Membrane-mimetic films containing thrombomodulin and heparin inhibit tissue factor-induced thrombin generation in a flow model

A rechargeable anti-thrombotic coating for blood-contacting devices

Despite the potential of anti-thrombogenic coatings, including heparinized surfaces, to improve the performance of blood-contacting devices, the inevitable deterioration of bioactivity remains an important factor in device failure and related thrombotic complications. As a consequence, the ability to restore the bioactivity of a surface coating after implantation of a blood-contacting device provides a potentially important strategy to enhance its clinical performance. Here, we report the regeneration of a multicomponent anti-thrombogenic coating through use of an evolved sortase A to mediate reversible transpeptidation. Both recombinant thrombomodulin and a chemoenzymatically synthesized ultra-low molecular weight heparin were repeatedly and selectively immobilized or removed in a sequential, alternating, or simultaneous manner. The generation of activated protein C (aPC) and inhibition of activated factor X (FXa) was consistent with the molecular composition of the surface. The fabrication of a rechargeable anti-thrombogenic surface was demonstrated on an expanded polytetrafluoroethylene (ePTFE) vascular graft with reconstitution of the surface bound coating 4 weeks after in vivo implantation in a rat model.

Post-intubation subglottic stenosis: aetiology at the cellular and molecular level

Subglottic stenosis (SGS) is a narrowing of the airway just below the vocal cords. This narrowing typically consists of fibrotic scar tissue, which may be due to a variety of diseases. This review focuses on post-intubation (PI) SGS. SGS can result in partial or complete narrowing of the airway. This narrowing is caused by fibrosis and can cause serious breathing difficulties. It can occur in both adults and children. The pathogenesis of post-intubation SGS is not well understood; however, it is considered to be the product of an abnormal healing process. This review discusses how intubation can change the local micro-environment, leading to dysregulated tissue repair. We discuss how mucosal inflammation, local hypoxia and biomechanical stress associated with intubation can promote excess tissue deposition that occurs during the pathological process of SGS.

COVID-19 may cause an increased incidence of subglottic stenosis (SGS). In this review, the cellular and molecular aetiology of post-intubation SGS is outlined and we discuss how better knowledge of the underlying biology can inform SGS management.https://bit.ly/2RSliRK

Single and multi-functional coating strategies for enhancing the biocompatibility and tissue integration of blood-contacting medical implants

Device-associated clot formation and poor tissue integration are ongoing problems with permanent and temporary implantable medical devices. These complications lead to increased rates of mortality and morbidity and impose a burden on healthcare systems. In this review, we outline the current approaches for developing single and multi-functional surface coating techniques that aim to circumvent the limitations associated with existing blood-contacting medical devices. We focus on surface coatings that possess dual hemocompatibility and biofunctionality features and discuss their advantages and shortcomings to providing a biocompatible and biodynamic interface between the medical implant and blood. Lastly, we outline the newly developed surface modification techniques that use lubricant-infused coatings and discuss their unique potential and limitations in mitigating medical device-associated complications.

Electrical Analysis Of Normal And Diabetic Blood For Evaluation Of Aggregation And Coagulation Under Different Rheological Conditions

Introduction

Erythrocyte aggregation and blood coagulation are of great interest and are still under investigation by many researchers. Erythrocytes have a direct effect on hemorheological properties. Real-time in vitro studies on blood coagulation and aggregation provide a chance to understand their mechanisms in normal and pathological conditions. Additionally, this method offers control over the physical and chemical conditions during the study.

Objective

The present study introduced a simple in vitro technique to study blood aggregation and coagulation under controlled conditions.

Methods

The technique used in this study is based on the measurement of the electrical properties of blood. A simple flow chamber was made from two cylinders with a gap between them. The outer cylinder remains stationary, and the inner cylinder rotates about its axis. The inner cylinder velocity is controlled by a stepper motor. Blood samples are introduced in the gap between the two cylinders. Capacitance and impedance of blood samples were recorded by two electrodes attached to the outer cylinders and in direct contact with blood.

