Paul W. Kopesky

Bio: Paul W. Kopesky is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Aggrecan & Cartilage. The author has an hindex of 12, co-authored 27 publications receiving 851 citations.

Methods and apparatus for making particles using spray dryer and in-line jet mill

Abstract: Methods and apparatus are provided for making particles comprising: (a) spraying an emulsion, solution, or suspension, which comprises a solvent and a bulk material (e.g., a pharmaceutical agent), through an atomizer and into a primary drying chamber, having a drying gas flowing therethrough, to form droplets comprising the solvent and bulk material dispersed in the drying gas; (b) evaporating, in the primary drying chamber, at least a portion of the solvent into the drying gas to solidify the droplets and form particles dispersed in drying gas; and (c) flowing the particles and at least a portion of the drying gas through a jet mill to deagglomerate or grind the particles. By coupling spray drying with “in-line” jet milling, a single step process is created from two separate unit operations, and an additional collection step is advantageously eliminated. The one-step, in-line process has further advantages in time and cost of processing.

Self-assembling peptide hydrogels modulate in vitro chondrogenesis of bovine bone marrow stromal cells.

Abstract: Our objective was to test the hypothesis that self-assembling peptide hydrogel scaffolds provide cues that enhance the chondrogenic differentiation of bone marrow stromal cells (BMSCs). BMSCs were encapsulated within two unique peptide hydrogel sequences, and chondrogenesis was compared with that in agarose hydrogels. BMSCs in all three hydrogels underwent transforming growth factor-beta1-mediated chondrogenesis as demonstrated by comparable gene expression and biosynthesis of extracellular matrix molecules. Expression of an osteogenic marker was unchanged, and an adipogenic marker was suppressed by transforming growth factor-beta1 in all hydrogels. Cell proliferation occurred only in the peptide hydrogels, not in agarose, resulting in higher glycosaminoglycan content and more spatially uniform proteoglycan and collagen type II deposition. The G1-positive aggrecan produced in peptide hydrogels was predominantly the full-length species, whereas that in agarose was predominantly the aggrecanase product G1-NITEGE. Unique cell morphologies were observed for BMSCs in each peptide hydrogel sequence, with extensive cell-cell contact present for both, whereas BMSCs in agarose remained rounded over 21 days in culture. Differences in cell morphology within the two peptide scaffolds may be related to sequence-specific cell adhesion. Taken together, this study demonstrates that self-assembling peptide hydrogels enhance chondrogenesis compared with agarose as shown by extracellular matrix production, DNA content, and aggrecan molecular structure.

Controlled delivery of transforming growth factor β1 by self-assembling peptide hydrogels induces chondrogenesis of bone marrow stromal cells and modulates Smad2/3 signaling.

Abstract: Self-assembling peptide hydrogels were modified to deliver transforming growth factor β1 (TGF-β1) to encapsulated bone-marrow-derived stromal cells (BMSCs) for cartilage tissue engineering applications using two different approaches: (i) biotin-streptavidin tethering; (ii) adsorption to the peptide scaffold. Initial studies to determine the duration of TGF-β1 medium supplementation necessary to stimulate chondrogenesis showed that 4 days of transient soluble TGF-β1 to newborn bovine BMSCs resulted in 10-fold higher proteoglycan accumulation than TGF-β1-free culture after 3 weeks. Subsequently, BMSC-seeded peptide hydrogels with either tethered TGF-β1 (Teth-TGF) or adsorbed TGF-β1 (Ads-TGF) were cultured in the TGF-β1-free medium, and chondrogenesis was compared to that for BMSCs encapsulated in unmodified peptide hydrogels, both with and without soluble TGF-β1 medium supplementation. Ads-TGF peptide hydrogels stimulated chondrogenesis of BMSCs as demonstrated by cell proliferation and cartilage-like extracellular matrix accumulation, whereas Teth-TGF did not stimulate chondrogenesis. In parallel experiments, TGF-β1 adsorbed to agarose hydrogels stimulated comparable chondrogenesis. Full-length aggrecan was produced by BMSCs in response to Ads-TGF in both peptide and agarose hydrogels, whereas medium-delivered TGF-β1 stimulated catabolic aggrecan cleavage product formation in agarose but not peptide scaffolds. Smad2/3 was transiently phosphorylated in response to Ads-TGF but not Teth-TGF, whereas medium-delivered TGF-β1 produced sustained signaling, suggesting that dose and signal duration are potentially important for minimizing aggrecan cleavage product formation. Robustness of this technology for use in multiple species and ages was demonstrated by effective chondrogenic stimulation of adult equine BMSCs, an important translational model used before the initiation of human clinical studies.

