Trauma‐induced, critical‐size bone defects pose a clinical challenge to heal. Albeit autografts are the standard‐of‐care, they are limited by their inability to be shaped to various defect geometries ...and often incur donor site complications. Herein, the combination of a “self‐fitting” shape memory polymer (SMP) scaffold and seeded mesenchymal stromal cells (MSCs) was investigated as an alternative. The porous SMP scaffold, prepared from poly(ε‐caprolactone) diacrylate (PCL‐DA) and coated with polydopamine, provided conformal shaping and cell adhesion. MSCs from five tissues, amniotic (AMSCs), chorionic tissue (CHSCs), umbilical cord (UCSCs), adipose (ADSCs), and bone marrow (BMSCs) were evaluated for viability, density, and osteogenic differentiation on the SMP scaffold. BMSCs exhibited the fastest increase in cell density by day 3, but after day 10, CHSCs, UCSCs, and ADSCs approached similar cell density. BMSCs also showed the greatest calcification among the cell types, followed closely by ADSCs, CHSCs and AMSCs. Alkaline phosphatase (ALP) activity peaked at day 7 for AMSCs, UCSCs, ADSCs and BMSCs, and at day 14 for CHSCs, which had the greatest overall ALP activity. Of all the cell types, only scaffolds cultured with ADSCs in osteogenic media had increased hardness and local modulus as compared to blank scaffolds after 21 days of cell culture and osteogenic differentiation. Overall, ADSCs performed most favorably on the SMP scaffold. The SMP scaffold was able to support key cellular behaviors of MSCs and could potentially be a viable, regenerative alternative to autograft.
The utility of poly(ε-caprolactone) (PCL) as a shape memory polymer (SMP) may be improved by accelerating its degradation. Recently, we have reported novel semi-interpenetrating networks (semi-IPNs) ...composed of cross-linked PCL diacrylate (PCL-DA) and thermoplastic poly(l-lactic acid) (PLLA) that exhibited SMP behavior, accelerated degradation, and enhanced moduli versus the PCL-DA control. Herein, we systematically varied the thermoplastic component of the PCL-based semi-IPNs, incorporating homo- and copolymers based on lactic acid of different
, hydrophilicity, and crystallinity. Specifically, semicrystalline PLLAs of different
s (7.5, 15, 30, and 120 kDa) were explored as the thermoplastics in the semi-IPNs. Additionally, to probe crystallinity and hydrophilicity, amorphous (or nearly amorphous) thermoplastics of different hydrophilicities (PDLLA and PLGAs 85:15, 70:30, and 50:50, l-lactide:glycolide mole % ratio) were employed. For all semi-IPNs, the wt % ratio of the cross-linked PCL-DA to thermoplastic was 75:25. The nature of the thermoplastics was linked to semi-IPN miscibility and the trends in accelerated degradation rates.
A comparative study on interfacial crystallization of isotactic polypropylene (iPP) surrounding macroscopic carbon nanotube and graphene fibers has been carried out in single fiber polymer composites ...by means of in situ polarized optical microscope, scanning electron microscope and X-ray diffraction. Ordered interfacial microstructures of iPP nucleate on both nanocarbon fibers in the form of a transcrystalline interphase. Nanotube fibers tend to promote negative birefringence transcrystals whereas graphene fibers induce positive birefringence transcrystals. The microstructures of transcrystals are strongly dependent on the thermal history and the double-layered transcrystals consisting of a negative inner layer and a positive outer layer occur under certain conditions. Transcrystallization kinetics has been studied and the Lauritzen–Hoffman theory of heterogeneous nucleation used to analyze the dynamic crystallization process. While the fold surface energy of iPP transcrystals surrounding both nanocarbon fibers shows little difference, the nanotube fiber promotes shorter induction time than the graphene fiber. Thermal resistance test demonstrates that the ordered interfacial microstructures possess higher melting temperature in the nanotube fiber composites than those in the graphene fiber composites. Under appropriate conditions, the β-form transcrystals of iPP are observed. The amount of the β-form iPP surrounding the nanotube fiber is much higher than that surrounding the graphene fiber. A theoretical model is proposed to interpret the difference between the nanotube and graphene fiber composites and the mechanisms behind its influence on interfacial crystallization.
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•Interfacial interactions between the polymer and nanocarbon fibers are evaluated.•Interfacial crystallization kinetics induced by nanocarbon fibers is determined.•Surface morphology of the fiber is determinative to transcrystallization.•Ordered interfacial structures enhance the thermal properties of composites.•Nanocarbons promote crystal polymorphism of the polymer.
