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Foreign body response (FBR) remains a persistent challenge limiting the longevity of medical devices. Upon implantation, non-specific protein adsorption on the implant surface can trigger FBR and result in fouling. This necessitates frequent replacements and surgical procedures. Biological host responses are influenced primarily by atomic-scale surface properties like wettability, roughness and cytotoxicity. This dissertation introduces robust and versatile surface modification techniques designed to suitably alter these properties to enhance biocompatibility, applicable to commercially available, industrial-strength materials used in orthopedic implants. Chemical modification via introduction of zwitterionic molecules is a proven strategy that greatly alters the thermodynamics of surface protein adsorption through strong interfacial hydration effects. This reduces non-specific protein adsorption and enhances surface lubricity through robust hydration layers and fluidity of adhered water. The techniques demonstrated herein use poly (sulfobetaine methacrylate) (pSBMA) due to its low cost and ease of synthesis relative to other zwitterionic molecules. In grafting these species on to implant surfaces, we leverage versatile chemical modification methods based on RFGD plasma and ARGET ATRP. The first part of this work thus focuses on surface modification protocols that involve surface activation using RFGD plasma deposition of HEMA, followed by macro-initiator covalent coupling and grafting pSBMA using ARGET ATRP (method 1). Next, we introduce a solvent free initiator for ARGET ATRP (method 2). A highly reactive bromoester, M3BP is deposited on the surface using RFGD plasma and used as initiator for synthesizing pSBMA coatings. Polyurethane and titanium are used as model substrates to demonstrate the versatility of these techniques. This dissertation also details the performance evaluation of the fabricated coatings, including quantification of surface composition, wettability, protein adsorption and lubricity, in addition to in vitro and in vivo studies. Surfaces prepared using methodology 1 achieve a 93% reduction in albumin adsorption and 95% reduction in the friction coefficients relative to bare surfaces. They are chemically robust, non-cytotoxic, and show good in vivo performance in mice and chicken models. Surfaces prepared using methodology 2 also exhibit comparable results for both protein adsorption and friction coefficients, while providing an alternative ARGET ATRP initiator chemistry that does not require harsh solvents and is compatible with various materials irrespective of surface chemistry or geometry. These results signify the potential of these techniques for substantially improving biocompatibility and represent a proof-of-concept for simple and reproducible surface modification techniques with applicability at scale, serving a critical complementary function in maximizing the longevity and performance of orthopedic implants.
This book presents for the first time, the scattered novel results that have been achieved in very recent years in study on various thin calcium phosphate coatings produced by very diverse techniques. The comparison of thin calcium phosphate coatings with the thick plasma-sprayed ones is also included in the book. Readers will find a comprehensive book reviewing the state-of-the-art of the field with critical assessment of the achievements of the different preparation techniques.
During the past decades, the demand for biomaterials with good biocompatibility is increasing with the rapid development of advanced medical technologies, such as biosensors, implantable chips, hemodialysis and biopharmaceutical application. Currently, high biocompatibility can be achieved by hydrophilic polymers, such as poly(ethylene glycol) (PEG), polysaccharides, and zwitterionic polymers. These hydrophilic polymers can form a stable hydration layer through hydrogen bonding with water molecules in their aqueous environment and these hydration layers further prevent non-specific protein adsorption onto, and immune recognition of, the material surfaces. Among all hydrophilic materials, zwitterionic carboxybetaine (CB) distinguishes itself from the rest for its exceptional biocompatibility, superior hydration capability, low immunogenicity, and high stability as well as its potential for further functionalization. However, a reliable method to successfully introduce the biocompatible polymer onto the target surfaces still persists as a challenge. For example, "graft-from" methods, exemplified by surface-initiated atom transfer radical polymerization (SI-ATRP) can provide a dense layer but the harsh polymerization conditions and high cost impeded its large scale industrialization. On the other hand, "graft-to" methods are economic and realistic but their performance is highly surface-dependent and needs challenging optimization. There is a realistic demand to develop facile yet effective coating techniques. In this thesis, we aim to develop a universal coating technique that can have the advantages of "graft-to" and "graft-from" methods, is facile to use and generates a dense coating layer. This coating method can create an excellent biocompatible layer onto all surfaces thought a simple dip-coating process. To achieve this goal, we developed a series of (PCB)m-(DOPA)n (m=1,4 and n=1,2,4) conjugates with different combinations of polycarboxybetaine (PCB) and mussel-inspired binding groups (DOPA) groups to find out what is the optimal molecular structure for modifying surfaces. We found that