The development of fibronectin-functionalised hydroxyapatite coatings to improve dermal fibroblast attachment in vitro

Soft Tissue Augmentation by Electrospun Membranes embedded With Nano-Hydroxyapatite: Histologic and Volumetric Analyses

PURPOSE

The aim of this study was to assess the histologic and volumetric alteration in gingival tissues following grafting with electrospinning collagen membranes blended with nanophased hydroxyapatite (nHA) on the buccal side of canine teeth.

METHODS

Four adult beagle dogs underwent hemisecting of the mandibular premolars, followed by the extraction of the mesial roots. Soft tissue augmentations were randomly conducted with collagen membranes composed of poly (L-Lactic-co-caprolactone) and porcine fibrinogen (PLCL/F-Fg), PLCL/F-Fg membranes blended with nHA (PLCL/F-Fg/nHA), or a sham-operated control. The animals were sacrificed at 12 weeks post-surgery and received volumetric analyses. Histological examinations at the meantime were carried out at five different depths below the crest (0, 1.5, 2.5, 3.5 and 5.5 mm).

RESULTS

Histological examinations showed a statistically significant increase in buccal gingival thickness between PLCL/F-Fg/20%nHA and PLCL/F-Fg (3.82 ± 1.56mm vs 1.78 ± 0.20mm (at 3.5 mm); 4.23 ± 0.63mm vs 1.80 ± 0.58mm (at 5.5 mm)) as well as between PLCL/F-Fg/20%nHA and PLCL/F-Fg/10%nHA (4.23 ± 0.63mm vs 1.97 ± 0.73mm (at 5.5 mm)). Volumetric analyses showed a statistically significant decrease in volume reduction between PLCL/F-Fg/20%nHA and PLCL/F-Fg (4.46 ± 2.75mm3 vs 10.27 ± 4.77mm3) as well as between PLCL/F-Fg/20%nHA and PLCL/F-Fg/10%nHA (4.46 ± 2.75mm3 vs 10.57 ± 2.88mm3).

CONCLUSION

PLCL/F-Fg/20%nHA membranes demonstrated effectiveness in the gingival thickness augmentation on the buccal side of canine teeth at 12 weeks postsurgery. The electrospinning collagen membranes blended with nHA rendered an alternative treatment for soft tissue volume augmentations at the pontic site.

Basic science review of transcutaneous osseointegration: current status, research gaps and needs, and defining future directions

Basic science research is vital for advancing the emerging field of bone-anchored limb replacement (BALR), or osseointegration (OI). This article discusses clinical challenges for BALR/OI, summarizes current basic science research regarding those challenges, identifies research gaps, and proposes future directions. OI research draws from related fields such as orthopaedic implants and dentistry. There is a need for small animal models to study critical questions related to osseointegration, including OI implant-associated infections. Small animal models are also critical to ensuring safety and efficacy of novel treatments in this vulnerable population. Key issues include infection prevention through implant surface modifications, biofilm-targeting technologies, and antimicrobial advancements. The skin-implant portal, unique to BALR, also poses significant challenges. Research on skin attachment and inflammatory processes is crucial. Noninfectious inflammatory loosening of implants, though infrequent, needs further investigation. This review emphasizes the need for collaborative efforts to develop effective preclinical models and innovative infection prevention strategies. Addressing these challenges is essential for optimizing patient outcomes and advancing this emerging field.

Skin adhesion to the percutaneous component of direct bone anchored systems: systematic review on preclinical approaches and biomaterials

Nowadays, direct bone anchored systems are an increasingly adopted approach in the therapeutic landscape for amputee patients. However, the percutaneous nature of these devices poses a major challenge to obtain a stable and lasting proper adhesion between the implant surface and the skin. A systematic review was carried out in three databases (PubMed, Scopus, Web of Science) to provide an overview of the innovative strategies tested with preclinical models (in vitro and in vivo) in the last ten years to improve the skin adhesion of direct bone anchored systems. Fifty five articles were selected after screening, also employing PECO question and inclusion criteria. A modified Cochrane RoB 2.0 tool for the in vitro studies and the SYRCLE tool for in in vivo studies were used to assess the risk of bias. The evidence collected suggests that the implementation of porous percutaneous structures could be one of the most favorable approach to improve proper skin adhesion, especially in association with bioactive coatings, as hydroxyapatite, and exploiting the field of nanostructure. Some issues still remain open as (a) the identification and characterization of the best material/coating association able to limit the shear stresses at the interface and (b) the role of keratinocyte turnover on the skin/biomaterial adhesion and integration processes.

