Biomaterials For Tissue Engineering Applications Research Articles

Facile and rapid ruthenium mediated photo-crosslinking of Bombyx mori silk fibroin.

A facile and rapid ruthenium catalysed photo-crosslinking method was employed to prepare Bombyx mori silk fibroin hydrogels for the first time that may be used for biomedical applications. The gels have been characterised by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), photo-acoustic Fourier transform infrared spectroscopy (PA-FTIR), and X-ray diffraction (XRD). We have reported the tuning of the properties of the chemically crosslinked gels through hydration level. DSC and DMA measurements have shown that the molecular chain dynamics and mechanical properties are dependent on the moisture/water content. The structural changes upon gelation were examined through the use of DSC, PA-FTIR and XRD, which confirmed that the gels were less crystalline than the original silk powder. Finally, the biocompatibility and hence, the potential tissue engineering application of the silk fibroin hydrogel was also assessed by culturing chondrocyte progenitor cells for up to one week on the engineered fibroin surfaces.

Synthesis, Physicochemical Characterization, and Cytocompatibility of Bioresorbable, Dual-Gelling Injectable Hydrogels

Injectable, dual-gelling hydrogels were successfully developed through the combination of physical thermogellation at 37 °C and favorable amine:epoxy chemical cross-linking. Poly(N-isopropylacrylamide)-based thermogelling macromers with a hydrolyzable lactone ring and epoxy pendant groups and a biodegradable diamine-functionalized polyamidoamine cross-linker were synthesized, characterized, and combined to produce nonsyneresing and bioresorbable hydrogels. Differential scanning calorimetry and oscillatory rheometry demonstrated the rapid and dual-gelling nature of the hydrogel formation. The postgelation dimensional stability, swelling, and mechanical behavior of the hydrogel system were shown to be easily tuned in the synthesis and formulation stages. The leachable products were found to be cytocompatible under all conditions, while the degradation products demonstrated a dose- and time-dependent response due to solution osmolality. Preliminary encapsulation studies showed mesenchymal stem cell viability could be maintained for 7 days. The results suggest that injectable and thermally and chemically cross-linkable hydrogels are promising alternatives to prefabricated biomaterials for tissue engineering applications, particularly for cell delivery.

Silk gland fibroin from indian muga silkworm Antheraea assama as potential biomaterial

There is an increasing demand for new versatile biomaterials. Silk is reported by many researchers as an ideal biomaterial for different biomedical applications. Most of the studies are carried out on mulberry silk Bombyx mori, however silk from Indian non-mulberry silkworms are relatively unexplored. In this report we fabricate 2D matrices from the regenerated aqueous silk fibroin protein of the glands of non-mulberry Indian muga silkworm Antheraea assama (assamensis). Its biochemical, biophysical characteristics and its cytocompatibility for biomedical uses are evaluated. The properties of this muga gland fibroin are compared with silk gland fibroin from non-mulberry Indian tropical tasar silkworm Antheraea mylitta and with the fibroin from the cocoon of mulberry silkworm Bombyx mori. The gland fibroin of Antheraea assama is observed to consist of two polypeptides of approximately 250 kDa each linked by disulfide bond. Fourier transformed infrared spectroscopy and X-ray diffraction studies indicate random coil structure of dissolved fibroin solution. The alpha-helical structure in 2D films changed to beta-sheets upon ethanol treatment, imparting crystallinity and insolubility. The fibroin film is found to be the least hydrophilic, followed by B. mori and A. mylitta silk. Biocompatibility of the films from all three species is investigated through the cell attachment and spreading study of MG-63 human osteoblast-like cells. The cytocompatibility of non-mulberry fibroin matrices are comparable with that of standard tissue culture plates. The results indicate that the non-mulberry Indian muga silk gland fibroin is also suitable matrix as a natural biomaterial for tissue engineering applications.

In vivo acute and humoral response to three-dimensional porous soy protein scaffolds

