Surface modification of neural recording electrodes with conducting polymer/biomolecule blends

The interface between micromachined neural microelectrodes and neural tissue plays an important role in chronic in vivo recording. Electrochemical polymerization was used to optimize the surface of the metal electrode sites. Electrically conductive polymers (polypyrrole) combined with biomolecules having cell adhesion functionality were deposited with great precision onto microelectrode sites of neural probes. The biomolecules used were a silk-like polymer having fibronectin fragments (SLPF) and nonapeptide CDPGYIGSR. The existence of protein polymers and peptides in the coatings was confirmed by reflective microfocusing Fourier transform infrared spectroscopy (FTIR). The morphology of the coating was rough and fuzzy, providing a high density of bioactive sites for interaction with neural cells. This high interfacial area also helped to lower the impedance of the electrode site and, consequently, to improve the signal transport. Impedance spectroscopy showed a lowered magnitude and phase of impedance around the biologically relevant frequency of 1 kHz. Cyclic voltammetry demonstrated the intrinsic redox reaction of the doped polypyrrole and the increased charge capacity of the coated electrodes. Rat glial cells and human neuroblastoma cells were seeded and cultured on neural probes with coated and uncoated electrodes. Glial cells appeared to attach better to polypyrrole/SLPF-coated electrodes than to uncoated gold electrodes. Neuroblastoma cells grew preferentially on and around the polypyrrole/CDPGYIGSR-coated electrode sites while the polypyrrole/CH(3)COO(-)-coated sites on the same probe did not show a preferential attraction to the cells. These results indicate that we can adjust the chemical composition, morphology, electronic transport, and bioactivity of polymer coatings on electrode surfaces on a multichannel micromachined neural probe by controlling electrochemical deposition conditions.     

Reactive groups on polymer coated electrodes, 8. Novel conducting polymer interfaces produced by electrochemical copolymerization of functionalized thiophene activated esters with 3-methylthiophene

With the synthesis of two new functionalized thiophene activated esters and their electrocopolymerization with 3-methylthiophene, two types of redox active polymers have been prepared. FTIR studies of the resultant polymers reveal that both types of activated ester groups withstand the applied electrooxidative conditions and are correctly integrated into the corresponding polymers. The electrocopolymerization experiments show that the composition of the obtained polymers strongly depends on the ratio of the components in the reaction medium. With the increase of the ratios of pentafluorophenyl thiophene-3-acetate-3-methylthiophene or succinimido thiophene-3-acetate/3-methylthiophene, a higher concentration of functionalized thiophene units is incorporated into the polymer chains. The measurement of the conductivity on these polymeric films gave a value in the range of 10⁻³ to 10⁻² S · cm⁻¹, which is comparable to that of the unsubstituted polythiophene and consistent with the conjugation grade suggested by electrochemical and UV-vis spectroscopic data. As expected, the pendant reactive ester groups on the electrode surfaces react rapidly with different amino compounds without loss of the electroactivity of the polymers. Therefore, these novel polymeric materials can be used as electrode interfaces for further functionalizations, especially for the immobilization of amines, peptides, and enzymes.     

Reactive groups on polymer coated electrodes, 12. New conducting carrier materials: polyalkylthiophene functionalized with amino group and its protected forms

The synthesis and electropolymerization of 3‐alkylthiophenes functionalized with a terminal amino group and its protected forms are reported. As expected, due to the strong electronic interference of the amino group, the electropolymerization of the unprotected monomer is fully inhibited. After protection of the amino group the polymerizability of the corresponding monomers is considerably improved; however, the successful polymerization process clearly depends on the nature of the used protective group. Only such monomers in which the nucleophilic character of the amino group is strongly suppressed by a suitable protective group undergo electropolymerization to form the corresponding electroactive polymers. The obtained polymers are electrochemically stable and, besides the typical properties such as redox behavior and electrochromism, they exhibit a distinct solvatochromic behavior. Electrical conductivity measurements on their oxidized forms by means of the two‐probe method give values in the range of 10^–3 to 10^–2 S·cm^–1. The feasibility of using the resulting polymers as conducting carrier materials was demonstrated by the removal of the protecting groups and the subsequent attachment of a redox active ferrocene compound. Electrochemical and spectroscopic experiments confirmed that after the polymer analogous reaction the used redox active ferrocene model compound is covalently immobilized onto the polymer surface and the electroactivity of the bonded redox groups as well as the carrier materials is retained.     