Engineering osteoinductive, self‐fitting scaffolds offers a potential treatment modality to repair irregularly shaped craniomaxillofacial bone defects. Recently, we innovated on osteoinductive ...poly(ε‐caprolactone)‐diacrylate (PCL‐DA) shape memory polymers (SMPs) to incorporate poly‐L‐lactic acid (PLLA) into the PCL‐DA network, forming a semi‐interpenetrating network (semi‐IPN). Scaffolds formed from these PCL‐DA/PLLA semi‐IPNs display stiffnesses within the range of trabecular bone and accelerated degradation relative to scaffolds formed from slowly degrading PCL‐DA SMPs. Herein, we demonstrate for the first time that PCL‐DA/PLLA semi‐IPN SMP scaffolds show increased intrinsic osteoinductivity relative to PCL‐DA. We also confirm that application of a bioinspired polydopamine (PD) coating further improves the osteoinductive capacity of these PCL‐DA/PLLA semi‐IPN SMPs. In the absence of osteogenic supplements, protein level assessment of human mesenchymal stem cells (h‐MSCs) cultured in PCL‐DA/PLLA scaffolds revealed an increase in expression of osteogenic markers osterix, bone morphogenetic protein‐4 (BMP‐4), and collagen 1 alpha 1 (COL1A1), relative to PCL‐DA scaffolds and osteogenic medium controls. Likewise, the expression of runt‐related transcription factor 2 (RUNX2) and BMP‐4 was elevated in the presence of PD‐coating. In contrast, the chondrogenic and adipogenic responses associated with the scaffolds matched or were reduced relative to osteogenic medium controls, indicating that the scaffolds display intrinsic osteoinductivity.
Self-fitting scaffolds prepared from biodegradable poly(ε-caprolactone)-diacrylate (PCL-DA) have been developed for the treatment of craniomaxillofacial (CMF) bone defects. As a thermoresponsive ...shape memory polymer (SMP), with the mere exposure to warm saline, these porous scaffolds achieve a conformal fit in defects. This behavior was expected to be advantageous to osseointegration and thus bone healing. Herein, for an initial assessment of their regenerative potential, a pilot in vivo study was performed using a rabbit calvarial defect model. Exogenous growth factors and cells were excluded from the scaffolds. Key scaffold material properties were confirmed to be maintained following gamma sterilization. To assess scaffold integration and neotissue infiltration along the defect perimeter, non-critically sized (d = 8 mm) bilateral calvarial defects were created in 12 New Zealand white rabbits. Bone formation was assessed at 4 and 16 weeks using histological analysis and micro-CT, comparing defects treated with an SMP scaffold (d = 9 mm x t = 1 or 2 mm) to untreated defects (i.e. defects able to heal without intervention). To further assess osseointegration, push-out tests were performed at 16 weeks and compared to defects treated with poly(ether ether ketone) (PEEK) discs (d = 8.5 mm x t = 2 mm). The results of this study confirmed that the SMP scaffolds were biocompatible and highly conducive to bone formation and ingrowth at the perimeter. Ultimately, this resulted in similar bone volume and surface area versus untreated defects and superior performance in push-out testing versus defects treated with PEEK discs.
Current treatments of craniomaxillofacial (CMF) bone defects include biologic and synthetic grafts but they are limited in their ability to form good contact with adjacent tissue. A regenerative engineering approach using a biologic-free scaffold able to achieve conformal fitting represents a potential “off-the-shelf” surgical product to heal CMF bone defects. Having not yet been evaluated in vivo, this study provided the preliminary assessment of the bone healing potential of self-fitting PCL scaffolds using a rabbit calvarial defect model. The study was designed to assess scaffold biocompatibility as well as bone formation and ingrowth using histology, micro-CT, and biomechanical push-out tests. The favorable results provide a basis to pursue establishing self-fitting scaffolds as a treatment option for CMF defects.
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"Self-fitting" shape memory polymer (SMP) scaffolds prepared as semi-interpenetrating networks (semi-IPNs) with crosslinked linear-poly(ε-caprolactone)-diacrylate (PCL-DA, M
∼10 kg mol
) and ...linear-poly(l-lactic acid) (PLLA, M
∼15 kg mol
) 75/25 wt% exhibited robust mechanical properties and accelerated degradation rates versus a PCL-DA scaffold control. However, their potential to treat irregular craniomaxillofacial (CMF) bone defects is limited by their relatively high fitting temperature (T
∼55 °C; related to the T
of PCL) required for shape recovery (i.e. expansion) and subsequent shape fixation during press fitting of the scaffold, which can be harmful to surrounding tissue. Additionally, the viscosity of the solvent-based precursor solutions, cast over a fused salt template during fabrication, can limit scaffold size. Thus, in this work, analogous semi-IPN SMP scaffolds were formed with a 4-arm star-PCL-tetracryalate (star-PCL-TA) (M
∼10 kg mol
) and star-PLLA (M
∼15 kg mol
). To assess the impact of a star-polymer architecture, four semi-IPN compositions were prepared: linear-PCL-DA/linear-PLLA (L/L), linear-PCL-DA/star-PLLA (L/S), star-PCL-TA/linear-PLLA (S/L) and star-PCL-TA/star-PLLA (S/S). Two PCL controls were also prepared: LPCL (i.e. 100% linear-PCL-DA) and SPCL (i.e. 100% star-PCL-TA). The S/S semi-IPN scaffold exhibited particularly desirable properties. In addition to achieving a lower, tissue-safe T
(∼45 °C), it exhibited the fastest rate of degradation which is anticipated to more favourably permit neotissue infiltration. The radial expansion pressure exerted by the S/S semi-IPN scaffold at T
was greater than that of LPCL, which is expected to enhance osseointegration and mechanical stability. The intrinsic viscosity of the S/S semi-IPN macromer solution was also reduced such that larger scaffold specimens could be prepared.