Increasing interest in using soy biomaterials for tissue engineering applications has prompted investigation into the in vivo biocompatibility of soy implants. In this study, the biocompatibility of soy protein scaffolds fabricated using freeze-drying and 3-D printing was assessed using a subcutaneous implant model in BALB/c mice. The main objectives of this study were: (1) to compare soy protein with bovine collagen, a well-characterized natural protein implant, by implanting scaffolds of the same protein weight, and (2) to observe the effects of soy scaffold microstructure and amount of protein loading, which also alters the degradation properties, on the acute and humoral immune responses towards soy. Results showed that freeze-dried soy scaffolds fully degraded after 14days, whereas collagen scaffolds (of the same protein weight) remained intact for 56days. Furthermore, Masson’s trichrome staining showed little evidence of damage or fibrosis at the soy implant site. Scaffolds of higher soy protein content, however, were still present after 56days. H&E staining revealed that macrophage infiltration was hindered in the denser bioplotted soy scaffolds, causing slower degradation. Analysis of soy-specific antibodies in mouse serum after implantation revealed levels of IgG1 that correlated with higher scaffold weight and protein density. However, no soy-specific IgE was detected, indicating the absence of an allergic response to the soy implants. These results demonstrate that soy protein could be an acceptable biocompatible implant for tissue regeneration, and that scaffold porosity, soy protein density and scaffold degradation rate significantly affect the acute and humoral immune response.

Electrically Conducting Polymer-Based Nanofibrous Scaffolds for Tissue Engineering Applications

Conducting polymers are attractive biomaterials for tissue engineering applications as they can deliver electrical signals to cells for the regeneration of injured tissues. To make conducting materials relevant and effective as tissue engineering scaffolds, incorporation of three-dimensional features and contact guidance cues into conducting polymers would be desirable. Recent studies have demonstrated the development of conducting nanofibrous scaffolds, which can simultaneously provide both electrical and topographical cues to cells. These materials can be further modified to deliver biological signals to promote cell growth and differentiation of various types of cells. This review highlights recent progress in fabrication of electrically conducting polymer-based nanofibers and their applications as potential tissue engineering scaffolds.

Improved neural progenitor cell proliferation and differentiation on poly(lactide‐co‐glycolide) scaffolds coated with elastin‐like polypeptide

Poly(lactide-co-glycolide) (PLGA) and elastin-like polypeptide (ELP) have been widely used as a biodegradable scaffold and thermoresponsive matrix, respectively. However, little attention has focused on the combinatorial use of these biomaterials for tissue engineering applications. An ELP matrix TGPG[VGRGD(VGVPG)6]20WPC (referred to as REP) contains multiple Arg-Gly-Asp motifs. This study fabricated porous PLGA scaffolds coated with various concentration of matrix via thermally induced phase transition to improve adhesion-mediated proliferation and differentiation of neural progenitor cells. Matrix-coated scaffolds were characterized by FTIR, SEM, and hematoxylin and eosin staining with respect to coating efficiency, porosity, and pore size and shape. On the matrix-coated scaffolds, cells grew as a single cell or associated each other to form a multicellular layer or cluster. In biological evaluations, cell adhesion and proliferation were significantly promoted in a matrix concentration-dependent manner. More importantly, in combination with retinoic acid, the differentiation of progenitor cells into neuronal and astroglial lineages was highly stimulated in the cells cultured on matrix-coated scaffolds than on untreated controls. Taken together, our results indicated that the REP matrix-functionalized PLGA scaffolds are suitable for improving neuronal cell functions, and thus applicable for neural tissue engineering.

Nano/bio interface:impact on drug delivery applications.

With the advent of the rapidly growing field of nanotechnology that has ushered new opportunities to develop multifunctional biomedical nanoparticles, nanoscientists are learning about the extraand intracellular interactions with these nanoparticles. This special issue of Drug Delivery and Translational Research is dedicated to publishing selected deliberations relating to drug delivery in the first NanoBio Collaborative International Conference 2012 (NBCIC 2012) that was organized by the University of South Florida Nanomedicine Research Center and was held in March 22–24, 2012. The goal of this conference was to promote closer research ties and networking opportunities within the nanoscience community of the State of Florida and to foster and encourage collaborative research efforts among national and international centers of excellence in nanotechnology. NBCIC 2012 brought together engineers, chemists, physicists, biologists, and clinicians from across the globe to discuss recent advances, opportunities, and barriers in nanoscience and nanotechnology and its applications to diagnosing and treating disease. The conference was comprised of several symposia, including nanobioengineering applications, cell technologies and regenerative medicine, theranostics, nanodrug delivery, and translational nanomedicine. This special issue presents four state-of-the-art reviews and four research articles highlighting the application of nanotechnology to drug delivery that were discussed in the conference. Sir Harold Kroto, Nobel Laureate in Chemistry (1996), was a Keynote Speaker discussing his vision of nanoscience and nanotechnology in the twenty-first century and has written a preface for this issue. He provided examples of technology use in the future from medicine and molecular electronics to civil engineering. Expanding on medical applications, he stated “the drug industry has focused on the production of relatively simple molecules... these molecules are now highlighting incredibly exciting new directions for molecular biological research and challenging new perspectives for pharmaceutical research and development”. The last decade has seen progress in development of biomaterials for tissue engineering applications; however, self-assembling peptide scaffolds especially for delivery of drugs to injured tissues or organs have been poorly investigated. The first review by Veronica et al. reviews the application of self-assembling peptide scaffolds as an innovative platform for drug and cell delivery to restore cardiac tissue after myocardial infarction. Targeted drug delivery has been the holy grail of cancer therapy. The review article byYin et al. discusses cyclodextrinbased supramolecules, polymers, and nanoparticles bearing targeting moieties such as folates, estrogens, carbohydrates, and peptides as a promising drug delivery system. While effective delivery of therapeutics to the central nervous system (CNS) remains a formidable challenge, the article by Shah et al. reviews the major barriers to CNS delivery and nanotechnology-based solutions for effective drug delivery to the CNS. The article discusses different forms of nanoparticlebased drug delivery systems with emphasis on different modes of delivery to the brain and their safety issues. Last but not least, theranostic nanoparticles that combine both therapeutic and imaging modalities has the promise to revolutionalize diagnosis, treatment, and post-therapy monitoring. The review of Howell et al. summarizes recent developments in theranostic platforms, their advantages and disadvantages in the diagnosis and treatment of various S. Mohapatra (*) Department of Molecular Medicine, and USF Nanomedicine Research Center, Morsani College of Medicine, University of South Florida, Tampa, FL, USA e-mail: smohapa2@health.usf.edu

