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Article Corrigendum to: Developing a novel resorptive hydroxyapatite-based bone substitute for over-critical size defect reconstruction: physicochemical and biological characterization and proof of concept in segmental rabbit’s ulna reconstruction was published on June 28, 2022 in the journal Biomedical Engineering / Biomedizinische Technik

The aim of this study was to develop novel hydroxyapatite (HAP)-based bioactive bone replacement materials for segmental osteotomy reconstruction. Customized three-dimensional (3D) bone construct was manufactured from nanohydroxyapatite (nHAP) with poly(lactide-co-glycolide) (PLGA) coating using 3D models derived from the computed tomography (CT) scanning of the rabbit's ulna and gradient 3D printing of the bone substitute mimicking the anatomical shape of the natural bone defect. Engineered construct revealed adequate micro-architectural design for successful bone regeneration having a total porosity of 64% and an average pore size of 256 μm. Radiography and micro-CT analysis depicted new bone apposition through the whole length of the reconstructed ulna with a small area of non-resorbed construct in the central area of defect. Histological analysis revealed new bone formation with both endochondral and endesmal type of ossification. Immunohistochemistry analysis depicted the presence of bone formation indicators-bone morphogenetic protein (BMP), osteocalcin (OCN) and osteopontin (OPN) within newly formed bone. Manufactured personalized construct acts as a "smart" responsive biomaterial capable of modulating the functionality and potential for the personalized bone reconstruction on a clinically relevant length scale.

Figure 1S. Change of the Ca concentration in the solution containing investigated nHAP granules with time. Figure 2S. Change of the Ca concentration with time in biological apatite (BioOss). Figure 3S. The correlation of the ALBO-OS compressive strenght and the time of the material’s soaking in Hank’s solution. Table 1S. Reference point indentation outcomes of the ALBOOS. MH – microhardness, ID 1st - 1st Cycle Indentation Distance; US 1st - 1st Cycle Unloading Slope; CID 1st -1st Cycle Creep Indentation Distance; TID - Total Indentation Distance; IDI - Indentation Distance Increase; Avg CID - Avg Creep Indentation Distance; Avg US - Average Unloading Slope; Avg US - Average Unloading Slope; Avg LS - Average Loading Slope; Avg ED - Average Energy Dissipated. Table 2S. Ph of nHAP after soaking in simulated body fluid. Figure 4S. Microacrhitectural and structural characteristics of nHAP in vitro and in contact with bone tissue in vivo. Adequate microstructure and surface nanotopography provide good environment for cells infiltration in vivo. Note the presence of porous paterns within material structure in vivo as well as the lamellar structure of ALBO-OS. Figure 5S. Schematic representation of the extruder design in custom made laboratory 3D printer: from technical reasons, 3D printer was modified to include two extruders: 1 – syringe extruder, 1.1 – glass syringe, 1.2 – external frame of the extruder 1, 1.3 – electrical heater coil, 1.4 –metal piston of the syringe, 1.5 – syringe nozzle (0,8mm in diameter), 1.6 – gears of the piston drive, 1.7 – piston drive motor with reduction, 1.8 – HAP PLA mixture, 2 – PLA extruder, 2.1 – heater block of the PLA extruder, 2.2 – extruder cooler, 2.3 – PLA extruder motor drive with reduction, 2.4 – PLA filament 1.75mm in diameter, 2.5 – PLA extruder nozzle 0,4mm in diameter. Figure 6S. Paste extruder attached to the head of the printer, with removed electrical heater coil, so the syringe with the metal piston can be visible. A) The