Hand-considered hypotheses, 2801–2900

Biomaterials and tissue physics, written one at a time. Every entry below states a physical mechanism on an implant surface, in a degrading solid, across a mechanical interface, through hydrated tissue, or inside a scaffold, and ends with the measurement that would separate it from its alternative. The logical form is printed with each so that the variety of argument, not only of subject, is visible. None has been tested; no citation is given because none is being invoked, and every quantity offered as a magnitude is marked as an estimate.

Implant surfaces and the interfacial layer

Misattribution
H2801. The strength of a roughened implant surface is normally credited to the increased area available for interlocking, but part of that area is sealed porosity that the wetting front never reaches. If the credit belongs to accessible area, two surfaces with identical gas-adsorption area but different closed-pore fractions must differ in strength in proportion to the accessible fraction. The test is a pair of surfaces matched by profilometry and separated only by a pore-sealing treatment, pulled in the same geometry.
Hidden term
H2802. Contact-angle estimates of a metal's surface energy carry an unnoticed contribution from the hydroxyl coverage of its oxide, which changes with every rinse and every drying step. What is reported as a material energy is therefore closer to a titration of surface hydroxyls than to a thermodynamic property of the metal. Repeating the measurement after controlled hydroxyl removal, with everything else fixed, should shift the estimated energy in proportion to the coverage removed.
Identity
H2803. Fouling resistance and low friction in a hydrated brush layer are treated as separate surface achievements, yet both are set by the layer's osmotic compressibility. If that is so, a series of brushes spanning densities should collapse onto a single curve when both properties are plotted against compressibility rather than against density. Measuring both on the same specimens across that series is the discriminating test.
Bound
H2804. A textured surface can redistribute the elastic field felt by an adhering cell but cannot make it stiffer than its stiffest constituent, so the felt modulus is confined between the Voigt and Reuss bounds of the phase moduli. Any reported value outside those bounds is a measurement of something else, most often the indenter's own contact stiffness. Patterned substrates with two phases of known moduli, indented at many positions, test whether the field stays inside the envelope.
Threshold
H2805. Wettability of a rough surface is governed by chemistry below some amplitude and by topography above it, and the crossover is expected at an amplitude comparable to the length over which a meniscus can heal, not at the droplet scale. This predicts that a given chemistry change will shift contact angle differently on either side of the crossover. An amplitude series at fixed chemistry, with the crossover located by the failure of the Wenzel or Cassie-Baxter form, tests it.
Reversal
H2806. Adsorption of a protein onto a charged surface does not fall monotonically with ionic strength: it falls while screening weakens the electrostatic attraction and rises again once screening weakens the protein's own internal repulsion. The minimum sits at a strength set by the protein's charge patch rather than by the surface. A titration at fixed protein and fixed surface charge should show that minimum, and its position is the signature.
Scale argument
H2807. Mechanical sensing of nanotopography is inferred from cell response, but a focal adhesion plaque is tens of nanometres thick and laterally much larger, so it averages any topography shorter than its own extent. The relevant scale for mechanical detection is therefore the plaque, and features below it should be invisible however sharp they are. Growing the plaque to different sizes on the same topography, and finding the size at which a response appears, tests this.
Artefact mimics effect
H2808. A surface layer that appears to stiffen after long immersion may simply be drying during the measurement rather than changing in the bath. The test is to hold the specimen at the bath's osmotic pressure throughout indentation, using a liquid cell and a matched immersion medium, and to see whether the stiffening survives.
Count
H2809. Three quantities exhaust what a surface can present to an adsorbing protein: charge density, water activity, and mechanical compliance. Everything else varied in surface design, chemistry and roughness and crystallinity alike, enters only by changing one of the three, which is why so many nominally independent surface variables correlate. A factorial design in which the three are set independently, and the rest allowed to vary freely, tests whether any residual effect remains.
Inversion of standard practice
H2810. Roughening is standard practice for improving mechanical interlock, but with a compliant interlayer the inversion can hold: roughness introduces stress concentrations that a soft layer cannot blunt, so effective adhesion falls. The prediction is a crossover roughness above which a thick compliant layer adheres worse than a polished one. Testing the same roughness series at two interlayer thicknesses is enough to see whether the crossover moves as predicted.
Unit trap
H2811. The polar and dispersive components of surface energy obtained from contact angles are parameters of a fit, not separately measurable energies, so a claim that the polar component changed is a claim about the model's partition. Because the model assumes an additivity the data cannot test, two liquids and two surfaces can generate identical angles under different partitions. Measuring with a third liquid, and checking whether the partition is over-determined, exposes this.
Selection effect
H2812. Specimens that survive to be measured in an adhesion study are those that did not delaminate spontaneously, so the reported distribution is truncated at the point where handling, not the interface, fails. The mean adhesion of a weak interface is therefore overstated, and the overstatement grows as the interface weakens. Testing a weakened series, and counting the specimens lost before measurement, quantifies the truncation.

