Concurrent delivery of dexamethasone and VEGF for localized inflammation control and angiogenesis

A Supramolecular Shear-Thinning Anti-Inflammatory Steroid Hydrogel

Shear-thinning and self-healing steroid-drug-based hydrogels are presented, which exhibit rapid and complete recovery of their mechanical properties within seconds following stress-induced flow. The hydrogels release steroid drug in vivo with no visible residue when release is complete.

Delivery of dexamethasone from bioactive nanofiber matrices stimulates odontogenesis of human dental pulp cells through integrin/BMP/mTOR signaling pathways

Therapeutically relevant design of scaffolds is of special importance in the repair and regeneration of tissues including dentin and pulp. Here we exploit nanofiber matrices that incorporate bioactive glass nanoparticles (BGNs) and deliver the odontogenic drug dexamethasone (DEX) to stimulate the odontogenic differentiation of human dental pulp cells (HDPCs). DEX molecules were first loaded onto the BGN, and then the DEX-BGN complex was incorporated within the biopolymer nanofiber matrix through electrospinning. The release of DEX continued over a month, showing a slow releasing profile. HDPCs cultured on the DEX-releasing BGN matrices were viable, proliferating well up to 14 days. The odontogenic differentiation, as assessed by alkaline phosphatase activity, mRNA expression of genes, and mineralization, was significantly stimulated on the matrices incorporating BGN and further on those releasing DEX. The DEX-releasing BGN matrices highly upregulated the expression of the integrin subsets α1, α5, and β3 as well as integrin downstream signaling molecules, including focal adhesion kinase (FAK), Paxillin, and RhoA, and activated bone morphogenetic protein mRNA and phosphorylation of Smad1/5/8. Furthermore, the DEX-releasing BGN-matrices stimulated Akt and mammalian target of rapamycin (mTOR), which was proven by the inhibition study. Collectively, the designed therapeutic nanofiber matrices that incorporate BGN and deliver DEX were demonstrated to promote odontogenesis of HDPCs, and the integrins, bone morphogenetic protein, and mTOR signaling pathways are proposed to be the possible molecular mechanisms. While further in vivo studies are still needed, the DEX-releasing bioactive scaffolds are considered as a potential therapeutic nanomatrix for regenerative endodontics and tissue engineering.

Cortisol regulates the paracrine action of macrophages by inducing vasoactive gene expression in endometrial cells

The human endometrium undergoes inflammation and tissue repair during menstruation. We hypothesized that the local availability of bioactive glucocorticoids plays an important role in immune cell-vascular cell interactions in endometrium during tissue repair at menstruation, acting either directly or indirectly via tissue resident macrophages. We sought to determine whether endometrial macrophages are direct targets for glucocorticoids; whether cortisol-treated macrophages have a paracrine effect on angiogenic gene expression by endometrial endothelial cells; and whether endometrial macrophages express angiogenic factors. Human endometrium (n = 41) was collected with ethical approval and subject consent. Donor peripheral blood monocyte-derived macrophages were treated with estradiol, progesterone, or cortisol. The effect of peripheral blood monocyte-derived macrophage secretory products on the expression of angiogenic RNAs by endothelial cells was examined. Immunofluorescence was used to examine localization in macrophages and other endometrial cell types across the menstrual cycle. Endometrial macrophages express the glucocorticoid receptor. In vitro culture with supernatants from cortisol-treated peripheral blood monocyte-derived macrophages resulted in altered endometrial endothelial cell expression of the angiogenic genes, CXCL2, CXCL8, CTGF, and VEGFC These data highlight the importance of local cortisol in regulating paracrine actions of macrophages in the endometrium. CXCL2 and CXCL8 were detected in endometrial macrophages in situ. The expression of these factors was highest in the endometrium during the menstrual phase, consistent with these factors having a role in endometrial repair. Our data have indicated that activation of macrophages with glucocorticoids might have paracrine effects by increasing angiogenic factor expression by endometrial endothelial cells. This might reflect possible roles for macrophages in endometrial repair of the vascular bed after menstruation.

Engineered hybrid cardiac patches with multifunctional electronics for online monitoring and regulation of tissue function

In cardiac tissue engineering approaches to treat myocardial infarction, cardiac cells are seeded within three-dimensional porous scaffolds to create functional cardiac patches. However, current cardiac patches do not allow for online monitoring and reporting of engineered-tissue performance, and do not interfere to deliver signals for patch activation or to enable its integration with the host. Here, we report an engineered cardiac patch that integrates cardiac cells with flexible, freestanding electronics and a 3D nanocomposite scaffold. The patch exhibited robust electronic properties, enabling the recording of cellular electrical activities and the on-demand provision of electrical stimulation for synchronizing cell contraction. We also show that electroactive polymers containing biological factors can be deposited on designated electrodes to release drugs in the patch microenvironment on demand. We expect that the integration of complex electronics within cardiac patches will eventually provide therapeutic control and regulation of cardiac function.

Seeing is believing, PLGA microsphere degradation revealed in PLGA microsphere/PVA hydrogel composites

The aim of this study was to understand the polymer degradation and drug release mechanism from PLGA microspheres embedded in a PVA hydrogel. Two types of microspheres were prepared with different molecular weight PLGA polymers (approximately 25 and 7 kDa) to achieve different drug release profiles, with a 9-day lag phase and without a lag phase, respectively. The kinetics of water uptake into the microspheres coincided with the drug release profiles for both formulations. For the 25 kDa microspheres, minimal water uptake was observed in the early part of the lag phase followed by substantial water uptake at the later stages and in the drug release phase. For the 7 kDa microspheres, water uptake occurred simultaneously with drug release. Water uptake was approximately 2-3 times that of the initial microsphere weight for both formulations. The internal structure of the PLGA microspheres was evaluated using low temperature scanning electron microscopy (cryo-SEM). Burst drug release occurred followed by pore forming from the exterior to the core of both microspheres. A well-defined hydrogel/microsphere interface was observed. For the 25 kDa microspheres, internal pore formation and swelling occurred before the second drug release phase. The surface layer of the microspheres remained intact whereas swelling, and degradation of the core continued throughout the drug release period. In addition, microsphere swelling reduced glucose transport through the coatings in PBS media and this was considered to be a as a consequence of the increased thickness of the coatings. The combination of the swelling and microdialysis results provides a fresh understanding on the competing processes affecting molecular transport of bioanalytes (i.e. glucose) through these composite coatings during prolonged exposure in PBS.

