Cartilage engineering: a crucial combination of cells, biomaterials and biofactors

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.

Intra-articular injections of expanded mesenchymal stem cells with and without addition of platelet-rich plasma are safe and effective for knee osteoarthritis

PURPOSE

To compare the effectiveness and safety of intra-articular injections of autologous expanded mesenchymal stromal stem cells alone (MSCs), or in combination with platelet-rich plasma (MSCs + PRP), in patients with knee osteoarthritis.

METHODS

Eighteen patients (57.6 ± 9.6 years) with radiographic symptomatic knee osteoarthritis (Dejour grades II-IV) were randomized to receive intra-articular injections of MSCs (n = 9) or MSCs + PRP (n = 9). Injections were performed 2-3 weeks after bone marrow aspiration (± 80-100 ml) which was obtained from both posterior iliac crests.

RESULTS

The Knee Injury and Osteoarthritis Outcome Score (KOOS) improved significantly throughout the 12 months for both groups (p < 0.05). No statistically significant differences between groups were found in KOOS subscales and global score improvements at 12-month end-point (n.s.). The MSCs group showed significant improvements in the pain, function and daily living activities, and sports and recreational activities subscales (p < 0.05). Similarly, the MSCs + PRP group showed significant improvements in the pain, function and daily living activities and quality of life subscales (p < 0.05). The average number of fibroblast colony forming units (CFU-F) was 56.8 + 21.9 for MSCs group and 50.7 ± 21.7 for MSCs + PRP group. Minimal adverse effects were seen in both groups (10 adverse events, in 5 patients).

CONCLUSIONS

Intra-articular injections of expanded MSCs alone or in combination with PRP are safe and have a beneficial effect on symptoms in patients with symptomatic knee osteoarthritis. Adding PRP to the MSCs injections did not provide additional benefit. These results are encouraging and support the recommendation of this minimally invasive procedure in patients with knee osteoarthritis, without requiring hospitalization. The CFU-F results may be used as reference for future research.

LEVEL OF EVIDENCE

Prospective cohort study, Level II.

In vitro evaluation of phytochemical loaded electrospun gelatin nanofibers for application in bone and cartilage tissue engineering

Wattakaka volubilis, a medicinal plant, is known to exhibit various potential health benefits and has traditionally been used in Ayurveda for various medicinal applications. In the present study, phytochemicals hexadecanoic acid, octadecanoic acid and N,N-Diisopropyl(2,2,3,3,3-pentafluoropropyl)amine isolated from W. volubilis leaf extract were co-electrospun with gelatin nanofibers for meniscus and osteoblast cell attachment and proliferation. The electrospun nanofibers were characterized using suitable techniques such as a scanning electron microscope and Fourier transform infrared spectroscopy. The mechanical property of electrospun gelatin nanofibers and phytochemicals incorporated gelatin nanofibers were tensile tested. Both the control and phytochemical loaded nanofiber exhibited a similar stress-strain trend. The average diameter of the control and phytocompound loaded gelatin nanofiber was found to be 300 ± 5.5 nm and 483 ± 12 nm, respectively. The rate of biodegradation of the control and phytochemical loaded nanofiber was analyzed in a simulated body fluid. The cell attachment and proliferation were monitored using a fluorescence microscope after appropriate staining. The cell viability, DNA content, extracellular secretion confirmed that the phytocompound loaded gelatin nanofibers were non-toxic and enhanced the meniscus and osteoblast cell growth and proliferation. This phytocompound loaded gelatin matrix may be used as a potential scaffold for cartilage and bone tissue engineering applications.

Autologous Bone Marrow Cell Stimulation and Allogenic Chondrocyte Implantation for the Repair of Full-Thickness Articular Cartilage Defects in a Rabbit Model

OBJECTIVE

The aim of this study was to evaluate the results of autologous bone marrow cell stimulation and allogenic chondrocyte implantation using 3-dimensional gel-type fibrin matrix in an animal model.

DESIGN

Eighteen rabbits were divided into 2 treatment groups. One group was treated with a microfracture and covering of it with gel-type fibrin (AutoBMS; n = 9), and the other group was treated with allogenic chondrocytes mixed gel-type fibrin at the cartilage defect (AlloCI; n = 9). The control group was untreated cartilage defect at the other side knee of each object. Twelve weeks after treatment, the cartilage was evaluated using the International Cartilage Repair Society (ICRS) scoring system, immunohistochemical staining, and modified O'Driscoll grading system.

RESULTS

The ICRS scores were similar in the AutoBMS (9.44 ± 2.44) and the AlloCI (9.33 ± 1.67) groups ( P < 0.05). Immunohistochemical staining confirmed higher expression of cartilaginous collagen for both groups. The average difference (AutoBMS, 31.89 ± 6.54; AlloCI, 32.89 ± 5.25) in the modified O'Driscoll scores appeared to be nonsignificant ( P > 0.05); however, both treatment groups showed significantly higher scores with respect to their control group (18.45 ± 1.65; 18.97 ± 1.58) ( P < 0.05).

CONCLUSION

This experimental study suggests autologous bone marrow cells stimulation and implantation of allogenic chondrocytes are both useful methodologies for regenerating hyaline-like cartilage in full-thickness cartilage defects in animal model.

Lyophilized Scaffolds Fabricated from 3D-Printed Photocurable Natural Hydrogel for Cartilage Regeneration

Repair of cartilage defects is highly challenging in clinical treatment. Tissue engineering provides a promising approach for cartilage regeneration and repair. As a core component of tissue engineering, scaffolds have a crucial influence on cartilage regeneration, especially in immunocompetent large animal and human. Native polymers, such as gelatin and hyaluronic acid, have known as ideal biomimetic scaffold sources for cartilage regeneration. However, how to precisely control their structure, degradation rate, and mechanical properties suitable for cartilage regeneration remains a great challenge. To address these issues, a series of strategies were introduced in the current study to optimize the scaffold fabrication. First, gelatin and hyaluronic acid were prepared into a hydrogel and 3D printing was adopted to ensure precise control in both the outer 3D shape and internal pore structure. Second, methacrylic anhydride and a photoinitiator were introduced into the hydrogel system to make the material photocurable during 3D printing. Finally, lyophilization was used to further enhance mechanical properties and prolong degradation time. According to the current results, by integrating photocuring 3D printing and lyophilization techniques, gelatin and hyaluronic acid were successfully fabricated into human ear- and nose-shaped scaffolds, and both scaffolds achieved shape similarity levels over 90% compared with the original digital models. The scaffolds with 50% infill density achieved proper internal pore structure suitable for cell distribution, adhesion, and proliferation. Besides, lyophilization further enhanced mechanical strength of the 3D-printed hydrogel and slowed its degradation rate matching to cartilage regeneration. Most importantly, the scaffolds combined with chondrocytes successfully regenerated mature cartilage with typical lacunae structure and cartilage-specific extracellular matrixes both in vitro and in the autologous goat model. The current study established novel scaffold-fabricated strategies for native polymers and provided a novel natural 3D scaffold with satisfactory outer shape, pore structure, mechanical strength, degradation rate, and weak immunogenicity for cartilage regeneration.