Techniques for fabrication and construction of three-dimensional scaffolds for tissue engineering

Three-dimensional biomimetic scaffolds have widespread applications in biomedical tissue engineering because of their nanoscaled architecture, eg, nanofibers and nanopores, similar to the native extracellular matrix. In the conventional “top-down” approach, cells are seeded onto a biocompatible and biodegradable scaffold, in which cells are expected to populate in the scaffold and create their own extracellular matrix. The top-down approach based on these scaffolds has successfully engineered thin tissues, including skin, bladder, and cartilage in vitro. However, it is still a challenge to fabricate complex and functional tissues (eg, liver and kidney) due to the lack of vascularization systems and limited diffusion properties of these large biomimetic scaffolds. The emerging “bottom-up” method may hold great potential to address these challenges, and focuses on fabricating microscale tissue building blocks with a specific microarchitecture and assembling these units to engineer larger tissue constructs from the bottom up. In this review, state-of-the-art methods for fabrication of three-dimensional biomimetic scaffolds are presented, and their advantages and drawbacks are discussed. The bottom-up methods used to assemble microscale building blocks (eg, microscale hydrogels) for tissue engineering are also reviewed. Finally, perspectives on future development of the bottom-up approach for tissue engineering are addressed.

Nanofibrous Structure of Chitosan for Biomedical Applications

Over the past decade, there has been a strong growing interest in using several forms of chitosan, more specifically nanofibers, for various biomedical applications. Chitosan has several impressive biological characteristics including but are not limited to its great biocompatibility and biodegradability, anti-bacterial properties, and cytocompatibility. In order to create nanofibers from this natural polymer, the electrospinning has been widely used as the most effective technique to produce a stable structure. Overtime, a number of challenges have been overcome through the development of mechanically and structurally intact, biocompatible and multi-functional nanofibers. The recent progress of the nanofibrous structure of chitosan and their biomedical applications in tissue engineering, drug delivery, wound dressing, and antimicrobial are discussed.

Multi-hierarchical self-assembly of a collagen mimetic peptide from triple helix to nanofibre and hydrogel

Replicating the multi-hierarchical self-assembly of collagen has long-attracted scientists, from both the perspective of the fundamental science of supramolecular chemistry and that of potential biomedical applications in tissue engineering. Many approaches to drive the self-assembly of synthetic systems through the same steps as those of natural collagen (peptide chain to triple helix to nanofibres and, finally, to a hydrogel) are partially successful, but none simultaneously demonstrate all the levels of structural assembly. Here we describe a peptide that replicates the self-assembly of collagen through each of these steps. The peptide features collagen's characteristic proline-hydroxyproline-glycine repeating unit, complemented by designed salt-bridged hydrogen bonds between lysine and aspartate to stabilize the triple helix in a sticky-ended assembly. This assembly is propagated into nanofibres with characteristic triple helical packing and lengths with a lower bound of several hundred nanometres. These nanofibres form a hydrogel that is degraded by collagenase at a similar rate to that of natural collagen.

Endothelialized biomaterials for tissue engineering applications in vivo.

