Cells resident to precision templated 40-µm pore scaffolds generate small extracellular vesicles that affect CD4+ T cell phenotypes through regulatory TLR4 signaling

Precision porous templated scaffolds (PTS) are a hydrogel construct of uniformly sized interconnected spherical pores that induce a pro-healing response (reducing the foreign body reaction, FBR) exclusively when the pores are 30-40µm in diameter. Our previous work demonstrated the necessity of Tregs in the maintenance of PTS pore size specific differences in CD4+ T cell phenotype. Work here characterizes the role of Tregs in the responses to implanted 40µm and 100µm PTS using WT and FoxP3+ cell (Treg) depleted mice. Proteomic analyses indicate that integrin signaling, monocytes/macrophages, cytoskeletal remodeling, inflammatory cues, and vesicule endocytosis may participate in Treg activation and the CD4+ T cell equilibrium modulated by PTS resident cell-derived small extracellular vesicles (sEVs). The role of MyD88-dependent and MyD88-independent TLR4 activation in PTS cell-derived sEV-to-T cell signaling is quantified by treating WT, TLR4ko, and MyD88ko splenic T cells with PTS cell-derived sEVs. STAT3 and mTOR are identified as mechanisms for further study for pore-size dependent PTS cell-derived sEV-to-T cell signaling. STATEMENT OF SIGNIFICANCE: Unique cell populations colonizing only within 40µm pore size PTS generate sEVs that resolve inflammation by modifying CD4+ T cell phenotypes through TLR4 signaling.

Epidermal and dermal integration into sphere-templated porous poly(2-hydroxyethyl methacrylate) implants in mice

Percutaneous medical devices remain susceptible to infection and failure. We hypothesize that healing of the skin into the percutaneous device will provide a seal, preventing bacterial attachment, biofilm formation, and subsequent device failure. Porous poly(2-hydroxyethyl methacrylate) [poly(HEMA)] with sphere-templated pores (40 microm) and interconnecting throats (16 microm) were implanted in normal C57BL/6 mice for 7, 14, and 28 days. Poly(HEMA) was either untreated, keeping the surface nonadhesive for cells and proteins, or modified with carbonyldiimidazole (CDI) or CDI reacted with laminin 332 to enhance adhesion. No clinical signs of infection were observed. Epidermal and dermal response within the poly(HEMA) pores was evaluated using light and transmission electron microscopy. Cells (keratinocytes, fibroblasts, endothelial cells, inflammatory cells) and basement membrane proteins (laminin 332, beta4 integrin, type VII collagen) could be demonstrated within the poly(HEMA) pores of all implants. Blood vessels and dermal collagen bundles were evident in all of the 14- and 28-day implants. Fibrous capsule formation and permigration were not observed. Sphere-templated polymers with 40 microm pores demonstrate an ability to recapitulate key elements of both the dermal and the epidermal layers of skin. Our morphological findings indicate that the implant model can be used to study the effects of biomaterial pore size, pore interconnect (throat) size, and surface treatments on cutaneous biointegration. Further, this model may be used for bacterial challenge studies.

A mouse model to evaluate the interface between skin and a percutaneous device

Percutaneous medical devices are integral in the management and treatment of disease. The space created between the skin and the device becomes a haven for bacterial invasion and biofilm formation and results in infection. We hypothesize that sealing this space via integration of the skin into the device will create a barrier against bacterial invasion. The purpose of this study was to develop an animal model in which the interaction between skin and biomaterials can be evaluated. Porous poly(2-hydroxyethyl methacrylate) [poly(HEMA)] rods were implanted for 7 days in the dorsal skin of C57 BL/6 mice. The porous poly(HEMA) rods were surface-modified with carbonyldiimidazole (CDI) or CDI plus laminin 5; unmodified rods served as control. Implant sites were sealed with 2-octyl cyanoacrylate; corn pads and adhesive dressings were tested for stabilization of implants. All rods remained intact for the duration of the study. There was histological evidence of both epidermal and dermal integration into all poly(HEMA) rods regardless of treatment. This in vivo model permits examination of the implant/skin interface and will be useful for future studies designed to facilitate skin cell attachment where percutaneous devices penetrate the skin.

Novel biophysical techniques for investigating long-term cell adhesion dynamics on biomaterial surfaces

Cell adhesion on biomaterial surface is crucial for the regeneration and function of clinically viable cell and tissues. In turn, the cellular phenotypes, following the mechanochemical transduction of adherent cells on biomaterials, are directly correlated to the biophysical responses of cells. However, the lack of an integrated bio-analytical system for probing the cell-substrate interface poses significant obstacles to understanding the behavior of cells on biomaterial surface. We have developed a novel method, based on the principle of confocal reflectance interference contrast microscopy (C-RICM) that has enabled us to study the biomechanical deformation of cells on biomaterial surfaces. In this article, we would like to describe our recent development of the C-RICM system that integrates a confocal fluorescence microscope, phase contrast microscope and GFP expression system. We shall demonstrate the system by determining the adhesion contact kinetics, initial deformation rate, cytoskeleton structures of adherent cells on extracellular matrices (e.g., collagen and fibronectin) and biodegradable polymer (e.g., poly(lactic acid)) during long-term culture. We shall demonstrate that this unique approach could provide valuable biophysical information necessary for designing optimized biomaterial surfaces for cell/tissue regeneration applications.

