Novel organ-slice culturing system to simulate meniscal repair: Proof of concept using a synovium-based pool of meniscoprogenitor cells

The chondrogenic potential of the bovine tendon sheath-a novel source of stem cells for cartilage repair

The human hand is traumatized more frequently than any other bodily part. Trauma and pathological processes (eg, rheumatoid arthritis, osteoarthritis) commonly implicate the finger joints and specifically damage also the layer of articular cartilage. Endeavors are now being made to surgically repair such cartilage lesions biologically using tissue-engineering approaches that draw on donor cells and/or donor tissues. The tendon sheaths, particularly their inner layers, that is, the peritendineum, surround the numerous tendons in the hand. The peritendineum is composed of mesenchymal tissue. We hypothesize that this tissue harbors pluripotent mesenchymal stem cells and thus could be used for cartilage repair, irrespective of the donor's age. Using a bovine model (young calves vs adult cows), the pluripotentiality of the peritendineal stem cells, namely, their osteogenicity, chondrogenicity, and adipogenicity, was investigated by implementing conventional techniques. Subsequently, the chondrogenic potential of the peritendineal tissue itself was analyzed. Its differentiation into cartilage was induced by the application of specific growth factors (members of the TGF-β-superfamily). The characteristics of the tissue formed were evaluated structurally (immuno) histochemically, histomorphometrically, and biochemically (gene expression and protein level). Our data confirm that the bovine peritendineum contains stem cells whose pluripotentiality is independent of donor age. This tissue could also be induced to differentiate into cartilage, likewise, irrespective of the donor's age. Preliminary investigations with adult human peritendineal biopsy material derived from the hand's peritendineal flexor tendon sheaths revealed that this tissue can also be induced to differentiate into cartilage.

Human Bone Typing Using Quantitative Cone-Beam Computed Tomography

INTRODUCTION

Bone typing is crucial to enable the choice of a suitable implant, the surgical technique, and the evaluation of the clinical outcome. Currently, bone typing is assessed subjectively by the surgeon.

OBJECTIVE

The aim of this study is to establish an automatic quantification method to determine local bone types by the use of cone-beam computed tomography (CBCT) for an observer-independent approach.

METHODS

Six adult human cadaver skulls were used. The 4 generally used bone types in dental implantology and orthodontics were identified, and specific Hounsfield unit (HU) ranges (grey-scale values) were assigned to each bone type for identification by quantitative CBCT (qCBCT). The selected scanned planes were labelled by nonradiolucent markers for reidentification in the backup/cross-check evaluation methods. The selected planes were then physically removed as thick bone tissue sections for in vitro correlation measurements by qCBCT, quantitative micro-computed tomography (micro-CT), and quantitative histomorphometry.

RESULTS

Correlation analyses between the different bone tissue quantification methods to identify bone types based on numerical ranges of HU values revealed that the Pearson correlation coefficient of qCBCT with micro-CT and quantitative histomorphometry was R = 0.9 (P = .001) for all 4 bone types .

CONCLUSIONS

We found that  qCBCT can reproducibly and objectively assess human bone types at implant sites.

The synovium of human osteoarthritic joints retains its chondrogenic potential irrespective of age

The autologous synovium is a potential tissue source for local induction of chondrogenesis by tissue engineering approaches to repair articular cartilage defects such as they occur in osteoarthritis. It was the aim of the present study to ascertain whether the aging of human osteoarthritic patients compromises the chondrogenic potential of their knee-joint synovium and the structural and metabolic stability of the transformed tissue. The patients were allocated to one of the following two age categories: 54 - 65 years and 66 - 86 years (n = 7-11 donors per time point and experimental group; total number of donors: 64). Synovial biopsies were induced in vitro to undergo chondrogenesis by exposure to either bone morphogenetic protein-2 (BMP-2) alone, transforming growth factor-ß1 (TGF-ß1) alone, or a combination of the two growth factors, for up to 6 weeks. The differentiated explants were evaluated morphologically and morphometrically for the volume fraction of metachromasia (sulfated proteoglycans), immunohistochemically for type-II collagen, and for the gene-expression levels of anabolic chondrogenic markers as well as catabolic factors by a real-time polymerase-chain-reaction (RT-PCR) analysis. Quantitative metachromasia revealed that chondrogenic differentiation of human synovial explants was induced to the greatest degree by either BMP-2 alone or the BMP-2/TGF-1 combination, i.e. to a comparable level with each of the two stimulation protocols and within both age categories. The BMP-2/TGF-1combination protocol resulted in chondrocytes of a physiological size for normal human articular cartilage, unlike the BMP-2 alone stimulation that resulted in cell sizes of terminal hypertrophy. The stable gene-expression levels of the anabolic chondrogenic markers confirmed the superiority of these two stimulation protocols and demonstrated the hyaline-like qualities of the generated cartilage matrix. The gene-expression levels of the catabolic markers remained extremely low. The data also confirmed the usefulness of experimental in vitro studies with bovine synovial tissue as a paradigm for human synovial investigations. Our data reveal the chondrogenic potential of the human knee-joint synovium of osteoarthritic patients to be uncompromised by ageing and catabolic processes. The potential of synovium-based clinical engineering (repair) of cartilage tissue using autologous synovium may thus not be reduced by the age of the human patient.

