniscal tissue as a novel substitute for meniscus transplantation.

METHODS

Medial meniscectomies were performed on the right knees of 48 New Zealand white rabbits. The inner one-third of pig meniscus was harvested and then irradiated and deeply frozen. The treated xenogeneic meniscal tissues were then transplanted to 24 right knees (Xeno group), whereas 24 other knees received meniscus allograft transplantations (Allo group). The left knees of the Xeno group and Allo group received meniscectomies (Meni group) and sham operations (Sham group), respectively. The rabbits were killed at weeks 6, 12, and 24 postoperatively. The newly formed structure of the implanted tissue and cartilage of the medial compartment of each group was assessed by gross and semiquantitative histologic analysis.

RESULTS

After 24 weeks, the implanted xenogeneic meniscal tissue completely healed to the synovium and formed meniscus-like tissue. The chondrocyte-like cell infiltrated into the tissue with extracellular matrix including type II collagen and proteoglycans. The Xeno group showed significantly less cartilage degeneration than that of the Meni group in the medial tibial plateau at week 24 (P < .05). No significant difference was found between the Xeno group and the Allo group except for the meniscus-covered regions at week 24. From week 12 to week 24, almost no advanced cartilage degeneration was found in weight-bearing regions of the medial tibial plateau of the Xeno group.

CONCLUSIONS

The treated xenogeneic meniscal tissue healed to the synovium with tissue regeneration and slowed down articular cartilage degeneration in the short-term. The chondroprotection of xenograft transplantation was similar to that of allograft transplantation.

CLINICAL RELEVANCE

The treated xenogeneic meniscal tissue showed the potential for viability and slowed cartilage degeneration, but more studies are required for application in humans in the future.

Decellularized cartilage matrix as a novel biomatrix for cartilage tissue-engineering applications

Damage of cartilage structures in the head and neck region as well as in orthopedic sites are frequently caused by trauma, tumor resection, or congenital defects. Despite a high demand in many clinical fields, until today, no adequate cartilage replacement matrix is available for these fields of application. Materials that are clinically applied for joint cartilage repair still need optimization due to difficult intraoperative handling and risk of early mechanical damage. We have developed and applied a novel chemical process to completely decellularize and sterilize human and porcine cartilage tissues (meniscus cartilage and nasal septum) to generate a new type of bioimplant matrix. To characterize this matrix and to determine the effect of the decellularization process, the content of denatured collagen (w(D)) and the content of glycosaminoglycans (GAGs) (w(G)) were determined. Possible cytotoxic effects and cellular compatibility of the matrix in vitro have been examined by seeding processed cartilage biomatrices with human primary chondrocytes as well as murine fibroblasts (L929). Vitality and state of metabolism of cells were measured using MTS assays. Both cell types adhered to scaffold surfaces and proliferated. No areas of growth inhibition or cytotoxic effects were detected. New synthesis of cartilage-specific extracellular matrix was observed. By histological staining, electron microscopy, and μCT analysis, an increase of matrix porosity, complete cell elimination, and high GAG removal were demonstrated. Being from natural-origin, processed xenogenic and allogeneic cartilage biomatrices are highly versatile with regard to shape, size, and biomechanics, making them promising candidates for various biomedical applications.

Tissue engineering for total meniscal substitution: animal study in sheep model--results at 12 months