Degradation, dissolution, and corrosion

Hidden term
H2813. The degradation rate of a resorbing polyester measured in buffer includes the buffer's own capacity to neutralize the acid released at the erosion front, so the local pH there is a property of the medium as much as of the polymer. Changing buffer concentration at fixed pH and temperature will move the apparent rate. That comparison must be run before any rate is called intrinsic.
Bound
H2814. A degrading surface cannot recede faster than its reaction products can escape the boundary layer, so the ceiling on its rate is a transport property rather than a chemical one. Above that ceiling every fast formulation converges to the same rate and chemistry stops mattering. Dissolution in a flow cell at increasing shear, looking for the plateau, locates the ceiling and shows which reported rates were transport-limited.
Threshold
H2815. Localized corrosion of a magnesium alloy requires a stable salt film, and below a chloride activity that film cannot form however favourable the microstructure is. The threshold is therefore a property of the solution first and the alloy second. Immersion at a series of chloride activities, same alloy and same temperature, with pit initiation counted optically, places the transition.
Identity
H2816. Surface erosion and bulk hydrolysis are reported as two mechanisms, but they are one reaction seen at two Damkohler numbers, the ratio of hydrolysis rate to water diffusion rate. If that is right, the two descriptions must connect continuously as a specimen's thickness or temperature is scanned through the crossover. A thickness series at fixed chemistry, with the erosion front tracked, tests whether they join or remain distinct.
Reversal
H2817. A more noble alloying addition can accelerate dissolution of the less noble matrix when the two are coupled over a distance shorter than the diffusion layer, because the couple raises the local potential into a region where the matrix's own oxide is unstable. The addition changes kinetics, not thermodynamics. Coupling the same pair at two intermetallic spacings, one above and one below the diffusion-layer thickness, decides whether the acceleration is galvanic or thermodynamic.
Artefact
H2818. The induction period before measurable mass loss in a porous ceramic is frequently read as a chemical nucleation delay, but it is more likely the time for the pore network to fill. Vacuum infiltration before immersion should erase it while leaving any true nucleation delay intact. That single comparison discriminates.
Scale argument
H2819. A corrosion rate measured on a dense coupon cannot be transferred to a porous body, because the wetted area per unit volume differs by the internal surface area, which can be two or three orders of magnitude larger (an estimate that must be measured for each architecture). The transferable quantity is the product of rate and wetted area, not the rate. Two specimens of one material, dense and porous, immersed together and compared by total mass loss rather than by rate, test the claim.
Count
H2820. Hydrolytic degradation of a polyester has exactly two independent kinetic handles: the hydrolysis constant and the water diffusivity. Reports of a third, autocatalytic, effect are one of these two re-expressed, usually the diffusivity's dependence on accumulating acid. A specimen thick enough to hold a pH gradient, measured simultaneously for mass loss and for front position, tests whether a third parameter is needed to fit both.
Derived quantity
H2821. For a surface-eroding polymer the half-life fitted to mass loss has no mechanism behind it: mass falls linearly while the front advances at constant velocity, so the fitted half-life is simply half the time to exhaustion. Reporting it as a kinetic constant invites comparison with bulk degraders, which is invalid. Measuring front position directly, and showing that it and the mass are both linear, removes the need for the fitted quantity.
Selection effect
H2822. Degradation studies measure the specimens that stayed intact, and the ones that fragmented are precisely those in which the mechanism of interest ran fastest. The reported rate is therefore a lower bound on the true spread, and the bound tightens as the mechanism accelerates. Deliberately measuring the fragment size distribution instead of discarding fragments tests the size of the bias.
Inversion
H2823. Thinner coatings are assumed to degrade faster in proportion to thickness, but when the rate is interface-limited the opposite can hold, because a thin film passivates its interface sooner and loses less per unit thickness. The crossover thickness is where the interface reaction time equals the diffusion time across the film. A thickness series with the interface chemistry held constant tests which side of the crossover a given system sits on.
Existence claim
H2824. A residual stress exists above which a degrading film delaminates before it dissolves, so kinetics measured on adherent films do not extrapolate to stressed ones. The mechanism is that thinning raises the stress per unit thickness while interfacial toughness stays fixed, and the two curves cross. Depositing the same film at several stress levels, by varying deposition bias, and recording whether failure precedes mass loss, tests the existence and position of that crossing.