Suppressing mesenchymal stem cell hypertrophy and endochondral ossification in 3D cartilage regeneration with nanofibrous poly(l-lactic acid) scaffold and matrilin-3

Articular cartilage has a very limited ability to self-heal after injury or degeneration due to its low cellularity, poor proliferative activity, and avascular nature. Current clinical options are able to alleviate patient suffering, but cannot sufficiently regenerate the lost tissue. Biomimetic scaffolds that recapitulate the important features of the extracellular matrix (ECM) of cartilage are hypothesized to be advantageous in supporting cell growth, chondrogenic differentiation, and integration of regenerated cartilage with native cartilage, ultimately restoring the injured tissue to its normal function. It remains a challenge to support and maintain articular cartilage regenerated by bone marrow-derived mesenchymal stem cells (BMSCs), which are prone to hypertrophy and endochondral ossification after implantation in vivo. In the present work, a nanofibrous poly(l-lactic acid) (NF PLLA) scaffold developed by our group was utilized because of the desired highly porous structure, high interconnectivity, and collagen-like NF architecture to support rabbit BMSCs for articular cartilage regeneration. We further hypothesized that matrilin-3 (MATN3), a non-collagenous, cartilage-specific ECM protein, would enhance the microenvironment of the NF PLLA scaffold for cartilage regeneration and maintain the cartilage property. To test this hypothesis, we seeded BMSCs on the NF PLLA scaffold with or without MATN3. We found that MATN3 suppresses hypertrophy in this 3D culture system in vitro. Subcutaneous implantation of the chondrogenic cell/scaffold constructs in a nude mouse model showed that pretreatment with MATN3 was able to maintain chondrogenesis and prevent hypertrophy and endochondral ossification in vivo. These results demonstrate that the porous NF PLLA scaffold treated with MATN3 represents an advantageous 3D microenvironment for cartilage regeneration and phenotype maintenance, and is a promising strategy for articular cartilage repair.

STATEMENT OF SIGNIFICANCE

Articular cartilage defects, caused by trauma, inflammation, or joint instability, may ultimately lead to debilitating pain and disability. Bone marrow-derived mesenchymal stem cells (BMSCs) are an attractive cell source for articular cartilage tissue engineering. However, chondrogenic induction of BMSCs is often accompanied by undesired hypertrophy, which can lead to calcification and ultimately damage the cartilage. Therefore, a therapy to prevent hypertrophy and endochondral ossification is of paramount importance to adequately regenerate articular cartilage. We hypothesized that MATN3 (a non-collagenous ECM protein expressed exclusively in cartilage) may improve regeneration of articular cartilage with BMSCs by maintaining chondrogenesis and preventing hypertrophic transition in an ECM mimicking nanofibrous scaffold. Our results showed that the administration of MATN3 to the cell/nanofibrous scaffold constructs favorably maintained chondrogenesis and prevented hypertrophy/endochondral ossification in the chondrogenic constructs in vitro and in vivo. The combination of nanofibrous PLLA scaffolds and MATN3 treatment provides a very promising strategy to generate chondrogenic grafts with phenotypic stability for articular cartilage repair.

Application of Millifluidics to Encapsulate and Support Viable Human Mesenchymal Stem Cells in a Polysaccharide Hydrogel

Human adipose-derived stromal cells (hASCs) are widely known for their immunomodulatory and anti-inflammatory properties. This study proposes a method to protect cells during and after their injection by encapsulation in a hydrogel using a droplet millifluidics technique. A biocompatible, self-hardening biomaterial composed of silanized-hydroxypropylmethylcellulose (Si-HPMC) hydrogel was used and dispersed in an oil continuous phase. Spherical particles with a mean diameter of 200 μm could be obtained in a reproducible manner. The viability of the encapsulated hASCs in the Si-HPMC particles was 70% after 14 days in vitro, confirming that the Si-HPMC particles supported the diffusion of nutrients, vitamins, and glucose essential for survival of the encapsulated hASCs. The combination of droplet millifluidics and biomaterials is therefore a very promising method for the development of new cellular microenvironments, with the potential for applications in biomedical engineering.

Effect of electric stimulation on human chondrocytes and mesenchymal stem cells under normoxia and hypoxia

During joint movement and mechanical loading, electric potentials occur within cartilage tissue guiding cell development and regeneration. Exposure of cartilage exogenous electric stimulation (ES) may imitate these endogenous electric fields and promote healing processes. Therefore, the present study investigated the influence of electric fields on human chondrocytes, mesenchymal stem cells and the co-culture of the two. Human chondrocytes isolated from articular cartilage obtained post-mortally and human mesenchymal stem cells derived from bone marrow (BM-MSCs) were seeded onto a collagen-based scaffold separately or as co-culture. Following incubation with the growth factors over 3 days, ES was performed using titanium electrodes applying an alternating electric field (700 mV, 1 kHz). Cells were exposed to an electric field over 7 days under either hypoxic or normoxic culture conditions. Following this, metabolic activity was investigated and synthesis rates of extracellular matrix proteins were analyzed. ES did not influence metabolic activity of chondrocytes or BM-MSCs. Gene expression analyses demonstrated that ES increased the expression of collagen type II mRNA and aggrecan mRNA in human chondrocytes under hypoxic culture conditions. Likewise, collagen type II synthesis was significantly increased following exposure to electric fields under hypoxia. BM-MSCs and the co-culture of chondrocytes and BM-MSCs revealed a similar though weaker response regarding the expression of cartilage matrix proteins. The electrode setup may be a valuable tool to investigate the influence of ES on human chondrocytes and BM-MSCs contributing to fundamental knowledge including future applications of ES in cartilage repair.

[Osteogenesis effect of dynamic mechanical loading on MC3T3-E1 cells in three-dimensional printing biomimetic composite scaffolds]

Objective

To observe the effect of dynamic mechanical loading on the proliferation, differentiation, and specific gene expression of MC3T3-E1 cells that on three-dimensional (3D) biomimetic composite scaffolds prepared by low temperature 3D printing technology combined with freeze-drying.

Methods

The silk fibroin, collagen type Ⅰ, and nano-hydroxyapatite (HA) were mixed at a mass ratio of 3∶9∶2 and were used to prepare the 3D biomimetic composite scaffolds via low temperature 3D printing technology combined with freeze-drying. General morphology of 3D biomimetic composite scaffold was observed. Micro-CT was used to observe the pore size and porosity of the scaffolds, and the water swelling rate, stress, strain, and elastic modulus were measured. Then, the MC3T3-E1 cells were seeded on the 3D biomimetic composite scaffolds and the cell-scaffold composites were randomly divided into 2 groups. The experimental group was subjected to dynamic mechanical loading (3 500 με, 1 Hz, 15 minutes per day); the control group was not subjected to loading treatment. After 7 days and 14 days, the cell-scaffold composites of 2 groups were harvested to observe the growth of cells on the scaffolds by HE staining and scanning electron microscope. And the gene and protein expressions of collagen type Ⅰ, BMP-2, and osteocalcin (OCN) were measured by real-time fluorescent quantitative PCR and Western blot.