Fibronectin grafting to enhance skin sealing around transcutaneous titanium implant

Intraosseous transcutaneous amputation prosthesis is a new approach in orthopedic implants that overcomes socket prosthesis problems. Its long-term performance requires a tight skin-implant seal to prevent infections. In this study, fibronectin (Fn), a widely used adhesion protein, was adsorbed or grafted onto titanium alloy. Fn grafting was performed using two different linking arms, dopamine/glutaric anhydride or phosphonate. The characterization of Fn-modified surfaces showed that Fn grating via phosphonate has led to the highest amount of Fn cell-binding site (RGD, arginine, glycine, and aspartate) available on the surface. Interestingly, cell culture studies revealed a strong correlation between the amount of available RGD ligands and cellular behavior, since enhanced proliferation and spreading of fibroblasts were noticed on Fn-grafted surfaces via phosphonate. In addition, an original in vitro mechanical test, inspired from the real situation, to better predict clinical outcomes after implant insertion, has been developed. Tensile test data showed that the adhesion strength of a bio-engineered dermal tissue was significantly higher around Fn-grafted surfaces via phosphonate, as compared to untreated surfaces. This study sheds light on the importance of an appropriate selection of the linking arm to tightly control the spatial conformation of biomolecules on the material surface, and consequently cell interactions at the interface tissue/implant.

New prospects in skin regeneration and repair using nanophased hydroxyapatite embedded in collagen nanofibers

This study reflects an exploitation of a composite matrix produced by electrospinning of collagen and electrospraying of nanophased hydroxyapatite (nanoHA), for skin regeneration applications. The main goal was to evaluate the effect of nanoHA, as source of localized calcium delivery, on human dermal fibroblasts, keratinocytes, and human mesenchymal stem cells (hMSCs) growth, proliferation, differentiation, and extracellular matrix production. This study revealed that calcium ions provided by nanoHA significantly enhanced cellular growth and proliferation rates and prevented adhesion of pathogenic bacteria strains typically found in human skin flora. Moreover, hMSCs were able to differentiate in both osteogenic and adipogenic lineages. Rat subcutaneous implantation of the membranes also revealed that no adverse reaction occurred. Therefore, the mechanically fit composite membrane presents a great potential to be used either as cell transplantation scaffold for skin wound regeneration or as wound dressing material in plastic surgery, burns treatment or skin diseases.

Aptamer-Functionalized Natural Protein-Based Polymers as Innovative Biomaterials

Biomaterials science is one of the most rapidly evolving fields in biomedicine. However, although novel biomaterials have achieved well-defined goals, such as the production of devices with improved biocompatibility and mechanical properties, their development could be more ambitious. Indeed, the integration of active targeting strategies has been shown to allow spatiotemporal control of cell-material interactions, thus leading to more specific and better-performing devices. This manuscript reviews recent advances that have led to enhanced biomaterials resulting from the use of natural structural macromolecules. In this regard, several structural macromolecules have been adapted or modified using biohybrid approaches for use in both regenerative medicine and therapeutic delivery. The integration of structural and functional features and aptamer targeting, although still incipient, has already shown its ability and wide-reaching potential. In this review, we discuss aptamer-functionalized hybrid protein-based or polymeric biomaterials derived from structural macromolecules, with a focus on bioresponsive/bioactive systems.

PTH(1‑34) activates the migration and adhesion of BMSCs through the rictor/mTORC2 pathway

