Biofunctionalized Electrospun Vascular Scaffolds for Enhanced Antithrombotic Properties and In Situ Endothelialization

The development of innovative vascular substitutes has become increasingly significant due to the prevalence of vascular diseases. In this study, we designed a biofunctionalized electrospun vascular scaffold by chemically conjugating heparin molecules as an antithrombotic agent with an endothelial cell (EC)-specific antibody to promote in situ endothelialization. To optimize this biofunctionalized electrospun vascular scaffolding system, we examined various parameters, including material compositions, cross-linker concentrations, and cross-linking and conjugation processes. The findings revealed that a higher degree of heparin conjugation onto the vascular scaffold resulted in improved antithrombotic properties, as confirmed by the platelet adhesion test. Additionally, the flow chamber study demonstrated that the EC-specific antibody immobilization enhanced the scaffold's EC-capturing capability compared to a nonconjugated vascular scaffold. The optimized biofunctionalized vascular scaffolds also displayed exceptional mechanical properties, such as suture retention strength and tensile properties. Our research demonstrated that the biofunctionalized vascular scaffolds and the directed immobilization of bioactive molecules could provide the necessary elements for successful acellular vascular tissue engineering applications.

Identification and characterization of stem cell secretome-based recombinant proteins for wound healing applications

Stem cells have been introduced as a promising therapy for acute and chronic wounds, including burn injuries. The effects of stem cell-based wound therapies are believed to result from the secreted bioactive molecules produced by stem cells. Therefore, treatments using stem cell-derived conditioned medium (CM) (referred to as secretome) have been proposed as an alternative option for wound care. However, safety and regulatory concerns exist due to the uncharacterized biochemical content and variability across different batches of CM samples. This study presents an alternative treatment strategy to mitigate these concerns by using fully characterized recombinant proteins identified by the CM analysis to promote pro-regenerative healing. This study analyzed the secretome profile generated from human placental stem cell (hPSC) cultures and identified nine predominantly expressed proteins (ANG-1, FGF-7, Follistatin, HGF, IL-6, Insulin, TGFβ-1, uPAR, and VEGF) that are known to contribute to wound healing and angiogenesis. These proteins, referred to as s (CMFs), were used in combination to test the effects on human dermal fibroblasts (HDFs). Our results showed that CMF treatment increased the HDF growth and accelerated cell migration and wound closure, similar to stem cell and CM treatments. In addition, the CMF treatment promoted angiogenesis by enhancing new vessel formation. These findings suggest that the defined CMF identified by the CM proteomic analysis could be an effective therapeutic solution for wound healing applications. Our strategy eliminates the regulatory concerns present with stem cell-derived secretomes and could be developed as an off-the-shelf product for immediate wound care and accelerating healing.

Bioreactor design and validation for manufacturing strategies in tissue engineering

The fields of regenerative medicine and tissue engineering offer new therapeutic options to restore, maintain or improve tissue function following disease or injury. To maximize the biological function of a tissue-engineered clinical product, specific conditions must be maintained within a bioreactor to allow the maturation of the product in preparation for implantation. Specifically, the bioreactor should be designed to mimic the mechanical, electrochemical and biochemical environment that the product will be exposed to in vivo. Real-time monitoring of the functional capacity of tissue-engineered products during manufacturing is a critical component of the quality management process. The present review provides a brief overview of bioreactor engineering considerations. In addition, strategies for bioreactor automation, in-line product monitoring and quality assurance are discussed.

