BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Lecture 6: Programmed/Pulsed Drug Delivery and Drug Delivery in Tissue Engineering Last time principles of controlled release from solid polymers Today Pulsatile/regulated/ multifactor controlled release 3 case studies of controlled release Reading Polymeric system for dual growth factor delivery, T.P. Richardson et al., Nat. Biotech 9,1029-1034(2001) Microchips as controlled drug-delivery devices, J.T. Santini et aL., Andegwandte Chemie lnt.Ed.39,23962047(2000) Requlated controlled release Applications of regulated and pulsatile release Many applications would be best-served by non-monotonic and multi-cargo release profiles oral pattern Definition: release of cargo in bursts followed by periods of little/no release in a defined ten o Motivation Single injection delivery of booster for vaccination Mimic natural secretion patterns of hormones Provide optimal therapy for tolerance-inducing drugs Constant drug levels cause receptor down-regulation accine boosting hormone release patterns in vivo mples of acted from a review article by Brabant et al. (Reference 7) references cited in the review artie Hormone w Pulses/Dav Growth hormo 4-9.7-2 Thyroid stimulating hormone 15.90-121 stimulating hormone 18-24,12-20.0 C 08-144.120 100 03,144 Progesterone 020406080100120140 Testosterone 13.8-12 Aldosterone Time in trial. weeks optisol Lecture 5- Programmed Drug Delivery 1 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Lecture 6: Programmed/Pulsed Drug Delivery and Drug Delivery in Tissue Engineering Last time: principles of controlled release from solid polymers Today: Pulsatile/regulated/multifactor controlled release: 3 case studies of controlled release Reading: ‘Polymeric system for dual growth factor delivery,’ T.P. Richardson et al., Nat. Biotech. 19, 1029-1034 (2001) ‘Microchips as controlled drug-delivery devices,’ J.T. Santini et al., Andegwandte Chemie Intl. Ed. 39, 2396-2047 (2000) Regulated controlled release Applications of regulated and pulsatile release • Definition: release of cargo in bursts followed by periods of little/no release in a defined temporal pattern1 • Many applications would be best-served by non-monotonic and multi-cargo release profiles o Motivation: Single injection delivery of ‘booster’ for vaccination Mimic natural secretion patterns of hormones Provide optimal therapy for tolerance-inducing drugs • Constant drug levels cause receptor down-regulation Vaccine boosting hormone release patterns in vivo Lecture 5 – Programmed Drug Delivery 1 of 12
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Example: HIV-1 DNA vaccine delivered with boosters to elevate Ab titers2 o Mechanical and electrical devices that can provide digitized release typically require larger devices and surgical implantation(e.g Pharm. Res. 1, 237(1984); also have high cost Show an example o Degradable polymers allow submicron, injectable devices · Two types Release profile is encoded in structure and composition of device o Triggered External signal drives release Multilayer surface-eroding delivery devices >drug-loaded PEBP laver NHCHICONHOCOC&Hs )y fN-P o- poly phosphazene (NHCH2COOCH:CHJ PLCA coating p polyanhydride(PSP or PSTP) polylactide block m2.[o是mC ∞xwox,[o CH3 CHa Fast-degrading Polyanhydride block (xy-30: 70 by molar) Hydrophilic PEG block · Polyphosphazene Base-catalyzed degradation, acid-inhibited degradation ·PEG-b- Polyanhydride o Rapid bulk erosion-use hydrophilic block to make hrs-long degradation time for mm-thick caps(very fast o .. becomes porous during erosion, so need a means to prevent next layer from starting to degrade as ater reaches drug-containing layer o creates acidic byproducts as it degrades o First polyphosphazene layer degrades quickly( first burst release) o Polyanhydride layer: degrades quickly, acidifies internal environment Even though water penetrates the polyanhydride. A ne polyanhydride has completely adation of polyphosphazene begins and no drug is released from the polyphosphazene layer until eroded and acidic products are removed from microenvironment Lecture 5- Programmed Drug Delivery 2 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Example: HIV-1 DNA vaccine delivered with boosters to elevate Ab titers2 : o Mechanical and electrical devices that can provide digitized release typically require larger devices and surgical implantation (e.g. Pharm. Res. 1, 237 (1984)); also have high