Prefabrication of a high-density porous polyethylene implant using a vascular induction technique

Scaffold vascularization method using an adipose-derived stem cell (ASC)-seeded scaffold prefabricated with a flow-through pedicle

Background

Vascularization is important for the clinical application of tissue engineered products. Both adipose-derived stem cells (ASCs) and surgical prefabrication can be used to induce angiogenesis in scaffolds. Our aim was to compare the angiogenic potential of ASC-seeded scaffolds combined with scaffold prefabrication with that of non-seeded, non-prefabricated scaffolds.

Methods

For prefabrication, functional blood vessels were introduced into the scaffold using a flow-through pedicle system. ASCs were isolated from rat fat deposits. Three-dimensional-printed cylindrical poly-ε-caprolactone scaffolds were fabricated by fused deposition modelling. Three groups, each containing six rats, were investigated by using non-seeded, ASC-seeded, and osteogenic induced ASC-seeded scaffolds. In each group, one rat was implanted with two scaffolds in the inguinal region. On the right side, a scaffold was implanted subcutaneously around the inferior epigastric vessels (classic prefabrication group). On the left side, the inferior epigastric vessels were placed inside the prefabricated scaffold in the flow-through pedicle system (flow-through prefabrication group). The vessel density and vascular architecture were examined histopathologically and by μCT imaging, respectively, at 2 months after implantation.

Results

The mean vessel densities were 10- and 5-fold higher in the ASC-seeded and osteogenic induced ASC-seeded scaffolds with flow-through prefabrication, respectively, than in the non-seeded classic prefabricated group (p < 0.001). μCT imaging revealed functional vessels within the scaffold.

Conclusion

ASC-seeded scaffolds with prefabrication showed significantly improved scaffold vasculogenesis and could be useful for application to tissue engineering products in the clinical settings.

Flap prefabrication using high-density porous polyethylene in an animal model – an experimental study

BACKGROUND

The search for new surgical flap techniques and modifications of already existing ones is gaining increasing popularity. Progress in flap designing and harvesting have improved the functional and aesthetic results, especially in head and neck reconstruction.

MATERIAL/METHODS

Ten pigs were used in this study. In the first operation, high-density porous polyethylene prefabrication was performed bilaterally in all pigs. After 8 weeks, each prefabricated complex was explored, resected, and macroscopically evaluated.

RESULTS

All of 20 prefabricated flaps survived. No serious surgical complications were observed. In 2 cases there was chronic inflammation and in 4 cases there was instability of the implant.

CONCLUSIONS

After this experimental study, we believe that the use of high-density porous polyethylene in flap prefabrication may be a good option for reconstruction of 3-dimensional defects, especially in patients with limited donor tissues.

The use of prefabrication technique in microvascular reconstructive surgery

AIM OF THE STUDY

The aim of the study was to develop standards for the prefabrication of free microvascular flaps in an animal model, followed by their application in clinical practice, and quantitative/qualitative microscopic assessment of the extent of development of a new microvascular network.

MATERIAL AND METHODS

The study was carried out in 10 experimental pigs. As the first stage, a total of 20 prefabricated flaps were created using polytetrafluoroethylene (PTFE) as a support material, placed horizontally over an isolated and distally closed vascular pedicle based on superficial abdominal vessels. After completing the animal model study, one patient was selected for the grafting of the prefabricated free flap.

RESULTS

All 20 free flaps prefabricated in the animal model were analyzed microscopically, exhibiting connective tissue rich in fibroblasts and small blood vessels in the porous areas across the entire thickness of the PTFE element.

CONCLUSIONS

Flap prefabrication is a new and fast developing reconstruction technique. The usefulness of prefabrication techniques and their status in reconstructive surgery still needs to be investigated experimentally and clinically. The method based on prefabricated free flaps is the first step towards anatomical bioengineering that will make it possible to replace missing organs with their anatomically perfect equivalents.

A New Method in the Treatment of Ear Amputation

There have been plenty of reconstruction methods for ear amputation, and replantation preserves its importance. In situations where replantation is not feasible, various methods were proposed. We indicate an alternative technique for the ear amputation without replantation indication. The method of replacing of a vascular structure into the tunnel formed on the posterior side of the amputated ear was used instead of replacing the ear cartilage into a vascular area that was described in the literature of ear prefabrication. The dorsal fascial flaps which were prepared from the back of 10 New Zealand rabbits were placed into the amputated ear. The 2 groups, control and the experimental, were consequently the ear that was adapted as a composite graft and the ear with the flap inserted. The ears were examined macroscopically and photographed on postoperative days 3, 7, 14, and 21. On the 21st day, the nourishment pattern of the ear, the dorsal fascia, and the dorsal fascia adapted ear were investigated with digital subtraction angiography (DSA). The group that received applied dorsal fascia possessed increased vascularity. The viability was evaluated with the biopsies taken from the control group and the group that received applied dorsal fascial flap on the 21st day. The cartilage and the connective tissue were viable in the flap-applied group, whereas there was necrosis in the control group. The reflection of the experimental study was performed on 2 subtotal and 1 total ear amputation cases, with the utilization of the superficial temporal artery. The nourishment of the flaps was evaluated with postoperative photographs, angiography, and bone scintigraphy.

