Electrospun micro/nanofibrous conduits composed of poly(epsilon-caprolactone) and small intestine submucosa powder for nerve tissue regeneration

Nonwoven fiber meshes for oxygen sensing

Accurate oxygen sensing and cost-effective fabrication are crucial for the adoption of wearable devices inside and outside the clinical setting. Here we introduce a simple strategy to create nonwoven polymeric fibrous mats for a notable contribution towards addressing this need. Although morphological manipulation of polymers for cell culture proliferation is commonplace, especially in the field of regenerative medicine, non-woven structures have not been used for oxygen sensing. We used an airbrush spraying, i.e. solution blowing, to obtain nonwoven fiber meshes embedded with a phosphorescent dye. The fibers serve as a polymer host for the phosphorescent dye and are shown to be non-cytotoxic. Different composite fibrous meshes were prepared and favorable mechanical and oxygen-sensing properties were demonstrated. A Young's modulus of 9.8 MPa was achieved and the maximum oxygen sensitivity improved by a factor of ∼2.9 compared to simple drop cast film. The fibers were also coated with silicone rubbers to produce mechanically robust sensing films. This reduced the sensing performance but improved flexibility and mechanical properties. Lastly, we are able to capture oxygen concentration maps via colorimetry using a smartphone camera, which should offer unique advantages in wider usage. Overall, the introduced composite fiber meshes show a potential to significantly improve cell cultures and healthcare monitoring via absolute oxygen sensing.

Potential of Aligned Electrospun PLGA/SIS Blended Nanofibrous Membrane for Tendon Tissue Engineering

Tendons are responsible for transmitting mechanical forces from muscles to bones for body locomotion and joint stability. However, tendons are frequently damaged with high mechanical forces. Various methods have been utilized for repairing damaged tendons, including sutures, soft tissue anchors, and biological grafts. However, tendons experience a higher rate of retear post-surgery due to their low cellularity and vascularity. Surgically sutured tendons are vulnerable to reinjury due to their inferior functionality when compared with native tendons. Surgical treatment using biological grafts also has complications such as joint stiffness, re-rupture, and donor-site morbidity. Therefore, current research is focused on developing novel materials that can facilitate the regeneration of tendons with histological and mechanical characteristics similar to those of intact tendons. With respect to the complications in association with the surgical treatment of tendon injuries, electrospinning may be an alternative for tendon tissue engineering. Electrospinning is an effective method for fabrication of polymeric fibers with diameters ranging from nanometers to micrometers. Thus, this method produces nanofibrous membranes with an extremely high surface area-to-volume ratio, which is similar to the extracellular matrix structure, making them suitable candidates for application in tissue engineering. Moreover, it is possible to fabricate nanofibers with specific orientations that are similar to those of the native tendon tissue using an adequate collector. To increase the hydrophilicity of the electrospun nanofibers, natural polymers in addition to synthetic polymers are used concurrently. Therefore, in this study, aligned nanofibers composed of poly-d,l-lactide-co-glycolide (PLGA) and small intestine submucosa (SIS) were fabricated using electrospinning with rotating mandrel. The diameter of aligned PLGA/SIS nanofibers was 568.44 ± 135.594 nm, which closely resembles that of native collagen fibrils. Compared to the results of the control group, the mechanical strength exhibited by the aligned nanofibers was anisotropic in terms of break strain, ultimate tensile strength, and elastic modulus. Elongated cellular behavior was observed in the aligned PLGA/SIS nanofibers using confocal laser scanning microscopy, indicating that the aligned nanofibers were highly effective with regard to tendon tissue engineering. In conclusion, considering its mechanical properties and cellular behavior, aligned PLGA/SIS is a promising candidate for tendon tissue engineering.

