Cracking the Code: How Graft Porosity and Pore Size Unlock Bone Graft Success

Bone is an extraordinary tissue: porous, self-renewing, and load-bearing; all thanks to a complex interplay of bone cells, blood vessels, and a matrix of organic (collagen, proteoglycans, osteocalcin, osteonectin, sialoproteins) and inorganic (hydroxyapatite, magnesium carbonate) components (Hing, 2005). These unique properties make it challenging to replicate with synthetic materials, particularly when treating severe trauma, revision arthroplasty, oncology resections, or large segmental defects.

Bone grafts, whether autograft, allograft, or synthetic, rely on the body’s innate ability to regenerate. The ideal bone graft supports new bone formation and fully remodels into native tissue. Yet, no single synthetic graft is suitable for all clinical situations (Hing, 2005; Koleva et al., 2019).

Porosity vs Pore Size: What’s the Difference?

When engineering bone graft scaffolds, porosity and pore size are not interchangeable – and both matter.

Porosity refers to the percentage of void space in the material. It governs the overall ability of the graft to allow vascular infiltration, cell migration, and nutrient exchange.
Pore size refers to the dimension of the individual pores and directly affects the type of tissue that fills the graft.

Scaffolds must strike a balance:

Enough porosity and interconnectivity to allow osteoblasts, mesenchymal stem cells, and capillaries to infiltrate.
Sufficient mechanical strength to withstand packing and in vivo loads.

The literature suggests that pores smaller than ~100 µm tend to fill with fibrous tissue rather than bone. A minimum pore size of ~100 µm is considered necessary for bone ingrowth, while pores in the 200–400 µm range appear optimal for osteogenesis, vascularization, and mineralization (Hing, 2005; Karageorgiou & Kaplan, 2005; Murphy O’Brien, 2010; ; Petrochenko & Narayan, 2010; Jiao et al., 2023). Pore sizes as large as 500–1,500 µm have been used experimentally, particularly where vascularization is paramount. However, increasing pore size can reduce initial mechanical strength and cell attachment, so careful design is required.

In short:

Small pores (<100 µm): promote fibrous tissue, restrict vascularization.
Optimal pores (200–400 µm): promote bone and vascular tissue infiltration.
Large pores (>500 µm): may favor vascularization but compromise mechanical integrity.

Porosity can be engineered through techniques like salt leaching, phase separation, sintering, and freeze-drying. Even pore geometry matters — hexagonal pores, for example, can offer both high porosity and strength (Hing, 2005).

Clinical Relevance: Choosing the Right Scaffold

In practice, the porosity and pore size chosen depend on the surgical application:

Impaction grafting: favors low-porosity materials for better packing and strength.
Spinal fusion & large bone defects: benefit from open, interconnected porosity to support vascularization and remodeling.

At Molecular Matrix, Inc., our novel Hyper-Crosslinked Carbohydrate Polymer (HCCP, commercial name Osteo-P® BGS) is engineered with pore sizes between 100-500 µm and a porosity of 75 – 95%. Osteo-P® BGS supports osteogenic cell infiltration and bone formation, even in the absence of added growth factors. For more information on how scaffold architecture affects bone healing, see www.molecularmatrix.com

Koleva, P. M., Keefer, J. H., Ayala, A. M., Lorenzo, I., Han, C. E., Pham, K., Ralston, S. E., Kim, K. D., & Lee, C. C. (2019). Hyper-Crosslinked Carbohydrate Polymer for Repair of Critical-

Sized Bone Defects. BioResearch Open Access, 8(1), 111–120.

https://doi.org/10.1089/biores.2019.0021

Additional References:

Hing, K. A. (2005). Bioceramic Bone Graft Substitutes: Influence of Porosity and Chemistry. International Journal of Applied Ceramic Technology, 2(3), 184–199. https://doi.org/10.1111/j.1744-7402.2005.02020.x

Jahir-Hussain, M. J., Maaruf, N. A., Esa, N. E. F., & Jusoh, N. (2021). The effect of pore geometry on the mechanical properties of 3D-printed bone scaffold due to compressive loading. IOP Conference Series: Materials Science and Engineering, 1051(1), 012016. https://doi.org/10.1111/j.1744-7402.2005.02020.x

Jiao, J., Hong, Q., Zhang, D., Wang, M., Tang, H., Yang, J., Qu, X., & Yue, B. (2023). Influence of porosity on osteogenesis, bone growth and osteointegration in trabecular tantalum scaffolds fabricated by additive manufacturing. Frontiers in Bioengineering and Biotechnology, 11, 1117954. https://doi.org/10.3389/fbioe.2023.1117954

Karageorgiou, V., & Kaplan, D. (2005). Porosity of 3D biomaterial scaffolds and osteogenesis. Biomaterials, 26(27), 5474–5491. https://doi.org/10.1016/j.biomaterials.2005.02.002

Murphy, C. M., & O’Brien, F. J. (2010). Understanding the effect of mean pore size on cell activity in collagen-glycosaminoglycan scaffolds. Cell Adhesion & Migration, 4(3), 377–381. https://doi.org/10.4161/cam.4.3.11747

Petrochenko, P., & Narayan, R. J. (2010). Novel Approaches to Bone Grafting: Porosity, Bone

Morphogenetic Proteins, Stem Cells, and the Periosteum. Journal of Long-Term Effects of

Medical Implants, 20(4), 303–315.

https://doi.org/10.1615/JLongTermEffMedImplants.v20.i4.50

Yuan, H., Kurashina, K., De Bruijn, J. D., Li, Y., De Groot, K., & Zhang, X. (1999). A preliminary study on osteoinduction of two kinds of calcium phosphate ceramics. Biomaterials, 20(19), 1799–1806. https://doi.org/10.1016/S0142-9612(99)00075-7

Cracking the Code: How Graft Porosity and Pore Size Unlock Bone Graft Success

Quick Links

Get in Touch

Billing & Collections

Sales & Customer Support