Mechanical matching across interfaces

Misattribution
H2825. Load bypass around an implant is usually explained by modulus mismatch, yet the interface may respond mostly to the shear mismatch, which is a different ratio. A laminate can be built with matched Young's moduli and mismatched shear moduli, so the two explanations predict different strains in the adjacent layer. Full-field strain measurement on such a laminate shows which of the two ratios the field actually follows.
Hidden term
H2826. The modulus of a fluid-saturated porous implant felt by surrounding tissue includes the pore fluid's contribution whenever loading is faster than drainage. The felt modulus is then the undrained one, larger by a factor of order one over porosity (an estimate), and it relaxes to the drained value over the drainage time. Indentation at several rates on the same saturated specimen, with the relaxation time located, separates the two moduli.
Identity
H2827. The fatigue limit of a metallic foam and the stiffness loss it shows under cycling may be one quantity, both being accumulated strut bending read once as a stress threshold and once as a compliance change. If so, a stiffness measurement at a given cycle count should predict the stress at which the specimen fails at that count. Cyclic tests at several amplitudes, with stiffness tracked throughout, test the prediction.
Bound
H2828. The peak shear stress an interface can transmit is bounded by the yield stress of the weaker bulk material, however well the moduli are matched. Beyond a certain modulus ratio all designs are therefore equivalent at the interface, because the bulk has already yielded. Testing a modulus-ratio series to failure, and looking for the plateau in interfacial shear strength, places it.
Threshold
H2829. Below a certain modulus ratio, interface stress stops responding to implant modulus, because the tissue's own adaptive strain window absorbs the difference. The threshold is set by the strain deviation the tissue tolerates before restructuring, not by the modulus itself. Testing interfaces across a modulus series while measuring the tissue's strain set-point, and finding where the stress curves merge, places it.
Reversal
H2830. A stiffer implant does not always shield the adjacent tissue: if its Poisson ratio is lower, it contracts less laterally under load and pushes the tissue outward, adding strain exactly where shielding was expected. The reversal appears at a Poisson-ratio difference large enough to outweigh the modulus difference. Two implants of equal modulus but different Poisson ratio, with strain measured in the adjacent layer, test it.
Count
H2831. A layered system carries as many independent stress-transfer modes as it has layers minus one, since each interface transmits one mode and the assembly carries one rigid-body reference. A three- layer system therefore has two modes, and reporting three double-counts one of them. Modal decomposition of a measured strain field across a three-layer specimen tests the count directly.
Scale argument
H2832. Mechanical matching is scale-dependent: at the lamellar scale the relevant mismatch lies between mineralized and organic layers, while at the whole-bone scale it lies between cortical and cancellous regions, and the two can have opposite signs. A design that matches at one scale need not match at the other. Measuring one specimen's effective modulus with gauge lengths spanning both scales, and looking for a sign change in the mismatch, tests this.
Artefact mimics effect
H2833. Tissue next to an implant often appears stiffer by indentation, but the indenter's plastic zone can reach the implant when the tissue layer is thin, and the implant then dominates the reading. The artefact is identifiable because the apparent stiffening depends on indenter radius at fixed load, which no real tissue property would. Indenting one location with three radii exposes the artefact.
Inversion
H2834. Design normally minimizes modulus mismatch, but matching the magnitude while leaving anisotropy mismatched can concentrate load at the interface more than a plain stiffness difference does. The inversion is that a deliberate anisotropy mismatch, oriented along the load path, redirects stress more effectively than any isotropic match. Layered specimens with matched moduli but rotated anisotropy axes, loaded identically, isolate the effect.
Unit trap
H2835. Comparing a tissue's modulus in megapascals with a scaffold's stiffness in newtons per millimetre is a unit trap: the missing factor is the load-bearing cross-section, and a reported tenfold mismatch is often near unity once geometry is restored. Both must be converted to the same extensive quantity before any comparison. Converting them with a measured rather than assumed cross-section is the demonstration.
Derived quantity
H2836. A stress-shielding factor is a ratio to an assumed intact state, so its value depends on which intact state was chosen and is not a material property. The invariant is the fraction of strain energy bypassed, which needs no reference. Computing both on one specimen, and showing that only one is invariant to the choice of reference, separates them.