Decellularization of Small Intestinal Submucosa

Small intestinal submucosa (SIS) is the most studied extracellular matrix (ECM) for repair and regeneration of different organs and tissues. Promising results of SIS-ECM as a vascular graft, led scientists to examine its applicability for repairing other tissues. Overall results indicated that SIS grafts induce tissue regeneration and remodeling to almost native condition. Investigating immunomodulatory effects of SIS is another interesting field of research. SIS can be utilized in different forms for multiple clinical and experimental studies. The aim of this chapter is to investigate the decellularization process of SIS and its common clinical application.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Bioactive Nanofiber-Based Conduits in a Peripheral Nerve Gap Management-An Animal Model Study

The aim was to examine the efficiency of a scaffold made of poly (L-lactic acid)-co-poly(ϵ-caprolactone), collagen (COL), polyaniline (PANI), and enriched with adipose-derived stem cells (ASCs) as a nerve conduit in a rat model. P(LLA-CL)-COL-PANI scaffold was optimized and electrospun into a tubular-shaped structure. Adipose tissue from 10 Lewis rats was harvested for ASCs culture. A total of 28 inbred male Lewis rats underwent sciatic nerve transection and excision of a 10 mm nerve trunk fragment. In Group A, the nerve gap remained untouched; in Group B, an excised trunk was used as an autograft; in Group C, nerve stumps were secured with P(LLA-CL)-COL-PANI conduit; in Group D, P(LLA-CL)-COL-PANI conduit was enriched with ASCs. After 6 months of observation, rats were sacrificed. Gastrocnemius muscles and sciatic nerves were harvested for weight, histology analysis, and nerve fiber count analyses. Group A showed advanced atrophy of the muscle, and each intervention (B, C, D) prevented muscle mass decrease (p < 0.0001); however, ASCs addition decreased efficiency vs. autograft (p < 0.05). Nerve fiber count revealed a superior effect in the nerve fiber density observed in the groups with the use of conduit (D vs. B p < 0.0001, C vs. B p < 0.001). P(LLA-CL)-COL-PANI conduits with ASCs showed promising results in managing nerve gap by decreasing muscle atrophy.

Material Characterisation and Stratification of Conjunctival Epithelial Cells on Electrospun Poly(ε-Caprolactone) Fibres Loaded with Decellularised Tissue Matrices

The conjunctiva, an under-researched yet incredibly important tissue, plays key roles in providing protection to the eye and maintaining homeostasis of its ocular surface. Multiple diseases can impair conjunctival function leading to severe consequences that require surgical intervention. Small conjunctival defects can be repaired relatively easily, but larger defects rely on tissue grafts which generally do not provide adequate healing. A tissue engineering approach involving a biomaterial substrate capable of supporting a stratified epithelium with embedded, mucin-secreting goblet cells offers a potential solution. As a first step, this study aimed to induce stratification of human conjunctival epithelial cells cultured on electrospun scaffolds composed from poly(ε-caprolactone) (PCL) and decellularised tissue matrix (small intestinal submucosa (SIS) or urinary bladder matrix (UBM)) and held at the air/liquid interface. Stratification, up to 5 cell layers, occurred more frequently on scaffolds containing PCL + UBM. Incorporation of these decellularised tissue matrices also impacted material properties, with significant changes occurring to their fibre diameter, tensile properties, and chemical composition throughout the scaffold structure compared to PCL alone. These matrix containing scaffolds warrant further long-term investigation as a potential advanced therapy medicinal product for conjunctiva repair and regeneration.

Surface modification of small intestine submucosa in tissue engineering

With the development of tissue engineering, the required biomaterials need to have the ability to promote cell adhesion and proliferation in vitro and in vivo. Especially, surface modification of the scaffold material has a great influence on biocompatibility and functionality of materials. The small intestine submucosa (SIS) is an extracellular matrix isolated from the submucosal layer of porcine jejunum, which has good tissue mechanical properties and regenerative activity, and is suitable for cell adhesion, proliferation and differentiation. In recent years, SIS is widely used in different areas of tissue reconstruction, such as blood vessels, bone, cartilage, bladder and ureter, etc. This paper discusses the main methods for surface modification of SIS to improve and optimize the performance of SIS bioscaffolds, including functional group bonding, protein adsorption, mineral coating, topography and formatting modification and drug combination. In addition, the reasonable combination of these methods also offers great improvement on SIS surface modification. This article makes a shallow review of the surface modification of SIS and its application in tissue engineering.

