Factors affecting product association as a mechanism of host-cell protein persistence in bioprocessing

Product association of host-cell proteins (HCPs) to monoclonal antibodies (mAbs) is widely regarded as a mechanism that can enable HCP persistence through multiple purification steps and even into the final drug substance. Discussion of this mechanism often implies that the existence or extent of persistence is directly related to the strength of binding but actual measurements of the binding affinity of such interactions remain sparse. Two separate avenues of investigation of HCP-mAb binding are reported here. One is the measurement of the affinity of binding of individual, commonly persistent Chinese hamster ovary (CHO) HCPs to each of a set of mAbs, and the other uses quantitative proteomic measurements to assess binding of HCPs in a null CHO harvested cell culture fluid (HCCF) to mAbs produced in the same cell line. The individual HCP measurements show that the binding affinities of individual HCPs to different mAbs can vary appreciably but are rarely very high, with only weak pH dependence. The measurements on the null HCCF allow estimation of individual HCP-mAb affinities; these are typically weaker than those seen in affinity measurements on isolated HCPs. Instead, the extent of binding appears correlated with the initial abundance of individual HCPs in the HCCF and the forms of the HCPs in the solution, i.e., whether HCPs are present as free molecules or as parts of large aggregates. Separate protein A chromatography experiments performed by feeding different fractions of a mAb-containing HCCF obtained by size-exclusion chromatography (SEC) showed clear differences in the number and identity of HCPs found in the protein A eluate. These results indicate a significant role for HCP-mAb association in determining HCP persistence through protein A chromatography, presumably through binding of HCP-mAb complexes to the resin. Overall, the results illustrate the importance of considering more fully the biophysical context of HCP-product association in assessing the factors that may affect the phenomenon and determine its implications. Knowledge of the abundances and the forms of individual or aggregated HCPs in HCCF are particularly significant, emphasizing the integration of upstream and downstream bioprocessing and the importance of understanding the collective properties of HCPs in addition to just the biophysical properties of individual HCPs.

Application of surface-layer matrix-assisted laser desorption/ionization mass spectrometry imaging to pharmaceutical-loaded poly(ester urea) films

Polymer thin films are often used in transdermal patches as a method of continuous drug administration for patients with chronic illness. Understanding the drug segregation and distribution within these films is important for monitoring proper drug release over time. Surface-layer matrix-assisted laser desorption/ionization mass spectrometry imaging (SL-MALDI-MSI) is a unique analytical technique that provides an optical representation of chemical compositions that exist at the surface of polymeric materials. Solvent-free sublimation is employed for application of matrix to the sample surface, so that only molecules in direct contact with the matrix layer are detected. Here, these methodologies are utilized to visualize variations in drug concentration at both the air and substrate interface in pharmaceutical-loaded polymer films.

Resorbable barrier polymers for flexible bioelectronics

Resorbable, implantable bioelectronic devices are emerging as powerful tools to reliably monitor critical physiological parameters in real time over extended periods. While degradable magnesium-based electronics have pioneered this effort, relatively short functional lifetimes have slowed clinical translation. Barrier films that are both flexible and resorbable over predictable timelines would enable tunability in device lifetime and expand the viability of these devices. Herein, we present a library of stereocontrolled succinate-based copolyesters which leverage copolymer composition and processing method to afford tunability over thermomechanical, crystalline, and barrier properties. One copolymer composition within this library has extended the functional lifetime of transient bioelectronic prototypes over existing systems by several weeks-representing a considerable step towards translational devices.

Mechanochromism and Strain-Induced Crystallization in Thiol-yne-Derived Stereoelastomers

Most elastomers undergo strain-induced crystallization (SIC) under tension; as individual chains are held rigidly in a fixed position by an applied strain, their alignment along the strain field results in a shift from strain-hardening (SH) to SIC. A similar degree of stretching is associated with the tension necessary to accelerate mechanically coupled, covalent chemical responses of mechanophores in overstretched chains, raising the possibility of an interplay between the macroscopic response of SIC and the molecular response of mechanophore activation. Here, thiol-yne-derived stereoelastomers doped covalently with a dipropiolate-derivatized spiropyran (SP) mechanophore (0.25-0.38 mol%) are reported. The material properties of SP-containing films are consistent with undoped controls, indicating that the SP is a reporter of the mechanical state of the polymer. Uniaxial tensile tests reveal correlations between mechanochromism and SIC, which are strain-rate-dependent. When mechanochromic films are stretched slowly to the point of mechanophore activation, the covalently tethered mechanophore remains trapped in a force-activated state, even after the applied stress is removed. Mechanophore reversion kinetics correlate with the applied strain rate, resulting in highly tunable decoloration rates. Because these polymers are not covalently crosslinked, they are recyclable by melt-pressing into new films, increasing their potential range of strain-sensing, morphology-sensing, and shape-memory applications.

