Biodegradable Polymer Substrates Research Articles

Ecofriendly Transfer Printing for Biodegradable Electronics Using Adhesion Controllable Self‐Assembled Monolayers

AbstractThe biodegradable electronics are on the rise, not just due to their role in medical implants, but also because of their eco‐friendly attributes. A variety of methods, including transfer printing, have been employed to integrate inorganic electronics onto biodegradable polymer substrates. However, the use of expensive materials, multiple intermediary steps, and labor‐intensive procedures can undermine their environment‐friendly benefits. Here, a straightforward yet efficient fabrication method is introduced for creating high‐performance biodegradable electronic devices. This method leverages the controlled adhesion between the biodegradable device and substrate using self‐assembled monolayers of octadecyltrichlorosilane. Mechanical and thermal analyses based on scratch tests and time‐domain thermoreflectance quantify the adhesion by adjusting the packing density of octadecyltrichlorosilane. Controlled adhesion allows the photolithography process without delamination while facilitating easy delamination during transfer printing. The authors demonstrate the direct fabrication of electronics consisted of inorganic materials (Mg, Zn, SiO2, Si nanomembrane) on wafers and transfer‐printing onto polymer substrates via a single transfer step. This streamlined approach enables wafer‐scale fabrication of biodegradable electronics, highlighting its potential for mass manufacturing. Pilot conceptual demonstration of mass‐produced edible hydration sensors and their application in salivation measurement through in vivo model show the potential capability of proposed fabrication method in the use of practical level.

Materials and processing approaches for foundry-compatible transient electronics

Foundry-based routes to transient silicon electronic devices have the potential to serve as the manufacturing basis for "green" electronic devices, biodegradable implants, hardware secure data storage systems, and unrecoverable remote devices. This article introduces materials and processing approaches that enable state-of-the-art silicon complementary metal-oxide-semiconductor (CMOS) foundries to be leveraged for high-performance, water-soluble forms of electronics. The key elements are (i) collections of biodegradable electronic materials (e.g., silicon, tungsten, silicon nitride, silicon dioxide) and device architectures that are compatible with manufacturing procedures currently used in the integrated circuit industry, (ii) release schemes and transfer printing methods for integration of multiple ultrathin components formed in this way onto biodegradable polymer substrates, and (iii) planarization and metallization techniques to yield interconnected and fully functional systems. Various CMOS devices and circuit elements created in this fashion and detailed measurements of their electrical characteristics highlight the capabilities. Accelerated dissolution studies in aqueous environments reveal the chemical kinetics associated with the underlying transient behaviors. The results demonstrate the technical feasibility for using foundry-based routes to sophisticated forms of transient electronic devices, with functional capabilities and cost structures that could support diverse applications in the biomedical, military, industrial, and consumer industries.

Substrate Fluidity Regulates Cell Adhesion and Morphology on Poly(ε-caprolactone)-Based Materials.

Although mechanostructural signals from the surrounding matrix have been known to regulate cell functions, the effects of substrate fluidity are poorly understood. Here, we demonstrate that the adhesion and morphology of cells are regulated by the fluidity on widely used biodegradable polymer substrates, rather than the substrate elasticity. We have designed cell culture films with different elasticity and fluidity using poly(ε-caprolactone-co-D,l-lactide) (CL-DLLA). The elasticity was successfully controlled by adjusting the amorphous-crystal phase transition temperature (Tm) of CL-DLLA without changing the surface wettability; i.e., the CL-DLLA displays more viscous (liquidlike) behavior at 37 °C with increasing DLLA contents. The fluidity was varied by chemically cross-linking the polymer networks. This CL-DLLA system was used to test the effect of variations in a substrate's fluidity on cell behavior. Differences were observed in adhesion, spreading and morphology of NIH 3T3 fibroblasts. Increasing the fluidity decreased cell spread area but enhanced the formation of spheroids. Although direct comparison of the elastic modulus between cross-linked and non-cross-linked samples are difficult, it was found that the substrate stiffness produced little changes in cell spread area, indicating that cells sense more dynamic nature of their surrounding environment. These findings will serve as the basis for new development of tissue engineering scaffolds and engineered stem cell niche as well as investigation of dynamic effects of mechanostructural stimuli on cell fate.

Aligned carbon nanotube containing scaffolds for neural tissue regeneration.

