Biomedical engineers at Tufts University’s School of Engineeringhave demonstrated the first all-polymeric bone scaffold materialthat is fully biodegradable and capable of providing significantmechanical support during repair. The new technology usesmicron-sized silk fibers to reinforce a silk matrix, much as steelrebar reinforces concrete. It could improve the way bones and othertissues are repaired following accident or disease. The discovery is reported in the Proceedings of the National Academy of Sciences Online Early Edition the week of April 30-May 4, 2012.
In the U.S. an estimated 1.3 million people undergo bone graftsurgeries each year, notes the paper. Human bones are hard but relatively lightweight, able to withstandconsiderable pressure while being sufficiently elastic to withstandmoderate torsion. Inside the hard, mineralized tissue is a matrixin which bone cells can proliferate and adhere. Natural bone is theobvious choice for grafts.
However autologous grafts mean putting the patient throughadditional surgery and the supply of self-donated tissue is,obviously, limited. Donor grafts pose risks of disease, graftrejection and other long-term complications. A handful of all-polymeric biomaterials, such as collagen, arecurrently used for bone regeneration, but they lack strength.Incorporating ceramics or metals into polymers improves mechanicalproperties but such composites often sacrifice optimum boneremodeling and regeneration. By bonding silk protein microfibers to a silk protein scaffold, theTufts bioengineers were able to develop a fully biodegradablecomposite with high-compressive strength and improved cellresponses related to bone formation in vitro. ISDB-T Receiver
The study found that silk microfiber-protein composite matricesmimicked the mechanical features of native bone including matrixstiffness and surface roughness that enhanced human mesenchymal stem cell differentiation compared to control silk sponges. In combinationwith inherent silk fiber strength, compact fiber reinforcementenhanced compressive properties within the scaffolds. “By adding the microfibers to the silk scaffolds, we get strongermechanical properties as well as better bone formation. Bothstructure and function are improved,” said David Kaplan, Ph.D.,chair of biomedical engineering at Tufts University. China DVB-T Set Top Box
“This approachcould be used for many other tissue systems where control ofmechanical properties is useful and has broad applications forregenerative medicine.” Other authors on the paper were Biman B. Mandal, former postdoctoral associate in the Department of Biomedical Engineering atTufts and now in the Department of Biotechnology, Indian Instituteof Technology; visiting biomedical engineering student ArielaGrinberg, who recently completed her degree in the Department ofTissue Engineering, Cell Therapy and Regenerative Medicine at theNational Institute of Rehabilitation, Mexico; and Eun Seok Gil andBruce Panilaitis, research associate and research assistantprofessor respectively in the Department of Biomedical Engineeringat Tufts. The Tufts scientists used a novel approach to manufacturing thesilk microfibers: applying alkaline hydrolysis (the use of alkalichemicals to break down complex molecules into their buildingblocks). This greatly reduced the time and cost of making themicrofibers in a variety of sizes. ISDB-T Receiver
Microfibers ranging from 10 to20 um were obtained in one minute, compared with production of 100um plus size fibers after 12 minutes of conventional processing. Although significant improvements in compressive properties wereobserved in the silk composite scaffolds, values were stillsignificantly lower than that of stronger native bone. The Tuftsresearchers suggest that such scaffolds can play a valuable role astemporary biodegradable support for native cells to grow andreplace. Additional References Citations.