The aim of the study was to investigate the use of a hyaluronic acid/polycaprolactone material for meniscal tissue engineering and to evaluate the tissue regeneration after the augmentation of the implant with expanded autologous chondrocytes. Eighteen skeletally mature sheep were treated. The animals were divided into three groups: cell-free scaffold, scaffold seeded with autologous chondrocytes, and meniscectomy alone. The implant was sutured to the capsule and to the meniscal ligament. At a 12-month gross assessment, histology and histomorphometry were used to assess the meniscus implant, knee joint, and osteoarthritis development. All implants showed excellent capsular ingrowth at the periphery. The implant gross assessment showed significant differences between cell-seeded and cell-free groups (p=0.011). The histological analysis indicated a cellular colonization throughout the implanted constructs. Avascular cartilaginous tissue formation was significantly more frequent in the cell-seeded constructs. Joint gross assessment showed that sheep treated with scaffold implantation achieved a significant higher score than those underwent meniscectomy (p<0.0005), and the Osteoarthritis Research Society International score showed that osteoarthritic changes were significantly less in the cell-seeded group than in the meniscectomy group (p=0.047), even though results were not significantly superior to those of the cell-free scaffold. Seeding of the scaffold with autologous chondrocytes increases its tissue regeneration capacity, providing a better fibrocartilaginous tissue formation. The study suggests the potential of the novel hyaluronic acid/polycaprolactone scaffold for total meniscal substitution, although this approach has to be further improved before being applied into clinical practice.

Supercritical CO2 in injection molding can produce open porous polyurethane scaffolds – a parameter study

There are several methods of producing open porous polymer structures for medical use. However, very few are applicable to industries and are therefore limited to both number of samples and batch variations. This study presents an industrial microcellular injection molding process, known as MuCell® technology, which was used to produce highly porous scaffolds of thermoplastic polyurethane. A parameter study was performed to quantify and analyze the effect of the processing parameters on the porous structure. Six key parameters (gas content, weight reduction, injection speed, mold temperature, plasticizing pressure, and temperature) were tested with an iteration method. The pore structure was determined with advanced micro Computer Tomography algorithm. All key processing parameters were identified. Gas content and weight reduction showed a more profound effect on the pore morphology than other parameters on the pore structure. It was possible to produce scaffolds with open porosity as high as 71%. The study concludes that MuCell® technology is an accurate and liable production method for large-scale production of open porous thermoplastic polyurethane scaffolds, and supercritical fluid could, therefore, be a potential production method for polymer scaffolds.

Tissue engineering and regenerative medicine strategies in meniscus lesions

PURPOSE

The aim of this systematic review was to address tissue engineering and regenerative medicine (TERM) strategies applied to the meniscus, specifically (1) clinical applications, indications, results, and pitfalls and (2) the main trends in research assessed by evaluation of preclinical (in vivo) studies.

METHODS

Three independent reviewers performed a search on PubMed, from 2006 to March 31, 2011, using the term "meniscus" with all of the following terms: "scaffolds," "constructs," "cells," "growth factors," "implant," "tissue engineering," and "regenerative medicine." Inclusion criteria were English language-written, original clinical research (Level of Evidence I to IV) and preclinical studies of TERM application in knee meniscal lesions. Reference lists and related articles on journal Web sites of selected articles were checked until prepublication for potential studies that could not be identified eventually by our original search. The modified Coleman Methodology score was used for study quality analysis of clinical trials.

RESULTS

The PubMed search identified 286 articles (a similar search from 2000 to 2005 identified 161 articles). Non-English-language articles (n = 9), Level V publications (n = 19), in vitro studies (n = 118), and 102 studies not related to the topic were excluded. One reference was identified outside of PubMed. Thirty-eight references that met the inclusion criteria were identified from the original search. On the basis of our prepublication search, 2 other references were included. A total of 9 clinical and 31 preclinical studies were selected for further analysis. Of the clinical trials, 1 was classified as Level I, 2 as Level II, and 6 as Level IV. Eight referred to acellular scaffold implantation for partial meniscal replacement, and one comprised fibrin clot application. The mean modified Coleman Methodology score was 48.0 (SD, 15.7). Of the preclinical studies, 11 original works reported on studies using large animal models whereas 20 research studies used small animals. In these studies the experimental design favored cell-seeded scaffolds or scaffolds enhanced with growth factors (GFs) in attempts to improve tissue healing, as opposed to the plain acellular scaffolds that were predominant in clinical trials. Injection of mesenchymal stem cells and gene therapy are also presented as alternative strategies.