the structure of the conjugates affects their coating performance: a star-shaped PCB chain structures combined with multiple DOPA groups can significantly increase the coating performance. In order to test the universal-protection ability of the molecules, we next applied this coating material on to respiratory devices to test the performance of a coating in an in vivo sheep and rabbit study. We demonstrated that through our universal coating technique, the PCB-DOPA coating can significantly improve the respiratory device lifespan from 4 hours to 35 hours and can reduce thrombosis in sheep studies. Expanding upon the well-known non-fouling ability of PCB coatings, we developed a new conjugate that can covalently immobilize bovine serum albumin antibody (anti-BSA) and fibrinogen antibody (anti-Fg) onto the PCB polymers. This coating was then applied onto a paper-based sensor surface via a "graft-to" immersion process to render the surface with both nonfouling and protein functionalizable properties. The coated paper sensor showed accelerated diffusion of analytes and improved sensitivity of glucose detection, particularly in real-world complex media such as human blood serum. Lastly, we propose a new method to detect the complement activation level in the blood exposed to biomaterials. This detection method can improve the current measuring techniques by achieving a more accurate measurement. By tailoring and molecule structure and chemistry, we have explored the strategies to improve the performance of non-fouling coating molecules. This new zwitterionic coating is developed to address major challenges associated with blood compatibility. These new molecules can not only greatly improve the life span and performance of medical devices, but also reduce the unfavorable immune response compare to current so-called "bio-inert" materials.
Abstract: Despite sterilization and aseptic procedures, bacterial infection remains a major impediment to the utility of medical implants including catheters, artificial prosthetics, and subcutaneous sensors. It has been estimated that upwards of 60% of nosocomial infections are associated with implants, with an estimated one million cases per year in the United States alone. In the orthopedic area, infections are the second most commonly attributed cause of implant failure, with the rate of infection associated with external fixators (e.g., pins) estimated to be as high as 85%. However, despite decades of prophylactic antibiotic use, high infection rates continue to persist, particularly with the emergence of drug-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA). Clearly, there is a pressing clinical need for new coatings and treatments to address the issues of implant infection and antimicrobial resistance, preferably using strategies that can be simply and robustly administered to implants. Herein, we report the development and characterization of a novel PEGylated-peptide surface coating for titanium (Ti), a standard orthopedic implant material. This coating consists of a hydrophilic PEG chain conjugated to a Ti-binding peptide (TBP) anchor. The TBP domain, selected from phage display, spontaneously assembles via adsorptive mechanisms onto Ti, with PEG extending into aqueous solution to afford a non-fouing adlayer resistant to protein adhesion and S. aureus colonization. Using a number of surface analytical techniques, we have further characterized the peptides and the resultant coatings on Ti to identify potential design variations for improved performance and to contribute to the design and engineering of future bacteriophobic coatings. In particular, the effect of multiple TBP repeats on coating efficacy and performance was examined. Furthermore, the modularity of this platform has general applicability to the enhancement of medical implant performance. The peptide-based approach also allows for robust modification of material surfaces without the need for complex reaction schemes, and is therefore amenable to simple, point-of-care application in a surgical setting.
Orthopedic implants are a group of medical devices which are primarily used to either restore or replace skeletal deformities. In the past few decades, the orthopedic industry has witnessed a remarkable surge in the number of cases for using various kinds of implants in patients. There are two important requirements for the successful working of orthopedic implants: 1) good osseointegration i.e. structural and functional connection between living bone/muscles and the implant surface and 2) prevention of bacterial infections or specifically surgical site infections (SSI). Even though a wide range of biomaterials like metals and polymers can be used in bone grafting procedures, most of them cannot bind to neighboring bone by themselves. Thus, in order to make the implants readily osseointegrable, various kinds of bioactive coatings have been developed over time. Among them, alkaline phosphate based bioactive coatings have garnered great deal of interest. For instance, calcium phosphate (CaP) coatings have been explored for more than four decades and is commercially used worldwide. However, they are not antibacterial by itself. A recent survey reported the chances of SSI to range from 0.71-6.82 % in hip and knee arthroplasties. It is indeed a grievous concern in orthopedics, and not only does it result in the working failure of the implant but often causes revision surgeries and deaths. Considering these complications, the primary aim of this dissertation is to develop innovative, alkaline phosphate-based implant coatings for orthopedic implants. We are the