Self-Assembling Peptide Solution Accelerates Hemostasis

Objective: One of the leading causes of death following traumatic injury is exsanguination. Biological material-based hemostatic agents such as fibrin, thrombin, and albumin have a high risk for causing infection. Synthetic peptide-based hemostatic agents offer an attractive alternative. The objective of this study is to explore the potential of h9e peptide as an effective hemostatic agent in both in vitro and in vivo models. Approach: In vitro blood coagulation kinetics in the presence of h9e peptide was determined as a function of gelation time using a dynamic rheometer. In vivo hemostatic effects were studied using the Wistar rat model. Results were compared to those of the commercial hemostatic product Celox™, a chitosan-based product. Adhesion of h9e peptide was evaluated using the platelet adhesion test. Biocompatibility of h9e peptide was studied in vivo using a mouse model. Results: After h9e peptide solution was mixed with blood, gelation started immediately, increased rapidly with time, and reached more than 100 Pa within 3 s. Blood coagulation strength increased as h9e peptide wt% concentration increased. In the rat model, h9e peptide solution at 5% weight concentration significantly reduced both bleeding time and blood loss, outperforming Celox. Preliminary pathological studies indicate that h9e peptide solution is biocompatible and did not have negative effects when injected subcutaneously in a mouse model. Innovation: For the first time, h9e peptide was found to have highly efficient hemostatic effects by forming nanoweb-like structures, which act as a preliminary thrombus and a surface to arrest bleeding 82% faster compared to the commercial hemostatic agent Celox. Conclusion: This study demonstrates that h9e peptide is a promising hemostatic biomaterial, not only because of its greater hemostatic effect than commercial product Celox but also because of its excellent biocompatibility based on the in vivo mouse model study.

Antibody-Conjugated Electrospun Vascular Scaffolds to Enhance In Situ Endothelialization

Tissue-engineered vascular grafts (TEVGs) are promising alternatives to small-diameter prosthetic grafts. Previous methods of seeding tubular scaffolds with autologous vascular cells have been successful; however, these methods require significant preparation time. Endothelial cell (EC) growth on the luminal surface of vascular scaffolds may be critical for the integration of a TEVG to the host environment. An alternative approach for TEVGs includes the in situ endothelialization of acellular scaffolds by capturing circulating endothelial progenitor cells (EPCs) and ECs from the bloodstream through the biofunctionalization of the vascular scaffolds. In this study, fibrous scaffolds were electrospun with a 1:1 poly(ε-caprolactone) (PCL)/collagen blend solution. The electrospun fibrous scaffolds were surface-modified by immobilizing EC-specific antibodies: CD31, vascular endothelial cadherin (VE-CAD), vascular endothelial growth factor receptor 2 (VEGFR2), and von Willebrand factor (vWF). Antibodies most efficacious at capturing ECs were then paired to examine their potential synergistic cell-capturing capabilities. The study demonstrated that vascular scaffolds bioconjugated with dual antibodies demonstrated synergistic capture efficacy compared to bioconjugation with a single antibody. The capture of circulating EPCs and ECs can be optimized with bioconjugation of one or more antibodies on the luminal surface of TEVGs.

A novel decellularized skeletal muscle-derived ECM scaffolding system for in situ muscle regeneration

The cell-based tissue engineering strategies have gained attention in restoring normal tissue function after skeletal muscle injuries; however, these approaches require a donor tissue biopsy and extensive cell expansion process prior to implantation. In order to avoid this limitation, we developed a novel cell-free muscle-specific scaffolding system that consisted of a skeletal muscle-derived decellularized extracellular matrix (dECM) and a myogenic factor, insulin growth factor-1 (IGF-1). Rheological, morphological, and biological properties of this muscle-specific scaffold (IGF-1/dECM) as well as collagen and dECM scaffolds were examined. The cell viability in all scaffolds had over 90% at 1, 3, and 7 days in culture. The cell proliferation in the IGF-1/dECM was significantly increased when compared with other groups. More importantly, the IGF-1/dECM strongly supported the myogenic differentiation in the scaffold as confirmed by myosin heavy chain (MHC) immunofluorescence. We also investigated the feasibility in a rabbit tibialis anterior (TA) muscle defect model. The IGF-1/dECM had a significantly greater number of myofibers when compared to both collagen and dECM groups at 1 and 2 months after implantation. We demonstrated that this novel muscle-specific scaffolding system could effectively promote the muscle tissue regeneration in situ.

