Up to date, i also finding the same answer for this questions. But then logically, for mechanical strength, nano size will be better. But for osteoconductive activity, yet to be investigated which one is better.

in natural bone the size of Ha is less than 100nm. natural bone is made of collagen, calcium phosphate (i.e. Ha) and water. in bone collagen are like filament (triploid structure) which provides elasticity and structural support to bone. HA are in needle or plates form present at the interconnects of collagen which provides strength and stiffness to the bone.

refer: Introduction to Bio-materials by donglu shi

Hi, Arun and Yanny, thanks for your feedback. I had borrowed the book and I found out the book is amazingly great for me as a beginner to understand for HAP. I found out there are a lot of debates for the minimum pore size of the scaffold to initiate bone growth. I read like at least 100 micro meter. And some depends whether it is in vitro or in vivo. However, I still have a few questions on my mind remain unsolved, mainly is my understanding about this topic. Please do correct me if I am wrong because I am still very new in this field.

1. If nanoparticle size HAP is used, then during sintering, densification process will take place to reduce the gap, maybe some binders burn off. If nano particle size used, will the pore size produced will appear in nano size? Logically it will have higher compaction compared to mico sized HAP. Because I read some journals, if the sintering temperature is too high, HAP will change phase and burn hole will appear. That will weaken the strength of the sintered HAP.

2. Is HAP a part of calcium phosphate? How does the phases like beta-TCP, alpha-TCP influence the sintered material?

1. while sintering at high temperature pore size wil get reduce it wil be in nano and meso pore size. the use of nano size Ha is to resorbed by the natural bone for bone regeneration. macro sized pore formation in the scaffold during sintering depends on the packing volume.

2. All three Ha, beta-TCP, alpha-TCP are different forms of calcium phosphate. in this three form Ha phase is present in bone.

As Karthik ji has told, that the size of natural HAp nanoparticle developed in physiological conditions is found to be 20-80 nm range. Therefore, it is most plausible that same range of size of nano particles of artificial HAp would have extremum biological response and compatibility

Hello Ms. Yanny,

to my opinion, the choice of particle size is important only to manage the sintering behavior of your material. If the sinterability is better, the density of scaffold struts would be higher, and your scaffold more mechanically reliable.

The size of pores is regulated rather by sacrificial material geometry (number of pores per inch (ppi) if you are using some polymer foams, e.g.) than by HAp particle size. Any consequence of HAp particle size on the pore size of the scaffold should be in the microporosity  (less than 20 nm) level, but it is not the tailored one.

Furthermore, HAp should sinter better if nanopowders are used, however, there are often many problems with it.

Finally, if there is a nanoparticulated HAp, use it first, at least.

you should use nanoparticle Hap mixed with macro size progens in range 100-300 micron.