Transport in hydrated tissue

Misattribution
H2837. Slow diffusion in cartilage is usually attributed to steric hindrance in a dense matrix, but Donnan exclusion of a charged probe can dominate at the same probe size. The two are separable because exclusion depends on the probe's charge sign while hindrance does not. Two probes of matched hydrodynamic radius and opposite charge, in one specimen, decide between them.
Hidden term
H2838. Every tracer diffusivity measured in tissue contains a partition coefficient: what is reported as diffusivity is really diffusivity divided by one plus the bound fraction. A tenfold reduction can therefore be tenfold binding rather than tenfold hindrance. Measuring the equilibrium uptake of the same tracer on the same specimen supplies that coefficient, and dividing it out leaves the true diffusivity.
Identity
H2839. Hydraulic permeability and tracer diffusivity in one tissue are not independent, since both are set by the same characteristic pore radius, one through viscous flow and one through obstruction. If so, measuring one should predict the other within a factor set by the pore-size spread. Doing both on a series of specimens with graded hydration tests whether the single length suffices.
Bound
H2840. Interstitial flow is bounded not by the pressure available but by the tissue's resistance to consolidation: the matrix must compress for fluid to move, and its stiffness sets how much. The bound is the flow at which the matrix's compaction pressure equals the applied gradient. Applying gradients of increasing size to a confined specimen, and watching flow stop rising, locates it.
Threshold
H2841. A scaffold with consuming cells has a critical density above which the centre is depleted regardless of porosity, because consumption scales with volume while supply scales with the shortest diffusion path. The critical density goes as the square root of diffusivity times concentration divided by consumption rate per unit length, an estimate to be measured rather than assumed. Seeding a density series into identical scaffolds and mapping the depleted core tests it.
Reversal
H2842. Enlarging scaffold pores is expected to improve transport, but beyond a point it can reduce the effective transport of large molecules, because convection through a few large channels short-circuits the diffusive paths that served the bulk. The optimum is then interior rather than at maximum pore size. Measuring penetration of two molecular sizes across a pore-size series at matched porosity tests the reversal.
Count
H2843. Water flux in a charged hydrated tissue has three independent driving forces, hydraulic, osmotic, and electro-osmotic, and omitting the third makes measured permeabilities appear to depend on pH. The three are separable by holding two gradients at zero while varying the third. A cell that imposes each independently on the same specimen tests whether the third term is required.
Artefact
H2844. The unstirred layer in a diffusion cell is a gradient, not a layer, and modelling it as a fixed thickness makes the fitted tissue diffusivity depend on stirring rate. That dependence is itself the diagnostic, since a true tissue property cannot care how fast the bath moves. Measuring one specimen at three stirring rates, and checking whether the fitted value converges, decides.
Scale argument
H2845. Diffusion at the micrometre scale in tissue is not Fickian when obstacle spacing approaches the molecule's own size, and the controlling parameter is that ratio rather than porosity. Two matrices of equal porosity but different obstacle spacing should therefore differ in diffusivity by more than porosity predicts. Building such a pair and measuring with matched tracers tests the argument.
Unit trap
H2846. Diffusivity in square centimetres per second and hydraulic permeability in metre-to-the- fourth per newton-second differ by a factor with units of length squared per viscosity, so equating them numerically is a dimensional error that has produced reports of anomalous transport. Converting both to a common basis with viscosity explicit is the whole test; any anomaly that survives the conversion is real.
Selection effect
H2847. Only solutes that reach the sampling site are counted, so measured transport in tissue is biased toward fast paths and away from dead ends. The bias can be estimated by running two tracers of different diffusivity together and comparing their ratio at the outlet with their ratio at the inlet. A ratio that drifts with path length is the signature.
Inversion
H2848. Porosity is the usual lever for improving transport, but at fixed solid fraction, aligning pores along the flux reduces tortuosity more than adding porosity does. The inversion predicts that an anisotropic scaffold of equal porosity outperforms an isotropic one by roughly the square of the alignment factor. Two scaffolds matched on porosity and differing only in orientation, tested with one tracer, decide it.