Results

Quantitative parameters were extracted from the capacitance and impedance time courses. These parameters were used to describe the aggregation and coagulation processes under different shear rates. Strong correlations between the aggregation index and shear rate were found for normal and diabetic blood samples. Additionally, strong negative correlations of coagulation time were found for normal and diabetic blood samples. In conclusion, the electrical analysis of blood reflects well the interactions between internal blood contents.

Conclusion

The parameters extracted from this technique can be used in the quantitative description of hemorheological processes under different physical conditions.

Utility of microfluidic devices to study the platelet-endothelium interface

The integration of biomaterials and understanding of vascular biology has led to the development of perfusable endothelialized flow models, which have been used as valuable tools to study the platelet-endothelium interface under shear. In these models, the parameters of geometry, compliance, biorheology, and cellular complexity are varied to recapitulate the physical biology of platelet recruitment and activation under physiologically relevant conditions of blood flow. In this review, we summarize the mechanistic insights learned from perfusable microvessel models and discuss the potential utility as well as challenges of endothelialized microfluidic devices to study platelet function in the bloodstream in vitro.

In situ regeneration of bioactive coatings enabled by an evolved Staphylococcus aureus sortase A

Surface immobilization of bioactive molecules is a central paradigm in the design of implantable devices and biosensors with improved clinical performance capabilities. However, in vivo degradation or denaturation of surface constituents often limits the long-term performance of bioactive films. Here we demonstrate the capacity to repeatedly regenerate a covalently immobilized monomolecular thin film of bioactive molecules through a two-step stripping and recharging cycle. Reversible transpeptidation by a laboratory evolved Staphylococcus aureus sortase A (eSrtA) enabled the rapid immobilization of an anti-thrombogenic film in the presence of whole blood and permitted multiple cycles of film regeneration in vitro that preserved its biological activity. Moreover, eSrtA transpeptidation facilitated surface re-engineering of medical devices in situ after in vivo implantation through removal and restoration film constituents. These studies establish a rapid, orthogonal and reversible biochemical scheme to regenerate selective molecular constituents with the potential to extend the lifetime of bioactive films.

Bioactive coatings offer a strategy to modulate host response to implants, but their translation to the clinic is hampered by their fast in vivo degradation. Here, the authors use an engineered bacterial protein to regenerate an anti-thrombogenic film in vitro and in situ after device implantation.

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

Simulated Thrombin Generation in the Presence of Surface-Bound Heparin and Circulating Tissue Factor

An expanded computational model of surface induced thrombin generation was developed that includes hemodynamic effects, 22 biochemical reactions and 44 distinct chemical species. Surface binding of factors V, VIII, IX, and X was included in order to more accurately simulate the formation of the surface complexes tenase and prothrombinase. In order to model these reactions, the non-activated, activated and inactivated forms were all considered. This model was used to investigate the impact of surface bound heparin on thrombin generation with and without the additive effects of thrombomodulin (TM). In total, 104 heparin/TM pairings were evaluated (52 under venous conditions, 52 under arterial conditions), the results demonstrating the synergistic ability of heparin and TM to reduce thrombin generation. Additionally, the role of circulating tissue factor (TF(p)) was investigated and compared to that of surface-bound tissue factor (TF(s)). The numerical results suggest that circulating TF has the power to amplify thrombin generation once the coagulation cascade is already initiated by surface-bound TF. TF(p) concentrations as low as 0.01 nM were found to have a significant impact on total thrombin generation.

Biocatalytic polymer coatings: on-demand drug synthesis and localized therapeutic effect under dynamic cell culture conditions

Biocatalytic surface coatings are prepared herein for localized synthesis of drugs and their on-demand, site-specific delivery to adhering cells. This novel approach is based on the incorporation of an enzyme into multilayered polymer coatings to accomplish enzyme-prodrug therapy (EPT). The build-up of enzyme-containing multilayered coatings is characterized and correlations are drawn between the multilayer film assembly conditions and the enzymatic activity of the resulting coatings. Therapeutic effect elicited by the substrate mediated EPT (SMEPT) strategy is investigated using a prodrug for an anticancer agent, SN-38. The performance of biocatalytic coatings under flow conditions is investigated and it is demonstrated that EPT allows synthesizing the drugs on-demand, at the time desired and in a controllable amount to suit particular applications. Finally, using cells cultured in sequentially connected flow chambers, it is demonstrated that SMEPT affords a site-specific drug delivery, that is, exerts a higher therapeutic effect in cells adhering directly to the biocatalytic coatings than in the cells cultured "downstream". Taken together, these data illustrate biomedical opportunities made possible by engineering tools of EPT into multilayered polymer coatings and present a novel, highly versatile tool for surface mediated drug delivery.