Reactive groups on polymer covered electrodes, 4. Lactate-oxidase-biosensor based on electrodes modified by polythiophene

Electrocopolymerization of 3-thiopheneacetic acid ( 1 ) and 3-methylthiophene ( 2 ) under various conditions produces poly{(3-methylthiophene-2,5-diyl)-co-[3-(carboxymethyl)thiophene-2,5-diyl]} ( 3 ). By activation of the carboxy groups with dicyclohexylcarbodiimide (DCC) lactate oxidase (LOD) is covalently bonded to the surface of the electrode. In this way a lactate sensor was formed which is applicable for the determination of lactate in micromolar concentrations.     

Bioactive hydroxyapatite coatings on polymer composites for orthopedic implants

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] coatings on polymer composite substrates were investigated for their bioactivity and their physicochemical and mechanical characteristics. HA holds key characteristics for use in orthopedic applications, such as for coating of the femoral stem in a hip replacement device. The plasma-spray technique was used to project HA onto a carbon fiber/polyamide 12 composite substrate. The resulting HA coatings exhibited mechanical adhesion as high as 23 MPa, depending on the surface treatment of the composite substrate. The purpose of this investigation was to evaluate the bioactivity of an HA-coated composite substrate. HA- coated samples have been immersed in simulated body fluid (SBF) and maintained within a shaker bath for periods of 1, 7, 14, 21, and 28 days at 37 degrees C. Scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques were performed on the samples before and after immersion into SBF. SBF was analyzed using inductively coupled plasma atomic emission spectrometry for element concentration and evaluation of the solution's purity. SBF conditioning led to the deposition of crystalline HA onto the surface of the coatings. The calcium-to-phosphorous ratios of initial HA coating and of newly deposited HA were respectively 1.72 and 1.65, close to the HA theoretical calcium/phosphorous value of 1.67. Results demonstrated that bioactive HA coatings were produced by plasma spraying, because SBF conditioning induced newly formed HA with high crystallinity. Mechanical adhesion of the HA coatings was not significantly affected upon SBF conditioning.     

Plasmin degradation of fibrin coatings on synthetic polymer substrates.

The goal of this research was to evaluate the in vitro stability of fibrin coatings on polymeric materials in the presence of plasmin. Factor XIIIa-crosslinked and noncrosslinked fibrin layers were coated on three different polyurethane substrates: Corethane, Tegaderm, and a biodegradable polyurethane, PCL/HDI/Phe. Degradation assays indicated that crosslinking the fibrin coatings enhanced the stability of the coatings on both Tegaderm and PCL/HDI/Phe; however, the persistence of the coating on the woven Corethane was not influenced by crosslinking. Degradation assay results also showed that the fibrin coating on the Corethane was significantly less stable than the fibrin coatings on the Tegaderm and PCL/HDI/Phe films. The chromogenic substrate assay data showed crosslinking did not affect the specific plasmin activity on the coatings; therefore, the increased stability resulting from crosslinking was not achieved through a reduction of fibrinolysis. The plasmin activity on the coated Corethane samples was much greater than that on either of the coated flat wound dressing materials. The large surface area of Corethane, a porous woven vascular graft material, may have had a direct influence on the fibrinolysis of its coatings by providing a large number of tissue-type plasminogen activator (tPA) binding sites. A thin, crosslinked, fibrin-coated polyurethane provides a theoretically attractive biomaterial for use in a wound dressing application and should be subject to ongoing research.     

Initiated chemical vapor deposition of antimicrobial polymer coatings

The vapor phase deposition of polymeric antimicrobial coatings is reported. Initiated chemical vapor deposition (iCVD), a solventless low-temperature process, is used to form thin films of polymers on fragile substrates. For this work, finished nylon fabric is coated by iCVD with no affect on the color or feel of the fabric. Infrared characterization confirms the polymer structure. Coatings of poly(dimethylaminomethyl styrene) of up to 540 microg/cm2 were deposited on the fabric. The antimicrobial properties were tested using standard method ASTM E2149-01. A coating of 40 microg/cm2 of fabric was found to be very effective against gram-negative Escherichia coli, with over a 99.99%, or 4 log, kill in just 2 min continuing to over a 99.9999%, or 6 log, reduction in viable bacteria in 60 min. A coating of 120 microg/cm2 was most effective against the gram-positive Bacillus subtilis. Further tests confirmed that the iCVD polymer did not leach off the fabric.     