Results

The 3D biomimetic composite scaffold was a white cubic grid. Micro-CT detection showed the pore network structure in the scaffold material with good pore connectivity. The diameters of large pore and micro-aperture were (506.37±18.63) μm and (62.14±17.35) μm, respectively. The porosity was 97.70%±1.37%, and the water absorption swelling rate was 1 341.97%±64.41%. Mechanical tests showed that the compression displacement of the scaffold was (0.376±0.004) mm, the compressive stress was (0.016±0.002) MPa, and the elastic modulus was (162.418±18.754) kPa when the scaffold was compressed to 10%. At 7 days and 14 days, HE staining and scanning electron microscope observation showed that the cells grew inside the scaffold, mainly distributed around the scaffold pore wall. The cells in experimental group were more than control group, and the cells morphology changed from shuttle to flat. There was no significant difference in the cell counting between 2 groups at 14 days after 200-fold microscopy ( t=-2.024， P=0.080), but significant differences were found between 2 groups at different time points under different magnifications ( P<0.05). Real-time fluorescent quantitative PCR showed that the mRNA relative expressions of collagen type Ⅰ and OCN in experimental group were significantly higher than those in control group at 7 and 14 days ( P<0.05). However, the mRNA relative expression of BMP-2 showing no significant difference between 2 groups ( P>0.05). The protein relative expressions of collagen type Ⅰ, BMP-2, and OCN in experimental group were significantly higher than those in control group at 7 and 14 days ( P<0.05).

Conclusion

After dynamic mechanical loading, the expressions of BMP-2, collagen type Ⅰ, and OCN in MC3T3-E1 cells inoculated into 3D biomimetic composite scaffolds are significantly up-regulated, indicating that appropriate mechanical loads favor osteoblast differentiation of MC3T3-E1 cells.

Targeted delivery of FGF2 to subchondral bone enhanced the repair of articular cartilage defect

It is reported that growth factor (GF) is able to enhance the repair of articular cartilage (AC) defect, however underlying mechanisms of which are not fully elucidated yet. Moreover, the strategy for delivering GF needs to be optimized. The crosstalk between AC and subchondral bone (SB) play important role in the homeostasis and integrity of AC, therefore SB targeted delivery of GF represents one promising way to facilitate the repair of AC defect. In this study, we firstly investigated the effects and mechanism of FGF2 on surrounding SB and cartilage of detect defects in rabbits by using a homogenous collagen-based membranes. It was found that FGF2 had a modulating effect on the defect-surrounding SB via upregulation of bone morphogenetic protein (BMP)-2, BMP4 and SOX9 at the early stage. Low dose FGF2 improved the repair upon directly injected to SB. Inhibition of BMP signaling pathway compromised the beneficial effects of FGF2, which indicated the pivotal roles of BMP in the process. To facilitate SB targeted FGF2 delivery, a double-layered inhomogeneous collagen membrane was prepared and it induced increase of BMP2 and BMP4 in the synovial fluid, and subsequent successful repair of AC defect. Taken together, this targeted delivery of FGF2 to SB provides a promising strategy for AC repair owing to the relatively clear mechanism, less amount of it, and short duration of delivery.

STATEMENT OF SIGNIFICANCE

Articular cartilage (AC) and subchondral bone (SB) form an integral functional unit. The homeostasis and integrity of AC depend on its crosstalk with the SB. However, the function of the SB in AC defect repair is not completely understood. The application of growth factors to promote the repair articular cartilage defect is a promising strategy, but still under the optimization. Our study demonstrate that SB plays important roles in the repair of AC defect. Particularly, SB is the effective target of fibroblast growth factor 2 (FGF2), and targeted delivery of FGF2 can modulate SB and thus significantly enhances the repair of AC defect. Therefore, targeted delivery of growth factor to SB is a novel promising strategy to improve the repair of AC defect.

Maintenance of human chondrogenic phenotype on a dendrimer-immobilized surface for an application of cell sheet engineering

BACKGROUND

Dedifferentiation of chondrocytes during cell expansion is one of the barriers in tissue construction for cartilage repair. To understand chondrocyte behavior and improve cell expansion in monolayer culture, this study investigated the effects of morphological changes and cellular aggregation on the maintenance of chondrogenic capacity by observing the expression patterns of chondrogenic (collagen type II and aggrecan) and dedifferentiation (collagen type I) markers. Primary human chondrocytes were cultured on either a polystyrene surface (PS) or a polyamidoamine dendrimer surface with a fifth-generation (G5) dendron structure to create a one-step process of cell expansion and the maintenance of chondrogenic activities prior to the construction of cell sheets.

RESULTS

During the first two passages (P0 - P2), the relative mRNA level of collagen type II decreased in all cultures, while that of collagen type I increased. Remarkably, the level of collagen type II was higher and aggrecan was retained in the chondrocytes, forming cell aggregates and showing some round-shaped cells with less production of stress fibers on the G5 surface compared to fibroblast-like chondrocytes with abundant stress fibers on the PS surface. The numbers of P2 chondrocytes on the G5 and PS surfaces were nearly the same and sufficient for construction of chondrocyte sheets using a temperature-responsive plate. Without a supporting material during cell sheet manipulation, chondrocyte sheets spontaneously detached and exhibited a honeycomb-like structure of stress fibers. Unlike the chondrocyte sheets constructed from cells on the PS surface, the chondrocyte sheets from cells on the G5 surface had higher chondrogenic activities, as evidenced by the high expression of chondrogenic markers and the low expression of dedifferentiation markers.

CONCLUSIONS

The one-step process of cell expansion and maintenance of chondrogenic activity could be obtained using the G5 surface. Human chondrocyte sheets were successfully constructed with high chondrogenic activity. These findings may lead to an alternative cultivation technique for human chondrocytes that offers high clinical potential in autologous chondrocyte implantation.