Ultrasonically controlled release of ciprofloxacin from self-assembled coatings on poly(2-hydroxyethyl methacrylate) hydrogels for Pseudomonas aeruginosa biofilm prevention

Indwelling prostheses and subcutaneous delivery devices are now routinely and indispensably employed in medical practice. However, these same devices often provide a highly suitable surface for bacterial adhesion and colonization, resulting in the formation of complex, differentiated, and structured communities known as biofilms. The University of Washington Engineered Biomaterials group has developed a novel drug delivery polymer matrix consisting of a poly(2-hydroxyethyl methacrylate) hydrogel coated with ordered methylene chains that form an ultrasound-responsive coating. This system was able to retain the drug ciprofloxacin inside the polymer in the absence of ultrasound but showed significant drug release when low-intensity ultrasound was applied. To assess the potential of this controlled drug delivery system for the targeting of infectious biofilms, we monitored the accumulation of Pseudomonas aeruginosa biofilms grown on hydrogels with and without ciprofloxacin and with and without exposure to ultrasound (a 43-kHz ultrasonic bath for 20 min daily) in an in vitro flow cell study. Biofilm accumulation from confocal images was quantified and statistically compared by using COMSTAT biofilm analysis software. Biofilm accumulation on ciprofloxacin-loaded hydrogels with ultrasound-induced drug delivery was significantly reduced compared to the accumulation of biofilms grown in control experiments. The results of these studies may ultimately facilitate the future development of medical devices sensitive to external ultrasonic impulses and capable of treating or preventing biofilm growth via "on-demand" drug release.

Albumin adsorption on alkanethiols self-assembled monolayers on gold electrodes studied by chronopotentiometry

Chronopotentiometry was used to study the adsorption of human serum albumin (HSA) to self-assembled monolayers with the following terminal functional groups: CH(3), COOH and OH. Surfaces were characterized by X-ray photoelectron spectroscopy, water contact angle measurements and cyclic voltammetry. HSA coverage of the different SAMs was investigated by chronopotentiometry and the total amount of adsorbed protein was determined using radiolabelled albumin. Both techniques have demonstrated that HSA adsorption to the different SAM-modified electrodes increases in the following order: OH<COOH<CH(3)-terminated SAMs. A good correlation between coverage and total amount of HSA adsorbed was observed for long adsorption times (900s).

Relative influence of polymer fiber diameter and surface charge on fibrous capsule thickness and vessel density for single-fiber implants

Single polypropylene microfibers plasma-coated with polymers of different surface charge [N,N-dimethylaminoethyl methacrylate (NN) (positive charge), methacrylic acid (MA) (negative charge), and hexafluoropropylene (HF) (neutral)] were implanted in the subcutaneous dorsum of Sprague-Dawley rats for 5-week intervals. Thee groups of fiber diameters were used: (I) 1.0 to 5.9 microm; (II) 6.0 to 10.9 microm; and (III) 11.0 to 15.9 microm. Fibrous capsule thickness and blood-vessel density (number of vessels within 100 microm of the fiber) were assessed in tissue sections in the planes of microfiber cross-sections. Results from a multifactorial analysis of variance demonstrated statistically significant main effects (p < 0.05) for microfiber diameter but not for surface-charge coating. The mean differences in capsule thickness among the microfiber diameter groups were: between groups II and I: 5.4 microm; between groups III and I: 10.2 microm; and between groups III and II: 4.7 microm. The mean differences in capsule thickness among surface-charge coatings were: between MA and NN: 0.7 microm; between MA and HF: 1.4 microm; and between NN and HF: 0.7 microm. Many of the 1.0 to 5.9 microm-in-diameter fibers had no capsule and no sign of a foreign-body reaction. For the vessel density analysis, neither microfiber diameter nor surface-charge coating had a statistically significant effect. Thus the geometric feature of microfiber diameter was more important than was surface charge relative to fibrous capsule formation but not relative to local vessel density. This ranking of the relative influence of design features in relation to tissue response provides useful information for prioritization in biomaterial design.

Plasma polymerized N-isopropylacrylamide: synthesis and characterization of a smart thermally responsive coating

A lower critical solution temperature (LCST) in an aqueous environment has been observed with poly(N-isopropylacrylamide) (pNIPAM) deposited onto solid surfaces from a plasma glow discharge of NIPAM vapor. The synthesis and spectroscopic data (ESCA, FTIR) for the plasma polymerized NIPAM (ppNIPAM) shows a remarkable retention of the monomer structure. The phase transition at 29 degrees C was measured by a novel AFM method. The phase transition was surprising because of the expectation that the plasma environment would destroy the specific NIPAM structure associated with the thermal responsiveness. The phase change of ppNIPAM is also responsible for the changes in the level of the meniscus when coated capillaries are placed in warm and cold water. Plasma polymerization of NIPAM represents a one-step method to fabricate thermally responsive coatings on real-world biomaterials without the need for specially prepared substrates and functionalized polymers.

Inhibition of monocyte adhesion and fibrinogen adsorption on glow discharge plasma deposited tetraethylene glycol dimethyl ether

Monocytes and macrophages play important roles in host responses to implanted biomedical devices. Monocyte and macrophage interactions with biomaterial surfaces are thought to be mediated by adsorbed adhesive proteins such as fibrinogen and fibronectin. Non-fouling surfaces that minimize protein adsorption may therefore minimize monocyte adhesion, activation, and the foreign body response. Radio-frequency glow discharge plasma deposition (RF-GDPD) of tetraethylene glycol dimethyl ether (tetraglyme) was used to produce polyethylene oxide (PEO)-like coatings on a fluorinated ethylene-propylene (FEP) surface. Electron spectroscopy for chemical analysis (ESCA) and static time of flight secondary ion mass spectrometry (ToF-SIMS) were used to characterize the surface chemistry of tetraglyme coating. Fibrinogen adsorption to the tetraglyme surface was measured with 125I-labeled fibrinogen and ToF-SIMS. Adsorption of fibrinogen to plasma deposited tetraglyme was less than 10 ng cm(-2), a 20-fold decrease compared to untreated FEP or tissue culture polystyrene (TCPS). Monocyte adhesion to plasma deposited tetraglyme was significantly lower than adhesion to FEP or TCPS. In addition, when the surfaces were preadsorbed with fibrinogen, fibronectin, or blood plasma, monocyte adhesion to plasma deposited tetraglyme after 2 h or 1 day was much lower than adhesion to FEP. RF-GDPD tetraglyme coating provides a promising approach to make non-fouling biomaterials that can inhibit non-specific material-host interactions and reduce the foreign body response.

