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Patients have benefited greatly from the steady stream of new medical devices approved each year by the US Food and Drug Administration and by regulatory agencies in countries around the world. But the number of such devices for tissue engineering and regenerative medicine is just a small fraction of these, perhaps 7 of the 194 devices (<5%) approved by the FDA since 2008 [1]. Few new tissue engineering and regenerative medicine devices have reached the clinic despite the proliferation of biomaterial matrices/scaffolds, cells, and regulators of cell function (e.g., growth factors); i.e., the three types of tool currently available for implantation or injection into a specific type of defect to facilitate regeneration (the paradigm of regenerative medicine), or for the formation of tissues and organs in vitro for subsequent implantation (the tissue engineering plan). While the number of new tools added to the tissue engineer's toolbox each year is continuing to grow dramatically, there are few tools being implemented for the production of new medical devices undergoing human trial (figure 1). What are the bottlenecks in getting the tools out of the toolbox and into clinical use to advance patient care?

Figure 1. The many ideas generated for biomaterials (B), cells (C), and regulators of cell function (R) as tools for tissue engineering and regenerative medicine generally first undergo testing in the laboratory to determine if their physical and biological properties are suitable for the anticipated clinical application. Many of those that successfully pass this first screening may go directly into the toolbox, while others undergo further testing in an in vivo model before being accepted for the toolbox (in this schematic two of the four failed the in vivo test). It is only relatively few tools in the toolbox that are then evaluated in a definitive animal model for the targeted clinical application. Of these, certain tools may fail when tested individually (as shown by the dashed blue line), but succeed when evaluated in judicious combination (dashed ellipse) with other tools.

The supposition of this editorial is that our toolbox already likely contains the solutions to many clinical problems, but there are two specific issues contributing to the holdup in the translation of tools to clinical use: (1) the necessity of using select tools in combination; and (2) the need for the systematic evaluation of such combinations of tools in a definitive animal model (figure 1), with the attendant challenge of funding. Dealing with issues to accelerate the implementation of tools for the production of medical devices for use in the clinic is, of course, of paramount importance to the patients with a myriad of problems waiting for medical devices to prolong their lives and/or improve the quality of the life that they have. Funding agencies need to know how to deal with these issues in order to judiciously allocate their financial resources, and companies/investors would like to know for obvious reasons. And journals, too, need to know the answers to questions related to the implementation of our tools in order to inform their scope and to select the most meaningful papers for publication, to do their part in disseminating important knowledge for the good of science and health.

Today's toolbox

What does the tissue engineer's toolbox look like? Quite a bit different from the little black bag which physicians in the 19th and first half of the 20th century used to carry in hand when they visited patients in their homes; that as small as it was, could contain all of the most essential tools available at the time. The tissue engineer's toolbox (also, the 'regeneration medic's bag') needs to have three quite different compartments to be able to accommodate: (1) the pre-formed biomaterial matrices and the liquid formulations of polymers that will undergo gelation once injected into the body; (2) the many cell types available for use; and (3) the regulatory molecules and apparatus to control the behavior of cells and tissues (figure 1). Over the past two decades numerous discoveries and technologies have enabled tissue engineering and regenerative medicine, and have filled our toolbox to its brim. The technologies include methods for the: synthesis of absorbable polymeric and mineral scaffolds with a wide range of properties; synthesis of limitless quantities of regulatory proteins using recombinant and other technologies; and isolation and proliferation in vitro of differentiated cell types, and stem and progenitor cells which can be driven along specific differentiation pathways. The development of these technologies underlying the generation of new tools has been driven by biomedical scientists and engineers dedicated to searching for solutions to medical problems and stimulated by the process of discovery. Moreover, professional interests and the financial rewards attendant to the commercial development of these agents for tissue regeneration, and the support of funding agencies and desire of journals for novelty, have motivated the generation of new tools.

But the bonanza in the types and numbers of tools resulting from these discoveries and technologies has not been followed by windfalls of new medical devices introduced into the clinic. Why haven't we yet been able to identify which existing tools to use clinically? One answer, and way forward, may relate to the necessity of evaluating the efficacy of tools in combination in clinically-relevant, controlled animal studies.

