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David Mills

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I am on the ‘road less traveled’ and have met few fellow travelers. I have a BA degree in Ancient History and Classics from Indiana University, an MA degree in Biological Anthropology and a PhD. in Anatomy and Cell Biology from the University of Illinois. I am a professor of Biology and Biomedical Engineering at Louisiana Tech. My research areas are targeted drug delivery, biocoatings, cancer therapeutics, halloysite enhanced dental and orthopedic biomaterials, and TMJ bioengineering.

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FARNAZ SADAT FATTAHI

Isfahan University of Technology

Katarzyna Czarnecka

Polish Academy of Sciences

Emmanuel Fortunato Gulino

Università degli Studi di Palermo

Anthony Sandler

Veronika Pavliňáková

Northumbria University

The University of Manchester

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Papers by David Mills

Biomedical Applications of Blow-Spun Coatings, Mats, and Scaffolds—A Mini-Review

Journal of Composites Science

Human tissues and disease models require well-defined biomimetic microenvironments. During the pa... more Human tissues and disease models require well-defined biomimetic microenvironments. During the past decade, innovative developments in materials science, microfabrication, and polymer science have provided us with the ability to manipulate cellular microenvironments for regenerative medicine and tissue engineering applications. Solution blow spinning is a facile fiber fabricating method that requires a simple apparatus, a concentrated polymer solution within a volatile solvent, and a high-pressure gas source. Commercially available airbrushes, typically used for painting and cosmetic makeup, have successfully generated a range of nanofibers and films. Applications under investigation are similar to electrospinning and include enzyme immobilization, drug delivery, filtration, infection protection, tissue engineering, and wound healing. This review will discuss fiber fabrication methods before a more detailed discussion of the potential of blow-spinning in biomedical applications.

Metallizing the Surface of Halloysite Nanotubes—A Review

Coatings

Halloysite nanotubes (HNTs) have been shown to be ideal nanoparticles for polymer reinforcement, ... more Halloysite nanotubes (HNTs) have been shown to be ideal nanoparticles for polymer reinforcement, sustained drug release, nano-reactor synthesis, toxic material removal, regenerative medicine, and as a substrate material for nanostructured coatings. Metal and metal oxide nanoparticles have been used for centuries in various medical applications, primarily for their antimicrobial, antifungal, and antiviral properties. The focus of this review is the metallization of HNT surfaces. Different technologies use specific metal compounds and multi-step chemical reactions to metalize the HNT surface. This review begins with a brief overview of the current methods for metallizing the HNT surface. Our focus then provides a detailed study on specific applications of metal-coated HNTs (mHNTs) in the field of nanomedicine. The focus is on using mHNTs and Mhnt polymer composites in anti-infective therapy, immunotherapy, dentistry, regenerative medicine, and wound healing. The importance of HNTs in ...

An Eco-Friendly, Simple, and Inexpensive Method for Metal-Coating Strontium onto Halloysite Nanotubes

Journal of Composites Science

Osteoporosis increases the risk of bone fracture by reducing bone mass and thereby increasing bon... more Osteoporosis increases the risk of bone fracture by reducing bone mass and thereby increasing bone fragility. The addition of strontium (Sr) nanoparticles in bone tissue results in a strengthening of the bone, induction bone formation by osteoblasts, and reduction of bone reabsorption by osteoclasts. The use of Sr for bone tissue regeneration has gained significant research interest in recent years due to its beneficial properties in treating osteoporotic-induced bone loss. We hypothesized that Sr-coated and antibiotic-doped HNTs could be used in antimicrobial coatings and as an antibacterial drug delivery vehicle. Accordingly, we coated HNTs with strontium carbonate (SrHNT) using a simple, novel, and effective electrodeposition method. We tested the antibacterial properties of SrHNT on Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermis using the disc diffusion method. We assessed the potential cytotoxic and proliferative effects of SrHNTs on pre-osteoblasts using...

Effect of high-aspect-ratio microstructures on cell growth and attachment

1st Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and Biology. Proceedings (Cat. No.00EX451)

Smooth muscle cells were cultured on a variety of high-aspect-ratio PMMA, PDMS, and SU-8 microstr... more Smooth muscle cells were cultured on a variety of high-aspect-ratio PMMA, PDMS, and SU-8 microstructures. Three basic microstructures were used in these experiments: columns, holes, and curved surfaces (microlenses). Typical PMMA features were over 500 µm in height, while the SU-8 and PDMS structures averaged 150 µm in height. The smooth muscle cells showed a clear preference for smooth surfaces as compared to the areas containing microstructures, though smooth muscle cells showed the ability to grow on all structures and to attach on the steep sidewalls associated with the microstructures. Smooth muscle cell alignment was not directly improved by the structures, though evidence indicates that smaller structures may be able to do so. Gap dimensions between columns were also shown to be critical with regard to cell spreading and movement.

Differential antimicrobial and cellular response of electrolytically metalized halloysite nanotubes having different amounts of surface metallization

Materials Advances, 2020

We demonstrate an electrolytic method to metalize the outer surface of halloysite nanotubes (HNTs... more

Voltage regulated electrophoretic deposition of silver nanoparticles on halloysite nanotubes

Results in Materials, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effectiveness and Applications of a Metal-Coated HNT/Polylactic Acid Antimicrobial Filtration System

Polymers

A broad-spectrum antimicrobial respiration apparatus designed to fight bacteria, viruses, fungi, ... more A broad-spectrum antimicrobial respiration apparatus designed to fight bacteria, viruses, fungi, and other biological agents is critical in halting the current pandemic’s trajectory and containing future outbreaks. We applied a simple and effective electrodeposition method for metal (copper, silver, and zinc) coating the surface of halloysite nanotubes (HNTs). These nanoparticles are known to possess potent antiviral and antimicrobial properties. Metal-coated HNTs (mHNTs) were then added to polylactic acid (PLA) and extruded to form an mHNT/PLA 3D composite printer filament. Our composite 3D printer filament was then used to fabricate an N95-style mask with an interchangeable/replaceable filter with surfaces designed to inactivate a virus and kill bacteria on contact, thus reducing deadly infections. The filter, made of a multilayered antimicrobial/mHNT blow spun polymer and fabric, is disposable, while the mask can be sanitized and reused. We used several in vitro means of assessin...