The ability of intermittent parathyroid hormone (1-34) [PTH(1-34)] treatment to enhance bone-implant osseo-integration was recently demonstrated in vivo. However, the mechanisms through which PTH (1-34) regulates bone marrow-derived stromal cells (BMSCs) remain unclear. The present study thus aimed to investigate the effects of PTH(1-34) on the migration and adhesion of, and rictor/mammalian target of rapamycin complex 2 (mTORC2) signaling in BMSCs. In the present study, BMSCs were isolated from Sprague-Dawley rats treated with various concentrations of PTH(1-34) for different periods of time. PTH(1-34) treatment was performed with or without an mTORC1 inhibitor (20 nM rapamycin) and mTORC1/2 inhibitor (10 µM PP242). Cell migration was assessed by Transwell cell migration assays and wound healing assays. Cell adhesion and related mRNA expression were investigated through adhesion assays and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), respectively. The protein expression of chemokine receptors (CXCR4 and CCR2) and adhesion factors [intercellular adhesion molecule 1 (ICAM-1), fibronectin and integrin β1] was examined by western blot analysis. The results revealed that various concentrations (1, 10, 20, 50 and 100 nM) of PTH(1-34) significantly increased the migration and adhesion of BMSCs, as well as the expression of CXCR4, CCR2, ICAM-1, fibronectin and integrin β1. In addition, the p-Akt and p-S6 levels were also upregulated by PTH(1-34). BMSCs subjected to mTORC1/2 signaling pathway inhibition or rictor silencing exhibited a markedly reduced PTH-induced migration and adhesion, while no such effect was observed for the BMSCs subjected to mTORC1 pathway inhibition or raptor silencing. These results indicate that PTH(1-34) promotes BMSC migration and adhesion through rictor/mTORC2 signaling in vitro. Taken together, the results of the present study reveal an important mechanism for the therapeutic effects of PTH(1-34) on bone-implant osseointegration and suggest a potential treatment strategy based on the effect of PTH(1-34) on BMSCs.

The state of the art of osseointegration for limb prosthesis

Osseointegration (OI) is the direct attachment of bone onto a titanium implant. Recently, the term is used to describe "transdermal" implants that allow an external prosthesis to be connected directly to the skeleton. This technology eliminates the challenges of conventional socket-based prostheses, such as skin breakdown and poor fit, which are common in patients with major extremity amputations. Osseointegration patients demonstrate encouraging improvements in quality of life and function. Patients report improvement in prosthetic use, prosthetic mobility, global health, and pain reduction on a variety of clinical assessment tools. Various implants have been developed for osseointegration for amputees. These implants use a variety of fixation strategies and surface augments to allow for successful integration into the host bone. Regardless of design, all OI implants face similar challenges, particularly infections. Other challenges include the inability to determine when integration has occurred and the inability to detect loss of integration. These challenges may be met by incorporating sensing systems into the implants. The percutaneous nature of the metal devices can be leveraged so that internal sensors need not be wireless, and can be interrogated by external monitoring systems, thus providing crucial, real-time information about the state of the implant. The purpose of this review is to (1) review the basic science behind osseointegration, (2) provide an overview of current implants, practice patterns, and clinical outcomes, and (3) preview sensor technologies which may prove useful in future generations of transdermal orthopaedic implants.

Future Research Directions in the Design of Versatile Extracellular Matrix in Tissue Engineering

Native and artificial extracellular matrices (ECMs) have been widely applied in biomedical fields as one of the most effective components in tissue regeneration. In particular, ECM-based drugs are expected to be applied to treat diseases in organs relevant to urology, because tissue regeneration is particularly important for preventing the recurrence of these diseases. Native ECMs provide a complex in vivo architecture and native physical and mechanical properties that support high biocompatibility. However, the applications of native ECMs are limited due to their tissue-specificity and chemical complexity. Artificial ECMs have been fabricated in an attempt to create a broadly applicable scaffold by using controllable components and a uniform formulation. On the other hands, artificial ECMs fail to mimic the properties of a native ECM; consequently, their applications in tissues are also limited. For that reason, the design of a versatile, hybrid ECM that can be universally applied to various tissues is an emerging area of interest in the biomedical field.

The impact of photofunctionalized gold nanoparticles on osseointegration

OBJECTIVES

The aims of this study were to create a new surface topography using simulated body fluids (SBF) and Gold Nanoparticles (GNPs) and then to assess the influence of UV Photofunctionalization (PhF) on the osteogenic capacity of these surfaces.

MATERIALS AND METHODS

Titanium plates were divided into six groups All were acid etched with 67% Sulfuric acid, 4 were immersed in SBF and 2 of these were treated with 10 nm GNPs. Half of the TiO2 plates were photofunctionalized to be compared with the non-PhF ones. Rat's bone marrow stem cells were seeded into the plates and then CCK8 assay, cell viability assay, immunofluorescence, and Scanning electron microscopy (SEM) were done after 24 hours. Gene expression analysis was done using real time quantitative PCR (qPCR) one week later to check for the mRNA expression of Collagen-1, Osteopontin and Osteocalcin. Alkaline phosphatase (ALP) activity was assessed after 2 weeks of cell seeding.