Modulation of Inflammatory Response and Induction of Bone Formation Based on Combinatorial Effects of Resveratrol

The success of bone tissue engineering strategies critically depends on the rapid formation of a mature vascular network in the scaffolds after implantation. Conventional methods to accelerate the infiltration of host vasculature into the scaffolds need to consider the role of host response in regulation of bone tissue ingrowth and extent of vascularization. The long term goal of this study was to harness the potential of inflammatory response to enhance angiogenesis and bone formation in three dimensional (3D) scaffolds. Towards this goal, we explored the use of resveratrol, a natural compound commonly used in complementary medicine, to enable the concurrently (i) mediate M1 to M2 macrophage plasticity, (ii) impart natural release of angiogenic factors by macrophages and (iii) enhance osteogenic differentiation of human mesenchymal stem cells (hMSCs). We mapped the time-dependent response of macrophage gene expression as well as hMSC osteogenic differentiation to varying doses of resveratrol. The utility of this approach was evaluated in 3D poly (lactide-co-glycolide) (PLGA) sintered microsphere scaffolds for bone tissue engineering applications. Our results altogether delineate the potential to synergistically accelerate angiogenic factor release and upregulate osteogenic signaling pathways by "dialing" the appropriate degree of resveratrol release.

Porous, Dexamethasone-loaded polyurethane coatings extend performance window of implantable glucose sensors in vivo

Continuous glucose sensors offer the promise of tight glycemic control for insulin dependent diabetics; however, utilization of such systems has been hindered by issues of tissue compatibility. Here we report on the in vivo performance of implanted glucose sensors coated with Dexamethasone-loaded (Dex-loaded) porous coatings employed to mediate the tissue-sensor interface. Two animal studies were conducted to (1) characterize the tissue modifying effects of the porous Dex-loaded coatings deployed on sensor surrogate implants and (2) investigate the effects of the same coatings on the in vivo performance of Medtronic MiniMed SOF-SENSOR™ glucose sensors. The tissue response to implants was evaluated by quantifying macrophage infiltration, blood vessel formation, and collagen density around implants. Sensor function was assessed by measuring changes in sensor sensitivity and time lag, calculating the Mean Absolute Relative Difference (MARD) for each sensor treatment, and performing functional glucose challenge test at relevant time points. Implants treated with porous Dex-loaded coatings diminished inflammation and enhanced vascularization of the tissue surrounding the implants. Functional sensors with Dex-loaded porous coatings showed enhanced sensor sensitivity over a 21-day period when compared to controls. Enhanced sensor sensitivity was accompanied with an increase in sensor signal lag and MARD score. These results indicate that Dex-loaded porous coatings were able to elicit an attenuated tissue response, and that such tissue microenvironment could be conducive towards extending the performance window of glucose sensors in vivo.

STATEMENT OF SIGNIFICANCE

In the present article, a coating to extend the functionality of implantable glucose sensors in vivo was developed. Our study showed that the delivery of an anti-inflammatory agent with the presentation of micro-sized topographical cues from coatings may lead to improved long-term glucose sensor function in vivo. We believe that improved function of sensors treated with the novel coatings was a result of the observed decreases in inflammatory cell density and increases in vessel density of the tissue adjacent to the devices. Furthermore, extending the in vivo functionality of implantable glucose sensors may lead to greater adoption of these devices by diabetic patients.

Materials for microfabricated implantable devices: a review

The application of microfabrication to the development of biomedical implants has produced a new generation of miniaturized technology for assisting treatment and research. Microfabricated implantable devices (μID) are an increasingly important tool, and the development of new μIDs is a rapidly growing field that requires new microtechnologies able to safely and accurately function in vivo. Here, we present a review of μID research that examines the critical role of material choice in design and fabrication. Materials commonly used for μID production are identified and presented along with their relevant physical properties and a survey of the state-of-the-art in μID development. The consequence of material choice as it pertains to microfabrication and biocompatibility is discussed in detail with a particular focus on the divide between hard, rigid materials and soft, pliable polymers.

In vitro and in vivo performance of dexamethasone loaded PLGA microspheres prepared using polymer blends

The foreign body reaction is the major cause of the dysfunction and relatively short lifetime associated with implanted glucose biosensors. An effective strategy to maintain sensor functionality is to apply biocompatible coatings that elute drug to counter the negative tissue reactions. This has been achieved using dexamethasone releasing poly(lactic-co-glycolic acid) (PLGA) microspheres embedded in a polyvinyl alcohol (PVA) hydrogel coating. Accordingly, the biosensor lifetime relies on the duration and dose of drug release from the coating. To achieve long-term drug release mixed populations of microspheres have been used. In the current study, microspheres were prepared by blending low (25KDa) and high (113KDa) molecular weight PLGA at different mass ratios to overcome problems associated with mixing multiple populations of microspheres. "Real-time" in vitro studies demonstrated dexamethasone release for approximately 5 months. An accelerated method with discriminatory ability was developed to shorten drug release to less than 2 weeks. An in vivo pharmacodynamics study demonstrated efficacy against the foreign body reaction for 4.5 months. Such composite coatings composed of PLGA microspheres prepared using polymer blends could potentially be used to ensure long-term performance of glucose sensors.

