Pattern of Bone Generation after Irradiation in Vascularized Tissue Engineered Constructs

Background Regenerative medicine modalities provide promising alternatives to conventional reconstruction techniques but are still deficient after malignant tumor excision or irradiation due to defective vascularization. Methods We investigated the pattern of bone formation in axially vascularized tissue engineering constructs (AVTECs) after irradiation in a study that mimics the clinical scenario after head and neck cancer. Heterotopic bone generation was induced in a subcutaneously implanted AVTEC in the thigh of six male New Zealand rabbits. The tissue construct was made up of Nanobone (Artoss GmbH; Rostock, Germany) granules mixed with autogenous bone marrow and 80 μL of bone morphogenic protein-2 at a concentration of 1.5 μg/μL. An arteriovenous loop was created microsurgically between the saphenous vessels and implanted in the core of the construct to induce axial vascularization. The constructs were subjected to external beam irradiation on postoperative day 20 with a single dose of 15 Gy. The constructs were removed 20 days after irradiation and subjected to histological and immunohistochemical analysis for vascularization, bone formation, apoptosis, and cellular proliferation. Results The vascularized constructs showed homogenous vascularization and bone formation both in their central and peripheral regions. Although vascularity, proliferation, and apoptosis were similar between central and peripheral regions of the constructs, significantly more bone was formed in the central regions of the constructs. Conclusion The study shows for the first time the pattern of bone formation in AVTECs after irradiation using doses comparable to those applied after head and neck cancer. Axial vascularization probably enhances the osteoinductive properties in the central regions of AVTECs after irradiation.

Enhancement of VEGF on Axial Vascularization of Nano-HA/Collagen/PLA Composites: A Histomorphometric Study on Rabbits

The aim of this study was to investigate whether the nanohydroxyapatite/collagen/poly(L-lactic acid) (nHAC/PLA) composite is suitable to be compounded with VEGF to enhance the axial vascularization in vivo. Thirty rabbits were divided into 2 groups of 15 animals each. In control group, a nHAC/PLA scaffold slice was vascularized axially by an inserted ligated femoral arteriovenous (AV) bundle in the animal. In experimental group, a slice compounded with VEGF gel was applied. The rabbits were sacrificed at 2 weeks, 6 weeks, and 10 weeks after surgery; the specimens of scaffold slices underwent histomorphometric examination; analysis of the microvessel density (MVD) of both groups was done. The combination with VEGF (Group B) did not enhance the vascularization in early phase (2 and 6 weeks,P>0.05) but worked in later phase (10 weeks,P<0.05). The data of the experiment demonstrated the suitability of the nHAC/PLA composite as carrier for the growth factor VEGF, enabling its sustained release in bioactive form with enough binding efficacy.

Axial Vascularization of Nano-HA/Collagen/PLA Composites by Arteriovenous Bundle

In previous studies, nano-hydroxyapatite/collagen/poly(L-lactic acid) (nHAC/PLA) composites have been prepared and confirmed to repair small sized bone defects. However, they are restricted to repair a large defect without sufficient oxygen and nutrition for cell survival. The result of this study confirmed that nHAC/PLA composites could be axially vascularized by being implanted intramuscularly with arteriovenous (AV) bundle (Group A) in the groins of rabbits. The combination with autologous bone marrow (Group B) could not enhance it the vascularization in early phase (2 weeks,P>0.05), but it could enhance in middle and later phases (6 and 10 weeks,P<0.01). It meant that nHAC/PLA could be prefabricated as a vascularized bone substitute for grafting.