Surface modification of polymers with self-assembled molecular structures: multitechnique surface characterization

A simple, one-step procedure for generating ordered, crystalline methylene chains on polymeric surfaces via urethane linkages was developed. The reaction of dodecyl isocyanate with surface hydroxyl functional groups, catalyzed by dibutyltin dilaurate, formed a predominantly all-trans, crystalline structure on a cross-linked poly(2-hydroxyethyl methacrylate) (pHEMA) substrate. Allophanate side-branching reactions were not observed. Both X-ray photoelectron spectrocopy and time-of-flight secondary ion mass spectrometry show that the surface reaction reached saturation after 30 min at 60 degrees C. Unpolarized Fourier transform infrared-attenuated total reflection showed that, after 30 min, the stretching frequencies, vCH2,asym and vCH2,sym, decreased and approached 2920 and 2850 cm-1, indicative of a crystalline phase. The distance between two hydroxyl groups is roughly 4 A. A tilt angle of 33.5 degrees +/- 2.4 degrees was estimated by dichoric ratios measured in polarized ATR according to the two-phase and Harrick thin film approximations. The findings reported here are significant in that the possibilities for using structures similar to self-assembled monolayers (SAMs) are expanded beyond the rigid gold and silicon surfaces used through most of the literature. Thus, SAMs, biomimetics for ordered lipid cell wall structures, can be applied to real-world biomedical polymers to modify biological interactions. The terminal groups of the SAM-like structure can be further functionalized with biomolecules or antibodies to develop surface-based diagnostics, biosensors, or biomaterials.

Replacing and renewing: synthetic materials, biomimetics, and tissue engineering in implant dentistry

Hundreds of thousands of implantations are performed each year in dental clinical practice. Dental implants are a small fraction of the total number of synthetic materials implanted into the human body in all fields of medicine. Basically, these millions of implants going into humans function adequately. But longevity and complications still are significant issues and provide opportunities for the creation of improved devices. This manuscript briefly reviews the history of dental implant devices and the concepts surrounding the word "biocompatibility." It then contrasts the foreign body reaction with normal healing. Finally, the article describes how ideas gleaned from the study of normal wound healing can be applied to improved dental implants. In a concluding section, three scenarios for dental implants twenty years from now are envisioned.

Self-assembled molecular structures as ultrasonically-responsive barrier membranes for pulsatile drug delivery

Noninvasive ultrasound has been shown to increase the release rate on demand from drug delivery systems; however, such systems generally suffer from background drug leaching. To address this issue, a drug-containing polymeric monolith coated with a novel ultrasound-responsive coating was developed. A self-assembled molecular structure coating based on relatively impermeable, ordered methylene chains forms an ultrasound-activated on-off switch in controlling drug release on demand, while keeping the drug inside the polymer carrier in the absence of ultrasound. The orderly structure and molecular orientation of these C12 n-alkyl methylene chains on polymeric surfaces resemble self-assembled monolayers on gold. Their preparation and characterization have been published recently (Kwok et al. [Biomacromolecules 2000;1(1):139-148]). Ultrasound release studies showed that a copolymer of 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate (MW 400) coated with such an ultrasound-responsive membrane maintained sufficient insulin for multiple insulin delivery, compared with a substantial burst release during the first 2 h from uncoated samples. With appropriate surface coating coverage, the background leach rate can be precisely controlled. The biological activity of the insulin releasate was tested by assessing its ability to regulate [C14]-deoxyglucose uptake in 3T3-L1 adipocyte cells in a controlled cell culture environment. Uptake triggered by released insulin was comparable to that of the positive insulin control. The data demonstrate that the released insulin remains active even after the insulin had been exposed to matrix synthesis and the methylene chain coating process.

Blood compatibility--a perspective

This perspective on blood- materials interactions is intended to introduce the set of papers stemming from the symposium, "Devices and Diagnostics in Contact with Blood: Issues in Blood Compatibility at the Close of the 20th Century," organized on August 4-6, 1999 at the University of Washington by the University of Washington Engineered Biomaterials (UWEB) Engineering Research Center. This article outlines some of the history of blood contacting materials, overviews the work that has originated at the University of Washington over the past 28 years, speculates on the origins of the controversies on blood compatibility and considers the issues that should be addressed in future studies.

Surface characterization of hydroxyapatite and related calcium phosphates by XPS and TOF-SIMS

The surfaces of six biologically interesting calcium phosphate (CaP) phases (hydroxyapatite, dibasic calcium phosphate dihydrate, dibasic calcium phosphate, monobasic calcium phosphate, beta-tribasic calcium phosphate, octacalcium phosphate) have been examined by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The intensity of an O(1s) shake-up satellite correlates with the phosphate oxygen content. Together with the Ca/P and O/Ca XPS peak ratios, this feature helps provide identification of the CaP phase(s) present in the surface of unknown samples and establish their mole fractions, as proven with a bone sample. Contributions from carbonate impurities can be quantified using its C(1s) peak at 279.9 eV and subtracted from the O(1s) line shape to aid identification. Principal component analysis (PCA) has been applied successfully to analyze TOF-SIMS spectra of these six CaP phases. Multivariate analysis can help differentiate these CaP phases using the first two PCs, which are dominated by the relative intensities of only a few key ions: PO3-, O-, Ca+, CaOH+, PO2-, and OH-.