Necessity (and power) of tools in combination

The hope of a tool developer is that the agent may be the solution to a clinical problem. As new tools are developed they are generally tested individually in the laboratory to determine their properties relevant to select clinical applications, and the cellular responses that they elicit in vitro (figure 1). In vivo investigations may be conducted to evaluate certain features of the tissue response, and collectively assessments can be made regarding the safety and clinical 'promise' of the tool. But relatively few tools are then tested in combination with other tools to see if the desired effect is further enhanced. One of the challenges is that the knowledge and resources necessary for the handling and evaluation of the three types of tools can be quite different, necessitating a dedicated effort of the tool developer to venture out of his/her own area and to obtain collaborative assistance.

For the treatment of some medical problems a single tool can have a profoundly beneficial effect. But for most applications is it not more likely that a combination of tools will be necessary to achieve the desired outcome? Regeneration which occurs spontaneously in the body (e.g., bone regeneration) is due to an exquisite choreography of many extracellular matrix and regulatory molecules and cell types. One exogenous therapeutic agent may initiate a cascade of processes involving many endogenous processes, but it is more likely that several tools will have to be delivered in conjunction in some fashion to achieve a meaningful degree of regeneration or improved reparative response. One notable example is the FDA-approved medical device, Medtronic's Infuse Bone Graft ®, which is a combination of bone morphogenetic protein (BMP)-2, an osteoinductive regulator of cell function, in an absorbable collagen sponge (ACS). Either tool (i.e., BMP-2 or ACS) employed alone has little effectiveness in stimulating an osteogenic response, but in combination they are a potent product to stimulate bone formation, even at ectopic sites [2]. A second example is a scaffold implanted or injected into a cavitary defect in order to provide an exogenous matrix permissive of endogenous cell migration into the matrix-filled defect. Adding a chemoattractant to the matrix would likely recruit a greater number of the target cells into the defect. For example, incorporation of nanoparticles delivering stromal cell-derived factor (SDF)-1α, a known chemoattractant for endogenous neural stem and progenitor cells in the brain, was found to increase substantially the number of such cells migrating into matrices in vitro [3]. Many other examples relate to cell therapies, which normally involve a bolus injection of an aqueous suspension of cells. Incorporation of the cells into a pre-formed or injectable matrix which also delivers certain regulatory molecules could serve to retain the cells at the desired site and provide them with the necessary cues to regulate their function. For example, in a rat model, subretinal injection of retinal stem-progenitor cells in hyaluronic acid-methylcellulose [4] and in hyaluronic acid [5] matrices resulted in a more even distribution of the cells than could be achieved with injection of the cells in a saline solution, and was permissive of differentiation of the progenitor cells into photoreceptor cells [5].

Failure of a tool to live up to expectations may only signal that it requires certain adjunctive agents to achieve clinical effectiveness.

Systematic evaluation of tools in the most clinically-relevant animal model

How to definitively test the tools already in the toolbox, whether alone or in combination? One straightforward answer could be the implementation of a standardized animal model for a specific clinical problem for the systematic testing of various tools. While many of the tools in our toolbox have been tested in vivo , relatively few have been evaluated in an animal model that is recognized as being the most meaningful for a specific disorder. For example, there are rat models that have been employed for the pre-clinical testing of agents for the treatment of some of the most complex and complicated of problems, the central nervous system disorders of stroke [6, 7], spinal cord injury [8, 9], and retinal disease [10]. Agents that have yielded positive results in certain of these rat models have proceeded directly to human trial, reflecting the relevance of the models. Evaluation of various tools in the same animal model for comparison with relevant controls and with each other would: identify the products in our toolbox ready for human trial; guide the selection of other tools to test; and inform the development of new tools. What then are the obstacles to employing an animal model to test various combinations of tools in a systematic fashion?

One obstacle, of course, is that validated animal models do not yet exist for many medical problems. That the absence of a definitive animal model is the bottleneck for the translation of tools from the toolbox to the clinic, further underscores the importance of animal model development. But even when accepted animal models are available, an obstacle to the systematic evaluation of combinations of tools is that not all tool developers have the background to conduct the animal work, and the groups that routinely employ the animal model or those that have the capability to do so, may not be engaged in work dealing with the local delivery of therapeutic agents, and may not be in range of collaborators who know how to handle such tools. And even when the groups with the necessary skills get together, it takes time and effort for each to climb their respective learning curves, to validate the model in their hands, and to learn to work together.