Tissue engineering: bridging the gap between replantation and composite tissue allografts

This article explores issues related to tissue engineering and composite tissue allografts that employ physiologic and anatomic autogenous replicates to restore tissue loss. Composite tissue allotransplantation has become a controversial option for reconstruction, most prominently for reconstruction involving the hand and, recently, the face. While the side-effect profile of systemic immunosuppression continues to improve, the long-term risks of immunosuppression leaves composite tissue allotransplantation a domain for cautious exploration. Meanwhile, tissue engineering could, conceivably, be the gap between replantation and composite tissue allografts. Whereas the perils of immunosuppression may limit the routine use of allografts, employing constructions made of the patient's own cells negates the need for any antirejection therapy.

Vascularized Tissue-Engineered Ears

BACKGROUND

A paucity of appropriate regional and local matching tissue can compromise the reconstruction efforts in areas of the body that require specialized tissue. The current study uses techniques of vascular prefabrication, tissue culturing, and capsule formation to form a vascularized ear construct that is reliably transferable on its blood supply.

METHODS

Thirty male Wistar rats (250 to 350 g) were anaesthetized. An incision was made over the right lower abdominal wall. A pocket was formed by blunt dissection just below the panniculus carnosus. A separate incision was made over the right femoral vessels, which were then isolated and transected distally. The vessels were transposed in a subcutaneous plane to the abdominal wound. A silicone mold in the shape of an ear (2 x 1.5 cm) was placed over the transposed vessels in the abdominal wound pocket. The wounds were closed. Auricular cartilage was minced, washed, and cultured. After 14 days, the chondrocyte culturing was complete and a vascularized capsule based on the incorporated, transposed femoral vessels was formed. The abdominal incision was then reopened, an incision was made in the lateral capsule, and the cultured chondrocytes were introduced into the molded capsule. Study groups included capsules filled with chondrocytes only, chondrocytes and a fibrin glue carrier, and the fibrin glue only. The capsule was closed and the wounds sutured. The prefabricated, prelaminated construct was isolated on its vascular pedicle 14 days later and traversed microsurgically to the contralateral leg vessels. Histologic analysis was performed.

RESULTS

All 30 capsules were completely vascularized and could be reliably isolated and transferred microsurgically on the transposed femoral vessels. The pedicle, being incorporated directly into the capsule, provided the dominant blood supply to the construct. None of the capsules with the fibrin glue only retained any shape and all were devoid of cartilage. Similarly, there was no evidence of retained cartilage in the capsules filled with chondrocytes alone. All capsules with the chondrocytes and the fibrin carrier had mature shaped cartilage preserved. External molds were required to maintain the shape of the ear. Extrusion, although almost uniform in the group with external molds, did not interfere with the end construct shape or vascularity. When molds were used, four of six had excellent maintenances of shape and two of six had only minor superior pole deformation. All constructs were reliably transferred as free flaps.

CONCLUSIONS

The authors have shown that transposing a vascular pedicle to a subcutaneously placed silicone block will result in a vascular capsule that can be mobilized and transferred based solely on the pedicle. Although the capsule provides vascularity to the chondrocytes, the cultured cartilage will fill the shape of the silicone mold only if an appropriate carrier such as fibrin glue is used and an external mold is applied.

The roles of tissue engineering and vascularisation in the development of micro-vascular networks: a review

The construction of tissue-engineered devices for medical applications is now possible in vitro using cell culture and bioreactors. Although methods of incorporating them back into the host are available, current constructs depend purely on diffusion which limits their potential. The absence of a vascular network capable of distributing oxygen and other nutrients within the tissue-engineered device is a major limiting factor in creating vascularised artificial tissues. Though bio-hybrid prostheses such as vascular bypass grafts and skin substitutes have already been developed and are being used clinically, the absence of a capillary bed linking the two systems remains the missing link. In this review, the different approaches currently being or that have been applied to vascularise tissues are identified and discussed.