CONCLUSIONS

Partial meniscal substitution using acellular scaffolds in selected patients with irreparable loss of tissue may be a safe and promising procedure. However, there is only 1 randomized controlled study supporting its application, and globally, many methodologic issues of published trials limit further conclusions. We registered a different trend in preclinical trials, with most considering augmentation of scaffolds by cells and/or GFs, as opposed to the predominantly acellular approach in clinical trials. Different TERM approaches to enhance meniscal repair or regeneration are in preclinical analysis, such as the use of mesenchymal stem cells, gene therapy, and GFs alone or in combination, and thus could be considered in the design of subsequent trials.

LEVEL OF EVIDENCE

Level IV, systematic review of Level I to IV studies.

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.

Frictional properties of the meniscus improve after scaffold-augmented repair of partial meniscectomy: a pilot study

BACKGROUND

To prevent further degeneration, it is desirable to fill a meniscal defect with a supportive scaffold that mimics the mechanics of native tissue. Degradable porous scaffolds have been used, but it is unclear whether the tissue that fills the site of implantation is mechanically adequate, particularly with respect to frictional performance.

QUESTIONS/PURPOSES

We therefore determined the frictional behavior of native and engineered meniscal replacement tissue from in vivo implantation over time.

METHODS

We evaluated boundary and mixed-mode friction coefficients of tissue generated in porous polyurethane scaffolds used to augment the repair of the meniscus of 13 skeletally mature sheep after partial meniscectomy. Implants were removed for evaluation at 3, 6, and 12 months. The friction coefficient, aggregate modulus, and hydraulic permeability were evaluated for tissue harvested from native meniscus adjacent to the implants, native meniscus from the intact contralateral knee, and repair tissue from the site of the scaffold implantation. The equilibrium friction coefficient (μ(eq)) was measured in the presence of a lubricant bath of either phosphate-buffered saline (PBS) or equine synovial fluid (ESF).

RESULTS

Boundary μ(eq) in PBS of engineered meniscus improved with time and was similar to native tissue after 6 months. ESF enhanced lubrication for all samples at nearly all time points demonstrating the efficacy of ESF as a joint lubricant for repair tissue as well as native meniscus. Modulus increased and permeability decreased with implantation, likely as a result of tissue ingrowth.

CONCLUSIONS

Promoting tissue ingrowth into porous scaffolds is a potential strategy for improving friction performance in meniscal repair.

Changes in articular cartilage after meniscectomy and meniscus replacement using a biodegradable porous polymer implant

PURPOSE

To evaluate the long-term effects of implantation of a biodegradable polymer meniscus implant on articular cartilage degeneration and compare this to articular cartilage degeneration after meniscectomy.

METHODS

Porous polymer polycaprolacton-based polyurethane meniscus implants were implanted for 6 or 24 months in the lateral compartment of Beagle dog knees. Contralateral knees were meniscectomized, or left intact and served as controls. Articular cartilage degeneration was evaluated in detail using India ink staining, routine histology, immunochemistry for denatured (Col2-¾M) and cleaved (Col2-¾C(short)) type II collagen, Mankin's grading system, and cartilage thickness measurements.

RESULTS

Histologically, fibrillation and substantial immunohistochemical staining for both denatured and cleaved type II collagen were found in all three treatment groups. The cartilage of the three groups showed identical degradation patterns. In the 24 months implant group, degradation appeared to be more severe when compared to the 6 months implant group and meniscectomy group. Significantly more cartilage damage (India ink staining, Mankin's grading system, and cartilage thickness measurements) was found in the 24 months implant group compared to the 6 months implant group and meniscectomy group.

CONCLUSION

Degradation of the cartilage matrix was the result of both mechanical overloading as well as localized cell-mediated degradation. The degeneration patterns were highly variable between animals. Clinical application of a porous polymer implant for total meniscus replacement is not supported by this study.