Influence of glass and polymer coatings on CHO cell morphology and adhesion

Successful development of cell-on-chip microsystems where living cells are deposited and grown in microfabricated structures is highly dependent on the control of cell/substrate interactions. In this study, several materials of interest were tested for CHO cell growth and morphology: (i) glass, fibronectin-, poly-L-lysine- and 3-aminopropyltriethoxysilane (APTES)--treated glass and UV/O(3)-modified PDMS coating on glass as well as (ii) silicon, poly-L-lysine-, APTES-, O(2) plasma-treated and oxide-coated silicon. In addition, we quantitatively characterized cell adhesion to these substrates using a radial flow detachment assay. Lack of correlation between cell adhesion and cell morphology was systematically observed for all substrates. In particular, we show that PDMS coatings on glass can be finely tuned by UV/O(3) treatment to enhance cell adhesion and induce elongated morphology. Moreover, we observed a low shear stress cell detachment mechanism on silicon oxide coatings on silicon wafers. It is therefore possible with these coatings to selectively influence either cell adhesion or morphology.     

Impact of co-incorporating laminin peptide dopants and neurotrophic growth factors on conducting polymer properties

Conductive neural interfaces tailored for cell interaction by incorporation of bioactive factors are hypothesized to produce superior neuroprostheses with improved charge transfer capabilities. This study examined the effect of entrapping nerve growth factor (NGF) within the conducting polymer poly(ethylene dioxythiophene) (PEDOT) during electrodeposition to create a polymer capable of stimulating neurite outgrowth from proximal neural tissue. NGF entrapment was performed on polymers doped with laminin peptides DEDEDYFQRYLI and DCDPGYIGSR and, additionally, a conventional dopant, paratoluene sulphonate (pTS). All polymer coatings were analysed for a range of physical, electrical and mechanical properties, with the biological activity of ligands examined using a PC12 neurite outgrowth assay. NGF was successfully entrapped in PEDOT during electrodeposition and was shown to produce a softer interface than conventional conducting polymers and films without the NGF modification. However, it was found that the use of a peptide dopant combined with NGF entrapment resulted in polymers with diminished electrical and mechanical stability. Entrapped NGF was determined to be biologically active, with PEDOT/pTS/NGF producing neurite outgrowth comparable with control films where NGF was supplied via the medium. Future studies will determine the effect of typical neural prosthetic stimulation regimes on the release of neurotrophins and subsequent cell response.     

Polyethylene glycol-containing polyurethane hydrogel coatings for improving the biocompatibility of neural electrodes

The instability of the interface between chronically implanted neuroprosthetic devices and neural tissue is a major obstacle to the long-term use of such devices in clinical practice. In this study, we investigate the feasibility of polyethylene glycol (PEG)-containing polyurethane (PU) hydrogel as coatings for polydimethylsiloxane (PDMS)-based neural electrodes in order to achieve a stable neural interface. The influence of PU hydrogel coatings on electrode electrochemical behaviour was investigated. Importantly, the biocompatibility of PU hydrogel coatings was evaluated in vitro and in vivo. Changes in the electrochemical impedance of microelectrodes with PU coatings were negligible. The amount of protein adsorption on the PDMS substrate was reduced by 93% after coating. Rat pheochromocytoma (PC12) cells exhibited more and longer neurites on PU films than on PDMS substrates. Furthermore, PDMS implants with (n=10) and without (n=8) PU coatings were implanted into the cortex of rats and the tissue response to the implants was evaluated 6 weeks post-implantation. GFAP staining for astrocytes and NeuN staining for neurons revealed that PU coatings attenuated glial scarring and reduced the neuronal cell loss around the implants. All of these findings suggest that PU hydrogel coating is feasible and favourable for neural electrode applications.     