The use of microfluidics in hemostasis: clinical diagnostics and biomimetic models of vascular injury

PURPOSE OF REVIEW

This article reviews the application of microfluidic technologies in hemostasis. The emphasis is on promising developments in devices for clinical applications and novel approaches to modeling complex hemodynamics.

RECENT FINDINGS

Microfluidics combined with micropatterning of prothrombotic substrates provides devices for measuring platelet function and coagulation with low blood volumes (∼100 μl) over a wide range of shear stresses. This technology has been applied to the diagnosis of bleeding and thrombotic disorders, as well as to dosing and monitoring of anticoagulation and antiplatelet agents. Microfluidic devices that mimic vascular geometries such as bifurcations, stenosis, and complex interconnected networks yield complex flow fields that have revealed new mechanisms of platelet adhesion and aggregation. Applying techniques from tissue engineering by endothelializing these networks is beginning to close the gap between in-vitro and in-vivo models of vascular injury.

SUMMARY

Microfluidic technology enables researchers to create in-vitro models of vascular disease with unprecedented control of the biochemical and biophysical conditions. Two promising directions are flow-dependent clinical assays and biomimetic vascular networks. These approaches are particularly well suited for modeling the microvasculature. However, caution should be used when extrapolating results from microfluidic channels to the pathophysiology of thrombosis in large arteries and veins.

Anti-inflammatory strategies to enhance islet engraftment and survival

Early innate inflammatory reaction strongly affects islet engraftment and survival after intrahepatic transplantation. This early immune response is triggered by ischemia-reperfusion injury and instant blood mediated inflammatory reaction (IBMIR) occurring hours and days after islet infusion. Evidence in both mouse model and in human counterpart suggest the involvement of coagulation, complement system, and proinflammatory chemokines/cytokines. Identification and targeting of pathway(s), playing a role as "master regulator(s)" in post-transplant detrimental inflammatory events, is now mandatory to improve islet transplantation success. This review will focus on inflammatory pathway(s) differentially modulated by islet isolation and mainly associated with the early post-transplant events. Moreover, we will take into account anti-inflammatory strategies that have been tested at 2 levels: on the graft, ex vivo, during islet culture (i.e., donor) and/or on the graft site, in vivo, early after islet infusion (i.e., recipient).

Evaluation of a novel vascular graft with a distal bifurcation designed to reduce the development of intimal hyperplasia. Experimental study in a porcine aorta model

OBJECTIVE

Abnormal haemodynamics is commonly agreed to be a major contributor to the development of distal anastomotic intimal hyperplasia. A new vascular graft design proposed by computational studies was used to demonstrate its surgical feasibility and to compare it with the conventional graft in a porcine model.

METHOD

The device was used in 12 eight-month-old pigs, six received the new graft and six had a conventional graft. The proximal graft end was implanted into the aorta, the distal graft end was implanted into the iliac artery. The host artery was ligated in order to simulate occlusion. At 20 weeks after surgery the pigs were killed and the device was excised for histological and morphometric analysis.

RESULTS

In five experimental grafts the reconstruction was occluded due to thrombosis; only one prosthesis was patent showing a minimum of neointimal hyperplasia. In the control group too only three of the six grafts were patent. A histological analysis revealed, as the cause of occlusion, fibrous tissue overgrowth corresponding in structure to neointimal hyperplasia. Differences in the number of obliterations and in occlusion rates between the profiles of the two groups were evaluated using the median test (P<0.05). The results were not statistically significant.

CONCLUSION

Although mathematical modelling had shown significant haemodynamic benefits of a naturally bifurcated graft, our study did not confirm its superiority over conventionally used prostheses.

