The clinical status of cartilage tissue regeneration in humans

Comparative effect of physicomechanical and biomolecular cues on zone-specific chondrogenic differentiation of mesenchymal stem cells

Current tissue engineering approaches to regeneration of articular cartilage rarely restore the tissue to its normal state because the generated tissue lacks the intricate zonal organization of the native cartilage. Zonal regeneration of articular cartilage is hampered by the lack of knowledge for the relation between physical, mechanical, and biomolecular cues and zone-specific chondrogenic differentiation of progenitor cells. This work investigated in 3D the effect of TGF-β1, zone-specific growth factors, optimum matrix stiffness, and adding nanofibers on the expression of chondrogenic markers specific to the superficial, middle, and calcified zones of articular cartilage by the differentiating human mesenchymal stem cells (hMSCs). Growth factors included BMP-7, IGF-1, and hydroxyapatite (HA) for the superficial, middle, and calcified zones, respectively; optimum matrix stiffness was 80 kPa, 2.1 MPa, and 320 MPa; and nanofibers were aligned horizontal, random, and perpendicular to the gel surface. hMSCs with zone-specific cell densities were encapsulated in engineered hydrogels and cultured with or without TGF-β1, zone-specific growth factor, optimum matrix modulus, and fiber addition and cultured in basic chondrogenic medium. The expression of encapsulated cells was measured by mRNA, protein, and biochemical analysis. Results indicated that zone-specific matrix stiffness had a dominating effect on chondrogenic differentiation of hMSCs to the superficial and calcified zone phenotypes. Addition of aligned nanofibers parallel to the direction of gel surface significantly enhanced expression of Col II in the superficial zone chondrogenic differentiation of hMSCs. Conversely, biomolecular factor IGF-1 in combination with TGF-β1 had a dominating effect on the middle zone chondrogenic differentiation of hMSCs. Results of this work could potentially lead to the development of multilayer grafts mimicking the zonal organization of articular cartilage.

Evaluation of an injectable thermoresponsive hyaluronan hydrogel in a rabbit osteochondral defect model

Articular cartilage displays very little self-healing capabilities, generating a major clinical need. Here, we introduce a thermoresponsive hyaluronan hydrogel for cartilage repair obtained by covalently grafting poly(N-isopropylacrylamide) to hyaluronan, to give a brush co-polymer HpN. The gel is fluid at room temperature and becomes gel at body temperature. In this pilot study HpN safety and repair response were evaluated in an osteochondral defect model in rabbit. Follow-up was of 1 week and 12 weeks and the empty defect served as a control, for a total of four experimental groups. At 12 weeks the defect sites were evaluated macroscopically and histologically. Local lymph nodes, spleen, liver, and kidneys were analyzed for histopathological evaluation. HpN could be easily injected and remained into the defect throughout the study. The macroscopic score was statistically superior for HpN versus empty. Histological score gave opposite trend but not statistically significant. A slight tissue reaction was observed around HpN, however, vascularization and subchondral bone formation were not impeded. An upper proteoglycans rich fibro-cartilaginous tissue with fairly good continuity and lateral integration into the existing articular cartilage was observed in all cases. No signs of local or systemic acute or subacute toxicity were observed. In conclusion, HpN is easily injectable, remains into an osteochondral defect within a moving synovial joint, is biocompatible and does not interfere with the intrinsic healing response of osteochondral defects in a rabbit model. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1469-1478, 2016.

Chondrogenic effect of cell-based scaffold of self-assembling peptides/PLGA-PLL loading the hTGFβ3 plasmid DNA

With the application of tissue engineering to tissue regeneration, additional new complexes have been made in response to the challenge of cartilage-injury repair. This study was performed to construct a rat precartilaginous stem cells-based scaffold of self-assembling peptides RADA16-I/PLGA-PLL (poly-L-lysine coated PLGA) as extracellular matrix loading the NLS-TAT as a peptide-based carrier for a plasmid DNA containing hTGFβ3. After composites were cultured for 1, 2, 3 and 4 weeks, respectively, the results showed that the levels of chondrogenic-related gene expression were higher in the experimental group with and hTGFβ3 gene by reverse transcription-polymerase chain reaction, and with higher histochemical and immunohistochemical expression. hTGFβ3 protein expression had increased at 4 weeks based on western blot analysis. The results of this study show that a complex may be a suitable scaffold for cartilage repair and offer a strategy for tissue regeneration through the use of tissue engineering.

