Abstract
Additive manufacturing enables the realization of the macro- and microarchitecture of bone substitutes. The macroarchitecture is determined by the bone defect and its shape makes the implant patient specific. The preset distribution of the 3D-printed material in the macroarchitecture defines the microarchitecture. At the lower scale, the nanoarchitecture of 3D-printed scaffolds is dependent on the post-processing methodology such as the sintering temperature. However, the role of microarchitecture and nanoarchitecture of scaffolds for osteoconduction is still elusive. To address these aspects in more detail, we produced lithography-based osteoconductive scaffolds from hydroxyapatite (HA) of identical macro- and microarchitecture and varied their nanoarchitecture, such as microporosity, by increasing the maximum sintering temperatures from 1100 to 1400 °C. The different scaffold types were characterized for microporosity, compression strength, and nanoarchitecture. The in vivo results, based on a rabbit calvarial defect model showed that bony ingrowth, as a measure of osteoconduction, was independent from scaffold’s microporosity. The same applies to in vitro osteoclastic resorbability, since on all tested scaffold types, osteoclasts formed on their surfaces and resorption pits upon exposure to mature osteoclasts were visible. Thus, for wide-open porous HA-based scaffolds, a low degree of microporosity and high mechanical strength yield optimal osteoconduction and creeping substitution. Based on our study, non-unions, the major complication during demanding bone regeneration procedures, could be prevented.
Highlights
Bone tissue engineering has emerged from the need to satisfy the current unmet demand of bone grafts and to alleviate the problems associated with autografts and allografts [1]
Since we suspected an indirect link between microporosity and osteoconductivity reflecting differences in ion dissolution, here, we extended our studies to hydroxyapatite (HA)-based scaffolds known for their slower ion dissolution rate as compared with tricalcium phosphate (TCP) [25]
We documented the positive influence of microporosity on osteoconduction of TCP-based scaffolds; here, we determined the effect of microporosity on osteoconduction and creeping substitution of HA-based scaffolds
Summary
Bone tissue engineering has emerged from the need to satisfy the current unmet demand of bone grafts and to alleviate the problems associated with autografts and allografts [1]. As for all tissue engineering specialties, bone tissue engineering can comprise materials, growth factors, and cells [3]. Such a combination can, for example, be realized by additive manufacturing with a synergistic combination of materials, growth factors, and cells, as defined previously [4]. Additive manufacturing is a methodology to build objects layer-by-layer This allows the spatial defined distribution of material, growth factors, and cells but is a key technology for personalized medicine realized by diverse methodologies [5]. Three-dimensional printing for the production of bone substitutes has been reviewed extensively [4,6,7,8] The architecture of such a personalized bone substitute is defined on three levels. All three levels are well known to be critical for osteoconduction [9,10]
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