Histologic analysis of prefabricated, vascularized bone grafts: an experimental study in rabbits

Large Animal Models of an In Vivo Bioreactor for Engineering Vascularized Bone

Reconstruction of large skeletal defects is challenging due to the requirement for large volumes of donor tissue and the often complex surgical procedures. Tissue engineering has the potential to serve as a new source of tissue for bone reconstruction, but current techniques are often limited in regards to the size and complexity of tissue that can be formed. Building tissue using an in vivo bioreactor approach may enable the production of appropriate amounts of specialized tissue, while reducing issues of donor site morbidity and infection. Large animals are required to screen and optimize new strategies for growing clinically appropriate volumes of tissues in vivo. In this article, we review both ovine and porcine models that serve as models of the technique proposed for clinical engineering of bone tissue in vivo. Recent findings are discussed with these systems, as well as description of next steps required for using these models, to develop clinically applicable tissue engineering applications.

A synergistic approach to the design, fabrication and evaluation of 3D printed micro and nano featured scaffolds for vascularized bone tissue repair

3D bioprinting has begun to show great promise in advancing the development of functional tissue/organ replacements. However, to realize the true potential of 3D bioprinted tissues for clinical use requires the fabrication of an interconnected and effective vascular network. Solving this challenge is critical, as human tissue relies on an adequate network of blood vessels to transport oxygen, nutrients, other chemicals, biological factors and waste, in and out of the tissue. Here, we have successfully designed and printed a series of novel 3D bone scaffolds with both bone formation supporting structures and highly interconnected 3D microvascular mimicking channels, for efficient and enhanced osteogenic bone regeneration as well as vascular cell growth. Using a chemical functionalization process, we have conjugated our samples with nano hydroxyapatite (nHA), for the creation of novel micro and nano featured devices for vascularized bone growth. We evaluated our scaffolds with mechanical testing, hydrodynamic measurements and in vitro human mesenchymal stem cell (hMSC) adhesion (4 h), proliferation (1, 3 and 5 d) and osteogenic differentiation (1, 2 and 3 weeks). These tests confirmed bone-like physical properties and vascular-like flow profiles, as well as demonstrated enhanced hMSC adhesion, proliferation and osteogenic differentiation. Additional in vitro experiments with human umbilical vein endothelial cells also demonstrated improved vascular cell growth, migration and organization on micro-nano featured scaffolds.

In vivo bioreactors for mandibular reconstruction

Large mandibular defects are difficult to reconstruct with good functional and aesthetic outcomes because of the complex geometry of craniofacial bone. While the current gold standard is free tissue flap transfer, this treatment is limited in fidelity by the shape of the harvested tissue and can result in significant donor site morbidity. To address these problems, in vivo bioreactors have been explored as an approach to generate autologous prefabricated tissue flaps. These bioreactors are implanted in an ectopic site in the body, where ossified tissue grows into the bioreactor in predefined geometries and local vessels are recruited to vascularize the developing construct. The prefabricated flap can then be harvested with vessels and transferred to a mandibular defect for optimal reconstruction. The objective of this review article is to introduce the concept of the in vivo bioreactor, describe important preclinical models in the field, summarize the human cases that have been reported through this strategy, and offer future directions for this exciting approach.

Historical review of bone prefabrication

Prefabricated tissue represents a bridge between traditional reconstructive surgery and tissue engineering. Initially used in the 1960s in reconstructive plastic surgery, in the 1980s it was also used in orthopedics. The term "prefabricated" indicates a process of neovascularization of a tissue by implanting a vascular pedicle inside the tissue itself; this tissue can be then reimplanted either at a short distance through the pedicle itself, or as a free graft by microvascular anastomosis. The purpose of prefabrication is to build a tissue (muscle, bone, skin, or composite) with characteristics as similar as possible to those of the defect to fill, thus minimizing morbidity in the donor site and improving the reconstructive effectiveness. We present a review of the literature that includes the main experiments performed until now in which a bone segment has been reconstructed using scaffolds and growth factors in relationship to the local blood supply or to the use of a vascular pedicle.

Extracorporeal hydroxyapatite-chamber for bone and biomaterial studies

Hydroxyapatite (HA) spherules and autologous bone (AB) with a central vascular pedicle were housed inside an HA-chamber to form the skeletal segment of specific shape. Experimental chambers were then inserted in a pocket between medial thigh muscles in 13 New Zealand male rabbits for 3 months. Three graft group were scheduled: (A) HA and AB without vascular pedicle, (B) HA with vascular pedicle, (C) HA and AB with vascular pedicle. At term, histology showed tissue and cellular degeneration in group A chambers. Due to spherules coalescence, fibrous tissue is formed in group B chambers. Group C chambers contained living osteocytes in the implanted bone, several newly formed vessels in soft tissue, bone and partial hydroxyapatite erosions. New bone was formed in apposition to both autologous bone and hydroxyapatite. Our study suggests that this experimental model could be used to grow adequately sized vascularized skeletal segments.