Fibrous Scaffolds with Varied Fiber Chemistry and Growth Factor Delivery Promote Repair in a Porcine Cartilage Defect Model

Current clinically approved methods for cartilage repair are generally based on either endogenous cell recruitment (e.g., microfracture) or chondrocyte delivery (e.g., autologous chondrocyte implantation). However, both methods culminate in repair tissue with inferior mechanical properties and the addition of biomaterials to these clinical interventions may improve their efficacy. To this end, the objective of this study was to investigate the ability of multipolymer acellular fibrous scaffolds to improve cartilage repair when combined with microfracture in a large animal (i.e., minipig) model. Composite scaffolds were formulated from a combination of hyaluronic acid (HA) fibers and poly(ɛ-caprolactone) (PCL) fibers, either with or without transforming growth factor-β3 (TGFβ3). After 12 weeks in vivo, material choice and TGFβ3 delivery had a significant impact on outcomes; specifically, PCL scaffolds without TGFβ3 had inferior gross appearance and reduced mechanical properties, whereas HA scaffolds that released TGFβ3 resulted in improved histological scores and increased type 2 collagen content. Importantly, analysis of the overall dataset revealed that histology, but not gross appearance, was a better predictor of mechanical properties. This study highlights the importance of scaffold properties on in vivo cartilage repair as well as the need for numerous quantitative outcome measures to fully evaluate treatment methods.

Strategies for improving the repair of focal cartilage defects

Articular cartilage, together with skin, was predicted to be one of the first tissues to be successfully engineered. However cartilage repair remains nowadays still elusive, as we are still not able to overcome the hurdles of creating biomaterials corresponding to the native properties of the tissue, and which operate in joints environment that is not favorable for regeneration. In this review, we give an overview of the outcome of current cartilage treatment techniques. Furthermore we present current research strategies for improving cartilage tissue engineering.

The Addition of Platelet-Rich Plasma to Scaffolds Used for Cartilage Repair: A Review of Human and Animal Studies

PURPOSE

To review the available literature on studies focusing on platelet-rich plasma (PRP)-enhanced scaffolds for cartilage lesion repair in animals and to analyze the clinical outcomes of similar biologically augmented cartilage regeneration techniques in humans.

METHODS

We conducted a literature search and subsequent review investigating the potential of PRP to enhance articular cartilage repair using scaffolds or bioengineered implants.

RESULTS

Of the 14 animal model studies reviewed, 10 reported positive effects with PRP whereas only 2 showed negative overall effects. The remaining 2 studies reported no significant differences, or neutral results, with the use of PRP. With the addition of PRP, the gross appearance and histologic analysis of repair cartilage were improved or no difference was seen compared with control (11 of 12 studies that looked at this). Human studies of the knee or talar dome showed improvements in clinical assessment scores as soon as 6 months after surgery. There was great variability in the method of PRP preparation, choice of scaffold, and cell source between studies.

CONCLUSIONS

PRP-augmented scaffolds have been shown to be beneficial in the articular cartilage repair process in animals and humans based on macroscopic, histologic, and biochemical analysis and based on clinical outcome scores, respectively. Comparison between studies is difficult because there is great variability in PRP preparation and administration.

LEVEL OF EVIDENCE

Level IV, systematic review of Level III and IV studies.

Osteoarthritis

Osteoarthritis is a major source of pain, disability, and socioeconomic cost worldwide. The epidemiology of the disorder is complex and multifactorial, with genetic, biological, and biomechanical components. Aetiological factors are also joint specific. Joint replacement is an effective treatment for symptomatic end-stage disease, although functional outcomes can be poor and the lifespan of prostheses is limited. Consequently, the focus is shifting to disease prevention and the treatment of early osteoarthritis. This task is challenging since conventional imaging techniques can detect only quite advanced disease and the relation between pain and structural degeneration is not close. Nevertheless, advances in both imaging and biochemical markers offer potential for diagnosis and as outcome measures for new treatments. Joint-preserving interventions under development include lifestyle modification and pharmaceutical and surgical modalities. Some show potential, but at present few have proven ability to arrest or delay disease progression.