Optimizing Anisotropic Polyurethane Scaffolds to Mechanically Match with Native Myocardium

Biodegradable cardiac patch is desirable to possess mechanical properties mimicking native myocardium for heart infarction treatment. We fabricated a series of anisotropic and biodegradable polyurethane porous scaffolds via thermally induced phase separation (TIPS) and tailored their mechanical properties by using various polyurethanes with different soft segments and varying polymer concentrations. The uniaxial mechanical properties, suture retention strength, ball-burst strength, and biaxial mechanical properties of the anisotropic porous scaffolds were optimized to mechanically match native myocardium. The optimal anisotropic scaffold had a ball burst strength (20.7 ± 1.5 N) comparable to that of native porcine myocardium (20.4 ± 6.0 N) and showed anisotropic behavior close to biaxial stretching behavior of the native porcine myocardium. Furthermore, the optimized porous scaffold was combined with a porcine myocardium-derived hydrogel to form a biohybrid scaffold. The biohybrid scaffold showed morphologies similar to the decellularized porcine myocardial matrix. This combination did not affect the mechanical properties of the synthetic scaffold alone. After in vivo rat subcutaneous implantation, the biohybrid scaffolds showed minimal immune response and exhibited higher cell penetration than the polyurethane scaffold alone. This biohybrid scaffold with biomimetic mechanics and good tissue compatibility would have great potential to be applied as a biodegradable acellular cardiac patch for myocardial infarction treatment.

Chondrogenic response in presence of cartilage extracellular matrix nanoparticles

Current studies based on regenerative medicine suggest, decellularized extracellular matrix (DC-ECM) components can regulate cell phenotype. In this regard, it is believed, presence of cartilage extracellular matrix particles in culture condition could produce physical and biochemical supportive cues for chondrogenesis. In this study, DC-ECM nanoparticles with average size of 61.5± 22.4 nm were produced by decellularization and mechanical processing. Homogenous distribution and nanoscale size of yield particles were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) microscopy imaging. Chemical structure preservation of cartilage ECM after decellularization was also confirmed by typical Fourier transform infrared (FTIR) spectrum mapping. The influence these nanoparticles on chondrogenic response of chondrocyte cells was investigated by direct and indirect addition of nanoparticles to culture medium. A clinical devitalized cartilage powder (DV-ECM) was also used as a positive control. Totally, MTS results showed that direct and indirect presence of both DC-ECM and DV-ECM particles in culture medium enhanced cellular metabolic activity except on day one of culture. Furthermore, on day 21, SOX9 and COL2 expression of cultured chondrocytes in the medium containing DC-ECM nanoparticles were up-regulated in comparison to negative control, which was further confirmed by presence more frequent number of larger size lacunae in micromass spheroids. Our findings support the use of ECM nanoparticles as condition supplement in culture medium and injectable biomaterials, especially for cell-based therapies for cartilage regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2463-2471, 2018.

Self-assembling peptides cross-linked with genipin: resilient hydrogels and self-standing electrospun scaffolds for tissue engineering applications

Self-assembling peptides (SAPs) are synthetic bioinspired biomaterials that can be feasibly multi-functionalized for applications in surgery, drug delivery, optics and tissue engineering (TE). Despite their promising biocompatibility and biomimetic properties, they have never been considered real competitors of polymers and/or cross-linked extracellular matrix (ECM) natural proteins. Indeed, synthetic SAP-made hydrogels usually feature modest mechanical properties, limiting their potential applications, due to the transient non-covalent interactions involved in the self-assembling phenomenon. Cross-linked SAP-hydrogels have been recently introduced to bridge this gap, but several questions remain open. New strategies leading to stiffer gels of SAPs may allow for a full exploitation of the SAP technology in TE and beyond. We have developed and characterized a genipin cross-linking strategy significantly increasing the stiffness and resiliency of FAQ(LDLK)3, a functionalized SAP already used for nervous cell cultures. We characterized different protocols of cross-linking, analyzing their dose and time-dependent efficiency, influencing stiffness, bioabsorption time and molecular arrangements. We choose the best developed protocol to electrospin into nanofibers, for the first time, self-standing, water-stable and flexible fibrous mats and micro-channels entirely made of SAPs. This work may open the door to the development and tailoring of bioprostheses entirely made of SAPs for different TE applications.