Bio-inspired liposomal thrombomodulin conjugate through bio-orthogonal chemistry

We report the synthesis of bioinspired liposomal thrombomodulin (TM) conjugates by chemoselective and site-specific liposomal conjugation of recombinant TM at C-terminus. TM is an endothelial cell membrane protein that acts as a major cofactor in the protein C anticoagulant pathway. To closely mimic membrane protein structural features of TM, we proposed membrane-mimetic re-expression of recombinant TM onto liposome. A recombinant TM containing the EGF-like 456 domains and an azidohomoalanine at C-terminus was expressed in E. coli. Conjugation of the recombinant TM onto liposome via Staudinger ligation and copper-free click chemistry were investigated as an optimal platform for exploring membrane protein TM's activity, respectively. The bioinspired liposomal TM conjugates were confirmed with Western blotting and protein C activation activity. The recombinant TM-liposome conjugates showed a 2-fold higher k(cat)/K(m) value for protein C activation than that of the recombinant TM alone, which indicated that the lipid membrane has a beneficiary effect on the recombinant TM's activity. The reported liposomal protein conjugate approach provides a rational design strategy for both studying membrane protein TM's functions and generating a membrane protein TM-based anticoagulant agent.

Short-term and long-term effects of orthopedic biodegradable implants

Presently, orthopedic and oral/maxillofacial implants represent a combined $2.8 billion market, a figure expected to experience significant and continued growth. Although traditional permanent implants have been proved clinically efficacious, they are also associated with several drawbacks, including secondary revision and removal surgeries. Non-permanent, biodegradable implants offer a promising alternative for patients, as they provide temporary support and degrade at a rate matching tissue formation, and thus, eliminate the need for secondary surgeries. These implants have been in clinical use for nearly 25 years, competing directly with, or maybe even exceeding, the performance of permanent implants. The initial implantation of biodegradable materials, as with permanent materials, mounts an acute host inflammatory response. Over time, the implant degradation profile and possible degradation product toxicity mediate long-term biodegradable implant-induced inflammation. However, unlike permanent implants, this inflammation is likely to cease once the material disappears. Implant-mediated inflammation is a critical determinant for implant success. Thus, for the development of a proactive biodegradable implant that has the ability to promote optimal bone regeneration and minimal detrimental inflammation, a thorough understanding of short- and long-term inflammatory events is required. Here, we discuss an array of biodegradable orthopedic implants, their associated short- and long- term inflammatory effects, and methods to mediate these inflammatory events.

The blood and vascular cell compatibility of heparin-modified ePTFE vascular grafts

Prosthetic vascular grafts do not mimic the antithrombogenic properties of native blood vessels and therefore have higher rates of complications that involve thrombosis and restenosis. We developed an approach for grafting bioactive heparin, a potent anticoagulant glycosaminoglycan, to the lumen of ePTFE vascular grafts to improve their interactions with blood and vascular cells. Heparin was bound to aminated poly(1,8-octanediol-co-citrate) (POC) via its carboxyl functional groups onto POC-modified ePTFE grafts. The bioactivity and stability of the POC-immobilized heparin (POC-Heparin) were characterized via platelet adhesion and clotting assays. The effects of POC-Heparin on the adhesion, viability and phenotype of primary endothelial cells (EC), blood outgrowth endothelial cells (BOECs) obtained from endothelial progenitor cells (EPCs) isolated from human peripheral blood, and smooth muscle cells were also investigated. POC-Heparin grafts maintained bioactivity under physiologically relevant conditions in vitro for at least one month. Specifically, POC-Heparin-coated ePTFE grafts significantly reduced platelet adhesion and inhibited whole blood clotting kinetics. POC-Heparin supported EC and BOEC adhesion, viability, proliferation, NO production, and expression of endothelial cell-specific markers von Willebrand factor (vWF) and vascular endothelial-cadherin (VE-cadherin). Smooth muscle cells cultured on POC-Heparin showed increased expression of α-actin and decreased cell proliferation. This approach can be easily adapted to modify other blood contacting devices such as stents where antithrombogenicity and improved endothelialization are desirable properties.