Zinc Doped Halloysite Cooperating with Polylactic Acid for Bone Regeneration

Three-dimensional (3D) printing techniques have received considerable focus in the area of bone e... more Three-dimensional (3D) printing techniques have received considerable focus in the area of bone engineering due to its precise control in the fabrication of complex structures with customizable shapes, internal and external architectures, mechanical strength, and bioactivity. In this study, we design a new composition biomaterial consisting of polylactic acid (PLA), and halloysite nanotubes (HNTs) loaded with zinc nanoparticles (PLA+H+Zn). The hydrophobic surface of the 3D printed scaffold was coated with two layers of fetal bovine serum (FBS) on the sides and one layer of NaOH in the middle. Additionally, a layer of gentamicin was coated on the outermost layer against bacterial infection. Scaffolds were cultured in standard cell culture medium without the addition of osteogenic medium. This surface modification strategy improved material hydrophilicity and enhanced cell adhesion. Pre-osteoblasts cultured on these scaffolds differentiated into osteoblasts and proceeded to produce a ...

Antibacterial and antibiofouling clay nanotubesilicone composite

Medical Devices: Evidence and Research

Introduction: Invasive medical devices are used in treating millions of patients each day. Bacter... more Introduction: Invasive medical devices are used in treating millions of patients each day. Bacterial adherence to their surface is an early step in biofilm formation that may lead to infection, health complications, longer hospital stays, and death. Prevention of bacterial adherence and biofilm development continues to be a major healthcare challenge. Accordingly, there is a pressing need to improve the anti-microbial properties of medical devices. Materials and Methods: Polydimethylsiloxane (PDMS) was doped with halloysite nanotubes (HNTs), and the PDMS-HNT composite surfaces were coated with PDMS-b-polyethylene oxide (PEO) and antibacterials. The composite material properties were examined using SEM, energy dispersive spectroscopy, water contact angle measurements, tensile testing, UV-Vis spectroscopy, and thermal gravimetric analysis. The antibacterial potential of the PDMS-HNT composites was compared to commercial urinary catheters using cultures of E. coli and S. aureus. Fibrinogen adsorption studies were also performed on the PDMS-HNT-PEO composites. Results: HNT addition increased drug load during solvent swelling without reducing material strength. The hydrophilic properties provided by PEO were maintained after HNT addition, and the composites displayed protein-repelling properties. Additionally, composites showed superiority over commercial catheters at inhibiting bacterial growth. Conclusion: PDMS-HNT composites showed superiority regarding their efficacy at inhibiting bacterial growth, in comparison to commercial antibacterial catheters. Our data suggest that PDMS-HNT composites have potential as a coating material for anti-bacterial invasive devices and in the prevention of institutional-acquired infections.

Therapeutic Applications of Halloysite

Applied Sciences

In recent years, nanomaterials have attracted significant research interest for applications in b... more In recent years, nanomaterials have attracted significant research interest for applications in biomedicine. Many kinds of engineered nanomaterials, such as lipid nanoparticles, polymeric nanoparticles, porous nanomaterials, silica, and clay nanoparticles, have been investigated for use in drug delivery systems, regenerative medicine, and scaffolds for tissue engineering. Some of the most attractive nanoparticles for biomedical applications are nanoclays. According to their mineralogical composition, approximately 30 different nanoclays exist, and the more commonly used clays are bentonite, halloysite, kaolinite, laponite, and montmorillonite. For millennia, clay minerals have been extensively investigated for use in antidiarrhea solutions, anti-inflammatory agents, blood purification, reducing infections, and healing of stomach ulcers. This widespread use is due to their high porosity, surface properties, large surface area, excellent biocompatibility, the potential for sustained d...

Understanding Cancer Cell Behavior Through 3D Printed Bone Microenvironments

3D Bioprinting in Medicine

Cancer is a significant health problem worldwide and forms through orchestrated and highly comple... more Cancer is a significant health problem worldwide and forms through orchestrated and highly complex biological processes. This process is mediated through biophysical and biochemical signals that develop from within the tumor microenvironment. Although two-dimensional culture systems of established breast cancer cell lines are the most widely used model for cancer biology and preclinical drug assessments, it poorly mimics the behavior of cancer cells in vivo and fails to reproduce the in vivo tumor microenvironment, and accordingly, the data it produces is not always predictive. Effective therapeutic strategies require a cost-efficient in vitro model that can more accurately resemble the in vivo tumor microenvironment, thus permitting a variety of in vitro studies. Rapid prototyping (RP) is one of the most promising techniques for designing and producing three-dimensional (3D) systems (hydrogels, scaffolds) for drug efficacy analysis, developing drug delivery systems, and tissue engineering applications. The application of 3D bioprinting in engineering a cancer cell microenvironment will be the focus of this chapter. We will describe previous model systems used to understand cancer cell behavior. In particular, bioprinting methods and strategies that emphasize recreation of a cancer microenvironment that promotes cultured cancer cells to express a more relevant phenotype will be examined. Our focus will be on the 3D bioprinted models that serve as a predictive model for understanding mechanisms leading to cancer cell metastasis, permit real-time study of cell–cell interactions, enable the analysis of growth factors and cytokine expression that supports tumor cell growth or survival, and the molecular cross-talk between tumor and stromal cells. The chapter will conclude with an assessment of the current state-of-the-art and future prospects.

