Evaluation of biodegradable synthetic scaffold coated on arterial prostheses implanted in rat subcutaneous tissue

In vitro and in vivo degradation correlations for polyurethane foams with tunable degradation rates

Polyurethane foams present a tunable biomaterial platform with potential for use in a range of regenerative medicine applications. Achieving a balance between scaffold degradation rates and tissue ingrowth is vital for successful wound healing, and significant in vivo testing is required to understand these processes. Vigorous in vitro testing can minimize the number of animals that are required to gather reliable data; however, it is difficult to accurately select in vitro degradation conditions that can effectively mimic in vivo results. To that end, we performed a comprehensive in vitro assessment of the degradation of porous shape memory polyurethane foams with tunable degradation rates using varying concentrations of hydrogen peroxide to identify the medium that closely mimics measured in vivo degradation rates. Material degradation was studied over 12 weeks in vitro in 1%, 2%, or 3% hydrogen peroxide and in vivo in subcutaneous pockets in Sprague Dawley rats. We found that the in vitro degradation conditions that best predicted in vivo degradation rates varied based on the number of mechanisms by which the polymer degraded and the polymer hydrophilicity. Namely, more hydrophilic materials that degrade by both hydrolysis and oxidation require lower concentrations of hydrogen peroxide (1%) to mimic in vivo rates, while more hydrophobic scaffolds that degrade by oxidation alone require higher concentrations of hydrogen peroxide (3%) to model in vivo degradation. This information can be used to rationally select in vitro degradation conditions that accurately identify in vivo degradation rates prior to characterization in an animal model.

Decellularized Pancreas Matrix Scaffolds for Tissue Engineering Using Ductal or Arterial Catheterization

Introduction: Diabetes is known as a worldwide disease with a great burden on society. Since therapeutic options cover a limited number of target points, new therapeutic strategies in the field of regenerative medicine are considered. Bioscaffolds along with islet cells would provide bioengineered tissue as a substitute for β-cells. The perfusion-decellularization technique is considered to create such scaffolds since they mimic the compositional, architectural, and biomechanical nature of a native organ. In this study, we investigated 2 decellularization methods preserving tissue microarchitecture. Methods: Procured pancreas from Sprague-Dawley rats was exposed to different percentages of detergent for 2, 4, and 6 h after cannulation via the common bile duct or aorta. Results: High concentrations of sodium dodecyl sulfate (SDS), i.e., > 0.05%, resulted in tissue disruption or incomplete cell removal depending on the duration of exposure. In both methods, 6-h exposure to 0.05% SDS created a bioscaffold with intact extracellular matrices and proper biomechanical characteristics. Tissue-specific stainings revealed that elastic, reticular, and collagen fiber concentrations were well preserved. Quantitative findings showed that glycosaminoglycan content was slightly different, but hydroxyproline was in the range of native pancreas tissue. Dye infusion through ductal and vascular cannulation proved that the vascular network was intact, and scanning electron microscopy indicated a homogeneous porous structure. Conclusions: Using the detergent-based method, an effective and time-efficient procedure, a whole pancreas extracellular matrix bioscaffold can be developed that can be used as a 3D structure for pancreas tissue engineering-based studies and regenerative medicine applications.

A novel surgical technique for a rat subcutaneous implantation of a tissue engineered scaffold

Objectives

Subcutaneous implantations in small animal models are currently required for preclinical studies of acellular tissue to evaluate biocompatibility, including host recellularization and immunogenic reactivity.

Methods

Three rat subcutaneous implantation methods were evaluated in six Sprague Dawley rats. An acellular xenograft made from porcine pericardium was used as the tissue-scaffold. Three implantation methods were performed; 1) Suture method is where a tissue-scaffold was implanted by suturing its border to the external oblique muscle, 2) Control method is where a tissue-scaffold was implanted without any suturing or support, 3) Frame method is where a tissue-scaffold was attached to a circular frame composed of polycaprolactone (PCL) biomaterial and placed subcutaneously. After 1 and 4 weeks, tissue-scaffolds were explanted and evaluated by hematoxylin and eosin (H&E), Masson’s trichrome, Picrosirius Red, transmission electron microscopy (TEM), immunohistochemistry, and mechanical testing.