The effect of hyperbranched polyglycerol coatings on drug delivery using degradable polymer nanoparticles

A key attribute for nanoparticles (NPs) that are used in medicine is the ability to avoid rapid uptake by phagocytic cells in the liver and other tissues. Poly(ethylene glycol) (PEG) coatings has been the gold standard in this regard for several decades. Here, we examined hyperbranched polyglycerols (HPG) as an alternate coating on NPs. In earlier work, HPG was modified with amines and subsequently conjugated to poly(lactic acid) (PLA), but that approach compromised the ability of HPG to resist non-specific adsorption of biomolecules. Instead, we synthesized a copolymer of PLA–HPG by a one-step esterification. NPs were produced from a single emulsion using PLA–HPG: fluorescent dye or the anti-tumor agent camptothecin (CPT) were encapsulated at high efficiency in the NPs. PLA–HPG NPs were quantitatively compared to PLA–PEG NPs, produced using approaches that have been extensively optimized for drug delivery in humans. Despite being similar in size, drug release profile and in vitro cytotoxicity, the PLA–HPG NPs showed significantly longer blood circulation and significantly less liver accumulation than PLA–PEG. CPT-loaded PLA–HPG NPs showed higher stability in suspension and better therapeutic effectiveness against tumors in vivo than CPT-loaded PLA–PEG NPs. Our results suggest that HPG is superior to PEG as a surface coating for NPs in drug delivery.     

Directing phenotype of vascular smooth muscle cells using electrically stimulated conducting polymer

Vascular smooth muscle cells (VSMCs) isolated from rabbit aorta and immortalised A7r5 cells were cultured on conducting polypyrrole (PPy) substrates and were subjected to a 50muA sinusoidal electrical stimulation at 0.05, 5 and 500 Hz. These substrates were doped with hyaluronic acid and coated with collagen IV followed by Matrigel in order to mimic the basement membrane and encourage cell attachment. Increased proliferation and expression of smooth muscle phenotype markers (smooth muscle alpha-actin and smooth muscle myosin heavy chain) were observed in cultures stimulated at 5 and 500 Hz. This increased proliferation and expression of contractile proteins were found to be significantly decreased when L-type voltage-gated calcium channels (VGCC) were blocked with the drug nifedipine. To the best of our knowledge, this is the first work that demonstrates that VSMCs cultured on a conducting polymer substrate and subject to electrical stimulation not only exhibit enhanced proliferation but can be simultaneously encouraged to increase contractile protein expression. This behaviour is somewhat contrary to the classical definition of smooth muscle contractile and synthetic phenotypes that, in general, requires a modulation in phenotype as a prerequisite for smooth muscle proliferation. This interesting result highlights both the inherent plasticity of vascular smooth muscle cells and the potential of electrical stimulation via conducting polymer substrates to manipulate their behaviour.     

A comparative study of nano-scale coatings on gold electrodes for bioimpedance studies of breast cancer cells

The relative sensitivity of standard gold microelectrodes for electric cell-substrate impedance sensing was compared with that of gold microelectrodes coated with gold nanoparticles, carbon nanotubes, or electroplated gold to introduce nano-scale roughness on the surface of the electrodes. For biological solutions, the electroplated gold coated electrodes had significantly higher sensitivity to changes in conductivity than electrodes with other coatings. In contrast, the carbon nanotube coated electrodes displayed the highest sensitivity to MDA-MB-231 metastatic breast cancer cells. There was also a significant shift in the peak frequency of the cancer cell bioimpedance signal based on the type of electrode coating. The results indicate that nano-scale coatings which introduce varying degrees of surface roughness can be used to modulate the frequency dependent sensitivity of the electrodes and optimize electrode sensitivity for different bioimpedance sensing applications.     

Interactions of human bone cells with diamond-like carbon polymer hybrid coatings

Diamond-like carbon (DLC) coatings produced using the plasma-accelerating filtered pulsed arc discharge (FPAD) method display excellent adherence to the substrate and improve its corrosion resistance. This article reports the interactions of human osteoblastic cells with DLC and two DLC polymer hybrid (DLC-p-h) coatings deposited on smooth, matt and rough silicon wafers by the FPAD method. The DLC-p-h materials were DLC–polytetrafluoroethylene hybrid (DLC-PTFE-h) and DLC–polydimethylsiloxane hybrid (DLC-PDMS-h) coatings. The biocompatibility of the coatings was assayed by using mesenchymal stem cells, primary osteoblasts and Saos-2 cells. Human mesenchymal stem cells proliferated when cultured on DLC and DLC-PTFE-h, but their numbers diminished on DLC-PDMS-h. In all three cell types studied, phalloidin–TRITC staining disclosed cell-type organization typical of an actin cytoskeleton on DLC and DLC-PTFE-h, but minimal and disorganized stress fibers on cells cultured on DLC-PDMS-h. The microtubular cytoskeleton was similarly disorganized on DLC-PDMS-h. Cells on DLC-PDMS-h developed a peculiar form of membrane damage, with nuclear staining by propidium iodide associated with granular calcein staining of the cytoplasm. Active caspase-3 labeling was only seen in cells cultured on DLC-PDMS-h, indicating that these cells undergo apoptosis induced by defective cell adhesion. Results suggest that DLC-PDMS-h coatings might be useful in orthopedic applications where an implant or implant-facet should be protected against bone overgrowth while DLC and DLC-PTFE-h coatings might improve osseointegration.     