Arthroscopic Transplantation of Synovial Stem Cells Improves Clinical Outcomes in Knees With Cartilage Defects

BACKGROUND

Transplantation of mesenchymal stem cells (MSCs) is one possible strategy to achieve articular cartilage repair. We previously reported that synovial MSCs were highly proliferative and able to undergo chondrogenesis. We also found that placing a suspension of synovial MSCs on a cartilage defect for 10 minutes promoted cartilage repair in rabbit and pig models. However, the in vivo efficacy of this approach has not been tested clinically.

QUESTIONS/PURPOSES

We asked whether transplantation of synovial MSCs improves (1) MRI features, (2) histologic features, and (3) clinical evaluation scores in patients with cartilage defects in the knee?

METHODS

Patients with a symptomatic single cartilage lesion of the femoral condyle were indicated for inclusion in our study, and between April 2008 and April 2011, 10 patients were enrolled in this study. All patients completed followups of 3 years or more. The average followup period was 52 months (range, 37-80 months). Synovial MSCs were expanded with 10% autologous human serum for 14 days after digestion. For transplantation, the patient was positioned so that the cartilage defect was facing upward, and synovial MSC suspension was placed on the cartilage defect with a syringe under arthroscopic control. The defect with the applied suspension then was held in the upward position for 10 minutes. Five patients underwent concomitant ACL reconstructions, among whom two had meniscus suturing performed simultaneously. For MRI quantification, the cartilage defect was scored from 0 to 5. Second-look arthroscopy was performed for four patients and biopsy specimens were evaluated histologically. Clinical outcome was assessed using the Lysholm score and Tegner Activity Level Scale at final followup. Comparisons of MRI and Lysholm scores before and after treatment for each patient were analyzed using the Wilcoxon signed-rank test.

RESULTS

MRI score (median ± 95% CI) was 1.0 ± 0.3 before and 5.0 ± 0.7 after, and increased after treatment in each patient (p = 0.005). Second-look arthroscopy in four patients showed that the cartilage defect appeared to be qualitatively better in all cases. Histologic analyses showed hyaline cartilage in three patients and fibrous cartilage in one at the deep zone. The Lysholm score (median ± 95% CI) was 76 ± 7 before and 95 ± 3 after, and increased after treatment in each patient (p = 0.005). The Tegner Activity Level Scale did not decrease after treatment in each patient.

CONCLUSIONS

For this small initial case series, transplantation of synovial MSCs was effective in terms of MRI score, qualitative histology, and Lysholm score. The use of synovial MSCs has an advantage in that the cells can be prepared at passage 0 in only 14 days. Transplantation of synovial MSCs may be less invasive than mosaicplasty and autologous chondrocyte implantation. To conclusively show the effectiveness of this treatment requires comparative studies, especially with more established arthroscopic procedures, such as marrow stimulation techniques.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Development and Characterization of Acellular Extracellular Matrix Scaffolds from Porcine Menisci for Use in Cartilage Tissue Engineering

Given the growing number of arthritis patients and the limitations of current treatments, there is great urgency to explore cartilage substitutes by tissue engineering. In this study, we developed a novel decellularization method for menisci to prepare acellular extracellular matrix (ECM) scaffolds with minimal adverse effects on the ECM. Among all the acid treatments, formic acid treatment removed most of the cellular contents and preserved the highest ECM contents in the decellularized porcine menisci. Compared with fresh porcine menisci, the content of DNA decreased to 4.10%±0.03%, and there was no significant damage to glycosaminoglycan (GAG) or collagen. Histological staining also confirmed the presence of ECM and the absence of cellularity. In addition, a highly hydrophilic scaffold with three-dimensional interconnected porous structure was fabricated from decellularized menisci tissue. Human chondrocytes showed enhanced cell proliferation and synthesis of chondrocyte ECM including type II collagen and GAG when cultured in this acellular scaffold. Moreover, the scaffold effectively supported chondrogenesis of human bone marrow-derived mesenchymal stem cells. Finally, in vivo implantation was conducted in rats to assess the biocompatibility of the scaffolds. No significant inflammatory response was observed. The acellular ECM scaffold provided a native environment for cells with diverse physiological functions to promote cell proliferation and new tissue formation. This study reported a novel way to prepare decellularized meniscus tissue and demonstrated the potential as scaffolds to support cartilage repair.

