Chitosan nanoparticles as a dual growth factor delivery system for tissue engineering applications.

Growth factors are essential in cellular signaling for migration, proliferation, differentiation and maturation. Sustainable delivery of therapeutic as well as functional proteins is largely required in the pharmacological and regenerative medicine. Here we have prepared chitosan nanoparticles (CNP) and incorporated growth factors such as epidermal growth factor (EGF) and fibroblast growth factor (FGF), either individually or in combination, which could ultimately be impregnated into engineered tissue construct. CNP was characterized by Fourier transform infrared (FTIR) spectroscopy, Zeta sizer and high resolution transmission electron microscope (HRTEM). The particles were in the size range of 50-100 nm with round and flat shape. The release kinetics of both EGF and FGF incorporated CNP showed the release of growth factors in a sustained manner. Growth factors incorporated nanoparticles did not show any toxicity against fibroblasts up to 4 mg/ml culture medium. Increased proliferation of fibroblasts in vitro evidenced the delivery of growth factors from CNP for cellular signaling. Western blotting results also revealed the poor inflammatory response showing less expression of proinflammatory cytokines such as IL-6 and TNFα in the macrophage cell line J774 A-1.

Carbon nanotubes in animal models: a systematic review on toxic potential.

Amongst the engineered nanomaterials, especially carbon nanotubes (CNTs) have received considerable attention for application in tissue engineering scaffolds. CNTs are considered promising on behalf of their physicochemical properties, yet such nanomaterials also have been associated with potentially hazardous effects on human health. To gain insight into the toxicity aspects of CNTs in vivo, the present study presents a systematic review of literature. After screening of literature through defined inclusion and exclusion criteria, and subsequent data extraction, it can be concluded that pulmonary administered CNTs have the capacity to induce toxicity in the lung area. However, conclusions for other organs, or on systemic toxicity, are yet premature. In addition, the carcinogenic potential of CNTs is also still ambiguous, because contradictive results are presented. Intrinsic factors, such as material characteristics, and associated distribution and agglomeration patterns influence the toxic potential of CNTs. Similarly, environmental factors such as the exposure route, preexisting allergies, pathological infections, or air pollutant exposure are significant. Despite the many reports published currently, more studies will be required to gain full understanding of the toxic potential of CNTs and especially the underlying mechanisms. For this end, development of standardized protocols and reliable nanodetection techniques will form prerequisites.

Disparate companions: tissue engineering meets cancer research.

Recreating an environment that supports and promotes fundamental homeostatic mechanisms is a significant challenge in tissue engineering. Optimizing cell survival, proliferation, differentiation, apoptosis and angiogenesis, and providing suitable stromal support and signalling cues are keys to successfully generating clinically useful tissues. Interestingly, those components are often subverted in the cancer setting, where aberrant angiogenesis, cellular proliferation, cell signalling and resistance to apoptosis drive malignant growth. In contrast to tissue engineering, identifying and inhibiting those pathways is a major challenge in cancer research. The recent discovery of adult tissue-specific stem cells has had a major impact on both tissue engineering and cancer research. The unique properties of these cells and their role in tissue and organ repair and regeneration hold great potential for engineering tissue-specific constructs. The emerging body of evidence implicating stem cells and progenitor cells as the source of oncogenic transformation prompts caution when using these cells for tissue-engineering purposes. While tissue engineering and cancer research may be considered as opposed fields of research with regard to their proclaimed goals, the compelling overlap in fundamental pathways underlying these processes suggests that cross-disciplinary research will benefit both fields. In this review article, tissue engineering and cancer research are brought together and explored with regard to discoveries that may be of mutual benefit.

Cartilage tissue engineering for auricular reconstruction: in vitro evaluation of potential genotoxic and cytotoxic effects of scaffold materials.