Effect of Cyclic Dynamic Compressive Loading on Chondrocytes and Adipose-Derived Stem Cells Co-Cultured in Highly Elastic Cryogel Scaffolds

In this study, we first used gelatin/chondroitin-6-sulfate/hyaluronan/chitosan highly elastic cryogels, which showed total recovery from large strains during repeated compression cycles, as 3D scaffolds to study the effects of cyclic dynamic compressive loading on chondrocyte gene expression and extracellular matrix (ECM) production. Dynamic culture of porcine chondrocytes was studied at 1 Hz, 10% to 40% strain and 1 to 9 h/day stimulation duration, in a mechanical-driven multi-chamber bioreactor for 14 days. From the experimental results, we could identify the optimum dynamic culture condition (20% and 3 h/day) to enhance the chondrocytic phenotype of chondrocytes from the expression of marker (Col I, Col II, Col X, TNF-α, TGF-β1 and IGF-1) genes by quantitative real-time polymerase chain reactions (qRT-PCR) and production of ECM (GAGs and Col II) by biochemical analysis and immunofluorescence staining. With up-regulated growth factor (TGF-β1 and IGF-1) genes, co-culture of chondrocytes with porcine adipose-derived stem cells (ASCs) was employed to facilitate chondrogenic differentiation of ASCs during dynamic culture in cryogel scaffolds. By replacing half of the chondrocytes with ASCs during co-culture, we could obtain similar production of ECM (GAGs and Col II) and expression of Col II, but reduced expression of Col I, Col X and TNF-α. Subcutaneous implantation of cells/scaffold constructs in nude mice after mono-culture (chondrocytes or ASCs) or co-culture (chondrocytes + ASCs) and subject to static or dynamic culture condition in vitro for 14 days was tested for tissue-engineering applications. The constructs were retrieved 8 weeks post-implantation for histological analysis by Alcian blue, Safranin O and Col II immunohistochemical staining. The most abundant ectopic cartilage tissue was found for the chondrocytes and chondrocytes + ASCs groups using dynamic culture, which showed similar neo-cartilage formation capability with half of the chondrocytes replaced by ASCs for co-culture. This combined co-culture/dynamic culture strategy is expected to cut down the amount of donor chondrocytes needed for cartilage-tissue engineering.

TGF-β1 affinity peptides incorporated within a chitosan sponge scaffold can significantly enhance cartilage regeneration

Scaffold incorporated with affinity peptides can efficiently promote cartilage regeneration without exogenous addition of growth factors and cells.

Emerging Concepts in Treating Cartilage, Osteochondral Defects, and Osteoarthritis of the Knee and Ankle

The management and treatment of cartilage lesions, osteochondral defects, and osteoarthritis remain a challenge in orthopedics. Moreover, these entities have different behaviors in different joints, such as the knee and the ankle, which have inherent differences in function, biology, and biomechanics. There has been a huge development on the conservative treatment (new technologies including orthobiologics) as well as on the surgical approach. Some surgical development upraises from technical improvements including advanced arthroscopic techniques but also from increased knowledge arriving from basic science research and tissue engineering and regenerative medicine approaches. This work addresses the state of the art concerning basic science comparing the knee and ankle as well as current options for treatment. Furthermore, the most promising research developments promising new options for the future are discussed.

Osteoarthritic human chondrocytes proliferate in 3D co-culture with mesenchymal stem cells in suspension bioreactors

Osteoarthritis (OA) is a painful disease, characterized by progressive surface erosion of articular cartilage. The use of human articular chondrocytes (hACs) sourced from OA patients has been proposed as a potential therapy for cartilage repair, but this approach is limited by the lack of scalable methods to produce clinically relevant quantities of cartilage-generating cells. Previous studies in static culture have shown that hACs co-cultured with human mesenchymal stem cells (hMSCs) as 3D pellets can upregulate proliferation and generate neocartilage with enhanced functional matrix formation relative to that produced from either cell type alone. However, because static culture flasks are not readily amenable to scale up, scalable suspension bioreactors were investigated to determine if they could support the co-culture of hMSCs and OA hACs under serum-free conditions to facilitate clinical translation of this approach. When hACs and hMSCs (1:3 ratio) were inoculated at 20,000 cells/ml into 125-ml suspension bioreactors and fed weekly, they spontaneously formed 3D aggregates and proliferated, resulting in a 4.75-fold increase over 16 days. Whereas the apparent growth rate was lower than that achieved during co-culture as a 2D monolayer in static culture flasks, bioreactor co-culture as 3D aggregates resulted in a significantly lower collagen I to II mRNA expression ratio and more than double the glycosaminoglycan/DNA content (5.8 vs. 2.5 μg/μg). The proliferation of hMSCs and hACs as 3D aggregates in serum-free suspension culture demonstrates that scalable bioreactors represent an accessible platform capable of supporting the generation of clinical quantities of cells for use in cell-based cartilage repair.

Functional and Biomimetic Materials for Engineering of the Three-Dimensional Cell Microenvironment

The cell microenvironment has emerged as a key determinant of cell behavior and function in development, physiology, and pathophysiology. The extracellular matrix (ECM) within the cell microenvironment serves not only as a structural foundation for cells but also as a source of three-dimensional (3D) biochemical and biophysical cues that trigger and regulate cell behaviors. Increasing evidence suggests that the 3D character of the microenvironment is required for development of many critical cell responses observed in vivo, fueling a surge in the development of functional and biomimetic materials for engineering the 3D cell microenvironment. Progress in the design of such materials has improved control of cell behaviors in 3D and advanced the fields of tissue regeneration, in vitro tissue models, large-scale cell differentiation, immunotherapy, and gene therapy. However, the field is still in its infancy, and discoveries about the nature of cell-microenvironment interactions continue to overturn much early progress in the field. Key challenges continue to be dissecting the roles of chemistry, structure, mechanics, and electrophysiology in the cell microenvironment, and understanding and harnessing the roles of periodicity and drift in these factors. This review encapsulates where recent advances appear to leave the ever-shifting state of the art, and it highlights areas in which substantial potential and uncertainty remain.

* Mimicking the Biochemical and Mechanical Extracellular Environment of the Endochondral Ossification Process to Enhance the In Vitro Mineralization Potential of Human Mesenchymal Stem Cells

Chondrogenesis and mechanical stimulation of the cartilage template are essential for bone formation through the endochondral ossification process in vivo. Recent studies have demonstrated that in vitro regeneration strategies that mimic these aspects separately, either chondrogenesis or mechanical stimulation, can promote mineralization to a certain extent both in vitro and in vivo. However, to date no study has sought to incorporate both the formation of the cartilage template and the application of mechanical stimulation simultaneously to induce osteogenesis. In this study, we test the hypothesis that mimicking both the biochemical and mechanical extracellular environment arising during endochondral ossification can enhance the in vitro mineralization potential of human mesenchymal stem cells (hMSCs). hMSC aggregates were cultured for 21 days under the following culture conditions; (1) Growth Medium - hydrostatic pressure (HP), (2) Chondrogenic Priming-HP, (3) Growth Medium + HP, and (4) Chondrogenic Priming +HP. Each group was then further cultured for another 21 days in the presence of osteogenic growth factors without HP. Biochemical (DNA, sulfate glycosaminoglycan, hydroxyproline, alkaline phosphatase activity, and calcium), histological (Alcian Blue and Alizarin Red), and immunohistological (Col I, II, and X, and BSP-2) analyses were conducted to investigate chondrogenic and osteogenic differentiation at various time points (14, 21, 35, and 42 days). Our results showed the application of HP-induced chondrogenesis similar to that of chondrogenic priming, but interestingly, there was a reduction in hypertrophy markers (collagen type X) by applying HP alone versus chondrogenic priming alone. Moreover, the results showed that both chondrogenic priming and HP in tandem during the priming period, followed by culture in osteogenic medium, accelerated the osteogenic potential of hMSCs.