Production of a tissue-like structure by contraction of collagen lattices by human fibroblasts of different proliferative

Abstract: Fibroblasts can condense a hydrated collagen lattice to a tissue-like structure 1/28th the area of the starting gel in 24 hr. The rate of the process can be regulated by varying the protein content of the lattice, the cell number, or the con- centration of an inhibitor such as Colcemid. Fibroblasts of high population doubling level propagated in vitro, which have left the cell cycle, can carry out the contraction at least as efficiently as cycling cells. The potential uses of the system as an immu- nologically tolerated "tissue" for wound hea ing and as a model for studying fibroblast function are discussed.

Design properties of hydrogel tissue-engineering scaffolds

Abstract: This article summarizes the recent progress in the design and synthesis of hydrogels as tissue-engineering scaffolds. Hydrogels are attractive scaffolding materials owing to their highly swollen network structure, ability to encapsulate cells and bioactive molecules, and efficient mass transfer. Various polymers, including natural, synthetic and natural/synthetic hybrid polymers, have been used to make hydrogels via chemical or physical crosslinking. Recently, bioactive synthetic hydrogels have emerged as promising scaffolds because they can provide molecularly tailored biofunctions and adjustable mechanical properties, as well as an extracellular matrix-like microenvironment for cell growth and tissue formation. This article addresses various strategies that have been explored to design synthetic hydrogels with extracellular matrix-mimetic bioactive properties, such as cell adhesion, proteolytic degradation and growth factor-binding.

Particle Engineering for Pulmonary Drug Delivery

Abstract: With the rapidly growing popularity and sophistication of inhalation therapy, there is an increasing demand for tailor-made inhalable drug particles capable of affording the most efficient delivery to the lungs and the most optimal therapeutic outcomes. To cope with this formulation demand, a wide variety of novel particle technologies have emerged over the past decade. The present review is intended to provide a critical account of the current goals and technologies of particle engineering for the development of pulmonary drug delivery systems. These technologies cover traditional micronization and powder blending, controlled solvent crystallization, spray drying, spray freeze drying, particle formation from liquid dispersion systems, supercritical fluid processing and particle coating. The merits and limitations of these technologies are discussed with reference to their applications to specific drug and/or excipient materials. The regulatory requirements applicable to particulate inhalation products are also reviewed briefly.

Functional and Biomimetic Materials for Engineering of the Three-Dimensional Cell Microenvironment

Abstract: The cell microenvironment has emerged as a key determinant of cell behavior and function in development, physiology, and pathophysiology. The extracellular matrix (ECM) within the cell microenvironment serves not only as a structural foundation for cells but also as a source of three-dimensional (3D) biochemical and biophysical cues that trigger and regulate cell behaviors. Increasing evidence suggests that the 3D character of the microenvironment is required for development of many critical cell responses observed in vivo, fueling a surge in the development of functional and biomimetic materials for engineering the 3D cell microenvironment. Progress in the design of such materials has improved control of cell behaviors in 3D and advanced the fields of tissue regeneration, in vitro tissue models, large-scale cell differentiation, immunotherapy, and gene therapy. However, the field is still in its infancy, and discoveries about the nature of cell–microenvironment interactions continue to overturn much earl...