From Fat to Cartilage: What a dECM Hydrogel Reveals About Stem Cell Behavior

A study from FIOCRUZ Paraná evaluates how a decellularized cartilage-derived hydrogel shapes the growth and differentiation of adipose-derived stem cells — with results pointing toward fibrocartilage rather than hyaline cartilage.

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Based on Josino & Stimamiglio,Frontiers in Bioengineering and Biotechnology, 2024

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A Tissue That Cannot Heal Itself

Cartilage is not self-repairing. When damaged — whether by injury or progressive degeneration — it lacks the necessary supplies required for spontaneous regeneration. Conditions like osteoarthritis, the most prevalent form of degenerative joint disease, emerge from exactly this gap: the damage accumulates, the tissue cannot compensate, and functional decline follows.

Current clinical strategies range from microfracture techniques — which try to recruit the body's own stem cells to the injury site — to direct cell injection with mesenchymal stem cells (MSCs). The problem with both approaches is retention: applied cells tend to migrate away from the target zone, diluting any therapeutic benefit. Biomaterial scaffolds that can hold cells in place while guiding their differentiation represent a logical response to that limitation.

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Why Adipose-Derived Stem Cells?

Human adipose-derived stem cells (hASCs) have become an increasingly practical option for cartilage repair research. As a source, adipose tissue is readily accessible — typically obtained from liposuction procedures that would otherwise discard the material. The cells it yields are multipotent, capable of differentiating along multiple lineages including the chondrogenic pathway. What remains less understood is how the environment in which these cells are placed affects their differentiation trajectory, a question that, according to the researchers involved in the study, “reframes stem cell differentiation as a process primarily shaped by the extracellular microenvironment, rather than by induction protocols alone”. That is the central question this study sets out to address.

The Biomaterial: MatriXpec™

The hydrogel used in this study — MatriXpec™, produced by TissueLabs — is derived from decellularized porcine tendon cartilage tissue. Decellularization removes cellular material while preserving the architecture and biochemical composition of the native extracellular matrix (ECM). The result is a substrate that retains the structural proteins and signaling molecules of the original tissue without the immunogenic cellular components. “Within this scientific context, we first came across TissueLabs; the focus on preserving tissue identity in decellularized matrices directly aligned with the questions we were already pursuing in the laboratory”, the authors report. 

Collagen proteins dominate the composition of MatriXpec™ — types 1, 2, 6, and 9 — reflecting the fibrocartilaginous origin of the source tissue.

Cell Behavior in 3D: Growth, Viability, and Morphology

hASCs were seeded onto MatriXpec™ and monitored over 21 days.

At days 2, 5, and 21, DNA quantification and nuclear counts showed no statistically significant difference between cells grown on MatriXpec™ and those grown on standard tissue culture plastic (TCP). During the intermediate window — days 7 and 14 — the MatriXpec™ cultures showed a lower cell count: approximately 883 versus 2,524 at day 7, and 1,204 versus 2,964 at day 14. By day 21, both conditions had converged to a comparable growth plateau.

The authors interpret this intermediate lag as an adaptation phase: the three-dimensional environment presents a substantially richer and more demanding set of structural signals than a flat surface, and cells appear to slow their proliferation as they process and respond to those cues.

Cell viability, assessed through both LDH release and LIVE/DEAD staining, remained high throughout. At day 2, cytotoxicity measured around 5.2% in TCP and 5.5% in MatriXpec™. At day 7, both conditions held in the 7–8% range. The qualitative LIVE/DEAD assay confirmed the same picture: the hydrogel environment did not elevate cell death relative to standard culture conditions.

Morphologically, the cells told a distinct story. hASCs on TCP maintained the flattened, spread-out shape typical of 2D culture. On MatriXpec™, cells adopted an elongated, fusiform morphology — and, critically, began migrating into the interior of the hydrogel. By day 7, immunofluorescence imaging showed cells in multiple focal planes within the material, not just on its surface. This pattern became more pronounced at days 14 and 21.

Differentiation: What Phenotype Does the Hydrogel Instruct?

To assess chondrogenic differentiation potential, hASCs were cultured for 10 and 21 days under two conditions: a standard chondrogenic induction medium (supplemented with TGF-β3 and other chondrogenic factors) and a non-induced maintenance medium. Both TCP and MatriXpec™ conditions were tested in parallel.

GAG Deposition

Glycosaminoglycans (GAGs) are a hallmark of cartilaginous ECM. Safranin O staining at day 21 showed more pronounced GAG deposition in the MatriXpec™ conditions than in TCP — and notably, this was observed even in the non-induced (control) group. Cells cultured on the hydrogel in maintenance medium deposited measurable GAGs without any chondrogenic chemical stimulus, suggesting that the biomaterial itself provides pro-chondrogenic cues. Quantitative DMMB assay confirmed a statistically significant increase in GAG content in the MatriXpec™ + chondrogenic medium condition at day 21.

Gene Expression Profile

RT-qPCR analysis at days 10 and 21 tracked seven chondrogenic and fibrocartilage-associated markers. The table below summarizes the pattern of upregulation observed in MatriXpec™ cultures compared to TCP under chondrogenic induction.

Gene Expression — MatriXpec™ vs TCP (day 21, chondrogenic induction)

SOX9 — the transcription factor that acts as a master switch for chondrogenesis — was significantly elevated in MatriXpec™ cultures. In addition, the significant upregulation concentrated in markers characteristic of fibrocartilage: COL1, COL10, and MMP13.

"The MatriXpec™ microtopography analysis revealed that this biomaterial has a fibrous ultrastructure composed mainly of collagen proteins. Cell culture on MatriXpec™ greatly maintained hASCs viability and growth."

This finding aligns with a growing body of literature on ECM-driven cell fate. The remaining molecular composition of a decellularized tissue — its collagen subtypes, GAG profile, and structural arrangement — does not merely support cells in a neutral manner. It actively instructs them. In this case, the fibrocartilaginous origin of the source tissue appears to be legible to the cells, which respond by shifting their differentiation program accordingly.

What This Means for Cartilage Research

The study contributes two concrete pieces of information to the field. First, MatriXpec™ is a viable 3D culture substrate for hASCs: it sustains cell viability, supports long-term growth, and enables a morphological transition to a more physiologically relevant cell shape. Second, and more specifically, the hydrogel actively biases hASC differentiation toward a fibrocartilage phenotype — an outcome that reflects, rather than contradicts, the nature of the source tissue.

The authors note the inherent variability among cell donors as a study limitation — a challenge shared across MSC research broadly. They also frame it as a strength: working across multiple donors produces findings that better reflect the heterogeneity of the clinical setting. “Understanding how different matrices modulate cell fate is therefore an essential step toward designing therapies that are more realistic, more specific, and, above all, more closely aligned with the biology of the tissues we aim to regenerate”, the authors conclude.

LABCET - FIOCRUZ TEAM

The TissueLabs team proudly recognizes and deeply admires the outstanding work carried out by Fiocruz. We are honored to see our solutions contributing to such meaningful scientific initiatives and look forward to strengthening this relationship through many more successful collaborations in the future.

References Josino R and Stimamiglio MA (2024). Bioactive decellularized extracellular matrix-based hydrogel supports human adipose tissue-derived stem cell maintenance and fibrocartilage phenotype. Frontiers in Bioengineering and Biotechnology, 11:1304030. DOI: 10.3389/fbioe.2023.1304030