Using synchrotron radiation inline phase‐contrast imaging computed tomography to visualize three‐dimensional printed hybrid constructs for cartilage tissue engineering

Synchrotron radiation inline phase‐contrast imaging combined with computed tomography (SR‐inline‐PCI‐CT) offers great potential for non‐invasive characterization and three‐dimensional visualization of fine features in weakly absorbing materials and tissues. For cartilage tissue engineering, the biomaterials and any associated cartilage extracellular matrix (ECM) that is secreted over time are difficult to image using conventional absorption‐based imaging techniques. For example, three‐dimensional printed polycaprolactone (PCL)/alginate/cell hybrid constructs have low, but different, refractive indices and thicknesses. This paper presents a study on the optimization and utilization of inline‐PCI‐CT for visualizing the components of three‐dimensional printed PCL/alginate/cell hybrid constructs for cartilage tissue engineering. First, histological analysis using Alcian blue staining and immunofluorescent staining assessed the secretion of sulfated glycosaminoglycan (GAGs) and collagen type II (Col2) in the cell‐laden hybrid constructs over time. Second, optimization of inline PCI‐CT was performed by investigating three sample‐to‐detector distances (SDD): 0.25, 1 and 3 m. Then, the optimal SDD was utilized to visualize structural changes in the constructs over a 42‐day culture period. The results showed that there was progressive secretion of cartilage‐specific ECM by ATDC5 cells in the hybrid constructs over time. An SDD of 3 m provided edge‐enhancement fringes that enabled simultaneous visualization of all components of hybrid constructs in aqueous solution. Structural changes that might reflect formation of ECM also were evident in SR‐inline‐PCI‐CT images. Summarily, SR‐inline‐PCI‐CT images captured at the optimized SDD enables visualization of the different components in hybrid cartilage constructs over a 42‐day culture period.     

Photocrosslinked methacrylated poly(vinyl alcohol)/hydroxyapatite nanocomposite hydrogels with enhanced mechanical strength and cell adhesion

Poly(vinyl alcohol) (PVA) hydrogels with high water content, good load‐bearing property, low frictional behavior as well as excellent biocompatibility have been considered as promising cartilage replacement materials. However, the lack of sufficient mechanical properties and cell adhesion are two critical barriers for their application as cartilage substitutes. To address these problems, herein, methacrylated PVA with low degree of substitution of methacryloyl group has been synthesized first. Then, methacrylated PVA‐glycidyl methacrylate/hydroxyapatite (PVA‐GMA/Hap) nanocomposite hydrogels have been developed by the photopolymerization approach subsequently. Markedly, both pure PVA‐GMA hydrogel and PVA‐GMA/Hap nanocomposite hydrogels exhibit excellent performance in compressive tests, and they are undamaged during compressive stress–strain tests. Moreover, compared to pure PVA‐GMA hydrogels, 8.5‐fold, 7.4‐fold, and 14.2‐fold increase in fracture stress, Young's modulus and toughness, respectively, can be obtained for PVA‐GMA/Hap nanocomposite hydrogels with 10 wt % Hap nanoparticles. These enhancements can be ascribed to the intrinsic property of PVA‐GMA and strong hydrogen bonding interactions between PVA‐GMA chain and Hap nanoparticles. More interestingly, significant improvement in the cell adhesion can also be successfully achieved by incorporation of Hap nanoparticles. These biocompatible nanocomposite hydrogels have great potential to be used as cartilage substitutes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1882–1889     

Characterization of human cartilage in degenerated spine disease with differential scanning calorimetry

The purpose of this study was to further characterize the altered metabolism spondylolisthesis that promotes disease progression. Degenerative human cartilage (intervertebral disc, facet joint and vertebral end-plate) was obtained during 15 posterior lumbar spine interbody fusion procedures performed at the University of Szeged. The thermal properties of samples were determined by differential scanning calorimetry (Mettler-Toledo DSC 821^e). Greatest change in the enthalpy was observed in the intervertebral disc samples: −1600.78 J g⁻¹. Denaturation caused by heating in the normal human hyaline cartilage needed −1493.31 J g⁻¹ energy. Characterization of the altered metabolism that promotes disease progression should lead to future treatment options.     

A Novel Double‐Network Hydrogel Induces Spontaneous Articular Cartilage Regeneration in vivo in a Large Osteochondral Defect

We have developed a novel method to induce spontaneous hyaline cartilage regeneration in vivo for a large osteochondral defect by implanting a plug made from a double‐network hydrogel composed of poly(2‐acrylamido‐2‐methylpropanesulfonic acid) and poly(N,N′‐dimethylacrylamide) at the bottom of the defect, leaving the cavity vacant. In cells regenerated in the treated defect, type‐2 collagen, Aggrican, and SOX9 mRNAs were highly expressed and the regenerated matrix was rich in proteoglycan and type‐2 collagen at 4 weeks. This fact gave a significant modification to the commonly established concept that hyaline cartilage tissue cannot regenerate in vivo. This study prompted an innovative strategy in the field of joint surgery to repair an osteochondral defect using an advanced, high‐function hydrogel.