RESULTS

Our new topography has shown remarkable osteogenic potential. The new surface was the most biocompatible, and the 10 nm GNPs did not show any cytotoxicity. There was a significant increase in bioactivity, enhanced gene expressions and ALP activity.

CONCLUSIONS

GNPs enhances osteogenic differentiation of stem cells and Photofunctionalizing GNPs highly increases this. We have further created a novel highly efficient topography which highly enhances the speed and extent of osseointegration. This may have great potential for improving treatment outcomes for implant, maxillofacial as well as orthopedic patients.

An important step towards a prevascularized islet macroencapsulation device-effect of micropatterned membranes on development of endothelial cell network

The development of immune protective islet encapsulation devices could allow for islet transplantation in the absence of immunosuppression. However, the immune protective membrane / barrier introduced there could also impose limitations in transport of oxygen and nutrients to the encapsulated cells resulting to limited islet viability. In the last years, it is well understood that achieving prevascularization of the device in vitro could facilitate its connection to the host vasculature after implantation, and therefore could provide sufficient blood supply and oxygenation to the encapsulated islets. However, the microvascular networks created in vitro need to mimic well the highly organized vasculature of the native tissue. In earlier study, we developed a functional macroencapsulation device consisting of two polyethersulfone/polyvinylpyrrolidone (PES/PVP) membranes, where a bottom microwell membrane provides good separation of encapsulated islets and the top flat membrane acts as a lid. In this work, we investigate the possibility of creating early microvascular networks on the lid of this device by combining novel membrane microfabrication with co-culture of human umbilical vein endothelial cell (HUVEC) and fibroblasts. We create thin porous microstructured PES/PVP membranes with solid and intermittent line-patterns and investigate the effect of cell alignment and cell interconnectivity as a first step towards the development of a stable prevascularized layer in vitro. Our results show that, in contrast to non-patterned membranes where HUVECs form unorganized HUVEC branch-like structures, for the micropatterned membranes, we can achieve cell alignment and the co-culture of HUVECs on a monolayer of fibroblasts attached on the membranes with intermittent line-pattern allows for the creation of HUVEC branch-like structures over the membrane surface. This important step towards creating early microvascular networks was achieved without the addition of hydrogels, often used in angiogenesis assays, as gels could block the pores of the membrane and limit the transport properties of the islet encapsulation device.

Strategies for Optimizing the Soft Tissue Seal around Osseointegrated Implants

Percutaneous and permucosal devices such as catheters, infusion pumps, orthopedic, and dental implants are commonly used in medical treatments. However, these useful devices breach the soft tissue barrier that protects the body from the outer environment, and thus increase bacterial infections resulting in morbidity and mortality. Such associated infections can be prevented if these devices are effectively integrated with the surrounding soft tissue, and thus creating a strong seal from the surrounding environment. However, so far, there are no percutaneous/permucosal medical devices able to prevent infection by achieving strong integration at the soft tissue-device interface. This review gives an insight into the current status of research into soft tissue-implant interface and the challenges associated with these interfaces. Biological soft/hard tissue interfaces may provide insights toward engineering better soft tissue interfaces around percutaneous devices. In this review, focus is put on the history and current findings as well as recent progress of the strategies aiming to develop a strong soft tissue seal around osseointegrated implants, such as orthopedic and dental implants.

The in vivo effect of a porous titanium alloy flange with hydroxyapatite, silver and fibronectin coatings on soft-tissue integration of intraosseous transcutaneous amputation prostheses

Aims

The Intraosseous Transcutaneous Amputation Prosthesis (ITAP) may improve quality of life for amputees by avoiding soft-tissue complications associated with socket prostheses and by improving sensory feedback and function. It relies on the formation of a seal between the soft tissues and the implant and currently has a flange with drilled holes to promote dermal attachment. Despite this, infection remains a significant risk. This study explored alternative strategies to enhance soft-tissue integration.