Plasma-deposited membranes for controlled release of antibiotic to prevent bacterial adhesion and biofilm formation

Bacterial infection on implanted medical devices is a significant clinical problem caused by the adhesion of bacteria to the biomaterial surface followed by biofilm formation and recruitment of other cells lines such as blood platelets, leading to potential thrombosis and thromboembolisms. To minimize biofilm formation and potential device-based infections, a polyurethane (Biospan) matrix was developed to release, in a controlled manner, an antibiotic (ciprofloxacin) locally at the implant interface. One material set consisted of the polyetherurethane (PEU) base matrix radiofrequency glow discharge plasma deposited with triethylene glycol dimethyl ether (triglyme); the other set had an additional coating of poly(butyl methyacrylate) (pBMA). Triglyme served as a nonfouling coating, whereas the pBMA served as a controlled porosity release membrane. The pBMA-coated PEU contained and released ciprofloxacin in a controlled manner. The efficacy of the modified PEU polymers against Pseudomonas aeruginosa suspensions was evaluated under flow conditions in a parallel plate flow cell. Bacterial adhesion and colonization, if any, to the test polymers were examined by direct microscopic image analysis and corroborated with destructive sampling, followed by direct cell counting. The rate of initial bacterial cell adhesion to triglyme-coated PEU was 0. 77%, and to the pBMA-coated PEU releasing ciprofloxacin was 6% of the observed adhesion rates for the control PEU. However, the rate of adherent cell accumulation due to cell growth and replication was approximately the same for the triglyme-coated PEU and the PEU controls, but was zero for the pBMA-coated PEU releasing ciprofloxacin.

Quantitative interrogation of micropatterned biomolecules by surface force microscopy

Synthetic biomaterials are widely used in medical implants with success in improving and extending quality of life. However, these materials were not originally designed to interact with cells through specific signaling pathways. As a result, the interaction with the body is mediated through passive adsorption of a disorganized protein monolayer. Next generation biomaterials have been proposed to be active in modifying the biological response of the host through the incorporation of specific biorecognition moieties. An important tool in the development of these novel active biomaterials is the scanning force microscope (SFM). The SFM allows for interrogation of bioactive biomaterials in mapping or spectroscopic modes. In this work, micropatterned protein surfaces were prepared using biomolecules implicated in wound healing. The surfaces were imaged via SFM and the specific binding forces between surface associated biomolecules and antibody functionalized tips were quantified.

Comprehensive surface analysis of hydrophobically functionalized SFM tips

Tip-sample interactions have been of interest since the early development of the scanning force microscope. Investigations of interfacial interactions at the molecular level are of importance for fundamental studies of bi-molecular interactions and for possible applications in biomedical research and industrial settings. By engineering the surface chemical properties of the SFM probes, specific force interactions may be measured. However, as these modification schemes become more widely applied, detailed chemical analysis of the modified cantilever surfaces becomes crucial. In this paper, we describe two approaches to coat SFM cantilevers with hydrophobic coatings: a silanization protocol and ratio frequency plasma enhanced chemical vapor deposition.

Characterization of combinatorially designed polyarylates by time-of-flight secondary ion mass spectrometry

A series of 16 polyarylates, with well-controlled and systematically varying chemistry, has been characterized by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The polymers are structurally identical except for the incremental additions of C2H4 units to the backbone and sidechain. From the spectra, peaks characteristic of all polyarylates are identified. Furthermore, evaluation of the spectra and identification of unique signals allow classification of the polyarylates according to sidechain and backbone chemistry.

Template recognition of protein-imprinted polymer surfaces

Synthetic materials capable of specifically recognizing proteins are important in separations, biosensors, and biomaterials. In this study, polysaccharide-like surfaces with tailored protein-binding nanocavities were prepared by a novel templating approach based on radiofrequency plasma deposition of thin films. The template-imprinted proteins included albumin, immunoglobulin, fibrinogen, lysozyme, ribonuclease A, alpha-lactalbumin, and glutamine synthetase. Transmission electron microscopy showed that nanometer-sized "pits" in the shape of imprinted protein were formed on the surfaces of template-imprinted polymer films. Electron spectroscopy for chemical analysis and time-of-flight secondary ion mass spectrometry indicated the saccharide covering of imprint surfaces and the removal of template proteins. (125)I-labeled protein adsorption from single solutions showed a similar amount of protein was adsorbed to its own imprint as to the imprint of another protein. However, more protein remained on the former surface than on the latter following elution with the detergents Tween 20 or sodium dodecyl sulfate. Competitive adsorption of a binary protein mixture showed a highly preferential adsorption of template protein to the corresponding imprint. This template recognition diminished as the number of protein-imprinted pits decreased. Structurally unstable proteins such as alpha-lactalbumin exhibited weaker template recognition that "robust" proteins such as lysozyme. The hypothesis that protein recognition is due to complementarity between the protein and its imprinted nanopit was supported by protein turnover experiments that showed template protein adsorbed to its own imprint was less readily displaced by a nontemplate protein.