Another obstacle to the systematic evaluation of tools, likely to be encountered, is funding. More than ever, most federal agencies prize novelty of the project as the principal criterion for funding, based on the understandable (but as we see here, uncertain) supposition that if a solution to a clinical problem had already been found (i.e., if a useful tool already existed) it would have been implemented; therefore, the need to conceive and investigate new tools. This obstacle to funding also generally applies to foundations even though they may be heavily supported by the patients who likely would be inclined to explore options currently in the toolbox in parallel to the continued search for new tools. And this approach of funding the testing of existing tools is not likely to appeal to commercial concerns whose basis for the evaluation of a tool is principally and understandably whether it is their intellectual property.

Finally, still another obstacle to the comparative testing of the tools already in our toolbox is finding a journal to publish such studies unless there is a notable success, which may take many trials to achieve. The challenge here, of course, is to formulate the study at the outset with working hypotheses or research questions and outcome metrics that are meaningful even if the principal goal of a successful treatment is not achieved. But there is no denying that that reports of the systematic evaluation of existing agents for the treatment of a clinical problem, no matter how profound, may be perceived as uninspired by reviewers.

Getting tools out of the toolbox and into patients

So how do we answer the patient who grabs our toolbox and entreats: isn't there already something in here that can help me? Shouldn't the simple answer be: we are currently conducting such tests. We do need more tools, and they are sure to come with the new knowledge being acquired from ongoing scientific investigations, but we also need to test the tools that we already have, in standardized animal models which have some of the features of the human condition to be treated. There is generally enough knowledge about how the tools will function and about past failures to make informed and rational decisions as to which combinations of tools to test. Perhaps an increasing awareness of the current situation by funding agencies and pressure from patient-advocacy groups will elevate this work to a higher priority. As regards publication of results of such testing, this journal has always appreciated the importance of in vivo evaluation of biomaterial matrices, alone or in combination with the other tools of tissue engineering, and will continue to see this work as compelling for dissemination to the scientific and clinical communities.

Perhaps this assessment of the current state of affairs will make the case for a 'tissue engineer's toolbox manifesto ': the systematic evaluation of combinations of existing tools in the definitive animal model by a consortium of laboratories? Don't we owe it to the patients who are counting on us to overcome these obstacles to execute this manifesto?

Acknowledgments

The author gratefully acknowledges the important contributions of Jonathan M Spector, MD, and Teck Chuan Lim, BS.

References

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Silver nanoparticles (Ag NPs) were synthesized rapidly in one pot via the Tollens reaction, in which quaternized chitosan (QCS) and rectorite (REC) acted as the reducing and stabilizing agent, while other chemical reducing and stabilizing agents and the surfactant were not included. X-ray diffraction, scanning electron microscopy and transmission electron microscopy results showed that spherical Ag NPs with uniform sizes were obtained, the layers of clay were peeled and thus exfoliated QCS/REC/Ag NP (QCRAg) nanocomposite was achieved. Moreover, Ag NPs dispersed well in the exfoliated nanocomposite matrix, some Ag NPs even entered into the interlayer of REC. QCRAg nanocomposites showed strong antimicrobial activity; the lowest minimum inhibitory concentration against Staphyloccocus aureus was only 0.0001% (w/v). The study reveals that the obtained QCRAg nanocomposites have great potential for biomedical applications.

Noting the abundance and importance of collagen as a biomaterial, we have developed a facile method for the production of a dense fibrillar extracellular matrix mimicking collagen–elastin hybrids with tunable mechanical properties. Through the use of excimer-laser technology, we have optimized conditions for the ablation of collagen lamellae without denaturation of protein, maintenance of fibrillar ultrastructure and preservation of native D-periodicity. Strengths of collagen–elastin hybrids ranged from 0.6 to 13 MPa, elongation at break from 9 to 70% and stiffness from 2.9 to 94 MPa, allowing for the design of a wide variety of tissue specific scaffolds. Further, large (centimeter scale) lamellae can be fabricated and embedded with recombinant elastin to generate collagen–elastin hybrids. Exposed collagen in hybrids act as cell adhesive sites for rat mesenchymal stem cells that conform to ablate waveforms. The ability to modulate these features allows for the generation of a class of biopolymers that can architecturally and physiologically replicate native tissue.

