TEST BANK For Lewis's Medical Surgical Nursing in Canada, 4th Edition by Jane...
superporus hydrogels
1.
2. Three-dimensional networks of
hydrophilic polymer chains that do not
dissolve but can swell in water
both solid like and liquid like properties
high biocompatibility
environmental stimuli respondent
(temperature, pH, light, specific molecules)
Ideal for controlled drug delivery
3. - various criteria for the classification of hydrogels
Origin Natural
Synthetic
Water content or Low swelling
degree of swelling Medium swelling
High swelling
Superabsorbent
Porosity Nonporous
Microporous
Macroporous
Superporous
Cross-linking Chemical (covalent
bonding)
Physical (noncovalent
bonding)
Biodegradability Biodegradable
4. Swelling property is influenced by:
•type and composition of monomers
•other environmental factors such as :
temperature, pH, ionic strength
•cross-linking Mechanical
strength and
permeability
Rs = (Ws-Wd) / Wd
Rs = swelling ratio
Ws = weight of swollen hydrogels
Wd = weight of dried hydrogels
Cross-linking and/or copolymerization with hydrophobic comonomers
density↑, mechanical strength↑, swelling property ↓
6. Chemical crosslinking
Polymerization of water soluble monomers in the presence
of bi- or multifunctional cross-linking agent
+ Copolymerizatio
n
MonomerCrosslinker
or
Polymerization Hydrogel
network
Vinyl group-containing water-soluble polymers
7. Physical crosslinking Chemical and Physical
crosslinking
• Cross-linking without
chemical reaction
• ionic interaction, hydrogen
bonding, antigen-antibody
interaction, supramolecular
association
• Ionic hydrogel
9. - Benefits of controlled drug delivery
more effective therapies with reduced side effects
the maintenance of effective drug concentration
levels in the blood
patient’s convenience as medicines hence increased
patient compliance
- Release mechanisms of drug molecules
: diffusion, dissolution, osmosis, ion exchange
10. - Diffusion controlled Drug Delivery
(1) Polymer matrix
Water-insoluble
Polymer matrices
time
(2) Reservoir system
Water-insoluble
Polymer membrane
time
11. Environment-Sensitive Hydrogels
• respond to environmental change
: temperature, pH, specific molecule
• reversible volume phase transition or sol-gel phase
transition
• “intelligent” or “smart” hydrogel
Drug-loaded gel
Change in pH for
gel swelling
Change in temperature for
gel collapse
Drug release through Drug release by the
the swollen network squeezing action
12. Environmental-Sensitive Hydrogels used for Drug Delivery
Environment Typical polymers Main Mechanism Applications
al Factor
Temperature PNIPAAm, PDEAAm, PEO- Competition between On/off drug release,
PPO block copolymers hydrophobic interaction and squeezing device
hydrogen bonding
pH Polyelectrolytes, PAA, PDEAEM Ionization of polymer chains pH-dependent oral drug
upon pH change delivery
Glucose pH-sensitive hydrogels; pH change caused by glucose Self-regulated insulin
Concanavalin A-grafted oxidase; reversible interaction delivery
polymers; polymers containing between glucose-containing
phenylborate groups polymers and Concanavalin A;
reversible solgel transformation
Electric Polyelectrolytes (pH-sensitive) Reversible swelling or Actuator, artificial muscle,
signal deswelling in the presence of on off drug release
electric field
Light Copolymer of PNIPAAm and Temperature change via the Optical switches,