Design of infection-resistant antibiotic-releasing polymers. II. Controlled release of antibiotics through a plasma-deposited thin film barrier

In the first paper in this series, we described the methods to synthesize an antibacterial polyurethane (PU) incorporating ciprofloxacin as the releasable antibiotic and poly(ethylene glycol) as the pore-forming agent. Here, we report that a thin, RF-plasma-deposited, n-butyl methacrylate (BMA) overlayer on this drug-loaded PU can act as a rate-limiting barrier to achieve a constant, sustained release of ciprofloxacin. Deposition power and deposition time during the coating process were optimized to give an appropriate crosslinked coating barrier that yielded desirable release rates, above the minimum required killing rate, N(kill). Electron spectroscopy for chemical analysis (ESCA), also known as X-ray photoelectron spectroscopy (XPS), was used to characterize the coating, and its crosslinking degree was indirectly related to the C/O ratio. Increasing either deposition power (10-60 W) or duration (5-25 min) resulted in increased C/O ratios and decreased ciprofloxacin release rates. The correlation between increased C/O ratios and reduced release rates is believed to be due to the increased crosslinking, increased hydrophobicity and increased thickness of the coating. The optimal plasma conditions to attain an appropriate crosslinked plasma-deposited film (PDF) required argon etching, pre-treatment of the matrices with an 80W-BMA plasma for 1 min, followed by immediate BMA plasma deposition at 40 W and 150 mT for 20 min. By using these plasma deposition protocols, we eliminated the initial burst effect, significantly reduced the release rates, and closely approached the zero order release kinetics for at least five days. In this study, we also showed that ESCA could be used as a powerful tool to explain the release behavior of molecules through the plasma-deposited films (PDFs).

Design of infection-resistant antibiotic-releasing polymers: I. Fabrication and formulation

Biomaterials-related infections are often observed with prosthetic implants and in many cases result in the failure of the devices. To design a biomedically useful polymer that is intrinsically infection-resistant, we have developed a ciprofloxacin-loaded polyurethane (PU) matrix that releases antibiotic locally at the implant surface, thereby minimizing bacterial accumulation. We report here the methods of fabrication and formulation for making such antibiotic-loaded devices, as well as evidence of their bactericidal properties. Specifically, various pore-forming agents and drug loadings were examined. An optimum formulation consisting of BIOSPAN PU, poly(ethylene glycol) and ciprofloxacin offered the longest effective period of sustained release (5 days). The bactericidal efficacy of the released ciprofloxacin against Pseudomonas aeruginosa (PA) was four times that of the control PU without antibiotics. This bactericidal efficiency was due to an increase in the PA detachment from the surface. These observations suggested that the released ciprofloxacin was biologically active in preventing the bacteria from permanently adhering to the substratum, and thus decreasing the possibility of biofilm-related infection.

Quantitative detection of silicone in skin by means of electron spectroscopy for chemical analysis (ESCA)

BACKGROUND

Evaluation of silicone-induced morbidity in skin has been hampered by the difficulty of detecting silicone in tissue because conventional methods are nonquantitative and insensitive.

OBJECTIVE

We attempted to determine whether silicone could be identified and quantitated in skin by means of electron spectroscopy for chemical analysis (ESCA).

METHODS

Skin biopsy specimens were obtained from the nose, chin, malar region, and inner arm of a patient who had received injections of silicone gel in his nose and chin. Frozen sections were dried under vacuum and examined by means of ESCA. Contiguous sections were examined by light microscopy.

RESULTS

The surface concentrations of silicone were as follows: chin, 20.6% +/- 3.6%; nose, 19.0%; malar region, 2.6% +/- 1.6%; inner arm, 0.0% +/- 0.0%. Light microscopy revealed homogeneous "globules" consistent with silicone in the chin and nose sections only; the malar region and inner arm sections showed no evidence of silicone.

CONCLUSION

ESCA can be used to detect silicone in skin in a specific, highly sensitive, and quantitative manner. This is the first report of quantification of silicone in skin by means of ESCA.

Template-imprinted nanostructured surfaces for protein recognition

Synthetic materials capable of selectively recognizing proteins are important in separations, biosensors and the development of biomedical materials. The technique of molecular imprinting creates specific recognition sites in polymers by using template molecules. Molecular recognition is attributed to binding sites that complement molecules in size, shape and chemical functionality. But attempts to imprint proteins have met with only limited success. Here we report a method for imprinting surfaces with protein-recognition sites. We use radio-frequency glow-discharge plasma deposition to form polymeric thin films around proteins coated with disaccharide molecules. The disaccharides become covalently attached to the polymer film, creating polysaccharide-like cavities that exhibit highly selective recognition for a variety of template proteins, including albumin, immunoglobulin G, lysozyme, ribonuclease and streptavidin. Direct imaging of template recognition is achieved by patterning a surface at the micrometre scale with imprinted regions.

Mice that lack the angiogenesis inhibitor, thrombospondin 2, mount an altered foreign body reaction characterized by increased vascularity

Disruption of the thrombospondin 2 gene (Thbs2) in mice results in a complex phenotype characterized chiefly by abnormalities in fibroblasts, connective tissues, and blood vessels. Consideration of this phenotype suggested to us that the foreign body reaction (FBR) might be altered in thrombospondin 2 (TSP2)-null mice. To investigate the participation of TSP2 in the FBR, polydimethylsiloxane (PDMS) and oxidized PDMS (ox-PDMS) disks were implanted in TSP2-null and control mice. Growth of TSP2-null and control skin fibroblasts in vitro also was evaluated on both types of disks. Normal fibroblasts grew as a monolayer on both surfaces, but attachment of the cells to ox-PDMS was weak and sensitive to movement. TSP2-null fibroblasts grew as aggregates on both surfaces, and their attachment was further compromised on ox-PDMS. After a 4-week implantation period, both types of PDMS elicited a similar FBR with a collagenous capsule in both TSP2-null and control mice. However, strikingly, the collagenous capsule that formed in TSP2-null mice was highly vascularized and thicker than that formed in normal mice. In addition, abnormally shaped collagen fibers were observed in capsules from mutant mice. These observations indicate that the presence or absence of an extracellular matrix component, TSP2, can influence the nature of the FBR, in particular its vascularity. The expression of TSP2 therefore could represent a molecular target for local inhibitory measures when vascularization of the tissue surrounding an implanted device is desired.