Prefabrication of Vascularized Bone Graft Using Guided Bone Regeneration

This article describes the prefabrication of a vascularized bone graft composed of autologous particulate cancellous bone and marrow (PCBM), a vessel bundle, and a biodegradable membrane. The PCBM was placed around the saphenous vessel bundle of rats and rolled with a biodegradable membrane of L-lactide-epsilon-caprolactone copolymer to prepare the prefabricated vascularized bone graft (group A). As controls, combinations of PCBM and membrane (group B), vessel bundle and membrane (group C), and PCBM and vessel bundle (group D) were prepared. A radiographic study revealed radio-opacity in the implantation site of group A 1 week later, in contrast to the other groups. Newly formed bone in the membrane roll was histologically confirmed, and neomicrovasculature circulating from the vessel bundle through the newly formed bone tissue was observed. The increase in alkaline phosphatase activity and osteocalcin content was significant for the group A preparation compared with the other groups. We concluded that the combination of autologous PCBM, a vessel bundle, and a biodegradable membrane was promising in the prefabrication of vascularized bone with good blood circulation.

Bone chips and diced cartilage: an anatomically adopted graft for the nasal dorsum

Since 1996, cranial bone chips or septal bone chips harvested during septal deviation surgery and small chips of ear or septal cartilage have been used in 67 patients for dorsal nasal augmentation or for smoothing dorsal nasal irregularities. In this study, 59 overresections of ostecartilaginous nose structures during previous aesthetic nose surgeries and 8 primary rhinoplasties occasioned the use of bone or cartilage grafts. For 57 patients both bone and ear cartilage grafts were used for the reconstruction. Bone grafts were used for seven cases and cartilage grafts for three cases. The results from 7 years, of experience with this method of nasal dorsum reconstruction were satisfactory and durable. The most important advantage of this method is that the bony side of the nose is reconstructed with bone and the cartilage side with cartilage. Another advantage is that the bone chips are incorporated with both nasal bones, building a strong dorsal nasal bony mono-black. This technique also is useful for augmenting mild saddle nose deformity and dorsal nasal projection deficiency on the bony part, cartilage part, or both parts.

Prefabricated galeal flap based on superficial temporal and posterior auricular vessels

Scalp layers are widely used in reconstructive procedures. The authors used prefabricated galeal flaps based on the superficial temporal or postauricular vessels for ear, cheek, mandible, and cranium reconstructions in three cases. In case 1, synchronous beard and ear reconstructions were accomplished by using the temporoparietal and retroauricular flaps. In case 2, a buccomandibular defect was reconstructed by transposing the supra-auricular and retroauricular galea with prefabricated bone and skin. In case 3, an epidural hematoma in the left frontoparietal area was evacuated after a circular craniectomy. The harvested bone was not put back on the defect area but buried between the periosteal and galeal layers because of brain edema. These layers were raised as an osteogaleoperiosteal flap and transposed onto the defect area after 7 weeks. When used with a prefabrication method, scalp layers offer versatile options for repairing composite defects of the head region. A galeal flap based on the posterior auricular vessels is practical and reliable in reconstructive procedures. The authors suggest that this flap is an option in cases in which the temporoparietal fascia artery or the superficial temporal artery is not available. Prefabrication of the harvested cranial bone inside the adjacent tissues offers several advantages in that a viable bone is provided at the end of the procedure, intervention at a distant area is avoided, the graft is placed on osteogenic tissue (periosteum) that is also transposed onto the defect, and sophisticated procedures such as microsurgical techniques are not needed.

Prefabricated bone graft induced from grafted periosteum for the repair of jaw defects: an experimental study in rabbits

PURPOSE

The purpose of the study was to determine whether a prefabricated graft of new bone induced from periosteum grafted into muscle was an effective material for the repair of jaw defects.

MATERIAL AND METHODS

Artificial mandibular jaw defects in young Japanese rabbits were covered either with free grafted periosteum (n = 5) or a prefabricated graft of newly formed bone induced from periosteum, which was first grafted into the floor of the mouth, and placed as a revascularized muscle-pedicled bone flap (n = 5). Bone formation in jaw defects was examined radiographically and histologically 28 days after grafting into defects.

RESULTS

Bone formation was confirmed radiographically and histologically in both groups. However, the free grafted periosteum formed thin bone and fibrous tissue existed between the new and the original bone. In contrast, more active bone formation was observed with the prefabricated graft. This grafted new bone developed further and fused to the mandible. Blood vessels surrounding the new bone were observed histologically.

CONCLUSION

These experimental findings suggested that prefabricated bone grafts induced from periosteum grafts are potentially useful for correction of jaw defects.