Polysaccharide Hydrogels Support the Long-Term Viability of Encapsulated Human Mesenchymal Stem Cells and Their Ability to Secrete Immunomodulatory Factors

While therapeutically interesting, the injection of MSCs suffers major limitations including cell death upon injection and a massive leakage outside the injection site. We proposed to entrap MSCs within spherical particles derived from alginate, as a control, or from silanized hydroxypropyl methylcellulose (Si-HPMC). We developed water in an oil dispersion method to produce small Si-HPMC particles with an average size of about 68 μm. We evidenced a faster diffusion of fluorescein isothiocyanate-dextran in Si-HPMC particles than in alginate ones. Human adipose-derived MSCs (hASC) were encapsulated either in alginate or in Si-HPMC, and the cellularized particles were cultured for up to 1 month. Both alginate and Si-HPMC particles supported cell survival, and the average number of encapsulated hASC per alginate and Si-HPMC particle (7102 and 5100, resp.) did not significantly change. The stimulation of encapsulated hASC with proinflammatory cytokines resulted in the production of IDO, PGE₂, and HGF whose concentration was always higher when cells were encapsulated in Si-HPMC particles than in alginate ones. We have demonstrated that Si-HPMC and alginate particles support hASC viability and the maintenance of their ability to secrete therapeutic factors.

RNA Interference and BMP-2 Stimulation Allows Equine Chondrocytes Redifferentiation in 3D-Hypoxia Cell Culture Model: Application for Matrix-Induced Autologous Chondrocyte Implantation

As in humans, osteoarthritis (OA) causes considerable economic loss to the equine industry. New hopes for cartilage repair have emerged with the matrix-associated autologous chondrocyte implantation (MACI). Nevertheless, its limitation is due to the dedifferentiation occurring during the chondrocyte amplification phase, leading to the loss of its capacity to produce a hyaline extracellular matrix (ECM). To enhance the MACI therapy efficiency, we have developed a strategy for chondrocyte redifferentiation, and demonstrated its feasibility in the equine model. Thus, to mimic the cartilage microenvironment, the equine dedifferentiated chondrocytes were cultured in type I/III collagen sponges for 7 days under hypoxia in the presence of BMP-2. In addition, chondrocytes were transfected by siRNA targeting Col1a1 and Htra1 mRNAs, which are overexpressed during dedifferentiation and OA. To investigate the quality of the neo-synthesized ECM, specific and atypical cartilage markers were evaluated by RT-qPCR and Western blot. Our results show that the combination of 3D hypoxia cell culture, BMP-2 (Bone morphogenetic protein-2), and RNA interference, increases the chondrocytes functional indexes (Col2a1/Col1a1, Acan/Col1a1), leading to an effective chondrocyte redifferentiation. These data represent a proof of concept for this process of application, in vitro, in the equine model, and will lead to the improvement of the MACI efficiency for cartilage tissue engineering therapy in preclinical/clinical trials, both in equine and human medicine.

Microgels of silylated HPMC as a multimodal system for drug co-encapsulation

Combined therapy is a global strategy developed to prevent drug resistance in cancer and infectious diseases. In this field, there is a need of multifunctional drug delivery systems able to co-encapsulate small drug molecules, peptides, proteins, associated to targeting functions, nanoparticles. Silylated hydrogels are alkoxysilane hybrid polymers that can be engaged in a sol-gel process, providing chemical cross linking in physiological conditions, and functionalized biocompatible hybrid materials. In the present work, microgels were prepared with silylated (hydroxypropyl)methyl cellulose (Si-HPMC) that was chemically cross linked in soft conditions of pH and temperature. They were prepared by an emulsion templating process, water in oil (W/O), as microreactors where the condensation reaction took place. The ability to functionalize the microgels, so-called FMGs, in a one-pot process, was evaluated by grafting a silylated hydrophilic model drug, fluorescein (Si-Fluor), using the same reaction of condensation. Biphasic microgels (BPMGs) were prepared to evaluate their potential to encapsulate lipophilic model drug (Nile red). They were composed of two separate compartments, one oily phase (sesame oil) trapped in the cross linked Si-HPMC hydrophilic phase. The FMGs and BPMGs were characterized by different microscopic techniques (optic, epi-fluorescence, Confocal Laser Scanning Microscopy and scanning electronic microscopy), the mechanical properties were monitored using nano indentation by Atomic Force Microscopy (AFM), and different preliminary tests were performed to evaluate their chemical and physical stability. Finally, it was demonstrated that it is possible to co-encapsulate both hydrophilic and hydrophobic drugs, in silylated microgels, that were physically and chemically stable. They were obtained by chemical cross linking in soft conditions, and without surfactant addition during the emulsification process. The amount of drug loaded was in favor of further biological activity. Mechanical stimulations should be necessary to trigger drug release.

Nanomedicine and epigenome. Possible health risks

Nanomedicine is an emerging field that combines knowledge of nanotechnology and material science with pharmaceutical and biomedical sciences, aiming to develop nanodrugs with increased efficacy and safety. Compared to conventional therapeutics, nanodrugs manifest higher stability and circulation time, reduced toxicity and improved targeted delivery. Despite the obvious benefit, the accumulation of imaging agents and nanocarriers in the body following their therapeutic or diagnostic application generates concerns about their safety for human health. Numerous toxicology studies have demonstrated that exposure to nanomaterials (NMs) might pose serious risks to humans. Epigenetic modifications, representing a non-genotoxic mechanism of toxicant-induced health effects, are becoming recognized as playing a potential causative role in the aetiology of many diseases including cancer. This review i) provides an overview of recent advances in medical applications of NMs and ii) summarizes current evidence on their possible epigenetic toxicity. To discern potential health risks of NMs, since current data are mostly based upon in vitro and animal models, a better understanding of functional relationships between NM exposure, epigenetic deregulation and phenotype is required.

Terapias Celulares y Productos de Ingeniería de Tejidos para el Tratamiento de Lesiones Condrales de Rodilla

El cartílago articular es un tejido vulnerable a las lesiones de diferente etiología; siendo uno de los más afectados,  el cartílago de la rodilla. Aunque la mayoría de los tratamientos convencionales reducen los síntomas, generalmente conducen a la formación de fibrocartílago; el cual, posee características diferentes a las del cartílago hialino de las articulaciones.  Son pocas las aproximaciones terapéuticas que promueven el  reemplazo del tejido dañado por cartílago hialino funcional; las más exitosas son las denominadas terapias avanzadas, que aplican células y  productos de ingeniería de tejidos con el fin de estimular la regeneración del cartílago. La mayoría de ellas se basan en colocar soportes  hechos con biomateriales de diferente origen, que sembrados o no con células exógenas o endógenas, reemplazan al cartílago dañado y promueven su regeneración. Este  trabajo revisa algunas de las aproximaciones terapéuticas enfocadas en la regeneración del cartílago articular de rodilla; así como, los biomateriales más empleados en la elaboración de soportes para terapia celular e ingeniería de tejido cartilaginoso.