Synovial fluid hyaluronan mediates MSC attachment to cartilage, a potential novel mechanism contributing to cartilage repair in osteoarthritis using knee joint distraction

Objectives

Knee joint distraction (KJD) is a novel, but poorly understood, treatment for osteoarthritis (OA) associated with remarkable ‘spontaneous’ cartilage repair in which resident synovial fluid (SF) multipotential mesenchymal stromal cells (MSCs) may play a role. We hypothesised that SF hyaluronic acid (HA) inhibited the initial interaction between MSCs and cartilage, a key first step to integration, and postulate that KJD environment favoured MSC/cartilage interactions.

Methods

Attachment of dual-labelled SF-MSCs were assessed in a novel in vitro human cartilage model using OA and rheumatoid arthritic (RA) SF. SF was digested with hyaluronidase (hyase) and its effect on adhesion was observed using confocal microscopy. MRI and microscopy were used to image autologous dual-labelled MSCs in an in vivo canine model of KJD. SF-HA was investigated using gel electrophoresis and densitometry.

Results

Osteoarthritic-synovial fluid (OA-SF) and purified high molecular weight (MW) HA inhibited SF-MSC adhesion to plastic, while hyase treatment of OA-SF but not RA-SF significantly increased MSC adhesion to cartilage (3.7-fold, p<0.05) These differences were linked to the SF mediated HA-coat which was larger in OA-SF than in RA-SF. OA-SF contained >9 MDa HA and this correlated with increases in adhesion (r=0.880). In the canine KJD model, MSC adhesion to cartilage was evident and also dependent on HA MW.

Conclusions

These findings highlight an unappreciated role of SF-HA on MSC interactions and provide proof of concept that endogenous SF-MSCs are capable of adhering to cartilage in a favourable biochemical and biomechanical environment in OA distracted joints, offering novel one-stage strategies towards joint repair.

Culture temperature affects redifferentiation and cartilaginous extracellular matrix formation in dedifferentiated human chondrocytes

To date, there have been few studies on how temperature affects the phenotype and metabolism of human chondrocytes. Thus, the purpose of this study was to elucidate the effects of culture temperature on chondrocyte redifferentiation and extracellular matrix (ECM) formation using dedifferentiated mature human chondrocytes in vitro. Dedifferentiated chondrocytes were cultured in a pellet culture system for up to 21 days. The pellets were randomly divided into three groups with different culture temperature (32, 37, and 41°C). Chondrocyte redifferentiation and ECM formation were evaluated by wet weight, messenger ribonucleic acid (mRNA), histological, and biochemical analyses. The results showed that the wet weight and the mRNA expressions of collagen type II A1 and cartilage oligomeric matrix protein at 37°C were higher than the corresponding values at 32°C. The histological and biochemical analyses revealed that the syntheses of type II collagen and proteoglycan were promoted at 37°C compared to those at 32°C, whereas they were considerably inhibited at 41°C. In conclusion, the results obtained herein indicated that temperature affects chondrocyte redifferentiation and ECM formation, and modulation of temperature might thus represent an advantageous means to regulate the phenotype and biosynthetic activity of chondrocytes.

An injectable extracellular matrix derived hydrogel for meniscus repair and regeneration

Tissue-derived extracellular matrix (ECM) biomaterials to regenerate the meniscus have gained increasing attention in treating meniscus injuries and diseases, particularly for aged persons and athletes. However, ECM scaffold has poor cell infiltration and can only be implanted using surgical procedures. To overcome these limitations, we developed an injectable ECM hydrogel material from porcine meniscus via modified decellularization and enzymatic digestion. This meniscus-derived ECM hydrogel exhibited a fibrous morphology with tunable compression and initial modulus. It had a good injectability evidenced by syringe injection into mouse subcutaneous tissue. The hydrogel showed good cellular compatibility by promoting the growth of both bovine chondrocytes and mouse 3T3 fibroblasts encapsulated in the hydrogel for 2 weeks. It also promoted cell infiltration as shown in both in vitro cell culture and in vivo mouse subcutaneous implantation. The in vivo study revealed that the ECM hydrogel possessed good tissue compatibility after 7 days of implantation. The results support the great potential of the newly produced injectable meniscus-derived ECM hydrogel specifically for meniscus repair and regeneration.

