Tendon scaffold mechanical testing under intermittent dynamic culture: when fibre architecture starts to matter

Discussions around tendon scaffold mechanical testing are often about a single tensile modulus number, pulled at the end of culture. In practice, that number caries a lot of hidden history: what the scaffold did under load, whether the structure drifted, how the cells were stimulated day to day, and whether the matrix that formed was mostly collagen or something else.

(if you want a quick refresher on how these tests get interpreted, see our guide to mechanical testing of biomaterials for non-engineers)

A research team led by Brian Amsden and Sean Mathew at Queen’s University in Kingston, ON, leaned into that messiness in a useful way. They built two melt electrowriting (MEW) scaffold architectures that were intentionally similar in pore size and baseline tensile behaviour, then asked what happens when primary Achilles tenocytes are exposed to intermittent dynamic culture. The loading itself was done in a CellScale MechanoCulture T6, and the tensile pulls were done on a CellScale UniVert, so the workflow stays anchored to real mechanical readouts rather than only microscopy.

What stands out is not that “loading helps” (that part is familiar). It’s that the scaffold design choice only starts to show up once cyclic tensile loading is part of the daily routine.

Full publication in Acta Biomaterialia here.

Tendon scaffold mechanical testing with melt electrowriting: controlling pore size while changing crimp

The authors printed polycaprolactone (PCL) scaffolds using melt electrowriting, aiming for tendon-like crimp rather than the usual straight fibre grids. They kept the pore size in the same ballpark across designs, because otherwise you end up arguing about infiltration and diffusion instead of architecture.

Two scaffold patterns were compared:

• Group A: aligned and crimped fibres in one direction, with straight fibres running orthogonally.

• Group X: bi-directional crimp, designed to behave as an auxetic scaffold under uniaxial tension (negative Poisson’s ratio).

If you’ve mostly seen “crimp” drawn as a single sinusoidal fibre, Group X is closer to what you might picture in a tendon fascicle where fibres aren’t only waviness in one axis. The intention is that when you pull it in one direction, the structure opens laterally instead of narrowing, shifting how strain is distributed through the network.

Publication Figure: Scaffold Designs

Intermittent dynamic culture and cyclic tensile loading: a daily “dose” instead of continuous stimulation

A lot of tenocyte tissue engineering methods either load continuously (which can drift into “just keep the motor running”) or load in short blocks without really justifying it. Here the protocol is explicit and repeatable, which makes it easier to connect to tendon scaffold mechanical testing outcomes later.

The constructs were seeded with primary rabbit Achilles tendon cells (tenocytes), given one week of static pre-culture, then split into:

• Static culture for two weeks, or

• Intermittent dynamic culture for two weeks: 4% strain, 1 Hz, 1 hour per day, at 37°C.

That “1 hour per day” detail matters more than it sounds. When the scaffold architecture is designed around fibre recruitment and crimp unfolding, intermittent loading gives the structure time to relax and recover, which may influence what the cells experience at the fibre scale. It also avoids turning the study into a fatigue experiment by accident, while still giving cells a repeated mechanical cue (related example: cyclic loading and tissue formation).

Publication Figure: Workflow and Loading Regimen (MCT6)

MechanoCulture T6 in a tendon scaffold mechanical testing workflow: validating the scaffold before loading cells

One thing they did that many people skip was to load the scaffolds without cells first, under the same intermittent regimen, and then check whether the geometry and mechanics stayed stable. It’s a small control step, but it changes how you interpret later “construct modulus increased” results.

If the scaffold itself softens, creeps, or loses crimp after two weeks of cycling in warm PBS, then any improvement in cell-laden mechanics is harder to pin on matrix deposition. Here, the scaffold-only checks suggest the architecture was reasonably durable under the regimen, so when the construct modulus shifts later, it’s at least plausible that the cells and their ECM are part of the reason.

This is where the MechanoCulture T6 sits in the story: not only as a bioreactor that “applied loading,” but as the place where the authors tried to separate scaffold mechanics from tissue production.

UniVert tensile testing and Poisson’s ratio: measuring architecture instead of assuming it

The UniVert shows up in two distinct ways in the study.

First, they used tensile testing to confirm that Group X and Group A were mechanically different in the way the designs implied. The auxetic claim, in particular, is not something you want to leave as a schematic. A negative Poisson’s ratio is a measurable behaviour, and it’s tied to how the scaffold deforms laterally under tension.

(here is more background on tension testing of biomaterials if you want the basics before diving into their modulus plots)

Second, they used tensile testing on the cell-laden constructs after culture to get an effective tensile modulus, which becomes the mechanical counterpart to the biochemical ECM readouts.