Materials and Methods

The effect of ITAP pins with a fully porous titanium alloy flange with interconnected pores on soft-tissue integration was investigated. The flanges were coated with fibronectin-functionalised hydroxyapatite and silver coatings, which have been shown to have an antibacterial effect, while also promoting viable fibroblast growth in vitro. The ITAP pins were implanted along the length of ovine tibias, and histological assessment was undertaken four weeks post-operatively.

Results

The porous titanium alloy flange reduced epithelial downgrowth and increased soft-tissue integration compared with the current drilled flange. The addition of coatings did not enhance these effects.

Conclusion

These results indicate that a fully porous titanium alloy flange has the potential to increase the soft-tissue seal around ITAP and reduce susceptibility to infection compared with the current design.

Cite this article: Bone Joint J 2017;99-B:393–400.

Enhanced intracellular signaling pathway in osteoblasts on ultraviolet lighttreated hydrophilic titanium

Ultraviolet (UV) light treatment of titanium immediately prior to use, or photofunctionalization, reactivates the time-dependent degradation of bioactivity of titanium (biological aging of titanium) and increases its osseointegration capacity beyond the inherent maximal level. Although the initial osteoblast attachment is reportedly enhanced on UV-treated titanium surfaces, the detailed mechanism behind the increase in osseointegration is unknown. This study examined the potential modulation of intracellular signaling pathway in osteoblasts on UV-treated titanium surfaces. Rat bone marrow-derived osteoblasts were cultured on 4-week-old, new, and UV-treated titanium surfaces. The new and UV-treated surfaces were superhydrophilic, whereas the 4-week-old surface was hydrophobic. Although the rate of protein adsorption was similarly increased on the new and UV-treated surfaces compared with the 4-week-old surface, the number of attached cells and their spreading behavior were further enhanced on the UV-treated surface. This additional enhancement was associated with the remarkably upregulated expression of paxillin and phospho-paxillin and exclusive upregulation of Rho GTPase family genes. This study provides with the first molecular evidence of the enhanced initial behavior of osteoblasts on UV-treated titanium surfaces. The enhancement was accentuated and distinct from the new titanium surface with similar hydrophilicity, suggesting that surface properties other than the level of hydrophilicity are responsible.

Improved scaffold biocompatibility through anti-Fibronectin aptamer functionalization

Protein adsorption is the first and decisive step to define cell-biomaterial interaction. Guiding the adsorption of desired protein species may represent a viable approach to promote cell activities conducive to tissue regeneration. The aim of the present study was to investigate whether immobilized anti-Fibronectin aptamers could promote the attachment and growth of osteoblastic cells. Polyethyleneglycole diacrylate/thiolated Hyaluronic Acid hydrogels (PEGDA/tHA) were coated with anti-Fibronectin aptamers. Hydrogel loading and Fibronectin bonding were investigated, through spectrophotometry and Bradford assay. Subsequently, human osteoblasts (hOBs) were cultured on hydrogels for 10days in 2D and 3D cultures. Cells were monitored through microscopy and stained for focal adhesions, microfilaments and nuclei using fluorescence microscopy. Samples were also included in paraffin and stained with Hematoxylin-Eosin. Cell number on hydrogels was quantitated over time. Cell migration into the hydrogels was also studied through Calcein AM staining. Aptamers increased the number of adherent hOBs and their cytoplasm appeared more spread and richer in adhesion complexes than on control hydrogels. Viability assays confirmed that significantly more cells were present on hydrogels in the presence of aptamers, already after 48h of culture. When hOBs were encapsulated into hydrogels, cells were more numerous on aptamer-containing PEGDA-tHA. Cells migrated deeper in the gel in the presence of DNA aptamers, appearing on different focus planes. Our data demonstrate that anti-Fibronectin aptamers promote scaffold enrichment for this protein, thus improving cell adhesion and scaffold colonization.

STATEMENT OF SIGNIFICANCE

We believe aptamer coating of biomaterials is a useful and viable approach to improve the performance of scaffold materials for both research and possibly clinical purposes, because different medical devices could be envisaged able to capture bioactive mediators from the patients' blood and concentrate them where they are needed, on the biomaterial itself. At the same time, this technology could be used to confer 3D cell culture scaffold with the ability to store proteins, such as Fibronectin, taking it from the medium and capture what is produced by cells. This is an improvement of traditional biomaterials that can be enriched with exogenous molecules but are not able to selectively capture a desired molecule.