[Effect of polycaprolactone-ascobic acid scaffold in repairing articular cartilage defects in rabbits]

OBJECTIVE

To investigate the effect of polycaprolactone-ascobic acid (PCL-AA) scaffolds in promoting repair of articular cartilage defects in a rabbit model.

METHODS

The cartilage defects (3.5 mm in diameter and 3.0 mm in depth) were created in the trochlear groove of the bilateral knees of eight 6-month-old male New Zealand white rabbits. The rabbit models were then randomized into 3 groups to receive implantation of PCL-AA scaffolds (group A, n=8), implantation of PCL scaffolds without AA (group B, n=5), or no treatment (group C, n=3). In groups A and B, the mixture of fibrin gel (10 µg) and thrombinogen (10 µg) was injected into the defects to fix the scaffolds during the surgery. Histological analyses and quantitative assessments of defect repair were conducted at 6 and 12 weeks after implantation of the scaffold.

RESULTS

At 6 weeks after scaffold implantation, macroscopic observation showed better filling of the cartilage defects in group A than in group B, while no obvious defect repair was observed in group C. The rabbits in group A showed a significant improvement of the Wakitani score than those in group B (4.05∓1.11 vs 7.05∓0.98, P<0.05). HE staining revealed the presence of newly generated cells in and around the PCL-AA scaffolds without inflammatory cells. Safranin O staining showed a significantly greater ECM of the newly regenerated tissue in groups A and B than in group C (P<0.05), and the volume of the regenerated cartilage and cells was significantly greater in group A than in group B (P<0.05). Samples harvested at 12 weeks showed more hyalione-like cartilage formation than that at 6 weeks in group A.

CONCLUSION

PCL-AA scaffolds have a good biocompatibility and promotes the healing of articular cartilage defects. Adding ascorbic acid into PCL scaffolds better promotes cartilage formation in terms of both quantity and quality of the regenerated tissues. PCL-AA scaffolds can serve as a promising biomaterial to promote the regeneration of articular cartilage using tissue engineering techniques.

Soluble Factors on Stage to Direct Mesenchymal Stem Cells Fate

Mesenchymal stem cells (MSCs) are multipotent stromal cells that are identified by in vitro plastic adherence, colony-forming capacity, expression of a panel of surface molecules, and ability to differentiate at least toward osteogenic, adipogenic, and chondrogenic lineages. They also produce trophic factors with immunomodulatory, proangiogenic, and antiapoptotic functions influencing the behavior of neighboring cells. On the other hand, a reciprocal regulation takes place; in fact, MSCs can be isolated from several tissues, and depending on the original microenvironment and the range of stimuli received from there, they can display differences in their essential characteristics. Here, we focus mainly on the bone tissue and how soluble factors, such as growth factors, cytokines, and hormones, present in this microenvironment can orchestrate bone marrow-derived MSCs fate. We also briefly describe the alteration of MSCs behavior in pathological settings such as hematological cancer, bone metastasis, and bone marrow failure syndromes. Overall, the possibility to modulate MSCs plasticity makes them an attractive tool for diverse applications of tissue regeneration in cell therapy. Therefore, the comprehensive understanding of the microenvironment characteristics and components better suited to obtain a specific MSCs response can be extremely useful for clinical use.

Guided Self-Generation of Vascularized Neo-Bone for Autologous Reconstruction of Large Mandibular Defects

Reconstruction of large mandibular defects is complex and challenging. The authors aimed to individually self-generate a large vascularized bone construct for autologous transplantation without the use of exogenous additives based on the concept of guided self-generation. Using computer-aided design and manufacturing a large size goat mandibular bone was reconstructed in 3 dimensions. Its negative mold printed from hydroxylapatite was temporarily embedded into the costal periosteum along with a contralateral demineralized bone matrix scaffold as control. After 3 months, a mandibular bone construct was obtained and used for autologous transplantation. Osteogenesis and angiogenesis were assessed by real-time imaging, histology, and biomechanical tests during neo-bone formation and up to 6 months after transplantation surgery. A total of 20 animals received implantation of a mandibular bone negative mold along with a contralateral demineralized bone matrix scaffold. Resulting negative mold mandibular bone constructs showed anatomically, histologically, and functionally similar characteristics compared with native controls. Only 1 goat presented partial fibrosis during construct generation with subsequent absorbtion after reconstruction. The absence of exogenous cells, growth factors, and scaffolds facilitated direct translation of this novel concept into clinical application. Further studies are needed to determine functional long-term outcomes and possible extensions to other tissues and organs.

Pathogenic or Therapeutic Extracellular Vesicles in Rheumatic Diseases: Role of Mesenchymal Stem Cell-Derived Vesicles

Extracellular vesicles (EVs) are important mediators of cell-to-cell communication pathways via the transport of proteins, mRNA, miRNA and lipids. There are three main types of EVs, exosomes, microparticles and apoptotic bodies, which are classified according to their size and biogenesis. EVs are secreted by all cell types and their function reproduces that of the parental cell. They are involved in many biological processes that regulate tissue homeostasis and physiopathology of diseases. In rheumatic diseases, namely osteoarthritis (OA) and rheumatoid arthritis (RA), EVs have been isolated from synovial fluid and shown to play pathogenic roles contributing to progression of both diseases. By contrast, EVs may have therapeutic effect via the delivery of molecules that may stop disease evolution. In particular, EVs derived from mesenchymal stem cells (MSCs) reproduce the main functions of the parental cells and therefore represent the ideal type of EVs for modulating the course of either disease. The aim of this review is to discuss the role of EVs in OA and RA focusing on their potential pathogenic effect and possible therapeutic options. Special attention is given to MSCs and MSC-derived EVs for modulating OA and RA progression with the perspective of developing innovative therapeutic strategies.

Combination of Collagen-Based Scaffold and Bioactive Factors Induces Adipose-Derived Mesenchymal Stem Cells Chondrogenic Differentiation In vitro

Recently, multipotent mesenchymal stem cells (MSCs) have attracted much attention in the field of regenerative medicine due to their ability to give rise to different cell types, including chondrocytes. Damaged articular cartilage repair is one of the most challenging issues for regenerative medicine, due to the intrinsic limited capability of cartilage to heal because of its avascular nature. While surgical approaches like chondral autografts and allografts provide symptoms and function improvement only for a short period, MSC based stimulation therapies, like microfracture surgery or autologous matrix-induced chondrogenesis demonstrate to be more effective. The use of adult chondrocytes, which are the main cellular constituent of cartilage, in medical practice, is indeed limited due to their instability in monolayer culture and difficulty to collect donor tissue (articular and nasal cartilage). The most recent cartilage engineering approaches combine cells, biomaterial scaffold and bioactive factors to promote functional tissue replacements. Many recent evidences demonstrate that scaffolds providing specific microenvironmental conditions can promote MSCs differentiation toward a functional phenotype. In the present work, the chondrogenic potential of a new Collagen I based 3D scaffold has been assessed in vitro, in combination with human adipose-derived MSCs which possess a higher chondrogenic potential compared to MSCs isolated from other tissues. Our data indicate that the scaffold was able to promote the early stages of chondrogenic commitment and that supplementation of specific soluble factors was able to induce the complete differentiation of MSCs in chondrocytes as demonstrated by the appearance of cartilage distinctive markers (Sox 9, Aggrecan, Matrilin-1, and Collagen II), as well as by the cartilage-specific Alcian Blue staining and by the acquisition of typical cellular morphology. Such evidences suggest that the investigated scaffold formulation could be suitable for the production of medical devices that can be beneficial in the field of articular cartilage engineering, thus improving the efficacy and durability of the current therapeutic options.