In vitro evaluation of functionalized decellularized muscle scaffold for in situ skeletal muscle regeneration

Current treatment options for repairing volumetric muscle loss injury involve the use of existing host tissue like muscular flaps or grafts. However, host muscle tissue may not be available and donor site morbidity, such as functional loss and volume deficiency, is often present. In this study, we developed a biofunctionalized muscle-derived decellularized extracellular matrix scaffolding system to utilize endogenous stem/progenitor cells for in situ muscle tissue regeneration. We optimized the decellularization process to enhance cellular infiltration and fabricated an insulin-like growth factor-binding protein 3 (IGFBP-3)-conjugated scaffold for controlled delivery of IGF-I. We then tested in vitro characterization including IGF-I release kinetics and cellular infiltration. In addition, we have analyzed the bioactivities of skeletal muscle cells (C2C12) to assess the indirect effect of released IGF-1 from the scaffold. The IGFBP-3 conjugated scaffolds demonstrated showed sustained release of IGF-1 and 1% SDS decellularized scaffold with IGF-1 showed higher cellular infiltration compared to control scaffolds (no conjugation). In indirect bioactivity assay, IGF-1 conjugated scaffold showed 2.1-fold increased cell activity compared to control (fresh media). Our results indicate that IGFBP-3/IGF-I conjugated scaffold has the potential to be used for in situ muscle tissue regeneration.

Electrospun vascular scaffold for cellularized small diameter blood vessels: A preclinical large animal study

The strategy of vascular tissue engineering is to create a vascular substitute by combining autologous vascular cells with a tubular-shaped biodegradable scaffold. We have previously developed a novel electrospun bilayered vascular scaffold that provides proper biological and biomechanical properties as well as structural configuration. In this study, we investigated the clinical feasibility of a cellularized vascular scaffold in a preclinical large animal model. We fabricated the cellularized vascular construct with autologous endothelial progenitor cell (EPC)-derived endothelial cells (ECs) and smooth muscle cells (SMCs) followed by a pulsatile bioreactor preconditioning. This fully cellularized vascular construct was tested in a sheep carotid arterial interposition model. After preconditioning, confluent and mature EC and SMC layers in the scaffold were achieved. The cellularized constructs sustained the structural integrity with a high degree of graft patency without eliciting an inflammatory response over the course of the 6-month period in sheep. Moreover, the matured EC coverage on the lumen and a thick smooth muscle layer were formed at 6months after transplantation. We demonstrated that electrospun bilayered vascular scaffolds in conjunction with autologous vascular cells may be a clinically applicable alternative to traditional prosthetic vascular graft substitutes.

STATEMENT OF SIGNIFICANCE

This study demonstrates the utility of tissue engineering to provide platform technologies for rehabilitation of patients recovering from severe, devastating cardiovascular diseases. The long-term goal is to provide alternatives to vascular grafting using bioengineered blood vessels derived from an autologous cell source with a functionalized vascular scaffold. This novel bilayered vascular construct for engineering blood vessels is designed to offer "off-the-shelf" availability for clinical translation.

CD133 antibody conjugation to decellularized human heart valves intended for circulating cell capture

The long term efficacy of tissue based heart valve grafts may be limited by progressive degeneration characterized by immune mediated inflammation and calcification. To avoid this degeneration, decellularized heart valves with functionalized surfaces capable of rapid in vivo endothelialization have been developed. The aim of this study is to examine the capacity of CD133 antibody-conjugated valve tissue to capture circulating endothelial progenitor cells (EPCs). Decellularized human pulmonary valve tissue was conjugated with CD133 antibody at varying concentrations and exposed to CD133 expressing NTERA-2 cl.D1 (NT2) cells in a microflow chamber. The amount of CD133 antibody conjugated on the valve tissue surface and the number of NT2 cells captured in the presence of shear stress was measured. Both the amount of CD133 antibody conjugated to the valve leaflet surface and the number of adherent NT2 cells increased as the concentration of CD133 antibody present in the surface immobilization procedure increased. The data presented in this study support the hypothesis that the rate of CD133(+) cell adhesion in the presence of shear stress to decellularized heart valve tissue functionalized by CD133 antibody conjugation increases as the quantity of CD133 antibody conjugated to the tissue surface increases.

A novel tissue-engineered trachea with a mechanical behavior similar to native trachea

A novel tissue-engineered trachea was developed with appropriate mechanical behavior and substantial regeneration of tracheal cartilage. We designed hollow bellows scaffold as a framework of a tissue-engineered trachea and demonstrated a reliable method for three-dimensional (3D) printing of monolithic bellows scaffold. We also functionalized gelatin sponge to allow sustained release of TGF-β1 for stimulating tracheal cartilage regeneration and confirmed that functionalized gelatin sponge induces cartilaginous tissue formation in vitro. A tissue-engineered trachea was then created by assembling chondrocytes-seeded functionalized gelatin sponges into the grooves of bellows scaffold and it showed very similar mechanical behavior to that of native trachea along with substantial regeneration of tracheal cartilage in vivo. The tissue-engineered trachea developed here represents a novel concept of tracheal substitute with appropriate mechanical behavior similar to native trachea for use in reconstruction of tracheal stenosis.