Applied machine learning as a driver for polymeric biomaterials design

Polymers are ubiquitous to almost every aspect of modern society and their use in medical products is similarly pervasive. Despite this, the diversity in commercial polymers used in medicine is stunningly low. Considerable time and resources have been extended over the years towards the development of new polymeric biomaterials which address unmet needs left by the current generation of medical-grade polymers. Machine learning (ML) presents an unprecedented opportunity in this field to bypass the need for trial-and-error synthesis, thus reducing the time and resources invested into new discoveries critical for advancing medical treatments. Current efforts pioneering applied ML in polymer design have employed combinatorial and high throughput experimental design to address data availability concerns. However, the lack of available and standardized characterization of parameters relevant to medicine, including degradation time and biocompatibility, represents a nearly insurmountable obstacle to ML-aided design of biomaterials. Herein, we identify a gap at the intersection of applied ML and biomedical polymer design, highlight current works at this junction more broadly and provide an outlook on challenges and future directions.

Calcium Trimetaphosphate-Loaded Electrospun Poly(Ester Urea) Nanofibers for Periodontal Tissue Engineering

The objective of this research was to create and appraise biodegradable polymer-based nanofibers containing distinct concentrations of calcium trimetaphosphate (Ca-TMP) for periodontal tissue engineering. Poly(ester urea) (PEU) (5% w/v) solutions containing Ca-TMP (15%, 30%, 45% w/w) were electrospun into fibrous scaffolds. The fibers were evaluated using SEM, EDS, TGA, FTIR, XRD, and mechanical tests. Degradation rate, swelling ratio, and calcium release were also evaluated. Cell/Ca-TMP and cell/scaffold interaction were assessed using stem cells from human exfoliated deciduous teeth (SHEDs) for cell viability, adhesion, and alkaline phosphatase (ALP) activity. Analysis of variance (ANOVA) and post-hoc tests were used (α = 0.05). The PEU and PEU/Ca-TMP-based membranes presented fiber diameters at 469 nm and 414-672 nm, respectively. Chemical characterization attested to the Ca-TMP incorporation into the fibers. Adding Ca-TMP led to higher degradation stability and lower dimensional variation than the pure PEU fibers; however, similar mechanical characteristics were observed. Minimal calcium was released after 21 days of incubation in a lipase-enriched solution. Ca-TMP extracts enhanced cell viability and ALP activity, although no differences were found between the scaffold groups. Overall, Ca-TMP was effectively incorporated into the PEU fibers without compromising the morphological properties but did not promote significant cell function.

Quantification of cell migration: metrics selection to model application

Cell migration plays an essential role in physiological and pathological states, such as immune response, tissue generation and tumor development. This phenomenon can occur spontaneously or it can be triggered by an external stimuli, including biochemical, mechanical, or electrical cues that induce or direct cells to migrate. The migratory response to these cues is foundational to several fields including neuroscience, cancer and regenerative medicine. Various platforms are available to qualitatively and quantitatively measure cell migration, making the measurements of cell motility straight-forward. Migratory behavior must be analyzed by multiple metrics and then models to connect the measurements to physiological meaning. This review will focus on describing and quantifying cell movement for individual cell migration.

Characterization and implications of host-cell protein aggregates in biopharmaceutical processing

In the production of biopharmaceuticals such as monoclonal antibodies (mAbs) and vaccines, the residual amounts of host-cell proteins (HCPs) are among the critical quality attributes. In addition to overall HCP levels, individual HCPs may elude purification, potentially causing issues in product stability or patient safety. Such HCP persistence has been attributed mainly to biophysical interactions between individual HCPs and the product, resin media, or residual chromatin particles. Based on measurements on process streams from seven mAb processes, we have found that HCPs in aggregates, not necessarily chromatin-derived, may play a significant role in the persistence of many HCPs. Such aggregates may also hinder accurate detection of HCPs using existing proteomics methods. The findings also highlight that certain HCPs may be difficult to remove because of their functional complementarity to the product; specifically, chaperones and other proteins involved in the unfolded protein response (UPR) are disproportionately present in the aggregates. The methods and findings described here expand our understanding of the origins and potential behavior of HCPs in cell-based biopharmaceutical processes and may be instrumental in improving existing techniques for HCP detection and clearance.

Anti-adhesive bioresorbable elastomer-coated composite hernia mesh that reduce intraperitoneal adhesions

Intraperitoneal adhesions (IAs) are a major complication arising from abdominal repair surgeries, including hernia repair procedures. Herein, we fabricated a composite mesh device using a macroporous monofilament polypropylene mesh and a degradable elastomer coating designed to meet the requirements of this clinical application. The degradable elastomer was synthesized using an organo-base catalyzed thiol-yne addition polymerization that affords independent control of degradation rate and mechanical properties. The elastomeric coating was further enhanced by the covalent tethering of antifouling zwitterion molecules. Mechanical testing demonstrated the elastomer forms a robust coating on the polypropylene mesh does not exhibit micro-fractures, cracks or mechanical delamination under cyclic fatigue testing that exceeds peak abdominal loads (50 N/cm). Quartz crystal microbalance measurements showed the zwitterionic functionalized elastomer further reduced fibrinogen adsorption by 73% in vitro when compared to unfunctionalized elastomer controls. The elastomer exhibited degradation with limited tissue response in a 10-week murine subcutaneous implantation model. We also evaluated the composite mesh in an 84-day study in a rabbit cecal abrasion hernia adhesion model. The zwitterionic composite mesh significantly reduced the extent and tenacity of IAs by 94% and 90% respectively with respect to uncoated polypropylene mesh. The resulting composite mesh device is an excellent candidate to reduce complications related to abdominal repair through suppressed fouling and adhesion formation, reduced tissue inflammation, and appropriate degradation rate.