Fabrication of injectable high strength hydrogel based on 4-arm star PEG for cartilage tissue engineering

Hydrogels prepared from poly(ethylene glycol) (PEG) are widely applied in tissue engineering, especially those derived from a combination of functional multi-arm star PEG and linear crosslinker, with an expectation to form a structurally ideal network. However, the poor mechanical strength still renders their further applications. Here we examined the relationship between the dynamics of the pre-gel solution and the mechanical property of the resultant hydrogel in a system consisting of 4-arm star PEG functionalized with vinyl sulfone and short dithiol crosslinker. A method to prepare mechanically strong hydrogel for cartilage tissue engineering is proposed. It is found that when gelation takes place at the overlap concentration, at which a slow relaxation mode just appears in dynamic light scattering (DLS), the resultant hydrogel has a local maximum compressive strength ∼20 MPa, while still keeps ultralow mass concentration and Young's modulus. Chondrocyte-laden hydrogel constructed under this condition was transplanted into the subcutaneous pocket and an osteochondral defect model in SCID mice. The in vivo results show that chondrocytes can proliferate and maintain their phenotypes in the hydrogel, with the production of abundant extracellular matrix (ECM) components, formation of typical chondrocyte lacunae structure and increase in Young's modulus over 12 weeks, as indicated by histological, immunohistochemistry, gene expression analyses and mechanical test. Moreover, newly formed hyaline cartilage was observed to be integrated with the host articular cartilage tissue in the defects injected with chondrocytes/hydrogel constructs. The results suggest that this hydrogel is a promising candidate scaffold for cartilage tissue engineering.

Osteoarthritis: from pathogenic mechanisms and recent clinical developments to novel prospective therapeutic options

Osteoarthritis (OA) is a degenerative joint disease that, despite recent progress, has no curative treatment. Considerable research has recently been initiated to identify new potential therapeutic targets. In this review, we will set forth some of the major discoveries in the past 5 years, notably those dealing with the identification of pathogenic factors [hypoxia-inducible factors (HIFs), complement, transforming growth factor (TGF)-β and zinc-ZIP8]. New drugs and concepts currently in clinical development [anti-nerve growth factor (NGF), mesenchymal stromal cells and fibroblast growth factor (FGF)-18] will then be addressed. Finally, we will consider prospective avenues that could lead to mid-to-long-term developments of novel therapeutic concepts, notably those dealing with autophagy regulation and induced pluripotent stem cells.

Autologous temporomandibular joint reconstruction independent of exogenous additives: a proof-of-concept study for guided self-generation

Joint defects are complex and difficult to reconstruct. By exploiting the body’s own regenerative capacity, we aimed to individually generate anatomically precise neo-tissue constructs for autologous joint reconstruction without using any exogenous additives. In a goat model, CT scans of the mandibular condyle including articular surface and a large portion of the ascending ramus were processed using computer-aided design and manufacturing. A corresponding hydroxylapatite negative mold was printed in 3D and temporarily embedded into the transition zone of costal periosteum and perichondrium. A demineralized bone matrix scaffold implanted on the contralateral side served as control. Neo-tissue constructs obtained by guided self-generation exhibited accurate configuration, robust vascularization, biomechanical stability, and function. After autologous replacement surgery, the constructs showed stable results with similar anatomical, histological, and functional findings compared to native controls. Further studies are required to assess long-term outcome and possible extensions to other further applications. The absence of exogenous cells, growth factors, and scaffolds may facilitate clinical translation of this approach.

Dual Function of Glucosamine in Gelatin/Hyaluronic Acid Cryogel to Modulate Scaffold Mechanical Properties and to Maintain Chondrogenic Phenotype for Cartilage Tissue Engineering

Glucosamine (GlcN) fulfills many of the requirements as an ideal component in scaffolds used in cartilage tissue engineering. The incorporation of GlcN in a gelatin/hyaluronic acid (GH) cryogel scaffold could provide biological cues in maintaining the phenotype of chondrocytes. Nonetheless, substituting gelatin with GlcN may also decrease the crosslinking density and modulate the mechanical properties of the cryogel scaffold, which may be beneficial as physical cues for chondrocytes in the scaffold. Thus, we prepared cryogel scaffolds containing 9% GlcN (GH-GlcN9) and 16% GlcN (GH-GlcN16) by carbodiimide-mediated crosslinking reactions at -16 °C. The crosslinking density and the mechanical properties of the cryogel matrix could be tuned by adjusting the content of GlcN used during cryogel preparation. In general, incorporation of GlcN did not influence scaffold pore size and ultimate compressive strain but increased porosity. The GH-GlcN16 cryogel showed the highest swelling ratio and degradation rate in hyaluronidase and collagenase solutions. On the contrary, the Young's modulus, storage modulus, ultimate compressive stress, energy dissipation level, and rate of stress relaxation decreased by increasing the GlcN content in the cryogel. The release of GlcN from the scaffolds in the culture medium of chondrocytes could be sustained for 21 days for GH-GlcN16 in contrast to only 7 days for GH-GlcN9. In vitro cell culture experiments using rabbit articular chondrocytes revealed that GlcN incorporation affected cell proliferation, morphology, and maintenance of chondrogenic phenotype. Overall, GH-GlcN16 showed the best performance in maintaining chondrogenic phenotype with reduced cell proliferation rate but enhanced glycosaminoglycans (GAGs) and type II collagen (COL II) secretion. Quantitative real-time polymerase chain reaction also showed time-dependent up-regulation of cartilage-specific marker genes (COL II, aggrecan and Sox9) for GH-GlcN16. Implantation of chondrocytes/GH-GlcN16 constructs into full-thickness articular cartilage defects of rabbits could regenerate neocartilage with positive staining for GAGs and COL II. The GH-GlcN16 cryogel will be suitable as a scaffold for the treatment of articular cartilage defects.

Repair of cartilage defects in osteoarthritis rats with induced pluripotent stem cell derived chondrocytes

Background

The incapacity of articular cartilage (AC) for self-repair after damage ultimately leads to the development of osteoarthritis. Stem cell-based therapy has been proposed for the treatment of osteoarthritis (OA) and induced pluripotent stem cells (iPSCs) are becoming a promising stem cell source.