Tissue engineering of autologous cartilage transplants is suggested as a new approach in reconstruction of external auricular deformities. 1.6-Hexanediol (HD), 1.8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 6-hydroxyhexanoic acid (HHA) are matrices of the open-pored polyurethane three-dimensional scaffold. Since these bioresorbable materials may interact with the human organism, cytotoxic effects on human chondrocytes and lymphocytes and genotoxic effects on human lymphocytes were monitored. Staining with propidium iodide and fluorescence diacetate as well as the EZ4U proliferation assay served for the detection of cytotoxic effects of the materials on human chondrocytes. Trypan blue staining was used to monitor cytotoxicity on lymphocytes. Genotoxic effects on lymphocytes in terms of strand breaks, alkali labile sites and incomplete excision repair were determined by the alkaline single cell microgel electrophoresis (Comet) assay. Cytotoxic effects in chondrocytes and lymphocytes as well as genotoxic effects in lymphocytes were dose-dependent with threshold values of 5mg/mL HD, 0.5mg/mL DBU and 0.03 mg/mL HHA showing no effects. These data suggest that these matrices could be safely used for scaffolds made of polyurethane unless these compounds are not released at a rate giving higher concentrations at the site of implantation or in body fluids, respectively.

An update on therapeutic angiogenesis for peripheral vascular disease.

BACKGROUND: We reviewed the issue of stem cells and therapeutic angiogenesis in the treatment of peripheral vascular disease. METHODS: MEDLINE (1997-2008) with the following search terms: "stem cell therapy," "endothelial progenitor cells," "peripheral blood mononuclear cells," and "peripheral vascular disease." Relevant published papers involving the above search terms, preclinical studies, and clinical trials using stem cells and progenitors for the treatment of peripheral occlusive vascular disease were included. RESULTS: Transplantation of bone marrow-derived progenitor cells or peripheral blood mononuclear cells promotes tissue angiogenesis, as has already been explored in preclinical studies; angiogenesis can also be sustained using genetic, protein therapeutic approaches. Engineered scaffolding with stem cells is a further strategy, which is still in its infancy. The treatment of patients with severe peripheral arterial disease is generally reported as a series of case reports; all studies generally show an improvement in clinical symptoms, e.g., rest pain and pain-free walking time, as well as transcutaneous oxygen pressure, without any important adverse reactions. The few clinical trials also report similar encouraging results. All the studies have their shortcomings, including absence of control groups and objective evaluation of the results of treatments as well as short-term follow-up. CONCLUSION: Promoting angiogenesis using genetic, protein, stem cell-based therapies is a promising option for the treatment of peripheral vascular disease when unresponsive to medical and surgical therapy.

The use of phospholipase A(2) to prepare acellular porcine corneal stroma as a tissue engineering scaffold.

This study was to develop a method using phospholipase A(2) (PLA(2)) to prepare acellular porcine corneal stroma (APCS) for tissue engineering. The APCS was prepared from native porcine cornea (NPC) that was treated with 200 U/ml PLA(2) and 0.5% sodium deoxycholate (SD). The removal of DNA content, representing decellularization efficiency, reached to 91%, while all hydroxyproline and 80% of glycosaminoglycan were retained in the APCS when compared with NPC. The residual PLA(2) and SD were 0.35+/-0.04 U/mg dry weight and 4.3+/-0.8 ng/mg dry weight respectively. The extracts of APCS had no inhibitory effects on proliferation of corneal epithelial and endothelial cells as well as keratocytes. There was no sign of infiltration of neutrophilic leukocytes or leukomonocytes at 2 weeks after subcutaneous implantation of APCS. The prepared APCS displayed similar light transmittance to NPC. There were no significant differences in the areal modulus and curvature variation between APCS and NPC. Rabbit lamellar keratoplasty showed that the grafts of APCS were epithelialized completely in 8+/-2 days, and their transparency was restored in 84+/-11 days when the light transmittance of APCS-transplanted corneas displayed no significant difference compared with native corneas. Corneal neovascularization, corneal deformation, and graft degradation were not observed within 12 months.