Nanopatterned Scaffolds for Neural Tissue Engineering and Regenerative Medicine

Biologically inspired approaches employing nanoengineering techniques have been influential in the progress of neural tissue repair and regeneration. Neural tissues are exposed to complex nanoscale environments such as nanofibrils. In this chapter, we summarize representative nanotechniques, such as electrospinning, lithography, and 3D bioprinting, and their use in the design and fabrication of nanopatterned scaffolds for neural tissue engineering and regenerative medicine. Nanotopographical cues in combination with other cues (e.g., chemical cues) are crucial to neural tissue repair and regeneration using cells, including various types of stem cells. Production of biologically inspired nanopatterned scaffolds may encourage the next revolution for studies aiming to advance neural tissue engineering and regenerative medicine.

Composite elastomeric polyurethane scaffolds incorporating small intestinal submucosa for soft tissue engineering

Although soft tissue replacement has been clinically successful in many cases, the corresponding procedure has many limitations including the lack of resilience and mechanical integrity, significant donor-site morbidity, volume loss with time, and fibrous capsular contracture. These disadvantages can be alleviated by utilizing bio-absorbable scaffolds with high resilience and large strain, which are capable of stimulating natural tissue regeneration. Hence, the chemically crosslinked tridimensional scaffolds obtained by incorporating water-based polyurethane (PU) (which was synthesized from polytetramethylene ether glycol, isophorone diisocyanate, and 2,2-bis(hydroxymethyl) butyric acid) into a bioactive extracellular matrix consisting of small intestinal submucosa (SIS) have been tested in this study to develop a new approach for soft tissue engineering. After characterizing the structure and properties of the produced PU/SIS composites, the strength, Young's modulus, and resilience of wet PU/SIS samples were compared with those of crosslinked PU. In addition, the fabricated specimens were investigated using human umbilical vein endothelial cells to evaluate their ability to enhance cell attachment and proliferation. As a result, the synthesized PU/SIS samples exhibited high resilience and were capable of enhancing cell viability with no evidence of cytotoxicity. Subcutaneous implantation in animals and the subsequent testing conducted after 2, 4, and 8weeks indicated that sound implant integration and vascularization occurred inside the PU/SIS composites, while the presence of SIS promoted cell infiltration, angiogenesis, and ultimately tissue regeneration. The obtained results revealed that the produced PU/SIS composites were characterized by high bioactivity and resilience, and, therefore, could be used for soft tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Hybrid composites containing synthetic polymers with high mechanical strength and naturally derived components, which create a bio-mimetic environment, are one of the most promising biomaterials. Although synthetic polymer/ECM composites have been previously used for soft tissue repair, their resilience properties were not investigated in sufficient detail, while the development of elastic composites composed of synthetic polymers and ECMs in nontoxic aqueous solutions remains a rather challenging task. In this study, porous PU/SIS composites were fabricated in a non-toxic manner; the obtained materials exhibited sufficient mechanical support, which promote cell growth, angiogenesis, and tissue regeneration. The described method can be adapted for the development of scaffolds with various acellular matrices and subsequently used during the restoration of particular types of tissue.

Preparation and properties of poly(ε-caprolactone)/bioactive glass nanofibre membranes for skin tissue engineering

Poly(ε-caprolactone) composite nanofibres for skin tissue engineering and regeneration applications were prepared via electrospinning of poly(ε-caprolactone) nanofibres with bioactive glass nanoparticles at bioactive glass contents of 0, 2, 4, 6 and 8 wt%. The surface properties, water absorptivities, porosities, mechanical properties and biocompatibilities of the composite electrospun nanofibres were characterised in detail. Addition of bioactive glass improved the hydrophilicity and elastic modulus of membranes. The fibre diameter of the neat poly(ε-caprolactone) nanofibres was only 700 nm, but reinforcement with 2, 4, 6 and 8 wt% bioactive glass nanofibres increased the diameter to 1000, 1100, 900 and 800 nm, respectively. The minimum elongation at break of the bioactive glass–reinforced poly(ε-caprolactone) exceeded 100%, which indicated that the composite nanofibres had good mechanical properties. The porosities of the various nanofibres containing different mass loadings of bioactive glass all exceeded 90%. The best performance in terms of cell proliferation and adhesion was found when the bioactive glass mass percent reached 6 wt%. However, higher loadings were unfavourable for cell growth. These preliminary results indicate that poly(ε-caprolactone)/bioactive glass composite nanofibres have promise for skin tissue engineering applications.

