Convergence of Scaffold-Guided Bone Reconstruction and Surgical Vascularization Strategies-A Quest for Regenerative Matching Axial Vascularization

Abstract

The prevalent challenge facing tissue engineering today is the lack of adequate vascularization to support the growth, function, and viability of tissue engineered constructs (TECs) that require blood vessel supply. The research and clinical community rely on the increasing knowledge of angiogenic and vasculogenic processes to stimulate a clinically-relevant vascular network formation within TECs. The regenerative matching axial vascularization approach presented in this manuscript incorporates the advantages of flap-based techniques for neo-vascularization yet also harnesses the in vivo bioreactor principle in a more directed "like for like" approach to further assist regeneration of the specific tissue type that is lost, such as a corticoperiosteal flap in critical sized bone defect reconstruction.

Keywords: blood vessel analysis; bone; regeneration; tissue engineering; vascularization.

Figure 1

The two patterns of blood supply to tissue following harvest with (Random) or without (Axial) preservation of the arteriovenous pedicle. © Beth Croce, Bioperspective.com.

Figure 2

Two patterns of axial vascularization for scaffold constructs, the intrinsic and extrinsic approaches. © Beth Croce, Bioperspective.com.

Figure 3

Described variations of vessel-based (VBAV) techniques for axial vascularization of scaffold constructs. © Beth Croce, Bioperspective.com.

Figure 4

Described variations of flap-based (FBAV) techniques for axial vascularization of scaffold constructs for bone regeneration. © Beth Croce, Bioperspective.com.

Figure 5

The patterns of blood supply to bone (Reproduced with permission from Sparks et al., 2017).

Figure 6

Schematic illustration detailing the steps involved in a regenerative matching approach to scaffold vascularization using a corticoperiosteal flap. Firstly the flap is harvested (A,B) prior to placement into the defect and is rolled on itself (C) so the corticoperiosteum effaces the scaffold with the periosteum and blood supply internal (D). The bone is then fixated (E) and neo-osteogenesis and scaffold vascularization ensues (F,G) to generate new autologous bone. © Beth Croce, Bioperspective.com.

Figure 7

An intra-operative photo series illustrating key components in the surgical approach for scaffold-guided bone regeneration using a corticoperiosteal flap. The flap is marked out sharply and raised off the medial and anterior surface of the tibia using a fine dental burr (A) prior to resection of the 3 cm defect (B). The flap is then rolled on itself so the corticoperiosteum effaces the lego-like half cylindrical scaffold with the periosteum and blood supply lying most internal (C). The corticoperiosteal flap with scaffold is then placed within the defect with the residual tibial diaphysis using a dynamic compression plate as internal fixation (D).

Figure 8

Overview of the 3 cm tibial corticoperiosteal flap results of a pilot study sheep. (A) X- ray image at 12 months' time point. (B) Sagittal plane of the μCT 3D reconstruction. (C) Undecalcified resin section stained with Goldner's trichrome. (D–F) Scanning electron microscopic (SEM) images of newly formed bone and interface with host bone. (D) Interface of the host bone (HB) with the new formed bone (NB) indicating excellent osteointegration of host bone, scaffold (SC) and the corticoperiosteal flap. (E) Higher magnification image showing integration of the corticoperiosteal within the newly formed bone and (F) higher magnification of the white square box in image (E) showing two osteocytes embedded in the new formed bone and directly attached to the corticoperiosteal flap, indicating direct interaction of corticoperiosteal with osteocytes. Fissures in images (D,E) are artifacts resulting from sample preparation. - - - Defect site; ^*Mechanical testing artifact; Scale bar: (B) 5 mm; (C) 5 mm; (D) 200 μm; (E) 100 μm and (F) 10 μm.

Figure 9

Overview of the 6 cm tibial corticoperiosteal flap results. (A) X- ray image at 12 months' time point. (B) Sagittal plane of the μCT 3D reconstruction. (C) Undecalcified resin section stained with Goldner's trichrome showing excellent osteointegration of host bone, scaffold and newly formed bone. (D–F) Scanning electron microscopic (SEM) images showing the osteocyte network of the newly formed tissue. (D) Osteointegration of new formed bone in the middle of the defect site. (E) Higher magnification image showing secondary osteon formation and osteocytes in the proximity of the osteon's central blood vessel and (F) higher magnification of an osteocyte embedded in the newly formed bone matrix. - - - Defect site; Scaffold collapse in C resulting from sample processing; ^*Mechanical testing fissure artifact; Scale bar: (B) 5 mm; (C) 10 mm; (D) 100 μm; (E) 50 μm and (F) 10 μm.