Effect of BMP-2 Adherent to Resorbable Sutures on Cartilage Repair: A Rat Model of Xyphoid Process

Meniscal tears are often seen in orthopedic practice. The current strategy for meniscal repair has only had limited success with a relatively high incidence of re-operative rate. This study evaluates the therapeutic effects of Bone morphogenetic protein-2 (BMP-2) soaked sutures for cartilage repair, using a rat model of xyphoid healing. Vicryl-resorbable sutures were presoaked in BMP-2 solutions prior to animal experimentation. Rat xyphoid process (an avascular hyaline cartilage structure) was surgically ruptured followed by repair procedures with regular suture or with sutures that were pre-soaked in BMP-2 solutions. In vitro assessment indicated that presoaking the Vicryl-resorbable sutures with 10 µg/mL BMP-2 resulted in a sustained amount of the growth factor release up to 7 days. Histological analysis suggested that application of this BMP-2 soaked suture on the rat xyphoid process model significantly improved the avascular cartilage healing compared to non-soaked control sutures. In conclusion, data here confirm that the rat xyphoid process repair is a reproducible and inexpensive animal model for meniscus and other cartilage repair. More importantly, coating of BMP-2 on sutures appears a potential avenue to improve cartilage repair and regeneration. Further study is warranted to explore the molecular mechanisms of this strategy.

3D Porous Gelatin/PVA Hydrogel as Meniscus Substitute Using Alginate Micro-Particles as Porogens

One of the current major challenges in orthopedic surgery is the treatment of meniscal lesions. Some of the main issues include mechanical consistency of meniscal implants, besides their fixation methods and integration with the host tissues. To tackle these aspects we realized a micro-porous, gelatin/polyvinyl alcohol (PVA)-based hydrogel to approach the high percentage of water present in the native meniscal tissue, recapitulating its biomechanical features, and, at the same time, realizing a porous implant, permissive to cell infiltration and tissue integration. In particular, we adopted aerodynamically-assisted jetting technology to realize sodium alginate micro-particles with controlled dimensions to be used as porogens. The porous hydrogels were realized through freezing-thawing cycles, followed by alginate particles leaching. Composite hydrogels showed a high porosity (74%) and an open porous structure, while preserving the elasticity behavior (E = 0.25 MPa) and high water content, typical of PVA-based hydrogels. The ex vivo animal model validation proved that the addition of gelatin, combined with the micro-porosity of the hydrogel, enhanced implant integration with the host tissue, allowing penetration of host cells within the construct boundaries. Altogether, these results show that the combined use of a water-insoluble micro-porogen and gelatin, as a bioactive agent, allowed the realization of a porous composite PVA-based hydrogel to be envisaged as a potential meniscal substitute.

The Influence of Articular Cartilage Thickness Reduction on Meniscus Biomechanics

OBJECTIVE

Evaluation of the biomechanical interaction between meniscus and cartilage in medial compartment knee osteoarthritis.

METHODS

The finite element method was used to simulate knee joint contact mechanics. Three knee models were created on the basis of knee geometry from the Open Knee project. We reduced the thickness of medial cartilages in the intact knee model by approximately 50% to obtain a medial knee osteoarthritis (OA) model. Two variants of medial knee OA model with congruent and incongruent contact surfaces were analysed to investigate the influence of congruency. A nonlinear static analysis for one compressive load case was performed. The focus of the study was the influence of cartilage degeneration on meniscal extrusion and the values of the contact forces and contact areas.

RESULTS

In the model with incongruent contact surfaces, we observed maximal compressive stress on the tibial plateau. In this model, the value of medial meniscus external shift was 95.3% greater, while the contact area between the tibial cartilage and medial meniscus was 50% lower than in the congruent contact surfaces model. After the non-uniform reduction of cartilage thickness, the medial meniscus carried only 48.4% of load in the medial compartment in comparison to 71.2% in the healthy knee model.

CONCLUSIONS

We have shown that the change in articular cartilage geometry may significantly reduce the role of meniscus in load transmission and the contact area between the meniscus and cartilage. Additionally, medial knee OA may increase the risk of meniscal extrusion in the medial compartment of the knee joint.