Results

Macroscopically, tissue-scaffold degradation with the suture method and tissue-scaffold folding with the control method were observed after 4 weeks. In comparison, the frame method demonstrated intact tissue scaffolds after 4 weeks. H&E staining showed progressive cell repopulation over the course of the experiment in all groups with acute and chronic inflammation observed in suture and control methods throughout the duration of the study. Immunohistochemistry quantification of CD3, CD 31, CD 34, CD 163, and αSMA showed a statistically significant differences between the suture, control and frame methods (P < 0.05) at both time points. The average tensile strength was 4.03 ± 0.49, 7.45 ± 0.49 and 5.72 ± 1.34 (MPa) after 1 week and 0.55 ± 0.26, 0.12 ± 0.03 and 0.41 ± 0.32 (MPa) after 4 weeks in the suture, control, and frame methods; respectively. TEM analysis showed an increase in inflammatory cells in both suture and control methods following implantation.

Conclusion

Rat subcutaneous implantation with the frame method was performed with success and ease. The surgical approach used for the frame technique was found to be the best methodology for in vivo evaluation of tissue engineered acellular scaffolds, where the frame method did not compromise mechanical strength, but it reduced inflammation significantly.

Development of intrinsically photoluminescent and photostable polylactones

A method of introducing intrinsically photo luminescent properties to biodegradable polymer is introduced, exemplified by the synthesis of intrinsically photoluminescent polylactones that enable non-invasive monitoring and tracking of material degradation in vivo in realtime, as well as the formation of theranostic nanoparticles for cancer imaging and drug delivery.

Biocompatibility and preclinical feasibility tests of a temperature-sensitive hydrogel for the purpose of surgical wound pain control and cartilage repair

We recently introduced a novel pluronic F127 and hyaluronic acid-based hydrogel (HG) designed to deliver a broad range of therapeutics. The reverse-thermal responsive HG exhibits physical properties that seem to be ideal for the local delivery of drug- and cell-based therapies to specific anatomic sites through percutaneous injection. However, questions related to the HG's safety and efficacy must first be addressed. To address these issues, we performed standard in vitro cytotoxicity and drug release tests and in vivo biocompatibility tests in a rat model. In addition, we determined whether the HG was an effective stem cell carrier in a rat cartilage defect model. We found that the HG showed viability and biocompatibility levels similar to those reported for F127 or hyaluronic acid alone. In vitro drug release studies with bupivacaine, a drug used clinically for local pain relief, revealed that after an initial burst bupivacaine was released continuously for 10 days. Stem cells loaded in the HG were retained in situ and stimulated cartilage regeneration in experimental defects. Taken as a whole, these findings support further efforts to develop the HG as a versatile system for the delivery of a wide range of therapeutic agents in humans. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.

Engineering a biocompatible scaffold with either micrometre or nanometre scale surface topography for promoting protein adsorption and cellular response

Surface topographical features on biomaterials, both at the submicrometre and nanometre scales, are known to influence the physicochemical interactions between biological processes involving proteins and cells. The nanometre-structured surface features tend to resemble the extracellular matrix, the natural environment in which cells live, communicate, and work together. It is believed that by engineering a well-defined nanometre scale surface topography, it should be possible to induce appropriate surface signals that can be used to manipulate cell function in a similar manner to the extracellular matrix. Therefore, there is a need to investigate, understand, and ultimately have the ability to produce tailor-made nanometre scale surface topographies with suitable surface chemistry to promote favourable biological interactions similar to those of the extracellular matrix. Recent advances in nanoscience and nanotechnology have produced many new nanomaterials and numerous manufacturing techniques that have the potential to significantly improve several fields such as biological sensing, cell culture technology, surgical implants, and medical devices. For these fields to progress, there is a definite need to develop a detailed understanding of the interaction between biological systems and fabricated surface structures at both the micrometre and nanometre scales.

