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Comment by A_D_E_P_T | Hacker News Reader

> The knots were not tied but rather manufactured in a knotted state by using advanced high-resolution 3D lithography capable of producing structures in the nanoscale.

This would be difficult to scale. And it's possible, even likely, that it can't be applied to existing strong fibers, which are drawn at very low diameters. The paper does its best to bury the lede, but the polymer they were using was acrylic-based, and likely very weak in comparison with, e.g., Dyneema or aramid fibers.

There are quite a lot of papers which examine the mechanical properties of nano-lattice and nano-architected materials, made with lithographic techniques, but I think that the commercial viability of these materials is effectively zero. And, in many cases, as here, it's not clear that they'd be superior to the standard high-strength materials that are already so ubiquitous.

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I'm shocked daily by HN comment depth, what a breadth of experience people have. Thanks for the insight.

This place is all culture. People are smart and varied everywhere. But here we try to enforce a culture is that assigns low status to low effort trash. It doesn't always work. But that's the expectation, I don't think anything else could work. Comments should be for the community not to spread low information barnacles on every piece of original thought.

This place also suffers from the Dunning-Kruger-Effekt.

I guess you could argue, that most places suffer from that, as everyone has a boundary, at which they don't understand things. But the effect itself, is probably more relevant in an organization, as it was used to describe management.

There's a fine line between a Cunning Drueger and Dunning Kruger.

I want to offer a tempered view. The comment does seem deep and it probably is. But I work in physical prototyping - new products, new technologies. I do the "design and manufacture from real materials in the real world" part. I own a few hundred thousand dollars in advanced machinery and make parts for FAANGs and tiny research startups. I'm a named inventor on something like 16 patents. And yet daily, I read confident, well worded answers here -- about my domain -- which reflect views completely divorced from reality, or in living in some strange parallel reality.

Personally, I try to recognize this as an opportunity for me to be humble (as I never know who may read my comments from a higher place of skill and domain knowledge), and also to take what is posted here with a grain of salt.

I don't see a reason why the lithography method is necessary here. One could design a manufacturing process which ties the knots mechanically, just like woven fabrics.

Caltech probably already has the lithography equipment and expertise on hand, so they did it that way. They aren't trying to do their research in a manufacturing-friendly way, just the way that is easiest for them.

Possibly lithography was used to avoid stress concentrations and kinking, which can potentially be troublesome in mechanically-tied knots. (Presumably, especially at that scale.)

With respect to knotted and woven fabrics, there's quite a lot of interesting research in "3D-woven" fabrics for high-impact applications like body armor. 3D fabrics are pinned by fibers running through the weave top-to-bottom (Z axis) and are effectively macroscopically knotted. They're also commercially available:

https://compositeenvisions.com/product/fiberglass-e-glass-3d...

Interesting stuff, but still very niche and not always clearly superior to plain woven composite materials.

IIRC with 3D weaves, the ratio of strands to empty space (that would get filled with epoxy in typical rigid part applications) is significantly lower.

That seems likely, though it does still seem like their results might fall into the "things behave differently at micro-scale and macro-scale" category. Normally we'd expect the (macro) knots we're familiar with to weaken -not strengthen - the cord or rope they're tied in (how much varies quite a bit with which knot we're talking about, but I don't know of any that don't have at least some negative impact). The little video almost implies the effect is similar to stretch, that the tangled version can't tighten up (with friction presumably absorbing some energy) like the knotted one does.

Why would lithography not scale? We've got plenty of mass production lithography with microchips.

Economically mass producing microchips is only possible because they are 100s of square millimeters in size and very valuable per square mm. Any bigger than that and error rates in the fab process start to destroy the yield.

These fibers are used in much bigger applications like body armor or mechanical composite parts where the surface area is on the order of square meters, not millimeters.

Modern panel fabs use fine masking over like 10sq. meters with precision on the same order of this (~dozens of micrometers), and people have successfully shown lithography over similar panel sizes by separate exposures.

The feature size is a LOT bigger than microchips though:

"Each knot is around 70 micrometers in height and width, and each fiber has a radius of around 1.7 micrometers"

That is, cheaper lithography methods could presumably be used.

Older processes are cheaper, but 5nm node costs something like $25,000 per square foot (with around 0.1 defects per square cm, which may result in waste) and doesn't do pieces larger than about 1 foot. That's pretty bad as far as textiles go.

Anybody who's worked with cables or ropes knows they spontaneously form knots quite easily. Would it be possible to utilize this property in manufacturing?

Shake a bunch of dry fibers before applying the matrix? Are they too stiff?

You're more-or-less describing nonwoven fabrics, which are used in a huge variety of applications. There's different fabrication methods, but they are typically not as strong as standard weaves since the patterning can't really be controlled.

https://en.wikipedia.org/wiki/Nonwoven_fabric

I believe nano-scale polymer materials composed of randomly formed knots are normally just called "plastic".

Could one shake that plastic while the chains are mobile to make these knots to make the material tougher?

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