A preliminary in vivo study of artificial meniscus using the uniaxial oriented reinforced compressive polyvinyl alcohol hydrogel.
|Abstract:||For severe meniscus injury patients with the future problem of degenerative change or osteoarthrosis (OA) in knee joint, we have newly developed a artficial meniscus using the uniaxial oriented compressive reinforced polyvinyl alcohol-hydrogel (PVA-H). In present study, the results up to six moths after animal operation to assess the use of artificial meniscus using this compressive PVA-H were evaluated. Consequently, the results proved that new artificial meniscus can compensate for meniscal function and might be clinically applicable.|
Polyvinyl alcohol (Properties)
Artificial organs (Properties)
Artificial organs (Health aspects)
Hyu, Hyon Suong
|Publication:||Name: Trends in Biomaterials and Artificial Organs Publisher: Society for Biomaterials and Artificial Organs Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2011 Society for Biomaterials and Artificial Organs ISSN: 0971-1198|
|Issue:||Date: July, 2011 Source Volume: 25 Source Issue: 3|
|Product:||Product Code: 2821230 Polyvinyl Alcohol; 3842132 Artificial Organs NAICS Code: 325211 Plastics Material and Resin Manufacturing; 339113 Surgical Appliance and Supplies Manufacturing SIC Code: 2821 Plastics materials and resins|
|Geographic:||Geographic Scope: Japan Geographic Code: 9JAPA Japan|
Meniscectomy is most commonly performed for knee meniscus injury resulting from traffic accidents or sports injuries. However, basic studies on meniscus function have suggested the important role of meniscus [1-3]. Many clinical reports have also shown articular degeneration in meniscectomized patients [4-7]. Therefore, the treatment for meniscus injury has been changed from meniscectomy to repair, however, meniscectomy cannot be avoided depending on the type of meniscus injury. In such cases, meniscus replacement is the only method for reconstruction of meniscus function. Thus, experimental and clinical studies have provided several approaches to meniscus replacement [8-14].
We have already developed artificial meniscus using polyvinyl alcohol-hydrogel (PVA-H), and performed many in vitro and in vivo studies for the purpose of clinical application. These results have indicated that PVA-H has excellent meniscus function and high potential for artificial meniscus [15-18]. However, to incarnate the clinical approach using this substitute, the fixation method of PVA-H meniscus should be solved as one important problem. PVA-H has strong bio-inert properties, therefore, it hardly adheres or binds directly to the living body. Although we tried to fix PVA-H implants with living bone by suturing in previous studies and found no trouble regarding the fixation of PVA-H meniscus and living tissues, further attempts to attach PVA-H to natural tissues more firmly are very important for a artificial meniscus implant.
For this background, we have newly developed the uniaxial oriented compressive reinforced PVA-H. Some characteristics of this new PVA-H material has been already evaluated by XRD and some mechanical tests (tensile tests) before this study. As a result, the mechanical binding strength of PVA-H and suture wire was improved. However, the meniscus function of this compressive reinforced PVA-H has not been confirmed yet. The purpose of present study was to assess new PVA-H artificial meniscus in the short term results (postoperative six months) after animal operation using rabbits.
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Preparation of compressive reinforced PVA-H
PVA-H used as a material for artificial meniscus in this study has been marked and studied extensively; and its excellent biocompatibility and mechanical properties have been confirmed [19-23]. In addition, viscoelastic characteristics similar to human's soft tissue can be provided by adjusting the water content in the gel production process.
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The uniaxial oriented compressive reinforced PVA-H with high water content was produced as follows (Fig 1). Polyvinyl alcohol (PVA) was completely dissolved with an organic solvent (DMSO) and water by heating and agitating under nitrogen air current, and a 20% PVA solution was obtained. This solution was left at a low temperature (4[degrees]C) for more than 12h for crystallization and cross-linking of PVA molecules. The obtained gel was immersed in alcohol for dozens of hours for substitution of the inorganic substrate, vacuum dried, and heated for annealing under the oriented compression loading at 100-140[degrees]C for 48h. After that, compressed gel was left in the water to adjust the water content of PVA-H by re-swelling. The obtained compressive reinforced PVA-H was a 80% water content, degree of polymerization 17500.
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The characteristics of compressive reinforced PVAH
The some characteristics of this compressive reinforced PVA-H have been already evaluated by XRD and some mechanical tests (tensile tests) before this study.
Fig 2 shows the images of Wide Angle X-Ray Diffraction (WAXD) analysis of the compressive PVAH. The WAXD spectra in through plane exhibited two scattering peaks (two phase) pattern, while the hallo pattern was found in the WAXD spectra in edge directionas well as original PVA-H with amorphous structure due to hydrogel. These WAXD profiles mean the compressive reinforced PVA-H has a oriented molecules structure ordered to through direction.
Fig 3 shows the results of tensile pulled out test. The binding strength between new PVA-H and suture string was improved than that of previous PVA-H. This data suggested the firm attachment of PVA-H meniscus to synivial joint tissue and bone for clinical application.
The prepared compressive reinforced PVA-H was a plate type, that was cut and processed into the meniscus form according to compressive direction, on which the loading stress in knee joint works vertically, and used as a prosthesis sample for animal experiments (Fig 4(a)).