The effect of engineered nanotopography of electrospun microfibers on fiber rigidity and macrophage cytokine production

Currently, it is unknown how the mechanical properties of electrospun fibers, and the presentation of surface nanotopography influence macrophage gene expression and protein production. By further elucidating how specific fiber properties (mechanical properties or surface properties) alter macrophage behavior, it may be possible to create electrospun fiber scaffolds capable of initiating unique cellular and tissue responses. In this study, we determined the elastic modulus and rigidity of fibers with varying topographies created by finely controlling humidity and including a non-solvent during electrospinning. In total,five fiber scaffold types were produced. Analysis of fiber physical properties demonstrated no change in fiber diameter amongst the five different fiber groups. However, the four different fibrous scaffolds with nanopits or divots each possessed different numbers of pits with different nanoscale dimensions. Unpolarized bone marrow derived murine macrophages (M0), macrophages polarized towards a pro-inflammatory phenotype (M1), or macrophages polarized towards anti-inflammatory phenotype (M2b) were placed onto each of the scaffolds and cytokine RNA expression and protein production were analyzed. Specific nanotopographies did not appreciably alter cytokine production from undifferentiated macrophages (M0) or anti-inflammatory macrophages (M2b), but a specific fiber (with many small pits) did increase IL-12 transcript and IL-12 protein production compared to fibers with small divots. When analyzing the mechanical properties between fibers with divots or with many small pits,divoted fibers possessed similar elastic moduli but different stiffness values. In total,we present techniques capable of creating unique electrospun fibers. These unique fibers have varying fiber mechanical characteristics and modestly modulate macrophage cytokine expression.

Can a Small Intestine Segment Be an Alternative Biological Conduit for Peripheral Nerve Regeneration?

BACKGROUND

Autologous nerve grafts are used to bridge peripheral nerve defects. Limited sources and donor site morbidity are the major problems with peripheral nerve grafts. Although various types of autologous grafts such as arteries, veins and muscles have been recommended, an ideal conduit has not yet been described.

AIMS

To investigate the effectiveness of a small intestinal conduit for peripheral nerve defects.

STUDY DESIGN

Animal experimentation.

METHODS

Twenty-one rats were divided into three groups (n=7). Following anaesthesia, sciatic nerve exploration was performed in the Sham group. The 10 mm nerve gap was bridged with a 15 mm ileal segment in the small intestinal conduit group and the defect was replaced with orthotopic nerve in autologous nerve graft group. The functional recovery was tested monthly by walking-track analysis and the sciatic functional index. Histological evaluation was performed on the 12th week.

RESULTS

Sciatic functional index tests are better in autologous nerve graft group (-55.09±6.35); however, during follow-up, progress in sciatic functional index was demonstrated, along with axonal regeneration and innervation of target muscles in the small intestinal conduit group (-76.36±12.08) (p<0.05). In histologic sections, distinctive sciatic nerve regeneration was examined in the small intestinal conduit group. The expression of S-100 and neurofilament was observed in small intestinal conduit group but was less organised than in the autologous nerve graft group. Although the counted number (7459.79±1833.50 vs. 4226.51±1063.06 mm2), measured diameter [2.19 (2.15-2.88) vs. 1.74 (1.50-2.09) µm] and myelin sheath thickness [1.18 (1.09-1.44) vs. 0.66 (0.40-1.07) µm] of axons is significantly high in the middle sections of autologous nerve graft compared to the small intestinal conduit group, respectively (p<0.05), the peripheral nerve regeneration was also observed in the small intestinal conduit group.

CONCLUSION

Small intestinal conduit should not be considered as an alternative to autologous nerve grafts in its current form; however, the results are promising. Even though the results are no better than autologous nerve grafts, with additional procedures, it might be a good alternative due to harvesting abundant sources without donor site morbidity.