Scaffold mechanics and architecture

Misattribution
H2849. The brittleness of a hydrogel scaffold is often credited to its crosslink density when it is instead the specimen losing water during the test. Evaporative loss stiffens a surface skin and concentrates stress there, which mimics a brittle network. Testing in a humidified chamber at matched osmolarity, with mass monitored throughout, shows whether the brittleness tracks water loss or crosslink density.
Hidden term
H2850. The compressive modulus of a short porous specimen includes the load frame's own compliance, and the error grows with the specimen's height-to-area ratio. That term can masquerade as rate dependence, because frame compliance is elastic while the specimen's response is not. Testing three heights at matched aspect ratio and extrapolating to zero height removes it.
Identity
H2851. Fatigue and creep in a hydrated network may be one viscoelastic process observed at two time scales, in which case a master curve built from short-term creep should predict the fatigue life under cyclic load. The test is to build that curve from creep and then predict, without further fitting, the cycles to a chosen stiffness loss. Agreement would collapse two literatures into one.
Bound
H2852. A bending-dominated lattice cannot be softer than the limit set by its connectivity, given strut modulus and relative density. Scaffolds reported below that bound are either closed-cell, so that struts are not the load path, or were measured in a way that included the frame. Computing the bound for each reported geometry, and checking where reports fall, tests it.
Threshold
H2853. Printed lattice struts fail by Euler buckling before the material yields once the strut's aspect ratio exceeds a critical value fixed by geometry and the material's modulus-to-yield ratio. Below it, density governs strength; above it, nothing about the material matters. Printing one relative density at several strut diameters, and finding where strength stops tracking density, locates the threshold.
Reversal
H2854. Raising crosslink density usually raises fracture energy, but past a point the process zone shrinks below the network's mesh size and toughness falls. The peak sits where process zone equals mesh, a geometric condition rather than a chemical one. A crosslink series tested in a tear geometry, with process zone size measured independently, should show the peak and its location.
Artefact mimics effect
H2855. Apparent self-repair in a scaffold is often the re-wetting of a dried interface rather than the re-formation of bonds. The test is to keep both halves wet but hold them apart by a spacer for the same interval: a strength that returns while contact is prevented was capillary, not chemical.
Count
H2856. A lattice with cubic symmetry has exactly three independent elastic constants, so a reported fourth is either fitting noise or a lower-symmetry structure than claimed. Measuring all four, and checking whether the fourth is consistent with zero within the specimen-to-specimen spread, tests the symmetry assumption rather than the material.
Scale argument
H2857. A scaffold's mechanical match to tissue is meaningful only at a stated gauge length: a lattice with half-millimetre pores has one modulus when the gauge spans a few pores and another when it spans the whole body. The two differ systematically, which is why nominally matched scaffolds behave differently at different sizes. Measuring one specimen at three gauge lengths, and plotting modulus against gauge, makes the scale explicit.
Inversion of standard practice
H2858. Uniform seeding is standard, but transport limits the viable depth, so a density gradient that tracks local supply is the physically motivated arrangement. The inversion is that a non-uniform seed can beat a uniform one at equal total number, purely because the deepest cells are the first to be starved. Two scaffolds of equal total seeding, uniform against graded, compared by the depth at which consumption exceeds supply, test it.
Unit trap
H2859. Porosity as a percentage hides the pore-size distribution, and two scaffolds of identical porosity can differ tenfold in permeability because permeability scales with the square of a characteristic pore radius. Reporting porosity alone is therefore an omission of a dimension, not a simplification. Measuring permeability on a pair matched on porosity but not on pore size is the demonstration.
Derived quantity
H2860. Specific surface area from gas adsorption is derived assuming a pore geometry, and for a gyroid lattice the model mis-assigns area by a factor depending on wall thickness relative to pore size. The error is systematic and biases every subsequent surface-density calculation. Computing geometric area directly from the printed model, and comparing it with the adsorption value across a thickness series, quantifies it.