Ionic dielectrics for fully printed carbon nanotube transistors: impact of composition and induced stresses

Printed carbon nanotube thin-film transistors (CNT-TFTs) are candidates for flexible electronics with printability on a wide range of substrates. Among the layers comprising a CNT-TFT, the gate dielectric has proven most difficult to additively print owing to challenges in film uniformity, thickness, and post-processing requirements. Printed ionic dielectrics show promise for addressing these issues and yielding devices that operate at low voltages thanks to their high-capacitance electric double layers. However, the printing of ionic dielectrics in their various compositions is not well understood, nor is the impact of certain stresses on these materials. In this work, we studied three compositionally distinct ionic dielectrics in fully printed CNT-TFTs: the polar-fluorinated polymer elastomer PVDF-HFP; an ion gel consisting of triblock polymer PS-PMMA-PS and ionic liquid EMIM-TFSI; and crystalline nanocellulose (CNC) with a salt concentration of 0.05%. Although ion gel has been thoroughly studied, e-PVDF-HFP and CNC printing are relatively new and this study provides insights into their ink formulation, print processing, and performance as gate dielectrics. Using a consistent aerosol jet printing approach, each ionic dielectric was printed into similar CNT-TFTs, allowing for direct comparison through extensive characterization, including mechanical and electrical stress tests. The ionic dielectrics were found to have distinct operational dependencies based on their compositional and ionic attributes. Overall, the results reveal a number of trade-offs that must be managed when selecting a printable ionic dielectric, with CNC showing the strongest performance for low-voltage operation but the ion gel and elastomer exhibiting better stability under bias and mechanical stresses.

Thiol-Based Three-Dimensional Printing of Fully Degradable Poly(propylene fumarate) Star Polymers

Poly(propylene fumarate) star polymers photochemically 3D printed with degradable thiol cross-linkers yielded highly tunable biodegradable polymeric materials. Tailoring the alkene:thiol ratio (5:1, 10:1, 20:1 and 30:1) and thus the cross-link density within the PPF star systems yielded a wide variation of both the mechanical and degradation properties of the printed materials. Fundamental trends were established between the polymer network cross-link density, glass transition temperature, and tensile and thermomechanical properties of the materials. The tensile properties of the PPF star-based systems were compared to commercial state-of-the-art non-degradable polymer resins. The thiolene-cross-linked materials are fully degradable and possess properties over a wide range of mechanical properties relevant to regenerative medicine applications.

Reassessing Undergraduate Polymer Chemistry Laboratory Experiments for Virtual Learning Environments

Chemistry laboratory experiments are invaluable to students' acquisition of necessary synthetic, analytical, and instrumental skills during their undergraduate studies. However, the COVID-19 pandemic rendered face-to-face (f2f), in-person teaching laboratory experiences impossible from late 2019-2020 and forced educators to rapidly develop new solutions to deliver chemistry laboratory education remotely. Unfortunately, achieving learning and teaching objectives to the same caliber of in-person experiments is very difficult through distance learning. To overcome these hurdles, educators have generated many virtual and remote learning options for not only foundational chemistry courses but also laboratory experiments. Although the pandemic challenged high-level chemistry education, it has also created an opportunity for both students and educators to be more cognizant of virtual learning opportunities and their potential benefits within chemistry curriculum. Irrespective of COVID-19, virtual learning techniques, especially virtual lab experiments, can complement f2f laboratories and offer a cost-efficient, safe, and environmentally sustainable alternative to their in-person counterparts. Implementation of virtual and distance learning techniques-including kitchen chemistry and at-home laboratories, prerecorded videos, live-stream video conferencing, digital lab environment, virtual and augmented reality, and others-can provide a wide-ranging venue to teach chemistry laboratories effectively and encourage diversity and inclusivity in the field. Despite their relevance to real-world applications and potential to expand upon fundamental chemical principles, polymer lab experiments are underrepresented in the virtual platform. Polymer chemistry education can help prepare students for industrial and academic positions. The impacts of polymers in our daily life can also promote students' interests in science and scientific research. Hence, the translation of polymer lab experiments into virtual settings improves the accessibility of polymer chemistry education. Herein, we assess polymer experiments in the emergence of virtual learning environments and provide suggestions for further incorporation of effective polymer teaching and learning techniques into virtual settings.

Degradable, Photochemically Printable Poly(propylene fumarate)-Based ABA Triblock Elastomers

Additive manufacturing is rapidly advancing tissue engineering, but the scope of its clinical translation is limited by a lack of materials designed to meet specific mechanical properties and resorption timelines. Materials that are printable via photochemical cross-linking, fully degradable, and elastomeric have proven to be particularly challenging to develop. Herein, we report the synthesis of a series of poly(propylene fumarate-b-γ-methyl-ε-caprolactone-b-propylene fumarate) ABA triblock polymers using sequential ring-opening polymerization and ring-opening copolymerization. When cross-linked photochemically using a continuous liquid interface production digital light processing Carbon M2 printer, these ABA-type triblock copolymers are durable elastomers with tunable degradation and elastic properties. The polymers are shown to undergo slow, hydrolytic degradation in vitro with minimal loss of mechanical performance during degradation.