Prediction of dexamethasone release from PLGA microspheres prepared with polymer blends using a design of experiment approach

Hydrophobic drug release from poly (lactic-co-glycolic acid) (PLGA) microspheres typically exhibits a tri-phasic profile with a burst release phase followed by a lag phase and a secondary release phase. High burst release can be associated with adverse effects and the efficacy of the formulation cannot be ensured during a long lag phase. Accordingly, the development of a long-acting microsphere product requires optimization of all drug release phases. The purpose of the current study was to investigate whether a blend of low and high molecular weight polymers can be used to reduce the burst release and eliminate/minimize the lag phase. A single emulsion solvent evaporation method was used to prepare microspheres using blends of two PLGA polymers (PLGA5050 (25 kDa) and PLGA9010 (113 kDa)). A central composite design approach was applied to investigate the effect of formulation composition on dexamethasone release from these microspheres. Mathematical models obtained from this design of experiments study were utilized to generate a design space with maximized microsphere drug loading and reduced burst release. Specifically, a drug loading close to 15% can be achieved and a burst release less than 10% when a composition of 80% PLGA9010 and 90 mg of dexamethasone is used. In order to better describe the lag phase, a heat map was generated based on dexamethasone release from the PLGA microsphere/PVA hydrogel composite coatings. Using the heat map an optimized formulation with minimum lag phase was selected. The microspheres were also characterized for particle size/size distribution, thermal properties and morphology. The particle size was demonstrated to be related to the polymer concentration and the ratio of the two polymers but not to the dexamethasone concentration.

A remotely operated drug delivery system with an electrolytic pump and a thermo-responsive valve

Implantable drug delivery devices are becoming attractive due to their abilities of targeted and controlled dose release. Currently, two important issues are functional lifetime and non-controlled drug diffusion. In this work, we present a drug delivery device combining an electrolytic pump and a thermo-responsive valve, which are both remotely controlled by an electromagnetic field (40.5 mT and 450 kHz). Our proposed device exhibits a novel operation mechanism for long-term therapeutic treatments using a solid drug in reservoir approach. Our device also prevents undesired drug liquid diffusions. When the electromagnetic field is on, the electrolysis-induced bubble drives the drug liquid towards the Poly (N-Isopropylacrylamide) (PNIPAM) valve that consists of PNIPAM and iron micro-particles. The heat generated by the iron micro-particles causes the PNIPAM to shrink, resulting in an open valve. When the electromagnetic field is turned off, the PNIPAM starts to swell. In the meantime, the bubbles are catalytically recombined into water, reducing the pressure inside the pumping chamber, which leads to the refilling of the fresh liquid from outside the device. A catalytic reformer is included, allowing more liquid refilling during the limited valve's closing time. The amount of body liquid that refills the drug reservoir can further dissolve the solid drug, forming a reproducible drug solution for the next dose. By repeatedly turning on and off the electromagnetic field, the drug dose can be cyclically released, and the exit port of the device is effectively controlled.

Foreign Body Reaction to Implantable Biosensors: Effects of Tissue Trauma and Implant Size

BACKGROUND

Implantable biosensors for continuous glucose monitoring can greatly improve diabetes management. However, their applications are still associated with some challenges and one of these is the gradual functionality loss postimplantation as a consequence of the foreign body response (FBR). Sensor miniaturization in combination with drug-eluting biocompatible coatings is a promising strategy to enhance in vivo performance. However, limited study has been performed to understand the effect of initial trauma and implant size on foreign body reaction as well as in vivo performance of implantable glucose sensors.

METHODS

Different initial trauma was induced by implanting composite coated dummy sensors into rats using various sized needles and 3 different-sized dummy sensors were implanted to examine the size effect. Histological evaluation was performed to relate the inflammatory cell counts and foreign body capsule thickness with the implantation needle size and sensor size respectively. The effect of biocompatible coating on the performance of implantable glucose sensors was determined using both coated amperometric glucose sensors and microdialysis probes.

RESULTS

The results revealed that the degree of acute inflammation was mainly controlled by the extent of the initial trauma: the greater the trauma, the greater the acute inflammatory response. Implant size did not affect the acute inflammatory phase. However, the extent of chronic inflammation and fibrous encapsulation were affected by sensor size: the smaller the size the less the extent of chronic inflammation and fibrous encapsulation. Glucose sensors implanted using 14 gauge needles showed significantly lower initial in vivo response compared to those implanted using 16 gauge needles. This was not observed for sensors with dexamethasone-eluting biocompatible coatings since inflammation was suppressed.

CONCLUSIONS

The results of the current study indicate that the extent of the inflammatory response post-sensor implantation varies as a function of the initial tissue trauma as well as the sensor size. Accordingly, miniaturization of implantable biosensors together with the utilization of a drug-eluting biocompatible composite coating may be a promising strategy to achieve long-term reliable continuous glucose monitoring.