Tissue responses against tissue-engineered cartilage consisting of chondrocytes encapsulated within non-absorbable hydrogel

To disclose the influence of foreign body responses raised against a non-absorbable hydrogel consisting of tissue-engineered cartilage, we embedded human/canine chondrocytes within agarose and transplanted them into subcutaneous pockets in nude mice and donor beagles. One month after transplantation, cartilage formation was observed in the experiments using human chondrocytes in nude mice. No significant invasion of blood cells was noted in the areas where the cartilage was newly formed. Around the tissue-engineered cartilage, agarose fragments, a dense fibrous connective tissue and many macrophages were observed. On the other hand, no cartilage tissue was detected in the autologous transplantation of canine chondrocytes. Few surviving chondrocytes were observed in the agarose and no accumulation of blood cells was observed in the inner parts of the transplants. Localizations of IgG and complements were noted in areas of agarose, and also in the devitalized cells embedded within the agarose. Even if we had inhibited the proximity of the blood cells to the transplanted cells, the survival of the cells could not be secured. We suggest that these cytotoxic mechanisms seem to be associated not only with macrophages but also with soluble factors, including antibodies and complements.

Vitamin E (α-tocopherol) addition modifies P(d,l)LA sponge degradation and protein release

Polylactic acid (PLA)-derived polymers are widely used in many biotechnological fields, thanks to their biocompatibility and resorbability through natural pathways. Moreover, PLA is one of the few polymers in which both the properties and the stereochemical structure can be easily modified, making possible a specific ‘tailoring’ of the final polymer according to the desired use. In this study, we obtained, by salt leaching technique, P(d,l)LA sponges in which various concentrations of α-tocopherol (Vit. E 10–40%, w/w) were incorporated. Vit.E is a natural biological antioxidant, also known to have anti-inflammatory activity, which has been extensively used to improve biostability and biocompatibility of different biomaterials. To assess whether Vit.E could modify the main physical–chemical properties of P(d,l)LA sponges, their morphology, water uptake and hydrolytic degradation kinetics, along with protein loading and releasing attitudes, were investigated. Our results highlighted that incorporation of Vit.E into P(d,l)LA sponges modified the sponge morphology, decreased P(d,l)LA water uptake and degradation, and modified protein releasing kinetics. These Vit.E-related effects could make P(d,l)LA more suitable as drug delivery system and tissue engineering scaffold.

Significance of novel bioinorganic anodic aluminum oxide nanoscaffolds for promoting cellular response

Tissue engineering is a multidisciplinary field that can directly benefit from the many advancements in nanotechnology and nanoscience. This article reviews a novel biocompatible anodic aluminum oxide (AAO, alumina) membrane in terms of tissue engineering. Cells respond and interact with their natural environment, the extracellular matrix, and the landscape of the substrate. The interaction with the topographical features of the landscape occurs both in the micrometer and nanoscales. If all these parameters are favorable to the cell, the cell will respond in terms of adhesion, proliferation, and migration. The role of the substrate/scaffold is crucial in soliciting a favorable response from the cell. The size and type of surface feature can directly influence the response and behavior of the cell. In the case of using an AAO membrane, the surface features and porosity of the membrane can be dictated at the nanoscale during the manufacturing stage. This is achieved by using general laboratory equipment to perform a relatively straightforward electrochemical process. During this technique, changing the operational parameters of the process directly controls the nanoscale features produced. For example, the pore size, pore density, and, hence, density can be effectively controlled during the synthesis of the AAO membrane. In addition, being able to control the pore size and porosity of a biomaterial such as AAO significantly broadens its application in tissue engineering.