Gradient versus End-Capped Degradable Polymer Sequence Variations Result in Stiff to Elastic Photochemically 3D-Printed Substrates

Additive manufacturing affords the construction of complex scaffolds for tissue engineering, yet the limitation in material choice remains a barrier to clinical translation. Herein, a series of poly(propylene fumarate-co-propylene succinate) were synthesized using both one-pot and sequential ring-opening copolymerization reactions. Continuous liquid interface production-based photochemical 3D printing utilizing thiol-ene chemistry was used to fabricate precise structures with improved build time over the traditional poly(propylene fumarate)/diethyl fumarate 3D printing processes. Significantly, the materials do not exhibit a yield point under tension and Young's modulus of the 3D printed products can be tuned by more than 2 orders of magnitude (0.6-110 MPa) using polymer composition and the degree of polymerization. Printed constructs degrade fully under hydrolytic conditions and degradation rates can be tailored using polymer composition, polymer sequence, and resin formulation.

Ultra-Tough Elastomers from Stereochemistry-Directed Hydrogen Bonding in Isosorbide-Based Polymers

The remarkable elasticity and tensile strength found in natural elastomers are challenging to mimic. Synthetic elastomers typically feature covalently cross-linked networks (rubbers), but this hinders their reprocessability. Physical cross-linking via hydrogen bonding or ordered crystallite domains can afford reprocessable elastomers, but often at the cost of performance. Herein, we report the synthesis of ultra-tough, reprocessable elastomers based on linear alternating polymers. The incorporation of a rigid isohexide adjacent to urethane moieties affords elastomers with exceptional strain hardening, strain rate dependent behavior, and high optical clarity. Distinct differences were observed between isomannide and isosorbide-based elastomers where the latter displays superior tensile strength and strain recovery. These phenomena are attributed to the regiochemical irregularities in the polymers arising from their distinct stereochemistry and respective inter-chain hydrogen bonding.

Sugar-Based Polymers with Stereochemistry-Dependent Degradability and Mechanical Properties

Stereochemistry in polymers can be used as an effective tool to control the mechanical and physical properties of the resulting materials. Typically, though, in synthetic polymers, differences among polymer stereoisomers leads to incremental property variation, i.e., no changes to the baseline plastic or elastic behavior. Here we show that stereochemical differences in sugar-based monomers yield a family of nonsegmented, alternating polyurethanes that can be either strong amorphous thermoplastic elastomers with properties that exceed most cross-linked rubbers or robust, semicrystalline thermoplastics with properties comparable to commercial plastics. The stereochemical differences in the monomers direct distinct intra- and interchain supramolecular hydrogen-bonding interactions in the bulk materials to define their behavior. The chemical similarity among these isohexide-based polymers enables both statistical copolymerization and blending, which each afford independent control over degradability and mechanical properties. The modular molecular design of the polymers provides an opportunity to create a family of materials with divergent properties that possess inherently built degradability and outstanding mechanical performance.

Shape Memory Behavior of Biocompatible Polyurethane Stereoelastomers Synthesized via Thiol-Yne Michael Addition

Biodegradable shape memory elastomers have the potential for use in soft tissue engineering, drug delivery, and device fabrication applications. Unfortunately, few materials are able to meet the targeted degradation and mechanical properties needed for long-term implantable devices. In order to overcome these limitations, we have designed and synthesized a series of unsaturated polyurethanes that are elastic, degradable, and nontoxic to cells in vitro. The polymerization included a nucleophilic thiol-yne Michael addition between a urethane-based dipropiolate and a dithiol to yield an α,β-unsaturated carbonyl moiety along the polymer backbone. The alkene stereochemistry of the materials was tuned between 32 and 82% cis content using a combination of an organic base and solvent polarity, which collectively direct the nucleophilic addition. The bulk properties such as tensile strength, modulus, and glass transition temperature can also be tuned broadly, and the hydrogen bonding imparted by the urethane moiety allows for these materials to elicit cyclic shape memory behavior. We also demonstrated that the in vitro degradation properties are highly dependent on the alkene stereochemistry.

Arene-Perfluoroarene Interactions Confer Enhanced Mechanical Properties to Synthetic Nanotubes

Supramolecular nanotubes prepared through macrocycle assembly offer unique properties that stem from their long-range order, structural predictability, and tunable microenvironments. However, assemblies that rely on weak non-covalent interactions often have limited aspect ratios and poor mechanical integrity, which diminish their utility. Here pentagonal imine-linked macrocycles are prepared by condensing a pyridine-containing diamine and either terephthalaldehyde or 2,3,5,6-tetrafluoroterephthalaldehyde. Atomic force microscopy and synchrotron in solvo X-ray diffraction demonstrate that protonation of the pyridine groups drives assembly into high-aspect ratio nanotube assemblies. A 1 : 1 mixture of each macrocycle yielded nanotubes with enhanced crystallinity upon protonation. UV-Vis and fluorescence spectroscopy indicate that nanotubes containing both arene and perfluoroarene subunits display spectroscopic signatures of arene–perfluoroarene interactions. Touch-spun polymeric fibers containing assembled nanotubes prepared from the perhydro- or perfluorinated macrocycles exhibited Young's moduli of 1.09 and 0.49 GPa, respectively. Fibers containing nanotube assemblies reinforced by arene–perfluoroarene interactions yielded a 93% increase in the Young's modulus over the perhydro derivative, up to 2.1 GPa. These findings demonstrate that tuning the chemical composition of the monomeric macrocycles can have profound effects on the mechanical strength of the resulting assemblies. More broadly, these results will inspire future studies into tuning orthogonal non-covalent interactions between macrocycles to yield nanotubes with emergent functions and technological potential.