Rapid postadsorptive changes in fibrinogen adsorbed from plasma to segmented polyurethanes

Fibrinogen adsorbed to biomaterials plays a key role in mediating platelet interactions that can lead to blood clotting so its behavior on surfaces is of fundamental interest. In previous work showing that fibrinogen adsorbed to surfaces quickly becomes non-displaceable upon exposure to blood plasma, the fibrinogen was adsorbed from buffer, so we performed new studies in which the displaceability of fibrinogen adsorbed from plasma was characterized. Fibrinogen was adsorbed from 1% plasma to seven different surfaces for 1-64 min and then transferred to 100% plasma lacking radiolabeled fibrinogen and the amount adsorbed before and after transfer measured. The surfaces were glass, Silicone rubber, and five different polyurethanes. As adsorption time increased, the fibrinogen became increasingly resistant to displacement during the 100% plasma step, but the rate of increase in resistance varied greatly with surface type. Fibrinogen adsorbed from 1% plasma evidently undergoes rapid, surface dependent transitions. This work shows that the transitions that occur when the fibrinogen is adsorbed from blood plasma are similar to what we have previously observed for fibrinogen adsorbed from buffer.

Glow discharge plasma deposition (GDPD) technique for the local controlled delivery of hirudin from biomaterials

PURPOSE

Biomaterials which release locally high concentrations of antithrombotic agents should lessen the thrombogenicity of the materials. To evaluate this approach, we prepared novel polyurethane matrices loaded with hirudin and coated them with 2-hydroxyethyl methacrylate (HEMA) by glow discharge plasma deposition (GDPD) to reduce the release rate.

METHODS

Polyurethane (BioSpan) matrices containing hirudin and pore former (d-mannitol or BSA) were prepared by the solvent casting method. HEMA plasma deposition was then applied using GDPD technique to create a diffusional barrier film on the surface of the matrices. The effect of pore former and HEMA plasma coating on the release of hirudin was systematically investigated. Surface properties of matrices was also studied using Scanning Electron Microscopy (SEM) and Electron Spectroscopy for Chemical Analysis (ESCA).

RESULTS

The release of hirudin from BioSpan matrix could be controlled by changing the weight fraction and particle size of pore former. HEMA plasma treatment of matrices produced a thin, highly cross-linked film on the surface. The initial burst and subsequent release of hirudin was significantly reduced after HEMA plasma coating, which suggested that the plasma disposition acted as a diffusional barrier and limited the release of hirudin incorporated in the polyurethane matrix.

CONCLUSIONS

The plasma coating served as a diffusional barrier, and could work to control the release kinetics of hirudin by changing the various plasma coating conditions. Local delivery of hirudin using these biomaterials at the site of cardiovascular diseases can have the advantage of regional high levels of hirudin, as well as lowering systemic hirudin exposure, thereby minimizing the possibility of side effects.

Scanning probe microscopy for the characterization of biomaterials and biological interactions

The scanning probe microscopies provide a unique view of biological and biomedical systems at a nanoscale appropriate to appreciate molecular events. The advent of these methods has brought the ability to acquire quantitative information at the molecular level. Given the proliferation of microscopes and associated methods, the probability for important discoveries is high. If tempered with an appreciation for the potential for artifacts, the SPMs may revolutionize our view of biological systems and biomaterials interactions with those systems.

A new method for straightening DNA molecules for optical restriction mapping

We have developed an improved method of straightening DNA molecules for use in optical restriction mapping. The DNA was straightened on 3-aminopropyltriethoxysilane-coated glass slides using surface tension generated by a moving meniscus. In our method the meniscus motion was controlled mechanically, which provides advantages of speed and uniformity of the straightened molecules. Variation in the affinity of the silanized surfaces for DNA was compensated by precoating the slide with single-stranded non-target blocking DNA. A small amount of MgCl2 added to the DNA suspension increased the DNA-surface affinity and was necessary for efficient restriction enzyme digestion of the straightened surface-bound DNA. By adjusting the amounts of blocking DNA and MgCl2, we prepared slides that contained many straight parallel DNA molecules. Straightened lambda phage DNA (48 kb) bound to a slide surface was digested by EcoRI restriction endonuclease, and the resulting restriction fragments were imaged by fluorescence microscopy using a CCD camera. The observed fragment lengths showed excellent agreement with their predicted lengths.

The engineering of biomaterials exhibiting recognition and specificity

Although synthetic materials are now widely used in implanted medical devices, they are not engineered for recognition and specificity. This article considers the design of polymer surfaces that might be specifically recognized and trigger normal healing pathways. The technological advances that will contribute to biorecognition biomaterials include surfaces to inhibit non-specific interactions, self-assembly to create ordered surface structures and strategies to place recognition sites on surfaces by random arrays of groups and by templates.

Silicone derivatives for contact lenses: functionalization, chemical characterization, and cell compatibility assessment

Epoxy ring-opening functionalization of polymers at random sites along chains with various chemical groups has been demonstrated. The reaction is performed in an aqueous solution under mild conditions in order to minimize degradation of the macromolecular chains. Silicone lenses made of copolymers with epoxy side chains were functionalized with 4-hydroxybutyric acid, sodium salt. The carboxylated silicone derivatives were characterized by ESCA and radiotracers. A mean value of 30% reaction yield was concluded, based upon data from both methods; nevertheless, the latter can be improved up to 50% or more if the conditions of preparation of the epoxydized silicone lenses are optimized. Derivatized silicones were coated in the wells of culture plates to evaluate the cell compatibility of these new polymers with a fibroblast cell line (McCoy's). No cellular toxicity was observed.

