15 research outputs found
Development of a 3D polymer reinforced calcium phosphate cement scaffold for cranial bone tissue engineering
The repair of critical-sized cranial bone defects represents an important clinical challenge. The limitations of autografts and alloplastic materials make a bone tissue engineering strategy desirable, but success depends on the development of an appropriate scaffold. Key scaffold properties include biocompatibility, osteoconductivity, sufficient strength to maintain its structure, and resorbability. Furthermore, amenability to rapid prototyping fabrication methods is desirable, as these approaches offer precise control over scaffold architecture and have the potential for customization. While calcium phosphate cements meet many of these criteria due to their composition and their injectability, which can be leveraged for scaffold fabrication via indirect casting, their mechanical properties are a major limitation. Thus, the overall goal of this work was to develop a 3D polymer reinforced calcium phosphate cement scaffold for use in cranial bone tissue engineering. Dicalcium phosphate dihydrate (DCPD) setting cements are of particular interest because of their excellent resorbability. We demonstrated for the first time that DCPD cement can be prepared from monocalcium phosphate monohydrate (MCPM)/hydroxyapatite (HA) mixtures. However, subsequent characterization revealed that MCPM/HA cements rapidly convert to HA during degradation, which is undesirable and led us to choose a more conventional formulation for scaffold fabrication. In addition, we developed a novel method for calcium phosphate cement reinforcement that is based on infiltrating a pre-set cement structure with a polymer, and then crosslinking the polymer in situ. Unlike prior methods of cement reinforcement, this method can be applied to the reinforcement of 3D scaffolds fabricated by indirect casting. Using our novel method, composites of poly(propylene fumarate) (PPF) reinforced DCPD were prepared and demonstrated as excellent candidate scaffold materials, as they had increased strength and ductility and were biocompatible in vitro. Furthermore, 3D PPF reinforced DCPD scaffolds had strengths comparable to trabecular bone. Based on these results, 3D PPF reinforced DCPD scaffolds were evaluated in vivo using a rabbit calvarial defect model. Although bone formation was not enhanced by the addition of mesenchymal stem cells, significant bone ingrowth from the surrounding tissue was observed. The results of this work provide a foundation for future research on 3D polymer reinforced calcium phosphate cement scaffolds
Shooting for the moon: Using tissue-mimetic hydrogels to gain new insight on cancer biology and screen therapeutics
Tissue engineering holds great promise for advancing cancer research and achieving the goals of the Cancer Moonshot by providing better models for basic research and testing novel therapeutics. This paper focuses on the use of hydrogel biomaterials due to their unique ability to entrap cells in three-dimensional (3D) matrix that mimics tissues and can be programmed with physical and chemical cues to recreate key aspects of tumor microenvironments. The chemistry of some commonly used hydrogel platforms is discussed, and important examples of their use in tissue engineering 3D cancer models are highlighted. Challenges and opportunities for future research are also discussed.</p
Coumarin-Based Photodegradable Hydrogel: Design, Synthesis, Gelation, and Degradation Kinetics
The design, synthesis, and characterization
of a new class of coumarin-based
photodegradable hydrogels are reported. Hydrogel formation was achieved
rapidly and efficiently under aqueous conditions using copper-catalyzed
click chemistry, which afforded excellent control over the rate of
network formation. Rapid photodegradation, to the point of reverse
gelation, was observed using both 365 and 405 nm light, and micrometer-scale
features were eroded using two-photon irradiation at wavelengths as
long as 860 nm
Synthetically Tractable Click Hydrogels for Three-Dimensional Cell Culture Formed Using Tetrazine–Norbornene Chemistry
The implementation of bio-orthogonal
click chemistries is a topic
of growing importance in the field of biomaterials, as it is enabling
the development of increasingly complex hydrogel materials capable
of providing dynamic, cell-instructive microenvironments. Here, we
introduce the tetrazine–norbornene inverse electron demand
Diels–Alder reaction as a new cross-linking chemistry for the
formation of cell laden hydrogels. The fast reaction rate and irreversible
nature of this click reaction allowed for hydrogel formation within
minutes when a multifunctional PEG-tetrazine macromer was reacted
with a dinorbornene peptide. In addition, the cytocompatibility of
the polymerization led to high postencapsulation viability of human
mesenchymal stem cells, and the specificity of the tetrazine–norbornene
reaction was exploited for sequential modification of the network
via thiol–ene photochemistry. These advantages, combined with
the synthetic accessibility of the tetrazine molecule compared to
other bio-orthogonal click reagents, make this cross-linking chemistry
an interesting and powerful new tool for the development of cell-instructive
hydrogels for tissue engineering applications
Photocontrolled Nanoparticles for On-Demand Release of Proteins
We describe here light-regulated swelling and degradation
features
of polymeric nanoparticles that are produced using an inverse microemulsion
polymerization method. We demonstrate the phototriggered release characteristics
of the nanoparticles by sequestering protein molecules and releasing
them using light as a trigger. Furthermore, the intracellular translocation
of the nanoparticles, along with its fluorescent protein payload,
was achieved using a cell-penetrating peptide-based surface modification.
We expect that the noncovalent encapsulation of proteins using nanoparticles
and their photo triggered release using an external light would provide
opportunities for achieving intracellular release of molecular therapeutics
for on-demand requirements
Sequential Thiol–Ene and Tetrazine Click Reactions for the Polymerization and Functionalization of Hydrogel Microparticles
Click
chemistry is a versatile tool for the synthesis and functionalization
of polymeric biomaterials. Here, we describe a versatile new strategy
for producing bioactive, protein-functionalized polyÂ(ethylene glycol)
(PEG) hydrogel microparticles that is based on sequential thiol–ene
and tetrazine click reactions. Briefly, tetra-functional PEG-norbornene
macromer and dithiothreitol (SH) cross-linker were combined at a 0.75:1
[SH]:[norbornene] ratio, emulsified in a continuous Dextran phase,
and then photopolymerized to form PEG hydrogel microparticles that
varied from 8 to 30 ÎĽm in diameter, depending on the PEG concentration
used. Subsequently, tetrazine-functionalized protein was conjugated
to unreacted norbornene groups in the PEG microparticles. Tetrazine-mediated
protein tethering to the microparticles was first demonstrated using
fluorescein-labeled ovalbumin as a model protein. Subsequently, bioactive
protein tethering was demonstrated using alkaline phosphatase (ALP)
and glucose oxidase (GOx). Enzyme activity assays demonstrated that
both ALP and GOx maintained their bioactivity and imparted tunable
bioactivity to the microparticles that depended on the amount of enzyme
added. ALP-functionalized microparticles were also observed to initiate
calcium phosphate mineralization <i>in vitro</i> when incubated
with calcium glycerophosphate. Collectively, these results show that
protein-functionalized hydrogel microparticles with tunable bioactive
properties can be easily synthesized using sequential click chemistry
reactions. This approach has potential for future applications in
tissue engineering, drug delivery, and biosensing