Arene–perfluoroarene interactions resulted in enhanced crystallinity between analogous perhydro- and perfluoro macrocycles in a supramolecular nanotube assembly.

Stereochemistry-Controlled Mechanical Properties and Degradation in 3D-Printable Photosets

Stereochemistry provides an appealing handle by which to control the properties of small molecules and polymers. While it is established that stereochemistry in linear polymers affects their bulk mechanical properties, the application of this concept to photocurable networks could allow for resins that can accommodate the increasing demand for mechanically diverse materials without the need to significantly change their formulation. Herein, we exploit cis and trans stereochemistry in pre-resin oligomers to create photoset materials with mechanical properties and degradation rates that are controlled by their stereochemistry and molecular weight. Both the synthesis of stereopure (cis or trans) acrylate-terminated pre-polymers and the subsequent UV-triggered cross-linking occurred with a retention of stereochemistry, close to 100%. The stereochemistry of a 4 kDa oligomer within the resin enabled the tuning of the formulation to either a fast eroding, soft cis elastomer or a stiff trans plastic that is more resistant to degradation. These results demonstrate that stereochemistry is a powerful tool to modify the stiffness, toughness, and degradability of high-resolution, three-dimensional printed scaffolds from the same formulated ratio of components.

Fabrication of Biomedical Scaffolds Using Biodegradable Polymers

Degradable polymers are used widely in tissue engineering and regenerative medicine. Maturing capabilities in additive manufacturing coupled with advances in orthogonal chemical functionalization methodologies have enabled a rapid evolution of defect-specific form factors and strategies for designing and creating bioactive scaffolds. However, these defect-specific scaffolds, especially when utilizing degradable polymers as the base material, present processing challenges that are distinct and unique from other classes of materials. The goal of this review is to provide a guide for the fabrication of biodegradable polymer-based scaffolds that includes the complete pathway starting from selecting materials, choosing the correct fabrication method, and considering the requirements for tissue specific applications of the scaffold.

Concomitant control of mechanical properties and degradation in resorbable elastomer-like materials using stereochemistry and stoichiometry for soft tissue engineering

Complex biological tissues are highly viscoelastic and dynamic. Efforts to repair or replace cartilage, tendon, muscle, and vasculature using materials that facilitate repair and regeneration have been ongoing for decades. However, materials that possess the mechanical, chemical, and resorption characteristics necessary to recapitulate these tissues have been difficult to mimic using synthetic resorbable biomaterials. Herein, we report a series of resorbable elastomer-like materials that are compositionally identical and possess varying ratios of cis:trans double bonds in the backbone. These features afford concomitant control over the mechanical and surface eroding degradation properties of these materials. We show the materials can be functionalized post-polymerization with bioactive species and enhance cell adhesion. Furthermore, an in vivo rat model demonstrates that degradation and resorption are dependent on succinate stoichiometry in the elastomers and the results show limited inflammation highlighting their potential for use in soft tissue regeneration and drug delivery.

The creation of biomaterials which are resorbable and have biomimetic mechanical properties is key to successful tissue engineering. Here the authors report on the creation of a new biopolymer where the mechanical properties can be tuned by changing the ratios of cis:trans double bonds in the backbone.

Polymeric Materials for Eye Surface and Intraocular Applications

Ocular applications of polymeric materials have been widely investigated for medical diagnostics, treatment, and vision improvement. The human eye is a vital organ that connects us to the outside world so when the eye is injured, infected, or impaired, it needs immediate medical treatment to maintain clear vision and quality of life. Moreover, several essential parts of the eye lose their functions upon aging, causing diminished vision. Modern polymer science and polymeric materials offer various alternatives, such as corneal and scleral implants, artificial ocular lenses, and vitreous substitutes, to replace the damaged parts of the eye. In addition to the use of polymers for medical treatment, polymeric contact lenses can provide not only vision correction, but they can also be used as wearable electronics. In this Review, we highlight the evolution of polymeric materials for specific ocular applications such as intraocular lenses and current state-of-the-art polymeric systems with unique properties for contact lens, corneal, scleral, and vitreous body applications. We organize this Review paper by following the path of light as it travels through the eye. Starting from the outside of the eye (contact lenses), we move onto the eye's surface (cornea and sclera) and conclude with intraocular applications (intraocular lens and vitreous body) of mostly synthetic polymers and several biopolymers. Initially, we briefly describe the anatomy and physiology of the eye as a reminder of the eye parts and their functions. The rest of the Review provides an overview of recent advancements in next-generation contact lenses and contact lens sensors, corneal and scleral implants, solid and injectable intraocular lenses, and artificial vitreous body. Current limitations for future improvements are also briefly discussed.