light sensitive chromophore, incorporated photosensitive ophthalmic drug delivery
such as triphenylmethane and molecules; dissociation into ion
leuco derivatives pairs by UV irradiation
Antigen Semi-IPN with grafted Competition between polymer- Modulated drug release in
antibodies or antigens grafted antigen and free the presence of a specific
antigen antigen; sensor for
immunoassay and antigen
14. Specific applications of Hydrogels in Oral Drug Delivery
Fast-disintegrating tablet formulations
fast swelling and superabsorbent properties
microparticles of superporous hydrogels
mucoadhesive hydrogels
• buccal drug delivery
Gastric emptying of oral dosage forms
• The physical properties (size and density) of
the oral dosage form
• The presence of food in the stomach
Intragastric floating system
• low density
• float on top of the gastric juice
15. Specific applications of Hydrogels in Oral Drug Delivery
Mucoadhesive system
• cross-linked PAA
• highly mucoadhesive at pH (1-3) of the stomach
(∵ hydrogen bonding)
Superporous hydrogels
• Swell to a very large size
• High swelling ratio ( > a few hundreds)
• Fast swelling property - avoid premature
emptying by the housekeeper waves
• Gastric retention device (ex. Dogs-from several
hours to a day)
• Ac-Di-Sol (cross-linked carboxymethylcellulose
sodium)
16. Specific applications of Hydrogels in Oral Drug Delivery
- Hydrotropic Hydrogels for delivery of poorly soluble drug
-Hydrotropic agent : Diverse class of water soluble compounds
at high
concentration, enhance water solubilities of poorly soluble
solutes
ex) N,N-dimethylnicotinamide (3.5M), N,N-
diethylnicotinamide
- Many drugs : poorly soluble in water
: low absorption and low bioavailability
- Low-molecular-weight hydrotropes : high concentration
- Polymeric forms of hydrotropes (e.g., hydrotropic hydrogels)
17. • Hydrogels have played role in the development
of various controlled-release formulation
• biocompatible and increasing the solubility of
poorly soluble drug
• Hydrogels with novel properties will continue to
play important role in drug delivery
• smart hydrogels and new controlled-release
formulation
Editor's Notes
Swelling ratio 는 하이드로겔이 물을 흡수하는 정도를 나타나는데 이것은 swelling 하이드로겔 무게 값을 dried 된 하이드로겔 무게 값을 뺸 값응 다시 dried 하이드로겔 값으로 나눈 값입니다 . Swelling ratio 는 모노머의 유형과 조성 , 주변환경 요소 , 가교 밀고에 따라 달라 질수 있습니다 . 가교밀도는 하이드로겔의 기계적 강도와 하이드로겔에 물이 침투하는 성질에 많은 영향을 주게 됩니다 . 가교 밀도가 높고 , 하이드로겔이 IPN 구조이면서 소수성 모노머들이 공중합 되어 있으면 기계적 강도는 높아지지만 swelling 은 낮아지게 됩니다 . 이러한 성질을 이용하여 우리가 원하고자 하는 물성을 갖는 하이드로겔을 만들수가 있습니다 .
하이드로겔은 화학적 , 물리적 결합으로 이루어진 하이드로겔로 나누어집니다 . 화학적 결합 하이드로겔은 공유결합으로 가교 되어 있으며 열경화서 하이드로겔입니다 . 그리고 부피 상 전이가 일어나며 모양이 안정하고 잘 변하지 않습니다 . 반면에 물리적 결합으로 이루어진 하이드로겔은 수소결합 , 소수성 상호작용 등과 같은 비공유 결합으로 이루어져 있으며 열가소성 하이드로겔입니다 . 이것은 sol-gel transition 이 일어나며 모양 안정성과 그 모양을 유지하는 데 제한적인 특징이 있습니다 .
화학적 가교는 두개 이상의 작용기를 가지고 있는 가교제 존재하에서 물에 잘 녹는 모노머들의 중합으로 생성합니다 . 그림에서 보시다시피 모노머가 가교제와 공중합이 일어나면서 하이드로겔 망상조직을 형성하는 것과 vinyl 그룹을 가진 물에 잘녹는 고분자를 중합하여 하이드로겔 망상조직을 생성할 수 있습니다 . 이것은 앞에서 말했다시피 공유결합으로 이루어진 화학적 결합으로 이루어진 하이드로겔입니다 .
첫번째는 물에 잘 녹는 고분자를 이용하여 그 안에 약물을 봉입하여 그것이 시간이 지남에 따라 약물이 고분자 밖으로 방출되는 방법입니다 . 둘째는 물에 잘녹는 고분자 membrane 을 이용하여 그안에 약물을 봉입하여 이것도 시간에 따라 약물이 서서히 membrane 밖으로 방출되는 방법입니다 . 두가지 모두다 중심에는 약물이 있고 , 약물 주위에는 물에 잘 녹는 고분자를 둘러 쌈으로 인해 우리 몸 안에 들어가게 되면 circulation time 이 좋게 할 뿐만 아니라 하이드로겔의 swelling ratio 에 따라 약물의 방출 속도를 조절할 수 있다는 특징이 있습니다 .