Neuropathologies include the deterioration and damage of the nervous system, especially neurons present in the brain, spinal cord and peripheral nervous system. Damage or alternations in neurons makes their structure and functionality abnormal. Every year over 90,000 people get affected by neurodegenerative diseases in the USA. Among all the neurological pathologies, the spinal cord injuries alone influence 10,000 people in the USA every year. Millions of cases of neurodegenerative pathologies are registered worldwide. Without proper treatment and cure to these cases, the toll for patients suffering from neurode-generative disease is expected to reach at least 12 million in the USA 30 years from now (John, 2015).

Biodegradable Nanotopography Combined with Neurotrophic Signals Enhances Contact Guidance and Neuronal Differentiation of Human Neural Stem Cells.

Biophysical cues provided by nanotopographical surfaces have been used as stimuli to guide neurite extension and regulate neural stem cell (NSC) differentiation. Here, we fabricated biodegradable polymer substrates with nanoscale topography for enhancing human NSC (hNSC) differentiation and guided neurite outgrowth. The substrate was constructed from biodegradable poly(lactic-co-glycolic acid) (PLGA) using solvent-assisted capillary force lithography. We found that precoating with 3,4-dihydroxy-l-phenylalanine (DOPA) facilitated the immobilization of poly-l-lysine and fibronectin on PLGA substrates via bio-inspired catechol chemistry. The DOPA-coated nanopatterned substrates directed cellular alignment along the patterned grooves by contact guidance, leading to enhanced focal adhesion, skeletal protein reorganization, and neuronal differentiation of hNSCs as indicated by highly extended neurites from cell bodies and increased expression of neuronal markers (Tuj1 and MAP2). The addition of nerve growth factor further enhanced neuronal differentiation of hNSCs, indicating a synergistic effect of biophysical and biochemical cues on NSC differentiation. These bio-inspired PLGA nanopatterned substrates could potentially be used as implantable biomaterials for improving the efficacy of hNSCs in treating neurodegenerative diseases.

Biomimetic mineralization of zein/calcium phosphate nanocomposite nanofibrous mats for bone tissue scaffolds

Biomimetic mineralization process has been extended to bio-inspired bone-like calcium phosphate coatings on biodegradable polymer substrates. The objective of the current work is to synthesize zein/calcium phosphate nanocomposite nanofibrous scaffolds by the biomimetic mineralization process for bone tissue engineering. After incubation in 10 times concentrated simulated body fluid for 2 hours, the surface of electrospun zein nanofibers was uniformly coated with plate-like calcium phosphate nanosheets which attach to fibers and preserve the fibrous morphology of electrospun zein fibers. The crystalline phases in the composite are hydroxyapatite and dicalcium phosphate dihydrate. The biological in vitro cell culture with adipose-derived stem cells demonstrated that mineralized electrospun zein scaffolds can improve specific biological functions like adhesion, spread and proliferation resulting from the retained fibrous morphology and bioactive environment provided by calcium phosphate minerals. This study has demonstrated that mineralization of electrospun zein fibers provides a simple platform to fabricate a new biomimetic scaffold for bone tissue engineering, which can recapitulate both the morphology of the extracellular matrix and the composition of the bone.

Integration of photo-crosslinking and breath figures to fabricate biodegradable polymer substrates with tunable pores that regulate cellular behavior

Honeycomb films of crosslinked poly(ε-caprolactone) triacrylate were fabricated by incorporating the breath-figure method with photo-curing. Two different pore sizes of 5.6 and 3.0 μm were achieved by modulating the airflow rate at 0 and 50 mL min−1, respectively. Mouse pre-osteoblastic MC3T3-E1 cell adhesion, spreading, proliferation, mineralization, and expression of integrin subunits of α1, α2, β1, and gene markers of osteocalcin, osteopontin, alkaline phosphatase (ALP), and collagen type I were investigated on these two series of honeycomb films and their flat control. The honeycomb films, especially those with smaller pores, could significantly promote MC3T3-E1 cell adhesion, spreading, proliferation, ALP activity, mineralization, and gene expression of osteoblastic markers, via fostering expression of integrin subunits.

Photocured Biodegradable Polymer Substrates of Varying Stiffness and Microgroove Dimensions for Promoting Nerve Cell Guidance and Differentiation