Engineered small diameter vascular grafts by combining cell sheet engineering and electrospinning technology

Tissue engineering offers an attractive approach to creating functional small-diameter (<5mm) blood vessels by combining autologous cells with a natural and/or synthetic scaffold under suitable culture conditions, which results in a tubular construct that can be implanted in vivo. We have previously developed a vascular scaffold fabricated by electrospinning poly(ε-caprolactone) (PCL) and type I collagen that mimics the structural and biomechanical properties of native vessels. In this study, we investigated whether a smooth muscle cell (SMC) sheet could be combined with the electrospun vascular scaffolds to produce a more mature smooth muscle layer as compared to the conventional cell seeding method. The pre-fabricated SMC sheet, wrapped around the vascular scaffold, provided high cell seeding efficiency (approx. 100%) and a mature smooth muscle layer that expressed strong cell-to-cell junction, connexin 43 (CX43), and contractile proteins, α smooth muscle actin (α-SMA) and myosin light chain kinase (MLCK). Moreover, bioreactor-associated preconditioning of the SMC sheet-combined vascular scaffold maintained high cell viability (95.9 ± 2.7%) and phenotypes and improved cellular infiltration and mechanical properties (35.7% of tensile strength, 47.5% of elasticity, and 113.2% of elongation at break).

In situ regeneration of skeletal muscle tissue through host cell recruitment

Standard reconstructive procedures for restoring normal function after skeletal muscle defects involve the use of existing host tissues such as muscular flaps. In many instances, this approach is not feasible and delays the rehabilitation process and restoration of tissue function. Currently, cell-based tissue engineering strategies have been used for reconstruction; however, donor tissue biopsy and ex vivo cell manipulation are required prior to implantation. The present study aimed to overcome these limitations by demonstrating mobilization of muscle cells into a target-specific site for in situ muscle regeneration. First, we investigated whether host muscle cells could be mobilized into an implanted scaffold. Poly(l-lactic acid) (PLLA) scaffolds were implanted in the tibialis anterior (TA) muscle of rats, and the retrieved scaffolds were characterized by examining host cell infiltration in the scaffolds. The host cell infiltrates, including Pax7+ cells, gradually increased with time. Second, we demonstrated that host muscle cells could be enriched by a myogenic factor released from the scaffolds. Gelatin-based scaffolds containing a myogenic factor were implanted in the TA muscle of rats, and the Pax7+ cell infiltration and newly formed muscle fibers were examined. By the second week after implantation, the Pax7+ cell infiltrates and muscle formation were significantly accelerated within the scaffolds containing insulin-like growth factor 1 (IGF-1). Our data suggest an ability of host stem cells to be recruited into the scaffolds with the capability of differentiating to muscle cells. In addition, the myogenic factor effectively promoted host cell recruitment, which resulted in accelerating muscle regeneration in situ.

Diaphragmatic muscle reconstruction with an aligned electrospun poly(ε-caprolactone)/collagen hybrid scaffold

Large diaphragmatic muscle defects in congenital diaphragmatic hernia (CDH) are reconstructed by prosthetic materials or autologous grafts, which are associated with high complications and reherniation. In this study we examined the feasibility of using aligned electrospun poly(ε-caprolactone) (PCL)/collagen hybrid scaffolds for diaphragmatic muscle reconstruction. The hybrid scaffolds were implanted into a central left hemi-diaphragmatic defect (approximately 70% of the diaphragmatic tissue on the left side) in rats. Radiographic and magnetic resonance imaging (MRI) analyses showed no evidence of herniation or retraction up to 6 months after implantation. Histological and immunohistochemical evaluations revealed ingrowth of muscle tissue into the scaffolds. The mechanical properties of the retrieved diaphragmatic scaffolds were similar to those of normal diaphragm at the designated time points. Our results show that the aligned electrospun hybrid scaffolds allowed muscle cell migration and tissue formation. The aligned scaffolds may provide implantable functional muscle tissues for patients with diaphragmatic muscle defects.