The bilateral knees of three mature female rabbits (body weight 2.5-3.0 Kg) were used. To make experimental conditions constant and facilitate the operative procedure, artificial meniscus replacement was performed in the lateral compartment of one knee, and lateral meniscectomy in the other knee as a control.
Under intravenous anesthesia, with Nembutal (2-3ml), the operation was performed using aseptic procedures. A longitudinal incision was made on the lateral side of one knee joint, and the joint was opened. After medical dislocation of the patella, the meniscus was pulled in anterior with the knee in flexion, and the lateral meniscus was completely removed from the periphery. A bone hole was made using a drill from the area corresponding to the anterior and posterior horn on the tibial surface toward the distal area, 30 nylon thread was passed through this hole and sutured to the anterior and posterior horns of the PVA-H artificial meniscus. As supplementary fixation, sutures with 5-0 nylon were added to several sites in the periphery of the capsule and of the artificial meniscus (Fig-4(b)).
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The anterior cruciate ligament (ACL) and collateral ligament (LCL) were preserved intact, and the meniscus was reduced. The capsule and each subcutaneous layer was serially sutured. In the other knee, only total meniscectomy was performed as a control.
No postoperative immobilization was performed. The rabbits were reared in cages, and sacrificed at six months after operation for the observation of the state of the knee joint and the artificial meniscus.
All the above manipulations in the experimental process were in conformity with the Guideline for Animal Experiments, Kyoto University of Japan.
The knee joint was resected en bloc, and soft tissue were removed. The knee joint was incised, and the color and luster of articular cartilage, the shape of the femur, tibia, the state of the synovial membrane, soft tissue, and the degree of injury in the artificial meniscus (PVA-H) were observed.
To observe the histological state of the knee joints, in particular, the articular cartilages of artificial meniscus replacement group and the control knee group, Safranin-O stain specimens were prepared. The femoral condyle area and tibial surface were resected together with subchondral bone, fixed in formalin, decalcified with Plank-Rycho solution, cut into sections, and stained with Safranin-O.
Fig 5 shows the state of knee joint replaced by PVA-H artificial meniscus. There were no significant pathological change in synovial joint tissue such as inflammation, foreign-body reaction and infection. In addition, no fracture nor degradation of PVA-H meniscus was found.
Fig 6 shows the macroscopic appearance of the articular cartilage surface of the femoral condyles and tibia in the artificial meniscus group (a) and the control knees (b) of six months after the operation. The erosion and degeneration in the articular cartilage were noted in both knees, however, the degree of degenerative change in the femur and tibia was more marked in the control knee group (!).
Fig 7 shows the microscopic appearances of postoperative six months articular cartilage of both groups.
Although the abrasion in the cartilage layer was noted in both group knees, it should be noted that the cartilage in control group showed decreased stainability and atrophy, and loss of chondrocytes compared to that of artificial meniscus group (!).
Nowadays there is an increasing understanding of the significance of meniscus function. It has been considered that meniscectomy results in degenerative changes in articular cartilage more or less. Therefore, artificial meniscus replacement for reconstruction of meniscus function was attempted, we have developed artificial meniscus using non-compressive polyvinyl alcohol-hydrogel (previous PVA-H), and performed many in vitro studies and animal experiments for the purpose of clinical application. These results also already reported, and indicated that PVA-H has excellent meniscus function and high potential for artificial meniscus [15-18].
In previous studies regarding PVA-H artificial meniscus, the state of the cartilage surface was compared between the knees with PVA-H meniscus replacement and control group according to macroscopic assessment criteria for the staging of cartilage osteoarthritis (OA) proposed by Chang to evaluate the meniscus function of PVA-H . In the control knees, OA progressed with time. On the other hands, in the group treated by previous normal PVA-H artificial meniscus replacement, slight OA changes were found at an early stage but there was no progression of degenerative changes beyond a certain period of time.
In this study, the meniscus function of two kinds of PVA-H, previous PVA-H and new modified compressive reinforced PVA-H was compared by same Chang's evaluation as shown in Fig-8. As for new compressive reinforced PVA-H group, the score addressed no significant difference from previous non-compressive PVA-H until postoperative six months. This result suggests that new PVA-H also has a excellent meniscus function as well as our previous non-compressive PVA-H.
To augment the strength of PVA-H suture fixation for clinical applications of artificial meniscus, we have developed the compressive reinforced PVA-H. Although further long term observations are necessary about the meniscus function of new PVA-H, this study indicated that this compressive PVA-H has a promising material for artificial meniscus with more excellent mechanical fixation strength to living tissue. The development of fixation method into human body using this compressive reinforced PVA-H is expected in future.
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Masanori Kobayashi *, Kazuaki Matsumura, Hyon Suong Hyu **
* Bio-Medical Engineering Department, Mechanical Engineering Faculty, Daido University, 10-3Takiharu-cho,Minami-ku, Nagoya, 457-8530 Japan.
** Department of Tissue Regeneration, Institute for Frontier Medical Sciences, Kyoto University, Japan.
Corresponding author: Dr. Masanori Kobayashi, email@example.com
Received 26 September 2010; Accepted 4 March 2011; Available online 29 May 2011
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