Photocross-linkable and biodegradable polymers have great promise in fabricating nerve conduits for guiding axonal growth in peripheral nerve regeneration. Here, we photocross-linked two poly(ε-caprolactone) triacrylates (PCLTAs) with number-average molecular weights of ~7000 and ~10,000 g mol(-1) into substrates with parallel microgrooves. Cross-linked PCLTA7k was amorphous and soft, while cross-linked PCLTA10k was semicrystalline with a stiffer surface. We employed different dimensions of interests for the parallel microgrooves, that is, groove widths of 5, 15, 45, and 90 μm and groove depths of 0.4, 1, 5, and 12 μm. The behaviors of rat Schwann cell precursor line (SpL201) cells with the glial nature and pheochromocytoma (PC12) cells with the neuronal nature were studied on these microgrooved substrates, showing distinct preference to the substrates with different mechanical properties. We found different threshold sensitivities of the two nerve cell types to topographical features when their cytoskeleton and nuclei were altered by varying the groove depth and width. Almost all of the cells were aligned in the narrowest and deepest microgrooves or around the edge of microgrooves. Oriented SpL201 cell movement had a higher motility as compared to unaligned ones. After forskolin treatment, SpL201 cells demonstrated significantly upregulated S-100 and O4 on stiffer substrates or narrower microgrooves, suggesting more differentiation toward early Schwann cells (SCs). PC12 neurites were oriented with enhanced extension in narrower microgrooves. The present results not only improve our fundamental understanding on nerve cell-substrate interactions, but also offer useful conduit materials and appropriate feature dimensions to foster guidance for axonal growth in peripheral nerve regeneration.

Mouse Retinal Progenitor Cell Dynamics on Electrospun Poly (ϵ-Caprolactone)

Age-related macular degeneration, retinitis pigmentosa and glaucoma are among the many retinal degenerative diseases where retinal cell death leads to irreversible vision loss and blindness. Working toward a cell-replacement-based therapy for such diseases, a number of research groups have recently evaluated the feasibility of using retinal progenitor cells (RPCs) cultured and transplanted on biodegradable polymer substrates to replace damaged retinal tissue. Appropriate polymer substrate design is essential to providing a three-dimensional environment that can facilitate cell adhesion, proliferation and post-transplantation migration into the host environment. In this study, we have designed and fabricated a novel, ultra-thin electrospun poly(ϵ-caprolactone) (PCL) scaffold with microscale fiber diameters, appropriate porosity for infiltration by RPCs, and biologically compatible mechanical characteristics. We have verified that our electrospun PCL scaffold supports robust mouse RPC proliferation, adhesion, and differentiation in vitro, as well as migration into mouse retinal explants. These promising results make PCL a strong candidate for further development as a cell transplantation substrate in retinal regenerative research.

Mineralization of hydroxyapatite crystallites on zein microspheres

AbstractBioinspired mineralization process has been extended to the formation of bonelike hydroxyapatite (HAp) coatings on biodegradable polymer substrates. HAp‐coated zein microspheres were prepared through phase separation procedure, followed by incubation in modified simulated body fluids (mSBF). The morphologies of mineralized zein microspheres with different diameters and incubation time were investigated by scanning electron microscopy (SEM). The nature of the deposited mineral phase was characterized by energy‐dispersive spectroscopy (EDS) and wide‐angle X‐ray diffraction (XRD). The results showed that as the average diameter of zein microspheres increased to 1.13 μm, randomly oriented minerals were observed on the surface of microspheres. Two characteristic HAp diffraction reflections 002 and 211 centered at 2θ of 25.6° and 32.0° were ascertained on the XRD patterns of the mineralized microspheres. Incubation of zein microspheres with larger diameters in mSBF led to nucleation and growth of minerals on the surface. Even larger number of minerals were deposited and a porous structure of platelike HAp crystals was obtained after incubation for 21 days. The novel zein/HAp microspheres may have a wide variety of potential applications in bone regeneration and tissue engineering. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Biodegradable Photo‐Crosslinked Polymer Substrates with Concentric Microgrooves for Regulating MC3T3‐E1 Cell Behavior

Both intrinsic material properties and topographical features are critical in influencing cell-biomaterial interactions. We present a systematic investigation of regulating mouse pre-osteoblastic MC3T3-E1 cell behavior on biodegradable polymer substrates with distinct mechanical properties and concentric microgrooves. The precursors for fabricating substrates used here were two poly(ϵ-caprolactone) triacrylates (PCLTAs) synthesized from poly(ϵ-caprolactone) triols with molecular weights of ∼7000 and ∼10000 g mol(-1) . These two PCLTAs were photo-crosslinked into PCL networks with distinct thermal, rheological, and mechanical properties at physiological temperature because of their different crystallinities and melting temperatures. Microgrooved substrates with four groove widths of 7.5, 16.1, 44.2, and 91.2 μm and three groove depths of 0.2, 1, and 10 μm were prepared through replica molding, i.e., photo-crosslinking PCLTA on micro-fabricated silicon wafers with pre-designed concentric groove patterns. MC3T3-E1 cell attachment and proliferation could be better supported by the stiffer substrates while not significantly influenced by the microgrooves. Microgroove dimensions could regulate MC3T3-E1 cell alignment, nuclear shape and distribution, mineralization, and gene expression. Among the microgrooves with a fixed depth of 10 μm, the smallest width of 7.5 μm could align and elongate the cytoskeleton and nuclei most efficiently. Strikingly, higher mineral deposition and upregulation of osteocalcin gene expression were found in the narrower microgrooves when the groove depth was 10 μm.