This study focuses on the phase behavior, rheology, and interactions of polymer latex particles and a hydrophobically modified ethoxylated urethane (HEUR) associative thickener in water. At constant ...0.25 latex particle volume fraction, increasing HEUR caused stable, followed by phase separated (syneresis), and stable mixtures as HEUR concentration increased from 0% to 2.0% (by weight) in the latex-thickener aqueous mixture. The mixtures that underwent syneresis were flocculated. The relationship between the flocculation behavior and the composition of the latex-HEUR mixtures is consistent with previous work reported by other investigators. However, detailed rheological data on systems like these that have undergone syneresis have not been reported. This paper presents detailed viscosity vs shear rate data and correlates viscosity trends with the both flocculation and syneresis behavior. The stable latex-HEUR mixtures at low HEUR levels show Newtonian or shear-thinning viscosity with well-defined low-shear Newtonian plateaus. As HEUR level is increased to levels at which syneresis is observed, erratic rheological profiles with shear thinning as well as thickening are observed. This type of shear thickening has been attributed to bridging flocculation by other investigators. When HEUR level is further increased to levels at which no syneresis is observed, low-shear Newtonian plateaus re-appeared, albeit at higher viscosities. Detailed analysis of syneresis and shear-thickening behavior of a latex-HEUR mixture containing 0.5% (by weight) HEUR showed two shear-thickening regions, one between 0.1 and 0.5 s
−1
shear rate range and another between 30 and 100 s
−1
shear rate range. Molecular weight distribution (MWD) of the HEUR thickener indicates that the two shear-thickening regions are related to the bi-modal nature of the thickener’s MWD.
High performance carbon fibers (CFs) have been a commercially available since their commercial boom in the 1970s, and are generally produced via carbonization of poly (acrylonitrile) (PAN). More ...recently, carbon nanomaterials like graphene and carbon nanotubes (CNTs) have been discovered and have shown excellent mechanical, thermal, and electrical properties due to their sp2 carbon repeating structure. Graphene and CNTs can both be organized into macroscopic fibers using a number of different techniques, resulting in fibers with promising mechanical performance that can be readily multifunctionalized. In some cases, the two materials have been combined, and the resulting hybrid fibers have been shown to display synergistically enhanced mechanical properties. The incredible intrinsic properties of graphene and CNTs has never been fully realized in their fiber assemblies, so part of the aim of this work is to discover methods to improve upon the performance of nanocarbon based fibers. Carbon nanomaterials can be difficult to work with because of the difficulty in processing them into commercially viable materials, and the challenges associated with scalable production techniques. So, the main goal of this work is to prepare hybrid graphene and CNT based fibers with optimal mechanical performance using simple, cost-effective methods.
High performance carbon fibers (CFs) have been a commercially available since their commercial boom in the 1970s, and are generally produced via carbonization of poly (acrylonitrile) (PAN). More ...recently, carbon nanomaterials like graphene and carbon nanotubes (CNTs) have been discovered and have shown excellent mechanical, thermal, and electrical properties due to their sp2 carbon repeating structure. Graphene and CNTs can both be organized into macroscopic fibers using a number of different techniques, resulting in fibers with promising mechanical performance that can be readily multifunctionalized. In some cases, the two materials have been combined, and the resulting hybrid fibers have been shown to display synergistically enhanced mechanical properties. The incredible intrinsic properties of graphene and CNTs has never been fully realized in their fiber assemblies, so part of the aim of this work is to discover methods to improve upon the performance of nanocarbon based fibers. Carbon nanomaterials can be difficult to work with because of the difficulty in processing them into commercially viable materials, and the challenges associated with scalable production techniques. So, the main goal of this work is to prepare hybrid graphene and CNT based fibers with optimal mechanical performance using simple, cost-effective methods.
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