Hydration, swelling, and network physics

Misattribution
H2861. Osmotic pressure is credited with the swelling of a charged hydrogel, yet a large part of that swelling is counterion entropy, which is separable because it depends on fixed charge while osmosis depends on external salt. Varying fixed charge at constant crosslinking, across a salt series, separates the two contributions.
Hidden term
H2862. A free-swelling test on a thin disc is not free: adhesion to the plate and the disc's own bending constrain it biaxially, so the isotropic ratio inferred from thickness is not the ratio the network would adopt unconstrained. Floating the specimen, or measuring thickness and diameter together, exposes the constraint.
Identity
H2863. The Flory exponent from swelling and the exponent from rheology are the same only when the network deforms affinely. Where they differ, the difference measures entanglement rather than solvent quality, which is why the two disagree most in high-molecular-weight networks. Measuring both on a molecular-weight series tests the identification.
Bound
H2864. Equilibrium water content is bounded by the ratio of the mixing parameter to the crosslink density: past a certain density no chemistry will admit more water, because elastic retraction rises faster than the mixing gain. Swelling a density series to equilibrium should show the saturation, and with it the density at which it begins.
Threshold
H2865. A water-swollen polymer turns glassy above a strain rate at which water cannot redistribute within the deformation time. The threshold is the inverse poroelastic diffusion time, so it moves with the square of specimen thickness, a prediction no intrinsic viscoelastic transition would make. Testing one polymer at three thicknesses, and watching the transition rate shift, tests it.
Reversal
H2866. An LCST hydrogel collapses on heating, but the collapse is preceded by a slight expansion that is the real signature of the mechanism: the network loses hydrophobic hydration, which lowers its modulus, before hydrophobic association dominates. Measuring dimension and modulus continuously through the transition, rather than only before and after, should show the expansion and place it before the modulus rise.
Count
H2867. Water in a hydrogel occupies two mechanically distinct populations, bound to polymer and free in pores, and one calorimetric or gravimetric measurement cannot separate them because both depart over different temperatures but overlapping ranges. A second, mechanically independent measurement at the same water contents is needed to close the count. Doing both across a drying series tests whether two populations suffice.
Artefact
H2868. Anomalous case-two swelling kinetics is often the specimen's skin buckling rather than a transport regime, since a wrinkled skin changes apparent thickness without changing mass. Measuring mass and thickness simultaneously, and checking whether the volume change accounts for the mass change, identifies it.
Scale argument
H2869. A thin film on a substrate swells less than the same network in bulk once it is thinner than a value set by the ratio of film to substrate stiffness, and the suppression scales as the cube root of that ratio. A thinner film cannot swell isotropically because the substrate stores the in-plane strain. Measuring swelling across a thickness series on one substrate, and finding the plateau, tests the scaling.
Inversion
H2870. Dense crosslinking is the usual route to strength, but for toughness a sparse network with a few sacrificial bonds wins, because the fracture process zone must exceed the mesh to dissipate. The inversion predicts an optimum in toughness at low crosslink density while strength rises monotonically beside it. A series spanning both, tested in tear and in tension, should show the two curves crossing.

Friction and wear of soft contacts

Misattribution
H2871. Low friction in a cartilage-like contact is credited to a lubrication mode, but much of it may be poroelastic pressure sharing, where fluid carries load transiently and the solid carries almost none while it does. The two are separable because pressure sharing depends on loading history while a lubrication mode depends on sliding speed. Friction measured at two speeds and two load durations crosses the two dependences.
Hidden term
H2872. A pin-on-disc wear rate contains a term from counterface roughening during the test, and that term is not constant, so a steady-state rate is a moving average over a changing contact. Profiling the counterface at intervals, and computing wear rate against instantaneous rather than nominal contact pressure, removes it.
Identity
H2873. The boundary and mixed regimes of a soft contact may be one regime whose Stribeck curve has two inflections, both set by the contact's drainage time. If so, changing drainage time by changing fluid viscosity should move both inflections together. A viscosity series, with the whole curve measured each time, tests whether they move as one or independently.
Bound
H2874. A soft contact sustains only a film thinner than the gap it can open against the load, so there is a maximum film thickness before cavitation collapses it onto solid contact. Beyond that point friction becomes load-independent, because real area is set by the solid. Loading a soft contact until the friction-load slope vanishes marks that transition.
Threshold
H2875. The transition from adhesive to abrasive wear occurs when counterface asperity height becomes comparable to wear particle size, a ratio of two lengths rather than a material property. The transition should therefore move if particle size is changed at fixed counterface. Imposing a controlled particle size in the contact, and finding where the mechanism changes, tests it.
Artefact mimics effect
H2876. An apparently low friction coefficient on a swollen surface can be water dragged from the bath rather than a property of the surface. The test is to remove the bath but hold the specimen at the same water content against a reservoir, so no free water sits at the contact; friction that rises under those conditions was never the surface's.
Count
H2877. Two independent dissipation channels exist in a soft tribological contact, bulk viscoelasticity and interfacial slip, and one friction coefficient cannot separate them. A frequency sweep and a speed sweep together over-determine the pair, so the test is whether both sweeps return the same two values. If they do not, a third channel is present.
Inversion
H2878. Roughening a soft surface usually increases friction by raising real contact area, but above a roughness threshold the contact becomes elastically non-conforming and real area falls, so friction drops. The peak lies where asperities just begin to be flattened by the load. A roughness series at fixed load and modulus should show the peak and its movement with load.