Immunogenicity and allogenicity: a challenge of stem cell therapy.

As age progresses, the regenerative power of one's own pluripotent stem cells is often inadequate to sustain normal tissue function. Consequently, the incidence of chronic and degenerative diseases has significantly increased. The derivation of adult tissues and organs from a variety of stem cell sources represents the starting mark for regenerative medicine. It is currently considered a developing mean to repair, restore, maintain, or enhance organ functioning through life span. Recent advances in human embryonic stem cells (hESC) research, however, made the prospect of cell replacement therapy even more compelling and highlighted hESC as a fast track in the therapeutic hope. Among the hurdles which have been largely overlooked in the excitement over the expected benefit is the immunogenicity. Indeed, beyond the clear need to establish the safety of hESC and their derived tissues in terms of tumorogenicity and potential to transmit infections, the challenge is to overcome the immunological barriers to their transplantation.

Existence of proviral porcine endogenous retrovirus in fresh and decellularised porcine tissues.

PURPOSE: Swine are expected to be utilized as xenograft donors for both whole organ and cellular transplantation. A major concern in using porcine organs for transplantation is the potential of transmission of porcine endogenous retrovirus (PERV). Tissue-engineered or decellularised heart valves have already been implanted in humans and have been marketed by certain companies after Food and Drug Administration (FDA) approval. The aim of this study was to examine the existence of porcine endogenous retrovirus (PERV) in fresh and decellularised porcine tissues. METHODS: Porcine tissues (both fresh and decellularised) were analysed using validated assays specific for PERV: polymerase chain reaction (PCR), reverse transcriptase polymerase chain reaction (RT-PCR). RESULTS: PERV specific GAG sequences were found in the porcine heart tissue samples using PCR for DNA and RT- PCR for RNA. All tissue samples (both fresh and treated tissues) like aortic valve, pulmonary valve and heart muscle showed the presence of PERV DNA. RT PCR for PERV was positive in all fresh tissues and was found to be negative in decellularised treated tissues. CONCLUSIONS: PCR is a rapid, specific test for the detection of PERV virus in xenografts. These findings have demonstrated that the presence of proviral DNA form of PERV in porcine tissues needs to be carefully considered when the infectious disease potential of xenotransplantation is being assessed.

Assessing infection risk in implanted tissue-engineered devices.

Peri-operative contamination is the major cause of biomaterial-associated infections, highly complicating surgical patient outcomes. While this risk in traditional implanted biomaterials is well-recognised, newer cell-seeded, biologically conducive tissue-engineered (TE) constructs now targeted for human use have not been assessed for this possibility. We investigated infection incidence of implanted, degradable polyester TE scaffold biomaterials in rabbit knee osteochondral defects. Sterile, polyester copolymer scaffolds of different compositions and cell-accessible pore volumes were surgically inserted into rabbit osteochondral defects for periods of 3 weeks up to 9 months, either with or without initial seeding with autologous or allogeneic chondrocytes. Infection assessment included observation of pus or abscesses in or near the knee joint and post-mortem histological evaluation. Of 228 implanted TE scaffolds, 10 appeared to be infected: 6 scaffolds without cell seeding (3.6%) and 4 cell-seeded scaffolds (6.3%). These infections were evident across all scaffold types, independent of polymer composition or available pore volume, and up to 9 months. We conclude that infections in TE implants pose a serious problem with incidences similar to current biomaterials-associated infections. Infection control measures should be developed in tissue engineering to avoid further complications when TE devices emerge clinically.

Progress and opportunities for tissue-engineered skin.

Tissue-engineered skin is now a reality. For patients with extensive full-thickness burns, laboratory expansion of skin cells to achieve barrier function can make the difference between life and death, and it was this acute need that drove the initiation of tissue engineering in the 1980s. A much larger group of patients have ulcers resistant to conventional healing, and treatments using cultured skin cells have been devised to restart the wound-healing process. In the laboratory, the use of tissue-engineered skin provides insight into the behaviour of skin cells in healthy skin and in diseases such as vitiligo, melanoma, psoriasis and blistering disorders.

