Strategies to refine the degradation behavior of polyester biomaterials, particularly to overcome the limitations of slow hydrolytic degradation, would broaden their utility. Herein, we examine the ...complexities of polyester degradation behavior, its assessment, and strategies for refinement. The factors governing polyester degradation are strikingly complex. In addition to the half-life of the hydrolytically labile bond, a series of interdependent material properties must be considered. Thus, methods used to characterize such material properties, both before and during degradation, must be carefully selected. Assessment of degradation behavior is further complicated by the variability of reported test protocols and the need for accelerated rather than real-time in vitro testing conditions. Ultimately, through better control of degradation behavior and correlation of in vitro, simulated degradation to that observed in vivo, the development of superior devices prepared with polyester biomaterials may be achieved.
Hydrogels are frequently used biomaterials due to their similarity in hydration and structure to biological tissues. However, their utility is limited by poor mechanical properties, namely, a lack of ...strength and stiffness that mimic that of tissues, particularly load-bearing tissues. Thus, numerous recent strategies have sought to enhance and tune these properties in hydrogels, including interpenetrating networks (IPNs), macromolecular cross-linking, composites, thermal conditioning, polyampholytes, and dual cross-linking. Individually, these approaches have achieved hydrogels with either high strength (σf > 10 MPa), high stiffness (E > 1 MPa), or, less commonly, both high strength and stiffness (σf > 10 MPa and E > 1 MPa). However, only certain unique combinations of these approaches have been able to synergistically achieve retention of a high, tissuelike water content as well as high strength and stiffness. Applying such methods to stimuli-responsive hydrogels has also produced robust, smart biomaterials. Overall, methods to achieve hydrogels that simultaneously mimic the hydration, strength, and stiffness of soft and load-bearing tissues have the potential to be used in a much broader range of biomedical applications.
Toward improving implantable medical devices as well as diagnostic performance, the development of polymeric biomaterials having resistance to proteins remains a priority. Herein, we highlight key ...strategies reported in the recent literature that have relied upon improvement of surface hydrophilicity via direct surface modification methods or with bulk modification using surface modifying additives (SMAs). These approaches have utilized a variety of techniques to incorporate the surface hydrophilization agent, including physisorption, hydrogel network formation, surface grafting, layer-by-layer (LbL) assembly and blending base polymers with SMAs. While poly(ethylene glycol) (PEG) remains the gold standard, new alternatives have emerged such as polyglycidols, poly(2-oxazoline)s (POx), polyzwitterions, and amphiphilic block copolymers. While these new strategies provide encouraging results, the need for improved correlation between in vitro and in vivo protein resistance is critical. This may be achieved by employing complex protein solutions as well as strides to enhance the sensitivity of protein adsorption measurements.
The development of a hydrogel-based synthetic cartilage has the potential to overcome many limitations of current chondral defect treatments. Many attempts have been made to replicate the unique ...characteristics of cartilage in hydrogels, but none have simultaneously achieved high modulus, strength, and toughness while maintaining the necessary hydration required for lubricity. Herein, double network (DN) hydrogels, composed of a poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) first network and a poly(N-isopropylacrylamide-co-acrylamide) P(NIPAAm-co-AAm) second network, are evaluated as a potential off-the-shelf material for cartilage replacement. While predominantly used for its thermosensitivity, PNIPAAm is employed to achieve superior mechanical properties with its thermal transition temperature tuned above the physiological range. These PNIPAAm-based DNs demonstrate a 50-fold increase in compressive strength (∼25 MPa, similar to cartilage) compared to traditional single network hydrogels while also achieving cartilage-like modulus (∼1 MPa) and hydration (∼80%). In direct comparison to healthy cartilage (porcine), these hydrogels were confirmed to not only parallel the strength, modulus, and hydration of native articular cartilage but also exhibit a 50% lower coefficient of friction (COF). The exceptional cartilage-like properties of the PAMPS/P(NIPAAm-co-AAm) DN hydrogels makes them candidates for synthetic cartilage grafts for chondral defect repair, even in load-bearing regions of the body.
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.
Silicone coatings with enhanced antifouling behavior towards bacteria, diatoms, and a diatom dominated slime were prepared by incorporating PEO-silane amphiphiles with varied siloxane tether lengths ...(a-c): α-(EtO)
3
Si(CH
2
)
2
-oligodimethylsiloxane
n
-block-poly(ethylene oxide)
8
-OCH
3
n = 0 (a), 4 (b), and 13 (c). Three modified silicone coatings (A-C) were prepared by the acid-catalyzed sol-gel cross-linking of a-c, respectively, each with a stoichiometric 2:3 M ratio of α, ω-bis(Si-OH)polydimethylsiloxane (M
n
= 3,000 g mol
−1
). The coatings were exposed to the marine bacterium Bacillus sp.416 and the diatom (microalga) Cylindrotheca closterium, as well as a mixed community of Bacillus sp. and C. closterium. In addition, in situ microfouling was assessed by maintaining the coatings in the Atlantic Ocean. Under all test conditions, biofouling was reduced to the highest extent on coating C which was prepared with the PEO-silane amphiphile having the longest siloxane tether length (c).
Silicones have a long history of use in biomedical devices, with unique properties stemming from the siloxane (Si–O–Si) backbone that feature a high degree of flexibility and chemical stability. ...However, surface, rheological, mechanical, and electrical properties of silicones can limit their utility. Successful modification of silicones to address these limitations could lead to superior and new biomedical devices. Toward improving such properties, recent additive strategies have been leveraged to modify biomedical silicones and are highlighted herein.
While tissue engineering is a promising alternative for treating critical-sized cranio-maxillofacial bone defects, improvements in scaffold design are needed. In particular, scaffolds that can ...precisely match the irregular boundaries of bone defects as well as exhibit an interconnected pore morphology and bioactivity would enhance tissue regeneration. In this study, a shape memory polymer (SMP) scaffold was developed exhibiting an open porous structure and the capacity to conformally "self-fit" into irregular defects. The SMP scaffold was prepared via photocrosslinking of poly(ε-caprolactone) (PCL) diacrylate using a SCPL method, which included a fused salt template. A bioactive polydopamine coating was applied to coat the pore walls. Following exposure to warm saline at T>T(trans) (T(trans)=T(m) of PCL), the scaffold became malleable and could be pressed into an irregular model defect. Cooling caused the scaffold to lock in its temporary shape within the defect. The polydopamine coating did not alter the physical properties of the scaffold. However, polydopamine-coated scaffolds exhibited superior bioactivity (i.e. formation of hydroxyapatite in vitro), osteoblast adhesion, proliferation, osteogenic gene expression and extracellular matrix deposition.
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.
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