Electrophoretic Deposition of Gentamicin-Loaded ZnHNTs-Chitosan on Titanium

Coatings

There is a need for titanium (Ti), an antimicrobial implant coating that provides sustained prote... more There is a need for titanium (Ti), an antimicrobial implant coating that provides sustained protection against bacterial infection. Chitosan (CS) coatings, combined with halloysite nanotubes (HNTs), are an attractive solution due to the inherent biocompatibility of halloysite, its ability to provide sustained drug release, and the antimicrobial properties of CS. In this study, the electrodeposition (EPD) method was used to coat titanium foil with CS blended with zinc-coated HNTs (ZnHNTs) and pre-loaded with the antibiotic gentamicin. The CS-ZnHNTs-gentamycin sulfate (GS) coatings were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and UV-visible spectroscopy. The coatings were further examined for their ability to sustain GS release, resist bacterial colonization and growth, and prevent biofilm formation. The CS-ZnHNTs-GS coatings w...

Calcium Phosphate/Clay Nanotube Bone Cement with Enhanced Mechanical Properties and Sustained Drug Release

Current Topics in the Utilization of Clay in Industrial and Medical Applications, Sep 12, 2018

Calcium phosphate cement (CPC) has limited use in bone repair due to their poor mechanical proper... more Calcium phosphate cement (CPC) has limited use in bone repair due to their poor mechanical properties. Halloysite nanotubes (HNTs) are clay tubes with an aluminosilicate composition. The physicochemical properties, cytocompatibility, and cellular response to the CPC/HNT composites were assayed. Compression strength, FTIR analysis, protein synthesis, and mineralization were assessed. The cumulative data show that composites of tricalcium phosphate (TCP), anhydrous calcium diphosphate (DCPA) as the solid phase agent, and 10% chitosan lactate solution as the setting liquid produced cement with sustained release properties without loss of material strength. The composite also showed enhanced material properties (adhesiveness, surface roughness, and increased strength). Cellular assays confirm its osteoconductive and osteoinductive nature. CPCs, loaded with gentamicin-and neomycin-doped HNTs, showed sustained antibacterial release and marked zone of growth inhibition. CPCs fabricated with drugdoped HNTs offer a means for inducing bone growth at the site of implantation while controlling infection. This treatment modality should hasten patient healing time and enhance restoration of function. The increase in materials properties suggests that this CPC may be clinically applied to repair injuries in load-bearing bones.

The Effect of Halloysite Addition on the Material Properties of Chitosan–Halloysite Hydrogel Composites

Gels

Chitosan-based hydrogels are being widely used in biomedical applications due to their eco-friend... more Chitosan-based hydrogels are being widely used in biomedical applications due to their eco-friendly, biodegradable, and biocompatible properties, and their ability to mimic the extracellular matrix of many tissues. However, the application of chitosan hydrogels has been limited due to their inherent mechanical weakness. Halloysite nanotubes (HNTs) are naturally occurring aluminosilicate clay minerals and are widely used as a bulk filler to improve the performance characteristics of many polymeric materials. HNTs have also been shown to be a viable nanocontainer able to provide the sustained release of antibiotics, chemicals, and growth factors. This study’s objective was to develop a stable drug delivery chitosan/HNT nanocomposite hydrogel that is biocompatible, biodegradable, and provides sustained drug release. In this study, chitosan/HNTs hydrogels containing undoped or gentamicin-doped HNTs were combined in different wt./wt. ratios and cross-linked with tripolyphosphate. The eff...

Bi-Functionalized Clay Nanotubes for Anti-Cancer Therapy

Applied Sciences

Systemic toxicity is an undesired consequence of the majority of chemotherapeutic drugs. Multifun... more Systemic toxicity is an undesired consequence of the majority of chemotherapeutic drugs. Multifunctional nanoparticles with combined diagnostic and therapeutic functions show great promise towards personalized nanomedicine. Halloysite clay nanotubes (HNTs) have shown potential as a drug delivery vehicle, and its surface can be modified and tailored as a targeted drug delivery system. In this short report, we modified the HNT surface by covalently bonding folic acid (FA) and fluorescein isothiocyanate (FITC). The modification of HNTs with folic acid imparts the potential to target tumor cells selectively. The addition of FITC offers a method for quantifying the effectiveness of the FA tagged HNTs ability to target tumor cells. We documented cell uptake of our bi-functionalized HNT (bHNT) through phase contrast and epi-fluorescent microscopy. bHNTs showed no signs of cytotoxicity up to a concentration of 150 µg/mL. The increase in cell death with increased bHNT concentration may be due to induced cytotoxicity resulting from intracellular bHNT accumulation that disrupts cellular function leading to cell death. With HNTs recognized as having the ability to serve as both a nanocontainer and nanocarrier, we envision our construct as a potential modular platform for potential use in cancer therapeutics. The HNT interior can be loaded with a variety of anti-cancer drugs (or other chemotherapeutics) and serve as a "death cargo" designed to kill cancer cells while providing feedback imaging data on drug efficacy. The surface of the HNT can be modified with gold or silver nanoparticles and used in photothermal therapy by converting light to heat inside tumors. Our HNT-based drug delivery system has the potential to provide localized and targeted therapies that limit or reduce side effects, reduce patient costs and length of hospital stays, and improve quality of life. However, further research is needed to validate the potential of this new chemotherapeutic drug delivery system.

