Faculty Bibliography

Few areas of translational medicine carry as much excitement and hope as stem cell therapies. Because of recent advances in material science and stem cell and developmental biology that help to target molecules and pathways to restore the body's regenerative capacity, the "engineering" of missing tissue is quickly becoming a reality. Classically, tissue engineering has been thought to require external regenerative resources including a scaffold, cells, and growth factors. The allure of providing an exact replica of a missing bone that incorporates to become indistinguishable from self, has the capacity to heal and grow, is resistant to infection, and has minimal morbidity is a "holy grail" to all surgeons who work with bone. This article attempts to shed light on the use of stem cells for craniofacial reconstruction, including important principles learned from other scientific disciplines, relevant animal models for tissue engineering, early clinical reports from our experience and that of others, and future directions.

Introduction: Bioengineering osseous tissue requires recapitulating the cellular, matrix, and lacunocanalicular components of bone. A construct must have a microvascular network which requires simultaneous co-culture of endothelial and osteogenic cells. Recreation of the matrix requires optimization of composition and microarchitecture. Engineering of constructs large enough to solve actual clinical problems requires novel strategies that address chemotransportative requirements by replicating lacunocanalicular flow. Methods: Cells: Adipose-derived mesenchymal stem cells (MSCs) were isolated and expanded from human lipoaspirate and differentiated into osteoprogenitor-rich (OPC) and endothelioprogenitor-rich (EPC), confirmed by RT-PCR. Normal human osteoblasts (NHOst) and human umbilical vein endothelial cells (HUVEC) served as terminally differentiated cell lines. The effects of coculture (e.g OPC + HUVEC, OPC + EPC etc) on capacity for bone formation was evaluated by von Kossa assay. Matrix: Murine alveolar defects were created. Scaffolds composed of either absorbable collagen sponge (ACS) or biphasic hydroxyapatite/tri-calcium phosphate (HA-TCP) in a 15/85 ratio were constructed and implanted. HA-TCP scaffolds were further investigated, comparing 15/85 and 60/40 HA/TCP in a rabbit calvarial model. Scaffold pore size (380/180 microns) and strut size (250/180 microns) were also investigated. New bone formation was analyzed histomorphometrically using micro-CT. Lacunocanalicular flow: We have developed a novel flow perfusion bioreactor designed to mimic lacunocanalicular flow. To validate, murine femurs were explanted to the bioreactor for 14 days. Viability and function were evaluated using thiazolyl blue tetrazolium bromide (MTT), DNA quantification, alkaline phosphatase (ALP) assay, and tetracycline labelling. Furthermore, optimal culture conditions were tested with MSC-seeded custom thick 3D HA-TCP scaffolds cultured in static conditions or in flow perfusion. Cellularity was assessed by SEM,!

Preoperative imaging is essential for abdominal perforator flap breast reconstruction because it allows for preoperative perforator selection, resulting in improved operative efficiency and flap design. The benefits of visualizing the vasculature preoperatively also extend to gluteal artery perforator flaps. Initially, our practice used computed tomography angiography (CTA) to image the gluteal vessels. However, with advances in magnetic resonance imaging angiography (MRA), perforating vessels of 1-mm diameter can reliably be visualized without exposing patients to ionizing radiation or iodinated intravenous contrast. In our original MRA protocol to image abdominal flaps, we found the accuracy of MRA compared favorably with CTA. With our increased experience with MRA, we decided to use MRA to image gluteal flaps. Technical changes were made to the MRA protocol to improve image quality and extend the field of view. Using our new MRA protocol, we can image the vasculature of the buttock, abdomen, and upper thigh in one study. We have found that the spatial resolution of MRA is sufficient to accurately map gluteal perforating vessels, as well as provide information on vessel caliber and course. This article details our experience with preoperative imaging for gluteal perforator flap breast reconstruction.

BACKGROUND: Perforator flaps represent the latest in the evolution of soft-tissue flaps. They allow the transfer of the patient's own skin and fat in a reliable manner with minimal donor-site morbidity. The powerful perforator flap concept allows transfer of tissue from numerous, well-described donor sites to almost any distant site with suitable recipient vessels. Large-volume flaps can be reliably supported with perforators from areas such as the buttock and transferred microsurgically for breast reconstruction. INDICATIONS: The ideal tissue for breast reconstruction is fat with or without skin, not implants or muscle. Absolute contraindications specific to perforator flaps in our practice include history of previous liposuction of the donor site, some previous donor-site surgery, or active smoking (within 1 month before surgery). METHODS: Perforator flaps are supplied by blood vessels that arise from named, axial vessels and perforate through or around overlying muscles and septa to vascularize the overlying skin and fat. During flap harvest, these perforators are meticulously dissected free from the surrounding muscle, which is spread in the direction of the muscle fibers and preserved intact. The pedicle is anastomosed to recipient vessels in the chest, and the donor site is closed without the use of synthetic mesh. CONCLUSION: Perforator flaps allow for safe, reliable tissue transfer from a variety of sites and provide ideal tissue for breast reconstruction, with minimal donor-site morbidity.

The tremendous variability of the inferior epigastric arterial system makes accurate imaging of the vasculature of the anterior abdominal wall an essential component of optimal perforator selection. Preoperative imaging of the abdominal vasculature allows for preoperative perforator selection, resulting in improved operative efficiency and flap design. Abdominal wall perforators of 1-mm diameter can be reliably visualized without exposing patients to ionizing radiation or iodinated intravenous contrast through advances in magnetic resonance imaging angiography (MRA). In this study, MRA imaging was performed on 31 patients who underwent 50 abdominal flaps. For each flap, the location, relative to the umbilicus, of the three largest perforators on both the left and right sides of the abdomen was determined with MRA. Vessel diameter and anatomic course were also evaluated. Postoperatively, a survey was completed by the surgeon to assess the accuracy of the MRA with respect to the intraoperative findings. All perforators visualized on MRA were found at surgery (0% false-positive). In 2 of 50 flaps, the surgeon transferred a flap based upon a vessel not visualized on the MRA (4% false-negative). This article details our experience with MRA as a reliable preoperative imaging technique for abdominal perforator flap breast reconstruction.