β beta-tricalcium phosphate (β-TCP) granules are suitable for repair of bone defects. They have an osteoconductive effect shortly after implantation. However, dry granules are difficult to handle in the surgical room because of low weight and lack of cohesion. Incorporation of granules in a hydrogel could be a satisfactory solution. We have investigated the use of hyaluronic acid (HyA) as an aqueous binder of the granules. β-TCP granules were prepared by the polyurethane foam technology. Commercially available linear (LHya) and reticulated hyaluronic acid (RHyA) in aqueous solution were used to prepare a pasty mixture that can be handled more easily than granules alone. Thirteen New Zealand White rabbits (3.5–3.75 kg) were used; a 4 mm hole was drilled in each femoral condyle. After flushing, holes were filled with either LHyA, RHyA, dry β-TCP granules alone, β-TCP granules + LHyA and β-TCP granules + RHyA. Rabbits were allowed to heal for one month, sacrificed and femurs were harvested and analysed by microCT and histomorphometry. The net amount of newly formed bone was derived from measurements done after thresholding the microCT images for the material and for the material+bone. LHyA and RHyA did not result in healing of the grafted area. LHyA was rapidly eluted from the grafted zone but allowed deposition of more granules, although the amount of formed bone was not significantly higher than with β-TCP granules alone. RHyA permitted the deposition of more granules which induced significantly more bone trabeculae without inducing an inflammatory reaction. RHyA appears to be a good vehicle to implant granules of β-TCP, since HyA does not interfere with bone remodeling.

Since acid etching is easily controlled and effective, it has become one of the most common methods of surface modification. However, the behavior of etching is seldom discussed. In this study, different surfaces of titanium were prepared by changing the etching temperature and time. Surface topography, roughness, contact angles, surface crystalline structure, hydrogen concentration and mechanical properties were observed. As a result, surface topography and roughness were more proportional to etching temperature; however, diffusion of hydrogen and tensile strength are more time-related to titanium hydride formation on the surface. Titanium becomes more hydrophilic after etching even though the micropits were not formed after etching. More and deeper cracks were found on the specimens with more hydrogen diffusion. Therefore, higher temperature and shorter time are an effective way to get a uniform surface and decrease the diffusion of hydrogen to prevent hydrogen embrittlement.

The classical simulated body fluids method cannot be employed to prepare biomimetic apatites encompassing metallic ions that lead to very stable phosphates. This is the case for heavy metals such as uranium, whose presence in bone mineral after contamination deserves toxicological study. We have demonstrated that existing methods, based on alternate dipping into calcium and phosphate ions solutions, can be adapted to achieve this aim. We have also especially studied the impact of the presence of carbonate ions in the medium as these are necessary to avoid hydrolysis of the contaminating metallic cations. Both the apatite–collagen complex method and a standard chemical (STD) method employing only mineral solutions lead to biomimetic apatites when calcium and carbonate ions are introduced simultaneously. The obtained materials were fully characterized and we established that the STD method tolerates the presence of carbonate ions much better, and this leads to homogeneous samples. Emphasis was set on the repeatability of the method to ensure the relevancy of further work performed on series of samples. Finally, osteoblasts cultured on these samples also proved a similar yield and standard-deviation in their adenosine triphosphate content when compared to commercially available substrates designed to study of such cell cultures.

In this study, an artificial multi-functional extracellular matrix (ECM) protein, tethered with a growth factor, was developed for neurite outgrowth induction. The designed ECM protein was comprised of an elastin-like peptide, as a structural unit, as well as the AG73 peptide sequence derived from the laminin and the C3 peptide sequence, which binds to neural cell adhesion molecules (derived from a synthetic peptide library) as functional units. Both AG73 and C3 have been demonstrated to promote cell adhesion and enhance neurite outgrowth. For the tethering of basic fibroblast growth factor (bFGF) to the ECM protein, helical peptides were fused to the ECM protein to form a coiled-coil helical structure with helical peptide-fused bFGF. Neurite outgrowth was induced in the PC12 cells that were cultured on this ECM protein as a result of the tethered-bFGF. Moreover, neurite outgrowth was enhanced by the AG73 and C3 peptides of the ECM protein.