Negative pressure wound therapy limits downgrowth in percutaneous devices

Maintenance of a soft tissue seal around percutaneous devices is challenged by the downgrowth of periprosthetic tissues-a gateway to potential infection. As negative pressure wound therapy (NPWT) is used clinically to facilitate healing of complex soft tissue pathologies, it was hypothesized that NPWT could limit downgrowth of periprosthetic tissues. To test this hypothesis, 20 hairless guinea pigs were randomly assigned into four groups (n = 5/group). Using a One-Stage (Groups 1 and 3) or a Two-Stage (Groups 2 and 4) surgical procedure, each animal was implanted with a titanium-alloy subdermal device porous-coated with commercially pure, medical grade titanium. Each subdermal device had a smooth titanium-alloy percutaneous post. The One-Stage procedure encompassed insertion of a fully assembled device during a single surgery. The Two-Stage procedure involved the implantation of a subdermal device during the first surgery, and then three weeks later, insertion of a percutaneous post. Groups 1 and 2 served as untreated controls and Groups 3 and 4 received NPWT. Four weeks postimplantation of the post, the devices and surrounding tissues were harvested, and histologically evaluated for downgrowth. Within the untreated control groups, the Two-Stage surgical procedure significantly decreased downgrowth (p = 0.027) when compared with the One-Stage procedure. Independent of the surgical procedures performed, NPWT significantly limited downgrowth (p ≤ 0.05) when compared with the untreated controls.

Engineering of Self-Assembled Fibronectin Matrix Protein and Its Effects on Mesenchymal Stem Cells

Fibronectin (FN) contributes to cell adhesion, proliferation, and differentiation in various cell types. To enhance the activity of fibronectin at the sites of focal adhesion, we engineered a novel recombinant fibronectin (FNIII10) fragment connected to the peptide amphiphile sequence (PA), LLLLLLCCCGGDS. In this study, the effects of FNIII10-PA on rat mesenchymal stem cells (rMSCs) were compared with those of FNIII10. FNIII10-PA showed the prominent protein adhesion activity. In addition, FNIII10-PA showed a significantly higher effect on adhesion, proliferation, and differentiation of rMSCs than FNIII10. Taken together, the FNIII10-containing self-assembled sequence enhanced rMSCs adhesion, proliferation, and differentiation.

Effect of 3D microgroove surface topography on plasma and cellular fibronectin of human gingival fibroblasts

OBJECTIVES

Fibronectin (FN), an extracellular matrix (ECM) glycoprotein, is a key factor in the compatibility of dental implant materials. Our objective was to determine the optimal dimensions of microgrooves in the transmucosal part of a dental implant, for optimal absorption of plasma FN and expression of cellular FN by human gingival fibroblasts (HGFs).

METHODS

Microgroove titanium surfaces were fabricated by photolithography with parallel grooves: 15μm, 30μm, or 60μm in width and 5μm or 10μm in depth. Smooth titanium surfaces were used as controls. Surface hydrophilicity, plasma FN adsorption and cellular FN expression by HGFs were measured for both microgroove and control samples.

RESULTS

We found that narrower and deeper microgrooves amplified surface hydrophobicity. A 15-μm wide microgroove was the most hydrophobic surface and a 60-μm wide microgroove was the most hydrophilic. The latter had more expression of cellular FN than any other surface, but less absorption of plasma FN than 15-μm wide microgrooves. Variation in microgroove depth did not appear to effect FN absorption or expression unless the groove was narrow (∼15 or 30μm). In those instances, the shallower depths resulted in greater expression of cellular FN.

CONCLUSIONS

Our microgrooves improved expression of cellular FN, which functionally compensated for plasma FN. A microgroove width of 60μm and depth of 5 or 10μm appears to be optimal for the transmucosal part of the dental implant.

Design features of implants for direct skeletal attachment of limb prostheses

In direct skeletal attachment (DSA) of limb prostheses, a construct is implanted into an amputee's residuum bone and protrudes out of the residuum's skin. This technology represents an alternative to traditional suspension of prostheses via various socket systems, with clear indications when the sockets cannot be properly fitted. Contemporary DSA was invented in the 1990s, and several implant systems have been introduced since then. The current review is intended to compare the design features of implants for DSA whose use in humans or in animal studies has been reported in the literature.