Controlled release of etoricoxib from poly(ester urea) films for post-operative pain management

Medical prescriptions for the alleviation of post-surgical pain are the most abundant source of opioids in circulation. As a systemic drug delivery source, opioids leave patients at high risk for side effects after being dosed. Given the significant rate of unauthorized use, distribution, addiction, and opioid related deaths, an alternative method of post-surgical analgesia is needed. Herein, we report the use of bio-resorbable poly(ester urea) (PEU) films that controllably deliver a non-opioid COX-2 inhibitor, etoricoxib, in vivo and in vitro as a model system for post-surgical pain control. PEU composition, drug-load, and film thickness were varied to selectively control etoricoxib elution. Elution data were fit to a Higuchi model, and the diffusion constant of etoricoxib was calculated in each of the films. Pharmacokinetic (pK) data from an in vivo rat model showed the local tissue concentration of etoricoxib at the study endpoint to be up to 23-fold higher in tissue then plasma. In a well-established mouse model of diabetic neuropathic pain in vivo film implantation showed effective relief of pain for more than 4 days post-implantation and efficacious local etoricoxib delivery. Overall, implementation of local drug delivery systems such as this could reduce the need for opioid prescriptions associated with current pain management strategies.

Advancing Toward 3D Printing of Bioresorbable Shape Memory Polymer Stents

Stents have evolved significantly since their introduction to the medical field in the early 1980s, becoming widely used in percutaneous coronary interventions and following nephrological procedures. However, the current commercially available stents do not degrade and remain in the body forever, leading to problems like restenosis in cardiovascular applications or requiring removal procedures in ureteral applications. Efforts to replace metal with resorbable materials have largely been halted after the commercial failure of and safety concerns elicited by Abbott's Absorb stent in 2017. Industry continues to use common polymers such as poly(l-lactide) (PLLA) and polycaprolactone (PCL) for biomedical products, but due to the weak mechanical properties of these bioresorbable materials in comparison to metals, these devices have struggled to accomplish the goals set, increasing risk of thrombosis. 3D printing stents using bioresorbable and shape memory materials could provide a method of patient-personalized production, remove the need for balloon expansion, and limit stent migration, thus bringing a new age of stent technology. The investigation of a range of 3D-printable and bioresorbable shape-memory polymers can provide solutions to the shortcomings of previously explored bioresorbable stents and revitalize the medical device industry efforts into advancing stent technology.

Antibiotic eluting poly(ester urea) films for control of a model cardiac implantable electronic device infection

Cardiac implantable electronic device (CIED) infections acquired during or after surgical procedures are a major complication that are challenging to treat therapeutically, resulting in chronic and sometimes fatal infections. Localized delivery of antibiotics at the surgical site could be used to supplement traditional systemic administration as a preventative measure. Herein, we investigate a cefazolin-eluting l-valine poly(ester urea) (PEU) films as a model system for localized antibiotic delivery for CIEDs. Poly(1-VAL-8) PEU was used to fabricate a series of antibiotic-loaded films with varied loading concentrations (2%, 5%, 10% wt/wt) and thicknesses (40 µm, 80 µm, 140 µm). In vitro release measurements show thickness and loading concentration influence the amount and rate of cefazolin release. Group 10%-140 µm (load-thickness) showed 22.5% release of active pharmaceutical ingredient (API) in the first 24 h and 81.2% of cumulative percent release through day 14 and was found most effective in bacterial clearance in vitro. This group was also effective in clearing a bacterial infection in a model in vivo rat study while eliciting a limited inflammatory response. Our results suggest the feasibility of cefazolin-loaded PEU films as an effective sustained release matrix for localized delivery of antibiotics. SIGNIFICANCE STATEMENT: Implant-associated infections acquired during surgical procedures are a major complication that have proven a challenge to treat clinically, resulting in chronic and sometimes fatal infections. In this manuscript, we investigate an antibiotic-eluting L-valine poly(ester urea) (PEU) films as a model system for localized delivery of cefazolin. Significantly, we demonstrate a wide variation in temporal delivery and dosing within this family of PEUs and show that the delivery can be extended by varying the film thickness. The in vivo results show efficacy in an infected wound model and suggest antibiotic loaded PEU films function as an effective sustained release matrix for localized delivery of antibiotics across a number of clinical indications.

Elastomeric polyamide biomaterials with stereochemically tuneable mechanical properties and shape memory

Biocompatible polymers are widely used in tissue engineering and biomedical device applications. However, few biomaterials are suitable for use as long-term implants and these examples usually possess limited property scope, can be difficult to process, and are non-responsive to external stimuli. Here, we report a class of easily processable polyamides with stereocontrolled mechanical properties and high-fidelity shape memory behaviour. We synthesise these materials using the efficient nucleophilic thiol-yne reaction between a dipropiolamide and dithiol to yield an α,β - unsaturated carbonyl moiety along the polymer backbone. By rationally exploiting reaction conditions, the alkene stereochemistry is modulated between 35-82% cis content and the stereochemistry dictates the bulk material properties such as tensile strength, modulus, and glass transition. Further access to materials possessing a broader range of thermal and mechanical properties is accomplished by polymerising a variety of commercially available dithiols with the dipropiolamide monomer.