Sequential co-immobilization of thrombomodulin and endothelial protein C receptor on polyurethane: activation of protein C

In an effort to control the surface-mediated activation of thrombin and clot formation, proteins and molecules which mimic the anticoagulant properties of the vascular endothelial lining were immobilized on material surfaces. When immobilized on biomaterial surfaces, thrombomodulin (TM), an endothelial glycoprotein that binds thrombin and activates protein C (PC), was shown to generate activated PC (APC) and delay clot formation. However, TM-mediated activation of PC on biomaterial surfaces was shown to be limited by the transport of PC to the surface, with maximum activation obtained at a surface density of ∼40 fmole TM cm(-2). This work investigates surface immobilized with TM and endothelial protein C receptor (EPCR), a natural cofactor to TM which increases the rate of activation of PC on the native endothelium. A sequential and ordered immobilization of TM and EPCR on polyurethane at an enzymatically relevant distance (<10 nm) resulted in higher amounts of APC compared with surfaces with immobilized TM or with TM and EPCR immobilized randomly and at TM surface densities (1400 fmole cm(-2)) which were previously shown to be transport limited. Ordered TM and EPCR samples also showed increased time to clot formation in experiments with platelet-poor plasma, as measured by thromboelastography. Surfaces immobilized with TM and its natural cofactor EPCR at an enzymatically relevant distance are able to overcome transport limitations, increasing anticoagulant activation and time to clot formation.

Anti-inflammatory polymeric coatings for implantable biomaterials and devices

Synthetic polymer coatings are used extensively in modern medical devices and implants because of their material versatility and processability. These coatings are designed for specific applications by controlling composition and physical and chemical properties, and they can be formed into a variety of complex structures and shapes. However, implantation of these materials into the body elicits a strong inflammatory host response that significantly limits the integration and biological performance of devices. Biomaterial-mediated inflammation is a complex reaction involving protein adsorption, leukocyte recruitment and activation, secretion of inflammatory mediators, and fibrous encapsulation of the implant. Significant research efforts have focused on modifying material properties using various anti-inflammatory polymeric surface coatings to generate more biocompatible implants. This minireview provides a brief background on the events of biomaterial-mediated inflammation and highlights various approaches used for modifying material surfaces to modulate inflammatory responses. These include both passive and active strategies, such as nonfouling surface treatments and delivery of anti-inflammatory agents, respectively. Novel approaches will be needed to extend the in vivo lifetime and performance of devices and reduce the need for multiple implantation surgeries.

Threshold response of initiation of blood coagulation by tissue factor in patterned microfluidic capillaries is controlled by shear rate

OBJECTIVE

Blood flow is considered one of the important parameters that contribute to venous thrombosis. We quantitatively test the relationship between initiation of coagulation and shear rate and suggest a biophysical mechanism to understand this relationship.

METHODS AND RESULTS

Flowing human blood and plasma were exposed to cylindrical surfaces patterned with patches of tissue factor (TF) by using microfluidics. Initiation of coagulation of normal pooled plasma depended on shear rate, not volumetric flow rate or flow velocity, and coagulation initiated only at shear rates below a critical value. Initiation of coagulation of platelet-rich plasma and whole blood showed similar behavior. At constant shear rate, coagulation of plasma also showed a threshold response to the size of a patch of TF, consistent with our previous work in the absence of flow.

CONCLUSIONS

Initiation of coagulation of flowing blood displays a threshold response to shear rate and to the size of a surface patch of TF. Combined with the results of others, these results set the range of shear rates that limit initiation of coagulation by small surface areas of TF and by shear activation of platelets. This range fits the relatively narrow range of physiological shear rates described by Murray's law.

Modified prosthetic vascular conduits

Atherosclerosis in the form of peripheral arterial disease results in significant morbidity. Surgical treatment options for peripheral arterial disease include angioplasty, endarterectomy, and bypass grafting. For bypass grafting, vein remains the conduit of choice; however, poor quality and limited availability have led to the use of prosthetic materials. Unfortunately, because of a lack of endothelium and compliance mismatch, neointimal hyperplasia develops aggressively, resulting in high failure rates. To improve graft patency, investigators have developed surgical, chemical, and biological graft modifications. This review describes common prosthetic materials, as well as approaches currently in use and under investigation to modify and improve prosthetic conduits for bypass grafting in an effort to improve graft patency rates.