The relationship between ligand-binding thermodynamics and protein-ligand interaction forces measured by atomic force microscopy

The interaction forces between biotin and a set of streptavidin site-directed mutants with altered biotin-binding equilibrium and activation thermodynamics have been measured by atomic force microscopy. The AFM technique readily discriminates differences in interaction force between the site-directed (Trp to Phe or Ala) mutants. The interaction force is poorly correlated with both the equilibrium free energy of biotin binding and the activation free energy barrier to dissociation of the biotin-streptavidin complex. The interaction force is generally well correlated with the equilibrium biotin-binding enthalpy as well as the enthalpic activation barrier, but in the one mutant where these two parameters are altered in opposite directions, the interaction force is clearly correlated with the activation enthalpy of dissociation. These results suggest that the AFM force measurements directly probe the enthalpic activation barrier to ligand dissociation.

Investigating the relationship between surface chemistry and endothelial cell growth: partial least-squares regression of the static secondary ion mass spectra of oxygen-containing plasma-deposited films

The relationship between endothelial cell growth and surface properties of plasma-deposited films (PDFs) was investigated using partial least-squares regression (PLS). PDFs of oxygen-containing precursors were prepared under various conditions, and bovine arterial endothelial cells (BAECs) were grown on these substrates. Secondary ion mass spectrometry (SIMS) in the static mode was used to characterize the surface chemistry of these substrates. The growth of BAECs on the PDFs was correlated to the positive and negative static SIMS spectra of the PDFs by PLS. A good correlation between the SIMS spectra of PDFs and endothelial cell growth was obtained. Qualitative information was also extracted from the multivariate model, giving some information as to the most important variables influencing BAEC growth.

Direct measurement of hydrogen bonding in DNA nucleotide bases by atomic force microscopy

We have used self-assembled purines and pyrimidines on planar gold surfaces and on gold-coated atomic force microscope (AFM) tips to directly probe intermolecular hydrogen bonds. Electron spectroscopy for chemical analysis (ESCA) and thermal programmed desorption (TPD) measurements of the molecular layers suggested monolayer coverage and a desorption energy of about 25 kcal/mol. Experiments were performed under water, with all four DNA bases immobilized on AFM tips and flat surfaces. Directional hydrogen-bonding interaction between the tip molecules and the surface molecules could be measured only when opposite base-pair coatings were used. The directional interactions were inhibited by excess nucleotide base in solution. Nondirectional van der Waals forces were present in all other cases. Forces as low as two interacting base pairs have been measured. With coated AFM tips, surface chemistry-sensitive recognition atomic force microscopy can be performed.

Oxidative degradation of Biomer fractions prepared by using preparative-scale gel permeation chromatography

The possibility that some macromolecular chains within a chemically heterogeneous polyether-urethane (PEU) may be more susceptible to degradation than others has been investigated. Preparative scale gel permeation chromatography has been used to separate chemically different fractions of a sample of the commercial PEU, Biomer. The fractions were characterized and then tested for susceptibility to oxidative degradation by exposing them to hydrogen peroxide. After exposure to hydrogen peroxide, the samples were analyzed using high pressure gel permeation chromatography (HPGPC), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). By using these methods, we were able to identify chemical changes in some of the Biomer fractions but not in others. Clear differences in the chemistry and reactivity of the fractions were observed. Changes in the weight average molecular weight varied from a decrease of 55.8% to an increase of 3.9%. A decrease in hard segment content at the surface and in the bulk was observed in some samples, but opposite trends were observed in others. The evidence suggests that there may be a number of mechanisms by which hydrogen peroxide can react with PEUs. Some fractions separated from the Biomer were not significantly affected by concentrated hydrogen peroxide solutions. This suggests an intrinsic stability in some PEUs and points the way to the development of more degradation-resistant PEUs.

Surface modification of polymers: chemical, biological and surface analytical challenges

Surface modification methods can optimise the biocompatibility or the specificity of biointeraction of a biosensor or medical device. With only the surface modified, the manufacture and implantation protocol remain unchanged. This review article summarises some of the chemical, surface analytical and biological challenges associated with surface modification of biosensors and biomedical devices.

Developing correlations between fibrinogen adsorption and surface properties using multivariate statistics. Student Research Award in the Doctoral Degree Candidate Category, 20th annual meeting of the Society for Biomaterials, Boston, MA, April 5-9, 1994

A multivariate model based on the partial least squares algorithm (PLS) was constructed in order to establish a correlation between the surface properties of common polymeric materials and the amount and retention of fibrinogen absorbed from a complex mixture. Surface characterization was performed by means of static secondary ion mass spectroscopy (SIMS), electron spectroscopy for chemical analysis (ESCA), and by contact angle measurements of several liquids on those materials. 125I-fibrinogen was adsorbed from a 1% plasma solution in buffer and the amount adsorbed after 2 h was determined. After 5 days of residence time in buffer, the adsorbed fibrinogen was eluted with a 1% solution of the surfactant sodium dodecyl sulfate (SDS). The percent of fibrinogen that remained on the surfaces after elution is referred to as fibrinogen retention. Correlations between surface properties and the amounts of fibrinogen adsorbed or fibrinogen retention were established. These models also show the most important variables that are related to the protein behavior on these surfaces.

In vitro study of the intrinsic toxicity of synthetic surfaces to cells

A trypan blue inclusion assay was used to measure cell death on poly(dimethyl siloxane) (PDMS), polyethylene (PE), poly(methyl methacrylate) (PMMA), polyurethanes, glass, and glow-discharge-treated polystyrene or poly(ethylene terephthalate). Cell lines used were bovine aortic endothelial, 3T3, mouse peritoneal macrophage, and BHK cells. In the absence of proteins in the media, PDMS, PE, PMMA, and some polyurethanes were consistently found to induce cell death. This toxic effect disappeared if the cells were seeded in serum-containing medium or if concentrated solutions of proteins (albumin, IgG, or fibronectin) were preadsorbed on the materials. The substrate toxicity appeared to be due to the physical properties of the substrate and not to the release of toxic leachables.