In vitro osteogenic differentiation of human amniotic fluid-derived stem cells on a poly(lactide-co-glycolide) (PLGA)-bladder submucosa matrix (BSM) composite scaffold for bone tissue engineering

Stem cells have become an important component of tissue regeneration, as they are able to differentiate into various cell types if guided appropriately. It is well known that cellular differentiation is greatly influenced by the surrounding microenvironment. We have developed a composite scaffold system using a collagen matrix derived from porcine bladder submucosa matrix (BSM) and poly(lactide-co-glycolide) (PLGA). In this study, we investigated whether a composite scaffold composed of naturally derived matrix combined with synthetic polymers would provide a microenvironment to facilitate the induction of osteogenic differentiation. We first showed that human amniotic fluid-derived stem cells (hAFSCs) adhered to the composite scaffolds and proliferated over time. We also showed that the composite scaffolds facilitated the differentiation of hAFSCs into an osteogenic lineage. The expression of osteogenic genes, including RUNX2, osteopontin (OPN) and osteocalcin (OCN) was upregulated in cells cultured on the composite scaffolds incubated in the osteogenic medium compared with ones without. Increased alkaline phosphatase (ALP) activity and calcium content indicates that hAFSCs seeded on 3D porous BSM-PLGA composite scaffolds resulted in higher mineralization rates as the duration of induction increased. This was also evidenced by the mineralized matrix within the scaffolds. The composite scaffold system provides a proper microenvironment that can facilitate osteogenic differentiation of AFSCs. This scaffold system may be a good candidate material for bone tissue engineering.

End-to-side neurorrhaphy using an electrospun PCL/collagen nerve conduit for complex peripheral motor nerve regeneration

In cases of complex neuromuscular defects, finding the proximal stump of a transected nerve in order to restore innervation to damaged muscle is often impossible. In this study we investigated whether a neighboring uninjured nerve could serve as a source of innervation of denervated damaged muscle through a biomaterial-based nerve conduit while preserving the uninjured nerve function. Tubular nerve conduits were fabricated by electrospinning a polymer blend consisting of poly(ε-caprolactone) (PCL) and type I collagen. Using a rat model of common peroneal injury, the proximal end of the nerve conduit was connected to the side of the adjacent uninjured tibial branch (TB) of the sciatic nerve after partial axotomy, and the distal end of the conduit was connected to the distal stump of the common peroneal nerve (CPN). The axonal continuity recovered through the nerve conduit at 8 weeks after surgery. Recovery of denervated muscle function was achieved, and simultaneously, the donor muscle, which was innervated by the axotomized TB also recovered at 20 weeks after surgery. Therefore, this end-to-side neurorrhaphy (ETS) technique using the electrospun PCL/collagen conduit appears to be clinically feasible and would be a useful alternative in instances where autologous nerve grafts or an adequate proximal nerve stump is unavailable.

Combined systemic and local delivery of stem cell inducing/recruiting factors for in situ tissue regeneration

Whereas the conventional tissue engineering strategy involves the use of scaffolds combined with appropriate cell types to restore normal functions, the concept of in situ tissue regeneration uses host responses to a target-specific scaffold to mobilize host cells to a site of injury without the need for cell seeding. For this purpose, local delivery of bioactive molecules from scaffolds has been generally used. However, this approach has limited stem cell recruitment into the implants. Thus, we developed a combination of systemic delivery of substance P (SP) and local release of stromal-derived factor-1α (SDF-1α) from an implant. In this study, we examined whether this combined system would significantly enhance recruitment of host stem cells into the implants. Flow cytometry and immunohistochemistry for CD29/CD45, CD146/α-smooth muscle actin, and c-kit demonstrated that this system significantly increased the number of stem cell-like cells within the implants when compared with other systems. In vitro culture of the cells that had infiltrated into the scaffolds from the combined system confirmed that host stem cells were recruited into these implants and indicated that they were capable of differentiation into multiple lineages. These results indicate that this combined system may lead to more efficient tissue regeneration.