In tendon scaffold mechanical testing, it’s common to see a late-stage modulus plot without much about what the scaffold did at baseline. Here, the mechanical characterisation is threaded into the study design, and that makes the later outcomes easier to follow.

Tenocyte tissue engineering outcomes: collagen, sGAG, and the collagen to sGAG ratio

For readers in the tissue engineering field, the biochemical data is where the architecture story becomes more than mechanics trivia.

They quantified:

• Total collagen, normalized to dsDNA

• sGAG, normalized to dsDNA

• The collagen:sGAG ratio, which is a blunt metric but often a useful one for tendon-like matrix balance

Under static culture, the two architectures are not dramatically separated. Once intermittent dynamic culture is applied, Group X tends to pull ahead on collagen production, and the collagen:sGAG ratio shifts in a direction that feels more tendon-like. I’d be cautious about treating the ratio as a definitive “quality score,” but it is a compact way to show that the ECM composition is changing under load, not just total mass.

Publication Figure: Biochemical ECM Composition (collagen, sGAG, ratio)

Tendon scaffold mechanical testing after dynamic culture: effective tensile modulus shifts with architecture

After the biochemical readouts, the paper comes back to a mechanical question: did the constructs actually get stiffer in tension, and does the architecture change that outcome under the same loading dose?

This is where the figure below is a useful summary. Under static culture, Group A and Group X sit relatively close. Under intermittent dynamic culture, the effective tensile modulus increases in both, but the increase is larger in Group X.

You can read that a few ways:

• Group X may be providing a strain environment that pushes more cells toward collagen deposition.

• The bi-directional crimp may recruit fibres differently during cyclic tensile loading, which could change local stress and mechanotransduction.

• Or it could simply be that the auxetic deformation keeps pores more open under tension, changing how cells bridge fibres and build matrix.

The paper doesn’t fully isolate mechanism, and I’m not sure it needs to. What it does show is that architecture was mostly a “latent variable” until dynamic culture was introduced, and then it started showing up in both biochemical and mechanical outcomes.

Publication Figure: Effective Tensile Modulus (UniVert)

Auxetic scaffold behaviour and Poisson’s ratio: why bidirectional crimp might change what cells build

“Auxetic” can sound like a design novelty unless it’s tied to what the cells are doing. In this context, negative Poisson’s ratio is less about a headline material property and more about deformation mode. If the scaffold expands laterally during tension, the internal fibre network is not just stretching, it’s reorganizing.

In tendon mechanobiology, cells respond to strain magnitude, but they also respond to fibre recruitment, tension directionality, and how the substrate moves around them. It’s plausible that the bi-directional crimp in Group X increases the fraction of cells that see meaningful cyclic strain, or changes how quickly fibres go from slack to taut during each cycle.

I wouldn’t claim that auxeticity directly “caused” higher collagen. But it’s hard to ignore that the architecture difference becomes more visible under intermittent dynamic culture, and that’s exactly when the scaffold deformation mode would matter most.

Instruments used in this tendon scaffold mechanical testing study

CellScale MechanoCulture T6: intermittent dynamic culture under controlled cyclic strain

In this study, the MechanoCulture T6 is not just a loading device bolted onto an incubator schedule. It’s used as the place where the authors applied a repeatable daily strain regimen (4% strain, 1 Hz, 1 h/day), first to the scaffold alone and then to cell-laden constructs. That scaffold-only precheck is the part I’d steal if I were adapting this workflow, because it makes later tissue outcomes easier to interpret.

Learn more about the MechanoCulture T6 bioreactor.

CellScale UniVert: tensile testing of scaffolds and constructs

The UniVert was used for tensile testing across stages: baseline scaffold mechanics (including deformation behaviour tied to Poisson’s ratio) and the effective tensile modulus of the constructs after culture. In a tissue engineering context, this is the step that turns “more collagen” into something mechanically tangible, even if it’s still early-stage tissue rather than a mature tendon analogue.

Learn more about the UniVert mechanical tester.

A practical note for tendon tissue engineering readers

If you’re thinking about scaffold design variables, one quiet lesson here is that architecture can look “neutral” under static culture and then show up strongly once you apply cyclic tensile loading. That’s not always convenient, because it means you can’t really screen architectures without a loading step. But it also suggests that some design choices only become meaningful in the same mechanical context the tissue is expected to experience.

Read the Full Publication

Sean O. Mathew, Brian G. Amsden, Acta Biomaterialia, https://doi.org/10.1016/j.actbio.2026.02.007