Bio-mimetic composite matrix that promotes endothelial cell growth for modification of biomaterial surface.

The incidence of thrombogenesis and occlusion of cardiovascular implants is likely to be reduced by endothelial cell (EC) growth promotion on biomaterials used for device fabrication. However, proper signaling between the matrix proteins deposited on the device surface and the cells grown on it is a prime requirement for growth and function. It was demonstrated earlier that a composition of matrix proteins that include fibrin, fibronectin, gelatin, and growth factors maintain a steady proliferation potential and prolong the survival of endothelial cells in vitro. In this study, assessment of the same matrix to prevent EC from dedifferentiation during in vitro culture and to promote endothelialization of biomaterials used for fabrication of cardiovascular implants is carried out. Up/down regulation of m-RNA expression for a prothrombotic molecule-plasminogen activator inhibitor (PAI), and two antithrombotic molecules- nitric oxide synthetase (eNOS) and tissue plasminogen activator (t-PA) are chosen as the indicators of cell dedifferentiation during cell culture and passaging. Immunostaining for vinculin and actin demonstrated that composite coating on biomaterials improves focal adhesion and cytoskeletal organization that increases the quality of EC grown on it. EC proliferation, measured by (3)H-thymidine uptake, on all bare materials was poor and high incidence of cell apoptosis was noticed within 72 h in culture, whereas once coated with composite all materials showed good proliferation and survival. The results suggest that the designed composition of biomimetic adhesive proteins and growth factors is suitable for EC growth, survival, and functional integrity, thus making it suitable for cardiovascular tissue engineering that requires in vitro EC culture.

Inherent risks associated with manufacture of bioengineered ocular surface tissue.

OBJECTIVE: To review the potential health risks associated with bioengineered ocular surface tissue, which serves as a bellwether for other tissues. METHODS: All clinical trials using bioengineered ocular surface tissue published between July 1, 1996, and June 30, 2005, were reviewed with respect to materials used and statements of risk assessment, risk remediation, adverse events, manufacturing standards, and regulatory oversight. RESULTS: Ninety-five percent of investigational protocols used 1 or more animal-derived products and an overlapping 95% used 1 or more donor human tissues. Consideration of risks reveals a very low probability of potential harm but a significant risk of disability or death if such an event were to occur. Details of ethics approval, patient consent, and donor serologic test results were not consistently provided. No references were made to risk assessment or to codes of manufacturing and clinical practice. CONCLUSION: While a degree of risk is associated with bioengineered ocular surface tissue, investigational reports of this new technology have yet to address issues of risk management and regulatory oversight. CLINICAL RELEVANCE: Attention to risk and codes of manufacturing and clinical practice will be required for advancement of the technology. We suggest the adoption of international standards to address these issues.

Biological fate of tissue-engineered porcine valvular conduits xenotransplanted in the sheep thoracic aorta.