cost Show an example o Degradable polymers allow submicron, injectable devices • Two types o Pre-programmed Release profile is encoded in structure and composition of device o Triggered External signal drives release Multilayer surface-eroding delivery devices Case study: multilayered delivery devices3 Fast-degrading Polyanhydride block Hydrophilic PEG block polyphosphazene slow-degrading polylactide block • Polyphosphazene: o Base-catalyzed degradation, acid-inhibited degradation • PEG-b-Polyanhydride: o Rapid bulk erosion- use hydrophilic block to make hrs-long degradation time for mm-thick caps (very fast) o …becomes porous during erosion, so need a means to prevent next layer from starting to degrade as water reaches drug-containing layer o creates acidic byproducts as it degrades • Function of complete device: o First polyphosphazene layer: degrades quickly (first burst release) o Polyanhydride layer: degrades quickly, acidifies internal environment Even though water penetrates the polyanhydride, no degradation of polyphosphazene begins and no drug is released from the polyphosphazene layer until the polyanhydride has completely eroded and acidic products are removed from microenvironment Lecture 5 – Programmed Drug Delivery 2 of 12
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 er acid ifies Water penetrates into device degrades sHow pht Fig. 2. Theoretical pulsatile release of a drug from a surface- oding polymeric system. The time between initial release and booster release is determined by the erosion of the drug free layer refs for theory: J Contr Rel 20, 201(1992); J Cont Rel 18, 159(1992 Regulated release devices: case example-drug delivery microchips work from M. Cima and R. Langer labs Lecture 5- Programmed Drug Delivery 3 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Polyanhydride layer acidifies Water penetrates into device Model drug release profiles: environment as it degrades: COO- O C OCOO- O C OCOO- O C O- Low pH Polyphosphazene only degrades quickly at neutral/basic pH : • refs for theory: J Contr Rel 20, 201 (1992); J Cont Rel 18, 159 (1992) Regulated release devices: case example- drug delivery microchips • work from M. Cima and R. Langer labs: 4 Lecture 5 – Programmed Drug Delivery 3 of 12
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Principle of a gold electrochemical cell in the presence of aqueous chloride solution O ON BOARD Au cathode Au anode Au+4 CI 4 CI+ Au [AuCl4 [AuCl4]:AucI4 H2o, Na*cl In reality, multiple reactions occur simultaneously at the anode under an applied voltage in the passive and transpassive' regime Au+4C|-->[AuC4}+3e o Au+ mH2O-> Au(H20)m+3e- o 2 AU+ 3H2O-> Au2O3+ 6H+ 6e- o2Cr→>Cl2+2e o Au2O3+ 8CI 6H-> 2(AuCl4] 3H2O · Design of anode o Need a material that is stable in the presence of chloride ions in the absence of a potential many metals corrode with 0 applied potential in vivo many metals spontaneously form an oxide layer by reaction with water/O2 in physiological conditions in presence of potential, reacts to form a biocompatible soluble compound Pourbaix diagram: shows thermodynamically favored species under applied potential at varying pH Evans diagram: shows current produced due to electrochemical dissolution of the anode; the current is a measure of the rate of electrons being produced and thus measures the kinetics of the reaction Lecture 5- Programmed Drug Delivery 4 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 • Principle of a gold electrochemical cell in the presence of aqueous chloride solution: o ON BOARD: H2O, Na+ClAu cathode Au anode 4 Cl- + Au [AuCl4]- 3 e- [AuCl4]- Au + 4 Cl- [AuCl4]- e- 3 ereduction oxidation • In reality, multiple reactions occur simultaneously at the anode under an applied voltage in the ‘passive and transpassive’ regime5 : o Au + 4Cl- -> [AuCl4]- + 3 eo Au + mH2O -> Au(H2O)m 3+ + 3 eo 2 Au + 3H2O -> Au2O3 + 6H+ + 6eo 2Cl- -> Cl2 + 2eo Au2O3 + 8Cl- + 6H+ -> 2[AuCl4] - + 3H2O • Design of anode: o Need a material that is: stable in the presence of chloride ions in the absence of a potential • many metals corrode with 0 applied potential in vivo • many metals spontaneously form an oxide layer by reaction with water/O2 in physiological conditions • in presence of potential, reacts to form a biocompatible soluble compound • Pourbaix diagram: shows thermodynamically favored species under applied potential at varying pH • Evans diagram: shows current produced due to electrochemical dissolution of the anode; the current is a measure of the rate of electrons being produced and thus measures the kinetics of the reaction Lecture 5 – Programmed Drug Delivery 4 of 12