Nanotechnology and bio-functionalisation for peripheral nerve regeneration

There is a high clinical demand for new smart biomaterials, which stimulate neuronal cell proliferation, migration and increase cell-material interaction to facilitate nerve regeneration across these critical-sized defects. This article briefly reviews several up-to-date published studies using Arginine-Glycine-Aspartic acid peptide sequence, nanocomposite based on polyhedral oligomeric silsesquioxane nanoparticle and nanofibrous scaffolds as promising strategies to enhance peripheral nerve regeneration by influencing cellular behaviour such as attachment, spreading and proliferation. The aim is to establish the potent manipulations, which are simple and easy to employ in the clinical conditions for nerve regeneration and repair.

Tissue extracellular matrix nanoparticle presentation in electrospun nanofibers

Biomaterials derived from the decellularization of mature tissues retain biological and architectural features that profoundly influence cellular activity. However, the clinical utility of such materials remains limited as the shape and physical properties are difficult to control. In contrast, scaffolds based on synthetic polymers can be engineered to exhibit specific physical properties, yet often suffer from limited biological functionality. This study characterizes composite materials that present decellularized extracellular matrix (DECM) particles in combination with synthetic nanofibers and examines the ability of these materials to influence stem cell differentiation. Mechanical processing of decellularized tissues yielded particles with diameters ranging from 71 to 334 nm. Nanofiber scaffolds containing up to 10% DECM particles (wt/wt) derived from six different tissues were engineered and evaluated to confirm DECM particle incorporation and to measure bioactivity. Scaffolds containing bone, cartilage, and fat promoted osteogenesis at 1 and 3 weeks compared to controls. In contrast, spleen and lung DECM significantly reduced osteogenic outcomes compared to controls. These findings highlight the potential to incorporate appropriate source DECM nanoparticles within nanofiber composites to design a scaffold with bioactivity targeted to specific applications.

Multilayered electrospun scaffolds for tendon tissue engineering

Full-thickness rotator cuff tears are one of the most common causes of shoulder pain in people over the age of 65. High retear rates and poor functional outcomes are common after surgical repair, and currently available extracellular matrix scaffold patches have limited abilities to enhance new tendon formation. In this regard, tissue-engineered scaffolds may provide a means to improve repair of rotator cuff tears. Electrospinning provides a versatile method for creating nanofibrous scaffolds with controlled architectures, but several challenges remain in its application to tissue engineering, such as cell infiltration through the full thickness of the scaffold as well as control of cell growth and differentiation. Previous studies have shown that ligament-derived extracellular matrix may enhance differentiation toward a tendon or ligament phenotype by human adipose stem cells (hASCs). In this study, we investigated the use of tendon-derived extracellular matrix (TDM)-coated electrospun multilayered scaffolds compared to fibronectin (FN) or phosphate-buffered saline (PBS) coating for use in rotator cuff tendon tissue engineering. Multilayered poly(ɛ-caprolactone) scaffolds were prepared by sequentially collecting electrospun layers onto the surface of a grounded saline solution into a single scaffold. Scaffolds were then coated with TDM, FN, or PBS and seeded with hASCs. Scaffolds were maintained without exogenous growth factors for 28 days in culture and evaluated for protein content (by immunofluorescence and biochemical assay), markers of tendon differentiation, and tensile mechanical properties. The collagen content was greatest by day 28 in TDM-scaffolds. Gene expression of type I collagen, decorin, and tenascin C increased over time, with no effect of scaffold coating. Sulfated glycosaminoglycan and dsDNA contents increased over time in culture, but there was no effect of scaffold coating. The Young's modulus did not change over time, but yield strain increased with time in culture. Histology demonstrated cell infiltration through the full thickness of all scaffolds and immunofluorescence demonstrated greater expression of type I, but not type III collagen through the full thickness of the scaffold in TDM-scaffolds compared to other treatment groups. Together, these data suggest that nonaligned multilayered electrospun scaffolds permit tenogenic differentiation by hASCs and that TDM may promote some aspects of this differentiation.