In vitro platelet interactions in whole human blood exposed to biomaterial surfaces: insights on blood compatibility

A short-term in vitro test to study platelet interactions with biomaterials is described. Using fresh human blood and a modified Chandler loop system, beta-thromboglobulin release was measured. Also, adherent platelets were observed by using scanning electron microscopy (SEM) and a colorimetric stain specific for human platelet GPIIIa. Materials studied in these experiments were polyethylene (PE), Biomer, poly(vinyl alcohol) (PVA), and a polyurethane prepared with octadecyl pendant groups (ODCE). Four blood reactions were observed: (1) Platelets continually adhere and activate on the Biomer; (2) platelets initially adhere and activate but then spread to a thin, passivating film on the PE; (3) platelets do not adhere to the PVA surface but continually react with it upon contact; and (4) platelets neither adhere to nor activate on the ODCE surface. Reactions (2) and (4) are considered characteristic of blood-compatible materials.

New ideas in biomaterials science--a path to engineered biomaterials

Our existing biomaterials, although demonstrating generally satisfactory clinical performance, were developed based upon a trial-and-error optimization approach rather than being engineered to produce the desired interfacial reaction. Most biomaterials exhibit a nonspecific biological reaction, with sluggish kinetics and a broad spectrum of active processes simultaneously occurring. This article describes materials science nanotechnology, and molecular biology techniques that may permit the synthesis of precisely engineered surfaces. Such surfaces might demonstrate rapid, precise reactions with proteins and cells. This opens the question, "what type of specific surface bioreactions do we want?" New thoughts on biocompatibility are presented that may be helpful in the design of specific surfaces yielding precise, defined biological responses.

Static secondary ion mass spectrometric investigation of the surface chemistry of organic plasma-deposited films created from oxygen-containing precursors. 3. Multivariate statistical modeling

Partial least squares (PLS) multivariate statistical models were developed to predict the surface composition and chemistry of a set of model homopolymers based on their static SIMS fragmentation patterns. In the calibration or model-building step, the positive and negative ion static SIMS spectra of different classes of model homopolymers were related to specific chemical attributes of the polymers. The models were then used to examine the surface chemistry of oxygen-containing plasma-deposited films prepared from a variety of precursors. PLS models were developed to predict the surface oxygen concentration and H/C ratios. The results obtained from the PLS models were compared with experimental results.

Surface analysis of hydrogel contact lenses by ESCA

We used electron spectroscopy for chemical analysis (ESCA) to examine the surface chemistry of polymacon, tefilcon, and bufilcon hydrogel contact lenses. Worn and unworn water-cleaned and surfactant-cleaned lenses were compared. The surface chemistry of unworn lenses, which were used as controls, consisted of approximately 70% carbon, 25% oxygen, and < 10% other elements (i.e., silicon, sulfur, sodium, nitrogen, and zinc). In general, surfactant cleaning removed silicon contamination, but left a residue containing sulfur and zinc. The increase in the nitrogen/carbon (N/C) ratio for worn bufilcon and polymacon lenses was significantly greater than the N/C ratio for unworn bufilcon and polymacon lenses. As a group the worn ionic lenses (bufilcon) showed a greater N/C ratio than the worn nonionic lenses (polymacon, tefilcon). The nitrogen that appears on all worn lenses probably represents adherent as well as adsorbed surface proteins. The highest N/C ratios were found on a pair of pathologically deposited lenses and on the lens with the longest wearing time (2 years). For the bufilcon and polymacon lenses, the differences observed in the ESCA data for the unworn and worn lenses suggest that contact lenses begin interacting with the tear film within 1 minute (the shortest wearing time in this study).

Effect of polyol type on the surface structure of sulfonate-containing polyurethanes

Polyurethanes based upon polytetramethylene oxide (PTMO) as the polyol and derivatized with propyl sulfonate functionality pendant from the urethane nitrogen have previously been shown to possess good blood-contacting properties. Other investigators have shown that sulfonated polyurethanes containing polyethylene oxide (PEO) as the soft segment are much more thrombogenic than those containing PTMO as the soft segment. In this article, the surface properties of sulfonated polyurethanes based upon either PTMO or PEO are compared. Dynamic contact angle measurements show a significant decrease in the receding angles of the sulfonated PTMO-containing polyurethane as compared to its nonsulfonated precursor polymer. No significant difference is seen between the receding contact angles of either the sulfonated PEO-based polyurethane or its nonsulfonated analog. Variable-angle electron spectroscopy for chemical analysis (ESCA) studies of sulfonated PTMO-based polyurethane performed at room temperature show that there is a significant decrease in sulfur content at the surface. In contrast, the sulfonated PEO-based polyurethane showed little change in sulfur content with take-off angle. Finally, ESCA studies of freeze-dried surfaces show a significant increase in sulfur near the surface of the sulfonated PTMO-based polymer as compared to vacuum-dried samples but show no such increase for the sulfonated PEO-based polyurethane. It is suggested that the ability of the sulfonate functionality to be expressed at the surface may explain the observed differences in blood compatibility between the sulfonated polyurethanes based upon polyols of varying hydrophilicity.

Static secondary ion mass spectrometry of adsorbed proteins

Static secondary ion mass spectrometry (SIMS) was used to analyze proteins adsorbed to biomaterial surfaces. A spectral interpretation protocol was established by examining homopolymers of 16 amino acids. This protocol allows for the assignment of peaks unique to the various amino acids. Static SIMS was used to analyze plasma proteins adsorbed to titanium. The various factors that contributed to the relative intensities observed in the spectra were explored. The potential application of the technique for studying protein-fouled materials was investigated by analyzing a fouled sensor membrane.