A dexamethasone-loaded PLGA microspheres/collagen scaffold composite for implantable glucose sensors

We have developed a new dexamethasone (Dex)-loaded poly(lactic-co-glycolic acid) microspheres/porous collagen scaffold composite for implantable glucose sensors. The scaffolds were fabricated around the sensing element of the sensors and crosslinked using nordihydroguaiaretic acid (NDGA). The microspheres containing Dex were incorporated into the NDGA-crosslinked collagen scaffold by dipping in microsphere suspension in either water or Pluronic. The loading efficiencies of Dex in the microspheres and the scaffold were determined using high performance liquid chromatography. The microspheres/scaffold composite fabricated using microspheres in the hydrogel solution had a better loading efficiency than when microspheres were in water suspension. The composite fabricated using the hydrogel also showed a slower and more sustained drug release than the standard microspheres in vitro during a 4 week study and did not significantly affect the function of the sensors in vitro. The sensors with the composite that were still functional retained above 50% of their original sensitivity at 2 weeks. Histology showed that the inflammatory response to the Dex-loaded composite was much lower than for the control scaffold at 2 and 4 weeks after implantation. The Dex-loaded composite system might be useful to reduce inflammation to implanted glucose sensors and therefore extend their function and lifetime.

A novel porous collagen scaffold around an implantable biosensor for improving biocompatibility. II. Long-term in vitro/in vivo sensitivity characteristics of sensors with NDGA- or GA-crosslinked collagen scaffolds

We have developed a new 3D porous and biostable collagen scaffold for implantable glucose sensors. The scaffolds were fabricated around the sensors and crosslinked using nordihydroguaiaretic acid (NDGA) or glutaraldehyde (GA) to enhance physical and biological stability. The effect of the scaffolds on sensor function and biocompatibility was examined during long-term (>or=28 days) in vitro and in vivo experiments and compared with control bare sensors. To evaluate the effect of the sensor length on micromotion and sensor function, we also fabricated short and long sensors. 3D porous scaffold application around glucose sensors did not significantly affect the long-term in vitro sensitivity of the sensors. The scaffolds, crosslinked by either NDGA or GA, remained stable around the sensors during the 4 week in vitro study. In the long-term in vivo study, the sensitivity of the short sensors was higher than the sensitivity of long sensors presumably because of less micromotion in the subcutis of the rats. The sensors with NDGA-crosslinked scaffolds had a higher sensitivity than the sensors with GA-crosslinked scaffolds. Histological examination showed that NDGA-crosslinked scaffolds retained their physical structure with reduced inflammation when compared with the GA-crosslinked scaffolds. Therefore, the application of NDGA-crosslinked collagen scaffolds might be a good method for enhancing the function and lifetime of implantable biosensors by minimizing the in vivo foreign body response.

A novel porous collagen scaffold around an implantable biosensor for improving biocompatibility. I. In vitro/in vivo stability of the scaffold and in vitro sensitivity of the glucose sensor with scaffold

A new 3D porous and biostable collagen scaffold has been developed to improve the biocompatibility of implantable glucose sensors by minimizing tissue reactions while stimulating angiogenesis around the sensors. The novel collagen scaffold was crosslinked using nordihydroguaiaretic acid (NDGA) to enhance biostability. NDGA-treated collagen scaffolds were stable without physical deformation in the subcutaneous tissue of rats for 4 weeks. In contrast, glutaraldehyde (GA)-treated collagen scaffolds were extremely damaged following implantation. Both types of scaffolds (NDGA- and GA-crosslinked) were stable in vitro in the presence of collagenase with 70% retention of original weight after 4 weeks of incubation. The response current (i.e. sensitivity) of sensors with porous scaffolds was not significantly changed when compared with control sensors (no scaffold), while the response time (T(95%)) was slightly delayed after a glucose concentration increase from 5 to 15 mM. Above this range, the sensors coated with scaffolds had only a slightly lower sensitivity than the control sensors. These results indicate that we have developed a stable NDGA-crosslinked collagen scaffold for biosensors, and that the scaffold does not impair the function of our sensor. We plan to use this scaffold to enhance the function and lifetime of the implantable biosensors by providing a controlled local environment around the sensors with the help of various drugs and growth factors (dexamethasone, VEGF, PDGF).