Results

Three steps were developed to differentiate human iPSCs into chondrocytes which were transplanted into rat OA models induced by monosodium iodoacetate (MIA). After 6 days embryonic body (EB) formation and 2 weeks differentiation, the gene and protein expression of Col2A1, GAG and Sox9 has significantly increased compare to undifferentiated hiPSCs. After 15 weeks transplantation, no immune responses were observed, micro-CT showed gradual engraftment and the improvement of subchondrol plate integrity, and histological examinations demonstrated articular cartilage matrix production.

Conclusions

hiPSC could be an efficient and clinically translatable approach for cartilage tissue regeneration in OA cartilages.

Effects of Platelet-Rich Plasma & Platelet-Rich Fibrin with and without Stromal Cell-Derived Factor-1 on Repairing Full-Thickness Cartilage Defects in Knees of Rabbits

BACKGROUND

The purpose of this study was to create biomaterial scaffolds like platelet-rich plasma (PRP) and platelet-rich fibrin (PRF) containing stromal cell-derived factor-1 (SDF1) as a chemokine to induce hyaline cartilage regeneration of rabbit knee in a full thickness defect.

METHODS

We created a full thickness defect in the trochlear groove of thirty-six bilateral knees of eighteen mature male rabbits. The knees were randomly divided into six groups (group I: untreated control, group II: PRP, group III: PRF, group IV: Gelatin+SDF1, group V: PRP+SDF1, and group VI: PRF+SDF1). After four weeks, the tissue specimens were evaluated by macroscopic examination and histological grading, immunofluorescent staining for collagen type II, and analyzed for cartilage marker genes by real-time PCR. The data were compared using statistical methods (SPSS 20, Kruskal-Wallis test, Bonferroni post hoc test and P<0.05).

RESULTS

Macroscopic evaluations revealed that international cartilage repair society (ICRS) scores of the PRF+SDF1 group were higher than other groups. Microscopic analysis showed that the ICRS score of the PRP group was significantly lower than other groups. Immunofluorescent staining for collagen II demonstrated a remarkable distribution of type II collagen in the Gel+SDF1, PRP+SDF1 and PRF+SDF1 groups compared with other groups. Real-time PCR analysis revealed that mRNA expression of SOX9 and aggrecan were significantly greater in the PRF+SDF1, PRP+SDF1, Gel+SDF1 and PRF groups than the control group (P<0.05).

CONCLUSION

Our results indicate that implantation of PRF scaffold containing SDF1 led to the greatest evaluation scores of full-thickness lesions in rabbits.

Devitalisation of human cartilage by high hydrostatic pressure treatment: Subsequent cultivation of chondrocytes and mesenchymal stem cells on the devitalised tissue

The regeneration of cartilage lesions still represents a major challenge. Cartilage has a tissue-specific architecture, complicating recreation by synthetic biomaterials. A novel approach for reconstruction is the use of devitalised cartilage. Treatment with high hydrostatic pressure (HHP) achieves devitalisation while biomechanical properties are remained. Therefore, in the present study, cartilage was devitalised using HHP treatment and the potential for revitalisation with chondrocytes and mesenchymal stem cells (MSCs) was investigated. The devitalisation of cartilage was performed by application of 480 MPa over 10 minutes. Effective cellular inactivation was demonstrated by the trypan blue exclusion test and DNA quantification. Histology and electron microscopy examinations showed undamaged cartilage structure after HHP treatment. For revitalisation chondrocytes and MSCs were cultured on devitalised cartilage without supplementation of chondrogenic growth factors. Both chondrocytes and MSCs significantly increased expression of cartilage-specific genes. ECM stainings showed neocartilage-like structure with positive AZAN staining as well as collagen type II and aggrecan deposition after three weeks of cultivation. Our results showed that HHP treatment caused devitalisation of cartilage tissue. ECM proteins were not influenced, thus, providing a scaffold for chondrogenic differentiation of MSCs and chondrocytes. Therefore, using HHP-treated tissue might be a promising approach for cartilage repair.

Evaluation of the potential of rhTGF- β3 encapsulated P(LLA-CL)/collagen nanofibers for tracheal cartilage regeneration using mesenchymal stems cells derived from Wharton's jelly of human umbilical cord

Tracheal injuries are one of major challenging issues in clinical medicine because of the poor intrinsic ability of tracheal cartilage for repair. Tissue engineering provides an alternative method for the treatment of tracheal defects by generating replacement tracheal structures. In this study, core-shell nanofibrous scaffold was fabricated to encapsulate bovine serum albumin & rhTGF-β3 (recombinant human transforming growth factor-β3) into the core of the nanofibers for tracheal cartilage regeneration. Characterization of the core-shell nanofibrous scaffold was carried out by scanning electron microscope (SEM), transmission electron microscope (TEM), laser scanning confocal microscopy (LSCM), and tensile mechanical test. The rhTGF-β3 released from the scaffolds in a sustained and stable manner for about 2months. The bioactivity of released rhTGF-β3 was evaluated by its effect on the synthesis of type II collagen (COL2) and glycosaminoglycans (GAGs) by chondrocytes. The results suggested that its bioactivity was retained during release process. The proliferation and morphology analyses of mesenchymal stems cells derived from Wharton's jelly of human umbilical cord (WMSCs) indicated the good biocompatibility of the fabricated nanofibrous scaffold. Meanwhile, the chondrogenic differentiation of WMSCs cultured on core-shell nanofibrous scaffold was evaluated by real-time qPCR and histological staining. The results suggested that the core-shell nanofibrous scaffold with rhTGF-β3 could promote the chondrogenic differentiation ability of WMSCs. Therefore, WMSCs could be a promising seed cells in the construction of tissue-engineered tracheal cartilage. Overall, the core-shell nanofibrous scaffold could be an effective delivery system for rhTGF-β3 and served as a promising tissue engineered scaffold for tracheal cartilage regeneration.

Applications of Chondrocyte-Based Cartilage Engineering: An Overview

Chondrocytes are the exclusive cells residing in cartilage and maintain the functionality of cartilage tissue. Series of biocomponents such as different growth factors, cytokines, and transcriptional factors regulate the mesenchymal stem cells (MSCs) differentiation to chondrocytes. The number of chondrocytes and dedifferentiation are the key limitations in subsequent clinical application of the chondrocytes. Different culture methods are being developed to overcome such issues. Using tissue engineering and cell based approaches, chondrocytes offer prominent therapeutic option specifically in orthopedics for cartilage repair and to treat ailments such as tracheal defects, facial reconstruction, and urinary incontinence. Matrix-assisted autologous chondrocyte transplantation/implantation is an improved version of traditional autologous chondrocyte transplantation (ACT) method. An increasing number of studies show the clinical significance of this technique for the chondral lesions treatment. Literature survey was carried out to address clinical and functional findings by using various ACT procedures. The current study was conducted to study the pharmacological significance and biomedical application of chondrocytes. Furthermore, it is inferred from the present study that long term follow-up studies are required to evaluate the potential of these methods and specific positive outcomes.