Drug Distribution in Microspheres Enhances Their Anti-Inflammatory Properties in the Gottingen Minipig

The foreign body reaction (FBR), one of the body's defense mechanisms against foreign materials, results in loss of implant biocompatibility. A popular strategy to prevent FBR is the constant release of dexamethasone in the tissue surrounding the implant. However, FBR prevention has not been sufficiently studied in large animal models, which offer a better representation of the human subcutaneous tissue physiology. Accordingly, a long-term strategy to prevent FBR to subcutaneous implants in a large animal model is necessary to translate the existing research for clinical applications. Here, a poly(lactic-co-glycolic) (PLGA) microsphere/poly(vinyl alcohol) (PVA) hydrogel composite coating for one-month prevention of FBR in Gottingen minipigs was developed. A modified PLGA microsphere formulation process is presented, that utilizes coprecipitation of dexamethasone and PLGA. Traditional methods result in heterogeneous distribution of large drug crystals in the microsphere matrix, which in turn results in low drug loading since the drug crystal size is close to that of the microspheres. The modified microsphere preparation method showed homogeneous distribution of dexamethasone, which in turn gave rise to increased drug loading, low burst release, and minimal lag phase. Elimination of the lag phase was dictated from previous work that compared FBR between rats and minipigs. The ability of the coatings to improve implant biocompatibility was successfully tested in vivo via histological examination of explanted tissue from the area surrounding the implants. The biocompatible coatings presented here are suitable for miniaturized implantable devices, such as biosensors, that require constant communication with the local microenvironment.

Multiple tissue response modifiers to promote angiogenesis and prevent the foreign body reaction around subcutaneous implants

Dexamethasone-releasing PLGA poly(lactic-co-glycolic acid) microsphere/PVA (polyvinyl alcohol) hydrogel composite coatings have been shown to prevent the foreign body reaction (FBR) to subcutaneous implants in small and large animal models. Such coatings were developed to extend the lifetime of implantable biosensors. However, long-term exposure of tissue to low levels of dexamethasone results in a reduction in blood vessel density due to the anti-angiogenic effect of dexamethasone. This mild effect, while not threatening to the subject's health, may interfere with analyte detection and the sensor response time over the long-term. The present work is focused on the development of coatings that deliver combinations of three tissue response modifiers (TRMs): dexamethasone, VEGF (vascular endothelial growth factor) and PDGF (platelet derived growth factor). Dexamethasone, VEGF and PDGF prevent the FBR, increase angiogenesis and promote blood vessel maturation (which increases blood flow), respectively. To minimize any potential interference among these three TRMs (for example, PDGF increases fibrosis), the relative doses of dexamethasone, VEGF and PDGF were adjusted. It was determined that: a) all three TRMs are required for maximum promotion of angiogenesis, blood vessel maturation and prevention of the FBR; b) VEGF has to be administered at higher doses than PDGF; c) an increase in dexamethasone dosing must be accompanied by a proportional increase in growth factor dosing; and d) modification of the TRM ratio can achieve a constant capillary density throughout the implantation period which is important for applications such as biosensors to maintain sensitivity and a stable sensor baseline. Moreover, an osmosis-driven process for encapsulation of proteins in PLGA microspheres that showed low burst release was developed.

Towards the design of 3D multiscale instructive tissue engineering constructs: Current approaches and trends

The design of 3D constructs with adequate properties to instruct and guide cells both in vitro and in vivo is one of the major focuses of tissue engineering. Successful tissue regeneration depends on the favorable crosstalk between the supporting structure, the cells and the host tissue so that a balanced matrix production and degradation are achieved. Herein, the major occurring events and players in normal and regenerative tissue are overviewed. These have been inspiring the selection or synthesis of instructive cues to include into the 3D constructs. We further highlight the importance of a multiscale perception of the range of features that can be included on the biomimetic structures. Lastly, we focus on the current and developing tissue-engineering approaches for the preparation of such 3D constructs: top-down, bottom-up and integrative. Bottom-up and integrative approaches present a higher potential for the design of tissue engineering devices with multiscale features and higher biochemical control than top-down strategies, and are the main focus of this review.

The paracrine effects of adipose-derived stem cells on neovascularization and biocompatibility of a macroencapsulation device

The foreign-body response to biomaterials compromises the performance of many biomedical devices by severe fibrosis and limited neovascularization. Mesenchymal stem cells are known to secrete cytokines for treating inflammatory conditions. In this study, we aim to investigate whether the paracrine products of adipose-derived mesenchymal stem cells (ADSCs) can affect the microenvironment of biomaterials and improve tissue responses to biomaterial implants. A model system was built by loading ADSC spheroids into a macroencapsulation device composed of polytetrafluoroethylene (PTFE) filtration membranes. Soluble ADSC factors that diffused out of the device in vitro promoted the angiogenetic activity of endothelial cells and affected the secretion pattern of macrophages. In vivo study was carried out by subcutaneously embedding blank or ADSC-laden devices in rats. Following a 4 week implantation, the ADSC-laden devices were better vascularized and induced significantly less fibrotic tissue formation in comparison to the non-cellular controls. This study may facilitate our understanding of foreign-body responses and suggest new ways to improve the tissue reaction of biomedical devices for cell-based therapy.

Osteoinductive fibrous scaffolds of biopolymer/mesoporous bioactive glass nanocarriers with excellent bioactivity and long-term delivery of osteogenic drug

Designing scaffolds with bioactive composition and long-term drug delivery capacity is a promising method to improve the therapeutic efficacy in bone regeneration. Herein, electrospun fibrous scaffolds of polycaprolactone-gelatin incorporating mesoporous bioactive glass nanoparticles (mBGn) were proposed to be excellent matrix platforms for bone tissue engineering. In particular, the mBGn were loaded with osteogenic drug Dexamethasone (DEX) to elicit additional therapeutic potential. The mBGn-added fiber scaffolds demonstrated excellent properties, including improved mechanical tensile strength, elasticity, and hydrophilicity compared to pure biopolymer matrix. The scaffolds could release substantial amounts of calcium and silicate ions. The loading of DEX onto mBGn was as high as 63%, that is, 0.63 mg DEX loaded per 1 mg of mBGn, demonstrating an effective nanodepot role of the mBGn. The release of DEX from the mBGn-added fiber scaffolds was highly sustainable, profiling an almost linear release kinetics up to the test period of 28 days, after a rapid initial release of ∼30% within 24 h. The proliferation and osteogenic differentiation of stem cells derived from periodontal ligament were significantly improved by the mBGn incorporation and synergistically stimulated with DEX loading, as confirmed by both direct and indirect cultures. The effects on bone regeneration in vivo, as analyzed by microcomputed tomography and histological stains in a rat calvarium model over 6 weeks, were substantial with the mBGn incorporation and even better with DEX loading, evidencing the osteogenic effects of the drug-eluting nanocomposite fiber scaffolds in bone formation. The current scaffolds with bone-bioactive composition and drug delivery capacity may be potentially useful for bone regeneration as novel osteogenic matrices.