Citocompatibilidade de blendas de poli(p-dioxanona)/ poli(hidroxi butirato) (PPD/PHB) para aplicações em engenharia de tecido cartilaginoso

Buscando estratégias que repercutam na melhoria da interação entre materiais poliméricos biorreabsorvíveis e o crescimento celular, o presente estudo in vitro teve como objetivo estudar a influência de blendas de PPD/PHB na adesão celular e crescimento de fibrocondrócitos obtidos a partir de cultura primária. As blendas de PPD/PHB foram preparadas pelo método de evaporação de solvente nas composições 100/0, 60/40 e 50/50 e caracterizadas por microscopia eletrônica de varredura (MEV). Observações ultra-estruturais mostraram alterações na morfologia celular, sugerindo que os fibrocondrócitos podem responder a alterações no substrato alterando seu perfil fenotípico. As análises com MTT demonstraram que as blendas não apresentaram citotoxicidade e permitiram a adesão e proliferação dos fibrocondrócitos sobre os substratos em todas as suas composições. O ensaio colorimétrico com Sirius Red evidenciou a capacidade de manutenção da síntese de matriz extracelular colágena sobre as amostras, concluindo-se que as blendas de PPD/PHB podem ser indicadas para o cultivo celular.

Evaluation of a porous polyurethane scaffold in a partial meniscal defect ovine model

PURPOSE

The objective of this study was to assess the performance of a degradable porous polyurethane scaffold in a partial meniscectomy ovine model.

METHODS

We subjected 42 skeletally mature ewes to unilateral partial excision of the lateral meniscus. In 19 animals the defect was left unfilled; in 23 animals a scaffold was inserted. Knees were examined by magnetic resonance imaging, gross inspection, and histologic inspection of the cartilage of the tibial plateau.

RESULTS

In contrast to what has been previously reported in a complete meniscal replacement model, cartilage damage did not occur under the site of scaffold implantation; this was likely influenced by the rapid infiltration of cells and the dense tissue that formed within the scaffold. Cartilage damage in both groups was located close to the midline of the joint. No significant difference in the condition of the articular cartilage of the tibial plateau was seen between groups up to 12 months postoperatively. This result was influenced by the fact that the partly meniscectomized knees also showed unexpected tissue regeneration within the defect site, which raises concern about the suitability of using a partial meniscectomy as a control in the ovine model.

CONCLUSIONS

Our study has shown that implantation of a polyurethane scaffold in a partial meniscectomy ovine model promotes tissue ingrowth without damaging the cartilage with which it articulates.

CLINICAL RELEVANCE

Meniscal deficiency is a common occurrence, the effective clinical management of which is limited by the absence of an off-the-shelf implantable construct.

Analysis of frictional behavior and changes in morphology resulting from cartilage articulation with porous polyurethane foams

Porous polyurethane foams (PUR) have been extensively evaluated as meniscal replacement materials and show great promise enabling infiltration of cells and fibrocartilage formation in vivo. Similar to most materials, PUR demonstrates progressive degeneration of opposing cartilage; however, the damage mechanism is impossible to determine because no information exists on the frictional properties of PUR-cartilage interfaces. The goals of this study were to characterize the frictional behavior of a cartilage-PUR interface across a range of articulating conditions and assess the resulting morphological changes to the cartilage surface following articulation. Articular cartilage was oscillated against PUR or stainless steel using phosphate-buffered saline (PBS) and synovial fluid as lubricants. Following friction testing, cartilage and PUR samples were analyzed with environmental scanning electron microscopy and histological staining to determine changes in tissue morphology. Stribeck-surface analysis demonstrated distinct lubrication modes; however, boundary mode lubrication was dominant in cartilage-PUR interfaces and the low-friction pressure-borne lubrication mechanism present in native joints was absent. Microscopy noted obvious wear, with disruption of the collagen architecture and concomitant proteoglycan loss in cartilage articulated against PUR. These data collectively point to the importance of frictional properties as design parameters for implants and materials for soft tissue replacement.