Doped Halloysite Nanotubes for Use in the 3D Printing of Medical Devices

Bioengineering (Basel, Switzerland), Jan 15, 2017

Previous studies have established halloysite nanotubes (HNTs) as viable nanocontainers capable of... more Previous studies have established halloysite nanotubes (HNTs) as viable nanocontainers capable of sustained release of a variety of antibiotics, corrosion agents, chemotherapeutics and growth factors either from their lumen or in outer surface coatings. Accordingly, halloysite nanotubes (HNTs) hold great promise as drug delivery carriers in the fields of pharmaceutical science and regenerative medicine. This study explored the potential of 3D printing drug doped HNT constructs. We used a model drug, gentamicin (GS) and polylactic acid (PLA) to fabricate GS releasing disks, beads, and pellets. Gentamicin was released from 3D printed constructs in a sustained manner and had a superior anti-bacterial growth inhibition effect that was dependent on GS doping concentration. While this study focused on a model drug, gentamicin, combination therapy is possible through the fabrication of medical devices containing HNTs doped with a suite of antibiotics or antifungals. Furthermore, tailored d...

Osteoblast Behavior on Silicon and Porous-Silicon Substrates

Journal of Coating Science and Technology

Osteoblast viability, proliferation, protein expression and mineralization were studied on bare, ... more Osteoblast viability, proliferation, protein expression and mineralization were studied on bare, micro-and nanoporous silicon (Si) substrates. Micro-and nano-porous-Si substrates were prepared by anodic etching of silicon in ethanolic hydrofluoric acid and characterized using scanning electron and atomic force microscopies. Mouse osteoblasts were cultured on these substrates and cellular response to these surfaces was assessed using the Live/Dead Cell Viability assay and the MTT assay for cell proliferation. Osteoblast functionality was assessed using immunohistochemistry for bone protein specific markers. Osteoblasts grew well on micro-and nanoporous silicon substrates over the twenty-one day experimental period supporting the assessment that these are suitable cell supportive surfaces. Cell proliferation rates on bare and nanoporous silicon were similar initially, however, nanoporous silicon displayed enhanced cell proliferation, in comparison to bare silicon, after 14 days in culture. Immunocytochemical assays, using bone specific markers, showed positive reactions for osteonectin and osteopontin expression on all substrates with staining intensity increasing over the 21-day experimental period. Calcium mineral deposits were quantified using the Alizarin Red histochemical assay and nanoporous silicon induced the highest level of calcium mineral production in comparison to bare and microporous silicon. The data supports the potential use of nanoporous silicon as a surface implant coating for dental and orthopedic applications. The ability to dope (and then release) drugs or growth factors from the silicon nanopores offers the potential for a multifunctional implant surface.

Growth and Functionality of Cells Cultured on Conducting and Semi-Conducting Surfaces Modified with Self-Assembled Monolayers (SAMs)

Coatings, 2016

Bioengineering of dermal and epidermal cells on surface modified substrates is an active area of ... more Bioengineering of dermal and epidermal cells on surface modified substrates is an active area of research. The cytotoxicity, maintenance of cell phenotype and long-term functionality of human dermal fibroblast (HDF) cells on conducting indium tin oxide (ITO) and semi-conducting, silicon (Si) and gallium arsenide (GaAs), surfaces modified with self-assembled monolayers (SAMs) containing amino (-NH 2) and methyl (-CH 3) end groups have been investigated. Contact angle measurements and infrared spectroscopic studies show that the monolayers are conformal and preserve their functional end groups. Morphological analyses indicate that HDFs grow well on all substrates except GaAs, exhibiting their normal spindle-shaped morphology and exhibit no visible signs of stress or cytoplasmic vacuolation. Cell viability analyses indicate little cell death after one week in culture on all substrates except GaAs, where cells died within 6 h. Cells on all surfaces proliferate except on GaAs and GaAs-ODT. Cell growth is observed to be greater on SAM modified ITO and Si-substrates. Preservation of cellular phenotype assessed through type I collagen immunostaining and positive staining of HDF cells were observed on all modified surfaces except that on GaAs. These results suggest that conducting and semi-conducting SAM-modified surfaces support HDF growth and functionality and represent a promising area of bioengineering research.

Sustained Release of Antibacterial Agents from Doped Halloysite Nanotubes

Bioengineering, 2015

The use of nanomaterials for improving drug delivery methods has been shown to be advantageous te... more The use of nanomaterials for improving drug delivery methods has been shown to be advantageous technically and viable economically. This study employed the use of halloysite nanotubes (HNTs) as nanocontainers, as well as enhancers of structural integrity in electrospun poly-e-caprolactone (PCL) scaffolds. HNTs were loaded with amoxicillin, Brilliant Green, chlorhexidine, doxycycline, gentamicin sulfate, iodine, and potassium calvulanate and release profiles assessed. Selected doped halloysite nanotubes (containing either Brilliant Green, amoxicillin and potassium calvulanate) were then mixed with poly-e-caprolactone (PLC) using the electrospinning method and woven into random and oriented-fibered nanocomposite mats. The rate of drug release from HNTs, HNTs/PCL nanocomposites, and their effect on inhibiting bacterial growth was investigated. Release profiles from nanocomposite mats showed a pattern of sustained release for all bacterial agents. Nanocomposites were able to inhibit bacterial growth for up to one-month with only a slight decrease in bacterial growth inhibition. We propose that halloysite doped nanotubes have the potential for use in a variety of medical applications including sutures and surgical dressings, without compromising material properties.

