A tough new bone scaffold material invented by Tufts University engineers uses micron-sized silk fibers to reinforce a silk fiber matrix. The composite material is the first all-polymeric bone scaffold material to provide enough temporary mechanical support during repair, and is the first that is fully biodegradable.
Biomedical engineers at the Tufts School of Engineering say the new technology could improve repair methods for bones and other tissues after patients experience accidents or disease. Some all-polymeric biomaterials, such as collagen, are used for bone regeneration, but they don't have enough compressive strength. Attempts to include ceramic or metal materials in polymers can achieve the goal of improving mechanical properties, but these composites often make bone remodeling and regeneration difficult or impossible.
A tough new bone scaffold material uses hydrolyzed silk microfibers to reinforce a silk matrix. (Source: Tufts University)
Grafts made of natural human bones can be used, since they withstand a high degree of pressure and are hard, yet are light in weight. They are also elastic enough to stand up to a moderate amount of torsion. In addition, the interior of human bone consists of a matrix structure that helps foster the growth of bone cells and which is easy for them to adhere to.
But human bone grafting is problematic. The amount of human bone taken from the patient is limited and requires additional surgery. Taking bone from donors is risky because of possible disease or rejection.
The silk microfiber-protein composite matrices mimic the mechanical features of native bone. These include the stiffness of bone's interior matrix and the surface roughness that enable differentiation of human mesenchymal stem cells from bone marrow to achieve bone formation. The team found that, combined with the inherent strength of silk fibers, the compressive properties inside the scaffolds were enhanced by the structure's compact fiber reinforcement.
To manufacture the silk microfibers, the Tufts researchers applied alkaline hydrolysis, which uses alkali chemicals to break down complex molecules into their building blocks. This method cut down on the time and cost required to make microfibers in a variety of sizes, compared to conventional processing methods for creating silk microfibers.
The Tufts bioengineers' silk composite material has a high compressive strength of 13 MPa in a hydrated state. Compressive strength, surface roughness, and porosity are tunable, depending on the length of the fibers. Although the values achieved are an overall improvement, they are still less than those for human bone. The researchers said that such scaffolds can be used as temporary biodegradable support while a patient's native cells are grown.
Ann, very interesting story. Is this technology being used on real patience or it is still in the development stages? I hope you will write future stories on this as it continues to develop.
gsmith, I doubt if this has been used on actual patients yet--this is an R&D project at a university, and the announcement would most likely have mentioned any beta testing. If we hear anything about actual testing, I'll be happy to report on it.
This is an exciting development, Ann. The biomedical field is just going to get more and more interesting in coming years. If this material could help those with osteoporosis, it could have a major impact of the quality of life for millions.
Thanks, Rob, I agree. I was really happy to see this. I especially like the cross-application aspect: silk has been used for years in sutures because it's biocompatible and biodegradable.
Good point, Ann. We're going to see tons of these developments in the coming decade. The timing is perfect given the approaching medical needs of aging boomers.
Rob, I agree. I think there are a few factors driving developments like this, including an aging population (at least in the US, Japan and Europe, although the opposite trend is occurring in the ROW and it, in fact, trumps the aging trend in these three areas).
You're right, Ann, the emerging economies are young. But the mature economies have the medical needs, and the mature economies also have the development dollars. The againg population will create a growing need that will support medical developments.
Wow, Ann! This is fantastic. I've worked with Poly(methyl methacrylate) (PMMA) bone cement along with researchers here at the Einstein Medical Center here in Philadelphia. Our research was investigating the mechanical properties (strength) of PMMA after having chemotherapeutic agents mixed in with the monomer before polymerization and the elution rates of the drugs after they were placed in vivo. The PMMA retained its strength for the most part, but the slow elution rates of most drugs meant a patient would have to endure low dose chemo drugs over many years to decades.
A biodegradable bone scaffold material such as this could be used to deliver the chemo drugs over a finite amount of time. Promising applications...
williamlweaver, thanks for the enthusiastic response from someone who's worked with materials aimed at similar applications. The scenario you mention sounds very similar to the idea the Tufts researchers mention, of drug delivery over a short period, and then the scaffold biodegrading in situ.
naperlou, I think you're right. This is yet another case of using natural materials to solve problems by taking advantage of their inherent characteristics, instead of trying to force synthetic materials to do something they are not made to do, or can't easily do (be bio-compatible and biodegradable, in this instance). Of course, the researchers had to design silk matrices to mimic bone, but that apparently wasn't too tough to achieve.
Nadine, there was no information about whether larvae are removed before the cocoons are boiled. It would be interesting to know if, when that is not done, that's for expediency or because it produces a better silk fiber.
Great post Ann.To me, the most fascinating part is fact that the material is biodegradable.It does its job then goes away—absorbed into the human "system".Do you know how long Tuffs University worked on the project and whether or not necessary medical approvals have been awarded?I would love to know what length of time was needed to develop this marvelous application.Again, great post.
Thanks, bobjengr, glad you like the story. This has just been announced in R&D, so I doubt if they've gotten any sort of medical approvals yet, or it would have been mentioned. More details about Tufts' work may be available on their website, or in the (unfortunately for-pay) research article we give a link to in the article. Let us know if you find out!
@Ann: Wow, another fascinating article. Not only did the Tufts research group use a biological material, but they also used a bio-inspired principle of combining large fibers with microfibers. It's also interesting that the fiber scaffolds that were most bone-like (i.e. the most rigid) were the most effective in promoting differentiation of stem cells into bone cells. In other words, not only are they strong, but they also help the body repair itself.
On the other hand, it's a little humbling that the best scaffold material still had a compressive strength that is nearly an order of magnitude less than that of bone (13 MPa vs. 100 MPa). Clearly, we have a long way to go before we can improve on what nature has, after all, taken billions of years to develop.
Thanks, Dave. I also noticed that the silk scaffold strength doesn't match up to the strength of bone, which was, after all, designed to do something silk was not. I often suspect that we may have to learn how to design new materials at the molecular level in order to make what we need out of non-original materials.
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