Protocatechuic acid benefits proliferation and phenotypic maintenance of rabbit articular chondrocytes: An in vitro study

Numerous antioxidants exhibit antiarthritic effects due to their inhibitory effect on inflammatory factors. Certain antioxidants, such as protocatechuic acid (PCA) and its analogs, have been reported to be effective in the treatment of arthritis. However, the effect of PCA on chondro-protection may be alleviated due to the induction of apoptosis, as has been demonstrated in stomatocytes. To clearly determine the effect of PCA on the biological and cellular metabolism of rabbit articular chondrocytes in vitro, examinations of cytotoxicity, proliferation and morphology were performed, in addition to analyses of glycosaminoglycan (GAG) synthesis and the expression of cartilage-specific genes. The results revealed that PCA effectively promoted chondrocyte growth, the synthesis of the extracellular matrix and the mRNA expression of aggrecan, collagen II and Sox9, while downregulating the expression of the collagen I gene, a marker of chondrocyte dedifferentiation. In addition, hypertrophy, which may result in chondrocyte ossification, was not detected in the groups. Among the doses (range, 0.05-0.3 mmol/l) of PCA that promoted the proliferation of chondrocytes, a concentration of 0.125 mmol/l produced the optimum performance. The results indicated that PCA, particularly at a dose of 0.125 mmol/l, accelerated the proliferation of rabbit articular chondrocytes in vitro and maintained their phenotype. This study may provide a basis for further research concerning the treatment of cartilage defects.

Cell-based articular cartilage repair: the link between development and regeneration

Clinical efforts to repair damaged articular cartilage (AC) currently face major obstacles due to limited intrinsic repair capacity of the tissue and unsuccessful biological interventions. This highlights a need for better therapeutic strategies. This review summarizes the recent advances in the field of cell-based AC repair. In both animals and humans, AC defects that penetrate into the subchondral bone marrow are mainly filled with fibrocartilaginous tissue through the differentiation of bone marrow mesenchymal stem cells (MSCs), followed by degeneration of repaired cartilage and osteoarthritis (OA). Cell therapy and tissue engineering techniques using culture-expanded chondrocytes, bone marrow MSCs, or pluripotent stem cells with chondroinductive growth factors may generate cartilaginous tissue in AC defects but do not form hyaline cartilage-based articular surface because repair cells often lose chondrogenic activity or result in chondrocyte hypertrophy. The new evidence that AC and synovium develop from the same pool of precursors with similar gene profiles and that synovium-derived chondrocytes have stable chondrogenic activity has promoted use of synovium as a new cell source for AC repair. The recent finding that NFAT1 and NFAT2 transcription factors (TFs) inhibit chondrocyte hypertrophy and maintain metabolic balance in AC is a significant advance in the field of AC repair. The use of synovial MSCs and discovery of upstream transcriptional regulators that help maintain the AC phenotype have opened new avenues to improve the outcome of AC regeneration.

Identification and specification of the mouse skeletal stem cell

How are skeletal tissues derived from skeletal stem cells? Here, we map bone, cartilage, and stromal development from a population of highly pure, postnatal skeletal stem cells (mouse skeletal stem cells, mSSCs) to their downstream progenitors of bone, cartilage, and stromal tissue. We then investigated the transcriptome of the stem/progenitor cells for unique gene-expression patterns that would indicate potential regulators of mSSC lineage commitment. We demonstrate that mSSC niche factors can be potent inducers of osteogenesis, and several specific combinations of recombinant mSSC niche factors can activate mSSC genetic programs in situ, even in nonskeletal tissues, resulting in de novo formation of cartilage or bone and bone marrow stroma. Inducing mSSC formation with soluble factors and subsequently regulating the mSSC niche to specify its differentiation toward bone, cartilage, or stromal cells could represent a paradigm shift in the therapeutic regeneration of skeletal tissues.

Effects of purified alginate sponge on the regeneration of chondrocytes: in vitro and in vivo