Experimental and theoretical characterization of implantable neural microelectrodes modified with conducting polymer nanotubes

Neural prostheses transduce bioelectric signals to electronic signals at the interface between neural tissue and neural microelectrodes. A low impedance electrode-tissue interface is important for the quality of signal during recording as well as quantity of applied charge density during stimulation. However, neural microelectrode sites exhibit high impedance because of their small geometric surface area. Here we analyze nanostructured-conducting polymers that can be used to significantly decrease the impedance of microelectrode typically by about two orders of magnitude and increase the charge transfer capacity of microelectrodes by three orders of magnitude. In this study poly(pyrrole) (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) nanotubes were electrochemically polymerized on the surface of neural microelectrode sites (1250 microm(2)). An equivalent circuit model comprising a coating capacitance in parallel with a pore resistance and interface impedance in series was developed and fitted to experimental results to characterize the physical and electrical properties of the interface. To confirm that the fitting parameters correlate with physical quantities of interface, theoretical equations were used to calculate the parameter values thereby validating the proposed model. Finally, an apparent diffusion coefficient was calculated for PPy film (29.2+/-1.1 x 10(-6) cm(2)/s), PPy nanotubes (PPy NTs) (72.4+/-3.3 x 10(-6) cm(2)/s), PEDOT film (7.4+/-2.1 x 10(-6) cm(2)/s), and PEDOT nanotubes (PEDOT NTs) (13.0+/-1.8 x 10(-6) cm(2)/s). The apparent diffusion coefficient of conducting polymer nanotubes was larger than the corresponding conducting polymer films.     

Carbon nanotube-based self-adhesive polymer electrodes for wireless long-term recording of electrocardiogram signals

In this study, the concept of polymer electrodes integrated with a wireless electrocardiogram (ECG) system was described. Polymer electrodes for long-term ECG measurements were fabricated by loading high content of carbon nanotubes (CNTs) in polydimethylsiloxane. Silver nanoparticles (Ag NPs) were added to increase the flexibility of the polymer and the conductivity of the electrode. An ECG electrode patch was fabricated by integrating the electrodes with an adhesive polydimethylsiloxane (aPDMS) layer. Holes in the electrode filled with aPDMS can enable robust contact between the electrode and skin, reducing motion artifacts. A wireless ECG measurement system was developed and adapted to the polymer electrodes. The polymer electrodes combined with the measurement system were successfully applied in wireless, long-term recording of ECG signals. An eleven-day continuous test showed that the ECG signal did not degrade over time. The results of attach/detach tests demonstrated that the ECG signal was affected by motion artifacts after six attach/detach cycles. The electrodes produced are flexible and exhibit good ECG performance, and therefore can be used in wearable medical monitoring systems. The approach proposed in this study holds significant promise for commercial application in medical fields.     

Ordered surfactant-templated poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer on microfabricated neural probes

Ordered conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically fabricated using a self-assembled medium of surfactant molecules as a template. The morphology and microstructure were extensively investigated by optical and electron microscopy, and results show that the coated films were composed of anisotropic domains having a characteristic size of 15-150 nm. The surfactant-templated ordered PEDOT films were electrochemically deposited on microfabricated neural probes with an electrode site area of 1,256 microm(2). The electrical properties were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). EIS showed a lowered magnitude of 35 kOmega (from an initial approximately 800 kOmega) at the biologically relevant frequency of 1 kHz. CV results show that the film has higher charge capacity and is more electrochemically stable than either nodular PEDOT or PPy. Furthermore, we have begun to probe the biological response to such a material intended to define the tissue-material interface. Results show that minute concentrations of the non-ionic surfactant are enough to kill all nearby cells in culture. It is possible however, to create surfactant-templated ordered PEDOT such that SH-SY5Y survive on the conductive polymer.     