     

Strategies for Zonal Cartilage Repair using Hydrogels

Articular cartilage is a highly hydrated tissue with depth‐dependent cellular and matrix properties that provide low‐friction load bearing in joints. However, the structure and function are frequently lost and there is insufficient repair response to regenerate high‐quality cartilage. Several hydrogel‐based tissue‐engineering strategies have recently been developed to form constructs with biomimetic zonal variations to improve cartilage repair. Modular hydrogel systems allow for systematic control over hydrogel properties, and advanced fabrication techniques allow for control over construct organization. These technologies have great potential to address many unanswered questions involved in prescribing zonal properties to tissue‐engineered constructs for cartilage repair.

     

Current Intelligent Injectable Hydrogels for In Situ Articular Cartilage Regeneration

Abstract

A high number of sport injuries result in damage to articular cartilage, a tissue type with poor self-healing capacity. Articular cartilage tissue is a sophisticated hydrogel, which contains 80% water and possesses strong mechanical properties. For this reason, synthetic hydrogels are thought to be an optimal material for cartilage regeneration. In the last decade, more than 2,000 research papers pertaining to “hydrogel and cartilage” have been published. Due to its biomimetic properties and user-friendly nature, especially in the field of minimal invasive surgery, intelligent injectable hydrogel have gradually become a focal point in cartilage research in recent years. In this review, we systematically summarize current “state-of-the-art” manufacture technologies of injectable hydrogels including ion-induced, thermo-induced, non-induced chemical, and light-induced crosslinking. We also review current strategies for designing intelligent injectable hydrogels, such as component-based, mechanical property-based and structure-based intelligent design to simulate the natural articular cartilage. Lastly, the applications of intelligent injectable hydrogels for cartilage regeneration are presented, and their outlooks for future clinical translation is dicussed.     

3D porous acellular cartilage matrix scaffold with surface mediated sustainable release of TGF-β3 for cartilage engineering

Acellular tissue matrix scaffolds are much closer to tissue’s complex natural structure and biological characteristics, thus assess great advantages in cartilage engineering. We used rabbit costal cartilage to prepare acellular microfilaments and further 3D porous acellular cartilage scaffold via crosslinking. Poly(l-lysine)/hyaluronic acid (PLL/HA) multilayer film was then built up onto the surface of the resulting porous scaffold. Furthermore, TGF-β3 was loaded into the PLL/HA multilayer film coated scaffold to obtain a 3D porous acellular cartilage scaffold with sustained releasing of TGF-β3 up to 60 days. The success of this project will provide a new way for the treatment of articular cartilage defects. Meanwhile, the anchoring and on-site sustained releasing of growth factors mediated by polyelectrolyte multilayered film can also provide a new method for improving the biocompatibility and the biofunctionality for other implanted biomaterials.     

Do formalin fixation and freeze‐thaw affect near‐infrared Raman spectroscopy of cartilaginous tissue? A preliminary ex vivo analysis of native human articular cartilage

Near‐infrared (NIR) Raman microprobe spectroscopy has been applied to the non‐invasive characterization of the biochemical structure of extracellular matrix in articular cartilage, a step forward along the path of in vivo diagnostic application of chondropathy. In most studies handling ex vivo cartilage specimens, formalin fixation or freeze‐thaw treatments have been applied in order to stabilize tissue and cell constituents prior to spectroscopic measurements. However, these pre‐processing manipulations might significantly affect certain target bands of the cartilage spectra, thus introducing biases in the characterizations, and potentially leading to data misinterpretation. In this study, we evaluated how formalin fixing and freeze‐thaw processes affect Raman spectra from human femur cartilage. Healthy cartilage specimens were fixed/stored either in a 10% neutral buffered formalin solution or in a deep freezer set at −80 °C. The results of this study show that formalin fixation significantly affects the NIR Raman spectra of cartilage specimens due to concurrent formalin absorption and water dehydration within both collagen and glycosaminoglycan macromolecules. Water dehydration was also confirmed in the amide I structure in the frozen‐thawed specimen, but to a much lesser extent. Furthermore, soaking the tissues in phosphate‐buffered saline solution minimized the storage‐induced Raman artifacts, but its immersion had limited effectiveness in formalin‐fixed specimens, predominantly due to an overlap of signals from the formalin liquid (i.e. emitting at 1046 and 1492 cm⁻¹). Therefore, to provide a highly accurate biochemical evaluation of extracellular matrix using NIR Raman spectroscopy, freeze‐thaw processes are more suitable for ex vivo samples of human cartilage than formalin fixation. Copyright © 2015 John Wiley & Sons, Ltd.