First step toward near-infrared continuous glucose monitoring: in vivo evaluation of antibody coupled biomaterials

Continuous glucose monitoring (CGM) is crucial in diabetic care. Long-term CGM systems however require an accurate sensor as well as a suitable measuring environment. Since large intravenous sensors are not feasible, measuring inside the interstitial fluid is considered the best alternative. This option, unfortunately, has the drawback of a lag time with blood glucose values. A good strategy to circumvent this is to enhance tissue integration and enrich the peri-implant vasculature. Implants of different optically transparent biomaterials (poly(methyl-methacrylate) [PMMA] and poly(dimethylsiloxane) [PDMS]) - enabling glucose monitoring in the near-infrared (NIR) spectrum - were surface-treated and subsequently implanted in goats at various implantation sites for up to 3 months. The overall in vivo biocompatibility, tissue integration, and vascularization at close proximity of the surfaces of these materials were assessed. Histological screening showed similar tissue reactions independent of the implantation site. No significant inflammation reaction was observed. Tissue integration and vascularization correlated, to some extent, with the biomaterial composition. A modification strategy, in which a vascular endothelial-cadherin antibody was coupled to the biomaterials surface through a dopamine layer, showed significantly enhanced vascularization 3 months after subcutaneous implantation. Our results suggest that the developed strategy enables the creation of tissue interactive NIR transparent packaging materials, opening the possibility of continuous glucose monitoring.

A poly(lactide) stereocomplex structure with modified magnesium oxide and its effects in enhancing the mechanical properties and suppressing inflammation

Biodegradable polymers such as poly(L-lactide) (PLLA) have been widely utilized as materials for biomedical applications. However, the relatively poor mechanical properties of PLLA and its acid-induced cell inflammation brought about by the acidic byproducts during biodegradation pose severe problems. In this study, these drawbacks of PLLA are addressed using a stereocomplex structure, where oligo-D-lactide-grafted magnesium hydroxide (MgO-ODLA) is synthesized by grafting d-lactide onto the surface of magnesium hydroxide, which is then blended with a PLLA film. The structure, morphology, pH change, thermal and mechanical properties, in-vitro cytotoxicity, and inflammation effect of the MgO-ODLAs and their PLLA composites are evaluated through various analyses. The PLLA/MgO70-ODLA30 (0-20 wt%) composite with a stereocomplex structure shows a 20% increase in its tensile strength and an improvement in the modulus compared to its oligo-L-lactide (PLLA/MgO70-OLLA30) counterpart. The interfacial interaction parameter of PLLA/MgO70-ODLA30 (5.459) has superior properties to those of PLLA/MgO70-OLLA30 (4.013) and PLLA/Mg(OH)2 (1.774). The cell cytotoxicity and acid-induced inflammatory response are suppressed by the neutralizing effect of the MgO-ODLAs. In addition, the inflammatory problem caused by the rapid acidification of the stereocomplex structure is also addressed. As a result, the stereocomplex structure of the MgO-ODLA/PLLA composite can be used to overcome the problems associated with the biomedical applications of PLLA films.

Porous PLGA microspheres tailored for dual delivery of biomolecules via layer-by-layer assembly

Tissue engineering is a complex and dynamic process that requires varied biomolecular cues to promote optimal tissue growth. Consequently, the development of delivery systems capable of sequestering more than one biomolecule with controllable release profiles is a key step in the advancement of this field. This study develops multilayered polyelectrolyte films incorporating alpha-melanocyte stimulating hormone (α-MSH), an anti-inflammatory molecule, and basic fibroblast growth factor (bFGF). The layers were successfully formed on macroporous poly lactic-co-glycolic acid microspheres produced using a combined inkjet and thermally induced phase separation technique. Release profiles could be varied by altering layer properties including the number of layers and concentrations of layering molecules. α-MSH and bFGF were released in a sustained manner and the bioactivity of α-MSH was shown to be preserved using an activated macrophage cell assay in vitro. The system performance was also tested in vivo subcutaneously in rats. The multilayered microspheres reduced the inflammatory response induced by a carrageenan stimulus 6 weeks after implantation compared to the non-layered microspheres without the anti-inflammatory and growth factors, demonstrating the potential of such multilayered constructs for the controlled delivery of bioactive molecules.

Polymeric delivery systems for dexamethasone

Glucocorticoids (GCs) are broadly used in the treatment of inflammation and in suppressing hyperactivity of the immune system expressed in allergies, asthma, autoimmune diseases and sepsis. They are pleiotropic in nature, showing a wide range of diverse effects, including those which are harmful for the organism. Dexamethasone (DEX) is one of the most frequently used GCs and is considered as one of the safest. Still serious side-effects have been observed for this drug, mostly due to its hydrophobicity and low bioavailability. The potentially promising polymeric carrier systems to deliver DEX effectively are revised.

Microdialysis sampling techniques applied to studies of the foreign body reaction

Implanted materials including drug delivery devices and chemical sensors undergo what is termed the foreign body reaction (FBR). Depending on the device and its intended application, the FBR can have differing consequences. An extensive scientific research effort has been devoted to elucidating the cellular and molecular mechanisms that drive the FBR. Important, yet relatively unexplored, research includes the localized tissue biochemistry and the chemical signaling events that occur throughout the FBR. This review provides an overview of the mechanisms of the FBR, describes how the FBR affects different implanted devices, and illustrates the role that microdialysis sampling can play in further elucidating the chemical communication processes that drive FBR outcomes.