Hemocompatibility of medical connectors with biopassive or bioactive surface coatings

Although medical connectors compose very small parts of the extracorporeal circulation (ECC) system they represent a critical localization where early thromboembolic processes can manifest. In the present study we modified an in vitro closed-loop model with fresh human whole blood for the preclinical evaluation of the hemocompatibility of three types of medical connectors: non-coated (control); with silicone-, and heparin-coating. Each single loop consists of five polycarbonate connectors joined together by five pieces of silicone tubes. Thrombin-antithrombin-III, beta-thromboglobulin (beta-TG), PMN-Elastase, terminal complement complex, CD 11b expression, and surface-absorbed fibrinogen were measured. After 1 and 2 h recirculation, platelet loss, release of beta-TG, and adsorption of fibrinogen were significantly higher (p<0.05) within the non-coated connectors compared to the silicone- and heparin-coated groups. Following this experiment, the connectors were filled again with fresh heparinized whole blood from the same donor to evaluate the influence of prior blood contact. Here, the activation of platelets and coagulation was dependent on the duration of the blood preincubation period. Probably, the coated surfaces possess a reduced, or selective adsorption of plasma proteins, which in turn leads to a faster creation of a blood-friendly secondary superficial membrane, and prevents a further denaturation and hence activation of the adsorbed proteins.     

Evaluation of electrospun PLLA/PEGDMA polymer coatings for vascular stent material

The field of percutaneous coronary intervention has seen a plethora of advances over the past few decades, which have allowed for its development into safe and effective treatments for patients suffering from cardiovascular diseases. However, stent thrombosis and in-stent restenosis remain clinically significant problems. Herein, we describe the synthesis and characterization of fibrous polymer coatings on stent material nitinol, in the hopes of developing a more suitable stent surface to enhance re-endothelialization. Electrospinning technique was used to fabricate polyethylene glycol dimethacrylate/poly l-lactide acid (PEGDMA/PLLA) blend fiber substrate with tunable elasticity and hydrophilicity for use as coatings. Attachment of platelets and arterial smooth muscle cells (SMC) onto the coatings as well as the secretory effect of mesenchymal stem cells cultured on the coatings on the proliferation and migration of arterial endothelial cells and SMCs were assessed. It was demonstrated that electrospun PEGDMA/PLLA coating with 1:1 ratio of the components on the nitinol stent-reduced platelet and SMC attachment and increased stem cell secretory factors that enhance endothelial proliferation. We therefore postulate that the fibrous coating surface would possess enhanced biological compatibility of nitinol stents and hold the potential in preventing stent failure through restenosis and thrombosis.     

Influence of extracellular matrix coatings on implant stability and osseointegration: an animal study

Aim of the present study was to test the hypothesis that the application of components of the extracellular matrix such as glycosaminoglycans used as implant surface coatings in combination with collagen, with and without growth factor, can lead to enhanced ossification and thus improve implant stability compared with collagen coatings alone. Twenty miniature pigs received 120 experimental titanium implants in the mandible. Three types of surface coatings were created: (1) collagen type I (coll), (2) collagen type I/chondroitin sulphate (coll/CS), (3) collagen type I/chondroitin sulphate/BMP-4 (coll/CS/BMP). Periimplant bone formation was assessed within a defined recess along the length axis of the implant. Bone-implant contact (BIC) and bone volume density (BVD) were determined, using both histomorphometry and synchrotron radiation micro computed tomography (SRmicroCT). To measure implant stability, resonance frequency analysis was applied after implantation and 1, 3, 7, and 22 weeks after placement. BIC was highest for coll/CS coated implants, followed by coll, p = 0.082. Histomorphometric BVD did not significantly change for any coating. SRmicroCT analysis showed an increased BVD for collagen coated implants, compared with the other two surface coatings. Implant stability showed a decrease for all coatings up to the third week. At 22 weeks, all coatings showed an increase in stability without reaching their initial level. Highest stability was reached for coll coated implants, p = 0.051. It was concluded that collagen and coll/CS implant coatings have advantageous characteristics for peri-implant bone formation, compared with the further integration of BMP-4.