Multiwalled CNT-pHEMA composite conduit for peripheral nerve repair

A nerve conduit is designed to improve peripheral nerve regeneration by providing guidance to the nerve cells. Conductivity of such guides is reported to enhance this process. In the current study, a nerve guide was constructed from poly(2-hydroxyethyl methacrylate) (pHEMA), which was loaded with multiwalled carbon nanotubes (mwCNT) to introduce conductivity. PHEMA hydrogels were designed to have a porous structure to facilitate the transportation of the compounds needed for cell nutrition and growth and also for waste removal. We showed that when loaded with relatively high concentrations of mwCNTs (6%, w/w in hydrogels), the pHEMA guide was more conductive and more hydrophobic than pristine pHEMA hydrogel. The mechanical properties of the composites were better when they carried mwCNT. Elastic modulus of 6% mwCNT loaded pHEMA was twofold higher (0.32 ± 0.06 MPa) and similar to that of the soft tissues. Electrical conductivity was significantly improved (11.4-fold) from 7 × 10(-3) Ω(-1).cm(-1) (pHEMA) to 8.0 × 10(-2) Ω(-1).cm(-1) (6% mwCNT loaded pHEMA). On application of electrical potential, the SHSY5Y neuroblastoma cells seeded on mwCNTs carrying pHEMA maintained their viability, whereas those on pure pHEMA could not, indicating that mwCNT helped conduct electricity and make them more suitable as nerve conduits.

Neural responses to electrical stimulation on patterned silk films

Peripheral nerve injury is a critical issue for patients with trauma. Following injury, incomplete axon regeneration or misguided axon innervation into tissue will result in loss of sensory and motor functions. The objective of this study was to examine axon outgrowth and axon alignment in response to surface patterning and electrical stimulation. To accomplish our objective, metal electrodes with dimensions of 1.5 mm × 4 cm, were sputter coated onto micropatterned silk protein films, with surface grooves 3.5 μm wide × 500 nm deep. P19 neurons were seeded on the patterned electronic silk films and stimulated at 120 mV, 1 kHz, for 45 min each day for 7 days. Responses were compared with neurons on flat electronic silk films, patterned silk films without stimulation, and flat silk films without stimulation. Significant alignment was found on the patterned film groups compared with the flat film groups. Axon outgrowth was greater (p < 0.05) on electronic films on days 5 and 7 compared with the unstimulated groups. In conclusion, electrical stimulation, at 120 mV, 1 kHz, for 45 min daily, in addition to surface patterning, of 3.5 μm wide × 500 nm deep grooves, offered control of nerve axon outgrowth and alignment.

An elastomeric patch electrospun from a blended solution of dermal extracellular matrix and biodegradable polyurethane for rat abdominal wall repair

A biodegradable elastomeric scaffold was created by electrospinning a mixed solution of poly(ester urethane)urea (PEUU) and porcine dermal extracellular matrix (dECM) digest, with PEUU included to provide elasticity, flexibility, and mechanical support and dECM used to enhance bioactivity and biocompatibility. Micrographs and differential scanning calorimetry demonstrated partial miscibility between PEUU and dECM. With greater dECM content, scaffolds were found to possess lower breaking strains and suture retention strength, although initial modulus was greater with higher dECM concentrations. The hybrid scaffolds containing 0% to 50% dECM had tensile strengths of 5 to 7 MPa, breaking strains of 138% to 611%, initial moduli of 3 to 11 Mpa, and suture retention strengths of 35 to 59 MPa. When hydrated, scaffolds were found to contract markedly with 50% dECM content. When used in a rat full-thickness abdominal wall replacement model, no herniation, infection, or tissue adhesion was observed after 4 and 8 weeks with a scaffold containing 25% dECM or a control 100% PEUU scaffold. Scaffolds incorporating dECM were significantly thicker at the time of explant, with greater numbers of associated smooth muscle actin-positive staining cells than in the control, but minimal cellular infiltration and remodeling of the scaffold were detected regardless of dECM addition. The processing of dECM and PEUU from a mixed solution thus provided a scaffold with evidence of better bioactivity and with mechanical properties not achievable with digested dECM alone.