Construction of polyfunctional coatings assisted by gallic acid to facilitate co-immobilization of diverse biomolecules

Designing a multifunctional surface based on the coimmobilization of two or more diverse biomolecules with synergic action is very important in certain cases. In this work, a facile method by two-step aimed to construct a polyfunctional coating containing -COOH, -NH2, and phenol/quinine groups was reported. The first-step was to introduce amine groups onto target modified-surface by coating with plasma polymerized allylamine (PPAam), followed by the second-step conjugation of gallic acid (3,4,5-trihydroxybenzoic acid) onto the PPAam surface. The density of -COOH, -NH2, and phenol/quinone groups could be regulated easily by adjusting the reaction time of GA conjugation, making it possible to coimmobilize two or three diverse molecules. This has been shown by the successful coimmobilization of anti-CD34 antibody and vascular endothelial growth factor (VEGF). The surface coimmobilized with the anti-CD34 antibody and VEGF presented significant enhancement in the capture of endothelial progenitor cells (EPCs) and the growth of human umbilical vein endothelial cells (HUVECs). These data suggest the huge potential of such polyfunctional coating for tailoring the desired interfacial properties of materials through selectively conjugating two or more diverse bioactive molecules with synergic action.

A miniaturized transcutaneous system for continuous glucose monitoring

Implantable sensors for continuous glucose monitoring hold great potential for optimal diabetes management. This is often undermined by a variety of issues associated with: (1) negative tissue response; (2) poor sensor performance; and (3) lack of device miniaturization needed to reduce implantation trauma. Herein, we report our initial results towards constructing an implantable device that simultaneously address all three aforementioned issues. In terms of device miniaturization, a highly miniaturized CMOS (complementary metal-oxide-semiconductor) potentiostat and signal processing unit was employed (with a combined area of 0.665 mm(2)). The signal processing unit converts the current generated by a transcutaneous, Clark-type amperometric sensor to output frequency in a linear fashion. The Clark-type amperometric sensor employs stratification of five functional layers to attain a well-balanced mass transfer which in turn yields a linear sensor response from 0 to 25 mM of glucose concentration, well beyond the physiologically observed (2 to 22 mM) range. In addition, it is coated with a thick polyvinyl alcohol (PVA) hydrogel with embedded poly(lactic-co-glycolic acid) (PLGA) microspheres intended to provide continuous, localized delivery of dexamethasone to suppress inflammation and fibrosis. In vivo evaluation in rat model has shown that the transcutaneous sensor system reproducibly tracks repeated glycemic events. Clarke's error grid analysis on the as-obtained glycemic data has indicated that all of the measured glucose readings fell in the desired Zones A & B and none fell in the erroneous Zones C, D and E. Such reproducible operation of the transcutaneous sensor system, together with low power (140 μW) consumption and capability for current-to-frequency conversion renders this a versatile platform for continuous glucose monitoring and other biomedical sensing devices.

Development and evaluation of sustained-release etoposide-loaded poly(ε-caprolactone) implants

Poly(ε-caprolactone) implants containing etoposide, an important chemotherapeutic agent and topoisomerase II inhibitor, were fabricated by a melt method and characterized in terms of content uniformity, morphology, drug physical state, and sterility. In vitro and in vivo drug release from the implants was also evaluated. The cytotoxic activity of implants against HeLa cells was studied. The short-term tolerance of the implants was investigated after subcutaneous implantation in mice. The original chemical structure of etoposide was preserved after incorporation into the polymeric matrix, in which the drug was dispersed uniformly. Etoposide was present in crystalline form in the polymeric implant. In vitro release study showed prolonged and controlled release of etoposide, which showed cytotoxicity activity against HeLa cells. After implantation, good correlation between in vitro and in vivo drug release was found. The implants demonstrated good short-term tolerance in mice. These results tend to show that etoposide-loaded implants could be potentially applied as a local etoposide delivery system.

Angiogenic therapy for cardiac repair based on protein delivery systems

Cardiovascular diseases remain the first cause of morbidity and mortality in the developed countries and are a major problem not only in the western nations but also in developing countries. Current standard approaches for treating patients with ischemic heart disease include angioplasty or bypass surgery. However, a large number of patients cannot be treated using these procedures. Novel curative approaches under investigation include gene, cell, and protein therapy. This review focuses on potential growth factors for cardiac repair. The role of these growth factors in the angiogenic process and the therapeutic implications are reviewed. Issues including aspects of growth factor delivery are presented in relation to protein stability, dosage, routes, and safety matters. Finally, different approaches for controlled growth factor delivery are discussed as novel protein delivery platforms for cardiac regeneration.

Enhancing the sensitivity of needle-implantable electrochemical glucose sensors via surface rebuilding

OBJECTIVE

Needle-implantable sensors have shown to provide reliable continuous glucose monitoring for diabetes management. In order to reduce tissue injury during sensor implantation, there is a constant need for device size reduction, which imposes challenges in terms of sensitivity and reliability, as part of decreasing signal-to-noise and increasing layer complexity. Herein, we report sensitivity enhancement via electrochemical surface rebuilding of the working electrode (WE), which creates a three-dimensional nanoporous configuration with increased surface area.

METHODS

The gold WE was electrochemically rebuilt to render its surface nanoporous followed by decoration with platinum nanoparticles. The efficacy of such process was studied using sensor sensitivity against hydrogen peroxide (H2O2). For glucose detection, the WE was further coated with five layers, namely, (1) polyphenol, (2) glucose oxidase, (3) polyurethane, (4) catalase, and (5) dexamethasone-releasing poly(vinyl alcohol)/poly(lactic-co-glycolic acid) composite. The amperometric response of the glucose sensor was noted in vitro and in vivo.