Beneficial effect of hydrophilized porous polymer scaffolds in tissue-engineered cartilage formation

Three dimensional (3D) porous poly(L-lactic acid) (PLLA) scaffolds were fabricated using a modified gas foaming method whose effervescent porogens were a mixture of sodium bicarbonate and citric acid. To improve chondrocyte adhesion, the scaffolds were then hydrophilized through oxygen plasma treatment and in situ graft polymerization of acrylic acid (AA). When the physical properties of AA-grafted scaffolds were examined, the porosity and pore size were 87 approximately 93% and 100 approximately 300 microm, respectively. The pore sizes were highly dependent on the varying ratios (w/w) between porogen and polymer solution. Influenced by their pore sizes, the compressive moduli of scaffolds significantly decreased with increasing pore size. The altered surface characteristics were clearly reflected in the reduced water contact angles that meant a significant hydrophilization with the modified polymer surface. Electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometer (ToF-SIMS) also confirmed the altered surface chemistry. When chondrocytes were seeded onto the AA-grafted PLLA scaffolds, cell adhesion and proliferation were substantially improved as compared to the unmodified scaffolds. The benefit of the modified scaffolds was clear in the gene expressions of collagen type II that was significantly upregulated after 4-week culture. Safranin-O staining also identified greater glycosaminoglycan (GAG) deposition in the modified scaffold. The AA-grafted porous polymer scaffolds were effective for cell adhesion and differentiation, making them a suitable platform for tissue-engineered cartilage.

Surface modification of biodegradable electrospun nanofiber scaffolds and their interaction with fibroblasts

Biodegradable polymers, such as poly(glycolic acid) (PGA), poly(L-lactic acid) (PLLA) and poly(lactic-co-glycolic acid) (PLGA), were dissolved individually in the proper solvents and then subjected to electrospinning process to make nanofibrous scaffolds. Their surfaces were then chemically modified using oxygen plasma treatment and in situ grafting of hydrophilic acrylic acid (AA). The fiber thickness, pore size and porosity were estimated to 200-800 nm, 2-30 microm and 94-96%, respectively, and these properties were insignificant in the PGA, PLLA and PLGA nanofibrous scaffolds. The ultimate tensile strength of PGA was about 2.5 MPa on average and that of PLGA and PLLA was less than 2 MPa. The elongation-at-break was 100-130% for the three nanofibrous scaffolds. When the surface properties of AA-grafted scaffolds were examined, higher ratios of oxygen to carbon, lower contact angles and the presence of carboxylic (-COOH) groups were identified. The properties were significantly different from those of the unmodified nanofibrous scaffolds. Fibroblasts once seeded on the scaffolds were spreading over large surface area on the AA-grafted surface as compared to the unmodified PGA, PLLA and PLGA nanofibrous scaffolds. Cultured for up to 6 days, the fibroblast proliferation was found to be much better on the surface-modified nanofibrous scaffolds. The present study showed that, with the use of plasma treatment and AA grafting, the hydrophilic functional groups could be successfully adapted on the surface of electrospun nanofibrous scaffolds. Those surface-modified scaffolds made significant improvement on cell attachment and proliferation in vitro.

Polyethylene oxide additive-entrapped polyvinyl chloride as a new blood bag material

Until now, most widely used blood bag material has been a plasticized polyvinyl chloride (PVC) because it has many desirable properties as a blood bag material. One of main concerns of using plasticized PVC as a blood bag material is the toxicity of the plasticizers that are leached out of the material. We tried to solve this problem by the addition of polyethylene oxide (PEO)-containing amphiphilic block copolymers as additives in the PVC. The PEO additives may play two roles: they can act as nontoxic plasticizers to PVC, and they can also act as blood-compatible surface modifiers. In this study, PEO additive-entrapped PVC films were prepared by the addition (up to 30 wt%) of PEO-alkyl carbon block copolymers or PEO-polypropylene oxide (PPO)-PEO triblock copolymers with different PEO chain lengths in the PVC. The prepared PEO additive-containing PVC films were characterized by the measurements of water contact angle, Fourier transform IR spectroscopy in the attenuated total reflectance mode, mechanical properties (tensile strength and elongation at break), water absorption, and stability of the PEO additives entrapped in the films. It was observed that the PEO additive-entrapped PVC films were flexible and transparent. It seems that the PEO additives are surface active, resulting in the considerable change of surface characteristics without a significant change of the mechanical properties of the films compared to the control PVC without any additives or a commercial blood bag. The adhesion of platelets on the film surfaces was significantly reduced by the addition of PEO additives. It seems that 10% addition of PEO additives is enough for the suppression of platelet adhesion on the surfaces. This study demonstrated that the use of PEO-containing block copolymers as additives to the PVC can be a feasible approach to prepare a new type of blood bag.