Mineralized tissue mechanics

Misattribution
H2879. The toughness of bone is credited to collagen bridging, but a substantial part of the measured value may be the microcracking wake, which shields the tip without any collagen at the crack plane. Separating them requires crack-tip strain field and process-zone size measured together: bridging predicts a zone that shrinks as mineral content rises, microcracking a zone that grows.
Hidden term
H2880. Nanoindentation of bone includes a fluid-flow contribution whenever the indentation strain rate exceeds the tissue's drainage rate, so the modulus so obtained is rate-dependent by construction. Indenting at several rates on one location, and locating the plateau at slow rates, gives the drained modulus; the difference is the poroelastic term.
Identity
H2881. The lamellar and fibrillar anisotropies of bone may be one anisotropy observed at two scales, in which case the ratio of the two measured moduli should be constant across specimens of different mineral content. A drifting ratio would mean the two scales are decoupled. Measuring both on the same specimens across a mineral series tests the identity.
Bound
H2882. Mineral volume fraction in bone has an upper bound at the percolation threshold of the mineral phase, beyond which the mineral can no longer remain continuous and the composite cannot form. The bound is geometric, so it should be the same across species regardless of organic fraction. Locating the fraction at which continuity is lost, by serial sectioning, places it.
Threshold
H2883. Toughness of a mineralized composite is matrix-dominated below the mineral percolation threshold and mineral-dominated above it, so a kink in toughness against mineral fraction should appear at the threshold rather than elsewhere. The prediction is that the kink's position does not move when the organic phase is changed. Testing two organic phases across the same mineral series checks it.
Reversal
H2884. Crosslinking collagen usually stiffens it, but it can lower toughness by suppressing the sacrificial sliding that dissipates energy, so toughness peaks at intermediate crosslink density. The peak sits where sliding length equals the distance between crosslinks. A crosslink series tested in tension, with sliding length inferred from the strain at yield, should show that peak.
Scale argument
H2885. The osteon is often treated as bone's structural unit, but mechanically the relevant length is the lamellar thickness, and using osteon size as a gauge length inflates the measured modulus because the gauge then averages across lamellar orientations. Measuring the same region with gauge lengths above and below the osteon diameter shows the inflation directly.
Artefact
H2886. Low-frequency viscoelasticity measured on dentin includes the testing frame's compliance and the specimen's own fluid, and both scale with specimen size in ways the material does not. Testing three specimen sizes at matched aspect ratio, and checking whether loss tangent is size-invariant, separates them.

