Plant Cellulose May Provide Novel Bone Implant Material

Aerogel Bone Implants
Researchers treated nanocrystals derived from plant cellulose so that they can link up and form a strong but lightweight sponge (an aerogel) that can compress or expand as needed to completely fill out a bone cavity. [Clare Kiernan, UBC]

Scientists from the University of British Columbia (UBC) and McMaster University say they have developed what could be new bone implant material: a foamlike substance that can be injected into the body and provide scaffolding for the growth of new bone.

It’s made by treating nanocrystals derived from plant cellulose so that they link up and form an aerogel that can compress or expand as needed to completely fill out a bone cavity.

“Most bone graft or implants are made of hard, brittle ceramic that doesn’t always conform to the shape of the hole, and those gaps can lead to poor growth of the bone and implant failure,” said study author Daniel Osorio, a PhD student in chemical engineering at McMaster. “We created this cellulose nanocrystal aerogel as a more effective alternative to these synthetic materials.”

For their research, the team worked with two groups of rats, with the first group receiving the aerogel implants and the second group receiving none. Results of the study (“Cross-linked cellulose nanocrystal aerogels as viable bone tissue scaffolds”), published in Acta BioMaterialiashowed that the group with implants saw 33% more bone growth at the 3-week mark and 50% more bone growth at the 12-week mark, compared to the controls.


Aerogel Bone Implants Graphical Abstract
Source: Acta BioMaterialia

“Chemically cross-linked cellulose nanocrystal (CNC) aerogels possess many properties beneficial for bone tissue scaffolding applications. CNCs were extracted using sulfuric acid or phosphoric acid, to produce CNCs with sulfate and phosphate half-ester surface groups, respectively. Hydrazone cross-linked aerogels fabricated from the two types of CNCs were investigated using scanning electron microscopy, x-ray micro-computed tomography, x-ray photoelectron spectroscopy, nitrogen sorption isotherms, and compression testing. CNC aerogels were evaluated in vitro with osteoblast-like Saos-2 cells and showed an increase in cell metabolism up to 7 days while alkaline phosphate assays revealed that cells maintained their phenotype. All aerogels demonstrated hydroxyapatite growth over 14 days while submerged in simulated body fluid solution with a 0.1 M CaCl2 pre-treatment,” wrote the investigators.

“Sulfated CNC aerogels slightly outperformed phosphated CNC aerogels in terms of compressive strength and long-term stability in liquid environments, and were implanted into the calvarian bone of adult male Long Evans rats. Compared to controls at 3- and 12-week time points, sulfated CNC aerogels showed increased bone volume fraction of 33% and 50%, respectively, compared to controls, and evidence of osteoconductivity. These results demonstrate that cross-linked CNC aerogels are flexible, porous and effectively facilitate bone growth after they are implanted in bone defects.”

Emily Cranston holding up Aerogel Bone Implants
Study co-author Emily Cranston, PhD, a professor of wood science and chemical and biological engineering at UBC. [Clare Kiernan, UBC]
“These findings show, for the first time in a lab setting, that a cellulose nanocrystal aerogel can support new bone growth,” said study co-author Emily Cranston, PhD, a professor of wood science and chemical and biological engineering who holds the President’s Excellence Chair in Forest Bio-products at UBC. She added that the implant should break down into nontoxic components in the body as the bone starts to heal.

The innovation can potentially fill a niche in the $2-billion bone graft market in North America, said study co-author Kathryn Grandfield, PhD, a professor of materials science and engineering, and biomedical engineering at McMaster who supervised the work.

“We can see this aerogel being used for a number of applications including dental implants and spinal and joint replacement surgeries,” said Grandfield. “And it will be economical because the raw material, the nanocellulose, is already being produced in commercial quantities.”

The researchers say it will be some time before the aerogel makes it out of the lab and into the operating room.

“This summer, we will study the mechanisms between the bone and implant that lead to bone growth,” said Grandfield. “We’ll also look at how the implant degrades using advanced microscopes. After that, more biological testing will be required before it is ready for clinical trials.”


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