Rebuilding tissues involves the creation of a vasculature to supply nutrients and this in turn means that the endothelial cells (ECs) of the resulting endothelium must be a quiescent non-thrombogenic blood contacting surface. Such ECs are deployed on biomaterials that are composed of natural materials such as extracellular matrix proteins or synthetic polymers in the form of vascular grafts or tissue-engineered constructs. Because EC function is influenced by their origin, biomaterial surface chemistry and hemodynamics, these issues must be considered to optimize implant performance. In this review, we examine the recent in vivo use of endothelialized biomaterials and discuss the fundamental issues that must be considered when engineering functional vasculature.

Comparison of the adhesion and proliferation characteristics of HUVEC and two endothelial cell lines (CRL 2922 and CRL 2873) on various substrata

Endothelial cell coverage of blood-contacting devices is crucial to their eventual success in the clinic. Two established human cell lines derived from HUVEC (human umbilical vascular endothelial cells), CRL 2922 and CRL 2873, have been widely utilized to study and model endothelial cell biology. However, it is not clear if these two cell lines would be useful for modeling primary endothelial cell interaction with newly-formulated biomaterials in tissue engineering applications. Hence, this study was conducted to compare the adhesion and proliferation characteristics of HUVEC grown on seven different substrata, tissue culture polystyrene (TCPS), gelatin, chitosan, poly-L-lysine, hyaluronan, poly-L-lactic acid (PLLA), and polylactic-co-glycolic acid (PLGA). The short-term adhesive behavior (2 h) of HUVEC on the various substrata was not closely-replicated by either CRL 2873 or CRL 2922. This was likely because the 2 h timeframe is too short for identification of differences in the interaction among the three cell types grown on various substrata. There was much faster proliferation of CRL 2922 on all seven substrata when compared to HUVEC and CRL 2873. Moreover, the proliferation rates of CRL 2922 on the various substrata showed little variation. In contrast, HUVEC and CRL 2873 displayed similar trends in proliferation rates, with gelatin and TCPS yielding the highest rates, and PLLA and PLGA yielding the lowest rates. Hence, CRL 2873 is better suited for modeling primary endothelial cell interaction with newly-formulated biomaterials than CRL 2922. The advantage of using CRL 2873 over HUVEC for biomaterial screening is that it is immortalized and displays much less inter-batch variability than primary culture.

Poly[octanediol‐co‐(citric acid)‐co‐(sebacic acid)] elastomers: novel bio‐elastomers for tissue engineering

AbstractThis review focuses on a new class of elastomers, namely poly[octanediol‐co‐(citric acid)‐co‐(sebacic acid)] (p(OCS)), synthesised from 1,8‐octanediol, citric acid and sebacic acid in a catalyst‐free polyesterification reaction. The review begins with a detailed description of the synthesis, characterisation and structure–property–performance relationship of some reported elastomers suitable for tissue engineering. The control of the physicochemical properties of the new p(OCS) by simple variation of initial monomer concentrations in polyesterification forms the pivotal part of the synthesis. As tissue engineering requires complex designs, thin films and porous three‐dimensional structures of p(OCS) were fabricated to demonstrate their ease of processing. The fundamental material properties of p(OCS) are discussed for p(OCS) pre‐polymers and final polymers. The elastomers exhibit versatility in mechanical properties, hydration and hydrolytic degradation, as determined by their chemical structure. Surface analysis of spin‐coated p(OCS) suggests that the surface morphology, chemistry and concentration of the surface functional groups can be controlled simply by varying the initial citric acid/sebacic acid concentration in polyesterification. These tunable molecular architectures and material properties are crucial in biological interactions. Thein vitrobiocompatibility testing of p(OCS) with MG63 osteoblast‐like cells suggests that p(OCS) is an excellent candidate for potential elastic biomaterials for tissue engineering applications without the need for any post‐synthesis modification. Copyright © 2011 Society of Chemical Industry

Polymeric Biomaterials for Tissue Engineering Applications 2011

Polymeric Biomaterials for Tissue Engineering Applications 2011

Porous Scaffolds Based on Cross‐Linking of Poly(L‐glutamic acid)

Porous scaffolds based on water-soluble PLGA and CS were prepared. The pores were verified to be alveolate, uniform and continuous. The effects of freezing temperature, freeze-drying time, solid content and molecular weight of reactants on the pore structure of the scaffolds were studied. The scaffold morphology could be adjusted by changing the freezing temperature and solid content of reacting polymer. Their degradation rate can be adjusted by changing the proportion of PLGA and CS. The porosity of scaffolds was higher than 90% and the high swelling ratio showed that these scaffolds had excellent hydrophilic performance. The in vitro culture of chondrocytes indicates that the obtained PLGA/CS porous scaffolds are very promising biomaterials for tissue engineering applications.