only group in USA and one of the very few in the world to explore microwave assisted coating techniques. Hence, coatings were synthesized using microwaves and were made multi-functional in nature with bioactive, biocompatible and antibacterial properties. The primary hypothesis is that single-phase coating compositions support homogenous material distribution and sustained dopant release. Silver (Ag) - a well-established bactericidal element was used as the dopant in the coatings. The antibacterial nature was appraised against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). In the first part of the thesis, single-phasic Ag-doped CaP (Ag-CaP) coating was developed using the microwave assisted technique. Given the fact that Ti6Al4V is widely used for implant fabrication, this was chosen as the substrate material. The accelerated coating deposition kinetics of microwaves remarkably shortened the coating duration to minutes. The benign processing temperature also helped in retaining the single-phase nature of Ag-CaP coatings, which exhibited outstanding antibacterial properties. The coatings did not induce cytotoxicity at any level of Ag doping. This study is first of its kind which explores microwave processed antibacterial CaP coatings. However, as opposed to widely explored CaP coatings, magnesium phosphate (MgP) coatings, a newer class of bioceramic materials, have not been explored much. This is why, newberyite (NB), an important MgP phase, was chosen as another coating material for Ti6Al4V. We are one of the very few groups in the world to explore MgPs and its applications. Further, to solve the problem of SSI, Ag doped NB (Ag-NB) coatings were developed. Results indicated the formation of coatings comprising of highly crystalline NB particulates. The NB coatings exhibited remarkably enhanced bioactivity and satisfactory antibacterial properties. Even though metallic implants are widely used in the orthopedic industry, the chances of stress-shielding remain. As opposed to high Young's modulus of Ti6Al4V, polyetheretherketone (PEEK) has a Young's modulus much closer to bone. However, it is extremely bioinert. Thus, in the second part of the dissertation, multi-functional coatings were fabricated on PEEK. A novel MgP phase known as tri-magnesium phosphate hydrate (TMPH) were developed as the coating material via microwaves. These exhibited nanosheet like morphology and the sub-micron surface roughness helped in rapid pre-osteoblast attachment and proliferation. Also, Ag doping in TMPH resulted in significant bacterial reduction right from 9h of incubation. These studies are the first ones to report the development and evaluation of antibacterial MgP particles and coatings. They provide important instances about varying applications and advantages of using MgPs over CaPs. Even though bioactive coatings help in enhancing the ossseointegration capabilities of the implant, the fear of coating delamination always remains. Therefore, finally, efforts have been made to develop of a novel bioactive composite material. The composites were made bioactive by using amorphous MgP (AMP) as the reinforcement material. Twin screw extrusion was used to homogenously mix AMP into PEEK by melt-blending technique. Copious amount of bone-like apatite was formed on PEEK-AMP composites as opposed to bare PEEK. In vitro cell studies confirmed increased MC3T3 pre-osteoblast proliferation on the bioactive composites. This highlighted the great potential of using AMP as a bioactive reinforcement in PEEK polymer matrix in contrary to widely used CaPs.
Replacement of joints is a significant subspecialty of bone replacement surgery that calls for mechanically robust and biologically compatible, or biocompatible, implants. Stainless steels (SS), cobalt chromium alloys, or titanium (Ti) and its alloys is typically used to make orthopaedic implants. In this study, incorporating tellurium dioxide with niobium pentoxide is an effective method to impart the coatings with antibacterial properties by a thermal deposition method on titanium substrate. The developed coatings were treated for alkaline treatment and was subjected for in vitro study in 1.5 Kukubo's simulated body fluid to enhance biogrowth and adhesion strength. The physico-chemical and surface characterization revealed the presence of nanocomposite coatings with the deposition apatite on the surface of titanium metal strip was confirmed by XRD, FTIR, EIS, CV and SEM analysis studies. The electrochemical experiments revealed that the developed coatings had high adhesion strength and high biomimetic growth characteristics. The antibacterial test was used to evaluate the antibacterial properties of tellurium dioxide-niobium pentoxide coatings respectively. Antibacterial assays determined that treatment with nanocomposite coating induced a decay in the growth of both Gram-negative and Gram-positive bacteria. The highest zone of inhibition was observed for Staphylococcus aureus and Escherichia coli respectively. Incorporating tellurium dioxide (TeO2) and selenium dioxide (SeO2) with HAp coatings is also an effective method to impart coatings with anti-infective and anti-inflammatory properties. In this study, the thermal decomposition method for the formation of TeO2-SeO2-HAp nanocomposite coatings on titanium substrate to fabricate its biological and osseointegration behavior of implants was employed. The resultant coatings were chosen for in vitro study in Kukubo's 1.5 simulated body fluid after alkaline treatment and subjected to physio-chemical characterization, electrochemical evaluation, surface and topographical analyses.