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

A High-Density Hydrogen Bond Locking Strategy for Constructing Anisotropic High-Strength Hydrogel-Based Meniscus Substitute

Mimicking anisotropic features is crucial for developing artificial load-bearing soft tissues such as menisci). Here, a high-density hydrogen bond locking (HDHBL) strategy, involving preloading a poly(N-acryloylsemicarbazide) (PNASC) hydrogel with an aqueous solution containing a hydrogen bond breaking agent, followed by water exchange, to fabricate anisotropic high-strength hydrogels are proposed. During this process, multiple high-density hydrogen bonds of the PNASC network are re-established, firmly freezing oriented molecular chains, and creating a network with an anisotropic microstructure. The resulting anisotropic hydrogels exhibit superior mechanical properties: tensile strength over 9 MPa, Young's modulus exceeding 120 MPa along the orientation direction, and fatigue thresholds exceeding 1900 J m-2. These properties meet the mechanical demands for load-bearing tissue substitutes compared to other reported anti-fatigue hydrogels. This strategy enables the construction of an anisotropic meniscal scaffold composed of circumferentially oriented microfibers by preloading a digital light processing-3D printed PNASC hydrogel-based wedge-shaped construct with a resilient poly(N-acryloyl glycinamide) hydrogel. The 12-week implantation of a meniscus scaffold in rabbit knee joints after meniscectomy demonstrates a chondroprotective effect on the femoral condyle and tibial plateau, substantially ameliorating the progression of osteoarthritis. The HDHBL strategy enables the fabrication of various anisotropic polymer hydrogels, broadening their scope of application.

Optimized Allogenic Decellularized Meniscal Scaffold Modified by Collagen Affinity Stromal Cell-Derived Factor SDF1α for Meniscal Regeneration: A 6- and 12-Week Animal Study in a Rabbit Model

BACKGROUND

Total meniscectomy for treating massive meniscal tears may lead to joint instability, cartilage degeneration, and even progressive osteoarthritis. The meniscal substitution strategies for advancing reconstruction of the meniscus deserve further investigation.

HYPOTHESIS

A decellularized meniscal scaffold (DMS) modified with collagen affinity stromal cell-derived factor (C-SDF1α) may facilitate meniscal regeneration and protect cartilage from abrasion.

STUDY DESIGN

Controlled laboratory study.

METHODS

The authors first modified DMS with C-SDF1α to fabricate a new meniscal graft (DMS-CBD [collagen-binding domain]). Second, they performed in vitro studies to evaluate the release dynamics, biocompatibility, and differentiation inducibility (osteogenic, chondrogenic, and tenogenic differentiation) on human bone marrow mesenchymal stem cells. Using in vivo studies, they subjected rabbits that received medial meniscectomy to a transplantation procedure to implement their meniscal graft. At postoperative weeks 6 and 12, the meniscal regeneration outcomes and chondroprotective efficacy of the new meniscal graft were evaluated by macroscopic observation, histology, micromechanics, and immunohistochemistry tests.

RESULTS

In in vitro studies, the optimized DMS-CBD graft showed notable biocompatibility, releasing efficiency, and chondrogenic inducibility. In in vivo studies, the implanted DMS-CBD graft after total meniscectomy promoted the migration of cells and extracellular matrix deposition in transplantation and further facilitated meniscal regeneration and protected articular cartilage from degeneration.

CONCLUSION

The new meniscal graft (DMS-CBD) accelerated extracellular matrix deposition and meniscal regeneration and protected articular cartilage from degeneration.

CLINICAL RELEVANCE

The results demonstrate that the DMS-CBD graft can serve as a potential meniscal substitution after meniscectomy.

Cell Count and Cell Density Decrease as Age Increases in Cadaveric Pediatric Medial Menisci

Purpose

To examine the histologic changes in terms of cellularity, cell density, and nuclear shape in medial meniscal cellularity during skeletal development using pediatric cadaver specimens.

Methods

Medial menisci from 26 pediatric cadavers, 11 female and 15 male (total 36 menisci), were obtained from tissue bank. Mean age of female donors was 34 months (1-108 months) and of male donors was 52 months (1-132 months). Menisci were processed and embedded in paraffin blocks. Each tissue block containing 6 representative areas of meniscus (anterior root, anterior horn, body [n = 2], posterior horn, and posterior root) was sectioned at 4 microns and stained with hematoxylin and eosin for evaluation of chondrocyte nuclei. Each of the 6 representative areas was imaged at 10×; one image on peripheral one-third of section, the second image on central two-thirds of the section. FIJI imaging software was used to measure cell count, cell density, and nuclear morphology (1 = perfect circle). Data analysis included linear mixed models, Type II analysis of variance tests, and pairwise tests with the Tukey correction to assess statistical significance.

Results

Peripheral meniscus was more cellular than central meniscus. The cell count was found to decrease by 14% per year of age. Peripheral cell count decreased at a rate similar to the cell count in the central meniscus. Meniscal cell density was 2× higher peripherally than centrally. Overall average cell density in all locations in the menisci decreased by an average of 14% per year of age.

Conclusions

The results of this study reveal decreases in cell count, cell density, and circularity as age increases in cadaveric pediatric medial menisci.

Clinical Relevance

To better understand the development of pediatric menisci at a cellular level and use this knowledge in the future on how to maintain the menisci in a younger, healthier state.