Clay Nanotube/Poly(methyl methacrylate) Bone Cement Composites with Sustained Antibiotic Release

Macromolecular Materials and Engineering, 2012

Orthopedic-grade PMMA bone cement, admixed with prophylactic antibiotics, is widely used in hip a... more

Biomedical Applications of Blow-Spun Coatings, Mats, and Scaffolds—A Mini-Review

Journal of Composites Science

Human tissues and disease models require well-defined biomimetic microenvironments. During the pa... more Human tissues and disease models require well-defined biomimetic microenvironments. During the past decade, innovative developments in materials science, microfabrication, and polymer science have provided us with the ability to manipulate cellular microenvironments for regenerative medicine and tissue engineering applications. Solution blow spinning is a facile fiber fabricating method that requires a simple apparatus, a concentrated polymer solution within a volatile solvent, and a high-pressure gas source. Commercially available airbrushes, typically used for painting and cosmetic makeup, have successfully generated a range of nanofibers and films. Applications under investigation are similar to electrospinning and include enzyme immobilization, drug delivery, filtration, infection protection, tissue engineering, and wound healing. This review will discuss fiber fabrication methods before a more detailed discussion of the potential of blow-spinning in biomedical applications.

Metallizing the Surface of Halloysite Nanotubes—A Review

Coatings

Halloysite nanotubes (HNTs) have been shown to be ideal nanoparticles for polymer reinforcement, ... more Halloysite nanotubes (HNTs) have been shown to be ideal nanoparticles for polymer reinforcement, sustained drug release, nano-reactor synthesis, toxic material removal, regenerative medicine, and as a substrate material for nanostructured coatings. Metal and metal oxide nanoparticles have been used for centuries in various medical applications, primarily for their antimicrobial, antifungal, and antiviral properties. The focus of this review is the metallization of HNT surfaces. Different technologies use specific metal compounds and multi-step chemical reactions to metalize the HNT surface. This review begins with a brief overview of the current methods for metallizing the HNT surface. Our focus then provides a detailed study on specific applications of metal-coated HNTs (mHNTs) in the field of nanomedicine. The focus is on using mHNTs and Mhnt polymer composites in anti-infective therapy, immunotherapy, dentistry, regenerative medicine, and wound healing. The importance of HNTs in ...

An Eco-Friendly, Simple, and Inexpensive Method for Metal-Coating Strontium onto Halloysite Nanotubes

Journal of Composites Science

Osteoporosis increases the risk of bone fracture by reducing bone mass and thereby increasing bon... more Osteoporosis increases the risk of bone fracture by reducing bone mass and thereby increasing bone fragility. The addition of strontium (Sr) nanoparticles in bone tissue results in a strengthening of the bone, induction bone formation by osteoblasts, and reduction of bone reabsorption by osteoclasts. The use of Sr for bone tissue regeneration has gained significant research interest in recent years due to its beneficial properties in treating osteoporotic-induced bone loss. We hypothesized that Sr-coated and antibiotic-doped HNTs could be used in antimicrobial coatings and as an antibacterial drug delivery vehicle. Accordingly, we coated HNTs with strontium carbonate (SrHNT) using a simple, novel, and effective electrodeposition method. We tested the antibacterial properties of SrHNT on Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermis using the disc diffusion method. We assessed the potential cytotoxic and proliferative effects of SrHNTs on pre-osteoblasts using...

Effect of high-aspect-ratio microstructures on cell growth and attachment

1st Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and Biology. Proceedings (Cat. No.00EX451)

Smooth muscle cells were cultured on a variety of high-aspect-ratio PMMA, PDMS, and SU-8 microstr... more Smooth muscle cells were cultured on a variety of high-aspect-ratio PMMA, PDMS, and SU-8 microstructures. Three basic microstructures were used in these experiments: columns, holes, and curved surfaces (microlenses). Typical PMMA features were over 500 µm in height, while the SU-8 and PDMS structures averaged 150 µm in height. The smooth muscle cells showed a clear preference for smooth surfaces as compared to the areas containing microstructures, though smooth muscle cells showed the ability to grow on all structures and to attach on the steep sidewalls associated with the microstructures. Smooth muscle cell alignment was not directly improved by the structures, though evidence indicates that smaller structures may be able to do so. Gap dimensions between columns were also shown to be critical with regard to cell spreading and movement.

Differential antimicrobial and cellular response of electrolytically metalized halloysite nanotubes having different amounts of surface metallization

Materials Advances, 2020

We demonstrate an electrolytic method to metalize the outer surface of halloysite nanotubes (HNTs... more

Voltage regulated electrophoretic deposition of silver nanoparticles on halloysite nanotubes

Results in Materials, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effectiveness and Applications of a Metal-Coated HNT/Polylactic Acid Antimicrobial Filtration System

Polymers

A broad-spectrum antimicrobial respiration apparatus designed to fight bacteria, viruses, fungi, ... more A broad-spectrum antimicrobial respiration apparatus designed to fight bacteria, viruses, fungi, and other biological agents is critical in halting the current pandemic’s trajectory and containing future outbreaks. We applied a simple and effective electrodeposition method for metal (copper, silver, and zinc) coating the surface of halloysite nanotubes (HNTs). These nanoparticles are known to possess potent antiviral and antimicrobial properties. Metal-coated HNTs (mHNTs) were then added to polylactic acid (PLA) and extruded to form an mHNT/PLA 3D composite printer filament. Our composite 3D printer filament was then used to fabricate an N95-style mask with an interchangeable/replaceable filter with surfaces designed to inactivate a virus and kill bacteria on contact, thus reducing deadly infections. The filter, made of a multilayered antimicrobial/mHNT blow spun polymer and fabric, is disposable, while the mask can be sanitized and reused. We used several in vitro means of assessin...