BEH. 462/3.962J Molecular Principles of Biomaterials Spring 2003 o Shows that gold membran de quickly Au(oH) 12 0.8 E/V e→2H2 -0,4 0.82H+2一H2 b)20 E/V Stirred 0.145 M NaCI solution e eshowe o H=585at25° Scan rate 0000 0.010 0015 0.020 j/A cm-2 Figure 6. a)A pourbaix diagram for the gold-chloride-water system containing 0. 145M chloride ion. b) An Evans diagram for the same gold chloride-water system obtained potentiodynamically. This diagram rep illustrating the principle of the electrochemical reservoir opening mech. resents the kinetics of the gold corrosion reaction in chloride-containint anism. The materials used in prototype microchips are described in Section 4.2 Structure of the controlled release microchip o anode is a gold membrane 0.3 um thick o current limitation in design is size of battery needed to operate the device: 1 cm microchip itself could be reduced to- 2 mmx 2mn Lecture 5- Programmed Drug Delivery 5 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 o Shows that gold membranes corrode quickly • Structure of the controlled release microchip: o anode is a gold membrane 0.3 µm thick o current limitation in design is size of battery needed to operate the device: ~ 1 cm2 microchip itself could be reduced to ~ 2 mmx 2mm Lecture 5 – Programmed Drug Delivery 5 of 12
BEH. 462/3.962J Molecular Principles of Biomaterials Spring 2003 Pourbaix diagram thermodynamic stability 12 Au(OH)3 C E/VO 4 45 M NaCI solution resents the kinetics of the gold corrosion reaction in choride containing 24681012m WHY DOES GOLD DISSOLVE AT PH 7? POURBAIX DIAGRAM SHOWS OXIDE IS STABLE FORM Figure 4. Photographs of a prototype ining front side, b)the back side e microchip. a) The electrode servoirs( Scale bar: 10 mm; photographs by Paul Horwitz. · Release properties Figure 7. ng electron micrographs of a gold covering a reservoir a) before and b) after the applicat +1.04 V vs SCE for seconds in phosphate-buffered saline and that ofCa(e)in units of 5na min". I in day Lecture 5- Programmed Drug Delivery 6 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Pourbaix diagram: thermodynamic stability 1.6 1.2 0.8 E/V0.4 0.0 -0.4 -0.8 -1.2 [AuCl4] Au(OH)3 2 4 6 8 10 12 Au pH • WHY DOES GOLD DISSOLVE AT PH 7? POURBAIX DIAGRAM SHOWS OXIDE IS STABLE FORM (Cima work) 6 • Release properties: Lecture 5 – Programmed Drug Delivery 6 of 12
BEH. 462/3.962J Molecular Principles of Biomaterials Spring 2003 Controlled Release in Tissue Engineering Tissue Engineering/Regenerative Medicine 2 major approaches for regenerative medicine vitro tissue genesis→ n o In vivo tissue genesis> in vivo application Schematic comparison of in vitro and in vivo tissue engineering approaches Kin: N VITRO SYNTHESIS N VITRO SYNTHESIS culture soluble IN VIVO SYNTHESIS regulators IN VIVO SYNTHESIS Role of scaffold o Provide functions of native ECm o Create a space for new tissue development o Deliver cells to site o Direct macroscopic size/shape of new tissue roles for soluble factor delivery in TE o chemoattractant gradients used to draw desired cell types into structure growth factors provided to induce cell proliferation to regenerate tissue o cytokines to induce tissue-specific cell functions Cytokine delivery from scaffolds Case Study: Induction of vascularization in TE scaffolds Challenge of providing nutrients and oxygen to large tissue constructs o Constructs -500 um thick or greater cannot be supported by diffusive transport- need vascularization Lecture 5- Programmed Drug Delivery 7 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Controlled Release in Tissue Engineering Tissue Engineering/Regenerative Medicine • 2 major approaches for regenerative medicine o In vitro tissue genesis → in vivo application o In vivo tissue genesis → in vivo application Schematic comparison of in vitro and in vivo tissue engineering approaches7 : Skin: bone: • Role of scaffold: o Provide functions of native ECM o Create a space for new tissue development o Deliver cells to site o Direct macroscopic size/shape of new tissue • roles for soluble factor delivery in TE: o chemoattractant gradients used to draw desired cell types into structure o growth factors provided to induce cell proliferation to regenerate tissue o cytokines to induce tissue-specific cell functions Cytokine delivery from scaffolds Case Study: Induction of vascularization in TE scaffolds • Challenge of providing nutrients and oxygen to large tissue constructs o Constructs ~500 µm thick or greater cannot be supported by diffusive transport- need vascularization Lecture 5 – Programmed Drug Delivery 7 of 12