Regeneration science has been studied using tissue engineering techniques due to the self-renewal difficulties of damaged or degenerated cartilage. A scaffold with biodegradability and biocompatibility features plays a key role in developing cartilage tissue similar to human biological materials. Herein, we have fabricated three-dimensional sponge using purified alginate for the regeneration of chondrocytes cells and formation of cartilage. We demonstrated that the alginate purification can effectively minimize inflammatory reaction through reducing the content of mannuronic acid causing immune rejection. Cartilage regeneration research was performed using three-dimensional non-purified and purified alginate sponges synthesized by modified Korbutt method. In vitro cell viability and specific gene expression in the cartilage cells were investigated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and reverse transcriptase-polymerase chain reaction (RT-PCR) after seeding chondrocytes on the as-fabricated sponges. Specific extracellular matrix (ECM) of chondrocytes, sGAG, and the content of collagen were also measured. Histological staining was carried out after purified alginate sponge seeded with chondrocytes and was implanted in subcutaneous nude mouse followed by extraction. Compared to the non-purified ones, the purified alginate sponges showed positive effects on maintaining affinities and phenotype of chondrocytes. From these results, it can be suggested that the purified alginate sponges provide a promising platform for cartilage regeneration.

The use of a cell-free chondroinductive implant in a child with massive cartilage loss of the talus after an open fracture dislocation of the ankle: a case report

BACKGROUND

We present a case report of a 3-year-old girl who sustained a severe open fracture dislocation of her talus with complete loss of full-thickness articular cartilage and subchondral bone over 80% of the talar dome. At presentation there was an extensive soft tissue defect including absent anterior joint capsule. She required a free anterolateral thigh flap to reconstruct this defect. The talar dome defect was treated with a cell-free chondroinductive implant made of resorbable polyglycolic acid felt and hyaluronic acid. This was the first use of such an implant in the United Kingdom and the first use in a child anywhere in the world.

METHODS

The case has been followed prospectively for 3 years.

RESULTS

At 3 years postoperative, the patient underwent thinning of the anterolateral thigh flap and trimming of an anterior tibial overgrowth, which was causing impingement. At surgery the talar dome cartilage looked pristine, with a line representing the tidemark between the original cartilage and the new formed. Biopsies were taken and histopathology performed.

CONCLUSIONS

This was a rare and difficult case that has achieved an excellent outcome at this follow-up stage.

LEVEL OF EVIDENCE

Level V.

Effects of immobilization and remobilization on the ankle joint in Wistar rats

A sprained ankle is a common musculoskeletal sports injury and it is often treated by immobilization of the joint. Despite the beneficial effects of this therapeutic measure, the high prevalence of residual symptoms affects the quality of life, and remobilization of the joint can reverse this situation. The aim of this study was to analyze the effects of immobilization and remobilization on the ankle joint of Wistar rats. Eighteen male rats had their right hindlimb immobilized for 15 days, and were divided into the following groups: G1, immobilized; G2, remobilized freely for 14 days; and G3, remobilized by swimming and jumping in water for 14 days, performed on alternate days, with progression of time and a series of exercises. The contralateral limb was the control. After the experimental period, the ankle joints were processed for microscopic analysis. Histomorphometry did not show any significant differences between the control and immobilized/remobilized groups and members, in terms of number of chondrocytes and thickness of the articular cartilage of the tibia and talus. Morphological analysis of animals from G1 showed significant degenerative lesions in the talus, such as exposure of the subchondral bone, flocculation, and cracks between the anterior and mid-regions of the articular cartilage and the synovial membrane. Remobilization by therapeutic exercise in water led to recovery in the articular cartilage and synovial membrane of the ankle joint when compared with free remobilization, and it was shown to be an effective therapeutic measure in the recovery of the ankle joint.

Towards the feasibility of using ultrasound to determine mechanical properties of tissues in a bioreactor

Our ultimate goal is to non-destructively evaluate mechanical properties of tissue-engineered (TE) cartilage using ultrasound (US). We used agarose gels as surrogates for TE cartilage. Previously, we showed that mechanical properties measured using conventional methods were related to those measured using US, which suggested a way to non-destructively predict mechanical properties of samples with known volume fractions. In this study, we sought to determine whether the mechanical properties of samples, with unknown volume fractions could be predicted by US. Aggregate moduli were calculated for hydrogels as a function of SOS, based on concentration and density using a poroelastic model. The data were used to train a statistical model, which we then used to predict volume fractions and mechanical properties of unknown samples. Young's and storage moduli were measured mechanically. The statistical model generally predicted the Young's moduli in compression to within <10% of their mechanically measured value. We defined positive linear correlations between the aggregate modulus predicted from US and both the storage and Young's moduli determined from mechanical tests. Mechanical properties of hydrogels with unknown volume fractions can be predicted successfully from US measurements. This method has the potential to predict mechanical properties of TE cartilage non-destructively in a bioreactor.