4D Printing of Resorbable Complex Shape-Memory Poly(propylene fumarate) Star Scaffolds

3D/4D printing is enabling transformative advances in device manufacturing and medicine but remains limited by the lack of printable resorbable materials with advanced properties and functions. Herein, we report the rapid and precise 4D printing of shape-memory scaffolds based on poly(propylene fumarate) (PPF) star polymers. Scaffolds with tunable and distinguishable properties can be produced with identical polymer formulation and stoichiometry. The resulting scaffold glass transition temperatures and Young's moduli increase with the postcuring time. Significantly, both the extent and rate of shape recovery following compression can be tuned by varying the strut design, the postcuring step duration, and/or the temperature applied for the recovery step. Finally, accelerated degradation studies confirmed the resorbability of the PPF star polymer gyroid scaffolds.

Alternating ring-opening copolymerization of epoxides with saturated and unsaturated cyclic anhydrides: reduced viscosity poly(propylene fumarate) oligomers for use in cDLP 3D printing

A ring-opening copolymerization of propylene oxide with saturated and unsaturated anhydrides using Mg(BHT)₂(THF)₂ catalyst followed by an isomerization yields poly(propylene fumarate) (PPF) oligomers with improved properties for 3D printing.

Postfabrication Tethering of Molecular Gradients on Aligned Nanofibers of Functional Poly(ε-caprolactone)s

Substrates with combinations of topographical and biochemical cues are highly useful for a number of fundamental biological investigations. Tethered molecular concentration gradients in particular are highly desired for a number of biomedical applications including cell migration. Herein, we report a versatile method for the fabrication of aligned nanofiber substrates with a tunable concentration gradient along the fiber direction. 4-Dibenzocyclooctynol (DIBO) was used as an initiator for the ring-opening copolymerization of ε-caprolactone (εCL) and allyl-functionalized ε-caprolactone (AεPCL), which yielded a well-defined polymer with orthogonal functional handles. These materials were fabricated into aligned nanofiber substrates via touch-spinning. Fibers were modified post-spinning with a concentration gradient of fluorescently labeled dye via a light activated thiol-ene reaction through a photomask. As a demonstration, the cell adhesive peptide RGD was chemically tethered to the fiber surface at a second functionalization site via strain-promoted azide-alkyne cycloaddition (SPAAC). This novel approach affords fabrication of dual functional nanofiber substrates.

Modulating Bioglass Concentration in 3D Printed Poly(propylene fumarate) Scaffolds for Post-Printing Functionalization with Bioactive Functional Groups

Poly(propylene fumarate) (PPF) has shown potential for the treatment of bone defects as it can be 3D printed into scaffolds to suit patient-specific needs with strength comparable to that of bone. However, the lack of specific cell attachment and osteogenic signaling moieties have limited their utility as it is necessary to provide these signals to aid in bone tissue formation. To address this issue and provide a platform for functionalization, Bioglass (∼1-2 μm) microparticles have been incorporated into PPF to create a 3D printable resin with concentrations ranging from 0 to 10 wt %. The zero-shear viscosity of PPF-Bioglass resins increased proportionally from 0 to 2.5 wt % Bioglass, with values of 0.22 and 0.34 Pa·s, respectively. At higher Bioglass concentrations, 5 and 10 wt %, the resin viscosity increased to 0.44 and 1.31 Pa·s, exhibiting a 2- and 6-fold increase from the 0 wt % Bioglass resin. Despite this increase in viscosity, all resins remained printable with no print failures. In addition, the surface available Bioglass can tether catechol containing molecules for postprinting functionalization. Analysis of PPF-Bioglass functionalization using a catechol dye analyte shows functionalization increases with Bioglass concentration, up to 157 nmol/cm², and demonstrates it is possible to modulate functionalization. This presents a versatile and highly translationally relevant strategy to functionalize 3D printed scaffolds post printing with a diverse array of functional species.

Optimization of photocrosslinkable resin components and 3D printing process parameters

The role of 3D printing in the biomedical field is growing. In this context, photocrosslink-based 3D printing procedures for resorbable polymers stand out. Despite much work, more studies are needed on photocuring stereochemistry, new resin additives, new polymers and resin components. As part of these studies it is vital to present the logic used to optimize the amount of each resin constituent and how that effects printing process parameters. The present manuscript aims to analyze the effects of poly(propylene fumarate) (PPF) resin components and their effect on 3D printing process parameters. Diethyl fumarate (DEF), bisacylphosphine oxide (BAPO), Irgacure 784, 2-hydroxy-4-methoxybenzophenone (HMB) and, for the first time, in biomedical 3D printing, ethyl acetate (EA), were the resin components under investigation in this study. Regarding printing process parameters, Exposure Time, Voxel Depth, and Overcuring Depth were the parameters studied. Taguchi Design of Experiments was used to search for the effect of varying these resin constituent concentrations and 3D printing parameters on the curing behavior of 3D printable PPF resins. Our results indicate that resins with higher polymer cross-link density, especially those with a higher content of PPF, are able to be printed at higher voxel depth and with greater success (i.e., high yield). High voxel depth, as long as it does not sacrifice required resolution, is desirable as it speeds printing. Nevertheless, the overall process is governed by the correct setup of the voxel depth in relation to overcuring depth. In regards to resin biocompatibility, it was observed that EA is more effective than DEF, the material we had previously relied on. Our preliminary in vitro cytotoxicity tests indicate that the use of EA does not reduce scaffold biocompatibility as measured by standard cytotoxicity testing (i.e., ISO 10993-5). We demonstrate a workpath for resin constituent concentration optimization through thin film tests and photocrosslinkable process optimization. STATEMENT OF SIGNIFICANCE: We report here the results of a study of photo-crosslinkable polymer resin component optimization for the 3D printing of resorbable poly(propylene fumarate) (PPF) scaffolds. Resin additives are initially optimized for PPF thin film printing. Once those parameters have been optimized the 3D printing process parameters for PPF objects with complex, porous shapes can be optimized. The design of experiments to optimize both polymer thin films and complex porous resorbable polymer scaffolds is important as a guess and check, or in some cases a systematic method, are very likely to be too time consuming to accomplish. Previously unstudied resin components and process parameters are reported.