Bone Flap Prefabrication

The usual method to prefabricate a bone flap is to harvest a nonvascularized bone graft and to implant the artery and vein bundle between segments of bone graft. The basic problem of this method is sacrificing an artery for prefabrication. Another method for creating flap donor sites without using an artery is venous flap prefabrication. There are a few articles describing bone flap prefabrication, and these include implantation of both artery and vein as a vascular bundle. Also, there is no experimental study in the literature using a vein or an arterialized vein pedicle for bone flap prefabrication. As an experimental model for bone flap prefabrication, the rabbit ear vascular model was chosen. For the experiments 3 groups were formed. Each group contained 5 rabbits. In the first experimental group a vein was implanted between the halves of bone graft. In the second experimental group an arterialized vein was implanted between the halves of bone graft. To compare the viability of the bone graft of the 2 prefabrication groups, a bone graft was implanted into the subcutaneous pocket of the posterior auricular area in the third group. The authors examined 5 rabbits in each group by microangiography at the end of 6 weeks except for group 3. On microangiographic analysis, groups 1 and 2 showed patency of the vascular pedicle. There was no difference between these 2 groups from the point of view of vascular patency and bone appearance. Bone scintigraphy was performed for 5 rabbits in each group. On bone scintigraphic scans, the bone component of the flaps was visualized in groups 1 and 2, but not in group 3. A quantitative analysis of images was performed by drawing symmetric spherical regions of interest (ROIs) over both the implanted area and cranial bone. The uptake ratios were computed by dividing the mean counts in the implanted ROI by mean counts in the cranial bone ROI. The mean value was 0.86 +/- 0.02 in group 1 and 0.86 +/- 0.04 in group 2. A statistically significant uptake difference was not seen between venous and arterialized venous groups (P < 0.01). Histologic examination was performed all rabbits in each group, and demonstrated that the bony component was viable, showing osteocytes containing lacunae, osteoblasts along bony trabeculae, and vascular channels in groups 1 and 2. In group 3, the bony architecture of the graft was still apparent, but all bone within it was dead. There were no significant microangiographic, histologic, and scintigraphic differences between the 2 experimental methods.

Osteocutaneous Flap Prefabrication in Rats

Composite tissue defects may involve skin, mucosa, muscle, and bone together or in combinations of two or three of these tissues. Defects involving bone and skin are frequently encountered. Osteocutaneous flaps may be used to reconstruct these composite tissue defects. Sometimes, it is not possible to obtain a vascular osteocutaneous flap. Another way of producing an osteocutaneous flap that has the desired feature is prefabrication. Prefabrication of osteocutaneous flaps can be performed in two ways: (1) a vascularized osseous flap may be grafted with skin and (2) an osteocutaneous flap can be prefabricated by implanting an osseous graft into an axial island flap. There are many articles describing osteocutaneous flap prefabrication, but there is no comparison of both methods in the literature. As an experimental model for osteocutaneous flap prefabrication, rat tail bone was chosen. For the experiments, five groups were formed. Each group contained 10 rats. In the first experimental group, a vascularized osseous segment was skin grafted and an osteocutaneous flap was prefabricated. In the second experimental group, an osseous graft was implanted into an axial skin flap. To compare viability of skin and bone components of the two prefabrication groups, vascularized tail bone was elevated with overlying skin in the third group, a bone flap was elevated in the fourth group, and a skin flap that had been prefabricated by using vascular implantation was elevated in the fifth group. The authors examined five rats in each group by microangiography at the end of 4 weeks. On microangiographic analysis, all groups showed patency of vascular pedicles. There was no difference among the groups from the point of view of vascular patency and bone appearance. Bone scintigraphy was performed on the five rats in each group. On bone scintigraphic scans, the bone component of flaps was visualized in all groups except for group 5. The mean radioactivity value on the flap side was 10,362 +/- 541.1 in group 1, 10,241 +/- 1173 in group 2, 10,696 +/- 647.1 in group 3, and 10,696 +/- 647.1 in group 4. When the radioactivity values on the flap side were compared, no statistically significant difference among groups was seen, except for group 5 (p < 0.05). To evaluate bone metabolic activity, the bone component of flap and remaining last tail bone was harvested and the radioactivity of each specimen was measured with a well-type gamma counter. The parameter of percentage radioactivity in counts per minute per unit per gram of tissue was calculated. The value of the bone component of the flap side and the value of normal bone were estimated and results were compared. The mean result was 0.86 +/- 0.08 in group 1, 0.88 +/- 0.07 in group 2, 0.87 +/- 0.07 in group 3, and 0.81 +/- 0.04 in group 4. The difference among all groups was not statistically significant. Histologic examination was performed on all rats in each group and demonstrated that the bony component was viable, showing a cellular bone marrow, osteoblasts along bony trabeculae, and vascular channels in bone-containing groups. There were no significant microangiographic, histologic, or scintigraphic differences between the two experimental methods.