Platelet adhesion onto segmented polyurethane film surfaces modified by addition and crosslinking of PEO-containing block copolymers

Polyethylene oxide (PEO) surfaces were prepared by the addition of PEO-containing amphiphilic block copolymers as surface modifying additives and of dicumyl peroxide (DCP) as a crosslinking agent in segmented polyurethane (PU). PEO-polypropylene oxide-PEO triblock copolymers (Pluronics) with different PEO chain length (from 0 to 98) were used as the surface modifying additives. The PEO additives in the PU film were then crosslinked to be stably entrapped in the PU matrix. The crosslinking was done by free radicals produced from the decomposition of DCP in the film through heating (120 degrees C) or ultraviolet irradiation (254 nm). The surface properties of the PEO additive-entrapped PU films were investigated by the measurement of water contact angles and electron spectroscopy for chemical analysis. The bulk properties such as water absorption, long-term film stability, and tensile strength and elongation at break, were also investigated. It was observed that addition of a small amount (5 wt% based on PU) of the PEO additives resulted in a considerable change of surface characteristics. The PEO additives were stably entrapped in the PU films by crosslinking of them, without significant changes of bulk properties of the films. From the platelet adhesion test on the prepared PEO additive-containing film surfaces, it was observed that the platelet adhesion on the surfaces decreases with increase in PEO chain length of PEO additives. The film surface containing additive with long PEO chains (chain length of 98) was particularly effective in preventing platelet adhesion. The crosslinking of the PEO additives in PU films did not affect the behavior of platelet adhesion on the surfaces; the films with crosslinked PEO additives showed similar platelet adhesion on the surfaces to the films with uncrosslinked ones.

Platelet adhesion onto segmented polyurethane surfaces modified by PEO- and sulfonated PEO-containing block copolymer additives

Polyethylene oxide (PEO) surfaces were prepared by the addition of PEO- and sulfonated PEO-containing amphiphilic block copolymers as surface-modifying additives in a segmented polyurethane (PU). PEO-PPO-PEO triblock copolymers (Pluronics) with different PEO chain lengths (from 2 to 80) were used as additives. The prepared film surfaces were characterized by the measurement of dynamic water contact angles and electron spectroscopy for chemical analysis. It was observed that the PU films containing 10 wt% of PEO additives were surface-saturated with the additives regardless of their PEO chain length, but the PEO chains were more projected from the film surfaces containing the additives with longer PEO chains. The water absorption of the films increased largely with the increasing PEO chain length of the additives. The addition of PEO additives produced film surfaces that were in a gel-like state. The films demonstrated some extraction of the PEO additives. However, the additives with higher molecular weights were entrapped more stably into the PU matrix. The mechanical properties (tensile strength and elongation) of the films were changed by the addition of PEO additives, but the differences were not significant compared to the control PU. The platelet adhesion on the film surfaces decreased with increasing PEO chain length of the additives. The film surface containing additives with long PEO chains (chain length of 80) was particularly effective in preventing platelet adhesion. The effect of negatively charged sulfonate groups on the prevention of platelet adhesion appeared only on the film surfaces containing additives with short PEO chains. For longer PEO chains, the chain mobility effect was more dominant than the negative charge effect on the prevention of platelet adhesion.

A case of post-traumatic coronary occlusion

Several cases of transmural myocardial infarction and ventricular aneurysm caused by a blunt trauma of the chest have been reported. Nevertheless, the cases documented with coronary and ventricular angiography are very few. There has always been a debate over the etiological mechanism of such lesions. Since in some cases there was no evidence of coronary lesions, it was postulated that they were produced by direct myocardial contusion, but in other instances the evidence of coronary occlusion was angiographically and pathologically proved. We experienced a case of acute myocardial infarction with ventricular aneurysm secondary to nonpenetrating chest trauma by an umbrella tip and wish to report this unusual case, along with a review of the literature.