Binary biocomposites were realized by combining yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) with a bioactive glass matrix. Few works are available regarding composites containing zirconia and a relatively high content of glass because the resulting samples are usually biocompatible but not bioactive after thermal treatment. In the present research, the promising properties of the new BG_Ca–K glass, with its low tendency to crystallize and high apatite-forming ability, allowed us to sinter the composites at a relatively low temperature with excellent effects in terms of bioactivity. In addition, it was possible to benefit from the good mechanical behaviour of Y-TZP, thus obtaining samples with microhardness values that were among the highest reported in the literature. After a detailed analysis regarding the thermal behaviour of the composite powders, the sintered bodies were fully characterized by means of x-ray diffraction, SEM equipped with EDS, density measurements, volumetric shrinkage determination, mechanical testing and in vitro evaluation in a simulated body fluid (SBF) solution. According to the experimental results, the presence of Y-TZP improved the mechanical performance. Meanwhile, the BG_Ca–K glass, which mainly preserved its amorphous structure after sintering, provided the composites with a good apatite-forming ability in SBF.

Magnesium (Mg) and its alloys are being widely investigated for their potential use as resorbable biomaterials for orthopaedic applications. However, the natural corrosion of the metals results in potentially harmful perturbations to the physiological environment, which requires a comprehensive understanding of their biocompatibility. Currently, most investigations proceed directly from in vitro biocompatibility studies to intraosseous implantation. However, this can result in the unnecessary elimination of appropriate materials due to over sensitive in vitro methods or the implantation of potentially harmful materials. This study involved the development of a relevant in vitro cell culture method, and an in vivo soft tissue implantation technique to provide an intermediate step between basic cell culture methods and large animal intraosseous investigations. A Live/Dead fluorescent assay was used to investigate the viability of both L929 and SaOS-2 cells exposed to Mg alloys, with the results compared to those seen with the intramuscular implantation of the same materials in Lewis rats. These methods were able to successfully provide data on the corrosion of Mg alloys, allowing the identification of slowly and safely corroding materials that may be used in future intraosseous investigations.

Biodegradable chitosan-graft-polylactide (PLA–CS) copolymers were prepared by the grafting of a poly(L-lactide) (PLLA) or poly(D-lactide) (PDLA) precursor to the backbone of chitosan using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC ⋅ HCl) and N-hydroxysuccinimide (NHS) as a coupling agent. The blood and cell compatibility of the graft copolymers were investigated in comparison to PLLA and PDLA homopolymers. The coagulation properties of PLA–CS were evaluated by hemolysis, plasma recalcification, dynamic blood clotting and protein absorption assays. PLA–CS copolymers present similar hemolysis ratio and plasma recalcification time as PLA, but slower dynamic blood clotting and lower protein absorption. The cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), agar diffusion and lactate dehydrogenase (LDH) experiments. All the samples presented no effect on the viability to cells. Inflammatory cytokine analysis using sandwich ELISAs revealed that PLA–CS would not stimulate inflammatory activity.

The potential for a successful integration of implants with surrounding tissue may be jeopardized in a number of compromised conditions. Biochemical surface modification is one of the choices to extend the spectrum of indications. We have previously successfully fabricated chitosan–gelatin (CS/G) coatings on a titanium surface via electrophoretic deposition, which may be promising candidates for further loading of functional agents. In this study, we have identified the microstructure, physicochemical properties and biological performance of CS/G coatings in vitro and in vivo. The in vitro degradation test indicated that CS/G coatings in the presence of lysozyme showed a significant weight loss after 28 days. The results of the cell culture exhibited that CS/G coatings could sustain MC3T3-E1 cell attachment, proliferation and migration. In vivo osteogenetic behavior evaluated by Micro-CT and histomorphometrical analysis revealed significant new bone formation around CS/G implants at 8 and 12 weeks, compared to sandblasted/acid-etched implants. Moreover, histological evaluation suggested the majority of CS/G coatings were degraded at 12 weeks. Therefore, we have concluded that the three-dimensional porous structure of scaffold-like CS/G coatings may facilitate osteogenesis and that such coatings can be biodegraded in the early bone healing process.