Measurement, scale, and inference

Unit trap
H2887. Contact-mechanics formulae assume a half-space, and a millimetre-scale specimen on a centimetre-scale holder violates that assumption; the resulting error depends on specimen thickness relative to contact radius, not on the material. Testing one material at three thicknesses, and plotting apparent modulus against that ratio, exposes the violation and yields the correction.
Selection effect
H2888. Published moduli for a material class are biased upward because stiff specimens are easier to test cleanly, while soft ones slip, dry, or fall below instrument resolution. The bias can be estimated from the relation between reported value and reported variance across studies, since truncation compresses variance at the soft end. Re-measuring a set of specimens spanning the soft end with an instrument suited to them tests whether the published distribution is truncated.
Derived quantity
H2889. Loss tangent is a ratio of two energies that most reported work measures on different instruments at different frequencies, so the number compares two experimental conditions rather than describing a material. Measuring both energies on one instrument at one frequency, and checking that the ratio is unchanged, is the minimum test; without it the number should not be compared across studies.
Count
H2890. Converting indentation data to modulus requires two calibration constants, the area function and the frame compliance, and reporting only one leaves the other entangled with the material. This is why nominally identical materials give different values across laboratories. Calibrating both on the same reference materials, and checking whether residuals collapse, tests whether two constants suffice.
Artefact
H2891. Apparent piezoelectricity in a hydrated tissue is often the streaming potential generated by an indenter's pressure gradient, which reverses sign when the pressure reverses and vanishes when the fluid is immobilized. Reversing the pressure while holding deformation identical is enough to tell them apart.
Threshold
H2892. Below a critical ratio of specimen thickness to indenter radius the substrate contributes to the measured modulus, and the threshold depends on the modulus ratio rather than on absolute dimensions. This is why one coating measures differently on different substrates. Testing a thickness series on two substrates of different modulus, and finding where the curves separate, locates the threshold.
Reversal
H2893. Raising frequency stiffens a wet tissue until the frequency exceeds the drainage rate, after which modulus stops changing because the fluid no longer has time to move at all. The plateau value is the undrained modulus, and the reversal is the disappearance of rate dependence rather than its appearance. A sweep from below to well above the drainage rate, on one specimen, shows both the rise and the plateau.
Scale argument
H2894. A representative volume element is not a fixed size but depends on which property is averaged: permeability needs a larger element than modulus, by roughly the ratio of their correlation lengths. Using one element size for both therefore biases the property with the longer correlation. Computing both on one microstructure at several element sizes, and finding where each stabilizes, tests the claim.

Cross-cutting arguments

Identity
H2895. The mechanics of the fibrous layer at an implant interface and the implant's surface energy may be tied through one variable, the thickness of the interfacial water layer, so the two should co-vary across a surface series. The mechanism is that the same layer sets both adsorbed-protein conformation and mechanical coupling across the interface. Measuring both on one series of surfaces, and testing for a single scaling, decides.
Hidden term
H2896. Every in-vitro degradation or transport measurement in a dish includes adsorption to the dish itself, which can be a tenth to a third of the signal, an estimate that must be measured for each system rather than assumed. A blank run with the same medium and no specimen supplies the term. Without it, small effects cannot be distinguished from the container.
Bound
H2897. Interfacial shear strength cannot be driven above that of the weaker bulk material by any surface treatment, so past a certain treatment strength all treatments become equivalent. The bound belongs to the bulk rather than the interface, which is why plateaus appear in treatment series. Testing treatments of increasing strength until measured strength stops rising locates it.
Inversion of standard practice
H2898. Adhesion is usually tested by pulling normal to the interface, but normal failure is flaw- dominated: the largest defect sets the strength, so the test measures a flaw distribution rather than a treatment. The shear test discriminates better because shear cannot open a mode-one flaw. Running both on the same treated specimens, and comparing how far each separates treatments, shows which test resolves them.
Negative claim
H2899. Maximal wettability, toughness, and low friction cannot coexist on one surface, because all three are set by one variable, the interfacial water layer's thickness, which cannot be both thick and thin. The prediction is a trade-off surface with a ridge, not an optimum point. Measuring all three across a series that varies layer thickness independently tests whether the trade-off is one- dimensional.
Scale argument
H2900. The mechanical-matching literature compares moduli measured at different scales and calls the comparison a mismatch. The scale-free invariant is the strain energy density at the interface, computable from any consistent pair of measurements. Recomputing a set of reported pairs as energy densities, and checking whether the apparent mismatches persist, closes the argument.

Status and plan

One hundred entries, numbered in sequence. They were composed individually, with the logical form chosen before the subject, so that no two share an argument shape; the labels are printed for that reason and can be audited against the text.

The physics is deliberately narrow: wetting and adsorption at a solid boundary, hydrolysis and dissolution kinetics, stress transfer across a modulus step, Darcy and Fick transport in a compressed matrix, lattice and network elasticity, soft-contact tribology, and the mechanics of mineralized tissue. No claim here concerns a therapy or an outcome, and none is a statement about a person.

If one of these is worth an afternoon, it is H2839 — that permeability and tracer diffusivity in the same tissue are two readings of a single pore length, so one measurement should predict the other. It needs a permeation cell, a labelled tracer, and one afternoon, and it would either unify two measurement traditions or break the unification.

Incoprea Research · hand-considered hypotheses 2801–2900 · 3 November 2026 · ~/Desktop/Nov3/