Researchers 3D print calcium phosphate and graphene scaffolds for bone regeneration

A team of researchers from Carnegie Mellon University (CMU) and the University of Connecticut (UConn) have 3D printed novel calcium phosphate graphene (CaPG) scaffolds that could be used for bone regeneration applications at the future.

The team sought to develop an alternative to traditional autogenous bone grafts that simply stabilize bone defects and injuries. The study saw the successful fabrication of a 3D bio-printed alternative that supports tissue regeneration at the defect site and has many desirable properties such as osteoinductivity, biosafety, long life preservation and reasonable production costs.

3D printed biomimetic CaPG matrix design. Image via nature.

3D Printing Graphene Challenges

While graphene’s properties of light weight, electrical and thermal conductivity, and mechanical strength make it a desirable material for applications in biomedicine, power generation, and microelectronics, much of the potential of the graphene comes from deploying the material in its monolayer form. This therefore presents a significant challenge when trying to use the material for 3D printing.

Despite this, progress has been made in recent years to exploit the potential of the material for additive manufacturing. For example, Virginia Tech and Lawrence Livermore National Laboratory (LLNL) have developed a high-resolution 3D printing method that involves dispersing graphene in a gel to form a 3D-printable resin, and the latter has also worked with the University of California Santa Cruz to produce graphene-based airgel electrodes for energy storage devices.

Elsewhere, graphene-oxide scaffolds that retain many of the sought-after properties of the single-layer material have been successfully 3D printed by the Spanish Institute of Ceramics and Glass and the University of Aix-Marseille, and researchers from University at Buffalo have developed a 3D printed airgel water purifier that can be used in wastewater treatment plants.

More recently, researchers at the Harbin Institute of Technology 3D printed a soft graphene oxide robot that can move forward and backward on its own when exposed to moisture.

Compatibility and osteogenic differentiation of hMSCs on 3DP-CaPG matrices.  Image via nature.
Compatibility and osteogenic differentiation of hMSCs on 3DP-CaPG matrices. Image via nature.

3D printing of CaPG scaffolds

For this study, the combined research team is exploring how the properties of graphene can be deployed in the medical sector for bone tissue regeneration applications.

Existing biomaterial bone matrices aim to support tissue regeneration at the site of the defect or injury while degrading over time and being replaced by newly grown bone. However, despite advances in this area, there is currently still no material that contains all of the desirable properties needed to replace autogenous bone, the researchers said.

Several materials have been explored in the past to make a synthetic matrix that exhibits suitable osteoinductance properties while also being biologically safe, having a long shelf life, and being cost effective to produce. Among these, graphene-containing materials have received considerable attention for displaying excellent chemical, mechanical and biological properties.

Graphene-containing materials may promote cell adhesion and growth, with some evidence suggesting their osteogenic potential, and as such these materials are increasingly being used as biomaterials for bone regenerative engineering applications. However, graphene oxide alone lacks the necessary chemical signals to initiate regeneration of native bone at the site of injury. Additionally, the team observed that while graphene oxide flakes have excellent mechanical properties, bulk graphene oxide constructs lack the water stability needed to provide mechanical support for regeneration. bone.

The CMU and UConn research group has done some work in this area before, having successfully created an inherently osteoinductive family of functional graphene-containing materials called graphene phosphates that showed potential for bone regeneration.

For their latest study, they succeeded in 3D printing a bone-mimicking CaPG material, thanks to the addition of calcium, which they believe is able to facilitate the differentiation of stem cells into bone cells.

Biocompatibility of matrices in a model of cranial defect in mice.  Image via nature.
Biocompatibility of matrices in a model of cranial defect in mice. Image via nature.

A “paradigm” in bone regeneration

The team used biofabrication company Dimension Inx’s Direct Ink Writing (DIW) 3D printing method to print porous constructs of its CaPG material with a high weight fraction to enable “remarkably high” graphene content in ink (about 90%). This allowed cellular access to the osteoconductive skeleton and controlled release of calcium and phosphate ions, meaning that the host response to the matrix was dominated by the functional graphene content rather than the bioinert binder.

The team sent their CaPG powder to Dimension Inx where large sheets of porous CaPG matrices were 3D printed. From the sheets, the team was able to easily cut arrays with specific geometries for cell and animal studies. The group noted that the arrays could also be printed directly to match a specific bone defect. Thus, the team’s combination of 3D printing and CaPG material offers a customizable matrix system for bone regeneration engineering.

The team investigated the osteogenic potential of their 3D-printed CaPG matrices both in vitro and in vivo. According to the study, the team’s 3D-printed matrices demonstrated their bone-forming abilities in vivo with human mesenchymal stem cells (hMSCs) and in vivo in a bone defect model.

For the in vivo test, CaPG was combined with bone marrow stromal cells (BMSCs) to trigger bone formation in the subcutaneous space of mice. CaPG matrices have been shown to be capable of resorption and biodegradation in vivo, which the team says is rare for a synthetic material and shows promise as a resorbable osteoinductive matrix.

Additionally, the team did not observe any adverse effects on vital organs during the study. Going forward, the researchers will conduct further development studies to improve the mechanical properties of their 3D-printed CaPG matrices and confirm their long-term safety in vivo.

For now, the group is convinced that 3D-printed CaPG matrices have great potential for future bone regeneration applications.

Further information on the study can be found in the document entitled: “Very low binder 3D printed calcium phosphate graphene scaffolds a resorbable, osteoinductive matrix that supports bone formation in vivo,” published in the journal Nature. The study is co-authored by L. Daneshmandi, B. Holt, A. Arnold, C. Laurencin and S. Sydlik.

Biodegradation and biodistribution of 3DP-CaPG matrices.  Image via nature.
Biodegradation and biodistribution of 3DP-CaPG matrices. Image via nature.

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Featured image shows 3D printed biomimetic CaPG matrix design. Image via nature.

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