This paper reports a novel approach for the formation of anti-inflammatory surface coating on a neural electrode. The surface coating is realized using a recombinant f88 filamentous bacteriophage, which displays a short platinum binding motif and a tumor necrosis factor alpha antagonist (TNF-α antagonist) on p3 and p8 proteins, respectively. The recombinant bacteriophages are immobilized on the platinum surface by a simple dip coating process. The selective and stable immobilization of bacteriophages on a platinum electrode is confirmed by quartz crystal microbalance with dissipation monitoring, atomic force microscope and fluorescence microscope. From the in vitro cell viability test, the inflammatory cytokine (TNF-α) induced cell death was prevented by presenting recombinant bacteriophage coating, albeit with no significant cytotoxic effect. It is also observed that the bacteriophage coating does not have critical effects on the electrochemical properties such as impedance and charge storage capacities. Thus, this approach demonstrates a promising anti-apoptotic as well as anti-inflammatory surface coating for neural implant applications.

An integrated approach is proposed to incorporate silicon and silver into hydroxyapatite (HA) to enhance the biological response and reduce implant-related infection in bone substitutes. This study examined the responses of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria to silver, silicon-containing apatite (Ag,Si-HA). Scanning electron microscopy images revealed significant reduction in adherence of S. aureus and E. coli bacteria on Ag,Si-HA as compared to HA. The antibacterial property of Ag,Si-HA was shown from a 7-log reduction of S. aureus population in the test solution and on the sample's surface as compared to HA at day 7. Rapid inhibition of the adherent bacteria suggested that the antibacterial action of Ag incorporated in Ag,Si-HA could be attributed to the Ag⁺ ions on the crystal surface rather than the released Ag⁺ ions. Presence of Ag may influence the biological response of HA and as such, the long-term interaction between human adipose-derived mesenchymal stem cells and Ag,Si-HA was evaluated in-vitro. An alamarBlue™ assay showed higher cell proliferation for Ag,Si-HA as compared to HA from day 3 onwards. Immunofluorescence staining revealed well-spread actin cytoskeletons on Ag,Si-HA. In addition, signs of extracellular matrix secretion and biomineralization were observed on Ag,Si-HA at day 14 onwards. Results demonstrated enhanced bone differentiation on Ag,Si-HA, as indicated by a higher level of protein expressions (type 1 collagen and osteocalcin) from day 14 to 21. Therefore, the incorporation of Ag and Si complement each other by endowing HA with antibacterial property, and concurrently promoting biological performance of the cells.

Thermosensitive hydrogels are renowned carriers that are used to deliver a variety of drugs with the aim of combating diseases. In this study, the injectability of thermosensitive hydrogels comprised of poly(ethylene glycol)-poly(lactic acid-co-glycolic acid)-poly(ethylene glycol) (PEG-PLGA-PEG, PELGE) and hydroxyapatite (HA) were examined for their ability to deliver bone morphological protein 2 (BMP-2). The physicochemical characteristics of PELGE, HA, and PELGE/HA hydrogel composites were investigated by ¹H NMR, GPC, FTIR, XRD, SEM, and TEM. The rheological properties, injectability, in vitro degradation, and in vivo biocompatibility were investigated. The hydrogel with a weight ratio of 4:6 of polymer to HA was found to be resistant to auto-catalyzed degradation of acidic monomers (LA, GA) for a period of 70 days owing to the presence of alkaline HA. Injectability was quantitatively determined by the ejected weight of the hydrogel composite at room temperature and was a close match to the weight amount predetermined by the syringe pump. The results not only revealed that the PELGE/HA hydrogel composite presented a minor tissue response in the subcutis of ICR mice at eight weeks, but they also indicated an acceptable tolerance of the hydrogel composite in animals. Thus, PELGE/HA hydrogel composite is expected to be a promising injectable orthopedic substitute because of its desirable thermosensitivity and injectability.