Zinc Doped Halloysite Cooperating with Polylactic Acid for Bone Regeneration

Three-dimensional (3D) printing techniques have received considerable focus in the area of bone e... more Three-dimensional (3D) printing techniques have received considerable focus in the area of bone engineering due to its precise control in the fabrication of complex structures with customizable shapes, internal and external architectures, mechanical strength, and bioactivity. In this study, we design a new composition biomaterial consisting of polylactic acid (PLA), and halloysite nanotubes (HNTs) loaded with zinc nanoparticles (PLA+H+Zn). The hydrophobic surface of the 3D printed scaffold was coated with two layers of fetal bovine serum (FBS) on the sides and one layer of NaOH in the middle. Additionally, a layer of gentamicin was coated on the outermost layer against bacterial infection. Scaffolds were cultured in standard cell culture medium without the addition of osteogenic medium. This surface modification strategy improved material hydrophilicity and enhanced cell adhesion. Pre-osteoblasts cultured on these scaffolds differentiated into osteoblasts and proceeded to produce a ...

Antibacterial and antibiofouling clay nanotubesilicone composite

Medical Devices: Evidence and Research

Introduction: Invasive medical devices are used in treating millions of patients each day. Bacter... more Introduction: Invasive medical devices are used in treating millions of patients each day. Bacterial adherence to their surface is an early step in biofilm formation that may lead to infection, health complications, longer hospital stays, and death. Prevention of bacterial adherence and biofilm development continues to be a major healthcare challenge. Accordingly, there is a pressing need to improve the anti-microbial properties of medical devices. Materials and Methods: Polydimethylsiloxane (PDMS) was doped with halloysite nanotubes (HNTs), and the PDMS-HNT composite surfaces were coated with PDMS-b-polyethylene oxide (PEO) and antibacterials. The composite material properties were examined using SEM, energy dispersive spectroscopy, water contact angle measurements, tensile testing, UV-Vis spectroscopy, and thermal gravimetric analysis. The antibacterial potential of the PDMS-HNT composites was compared to commercial urinary catheters using cultures of E. coli and S. aureus. Fibrinogen adsorption studies were also performed on the PDMS-HNT-PEO composites. Results: HNT addition increased drug load during solvent swelling without reducing material strength. The hydrophilic properties provided by PEO were maintained after HNT addition, and the composites displayed protein-repelling properties. Additionally, composites showed superiority over commercial catheters at inhibiting bacterial growth. Conclusion: PDMS-HNT composites showed superiority regarding their efficacy at inhibiting bacterial growth, in comparison to commercial antibacterial catheters. Our data suggest that PDMS-HNT composites have potential as a coating material for anti-bacterial invasive devices and in the prevention of institutional-acquired infections.

Therapeutic Applications of Halloysite

Applied Sciences

In recent years, nanomaterials have attracted significant research interest for applications in b... more In recent years, nanomaterials have attracted significant research interest for applications in biomedicine. Many kinds of engineered nanomaterials, such as lipid nanoparticles, polymeric nanoparticles, porous nanomaterials, silica, and clay nanoparticles, have been investigated for use in drug delivery systems, regenerative medicine, and scaffolds for tissue engineering. Some of the most attractive nanoparticles for biomedical applications are nanoclays. According to their mineralogical composition, approximately 30 different nanoclays exist, and the more commonly used clays are bentonite, halloysite, kaolinite, laponite, and montmorillonite. For millennia, clay minerals have been extensively investigated for use in antidiarrhea solutions, anti-inflammatory agents, blood purification, reducing infections, and healing of stomach ulcers. This widespread use is due to their high porosity, surface properties, large surface area, excellent biocompatibility, the potential for sustained d...

Understanding Cancer Cell Behavior Through 3D Printed Bone Microenvironments

3D Bioprinting in Medicine

Cancer is a significant health problem worldwide and forms through orchestrated and highly comple... more Cancer is a significant health problem worldwide and forms through orchestrated and highly complex biological processes. This process is mediated through biophysical and biochemical signals that develop from within the tumor microenvironment. Although two-dimensional culture systems of established breast cancer cell lines are the most widely used model for cancer biology and preclinical drug assessments, it poorly mimics the behavior of cancer cells in vivo and fails to reproduce the in vivo tumor microenvironment, and accordingly, the data it produces is not always predictive. Effective therapeutic strategies require a cost-efficient in vitro model that can more accurately resemble the in vivo tumor microenvironment, thus permitting a variety of in vitro studies. Rapid prototyping (RP) is one of the most promising techniques for designing and producing three-dimensional (3D) systems (hydrogels, scaffolds) for drug efficacy analysis, developing drug delivery systems, and tissue engineering applications. The application of 3D bioprinting in engineering a cancer cell microenvironment will be the focus of this chapter. We will describe previous model systems used to understand cancer cell behavior. In particular, bioprinting methods and strategies that emphasize recreation of a cancer microenvironment that promotes cultured cancer cells to express a more relevant phenotype will be examined. Our focus will be on the 3D bioprinted models that serve as a predictive model for understanding mechanisms leading to cancer cell metastasis, permit real-time study of cell–cell interactions, enable the analysis of growth factors and cytokine expression that supports tumor cell growth or survival, and the molecular cross-talk between tumor and stromal cells. The chapter will conclude with an assessment of the current state-of-the-art and future prospects.