Novel thin-walled nerve conduit with microgrooved surface patterns for enhanced peripheral nerve repair

Randomly aligned nerve cells in vitro on conventional culture substrata do not represent the complex neuronal network in vivo and neurites growing in uncontrolled manner may form neuroma. It is of great importance to mimic the organised growth pattern of nerve cells in the study of peripheral nerve repair. The aim of this work was to modify and optimize the photolithographic technique in creating a reusable template in the form of a silicon wafer that could be used to produce contact guidance on biodegradable polymer surface for the orientated growth of nerve cells. Micro-grooves (approximately 3 μm in depth) were etched into the silicon template using KOH at increased temperature. The originality of this work lies in the low cost and high efficiency method in producing microgrooves on the surface of biodegradable ultra-thin polymer substrates (50-100 μm), which can be readily rolled up to form clinically implantable nerve conduits. The design of a pattern with small ridge width (i.e., 5 μm) and bigger groove width (i.e., 20 μm) favored the alignment of cells along the grooves rather than on the ridges of the patterns, which minimized the effect of cross growing of neurites between adjacent grooves. Effectively, enhanced nerve regeneration could be anticipated from these patterned conduits.

Cellular orientation on micro-patterned biocompatible PHBV film

Cellular orientation control is important for tissue regeneration. Design of oriented structures for cells with suitable features can be used in tissue engineering. One of the methods of cellular orientation with the aim of regenerating which damaged tissues is utilizing oriented biocompatible substrates. Different methods can be used to design these structures such as utilizing magnetic fields, electrospinned oriented fibers or methods such as directional solidification. This paper investigates the influence of grooved substrate-mediated physical guidance on the growth and alignment of cells in vitro. A novel technique was developed to fabricate microgrooves on biodegradable polymer substrates made of poly hydroxyl buthyratevalerate. Solvent-castings were used to transfer micro patterns from quartz and silicon substrates onto biodegradable polymer films. The cells were successfully oriented on micro grooved polymeric substrate which can be used for axon guidance and nerve regeneration.

In vitro study of human vascular endothelial cell function on materials with various surface roughness.

In recent years, creating a biodegradable polymer scaffold with an endothelialized surface has become an attractive concept for replacement of small-diameter blood vessels. Toward this end, a better understanding of the interaction between endothelial cells and biodegradable polymer substrates is particularly important. Surface roughness of biomaterials is one of the important parameters that affect cell behavior. In this study, human vascular endothelial cells were cultured on electrospun and solvent-cast poly(L-lactic acid) substrates with different surface roughness. Cell responses were evaluated via both qualitative examinations of cell morphology changes as well as quantitative assessment of cell adhesion and proliferation rate on the different substrates. The results proved that endothelial cell function was enhanced on the smooth solvent-cast surface rather than on the rough electrospun surface of poly(L-lactic acid). Together with our previous findings that electrospun substrates favor vascular smooth muscle cell behavior, it is possible to design a unique three-dimensional scaffold for application of tissue-engineered small-diameter vessel replacement by combining the fabrication technique of solvent casting and electrospinning.

Synergistic effects of physical and chemical guidance cues on neurite alignment and outgrowth on biodegradable polymer substrates.

This article demonstrates that directional outgrowth of neurites is promoted by applying a combination of physical and chemical cues to biodegradable polymer substrates. Films of poly-D,L-lactic acid and poly(lactide-co-glycolide) were micropatterned to form grooves on substrate surfaces, using novel indirect transfer techniques developed specifically for biodegradable polymers that cannot be micropatterned directly. Laminin was selectively adsorbed in the grooves. Whole and dissociated dorsal root ganglia were seeded on the substrates and neurite outgrowth and alignment along the microgrooves were measured. The microgrooves provide physical guidance, whereas laminin provides chemical cues to the neurons. The groove depth and spacing were found to significantly influence neurite alignment. The presence of laminin was found to promote neurite adhesion and outgrowth along the grooves. Using a combination of optimized physical and chemical cues, excellent spatial control of directional neurite outgrowth, with up to 95% alignment of neurites, was obtained. The synergistic effect of physical and chemical guidance cues was found to be more effective than individual cues in promoting directional outgrowth of neurites.