Acellular porcine small intestinal submucosa (SIS) has been successfully used for reconstructing esophagus with half circumferential defects. However, repairing full circumferential esophageal defects with SIS has been restricted due to the latter's poor mechanical properties. In the present study, synthetic polyesters biomaterial poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and poly(lactide-co-glycolide) (PLGA) have been used to improve the mechanical properties of SIS. Feasibility of SIS/PHBHHx-PLGA composite material scaffold for esophageal tissue engineering has been assessed through a series of testing. The appropriate mixing ratio of PHBHHx and PLGA polymers has been determined as 5:5 by mechanical testing and in vitro degradation experiment. The morphology of constructed membranous and tubular scaffolds was also characterized. As confirmed by enzyme-linked immunosorbent assay, the contents of VEGF and TGF-β have respectively reached 657 ± 18 ng mL⁻¹ and 130 ± 4 pg mL⁻¹ within the SIS/PHBHHx-PLGA specimens. Biocompatibility of the SIS/PHBHHx-PLGA specimens with rat bone marrow mesenchymal stem cells (MSCs) was also evaluated by scanning electron microscopy and a live–dead cell viability assay. Actin filaments of MSCs on the composite materials were labeled. Biological safety of the extract from SIS/PHBHHx-PLGA specimens, measured as hemolysis rate, was all lower than 5%. Compared with SIS and SIS/PHBHHx-PLGA specimens, inflammatory reaction provoked by the PHBHHx-PLGA specimens in rats was however more severe. Our results have suggested that SIS/PHBHHx-PLGA composite material can offer a new approach for esophageal tissue engineering.

Understanding the distribution of critical elements (e.g. silicon and calcium) within silica-based bone scaffolds synthesized by different methods is central to the optimization of these materials. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to determine this information due to its very high surface sensitivity and its ability to map all the elements and compounds in the periodic table with high spatial resolution. The SIMS image data can also be combined with depth profiles to construct three-dimensional chemical maps. However, the scaffolds have interconnected pore networks, which are very challenging structures for the SIMS technique. To overcome this problem two experimental methodologies have been developed. The first method involved the use of the focused ion beam technique to obtain clear images of the regions of interest and subsequently mark them by introducing fiducial marks; the samples were then analysed using the ToF-SIMS technique to yield the chemical analyses of the regions of interest. The second method involved impregnating the pores using a suitable reagent so that a flat surface could be achieved, and this was followed by secondary ion mapping and 3D chemical imaging with ToF-SIMS. The samples used in this work were sol–gel 70S30C foam and electrospun fibres and calcium-containing silica/gelatin hybrid scaffolds. The results demonstrate the feasibility of both these experimental methodologies and indicate that these methods can provide an opportunity to compare various artificial bone scaffolds, which will be of help in improving scaffold synthesis and processing routes. The techniques are also transferable to many other types of porous material.

As one of the most important potential candidate alloys for vascular stent application, Mg–Y–Zr based Mg–4.2wt%Y–2.4wt%Nd–0.6wt%Ce(La)–0.5wt%Zr (WE43) alloys were investigated in combination with the forming processes of micro-tubes with 2.0 mm diameter and 0.1 mm wall thickness. Orthogonal experimental design for alloy composition, vacuum melting ingot, heat treatment, integrated plastic deformation and micro-tube forward extrusion are included in the processing procedures. Significant improvements in both the mechanical properties and corrosion resistance in phosphate buffered saline solution for WE43 alloys were achieved through this processing sequence. The influence of the heat treatment and hot extrusion on in vitro degradation and plasticity was found to be associated with grain size reduction and the redistribution of intermetallic particles within the microstructure. As a result, the mechanical properties and the corrosion resistance of Mg alloys can be improved through fine-grain strengthening and solid-solution strengthening to some extent.

Recent experimental studies have shown the suitability of silk fibroin scaffold (SFS) and porcine-derived acellular collagen I/III scaffold (ACS) as onlay graft materials for tympanic membrane perforation repair. The aims of this study were to further characterize and evaluate the in vivo biocompatibility of SFS and ACS compared with commonly used materials such as Gelfoam and paper in a rat model. The scaffolds were implanted in subcutaneous (SC) tissue and middle ear (ME) cavity followed by histological and otoscopic evaluation for up to 26 weeks. Our results revealed that SFS and ACS were well tolerated and compatible in rat SC and ME tissues throughout the study. The tissue response adjacent to the implants evaluated by histology and otoscopy showed SFS and ACS to have a milder tissue response with minimal inflammation compared to that of paper. Gelfoam gave similar results to SFS and ACS after SC implantation, but it was found to be associated with pronounced fibrosis and osteoneogenesis after ME implantation. It is concluded that SFS and ACS both were biocompatible and could serve as potential alternative scaffolds for tissue engineering in the ear.