Electrophoretic Deposition of Gentamicin-Loaded ZnHNTs-Chitosan on Titanium

Coatings

There is a need for titanium (Ti), an antimicrobial implant coating that provides sustained prote... more There is a need for titanium (Ti), an antimicrobial implant coating that provides sustained protection against bacterial infection. Chitosan (CS) coatings, combined with halloysite nanotubes (HNTs), are an attractive solution due to the inherent biocompatibility of halloysite, its ability to provide sustained drug release, and the antimicrobial properties of CS. In this study, the electrodeposition (EPD) method was used to coat titanium foil with CS blended with zinc-coated HNTs (ZnHNTs) and pre-loaded with the antibiotic gentamicin. The CS-ZnHNTs-gentamycin sulfate (GS) coatings were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and UV-visible spectroscopy. The coatings were further examined for their ability to sustain GS release, resist bacterial colonization and growth, and prevent biofilm formation. The CS-ZnHNTs-GS coatings w...

Calcium Phosphate/Clay Nanotube Bone Cement with Enhanced Mechanical Properties and Sustained Drug Release

Current Topics in the Utilization of Clay in Industrial and Medical Applications, Sep 12, 2018

Calcium phosphate cement (CPC) has limited use in bone repair due to their poor mechanical proper... more Calcium phosphate cement (CPC) has limited use in bone repair due to their poor mechanical properties. Halloysite nanotubes (HNTs) are clay tubes with an aluminosilicate composition. The physicochemical properties, cytocompatibility, and cellular response to the CPC/HNT composites were assayed. Compression strength, FTIR analysis, protein synthesis, and mineralization were assessed. The cumulative data show that composites of tricalcium phosphate (TCP), anhydrous calcium diphosphate (DCPA) as the solid phase agent, and 10% chitosan lactate solution as the setting liquid produced cement with sustained release properties without loss of material strength. The composite also showed enhanced material properties (adhesiveness, surface roughness, and increased strength). Cellular assays confirm its osteoconductive and osteoinductive nature. CPCs, loaded with gentamicin-and neomycin-doped HNTs, showed sustained antibacterial release and marked zone of growth inhibition. CPCs fabricated with drugdoped HNTs offer a means for inducing bone growth at the site of implantation while controlling infection. This treatment modality should hasten patient healing time and enhance restoration of function. The increase in materials properties suggests that this CPC may be clinically applied to repair injuries in load-bearing bones.

The Effect of Halloysite Addition on the Material Properties of Chitosan–Halloysite Hydrogel Composites

Gels

Chitosan-based hydrogels are being widely used in biomedical applications due to their eco-friend... more Chitosan-based hydrogels are being widely used in biomedical applications due to their eco-friendly, biodegradable, and biocompatible properties, and their ability to mimic the extracellular matrix of many tissues. However, the application of chitosan hydrogels has been limited due to their inherent mechanical weakness. Halloysite nanotubes (HNTs) are naturally occurring aluminosilicate clay minerals and are widely used as a bulk filler to improve the performance characteristics of many polymeric materials. HNTs have also been shown to be a viable nanocontainer able to provide the sustained release of antibiotics, chemicals, and growth factors. This study’s objective was to develop a stable drug delivery chitosan/HNT nanocomposite hydrogel that is biocompatible, biodegradable, and provides sustained drug release. In this study, chitosan/HNTs hydrogels containing undoped or gentamicin-doped HNTs were combined in different wt./wt. ratios and cross-linked with tripolyphosphate. The eff...

Bi-Functionalized Clay Nanotubes for Anti-Cancer Therapy

Applied Sciences

Systemic toxicity is an undesired consequence of the majority of chemotherapeutic drugs. Multifun... more Systemic toxicity is an undesired consequence of the majority of chemotherapeutic drugs. Multifunctional nanoparticles with combined diagnostic and therapeutic functions show great promise towards personalized nanomedicine. Halloysite clay nanotubes (HNTs) have shown potential as a drug delivery vehicle, and its surface can be modified and tailored as a targeted drug delivery system. In this short report, we modified the HNT surface by covalently bonding folic acid (FA) and fluorescein isothiocyanate (FITC). The modification of HNTs with folic acid imparts the potential to target tumor cells selectively. The addition of FITC offers a method for quantifying the effectiveness of the FA tagged HNTs ability to target tumor cells. We documented cell uptake of our bi-functionalized HNT (bHNT) through phase contrast and epi-fluorescent microscopy. bHNTs showed no signs of cytotoxicity up to a concentration of 150 µg/mL. The increase in cell death with increased bHNT concentration may be due to induced cytotoxicity resulting from intracellular bHNT accumulation that disrupts cellular function leading to cell death. With HNTs recognized as having the ability to serve as both a nanocontainer and nanocarrier, we envision our construct as a potential modular platform for potential use in cancer therapeutics. The HNT interior can be loaded with a variety of anti-cancer drugs (or other chemotherapeutics) and serve as a "death cargo" designed to kill cancer cells while providing feedback imaging data on drug efficacy. The surface of the HNT can be modified with gold or silver nanoparticles and used in photothermal therapy by converting light to heat inside tumors. Our HNT-based drug delivery system has the potential to provide localized and targeted therapies that limit or reduce side effects, reduce patient costs and length of hospital stays, and improve quality of life. However, further research is needed to validate the potential of this new chemotherapeutic drug delivery system.