Challenges and emerging technologies in the immunoisolation of cells and tissues

Protection of transplanted cells from the host immune system using immunoisolation technology will be important in realizing the full potential of cell-based therapeutics. Microencapsulation of cells and cell aggregates has been the most widely explored immunoisolation strategy, but widespread clinical application of this technology has been limited, in part, by inadequate transport of nutrients, deleterious innate inflammatory responses, and immune recognition of encapsulated cells via indirect antigen presentation pathways. To reduce mass transport limitations and decrease void volume, recent efforts have focused on developing conformal coatings of micron and submicron scale on individual cells or cell aggregates. Additionally, anti-inflammatory and immunomodulatory capabilities are being integrated into immunoisolation devices to generate bioactive barriers that locally modulate host responses to encapsulated cells. Continued exploration of emerging paradigms governed by the inherent challenges associated with immunoisolation will be critical to actualizing the clinical potential of cell-based therapeutics.

Novel thromboresistant materials

The development of a clinically durable small-diameter vascular graft as well as permanently implantable biosensors and artificial organ systems that interface with blood, including the artificial heart, kidney, liver, and lung, remain limited by surface-induced thrombotic responses. Recent breakthroughs in materials science, along with a growing understanding of the molecular events that underlay thrombosis, has led to the design and clinical evaluation of a variety of biologically active coatings that inhibit components of the coagulation pathway and platelet responses by surface immobilization or controlled release of bioactive agents. This report reviews recent progress in generating synthetic thromboresistant surfaces that inhibit (1) protein and cell adsorption, (2) thrombin and fibrin formation, and (3) platelet activation and aggregation.

Characterization of the threshold response of initiation of blood clotting to stimulus patch size

This article demonstrates that the threshold response of initiation of blood clotting to the size of a patch of stimulus is a robust phenomenon under a wide range of conditions and follows a simple scaling relationship based on the Damköhler number. Human blood and plasma were exposed to surfaces patterned with patches presenting clotting stimuli using microfluidics. Perturbations of the complex network of hemostasis, including temperature, variations in the concentration of stimulus (tissue factor), and the absence or inhibition of individual components of the network (factor IIa, factor V, factor VIII, and thrombomodulin), did not affect the existence of this response. A scaling relationship between the threshold patch size and the timescale of reaction for clotting was supported in numerical simulations, a simple chemical model system, and experiments with human blood plasma. These results may be useful for understanding the spatiotemporal dynamics of other autocatalytic systems and emphasize the relevance of clustering of proteins and lipids in the regulation of signaling processes.

In vivo biocompatibility and stability of a substrate-supported polymerizable membrane-mimetic film

The cell membrane establishes an important paradigm for the molecular engineering of coatings for implantable devices because of its intrinsic biocompatibility and ability to act as a template for the assembly of diverse membrane-associated macromolecules. A stabilized membrane-mimetic film was assembled on alginate/Ca(2+) hydrogel microcapsules by in situ polymerization of an acrylate functionalized phospholipid. The phospholipid monomer was prepared as unilamellar vesicles and fused onto octadecyl chains that were components of an amphiphilic terpolymer anchored onto a polyelectrolyte multilayer (PEM) by electrostatic interactions. Microcapsules coated with a membrane-mimetic film were implanted into the peritoneal cavity of C57BL/6 mice, and the short-term biostability and biocompatibility of membrane-mimetic films assembled on two different alginate/poly(l-lysine) PEM cushions were compared. The nature of the underlying PEM support had a profound impact on the biocompatibility of the membrane-mimetic film, as the percentage of retrieved microcapsules completely overgrown with host cells shifted from 66+/-5.9% to less than 1% when modifications to the PEM were made. When assembled on the appropriate PEM support, biocompatibility of membrane-mimetic-coated microspheres was high wherein 87.5+/-5.7% of the implanted microspheres were retrieved 4 weeks after implantation and 92.6+/-6.4% of the retrieved capsules were free of cell adhesion or fibrotic overgrowth. Finally, 4 weeks after implantation, microspheres coated with a Texas red-labeled membrane-mimetic film were imaged with confocal microscopy and exhibited a uniform film around the periphery of the implant, indicating a high degree of film biostability. Hence, membrane-mimetic films provide a new route for generating robust, biocompatible, and biochemically heterogeneous coatings for implantable devices through molecular self-assembly.