Polymer coating of porcine decellularized and cross-linked aortic grafts

This article investigates a method of modifying and optimizing the biocompatibility of decellularized vascular bioimplants when treated with a specialized, drug eluting coating. For this purpose, we carried out aortic transplantations using a porcine model. Decellularized, cross-linked aortic grafts were coated with poly(D,L-lactide) (PDLLA). To this coating, we added the anticoagulant drug lepirudin which, following transplantation, would be linearly eluted. These aortic grafts are easily manipulated in surgery. It was shown that, as a result of the lepirudin-eluting coating, the rate of thrombogenesis was reduced and the patency rate was significantly improved. However, lumen-stenosing pseudointima developed in all of the transplants and was not effected by PDLLA coating. Furthermore, no evidence of recellularisation was documented. This trial demonstrates that polymer coating of decellularized tissue is possible. Neointimal hyperplasia and the absence of cellular repopulation mark the negative consequences of this concept.

Fabrication of porous gelatin microfibers using an aqueous wet spinning process

Alginate has a unique property of gel formation by chelating with divalent cations such as Ca(+2) in aqueous solution. The sol-gel characteristic of alginate has been utilized to fabricate both microsphere and microcapsule for cell immobilization. In this study, a wet spinning process was employed to prepare fibers comprised of gelatin and sodium alginate. Gelatin fibers containing interconnected porous structure were fabricated by the extraction of alginate from these gelatin/alginate composite fibers with phosphate buffer. The application of these porous gelatin fibers for enzyme immobilization was demonstrated by its usage as the base material of glucose biosensor.

The cultivation of human multipotent mesenchymal stromal cells in clinical grade medium for bone tissue engineering

Clinical application of human multipotent mesenchymal stromal cells (hMSCs) requires their expansion to be safe and rapid. We aimed to develop an expansion protocol which would avoid xenogeneic proteins, including fetal calf serum (FCS), and which would shorten the cultivation time and avoid multiple passaging. First, we have compared research-grade alpha-MEM medium with clinical grade CellGro for Hematopoietic Cells' Medium. When FCS was used for supplementation and non-adherent cells were discarded, both media were comparable. Both media were comparable also when pooled human serum (hS) was used instead of FCS, but the numbers of hMSCs were lower when non-adherent cells were discarded. However, significantly more hMSCs were obtained both in alpha-MEM and in CellGro supplemented with hS when the non-adherent cells were left in the culture. Furthermore, addition of recombinant cytokines and other supplements (EGF, PDGF-BB, M-CSF, FGF-2, dexamethasone, insulin and ascorbic acid) to the CellGro co-culture system with hS led to 40-fold increase of hMSCs' yield after two weeks of cultivation compared to alpha-MEM with FCS. The hMSCs expanded in the described co-culture system retain their osteogenic, adipogenic and chondrogenic differentiation potential in vitro and produce bone-like mineralized tissue when propagated on 3D polylactide scaffolds in immunodeficient mice. Our protocol thus allows for very effective one-step, xenogeneic protein-free expansion of hMSCs, which can be easily transferred into good manufacturing practice (GMP) conditions for large-scale, clinical-grade production of hMSCs for purposes of tissue engineering.

In vitro homogeneous and heterogeneous degradation of poly(ε-caprolactone/polyethylene glycol/L-lactide): The absence of autocatalysis and the role of enzymes

This study investigated the in vitro degradation behavior of poly(epsilon-caprolactone/polyethylene glycol/L-lactide) (PCEL) in comparison with that of three other biodegradable polymers. Polymer membranes were incubated in pancreatin solution, Ringer's solution, and distilled water at 37 degrees C for up to 20 weeks. Characterization involved measuring weight loss, observing the morphological changes by scanning electron microscopy (SEM), analyzing molecular weight using size exclusion chromatography (SEC), and studying the crystalline structure using differential scanning calorimetry (DSC). The hydrolysis in a simple aqueous solution experienced no autocatalysis, which was attributed to the high permeability of PCEL to water-soluble degradation products. Similar degradation rates were recorded for the PCEL and poly(L,L-lactide) (PLLA) test membranes. In the presence of pancreatin, the PCEL membrane experienced rapid heterogeneous surface erosion likely caused by the selective loss of its surface PEG components under enzymatic action. Pancreatin also substantially increased the even physical resorption of the other test polymers by eliminating autocatalysis. This study demonstrated that autocatalysis commonly experienced by poly(alpha-hydroxyl acid) can be reduced through chemical formulation or high enzyme activity.