Micropatterned Schwann cell-seeded biodegradable polymer substrates significantly enhance neurite alignment and outgrowth.

Biomimetic strategies were employed to promote directional outgrowth of neurites in vitro by using a synergistic combination of physical, chemical, and cellular cues. Compression molded and solvent cast biodegradable polymer substrates made of poly(D,L-lactic acid) were micropatterned to form grooves on the substrate surfaces. Laminin was localized in the grooves, and rat sciatic Schwann cells were seeded on the substrates. Whole as well as dissociated rat dorsal root ganglia were seeded on the substrates along with Schwann cells, and neurite outgrowth and alignment were measured. The micropatterns provide physical guidance, laminin provides chemical cues, and the Schwann cells provide biological cues to the axons. The presence of Schwann cells in the grooves was found to promote neurite alignment as well as outgrowth and help the neurites orient even on shallower grooves and exhibit continued alignment even as the grooves degrade. The synergistic combination of physical, chemical, and cellular guidance enabled greater than 98% alignment of neurites and accelerated outgrowth of neurites in the direction of the microgrooves.

Oriented Schwann cell growth on micropatterned biodegradable polymer substrates

This paper investigates the influence of substrate-mediated chemical and physical guidance on the growth and alignment of Schwann cells in vitro. Novel techniques were developed to fabricate microgrooves with adsorbed proteins on biodegradable polymer substrates made of poly( d, l-lactic acid). Compression molding and solvent-casting were used to transfer micropatterns from quartz and silicon substrates onto biodegradable polymer films. Laminin was selectively adsorbed onto the grooves and rat sciatic Schwann cells were seeded on the substrates. Laminin was found to improve adhesion of Schwann cells on the substrates. The microgrooves were found to cause the Schwann cells to align along the direction of the grooves. The groove width influenced Schwann cell alignment the most, while groove depth did not seem to play a significant role. The degradation of the grooves in the solvent cast films was much slower than those in the compression-molded films, making them the preferred substrates for Schwann cell culture.

Retinal pigment epithelial cell adhesion on novel micropatterned surfaces fabricated from synthetic biodegradable polymers

Novel synthetic biodegradable polymer substrates with specific chemical micropatterns were fabricated from poly( dl-lactic- co-glycolic acid) (PLGA) and diblock copolymers of poly(ethylene glycol) and poly( dl-lactic acid) (PEG/PLA). Thin films of PLGA and PEG/PLA supported and inhibited, respectively, retinal pigment epithelial (RPE) cell proliferation, with a corresponding cell density of 352 900 and 850 cells/cm 2 after 7 days (from an initial seeding density of 15 000 cells/cm 2). A microcontact printing technique was used to define arrays of circular (diameter of 50 μm) PLGA domains surrounded and separated by regions (width of 50 μm) of PEG/PLA. Reversed patterns composed of PEG/PLA circular domains surrounded by PLGA regions were also fabricated. Both micropatterned surfaces were shown to affect initial RPE cell attachment, limit cell spreading, and promote the characteristic cuboidal cell morphology during the 8-h period of the experiments. In contrast, RPE cells on plain PLGA (control films) were elongated and appeared fibroblast-like. The reversed patterns had continuous PLGA regions that allowed cell–cell interactions and thus higher cell adhesion. These results demonstrate the feasibility of fabricating micropatterned synthetic biodegradable polymer surfaces to control RPE cell morphology.

Wetting of poly( l-lactic acid) and poly( dl-lactic-co-glycolic acid) foams for tissue culture

Biodegradable foams of hydrophobic polymers can be efficiently wet by two-step immersion in ethanol and water, which overcomes the hindered entry of water into air-filled pores. Ethanol readily enters into the porous polymer, after which it is diluted and replaced by water. This method was evaluated for porous disks of poly( l-lactic acid) (PLLA) and poly( dl-lactic-co-glycolic acid) (PLGA) foams of copolymer ratios 85:15 and 50:50. For PLLA disks of 0.88 porosity and 1730μm thickness, prewetting with ethanol for 1 h increased the percentage of void volume filled with water after 48 h from 23 to 79%. The same enhanced entry of water was also observed for prewet PLGA 85:15 disks of 0.86 porosity and 1300 μm thickness, which exhibited an increase from 59 to 97% void volume occupied by water. Furthermore, the water entry even after 1 h was very close to its plateau value for all prewet polymers tested. In recent studies, this method has been useful in uniformly seeding three-dimensional biodegradable polymer substrates for cell and tissue culture.