RESULTS

Scanning electron microscopy revealed that electrochemical rebuilding of the WE produced a nanoporous morphology that resulted in a 20-fold enhancement in H2O2 sensitivity, while retaining >98% selectivity. This afforded a 4-5-fold increase in overall glucose response of the glucose sensor when compared with a control sensor with no surface rebuilding and fittable only within an 18 G needle. The sensor was able to reproducibly track in vivo glycemic events, despite the large background currents typically encountered during animal testing.

CONCLUSION

Enhanced sensor performance in terms of sensitivity and large signal-to-noise ratio has been attained via electrochemical rebuilding of the WE. This approach also bypasses the need for conventional and nanostructured mediators currently employed to enhance sensor performance.

Enhanced cytotoxicity for colon 26 cells using doxorubicin-loaded sorbitan monooleate (Span 80) vesicles

Span 80 (sorbitan monooleate) vesicles behaved differently from conventional phospholipid vesicles (liposomes) because the former had a more fluid interface. After doxorubicin hydrochloride (DOX) was encapsulated into the Span 80 vesicle (loading efficiency: 63 %), DOX-loaded Span 80 vesicles (DVs) were thereafter added to Colon 26 cells. It was suggested, from the flow cytometric analysis and confocal laser microscopic observation, that DVs directly deliver DOX into the cytoplasm of Colon 26 cells. DVs showed the different delivery manner from the DOX-loaded liposomes (DLs). It is considered that the difference of delivery manner between DVs and DLs resulted in the difference of cytotoxicity (IC₅₀); i.e. IC₅₀ values for DVs and DLs were 5 and > 30 μM, respectively. The results obtained herein would give the fundamental findings which can contribute to the improvement of formulation of conventional liposome-based carrier and its cytotoxicity.

Polymeric "smart" coatings to prevent foreign body response to implantable biosensors

Application of implantable glucose biosensors for "real-time" monitoring is reliant on controlling the negative tissue reaction at the sensor tissue interphase. A novel polymer coating consisting of poly(lactic-co-glycolic) acid (PLGA) microsphere dispersed in poly(vinyl alcohol) (PVA) hydrogels was evaluated in combination with dummy sensors as a "smart" drug eluting biocompatible coating for implantable biosensors to prevent the foreign body response, and thus enhance sensor performance in vivo. The polymeric microspheres slowly release tissue-modifying drugs at the implantation sites to control the inflammation and fibrous encapsulation, while the hydrogel allows rapid analyte diffusion to the sensing elements. Dummy sensors with identical dimensions to that of the functional glucose sensors (0.5×0.5×5mm) were coated with the PLGA/PVA composites using a mold fabrication process. Both normal and diabetic rats were used in the current study to investigate the effect of the diabetic state on tissue sensor interactions. It was evident that the PLGA/PVA hydrogel composite was able to form a uniform coating around the dummy sensor and stayed intact throughout the course of the study (one month). Tissue samples containing dummy sensors that were coated with dexamethasone free composites exhibited acute and chronic inflammation as well as fibrous encapsulation in both normal and diabetic rats. However, the diabetic rats exhibited decreased intensity and delayed onset of the foreign body response following implantation of drug free dummy sensors in comparison to those of normal rats. On the other hand, tissues containing dummy sensors that were coated with dexamethasone containing composites remained normal (i.e. similar to untreated tissues), with no inflammatory reaction or fibrous encapsulation occurring over the one-month period in both the normal and diabetic rats. The feasibility of utilizing PLGA microsphere/PVA hydrogel composites as coatings for implantable biosensors was demonstrated. This polymeric composite is an innovative approach to control the foreign body reaction at the tissue-device interface to prolong biosensor lifetime.

Controlling fibrous capsule formation through long-term down-regulation of collagen type I (COL1A1) expression by nanofiber-mediated siRNA gene silencing

The foreign body reaction often interferes with the long-term functionality and performance of implanted biomedical devices through fibrous capsule formation. While many implant modification techniques have been adopted in attempts to control fibrous encapsulation, the outcomes remained sub-optimal. Nanofiber scaffold-mediated RNA interference may serve as an alternative approach through the localized and sustained delivery of siRNA at implant sites. In this study, we investigated the efficacy of siRNA-poly(caprolactone-co-ethylethylene phosphate) nanofibers in controlling fibrous capsule formation through the down-regulation of collagen type I (COL1A1) in vitro and in vivo. By encapsulating complexes of COL1A1 siRNA with a transfection reagent (Transit TKO) or the cell penetrating peptides CADY or MPG within the nanofibers (550-650 nm in diameter), a sustained release of siRNA was obtained for at least 28 days (loading efficiency ~60-67%). Scaffold-mediated transfection significantly enhanced cellular uptake of oligonucleotides and prolonged in vitro gene silencing duration by at least 2-3 times as compared to conventional bolus delivery of siRNA (14 days vs. 5-7 days by bolus delivery). In vivo subcutaneous implantation of siRNA scaffolds revealed a significant decrease in fibrous capsule thickness at weeks 2 and 4 as compared to plain nanofibers (p<0.05). Taken together, the results demonstrated the efficacy of scaffold-mediated siRNA gene-silencing in providing effective long-term control of fibrous capsule formation.

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.