Morphology of Photopolymerized End-Linked Poly(ethylene glycol) Hydrogels by Small-Angle X-ray Scattering

Due to the biocompatibility of poly(ethylene glycol) (PEG), PEG-based hydrogels have attracted considerable interest for use as biomaterials in tissue engineering applications. In this work, we show that PEG-based hydrogels prepared by photopolymerization of PEG macromonomers functionalized with either acrylate or acrylamide end-groups generate networks with crosslink junctions of high functionality. Although the crosslink functionality is not well controlled, the resultant networks are sufficiently well ordered to generate a distinct correlation peak in the small angle x-ray scattering (SAXS) related to the distance between crosslink junctions within the PEG network. The crosslink spacing is a useful probe of the PEG chain conformation within the hydrogel and ranges from approximately 6 to 16 nm, dependent upon both the volume fraction of polymer and the molecular weight of the PEG macromonomers. The presence of a peak in the scattering of photopolymerized PEG networks is also correlated with an enhanced compressive modulus in comparison to PEG networks reported in the literature with much lower crosslink functionality that exhibit no scattering peak. This comparison demonstrates that the method used to link together PEG macromonomers has a critical impact on both the nanoscale structure and the macroscopic properties of the resultant hydrogel network.

Effects of surfactant and gentle agitation on inkjet dispensing of living cells

Inkjet dispensing is a promising method for patterning cells and biomaterials for tissue engineering applications. In a novel approach, this work uses a biocompatible surfactant to improve the reliability of droplet formation in piezoelectric drop-on-demand inkjet printing of Hep G2 hepatocytes onto hydrogels. During a long printing process, cell aggregation and sedimentation within the inkjet reservoir can lead to inconsistent printing results. In order to improve repeatability, the effects of gentle agitation on cell sedimentation and aggregation within the inkjet reservoir were also investigated. Cell viability and proliferation when printed onto prepared collagen substrates were assessed using live/dead staining and the Alamar Blue metabolic assay. The addition of 0.05% Pluronic as a surfactant did not reduce cell viability, which remained above 95% 2 days after printing. The surfactant improved the reliability of droplet formation. Although gentle stirring of the inkjet reservoir was sufficient to maintain a cell suspension and reduce sedimentation, aggregation within the suspension continued to affect printing performance over a 180 min printing period.

Collagen-Based Biomaterials for Tissue Engineering Applications

Collagen is the most widely distributed class of proteins in the human body. The use of collagen-based biomaterials in the field of tissue engineering applications has been intensively growing over the past decades. Multiple cross-linking methods were investigated and different combinations with other biopolymers were explored in order to improve tissue function. Collagen possesses a major advantage in being biodegradable, biocompatible, easily available and highly versatile. However, since collagen is a protein, it remains difficult to sterilize without alterations to its structure. This review presents a comprehensive overview of the various applications of collagen-based biomaterials developed for tissue engineering, aimed at providing a functional material for use in regenerative medicine from the laboratory bench to the patient bedside.

Physical surface and electromechanical properties of doped polypyrrole biomaterials

Conducting polymers doped with biomolecules (biodopants) are becoming more widely evaluated for use as biomaterials. The use of biodopants is intended to enhance the compatibility of the polymers, however their effect on the physical properties of the final composite material has generally been less of a consideration. Here, we have characterised the physical surface properties of polypyrrole substrates doped with extracellular matrix and non-biological molecules using Atomic Force Microscopy (AFM) and Electrochemical AFM (EC-AFM) techniques. The physical parameters of the differently doped films ranged between 5 and 32 nm for the RMS roughness, 30–1000 MPa for the Young's modulus, and 1.6–4.7% for the actuation strain. It was found that irrespective of whether the dopant was biologically derived, the physical properties tended to group together with films having either a low roughness, low modulus and high strain, or vice versa. When compared to our previous study, which investigated these polymers as potential biomaterials for supporting the growth and differentiation of skeletal muscle cells, these two groupings of the parameters correlated with the differing ability of the polypyrrole substrates to support the cells. Thus, in addition to the chemical advantage gained from using biodopants, the resulting physical properties of the polymer material should also be considered in their design as biomaterials for tissue engineering applications.

Polymeric Biomaterials for Tissue Engineering Applications

1Department of Materials Science & Engineering, The University of Tennessee, Knoxville, TN 37996, USA 2Departments of Biomedical Engineering and Orthopaedic Surgery, Mayo Clinic College of Medicine, Rochester, MN 55905, USA 3Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA 4Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China 5 School of Chemistry, University of Leeds, Leeds LS2 9JT, UK