Doped Halloysite Nanotubes for Use in the 3D Printing of Medical Devices

Bioengineering (Basel, Switzerland), Jan 15, 2017

Previous studies have established halloysite nanotubes (HNTs) as viable nanocontainers capable of... more Previous studies have established halloysite nanotubes (HNTs) as viable nanocontainers capable of sustained release of a variety of antibiotics, corrosion agents, chemotherapeutics and growth factors either from their lumen or in outer surface coatings. Accordingly, halloysite nanotubes (HNTs) hold great promise as drug delivery carriers in the fields of pharmaceutical science and regenerative medicine. This study explored the potential of 3D printing drug doped HNT constructs. We used a model drug, gentamicin (GS) and polylactic acid (PLA) to fabricate GS releasing disks, beads, and pellets. Gentamicin was released from 3D printed constructs in a sustained manner and had a superior anti-bacterial growth inhibition effect that was dependent on GS doping concentration. While this study focused on a model drug, gentamicin, combination therapy is possible through the fabrication of medical devices containing HNTs doped with a suite of antibiotics or antifungals. Furthermore, tailored d...

Osteoblast Behavior on Silicon and Porous-Silicon Substrates

Journal of Coating Science and Technology

Osteoblast viability, proliferation, protein expression and mineralization were studied on bare, ... more Osteoblast viability, proliferation, protein expression and mineralization were studied on bare, micro-and nanoporous silicon (Si) substrates. Micro-and nano-porous-Si substrates were prepared by anodic etching of silicon in ethanolic hydrofluoric acid and characterized using scanning electron and atomic force microscopies. Mouse osteoblasts were cultured on these substrates and cellular response to these surfaces was assessed using the Live/Dead Cell Viability assay and the MTT assay for cell proliferation. Osteoblast functionality was assessed using immunohistochemistry for bone protein specific markers. Osteoblasts grew well on micro-and nanoporous silicon substrates over the twenty-one day experimental period supporting the assessment that these are suitable cell supportive surfaces. Cell proliferation rates on bare and nanoporous silicon were similar initially, however, nanoporous silicon displayed enhanced cell proliferation, in comparison to bare silicon, after 14 days in culture. Immunocytochemical assays, using bone specific markers, showed positive reactions for osteonectin and osteopontin expression on all substrates with staining intensity increasing over the 21-day experimental period. Calcium mineral deposits were quantified using the Alizarin Red histochemical assay and nanoporous silicon induced the highest level of calcium mineral production in comparison to bare and microporous silicon. The data supports the potential use of nanoporous silicon as a surface implant coating for dental and orthopedic applications. The ability to dope (and then release) drugs or growth factors from the silicon nanopores offers the potential for a multifunctional implant surface.

Growth and Functionality of Cells Cultured on Conducting and Semi-Conducting Surfaces Modified with Self-Assembled Monolayers (SAMs)

Coatings, 2016

Bioengineering of dermal and epidermal cells on surface modified substrates is an active area of ... more Bioengineering of dermal and epidermal cells on surface modified substrates is an active area of research. The cytotoxicity, maintenance of cell phenotype and long-term functionality of human dermal fibroblast (HDF) cells on conducting indium tin oxide (ITO) and semi-conducting, silicon (Si) and gallium arsenide (GaAs), surfaces modified with self-assembled monolayers (SAMs) containing amino (-NH 2) and methyl (-CH 3) end groups have been investigated. Contact angle measurements and infrared spectroscopic studies show that the monolayers are conformal and preserve their functional end groups. Morphological analyses indicate that HDFs grow well on all substrates except GaAs, exhibiting their normal spindle-shaped morphology and exhibit no visible signs of stress or cytoplasmic vacuolation. Cell viability analyses indicate little cell death after one week in culture on all substrates except GaAs, where cells died within 6 h. Cells on all surfaces proliferate except on GaAs and GaAs-ODT. Cell growth is observed to be greater on SAM modified ITO and Si-substrates. Preservation of cellular phenotype assessed through type I collagen immunostaining and positive staining of HDF cells were observed on all modified surfaces except that on GaAs. These results suggest that conducting and semi-conducting SAM-modified surfaces support HDF growth and functionality and represent a promising area of bioengineering research.

Sustained Release of Antibacterial Agents from Doped Halloysite Nanotubes

Bioengineering, 2015

The use of nanomaterials for improving drug delivery methods has been shown to be advantageous te... more The use of nanomaterials for improving drug delivery methods has been shown to be advantageous technically and viable economically. This study employed the use of halloysite nanotubes (HNTs) as nanocontainers, as well as enhancers of structural integrity in electrospun poly-e-caprolactone (PCL) scaffolds. HNTs were loaded with amoxicillin, Brilliant Green, chlorhexidine, doxycycline, gentamicin sulfate, iodine, and potassium calvulanate and release profiles assessed. Selected doped halloysite nanotubes (containing either Brilliant Green, amoxicillin and potassium calvulanate) were then mixed with poly-e-caprolactone (PLC) using the electrospinning method and woven into random and oriented-fibered nanocomposite mats. The rate of drug release from HNTs, HNTs/PCL nanocomposites, and their effect on inhibiting bacterial growth was investigated. Release profiles from nanocomposite mats showed a pattern of sustained release for all bacterial agents. Nanocomposites were able to inhibit bacterial growth for up to one-month with only a slight decrease in bacterial growth inhibition. We propose that halloysite doped nanotubes have the potential for use in a variety of medical applications including sutures and surgical dressings, without compromising material properties.

Clay Nanotube/Poly(methyl methacrylate) Bone Cement Composites with Sustained Antibiotic Release

Macromolecular Materials and Engineering, 2012

Orthopedic-grade PMMA bone cement, admixed with prophylactic antibiotics, is widely used in hip a... more