VEGF microsphere technology to enhance vascularization in fat grafting

Vascularization is crucial for implantation of engineered tissues in reconstructive surgery. Polypeptides encapsulated in microspheres can be efficiently transported to their site of action and released in a sustained dosage. We evaluated the effect of delivering vascular endothelial growth factor (VEGF)-encapsulated microspheres in a lipoaspirate scaffold on vascularization and tissue survival. The VEGF-loaded (n=6) and empty (n=6) poly(lactic-co-glycolic acid) microspheres in human lipoaspirate and the human lipoaspirate alone (n=6) were injected subcutaneously into the flanks of athymic nude mice. Three mice from each group were killed, and grafts were explanted at weeks 3 and 6. Increases in mass and volume of VEGF samples, as well as decreases in empty and lipoaspirate-only samples, were observed at 3 and 6 weeks, reaching statistical significance at 6 weeks. Hematoxylin and eosin and CD31+ imaging demonstrated significantly greater vascularization in VEGF samples than in both the empty and lipoaspirate-only groups at both 3 and 6 weeks.

Effect of dexamethasone-loaded poly(lactic-co-glycolic acid) microsphere/poly(vinyl alcohol) hydrogel composite coatings on the basic characteristics of implantable glucose sensors

BACKGROUND

Hydrogels alone and in combination with microsphere drug delivery systems are being considered as biocompatible coatings for implantable glucose biosensors to prevent/minimize the foreign body response. Previously, our group has demonstrated that continuous release of dexamethasone from poly(lactic-co-glycolic acid) (PLGA) microsphere/poly(vinyl alcohol) (PVA) hydrogel composites can successfully prevent foreign body response at the implantation site. The objective of this study was to investigate the effect of this composite coating on sensor functionality.

METHODS

The PLGA microsphere/PVA hydrogel coatings were prepared and applied to glucose biosensors. The swelling properties of the composite coatings and their diffusivity to glucose were evaluated as a function of microsphere loading. Sensor linearity, response time, and sensitivity were also evaluated as a function of coating composition.

RESULTS

The PLGA microsphere/PVA hydrogel composite coating did not compromise sensor linearity (sensors were linear up to 30 mM), which is well beyond the physiological glucose range (2 to 22 mM). The sensor response time did increase in the presence of the coating (from 10 to 19 s); however, this response time was still less than the average reported values. Although the sensitivity of the sensors decreased from 73 to 62 nA/mM glucose when the PLGA microsphere loading in the PVA hydrogel changed from 0 to 100 mg/ml, this reduced sensitivity is acceptable for sensor functionality. The changes in sensor response time and sensitivity were due to changes in glucose permeability as a result of the coatings. The embedded PLGA microspheres reduced the fraction of bulk water present in the hydrogel matrix and consequently reduced glucose diffusion.

CONCLUSIONS

This study demonstrates that the PLGA microsphere/PVA hydrogel composite coatings allow sufficient glucose diffusion and sensor functionality and therefore may be utilized as a smart coating for implantable glucose biosensors to enhance their in vivo functionality.

Host response to xenograft ECM implantation is not different between the shoulder and body wall sites in the rat model

In the context of tendon and ligament repair, mechanical loading and the presence of joint synovial fluid are known to profoundly influence the form and function of the repair tissue and potentially the host response to biomaterials. Previously, we demonstrated that a xenograft extra cellular matrix (ECM) scaffold implanted in the rat shoulder elicited a unique host response from that seen in the body wall. However, the host response to xenografts implanted in shoulders with a tendon/capsule injury was not different from xenografts implanted in shoulders with no injury. In the current study, we hypothesized that varying clinically relevant surgical and environmental factors would introduce significant differences in host response to xenograft implantation at the shoulder. Contrary to our hypothesis, we found no significant differences in host response between any shoulder implantation conditions or between shoulder and body wall implantation in the rat model. These findings suggest that there is no advantage to using an orthotopic shoulder model to investigate the host response to rotator cuff scaffold materials in the rat model, and due to the insensitivity of its host response to various clinically relevant surgical conditions, may suggest that the rat does not provide a surrogate for directly translating the host response to biomaterials to the human application.

Microsphere erosion in outer hydrogel membranes creating macroscopic porosity to counter biofouling-induced sensor degradation

Biofouling and tissue inflammation present major challenges toward the realization of long-term implantable glucose sensors. Following sensor implantation, proteins and cells adsorb on sensor surfaces to not only inhibit glucose flux but also signal a cascade of inflammatory events that eventually lead to permeability-reducing fibrotic encapsulation. The use of drug-eluting hydrogels as outer sensor coatings has shown considerable promise to mitigate these problems via the localized delivery of tissue response modifiers to suppress inflammation and fibrosis, along with reducing protein and cell absorption. Biodegradable poly (lactic-co-glycolic) acid (PLGA) microspheres, encapsulated within a poly (vinyl alcohol) (PVA) hydrogel matrix, present a model coating where the localized delivery of the potent anti-inflammatory drug dexamethasone has been shown to suppress inflammation over a period of 1-3 months. Here, it is shown that the degradation of the PLGA microspheres provides an auxiliary venue to offset the negative effects of protein adsorption. This was realized by: (1) the creation of fresh porosity within the PVA hydrogel following microsphere degradation (which is sustained until the complete microsphere degradation) and (2) rigidification of the PVA hydrogel to prevent its complete collapse onto the newly created void space. Incubation of the coated sensors in phosphate buffered saline (PBS) led to a monotonic increase in glucose permeability (50%), with a corresponding enhancement in sensor sensitivity over a 1 month period. Incubation in serum resulted in biofouling and consequent clogging of the hydrogel microporosity. This, however, was partially offset by the generated macroscopic porosity following microsphere degradation. As a result of this, a 2-fold recovery in sensor sensitivity for devices with microsphere/hydrogel composite coatings was observed as opposed to similar devices with blank hydrogel coatings. These findings suggest that the use of macroscopic porosity can reduce sensitivity drifts resulting from biofouling, and this can be achieved synergistically with current efforts to mitigate negative tissue responses through localized and sustained drug delivery.