BEH. 462/3.962J Molecular Principles of Biomaterials Spring 2003 Structure of vasculature blood vessel structure Endothelial cell lining Smooth muscle pO2 Blood flow (supportive ECM Extensive cell death in center of construct · Angiogenesis° enchymal cell tins are clearly implicated, though their precise Mature Angiogonosiz PDGF日 Steps in angiogenesis 1. VEGF(vascular endothelial growth factor) - attracts endothelial cells, induces proliferation -induces tube formation 2. PDGF(platelet-derived growth factor) -attracts smooth muscle cells stabilizes new vessels Lecture 5- Programmed Drug Delivery 8 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Lecture 5 – Programmed Drug Delivery 8 of 12 • Structure of vasculature O2 O2 O2 z pO2 Blood flow blood vessel structure: Intima (supportive ECM layer) Endothelial cell lining Smooth muscle cells Extensive cell death in center of construct • Angiogenesis8 Steps in angiogenesis: 1. -attracts endothelial cells, induces proliferation -induces tube formation 2. -attracts smooth muscle cells, stabilizes new vessels VEGF (vascular endothelial growth factor) PDGF (platelet-derived growth factor)
BEH. 462/3.962J Molecular Principles of Biomaterials Spring 2003 Dual growth factor delivery from degradable scaffolds for de novo blood vessel synthesis Nacl particles · Fabrication process o PDGF encapsulated in PLGA microspheres by double emulsion approach o Microspheres(5-50 um) mixed with PLGA particles(150-250 um), Nacl particles(250-500 um), and lyophilized VEGF particles(5-50 um) in mold and compression molded to form a solid disk Disk equilibrated with COz at 800 psi 48hrs o Pressure rapidly dropped to ambient (14 psi) o Salt leached by soaking in distilled water 48 hrs 2. Rapidly depressurize Soak with water to leach out Nacl Lecture 5- Programmed Drug Delivery 9 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Lecture 5 – Programmed Drug Delivery 9 of 12 • Dual growth factor delivery from degradable scaffolds for de novo blood vessel synthesis9 : Compression mold PLGA particles Lyophilized VEGF PDGF-containing microspheres NaCl particles • Fabrication process:10 o PDGF encapsulated in PLGA microspheres by double emulsion approach o Microspheres (5-50 µm) mixed with PLGA particles (150-250 µm), NaCl particles (250-500 µm), and lyophilized VEGF particles (5-50 µm) in mold and compression molded to form a solid disk o Disk equilibrated with CO2 at 800 psi 48hrs o Pressure rapidly dropped to ambient (14 psi) o Salt leached by soaking in distilled water 48 hrs 1. Fill with high-pressure CO2 2. Rapidly depressurize Soak with water to leach out NaCl
BEH. 462/3.962J Molecular Principles of Biomaterials Spring 2003 D Time(days Time(days Figure 1 Schematic of scaffold fabrication process and growth factor release kinatics (A) Growth factors were inoerporatod into polymor scaffolds by othor mixng wish polymor particles bofore proooeeing into eooffolde (VEGR) P时计PBvE5mm contrast, the PDGF incorp broach is pre polymar, with release regu ated by the iom t polymer microspheres containing pre-ancap ⊙9 PDGF with lyophil zed vEGF before process ng into scaffolds.(B)Sc raph of a typica from PLG oide), measured using Labeled tracers ( D)in vitro release kinetics of PDGF pre-ancapsulsted in PLG crospheres(4 75 25, intrinsic viscosity =0.69 dug 7525, intrinsic viscosity =0.2 d/g), before scaffold bncston, Data represent the mean(n= 5), and error bars represent standard deviation bare not vs are In vivo experiments o Scaffolds implanted subcutaneously in Lewis rats, examined histologically at 2 weeks and 4 weeks o Comparisons Free cytokine injections with scaffolds vs controlled release scaffolds Dual vS single factor controlled release scaffolds Lecture 5- Programmed Drug Delivery 10 of 12
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 • In vivo experiments: o Scaffolds implanted subcutaneously in Lewis rats, examined histologically at 2 weeks and 4 weeks o Comparisons: Free cytokine injections with scaffolds vs. controlled release scaffolds Dual vs. single factor controlled release scaffolds Lecture 5 – Programmed Drug Delivery 10 of 12