Enhancing Schwann cell migration using concentration gradients of laminin-derived peptides

Neuroregeneration following peripheral nerve injury is largely mediated by Schwann cells (SC), the principal glial cell that supports neurons in the peripheral nervous system. Axonal regeneration in vivo is limited by the extent of SC migration into the gap between the proximal and distal nerve, however, little is known regarding the principal driving forces for SC migration. Engineered microenvironments, such as molecular and protein gradients, play a role in the migration of many cell types, including cancer cells and fibroblasts. However, haptotactic strategies have not been applied widely to SC. Herein, a series of tethered laminin-derived peptides were analyzed for their influence on SC adhesion, proliferation, and alignment. Concentration gradient substrates were fabricated using a controlled vapor deposition method, followed by covalent peptide attachment via a thiol-ene reaction, and characterized by X-ray photoelectron spectroscopy (XPS) and MALDI-MS imaging. While tethered RGD peptides supported SC adhesion and proliferation, concentration gradients of RGD had little influence on biased SC directional migration. In contrast, YIGSR promoted less SC attachment than RGD, yet YIGSR peptide gradients directed migration with a strong bias to the concentration profile. With YIGSR peptide, overall speed increased with the steepness of the peptide concentration profile. YIGSR gradients had no haptotactic effect on rat dermal fibroblast migration, in contrast to fibroblast migration on RGD gradients. The response of SC to these tethered peptide gradients will guide the development of translationally relevant constructs designed to facilitate endogenous SC infiltration into defects for nerve regeneration.

Molecular Mass-Dependent Resorption and Bone Regeneration of 3D Printed PPF Scaffolds in a Critical-Sized Rat Cranial Defect Model

The emergence of additive manufacturing has afforded the ability to fabricate intricate, high resolution, and patient-specific polymeric implants. However, the availability of biocompatible resins with tunable resorption profiles remains a significant hurdle to clinical translation. In this study, 3D scaffolds are fabricated via stereolithographic cDLP printing of poly(propylene fumarate) (PPF) and assessed for bone regeneration in a rat critical-sized cranial defect model. Scaffolds are printed with two different molecular mass resin formulations (1000 and 1900 Da) with narrow molecular mass distributions and implanted to determine if these polymer characteristics influence scaffold resorption and bone regeneration in vivo. X-ray microcomputed tomography (µ-CT) data reveal that at 4 weeks the lower molecular mass polymer degrades faster than the higher molecular mass PPF and thus more new bone is able to infiltrate the defect. However, at 12 weeks, the regenerated bone volume of the 1900 Da formulation is nearly equivalent to the lower molecular mass 1000 Da formulation. Significantly, lamellar bone bridges the defect at 12 weeks with both PPF formulations and there is no indication of an acute inflammatory response.

Zwitterionic amino acid-based Poly(ester urea)s suppress adhesion formation in a rat intra-abdominal cecal abrasion model

Hernia repair outcomes have improved with more robust material options for surgeons and optimized surgical techniques. However, ventral hernia repairs remain challenging with an inherent risk of post-surgical adhesions in the peritoneal space which can occur regardless of interventional material or its surgical placement. Herein, amino acid-based poly(ester urea)s (PEUs) with varied amount of an allyl ether side chains were modified post polymerization modification with the zwitterionic sulfnate group (3-((3-((3-mercaptopropanoyl)oxy)propyl) dimethylammonio)propane-1-sulfonate) to promote anti-adhesive properties. These alloc-PEUs were processed using roll-to-roll fabrication methods to afford films that were amenable to surface functionalization via a zwitterion-thiol. Functional group availability on the surface was confirmed via fluorescence microscopy, x-ray photoelectron spectroscopy (XPS), and quartz crystal microbalance (QCM) measurements. Zwitterionic treated PEUs exhibited reduced fibrinogen adsorption in vitro when compared to unfunctionalized control polymer. A rat intrabdominal cecal abrasion adhesion model was used to assess the extent and tenacity of adhesion formation in the presence of the PEUs. The 10% alloc-PEU zwitterion functionalized material was found to reduce the extent and tenacity of adhesions when compared to adhesion controls and the unfunctionalized PEU controls.