The ideal prosthesis to replace the diseased human aortic valve is not yet available. We have previously shown that porcine acellular aortic-valve conduits, obtained by detergent-enzymatic method, display hemodynamic performances similar to those of their native counterparts. Hence, it seemed worthwhile to ascertain whether these tissue-engineered prostheses can be successfully xenotransplanted. Porcine acellular conduits, which immunocytochemistry demonstrated to lack MHC class I and II antigens, were implanted in the thoracic aorta of 9 sheep. Two animals died just after surgery, and the other 7 sheep were sacrificed 1 or 5 months after transplantation. A rather favorable outcome of the implant was observed in 4 sheep. In these animals, aortic valves remained pliable and coaptive, and the luminal surface of the conduits was endothelized just after one month from surgery. An intense inflammatory response was present at 1 month, and, although attennuated, it persisted for 5 months, located mainly between the tunica intima and media and at the border of the implant. Vimentin-positive and smooth muscle actin-positive myofibroblasts proliferated within tunica media and adventitia, and an obvious thickening of the tunica intima was also observed. Small vessels were seen in the adventitia, and elastic fibers were well-preserved in both the aorta wall and valve leaflets. In the cases of unfavorable outcome (3 of 7 survived sheep), implants were detached from the aorta recipient and surrounded by a connective mass that almost completely obstructed their lumen. These masses were composed of a fibromyxoid background where proliferating cells, resembling those occurring in human reactive myofibroblastic lesions (proliferative fascitis), were embedded. Collectively, these rather disappointing findings indicate that acellular valve conduits, obtained by the detergent-enzymatic method, are presently not suitable for clinical applications because of the persistent inflammatory response, which conceivably triggers overgrowth mechanisms that lead to implant failure.

[Stem cell therapy for urinary incontinence]. / Stammzelltherapie der Harninkontinenz.

Experimental and clinical studies investigated whether urinary incontinence can be effectively treated with transurethral ultrasound-guided injections of autologous myoblasts and fibroblasts.This new therapy was performed in eight female pigs. It could be shown that the injected cells survived well and that new muscle tissue was formed. Next, 42 patients (29 women, 13 men) suffering from urinary stress incontinence were treated. The fibroblasts were mixed with a small amount of collagen as carrier material and injected into the urethral submucosa to treat atrophies of the mucosa. The myoblasts were directly injected into the rhabdosphincter to reconstruct the muscle and to heal morphological and functional defects. In 35 patients urinary incontinence could be completely cured. In seven patients who had undergone multiple surgical procedures and radiotherapy urinary incontinence improved. No side effects or complications were encountered postoperatively. The experimental as well as the clinical data clearly demonstrate that urinary incontinence can be treated effectively with autologous stem cells. The present data support the conclusion that this new therapeutic concept may represent a very promising treatment modality in the future.

Guided tissue regeneration: porcine matrix does not transmit PERV.

OBJECTIVE: For cardiovascular tissue engineering, acellularized scaffolds of porcine matrices have been successfully used. However, the possibility of porcine endogenous retrovirus (PERV) transmission remains debatable. In this study, we investigated whether acellularized porcine vascular scaffolds cause cross-species transmission of PERV in a xenogenic model. METHODS: Porcine pulmonary arteries were acellularized and implanted into sheep in orthotopic position (n=6). Cardiopulmonary bypass support was used for all operations. Blood samples were collected regularly up to 6 months after the operation, and cellular components were tested for PERV infection by PCR and RT-PCR. Grafts were explanted 6 and 12 months after implantation. Tissue samples were characterized by histology and electron microscopy and tested for PERV sequences. RESULTS: All animals survived the procedure and follow up until explantation of the grafts. PERV DNA was detectable in acellularized scaffolds of porcine matrices. Acellular porcine pulmonary arteries scaffolds were repopulated in vivo by autologous cells of the host, leading to a vessel consisting of all cellular components of the vessel wall. No PERV sequences were detectable neither in all tested peripheral blood samples nor in tissue samples of in vivo recellularized grafts up to 6 months after implantation. Electron microscopy revealed no signs of graft infection by retrovirus. CONCLUSIONS: Guided tissue regeneration of acellularized vascular porcine matrix scaffolds leads to structured vessels up to one year without risk of PERV transmisson.

Scaffolds and biomaterials for tissue engineering: a review of clinical applications.

Tissue engineering is a multidisciplinary area of research aimed at regeneration of tissues and restoration of organ function. This is achieved through implantation of cells/tissues grown outside the body or by stimulating cells to grow into an implanted matrix. In this short review, we discuss the use of biomaterials, in the form of scaffolds, for tissue engineering and review clinical applications to otorhinolaryngology-head and neck surgery.